CH2OH CH2OH
O O
OH O OH
O
OH n α-1, 6-Glyoside OH O
Repeating monomer bonds
CH2OH CH2 CH2OH
O O
O
O OH O OH O OH O
OH OH OH
α-1, 4-Glycoside bonds Repeating monomer
Structure of amylopectin
Uses : Starch and its derivatives are used
(i) As the most valuable constituent of food as rice, bread, potato and corn-flour, etc.
(ii) In the manufacture of glucose, dextrin and adhesives (starch paste).
(iii) In paper and textile industry.
(iv) In calico printing as a thickening agent for colours.
(v) Nitro starch is used as an explosive.
(vi) Starch-acetate is a transparent gelatin like mass and is used mainly for making sweets.
Distinction between glucose, sucrose, starch
Test Glucose Sucrose Starch
With iodine solution No effect No effect Blue colour
With Fehling’s solution Gives red precipitate No effect
With Tollen’s reagent Gives silver mirror No effect No effect
With phenyl hydrazine Forms yellow osazone No effect No effect
Solubility in water Soluble Soluble No effect
Taste Sweet Insoluble
Sweet No taste
(2) Cellulose and its uses : It is found in all plants and so is the most abundant of all carbohydrates. It is
the material used to form cell walls and other structural features of the plants. Wood is about 50% cellulose and the
rest is lignin. Cotton and paper are largely composed of cellulose.
Pure cellulose is obtained by successively treating cotton, wool, flax or paper with dilute alkali, dilute HCl or
HF . This treatment removes mineral matter, water, alcohol and ether. Cellulose is left behind as a white amorphous
powder.
Cellulose is insoluble in water and in most of the organic solvents. It decomposes on heating but does not
melt. It dissolves in ammonical copper hydroxide solution (Schwitzer’s reagent). Cellulose also dissolves in a
solution of zinc chloride in hydrochloric acid.
When it is treated with concentrated H 2SO4 in cold, it slowly passes into solution. The solution when diluted
with water, a starch like substance amyloid is precipitated and is called parchment paper. When boiled with dilute
H 2SO4 , it is completely hydrolysed into D-glucose.
(C6 H10O5 )n + nH 2O → nC6 H12O6
Cellulose Glucose
The cattle, goats and other ruminants can feed directly cellulose (grass, straw, etc.) as they have digestive
enzymes (celluloses) capable of hydrolysing cellulose into glucose. Man and many other mammals lack the
necessary enzymes in their digestive tract and thus cannot use cellulose as food stuff.
Cellulose is a straight chain polysaccharide composed of D-glucose units which are joined by B-glycosidic
linkages between C-1 of one glucose unit and C-4 of the next glucose unit. The number of D-glucose units in
cellulose ranges from 300 to 50000.
CH2OH H OH CH2OH H OH CH2OH H OH
HH O OH H HH H O H H HH O OH H H
–O O H O OH O
O O–
OH HH H O OH O O OH HH H H
HH HH O
H OH CH2OH H OH CH2OH H OH CH2OH
Uses : Cellulose is used Structure of celluose
(i) As such in the manufacture of cloth (cotton), canvas and gunny bags (jute) and paper (wood, bamboo,
straw, etc.)
(ii) In the form of cellulose nitrates for the manufacture of explosives (gun-powder), medicines, paints and
lacquers. The cellulose nitrates with camphor yield celluloid which is used in the manufacture of toys, decorative
articles and photographic films.
(iii) In the form of cellulose acetate for the manufacture of rayon (artificial silk) and plastics.
Proteins and amino acids.
Proteins : Proteins are a class of biologically important compounds. They are crucial to virtually all processes
in living systems. Some of them are hormones which serve as chemical messengers that coordinate certain biochemical
activities. Insulin, for example, controls the level of sugar in the blood stream. Some proteins serve to transport the
substances through the organism. Haemoglobin, for instance, carries oxygen in blood stream and delivers to different
parts of the body. α-keratin, serves as a major constituent of hairs, nails and skin, while collegen is the prime constituent
of tendons. Proteins are also found in toxins (poisonous materials) as well as in antibiotics.
Amino acids : An amino acid is a bifunctional organic molecule that contains both a carboxyl group,
– COOH, as well as an amine group, –NH2. They are classified as acidic basic or neutral according to number of
amine and carboxyl groups in a molecule. Neutral amino acids contain only one amine and one carboxyl group.
They are further classified according to the position of amine group in relation to carboxyl group into α-, β-, γ-and
δ-amino acids. Out of these α-amino acids are most important as they are building blocks of bio-proteins.
In an α-amino acid, the amine group is located on the carbon atom adjacent to the carboxyl group (the α-
carbon atom). The general structure of the α-amino acids is represented as
H Carboxyl group
|
R – C – COOH
|
NH2 ← Amine group
R may be alkyl, aryl or any other group. α-Carbon atom
The proteins differ in the nature of R-group bonded to α-carbon atom. The nature of R-group determines the
properties of proteins. There are about 20 amino acids which make up the bio-proteins. Out of these 10 amino
acids (non-essential) are synthesised by our bodies and rest are essential in the diet (essential amino acids) and
supplied to our bodies by food which we take because they cannot be synthesised in the body. The α-amino acids
are classified into the following four types.
Amino acids with non polar side chain : Examples are :
Name Structure Three letter symbol One letter code
Glycine Gly G
NH2
CH2
COOH
Alanine CH3CH NH2 Ala A
Valine COOH Val V
Leucine Leu L
Isoleucine (CH3)2CH–CH NH2 ILE I
(Essential) COOH
Phenyl alanine PHE F
(CH3)2CH–CH2CH NH2
(Essential) COOH
NH2
C2H5–C| H–CH COOH
CH3
(Essential)
C6H5CH2CH NH2
(Essential) COOH
Proline H2C CH2 Pro P
H2C CHCOOH
One letter code
N W
H
Amino acids with polar but neutral side chain: Examples are
Name Structure Three letter symbol
Trp.
Tryptophan
H
|
N
CH NH2
|| |
C – CH2 – COOH
(Essential)
Serine HO–CH2–CH NH2 Ser S
Threonine COOH Thr T
Tyrosine Tyr Y
Cysteine NH2 Cys C
Methionine CH3CHOH–CH Met M
Aspargine COOH Asn N
(Essential)
NH2
|
HO CH2–CH–COOH
HS–CH2–CH NH2
COOH
CH3·S·CH2·CH2·CH NH2
(Essential) COOH
H2N C·CH2·CH NH2
O COOH
Glutamine
H2N C·CH2·CH2·CH NH2 Gln Q
O COOH Asp D
Glu E
Amino acids with acidic side chains : Examples are Lys K
Arg R
Aspartic acid NH2 His H
HOOC·CH2·CH
COOH
Glutamic acid NH2
COOH
HOOC·CH2·CH2CH
Amino acids with basic side chains : Examples are
Lysine NH2
H2N(CH2)4CH
COOH
(Essential)
Arginine NH NH2
H2N COOH
C·NH.(CH2)3CH
(Essential)
Histidine NH2
COOH
C — CH2 — CH
HC
N NH
CH
(Essential)
Biomolecules
(1) Methods of preparation of α-amino acids
Amination of α-halo acids
(i) : CH 3 CHCOOH + 2NH 3 → CH 3 CHCOOH + NH 4 Cl
| |
Br NH2
α -Bromo propionic acid α - Amino propionic acid
(Alanine)
Lab preparation of glycine : Cl.CH2COOH+ 3NH3 50°C → H2 N.CH2COONH4 + NH4Cl
α -Chloro acetic acid liquid Amm. salt of glycine
The ammonium salt so obtained is boiled with copper carbonate and cooled when blue colour needles of
copper salt of glycine are obtained.
2[H 2 N − CH 2COONH4 ] + CuCO3 Boiled →(H 2 NCH 2COO)2 Cu+ (NH4 )2 CO3
Copper salt of glycine
It is now dissolved in water and H2S is passed till whole of the copper precipitates as copper sulphide leaving
glycine as the aqueous solution.
(H 2 N − CH 2COO)2 Cu + H2S → 2H 2 NCH 2COOH+ CuS ↓
Glycine
Black ppt.
(ii) Gabriel pthalimide synthesis
CO CO 2H2O COOH
HCl COOH
NK + ClCH2COOC2H5 – KCl NCH2COOC2H5
Chloro ethyl acetate Phthalic acid
CO CO
Pot. phthalimide
+ CH2NH2COOH + C2H5OH
Glycine
(iii) Knoop synthesis : CH3COCOOH NH3 → CH 3 C− COOH H2 / Pd→ CH3 − C H − COOH
Pyruvic acid || or Na / C2H5OH |
NH NH2
Alanine
HH H H
|| | |
(iv) Streker synthesis : R −C = O HCN → R C| − OH NH3 → R C| − NH 2 H2O → R C| − NH 2
− − H+ −
Aldehyde
CN CN COOH
Cyanohydrin Amino nitrile
α -Amino acid
(v) From natural protein : Natural proteins are hydrolysed with dil. HCl or H 2SO4 at 250°C in an
autoclave when a mixture of α-amino acids is obtained. This mixture is esterified and the various esters are
separated by fractional distillation. The esters are then hydrolysed into respective α-amino acids.
(2) Physical properties
(i) Amino acids are colourless, crystalline substances having sweet taste. They melt with decomposition at
higher temperature (more than 200°C). They are soluble in water but insoluble in organic solvents.
(ii) Except glycine, all the α-amino acids are optically active and have an asymmetric carbon atom (α-carbon
atom). Hence, each of these amino acids can exist in two optical isomers. In proteins, however, only one isomer of
each is commonly involved.
(iii) Zwitter ion and isoelectric point : Since the − NH 2 group is basic and – COOH group is acidic, in
neutral solution it exists in an internal ionic form called a Zwitter ion where the proton of –COOH group is
transferred to the − NH 2 group to form inner salt, also known as dipolar ion.
R RR
| | |
H2 •• CHCOOH In water → H 2 •• CH − COO− + H+ → H 3 N+ − CH − COO−
N− N−
α -Amino acid Zwitter ion
(Dipolar ion)
The Zwitter ion is dipolar, charged but overall electrically neutral and contains both a positive and negative charge.
(3) Chemical properties : Amino acids are amphoteric in nature. Depending on the pH of the solution, the
amino acid can donate or accept proton.
HO HO HO
| || | || | ||
H3 N+ − C| − C− OH ←H+ H3 N+ − C| − C− O− OH− → H 2 N − C| − C− O−
−H2O
R R (Proton removed) R
Low pH (Acidic soln.) Zwitter ion (I) High pH (Basic soln.)
Positive form (II) Neutral form Negative form (III)
(Cation) (Anion)
When an ionised form of amino acid is placed in an electric field, it will migrate towards the opposite
electrode. Depending on the pH of the medium, following three things may happen
• In acidic solution (low pH), the positive ion moves towards cathode.
• In basic solution (high pH), the negative ion moves towards anode.
• The Zwitter ion does not move towards any of the electrodes.
The intermediate pH at which the amino acid shows no tendency to migrate towards any of the
electrodes and exists the equilibrium when placed in an electric field is known as isoelectric point.
This is characteristic of a given amino acid and depends on the nature of R-linked to α-carbon atom.
(i) α-amino acids show the reactions of –NH2 group, –COOH groups and in which both the
groups are involved. A summary of chemical properties is given below
NH2 NaOH RCHNH2COONa
RCH C2H5OH
Dry HCl +Sodium salt
COOH
Decarboxylation H3NCHCOOC2H5
α-Amino acid Ba(OH)2, ∆ | AgOH
R
LiAlH4
4H H2NCH – COOC2H5
| Ethyl ester
Alkylation
CH3Br R
H2N – CH2
Acetylation
CH3COCl |
R
HNO2 Amine NH2
R – CH
HCl
CH2OH
PCl5
Amino alcohol
NHCH3
RCH
COOH
N-Methyl derivative
NHCOH3
RCH
COOH
N-Acetyl derivative
RCHOHCOOH
α-Hydroxy acid
N+ H3C– l
RCH
COOH
Salt formation
NH2(HCl)
R.CH
COCl
Amino acid chloride
Note : Proline is the only natural α-amino acid which is a secondary amine.
Only achiral α-amino acid found in protein is glycine.
(ii) Action of heat
(a) For α-amino acids
O
||
NH H OH OC NH − C
R − CH CH − R ∆ → R − CH |C| − NH CH − R + 2H 2O
+
CO OH H HN O
α -amino acid
Cyclic amide
(b) For β-amino acids : C|H 2 − C| H − COOH heat → CH 2 = CH − COOH
(− NH3 )
NH2 H Acrylic acid
(α , β -Unsaturated acid)
β -Amino propionic acid
CH3 − C| H − C| H − COOH heat → CH 3CH = CHCOOH
(− NH3 ) Crotonic acid
NH2 H
β - Amino butyric acid
(c) For γ and δ amino acids
C| H 2 − CH 2 − CH 2 − C|O heat → CH 2 − CH 2 − CH 2 − CO
(− H 2O)
NH H H −O NH
γ -Butyrolactam
γ -Amino butyric acid
CH 2C H 2CH 2CH 2CO | heat → CH 2CH 2CH 2CH 2CO
| (− H 2O)
H −O NH
NH H δ - Valerolactum
δ - Amino valeric acid
These lactams have stable five or six membered rings.
(iii) Formation of proteins-peptide bond : Proteins are formed by joining the carboxyl group of one
amino acid to the α-amino group of another amino acid. The bond formed between two amino acids by the
elimination of a water molecule is called a peptide linkage or bond. The peptide bond is simply another
name for amide bond.
− |C| OH + H − N| − → − |C|− N| −+ H 2O
O H OH
Carboxyl group Amine group of Peptide bond
of one amino acid other amino acid
The product formed by linking amino acid molecules through peptide linkages, − CO − NH − , is called a
peptide. Peptides are further designated as di, tri, tetra or penta peptides accordingly as they contain two, three,
four or five amino acid molecules, same or different, joined together in the following fashions.
O HO OH O
|| | || || | ||
H2 N C| H C− OH H N− C| H C− OH (−H2O) → H2 N C| H C−N C| H C− OH
− R − + − R − − R − − R −
Peptide
linkage
(2 molecules) (Dipeptide)
When the number of amino molecules is large, the product is termed polypeptide which may be represented
as,
O NH C| H O NH C| H COOH
|| R′ || R′′
H2 N C| H C− C−
− R − − − − − − −
n
(4) Composition : Composition of a protein varies with source. An approximate composition is as follows :
Carbon 50-53%; hydrogen 6-7%; oxygen 23-25%; nitrogen 16-17%; Sulphur about 1%. Other elements may
also be present, e.g., phosphorus (in nucleoproteins), iodine (in thyroid proteins) and iron (in haemoglobin).
(5) Structure of proteins : The structure of proteins is very complex. The primary structure of a protein
refers to the number and sequence of the amino acids in its polypeptide chains (discussed in the
formation of proteins). The primary structure is represented beginning with the amino acid whose amino group is
free (the N-terminal end) and it forms the one end of the chain. Free carboxyl group (C-terminal end) forms the
other end of the chain.
OO
Left hand side || || Right hand side
H 2 N − C|H − C− NH − C| H − C− NH... C|H− COOH
One end R R′ R′′
Other end
(N-terminal end) (R, R′, R′′ …may be same or different) (C-terminal end)
Side chains may have basic groups or acidic groups as − NH 2 in lysine and –COOH in aspartic acid. Because
of these acidic and basic side chains, there are positively and negatively charged centres. Though the peptide
linkage is stable, the reactivity is due to these charged centres in the side chains.
Primary structure tells us nothing about the shape or conformation of the molecule. Most of the bonds in
protein molecules being single bonds can assume infinite number of shapes due to free rotation about single bonds.
However, it has been confirmed that each protein has only a single three dimensional conformation. The fixed
configuration of a polypeptide skeleton is referred to as the secondary structure of a protein. It gives
information :
• About the manner in which the protein chain is folded and bent;
• About the nature of the bonds which stabilise this structure.
Secondary structure of protein is mainly of two types
(i) α-helix : This structure is formed when the chain of α-amino acids coils as a right handed screw (called α-
helix) because of the formation of hydrogen bonds between amide groups of the same peptide chain, i.e., NH
group in one unit is linked to carbonyl oxygen of the third unit by hydrogen bonding. This hydrogen bonding
between different units is responsible for holding helix in a position. The side chains of these units project outward
from the coiled backbone.
Such proteins are elastic, i.e., they can be stretched. On stretching weak hydrogen bonds break up and the
peptide chain acts like a spring. The hydrogen bonds are reformed on releasing the tension. Wool and hair have α-
helix structure.
C C
O
||
·O·· N
C Side group
H
C ||
·O··
||
H ·O··
C | H
|| N C|
·O·· H || ·N·
|
H ·O· ·· C
N C N ||
||
·O···
·O··
H
|H
N
H ·N· H
|
N·· Side group
N O
C
(a) Representation of a polypeptide chain in an α-helical configuration.
(b) Stabilization of an α-helical configuration by hydrogen bonding. The shaded spheres represent carbon-
atoms or residues (R) of amino acids.
(ii) β-pleated sheet : A different type of secondary structure is possible when polypeptide chains are
arranged side by side. The chains are held together by a very large number of hydrogen bonds between C = O and
NH of different chains. Thus, the chains are bonded together forming a sheet. These sheets can slide over each
other to form a three dimensional structure called a beta pleated sheet. Silk has a beta pleated structure.
The beta pleated sheet structure of proteins
SertLeuTyrGinLeuGluAsnTyrCyAsn CO2– A-chain
CyVal S
Disulphide S Ser Inter chain S
loop S Ala bridges
CyGlyGluArgGlyPhePheTyrThrProLysAia-CO2
+NH3 GlyLieValGluGinCyCy Val B-chain
S Leu
S Tyr
+NH3 PheAsnGlnHisLeuCyGlySerHisLeuValGluAlaLeu
Tertiary Structure of proteins
Further folding and bending of secondary structure is called the tertiary structure of proteins
1 nm
Tertiary structure of proteins
Globular proteins possess tertiary structure. In general globular proteins are very tightly folded into a compact
spherical form.
(6) Classification of proteins : According to chemical composition, proteins are divided into two classes
(i) Simple proteins : Simple proteins are composed of chains of amino acid units only joined by peptide
linkages. These proteins on hydrolysis yield only mixture of amino acids. Examples are
Egg albumin, serum globulins, glutelin in wheat, coryzenin in rice, tissue globulin, etc.
(ii) Conjugated proteins : The molecules of conjugated proteins are composed of simple proteins and non
protein material. The non-protein material is called prosthetic group or cofactor. These proteins on hydrolysis
yield amino acids and non-protein material. Examples are
Mucin in saliva (prosthetic group, carbohydrate), casein in milk (prosthetic group, phosphoric acid),
haemoglobin in blood (prosthetic group, iron pigment), etc.
According to molecular shape, proteins are divided into two types
(i) Fibrous proteins : These are made up of polypeptide chains that run parallel to the axis and are held
together by strong hydrogen and disulphide bonds. They can be stretched and contracted like a thread. These are
usually insoluble in water. Examples are : α-keratin (hair, wool, silk and nails); myosin (muscles); collagen (tendons,
bones), etc.
(ii) Globular proteins : These have more or less spherical shape (compact structure). α-helics are tightly
held up by weak attractive forces of various types: Hydrogen bonding, disulphide bridges, ionic or salt bridges.
These are usually soluble in water. Examples are: Insulin, pepsin, haemoglobin, cytochromes, albumins, etc.
Proteins can also be classified on the basis of their function
Protein Function Examples
Enzymes Trypsin, pepsin.
Structural proteins Biological catalysts, vital to all living systems. Collagen.
Hormones Proteins that hold living systems together. Insulin.
Transport proteins Act as messengers. Haemoglobin.
Protective proteins Carry ions or molecules from place to another in the living Gamma
(antibiotics) system. globulin.
Destroy any foreign substance released into the living Snake venom.
Toxins system.
Poisonous in nature.
(7) General and physical characteristic of proteins
(i) Most of them (except chromoproteins) are colourless, tasteless, and odourless. Many are amorphous but
few are crystalline. They are nonvolatile and do not have a sharp melting point .
(ii) Most of them are insoluble in water and alcohol. But many of them dissolve in salt solutions, dilute acids
and alkalies. Some proteins such as keratins (skin, hair and nails) are completely insoluble.
(iii) Protein molecules are very complex and possess very high molecular masses. They are hydrophilic colloids
which cannot pass through vegetable or animal membrane. On addition of sodium chloride, ammonium sulphate
magnesium sulphate, etc., some proteins are precipitated. The precipitate can be filtered and redissolved in water.
(iv) The solution of proteins are optically active. Most of them are laevorotatory. The optical activity is due to
the presence of asymmetric carbon atoms in the constituent α-amino acids.
(v) Isoelectric point : Every protein has a characteristic isoelectric point at which its ionisation is minimum.
Like amino acids, proteins, having charged groups ( N+ H3 and COO− ) at the ends of the peptide chain, are
amphoteric in nature. In strong acid solution, protein molecule accepts a proton while in strong basic solution it
loses a proton. The pH at which the protein molecule has no net charge is called its isoelectric point.
This property can be used to separate proteins from mixture by electrophoresis.
(vi) Denaturation : The structure of the natural proteins is responsible for their biological activity. These
structures are maintained by various attractive forces between different parts of the polypeptide chains. The
breaking of these forces by a physical or a chemical change makes the proteins to lose all or part of their biological
activity. This is called denaturation of proteins. The denaturing of proteins can be done by adding chemicals such as
acids, bases, organic solvents, heavy metal ions, or urea. It can also be done with the help of heat and ultraviolet
light. Denaturation can be irreversible or reversible. In irreversible denaturation, the denaturated protein does not
return to its original shape. For example, the heating of white of an egg (water soluble) gives a hard and rubbery
insoluble mass.
(8) Chemical properties
(i) Salt formation : Due to presence of both − NH2 and –COOH groups in proteins, they form salts with
acids and bases. Casein is present in milk as calcium salt.
(ii) Hydrolysis : The simple proteins are hydrolysed by acids, alkalies or enzymes to produce amino acids.
Following steps are involved in the hydrolysis and the final product is a mixture of amino acids.
Protein → Proteose → Peptone → Polypeptide → Simple peptide → Mixture of amino acids
(iii) Oxidation : Proteins are oxidised on burning and putrefaction. The products include amines, nitrogen,
carbon dioxide and water. The bad smell from decaying dead animals is largely due to the formation of amines by
bacterial oxidation of body proteins.
(9) Test of proteins
(i) Biuret test : On adding a dilute solution of copper sulphate to alkaline solution of protein, a violet colour
is developed. This test is due to the presence of peptide (–CO–NH–) linkage.
(ii) Xanthoproteic test : Some proteins give yellow colour with concentrated nitric acid (formation of yellow
stains on fingers while working with nitric acid in laboratory). The formation of yellow colour is due to reaction of
nitric acid with benzenoid structures. Thus, when a protein solution is warmed with nitric acid a yellow colour may
be developed which turns orange on addition of NH4 OH solution.
(iii) Millon’s test : When millon’s reagent (mercurous and mercuric nitrate in nitric acid) is added to a protein
solution, a white precipitate which turns brick red on heating, may be formed. This test is given by proteins which
yield tyrosine on hydrolysis. This is due to presence of phenolic group.
(iv) Ninhydrin test : This test is given by all proteins. When a protein is boiled with a dilute solution of
ninhydrin, a violet colour is produced.
(v) Nitroprusside test : Proteins containing –SH group give this test. When sodium nitroprusside solution is
added to proteins having –SH group, a violet colour is developed.
O OH H O OH
|| | || |
C + RCCOOH CC
|
C OH NH2 C=N–C
C Amino acid CC
|| || ||
O OO
Ninhydrin Violet complex
(vi) Molisch’s test : This test is given by those proteins which contain carbohydrate residue. On adding a few
drops of alcoholic solution of α-naphthol and concentrated sulphuric acid to the protein solution, a violet ring is
formed.
(vii) Hopkins-Cole test : On adding concentrated sulphuric acid down the side containing a solution of
protein and glyoxalic acid, a violet colour is developed.
(10) Uses
(i) Proteins constitute as essential part of our food. Meat, eggs, fish, cheese provide proteins to human beings.
(ii) In textile : Casein (a milk protein) is used in the manufacture of artificial wool and silk.
(iii) In the manufacture of amino acids : Amino acids, needed for medicinal use and feeding experiments,
are prepared by hydrolysis of proteins.
(iv) In industry : Gelatin (protein) is used in food products, capsules and photographic plates. Glue (protein)
is used as adhesive and in sizing paper. Leather is obtained by tanning the proteins of animal hides.
(v) In controlling body processes : Haemoglobin present in blood is responsible for carrying oxygen and
carbon dioxide. Hormones (proteins) control various body processes.
(vi) As enzymes : Reactions in living systems always occur with the aid of substances called enzymes.
Enzymes are proteins produced by living systems and catalyse specific biological reactions.
Important enzymes are
Enzymes Reaction catalysed
Urease Urea → CO2 + NH3
Invertase Sucrose → Glucose + Fructose
Maltase Maltose → 2 Glucose
Amylase Starch → n Glucose
Pepsin Proteins → Amino acids
Trypsin Proteins → Amino acids
Carbonic anhydrase H2CO3 → H2O + CO2
Nuclease DNA, RNA → Nucleotides
Nucleic acids.
In every living cell there are found nucleo-proteins which are made up of proteins and natural polymers of
great biological importance called nucleic acids. Nucleic acids are complex compounds of carbon, hydrogen,
oxygen, nitrogen and phosphorus. They play an essential role in transmission of the hereditary characteristics and
biosynthesis of proteins. The genetic information coded in nucleic acids programmes the structure of all proteins
including enzymes and thereby all metabolic activity of living organisms.
Two types of nucleic acids are found in biological systems, these are
Deoxyribonucleic acid (DNA) and
Ribonucleic acid (RNA)
The nucleic acid was first isolated by Friedrich Miescher in 1868 from the nuclei of pus cells and was named
nuclein. The term nuclein was given by Altman.
(1) Composition : Nucleic acids like proteins and carbohydrates are polymers. The simple units that
make up the nucleic acid are called nucleotides. Nucleotides are themselves composed of following three simple
molecules.
(i) Nitrogenous base : These are heterocyclic organic compound having two or more nitrogen atoms in ring
skeleton. These are called bases because the lone pairs of electrons on the nitrogen atoms make them as Lewis bases.
Their structures are given below
(a) Pyrimidine derivatives
O OH NH2
HN 6
or N1 5 ;N
HO 2 N3 4
O N O N
H H
Uracil (U)
Cytosine (C)
RNA
RNA
DNA
NH2 O OH
CH3
or 6 ; HN or N1 6 5 CH3
N1 5 HO 2 N3
4
HO 2 4 N
H
N3 O
Cytosine (C)
Thymine (T)
DNA
NH2 NH2
N CH3 ; N CH2OH
HO N HO N
5-Methyl cytosine 5-Hydroxy methyl
cytosine
(b) Purine derivatives
NH2 N OH N
7 C8 H
N1 6 5 7 C8 H ; N2 1 6 N9
H2N 3 N4 5 H
2 4 N9
N3 H
Adenine (A) Guanine (G)
DNA DNA
RNA
RNA
(ii) Five carbon sugar (Pentose) : In RNA, the sugar is ribose where as in DNA, the sugar is deoxyribose.
5 O OH 1′ CHOH 5 O OH 1′ CHOH
2′ CHOH 2′ CH2
CH2OH 1 or 3′ CHOH O CH2OH 1 or 3′ CHOH O
4′ CH 4′ CH
4 C 5′ CH2OH 4 C 5′ CH2OH
C C
H H HH HH
H H C3 C2
C3 C2
HO OH OH H
Ribose Deoxyribose
Both differ only at carbon atom 2′ in the ring.
(iii) Phosphoric acid, H3PO4 : Phosphoric acid forms esters to –OH groups of the sugars to bind nucleotide
segments together. A molecule called nucleoside is formed by condensing a molecules of the base with the
appropriate pentose. (i.e., Base + Sugar). NH2
N N Adenine
N N N NH2
| OH
5′ H 5′ O N N
+ N
CH2OH O CH2OH 1′
C4′ 1′ – H2O 4′
C CC
HH HH HH HH
C3′ C2′ C3′ C2′
HO OH HO OH
Ribose Adenosine
(nucleoside)
A nucleotide results when the nucleoside combined with phosphoric acid mainly at carbon 5′ of the pentose.
(i.e., Base + Sugar + Phosphoric acid). N NH2
N
OH N
| N
HO — P — O — 5′ O 1′
CH2 C
|| 4′
OC
H H
H H
C3′ C2′
HO OH
Nucleotide-adenosine 5′-phosphoric acid
This nucleotide is the building block of both DNA and RNA. The nucleic acids are condensation polymers of
the nucleotide monomers and are formed by the creation of an ester linkage from phosphoric residue on one
nucleotide to the hydroxy group on carbon 3′ in the pentose of the second nucleotide. The result is a very long
chain possessing upto a billion or so nucleotides units in DNA.
|
HO – P – O – Sugar – Base
|| |
OO
|
HO – P – O – Sugar – Base
|| |
OO
|
HO – P – O – Sugar – Base
|| |
OO
|
HO – P – O – Sugar – Base
|| |
OO
|
Thus, the formation of a nucleic acid can be summarised in the following general way
Sugar (Ribose Base (Purine
or deoxy ribose) or pyrimidine)
Phosphoric Nucleoside
acid
Nucleotide
Poly Nucleotide
(Nucleic acid)
RNA nucleotides
Base + Ribose → (Nucleoside) + Phosphoric acid → Nucleotide
Adenine
Guanine + Ribose → (Adenosine) + Phosphoric acid → Adenylic acid
Cytosine
Uracil + Ribose → (Guanosine) + Phosphoric acid → Guanylic acid
Adenine + Ribose → (Cytidine) + Phosphoric acid → Cytidylic acid
Guanine
Cytosine + Ribose → (Uridine) + Phosphoric acid → Uridylic acid
Thymine
DNA nucleotides
+ Deoxy ribose sugar + Phosphate → Adenosine phosphate
+ Deoxy ribose sugar + Phosphate → Guanosine phosphate
+ Deoxy ribose sugar + Phosphate → Cytosine phosphate
+ Deoxy ribose sugar + Phosphate → Thymidine phosphate
(2) Structure : The sequence of bases along the DNA and RNA
chain establishes its primary structure which controls the specific
properties of the nucleic acid. An RNA molecule is usually a single chain
of ribose-containing nucleotides. DNA molecule is a long and highly
complex, spirally twisted, double helix, ladder like structure. The two
polynucleotide chains or strands are linked up by hydrogen bonding
between the nitrogenous base molecules of their nucleotide monomers.
Adenine (purine) always links with thymine (pyrimidine) with the help of
two hydrogen bonds and guanine (purine) with cytosine (pyrimidine)
with the help of three hydrogen bonds. Hence, the two strands extend in
opposite directions, i.e., are antiparallel and complimentary. The
following fundamental relationship exist.
Note : Thymine combines only with deoxyribose sugar and
uracil only with ribose sugar. Other bases can combine
with either of the two sugars.
• The sum of purines equals the sum of pyrimidines.
• The molar proportion of adenine equals to that of
thymine.
• The molar proportion of guanine equals to that of
cytosine.
The double helix is 20 Å. It completes a spiral at every 10
nucleotide pairs at a length of 34 Å. Sequences of
monomers (nucleotides) may present innumerable
variations. Evidently, innumerable varities of DNA exist in Fig : Helical structure of DNA as suggested
the organism. by Watson and Crick
Watson, Crick and Witkins were awarded Noble prize in 1962 for suggesting the structure of
DNA.
Difference between DNA and RNA
DNA RNA
It has a double helix structure. It has a single helix structure.
Sugar unit is deoxyribose. Sugar unit is Ribose.
Base units are adanine, guanine, thyamine and It contains uracil base instead of thyamine, other
cytosine. bases being same as those in DNA.
Responsible for inheritance of character. It is responsible for protein synthesis.
(3) Functions of nucleic acid : Nucleic acid have two important functions
(i) Replication and (ii) Protein synthesis.
(i) Replication : The genetic information for the cell is contained in the sequence of the bases A, T, G and C
(adenine, thymine, guanine and cytosine) in the DNA molecule. The sequence of bases in one chain of the double
helix controls the sequence in other chain. The two chains fit together like a hand and a glove. They separate and
about the hand is formed a new glove, and inside the glove is formed a new hand. Thus, the pattern is preserved in
the two new molecules of DNA.
[If one strand of DNA has the sequence ATGCTTGA, then the sequence of complimentary strand will be
TACGAACT].
(ii) Synthesis of proteins : The DNA contains the genetic code and directs protein synthesis through RNA.
The double helix of DNA partially uncoils and about the individual strands are formed chains of RNA. The new
chains contain ribose instead of deoxyribose and the base sequence is different which is determined by DNA, i.e.,
opposite each adenine of DNA, there appears on RNA a uracil; opposite guanine, cytosine; opposite thymine,
adenine, opposite cytosine, guanine. Thus, AATCAGTT on DNA becomes UUAGUCAA on RNA.
One kind of RNA, called messenger RNA, carries a message to the ribosome, where protein synthesis actually
takes place. At the ribosome, messenger RNA calls up a series of transport RNA molecules, each of which is loaded
with a particular amino acid. The order in which the transport RNA molecules are called (–the sequence in which
the amino acids are arranged to form the protein chain) depends upon the sequence of bases along the messenger
RNA chain. Thus GAU is the code for aspartic acid; UUU, phenyl alanine; GUG, valine. There are 64-three letter
code words (codons) and only 20-odd amino acids, so that more than one codon call the same amino acid.
The relation between the nucleotide triplets and the amino acids is called Genetic code. Nirenberg, Hollay and
Khorana presented the genetic code for which they were awarded Noble prize in 1968.
(4) Mutation : A mutation is a chemical or physical change that alters the sequence of bases in DNA
molecule. Anything that causes mutation is called mutagen. A mutation results from ultraviolet light, ionisation
radiations, chemicals or viruses. The changes in sequence of bases in DNA are repaired by special enzymes in the
cell. If it is not, the protein produced has no biological activity and the cell dies.
These mutations often prove harmful and give rise to symptoms that cause diseases. Sickle-cell anaemia is one
such example. Such disease is passed on from one generation to the next generation.
Lipids.
Lipids are constituents of plants and tissues which are insoluble in water but soluble in organic solvents such as
chloroform, carbon tetrachloride, ether or benzene. They include a large variety of compounds of varying structures
such as oils and fats; phospholipids, steroids, etc. Lipids are mainly made of carbon, hydrogen and oxygen. The
number of oxygen atoms in a lipid molecule is always small as compared to the number of carbon atoms.
Sometimes small amounts of phosphorus, nitrogen and sulphur are also present. They have a major portion of their
structure like a hydrocarbon (aliphatic or fused carbon rings). Lipids serve as energy reserve for use in metabolism
and as a major structural material in cell membranes for regulating the activities of cell and tissues.
Simple lipids are esters of glycerol with long chain monocarboxylic acids which can be saturated or
unsaturated. These are generally called glycerides of fats and oils. Waxes are esters of fatty acids with certain
alcohols, not glycerol. Fats and oils have biological importance but waxes have no value as these are not digested.
The functions of triglycerides are the following
(1) They are energy reserves in the cells and tissues of living system. When digested, triglycerides are
hydrolysed to fatty acids and glycerol.
(2) Catabolism of fatty acids form acetyl-coenzyme-A. Most of the energy of fatty acids is converted into ATP.
(3) Acetyl coenzyme is the starting material for the synthesis of many compounds.
(4) Fats deposited beneath the skin and around the internal organs minimise loss of body heat and also act as
cushions to absorb mechanical impacts.
Another very important class of lipids are the phospholipids. These are polar lipids and like the fats, are esters
of glycerol. In this case, however, only two fatty acid molecules are esterified to glycerol, at the first and second
carbon atom. The remaining end position of the glycerol is esterified to a molecule of phosphoric acid, which in turn
is also esterified to another alcohol. This gives a general structure.
R′′
|
O
|
O = P – O – CH2 O
|| ||
OH CH – O – C – R′
|
CH2O – C – R
||
O
The alcoholic compound linked to phosphoric group may be choline, ethanol, amine, serine or inositol. The
phosphate groups forms a polar end, i.e., hydrophilic (water-attracting) and the two fatty acid chains constitute the
non-polar tail, i.e., hydrophobic (water repelling). This structure gives the phospholipids good emulsifying and
membrane forming properties.
Cell membranes are composed of phopholipids and proteins in about equal, proportion. The phospholipids in
the membrane appear to be arranged in a double layer or bilayer in which the non-polar tails face each other,
thereby exposing the polar heads to the aqueous environment on either side of the membrane. Proteins found in
the membrane are embedded in the mossaic formed by the lipids. Phospholipids facilitate the transport of ions and
molecules in and out of the cell and regulate the concentration of molecules and ions within the cell. They provide
structural support for certain proteins.
The above mentioned lipids are mainly straight chain compounds. There is a third class of lipids which are not
straight chain compounds. They are called Sterols. The sterols are composed of fused hydrocarbon rings and a
long hydrocarbon side chain. Cholestrol is most important compound of this class and is found in animals only. It
exists either free or as ester with a fatty acid. Cholestrol is also the precursor of hormones. Cholestrol and its esters
are insoluble in water. So they are deposited in the arteries and veins if the blood cholestrol rises. This leads to high
blood pressure and heart diseases. Cholestrol is a part of animal cell membrane and is used to synthesis steroid
hormones, vitamin-D and bile salts.
Energy cycle or metabolism.
A cell has small molecules (micromolecules) as well as large molecules (macromolecules). The chemical
reactions of a living organism can be divided into main two types
(1) The chemical reactions by which the large molecules are constantly broken down into smaller ones are
called catabolism.
(2) The chemical reactions by which the macromolecules are synthesised within the cell are called anabolism.
The two processes i.e., degradation and synthesis are collectively called metabolism. Catabolism reactions
are usually accompanied by release of energy whereas anabolism reactions require energy to occur.
The primary energy found in living cells is chemical energy, which can be easily stored, transferred and
transformed. For this, the living cells contain a chemical compound called adenosine triphosphate (ATP). It is
regarded as energy currency of living cells because it can trap, store and release small packets of energy with ease.
ATP consists of a purine base called adenine linked to a five carbon sugar named ribose which is further
attached to three molecules of phosphate.
ATP is energy rich molecule, this is because of the presence of four negatively charged oxygen atom very close
to each other. These four negatively charged o-atoms experience very high repulsive energy.
NH2
O– O– O– N CCN
|| | HC
N CN CH
O– — P~O– P~O—P—O— CH2 O
|| || ||
OO O
Point of cleavage to HH HH
form ADP HO OH
ATP Hydrolysis → ADP + Pi ∆H = –30.93 kJ mol–1
Adenosine
diphosphate
ADP Hydrolysis → AMP + 2Pi ∆H = –28.4 kJ mol–1
Adenosine
monophosphate
ADP can change to ATP in the presence of inoraganic phosphate. This process is called phosphorylation.
ATP
Gains Doing work
inorganic ⇒ Catabolism
phosphate ⇒
Loses
phosphate
ADP group
O2
Fuels
Digestion of food.
Digestion is the process by which complex constituents of food are broken down into simple molecules by a
number of enzymes in mouth, stomach and small intestine. The simple molecules thus formed are absorbed into
blood stream and reach various organs.
Raw food may be taken as such or after cooking. It is chewed in the mouth and swallowed when it passes
through a long passage in the body called alimentary canal. During this passage it gets mixed with various enzymes
in different parts of the alimentary canal. The carbohydrates, proteins and fats are converted into simpler forms
which are then carried by blood to different parts of the body for utilisation. Digestion of food can be summarised in
the following form
(1) Polysaccharide Amylase → Disaccharides (maltose, etc.) Maltase → Glucose
Saliva (mouth); (Intestine)
Pancreatic juice
(Intestine)
(2) Proteins Pepsin/HCl → Proteases and Peptones Trypsin → Peptides Peptidases → Amino acids
(Stomach) Chemotrypsin (Intestine)
Pancreatic juice
(Intestine)
(3) Fats Bilesalts → Emulsified fat Lipases → Fatty acids + Glycerol
(From liver) Pancreatic and
intestine juice
After digestion, there are present glucose, aminoacids, fatty acids along with vitamins and mineral salts.
Undigested food and secretions are pushed forward into the rectum from where these are excreted.
Vitamins.
In addition to air, water, carbohydrates, proteins, fats and mineral salts, certain organic substances required for
regulating some of the body processes and preventing certain diseases are called vitamins. These compounds
cannot be synthesised by an organism. These vitamins are required in small amounts and deficiency of any one
causes one disease or the other. Thus, vitamins are essential constituents of our diet. Several of these vitamins are
known and are designated as A, B, C, D, E and so on. Many of these are now synthesised on commercial scale. On
the basis of solubility, the vitamins are divided into two groups.
(1) Fat soluble; Vitamin A, D, E and K. (2) Water soluble; Vitamin B and C.
Name Sources Functions Effects of defficiency
Water soluble vitamins
B1 Rice polishings, wheat Major component of co- Beri-beri, loss of appetite
(Thiamine or Aneurin) flour, oat meal, eggs, enzyme co-carboxylase and vigour, constipation,
(C12H18N4SOCl2) required for carbohydrate weak heart beat, muscle
yeast, meat, liver, etc. and amino acid
metabolism. atrophy, even paralysis.
B2 or G Cheese, eggs, yeast, Combines with Cheilosis, digestive
(Riboflavin
Lactoflavin) or tomatoes, green phosphoric acid to form disorders, burning
(C17H20N4O6) vegetables, liver, meat, coenzyme FAD essential sensations in skin and
cereals, etc. for oxidative metabolism. eyes, headache, mental
depession, scaly
dermatitis at angles of
nares, corneal opacity,
etc.
B3 All food; more in yeast, Important component of Dermatitis, in cocks;
(Pantothenic acid) greying of hairs, retarded
(C9H17O5N) liver, kidneys, eggs, meat, Co-A required for body and mental growth,
milk, sugarcane, oxidative metabolism. reproductive debility.
groundnut, tomatoes.
B5 or P-P Fresh meat, liver, fish, Active group in coenzyme Pellagra, dermatitis,
cereals, milk, pulses,
(Nicotinic acid or yeast, etc. NAD required for diarrhoea, demenia,
Niacin) (C5H4N–
oxidative metabolism. muscle atrophy,
C6H5NO2
COOH) inflammation of mucous
membrane of gut.
B6 Milk, cereals, fish, meat, Important coenzyme Dermatitis, anaemia,
(Pyridoxine
Adermin) or liver, yeast synthesised by required in protein and convulsions, nausea,
intestinal bacteria. amino acid metabolism. insomnia, vomiting,
(C8H11O3N)
mental disorders,
depressed appetite.
Vit. H (Biotin) Yeast, vegetables, fruits, Essential for fat synthesis Skin lesions, loss of
(C10H16N2O3S)
wheat, chocolate, eggs, and energy production. appetite, weakness,
groundnut synthesised by hairfall, paralysis.
intestinal bacteria.
Folic acid group Green vegetables, Essential for synthesis of Retarded growth,
DNA and maturation of anaemia.
soyabean, yeast, kidneys, blood corpuscles.
liver, synthesised by Required for chromosome
duplication and formation
intestinal bacteria. of blood corpuscles.
Essential for formation of
B12 Meat, fish, liver, eggs, collagen, cartilage, bone, Retarded growth,
(Cyanocobalamine) milk synthesised by teeth, connective tissue pernicious anaemia
and RBCs and for iron
(C63H88O14N14PCo) intestinal bacteria. metabolism.
Vit. C
Lemon, orange and other Essential for synthesis of Wound-healing and
visual pigments; growth growth retarded, scurvy,
(Ascorbic acid) cirtus fruits, tomatoes, and division of epithelial breakdown of immune
(CH8O6) cells. defence system, spongy
green vegetables, and bleeding gums,
Regulates absorption of fragile blood vessels and
potatoes, carrots, pepper, calcium and phosphorus bones, exhaustion,
in intestine, mineral nervous breakdown, high
etc. deposition in bones and
teeth. fever.
Fat soluble vitamins Essential for proper
spermatogenesis,
Vit. A Synthesised in cells of pregnancy, lactation and Xerophthalmia-keratini-
muscular function.
(Retinol or liver and intestinal Essential for synthesis of zed conjunctive and
Axerophthol) prothrombin in liver,
mucous membrane from which is required for opaque and soft cornea.
blood clotting. Stratification and
(C20H30O) carotenoid pigments
found in milk, butter, keratinization in epithelia
kidneys, egg yolk, liver, of skin, respiratory
passages, urinary bladder,
fish oil, etc.
ureters and intestinal
mucosa, night-blindness,
impaired growth,
glandular secretion and
reproduction.
Vit. D Synthesised in skin cells Rickets with
(Ergocalciferol), (Sun in sunlight from 7-
shine vitamin) C28H44O dehydro-cholesterol also osteomalacia; soft and
and cholecalciferol found in butter, liver,
kidneys, egg yolk, fish oil, fragile teeth.
Vit. E group etc.
Tocopherols (α, β, γ) Green vegetables, oil, egg Sterility (impotency) and
(C29G50O2) yolk, wheat, animal muscular atrophy.
tissues.
Vit. K (Phylloquinone) Haemorrhages, excessive
(C31H46O2) Carrots, lettuce, cabbage, bleeding in injury, poor
tomatoes, liver, egg yolk, coagulation of blood.
cheese; synthesized by
colon bacteria.
Hormones.
Harmones are the chemical substances secreated by duetless glands, which influence and control biological
reactions. Some important harmones alongwith their source and function are being given below.
Hormone Source Functions
Steroid hormones
Testosterone (Androgens) Testis Regulates development of reproductive male organs.
Estrogene and progesterons Ovary (Uterus)
Female sex hormones : control normal functioning of
female sex organs.
Cortisone and related Adrenal cortex Regulates the metabolism of fats, proteins, carbohydrates
hormones and mineral salts.
Amine hormones
Adrenalino (Epinephrine) Adrenal medulla Increase the pulse rate and blood pressure : reduces
Thyroxine Thyroid glucose from glycogen and fatty acids from fats.
Stimulates rate of oxidative metabolism and regulates
general growth and development.
Peptide hormones Posterior Causes contraction of some smooth muscle. Also causes
Oxytocino pituitary contraction of uterus during child birth.
Vasopressin Posterior Inhibits excretion of water from the body by way of urine.
pituitary
Insulin Pancreas Decrease blood glucose level.
Glucogen Pancreas Elevates blood glucose level.
Product Applications
Human insulin hormone Treatment of diabetes
Interferon Antiviral agent
Growth hormones Treatment of abnormal growth related diseases
Tissue plasminogen factor Dissolving unwanted blood clots
Blood clotting factor VIII Treatment of haemophilias
Vaccines Against various infective diseases
Polymers
Polymers are compound of very high molecular masses formed by the combination of a large number of simple
molecules.
The simple molecules which combine to give polymers are called monomers. The process by which the simple
molecule (i.e. monomers) are converted into polymers is called polymerisation.
Example : Polyethylene or polythene is a polymer of ethylene (monomer unit).
nCH 2 = CH 2 Polymerisation → − (CH 2 − CH 2 −)n
Ethylene Polyethylene
(monomers) (polymer)
Polymer are also called macromolecule because of their big size.
Note : All polymers are macromolecule but all macromolecules are not polymers because polymer
consist repeating unit of monomer e.g., chlorophyll is a macromolecule but not a polymer.
Classification of polymers.
Polymers are classified in a number of ways as described below.
(1) Classification based on source of availability.
(2) Classification based upon structure.
(3) Classification based upon molecular forces.
(4) Classification based upon mode of synthesis.
(5) Classification based upon the nature of monomers.
(1) Classification based on source of availability : They are classified as
(i) Natural polymers (ii) Synthetic polymers (iii) Semi-synthetic polymers
(i) Natural polymers : The polymers obtained from nature (plants and animals) are called natural polymers.
These polymers are very essential for life. They are as under.
(a) Starch : It is polymer of glucose and it is food reserve of plant.
(b) Cellulose : It also a polymer of glucose. It is a chief structural material of the plant both starch and cellulose
are made by plants from glucose produced during photosynthesis.
(c) Proteins : These are polymers of α-amino acids, they have generally 20 to 1000 α amino acid joined
together in a highly organized arrangement. These are building blocks of animal body and constitute an essential
part of our food.
(d) Nucleic acids : These are polymers of various nucleotides. For example RNA and DNA are common
nucleotides.
Note : It may be noted that polymers such as polysaccharides (starch, cellulose), proteins and
nucleic acids etc. which control various life processes in plants and animals are also called biopolymers.
(ii) Synthetic polymers : The polymers which are prepared in the laboratories are called synthetic polymers.
These are also called man made polymers. For example polyethene, PVC nylon, teflon, bakelite terylene, synthetic
rubber etc.
(iii) Semisynthetic polymers : These polymers are mostly derived from naturally occurring polymers by
chemical modifications. For example cellulose is naturally occurring polymers, cellulose on acetylation with acetic
anhydride in the presence of sulphuric acid forms cellulose diacetate polymers. It is used in making thread and
materials like films glasses etc. Vulcanized rubber is also a example of semisynthetic polymers used in making tyres
etc. gun cotton which is cellulose nitrate used in making explosive.
Note : Semi-synthetic polymers : Rayon and other cellulose derivatives like cellulose nitrate,
cellulose acetate etc., are semi-synthetic polymers. These are thermoplastic polymers. Viscose rayon
in the form of a thin transparent film is known as cellophane. Cellophane is softened with glycerol.
Unlike plastic sheets it absorbs water.
Rayon : Rayon is a man made material which consists of purified cellulose in the form of long
fibres. Cellulose is treated with cold NaOH solution to purify it and then treated with CS2 to form a
viscose solution. This is why rayon is sometimes called viscose rayon. This solution is allowed to pass
through fine pores in metal cylinder, into a dilute solution of H2SO4. This results in the formation of
long fibres. Rayon fibre is chemically identical to cotton but has a shine like silk. As such rayon is
also known as artificial silk. Rayon is used on a large scale for making textiles, tyre-chord, carpets
and surgical dressings. Unlike fully synthetic polymers, it absorbs moisture and is bio-degradable.
(2) Classification based upon structure : On the basis of structure of polymers these can be classified as
(i) Linear polymers (ii) Branched chain polymers (iii) Cross linked polymers
(i) Linear polymers : These are polymers in which monomeric Linear polymer
units are linked together to form linear chain (as of figure). These linear
polymers are well packed and therefore have high densities, high tensil
(pulling) strength and high melting points. Some common example of
linear polymers are polyethylene nylon, polyester, PVC, PAN etc.
(ii) Branched chain polymers : These are polymers in which the Branched chain polymer
monomers are joined to form long chains with side chains or branches of
different lengths (as of figure). These branched chain polymers are
irregularly packed and therefore, they have low tensile strength and
melting points than linear polymers. Some common examples are low
density polythene, glycogen, starch etc. (Amylopectin).
(iii) Cross linked polymers : These are polymers in which Cross-linked polymer
monomers unit are crosslinked together to form a three dimensional
network polymers. These polymers are hard, rigid and brittle because of
network structure (as of figure) e.g., Bakelite, malamine formaldehyde
resin etc.
Note : Linear polymers generally have higher magnitude of inter particle forces and thus possess
high density and high melting point. Such polymers have high tensile strength in the direction of
polymer chain and very low tensile strength at right angle to it.
Branched chain polymers generally have low density and low melting point. Such polymers have
almost equal tensile strength in all directions, which is less than that in linear chain polymers.
(3) Classification based upon molecular forces : Depending upon the intermolecular forces, the
polymers have been classified into four type.
(i) Elastomers (ii) Fibres (iii) Thermoplastics (iv) Thermosetting polymers
(i) Elastomers : The polymers that have elastic character like rubber (a material that can return to its original
shape after stretching is said to be elastic) are called elastomers. In elastomers the polymers chains are held together
by weak intermolecular forces. Because of the presence of weak forces, the polymers can be easily stretched by
applying small stress and regains their original shape when the stress is removed. The most important example of
elastomers is natural rubber.
(ii) Fibres : These are the polymers which have strong intermolecular forces between the chain. These forces
are either hydrogen bonds or dipole-dipole interaction. Because of strong forces, the chains are closely packed
giving them high tensil strength and less elasticity. Therefore, these polymers have sharp melting points. These
polymers are long, thin and thread like and can be woven in fabric. Therefore, these are used for making fibres.
Example : Nylon 66, dacron, silk etc.
(iii) Thermoplastics : These are the polymers which can be easily softened repeatedly when heated and
hardened when cooled with little change in their properties. The intermolecular forces in these polymers are
intermediate between those of elastomers and fibres. There is no cross linking between the chain. The softening
occurs as the polymer chain move more and more freely because of absence of cross link. When heated, they melt
and form a fluid which can be moulded into any desired shapes and then cooled to get the desired product.
Example : Polythene, polystyrene, PVC, teflon etc.
(iv) Thermosetting polymers : These are the polymers which undergo permanent change on heating. They
become hard and infusible on heating. They are generally prepared from low molecular mass semifluid substances.
When heated they get highly cross linked to form hard infusible and insoluble products. The cross links hold the
molecule in place so that heating does not allow them to move freely. Therefore a thermosetting plastic is cross
linked and is permanently rigid.
Example : Bakelite, melamine formaldehyde etc.
Note : Plasticizers do lower the softening point (so called melting point) of a polymer. A plasticizer
cannot convert a thermosetting polymer into thermoplastic one. In fact plasticizers can convert a
hard and brittle plastic into soft and easily pliable. Plasticizers reduce the interparticle forces between
polymer molecules. Plasticizers are generally high-boiling esters or high-boiling haloalkanes. They
are added to plastics to make them soft and rubber-like. For example, polyvinyl chloride as such is
hard, stiff and glass-like, but the addition of plasticizers like dioctylphthalate (DOP) or
dibutylphthalate (DBP) can make it soft and rubber like. Similarly, chlorinated paraffin wax (CPW) is
used as a plasticizer in polythene. On long exposure to air and sunlight, these plasticizers evaporate
and the plastic articles become hard and brittle.
Difference between thermoplastic and thermosetting polymers
Thermoplastic polymers Thermosetting polymers
(1) These soften and melt on heating. These do not soften on heating but rather become
hard in case prolonged heating is done these start
burning.
(2) These can be remoulded recast and reshaped. These can not be remoulded or reshaped.
(3) These are less brittle and soluble in some organic These are more brittle and insoluble in organic
solvents. solvents.
(4) These are formed by addition polymerisation. These are formed by condensation polymerisation.
(5) These have usually linear structures. These have three dimensional cross linked
Ex. Polyethylene, PVC, teflon. structures.
Ex. Bakelite, urea, formaldehyde, resin.
(4) Classification based upon mode of synthesis : They are of two types on the basis of their synthesis.
(i) Addition polymers (ii) Condensation polymers
(i) Addition polymers : A polymer formed by direct addition of repeated monomers without the elimination
of by product molecule is called addition polymers. For example,
nCH 2 = CH 2 → − (CH 2 − CH 2 −)n
Ethene Polyethene
− CC| HH3−n
nCH 3 − CH = CH 2 → CH 2 −
Propylene
Polypropylene
(ii) Condensation polymers : A polymer formed by the condensation of two or more than two monomers
with the elimination of simple molecule like water, ammonia HCl, alcohol etc. is called condensation polymers. For
example,
O
−nH2O → −
nH 2 N − (CH 2 )6 − NH 2 + nHOOC − (CH 2 )4 − COOH NH − (CH 2 )6 − NH || − C −
Hexamethylenediamine Adipic acid − C− (CH 2 )4 ||
O
Nylon-66 n
Difference between addition and condensation polymers
Addition polymers Condensation polymers
Formed by addition reaction. Formed by condensation process with elimination of
small molecules like H2O.
Molecular mass is a whole number multiple of the
monomer. Molecular mass is not whole number multiple of the
monomer units.
Generally involve one monomer unit. Generally involve more than one monomer unit.
Monomers are unsaturated molecules. Monomer units must have two active functional
groups.
They are generally chain growth polymers. They are generally step growth polymers.
(5) Classification based upon the nature of monomer : On the basis of nature of monomer. Polymer are
of two type
(i) Homopolymer s (ii) Copolymers
(i) Homopolymers : A polymer formed from one type of monomers is called homopolymer. For example,
polythene is a homopolymer of monomer ethene.
nH 2C = CH 2 Polymerisation → −(CH 2 − CH 2 −)n Homopolymer
Ethene Polythene
(ii) Copolymers : A polymer formed from two or more different monomers is called copolymer or mixed
polymer. For example, nylon-66 is a polymer of two types of monomers : hexamethylenediamine and adipic acid.
nH 2 N − (CH 2 )6 − NH 2 + nHOOC − (CH 2 )4 − COOH
Hexamethylenediamine Adipic acid
monomers
Polymerisation
–(NH – (CH2)6 – NH – CO – (CH2)4 – CO –)n + nH2O
Nylon-66 (Copolymer)
Copolymer are commercially more important.
For example copolymerisation of vinyl chloride with vinylidene chloride (1, 1 dichloroethane) in a 1 : 4 ratio
forms a copolymer known as saran.
CH Cl Cl
Polymerisation → −
| | |
H2C CH 2 = C Cl2 CH 2 CH CH C−
= + − 2 − | n
Vinylidene chloride
Cl Cl
m
Vinyl chloride Saran polymer
Copolymerisation of monomer mixtures often leads to the formation of polymers which have quite different
properties than those of either corresponding homopolymer. For example, a mixture of styrene and methyl
methacrylate can form a copolymer.
CH2 CH3
||
CH 2 CH H2C C ~ CH 2 − CH − CH 2 C ~
= + = → | −
| | |
C6 H5 COOCH3 C6 H5 COOCH3
Styrene Methyl Copolymer
methacrylate
The composition of the copolymer depends on the proportion of the monomers and their reactivity. It may be
noted that some monomers do not polymerise at all but copolymerize. For example, maleic anhydride does not
polymerise as such. However, it copolymerises with styrene in a highly symmetrical manner to form styrene maleic
anhydride copolymer.
It may be noted that many types of copolymers can be obtained depending upon the distribution of monomer
units in the chain. Two monomers can combine in either regular fashion (although this is rare) or random fashion.
For example, if monomer A is copolymerised with monomer B, the resultant product may have a random
distribution of the two units throughout the chain or it might have alternating distribution.
(– A – B – A – B – A – B – A – B –) Alternating copolymer
(– A – A – A – B – A – B – B – A – B –) Random copolymer
The exact distribution of monomer units depends on the initial proportion of the two reactant monomers and
their reactivities. Most copolymers have varying distributions. Two other types of copolymers that can be prepared
under certain conditions are called block copolymers and graft copolymers.
(a) Block copolymers are those in which different blocks of identical monomer units alternate with each
other as
(– A – A – A – A – B – B – B – B – A – A – A – A – B – B – B – B –)n
These are prepared by initiating the polymerisation of one monomer as if growing a homopolymer and then
adding an excess of second monomer to the active reaction mixture.
(b) Graft polymers are those in which homopolymer branches of one monomer units are grafted on the
homopolymer chains of another monomer units as :
− (A − A− A − A − A − A − A− A − A − A − A− A−)n
| | |
B BB
| ||
B BB
| ||
B BB
|n |n |n
These are prepared by radiation of γ-rays on a completed homopolymer chain in the presence of the second
monomer. The high energy radiation knocks hydrogen atoms of the homopolymer chain at random points resulting
radical sites for initiation of the added monomer. By careful control of the polymerisation reaction, we can produce
copolymers of desired properties by combination of different monomers in various ratios and geometric
arrangements.
General method and mechanism of polymerisation.
(1) Chain growth or addition polymerisation : It involve a series of reaction each of which consumes a
reactive particle and produces another similar one. The reactive particle may be free radicals or ion (cation or
anion) to which monomers get added by a chain reaction. The polymers thus formed are known as chain growth
polymers. Chain growth polymerisation is an important reaction of alkenes and conjugated dienes or indeed of all
kinds of compounds that contain carbon-carbon double bond polythene, polypropylene, polybutadiene, teflon
PVC, polystyrene are some of chain growth polymers. It is based on three mechanism
(i) Free radical mechanism (ii) Cation mechanism (iii) Anion mechanism
Each mechanism of polymerisation reaction involves an initiator of their corresponding nature. The addition
polymerisation reaction is very rapid and is also characterized by three steps i.e. chain initiation, chain propogation
and chain termination step.
(i) Free-radical mechanism : Free-radical polymerisation is initiated by organic peroxide or other reagents
which decompose to give free radicals. Following steps are involved.
(a) Chain initiation : Organic peroxides undergo homolytic fission to form free radicals.
O O O
|| || heat → R ||
R − O − − O − R − O• → R• + CO2
C− C− C−
Unstable
Peroxide
(b) Chain propagation : Free radical adds to an alkene molecule to form a new free radical.
R• + CH2 •• → R − CH2 − C• H2
− CH2
The free radical formed attacks another alkene molecule and the process continues in building a long chain.
RCH 2 C• H 2 + CH 2 •• → RCH 2CH 2CH 2C• H 2
− CH 2
(c) Chain termination : The chain reaction comes to halt when two free radical chains combine.
2R(CH 2CH 2 )n CH 2C• H 2 → R(CH 2CH 2 )n CH 2CH 2 : CH 2CH 2 (CH 2CH 2 )n R
Note : Benzoyl or t-Butyl peroxide are common initiators, used.
Free radical polymerisation can also be initiated by a mixture of ferrous sulphate and hydrogen peroxide
(FeSO4 + H 2O2 ) .
(ii) Cationic mechanism : Cationic polymerisation is initiated by use of acids such as H 2SO4 , HF or BF3 in
H 2O . The following steps are involved :
(a) Chain initiation : The acid furnishes proton.
H 2SO4 ⇌ H + + HSO4−
HF ⇌ H + + F −
BF3 + H 2O ⇌ H + + BF3 (OH)−
The proton adds to the carbon of the double bond of the alkene to form a carbonium ion.
H + + CH 2 = CH 2 → CH 3 C+ H 2
(b) Chain propagation : The carbonium ion combines with another molecule of alkene to form a new
carbonium ion and the process continues to form a long chain.
CH3C+ H 2 + CH 2 = CH3 → CH3CH 2CH 2C+ H 2
CH 3CH 2CH 2C+ H 2 + nCH 2 = CH 2 → CH 3CH 2 (CH 2CH 2 )n CH 2C+ H 2
(c) Chain termination : The chain may be halted by combination with negative ion or loss of a proton.
CH 3CH 2 (CH 2CH 2 )n CH − C+ H 2 → CH 3CH 2 (CH 2CH 2 )n CH = CH 2 + H 2SO4
Polymer
| HSO4−
H
(iii) Anionic polymerisation : This type of polymerisation is initiated by anion (Bases nucleophiles) it
proceeds through the formation of carbanion. The initiation may be brought about by K + NH 2 of L+ NH 2 .
The following steps are involved
(a) Chain initiation : Nu− + CH 2 = CH → Nu − CH 2 − CH
| |
WW
(b) Chain propagation :
Nu − CH 2 − C H + CH 2 = CH → Nu − CH 2 − CH − CH 2 Repeat → Nu − CH 2 − CH − CH 2 −
2 | | |
| W W − CH W
W |
W n
(c) Termination : Nu − CH 2 − CH + H+ → Nu − CH 2 − CH − CH 3
| − CH 2 |
W n W n
Polymer
Chain transfer agents : In Vinylic polymerisation various other molecules react with main growing chain to
interrupt the further growth of the original chain. This leads to lowering of average molecular mass of the polymer
such reagents are called chain transfer agents. The common example CCl4 , CBr4 etc.
For example in the presence of CCl4 styrene polymerizes to form a polymer of lower average molecular mass
which also contains some chlorine.
CH 2 = CH Initiator → C• H 2 − C• H → CH 2 − CH − Cl + C• Cl3
| | |
C6 H5 C6 H5 C6 H5
• − C• H Styrene → CH H
|
CCl3 → Cl3C − CH 2 C6 H5 |
CH 2 CH Cl 3C C H CH − C−
= − 2 − − 2 |
| |
C6 H5 C6 H5
C6 H5
n
Chain transfer agents determinate chain reaction and inhibit further polymerisation and are also called inhibitors.
(2) Step growth or condensation polymerisation : In this type of polymerisation monomers generally
contain two functional groups, i.e., difunctional monomers. In this process no initiator is needed and each step is
the same type of chemical reaction. Since in this polymerisation reaction the polymer is formed in a stepwise
manner. It is called step growth polymer and the process is called step growth polymerisation. The process for two
monomer A and B may be expressed as.
A + B Condense → A − B ; A − B + A Condense → A − B − A ; A − B − A + B → A − B − A − B
Monomers Dimer Trimer
Alternatively, step growth can proceed as
A + B → A − B ; A − B + A − B → A − B − A − B or (A − B)2 ;
A − B − A − B + A − B − A − B Polymer →(A − B)n
Some common examples of step growth polymers are
Polymers Monomers
Nylon-66
Hexamethylenediamine and adipic
Bakelite acid
Dacron (polyester)
Phenol and formaldehyde
Terephthalic acid and ethylene
glycol
Rubber.
It is a polymer which is capable of returning to its original length, shape or size after being stretched or
deformed. It is the example of elastomer. Rubber are of two types.
(1) Natural rubber (2) Synthetic rubber
(1) Natural rubber : It is obtained as latex from rubber trees found in tropical and semitropical countries like
India (south), Malaysia, Indonesia, Ceylon, South America etc. latex is a colloidal suspension of rubber in water.
The latex is coagulated with acetic acid or formic acid. The coagulated mass is then squeezed.
The raw natural rubber is a soft gummy and sticky mass. It is insoluble in water, dil. Acids and alkalies but
soluble in benzene, chloroform, ether, petrol and carbon disulphide. It absorb a large amount of water. It has low
elasticity and tensile strength.
Destructive distillation of natural rubber gives mainly isoprene (2-methyl butadiene).
Thus isoprene is a monomer of natural rubber the no. of isoprene unit are 11,000 to 20,000 which linked
together in a chain.
C| H3 C| H3
C− CH − C = CH − CH 2
nCH 2 = = CH 2 Polymerisation → − CH 2 −
Isopreme
n
Natural rubber
Note : It may be noted that natural rubber is cis-1,4-polyisoprene and has all cis configuration about the
double bond as shown below
CH3 H CH3 H
C=C CH2 CH2 C = C
~ H2C CH2 C = C CH2 CH2 ~
H3C H
All cis configuration
There are weak Vander Waal forces and therefore, it is elastic and non-crystalline. However, its trans
configuration has highly regular zig-zags which fit together well. The all trans configuration occurs
naturally as gutta percha, which is highly crystalline and non-elastic because of packing of chains.
Extended chains of natural rubber and gutta percha are shown :
All cis configuration in natural rubber
All trans configuration in gutta percha
(2) Synthetic rubber : The synthetic rubber is obtained by polymerising certain organic compounds which
may have properties similar to rubber and some desirable properties. Most of these are derived from butadiene
derivatives and contain carbon-carbon double bonds. The synthetic rubbers are either homopolymers of 1, 3
butadiene or copolymer in which one of the monomers is 1, 3 butadiene or its derivative so that the polymer has
the availability of double bonds for its vulcanization. Some important examples are Neoprene, styrene, butadiene
rubber (SBR) thiokol, silicones, polyurethane, rubber etc.
Vulcanization of rubber : The process of heating natural rubber with sulphur to improve its properties is
called vulcanization. Vulcanization was introduced by Charles Goodyear.
Although natural rubber is thermoplastic substance in which there are no cross link between the polymer chain
and it on vulcanization set into a given shape which is retained.
The vulcanization process performed originally was slow. Now a days, some
additives such as zinc oxide etc. are used to accelerate the rate of vulcanization. CH3
During vulcanization, sulphur cross links are formed (figure) the double bonds in the
rubber molecule acts as reactive sites. The allylic − CH 2 , alpha to double bond is |
also very reactive. During vulcanization, suphur forms cross links at these reactive
sites. As a result, rubber gets stiffened and intermolecular movement of rubber ~CH2 – C – CH – CH2~
springs is prevented resulting in physical character of rubber. The extent of stiffness ||
of vulcanized rubber depend upon the amount of sulphur added. For example about SS
5% sulphur is used for making tyre rubber while 30% of the sulphur is used for ||
making battery case rubber.
~CH2 – C – CH – CH2~
In a polymer, the chains are normally tangled up with each other. When the |
rubber is stretched, the chains straighten out to some extent. The chains cannot slip CH3 CH3
past each other because of the polysulphide bridges. Thus, rubber can be stretched |
~CH – C = CH – CH2~
|
S
|
~CH – CH = C – CH2~
only to a limited extent. When the tension is removed, the chains try to coil up again and the rubber resumes its
original shape. CH3 H CH3
H
C=C CH2 CH2 C = C
~CH2 CH2 C = C CH2 CH2~
CH3 H
Natural rubber
All cis configuration
The comparison of the main properties of natural rubber and vulcanized rubber are given below
Natural rubber Vulcanized rubber
(1) Natural rubber is soft and sticky Vulcanized rubber is hard and non-sticky.
(2) It has low tensile strength. It has high tensile strength.
(3) It has low elasticity. It has high elasticity.
(4) It can be used over a narrow range of It can be used over a wide range of temperature (–
temperature (from 10° to 60°C). 40° to 100°C).
(5) It has low wear and tear resistance. It has high wear and tear resistance.
(6) It is soluble in solvents like ether, carbon, It is insoluble in all the common solvents.
tetrachloride, petrol, etc.
Some important polymer and their uses.
(1) Rubber : Are as under all are addition polymer.
Rubber Monomers Formula Application
(i) CH2 = C− CH = CH2 Making
Neoprene automobile,
rubber | refrigerator
Cl CH 2 C = CH CH 2 parts and
− − − − electric wire.
Chloroprene | n Making of
tyre and
Cl other
mechanical
(ii) Styrene CH 2 = CH − CH = CH 2 and CH = CH2 − CH2 − CH = CH − CH2 − CH − CH2 − rubber
Butadiene goods.
Rubber Butadiene (75%) Making of
(SBR) or n toys, tyre,
Buna-S Styrene (25%) tube etc.
(iii) Butyl C| H3 and C| H3 C| H3
rubber CH 2 C
= − CH 2 − C = CH − CH 2 − C− CH 2 −
(iv) Nitrile |
rubber or CH3 |
Buna N or CH3 n
GRA Isobutylene (98 %)
CH 2 = C− CH = CH2
|
CH3
Isoprene (2- 3 %)
CH 2 = CH − CH = CH 2 and Used for
− − make of fuel
Butadiene (75%) CH 2 − CH − CH 2 − CH = CH − CH 2 tank.
n
CH 2 = CH − CN |
Acrylonitrile (25%) CN
(v) Cl − CH 2 − CH 2 − Cl (−CH 2 − CH 2 − S − S − S − S−)n Used in the
Polysulphi manufacture
de rubber Ethylene dichloride of hoses and
(Thiokol) tank lining,
and Na2S4 engine
gasket and
Sodium polysulphide rocket fuel.
Silicon
(vi) CH3 CH3 rubber
Silicone | In the
rubber Cl Si CH 3 | manufacture
(vii) − − − O − Si − of fibre.
Polyuretha | | Paints and
ne rubber Cl CH3 n heat
insulator.
Chlorosilanes Applications
Packing material
HOCH 2 − CH 2OH
Ethylene glycol
O
||
and C = N − CH = CH − N = C = O
Ethylene di-isocyanate
(2) Plastics and resin
Name of polymer Abbreviat- Starting materials Nature of Properties
ion CH 2 = CH 2 polymer
(i) Polyolefines
(a) Polyethylene or HDPE Low density Transparent,
polyethene (High homopolyme moderate carry bags,
density r (branched) tensile insulation for
polyethen chain strength, electrical wires
e) growth. high and cables.
toughness. Buckets, tubs,
High density house ware,
homopolyme Transluscent, pipes, bottles and
r (linear) chemically toys.
chain inert, greater
LDPE CH 2 = CH 2 growth. tensile
(Low strength,
density toughness.
polyethen
e)
(b) Polypropylene or PP CH 3CH = CH 2 Homopolyme Harder and Packing of
polypropene r, linear, stronger than textiles and foods,
chain polyethene. liners for bags,
growth. heat shrinkage
wraps, carpet
fibres, ropes,
automobile
mouldings,
stronger pipes and
bottles.
(c) Polystyrene or C6 H 5 CH = CH 2 Homopolyme Transparent Plastic toys,
Styron r, linear, house hold wares,
chain growth radio and
television bodies,
refrigerator
linings.
(ii) Polyhaloolefines
(a) Polyvinyl PVC CH 2 = CH − Cl Homopolyme Thermoplasti (i) Plasticised
chloride r chains c with high boiling
Vinyl chloride growth esters PVC used
in rain coats,
hand bags,
shower curtains,
fabrics, shoe
soles, vinyl
flooring (ii) Good
electrical
insulator (iii)
Hose pipes.
(b) PTFE F2C = CF2 Homopolyme Flexible and (i) For nonstick
Polytetrafluoroet- ClFC = CF2 r, high inert to utensiles coating
hylene or Teflon melting solvents (ii) Making
point boiling acids gaskets, pump
even aqua packings valves,
regia. Stable seals, non
upto 598 K. lubricated
bearings.
(c) PCTFE Homopolyme Less
Polymonochlorotri- r resistant to Similar to those
fluroroethylene heat and of teflon.
chemicals
due to
presence of
chlorine
atoms.
(iii) Formaladehyde Phenol and Copolymer, Thermosettin (i) With low
resins formaldehyde step growth g polymer, degree
hard and polymerisation as
(a) Phenol Melamine and Copolymer, brittle bindings glue for
formaldehyde resin formaldehyde step growth wood varnishes,
or Bakelite Thermosettin lacquers.
g polymer,
(b) Melamine hard but not (ii) With high
formaldehyde resin so breakable. degree
polymerisation for
combs, for mica
table tops,
fountain pen
barrels electrical
goods (switches
and plugs).
Non-breakable
crockery.
(iv) Polyacrylates PMMA CH3 Copolymer Hard Lenses light
transparent, covers lights,
(a) | excellent shades signboards
Polymethacrylate light transparent
(lucite, acrylite and CH 2 = C− C OOCH 3 transmission, domes skylight
plexiglass and optical aircraft window,
perspex)
clarity better dentures and
than glass plastic jewellery.
takes up
(b) CH 2 = CH − COOC2 H5 Copolymer colours.
Polyethylacrylate
Tough,
rubber like
product
(3) Fibre PET HO − CH 2 − CH 2 − OH Copolymer, Fibre crease For wash and
(i) Polysters (Polyethylen step growth resistant, low wear fabrics,
(a) Terylene or e Ethylene glycol or Ethane -1, 2-diol linear moisture tyre cords seat
Dacron terephthalat condensation absorption, belts and salts.
e) and O polymer not damaged
(b) Glyptal or O by pests like Paints and
alkyl resin || Copolymer, moths etc. lacqures.
|| linear step
(ii) Polyamides C – OH growth Thermoplasti
(a) Nylon-66 HO – C condensation c, dissolves in
polymer suitable
(b) Nylon-610 Terephthalic acid solvents and
solutions on
(c) Nylon-6 or HO − CH2 − CH2 − OH evaporation
Perlon leaves a tough
Ethylene glycol but not
flexible film.
and COOH
Phthalic acidCOOH
OO Copolymer, Thermoplasti Textile fabrics,
linear, step c high tensile bristles for
|| || growth strength brushes etc.
condensation abrasion
HO − C[CH 2 ]4 C− OH polymer resistant. (i) Textile
Copolymer, Thermoplasti fabrics,
Adipic acid linear, step c, high tensile carpets,
growth strength, bristles for
and H 2 N − [CH 2 ]6 − NH 2 abrasion brushes etc.
Homopolyme resistant (ii) Substitute
Hexamethyllenediamine r, linear of metals in
Thermoplasti bearings.
H 2 N − [CH 2 ]6 − NH 2 c high tensile (iii) Gears
strength elastic hosiery.
Hexamethyllene diamine Mountaineerin
g ropes, tyre
and HOOC[CH 2 ]8 COOH cords, fabrics.
Sebacic acid
H
NO
Caprolactum or
H2N – [CH2]5 – COOH
∈-Aminocaproic acid
abraison
resistant.
(iii) PAN CH 2 = CH − CN Copolymer Hard, horney Orlon, acrilon
Polyacryloni- and high used for
trile or orlon or melting making
acrilon materials. clothes,
carpets
blankets and
preparation of
other
polymers.
Note : Copolymer of acrylonitrile (40%) and vinyl chloride (60%) is called dynel it is used in hair wigs.
Artificial silk is the term given to fibres derived from cellulose. The most important process for the
production of artificial silk is viscose process. The difference between natural and artificial silk is
natural silk contain nitrogen while artificial silk may not have nitrogen. Natural silk on burning gives
a smell of burning hair and shrinks into a ball of cinder while artificial silk gives a thread of ash.
Biodegradable polymers.
These are the polymers which are degraded by micro-organisms within a suitable period so that biodegradable
polymers and their degraded products do not cause any serious affects on the environment.
In biological systems, biopolymers degrade mainly by enzymatic hydrolysis and to some extent by oxidation.
Therefore, in view of the disposal problems of polymer waste and for developing polymers for other safe uses in
human systems, attempts have been made to develop biodegradable synthetic polymers. These synthetic polymers
mostly have functional groups which are normally present in biopolymers and lipids.
Among these aliphatic polyesters are one important class of biodegradable polymers which are commercially
potential biomaterials. The common examples of biodegradable polymers are polyhydroxy butyrate (PHB),
polyhydroxy butyrate –co-β-hydroxy valerate (PHBV), polyglycolic acid (PGA), polylactic acid (PLA), poly (∈-
caprolactone) (PCL), etc.
Uses : Biodegradable polymers are used mainly for medical goods such as surgical sutures, tissue in growth
materials or for controlled drug release devices, plasma substitutes etc. The decomposition reactions usually involve
hydrolysis (either enzymatically induced or by non-enzymatic mechanisms) to non-toxic small molecules which can
be metabolized by or excreted from the body. These are also finding use in agriculture materials (such as films, seed
coatings), fast food wrappers, personal hygiene products, etc.
(i) Polyhydroxy butyrate (PHB)
Polyhydroxy butyrate (PHB) is obtained from hydroxy butyric acid (3-hydroxy butanoic acid)
O O
|| − || −
HO CHCH C OH Condensation → O CHCH
2 − 2 C n
| acid |
CH3
3-Hydroxy butanoic CH3
Polyhydroxybutyrate (PHB)
(ii) Poly-Hydroxybutyrate-co-β-Hydroxy valerate (PHBV) : It is copolymer of 3-hydroxy butanoic acid
and 3-hydroxy pentanoic acid, in which the monomer units are joined by ester linkages.
CH 3 − CH − CH 2 COOH + CH 3 − CH 2 − CH − CH 2 − COOH → − O − CH − CH 2 − CO − ,
| ||
| | R PHBV O
OH OH
3-Hydroxy butanoic acid 3-Hydroxy pentanoic acid n
R = CH 3 , C2 H5
The properties of PHBV vary according to the ratio of both the acids. 3-Hydroxy butanoic acid provides
stiffness while 3-Hydroxypentanoic acid gives flexibility to the copolymer.
(iii) Polyglycolic acid (PGA) : Polyglycolic acid (PGA) is obtained by the chain polymerisation of cyclic
dimer of glycolic acid, HO − CH 2 − COOH .
nHO − CH 2COOH Heat → − OCH 2 O
||
C−
Glycolic acid
n
Polyglycolic acid (PGA)
(iv) Polylactic acid (PLA) : Polylactic acid (PLA) is obtained by polymerisation of the cyclic dimer of lactic
acid (HO − CH(CH3 )COOH) or by microbiological synthesis of lactic acid followed by the polycondensation and
removal of water by evaporation.
O Condensation → O
|| ||
OH OCH C−
HOCHC− − | −
|
CH3
CH3 n
Polylactic acid (PLA)
Lactic acid
(v) Poly (∈-caprolactone) (PCL) : It is obtained by chain polymerisation of the lactone of 6-hydroxy
hexanoic acid.
O
||
− O − (CH 2 )2 − C−
n
PCL
Uses : PGA and PLA (90 : 10) is used to make absorbable structure to close an internal of external wound
and has replaced cat gut these are completely degraded and absorbed by the body within 15 days to one month of
the surgery.
Polyhydroxybutyrate (PHB) and (PHBV) have been used for making films for packaging and into moulded
items.
Molecular masses of polymers.
A polymer sample contains chain of varying lengths and therefore its molecular mass is always expressed as an
average on the other hand natural polymer such as proteins contain chain of identical length and therefore they
have definite molecular mass.
The molecular mass of a polymer can be expressed in two ways.
(1) Number average molecular mass (M N ) (2) Weight average molecular mass (MW ).
(1) Number average molecular mass (M N ) : If N1, N 2, N 3 ….. are the number of molecules with
molecular masses M1, M 2, M 3 …… respectively, then the number average molecular mass is
MN = N1M1 + N2M2 + N3M3 + ...
N1 + N 2 + N 3 ...
This may be expressed as : MN = ∑ NiMi
∑ Ni
Where Ni is the number of molecules of the ith type with molecular mass Mi .
(2) Weight average molecular mass (MW ) : If m1,m2,m3 …. are the masses of species with molecular
masses M1, M 2, M 3 ….. respectively, then the weight average molecular mass is
MW = m1 M1 + m2 M 2 + m3 M 3 .... or MW = ∑ mi Mi
m1 + m2 + m3 + ... ∑ mi
But mi = Ni Mi , so that MW = ∑ N i M 2
i
∑ NiMi
where Ni is the number of molecules of mass Mi .
Note : Polydispersity index : The ratio of mass average molecular mass to the number average
molecular mass is called polydispersity index, PDI.
PDI = MW
Mn
This gives an idea about the homogeneity of a polymer.
(i) The polymers whose molecules have nearly same molecular masses are called monodisperse
polymers. For these molecules, MW = M N and therefore, PDI is one.
(ii) The polymers whose molecules have wide range of molecular masses are called polydisperse
polymers. For these polymers, MW > M N and therefore, their PDI is greater than one.
Thus, it may be concluded that in general, natural polymers are more homogeneous than
synthetic polymers.
For natural polymers, PDI is usually unity and therefore, natural polymers are monodisperse.
Example: 1 For synthetic polymers, the PDI is greater than one and therefore MW is always greater than M N .
M N is always determined by employing methods which depend upon the number of molecules
present in the polymer sample. For example, colligative property such as osmotic pressure is used.
On the other hand, weight average molecular mass is measured by using the methods such as light
scattering and ultracentrifugation, sedimentation, etc. which depend upon the mass of individual
molecules.
In a polymer sample 30% molecules have a molecular mass 20,000 40% have molecular mass 30,000 and
rest have 60,000. Calculate mass average and number average molecular masses ?
Solution : The polymer contains 30% molecules of mass 20,000 40% molecules of molecular mass 30,000 and rest 30%
of molecular mass 60,000. Thus
MN = ∑ NiMi = (20 × 20000) + (40 × 30000) + (30 × 60000) = 3600
∑ Ni 30 + 40 + 30
MW = ∑ NiM 2 = 30(20,000)2 + 40(30000)2 + 30(60000)2 = 43333
∑ NiMi 30 × 20000 + 40 × 30000 + 30 × 60000
(3) Polymer in increasing order of their intermolecular forces are polythene < Buna S < Nylon-66.
(4) We always use purest monomer in free radical polymerisation reaction because the impurities can act as
chain transfer agent and may combine with the free radical to slow down the reaction or even stop the reaction.
(5) Benzoquinone inhibit the free radical polymerisation of vinyl derivative because it combine with free
radical intermediate to form a non reactive radical which is highly stabilized by resonance because of the lack of
reactivity of the new radical formed, it inhibit the further progress of the chain reaction. Therefore the reaction stops.
O OR OR OR OR OR
;
R• + •
Free radical •
O O• O• O OO
Benzoquinone Resonance stabilized
(6) A thin film of polyester is known as Mylar film.
(7) PET plastic commonly used for soft drink bottles, transparent jars and bottles for use in kitchen are made
up of polyethylene terephthalate, chemically same as terylerte - a polyester.
(8) Glyptal resins or Alkyl resins obtained from ethylene glycol and phthalic acid are thermoplastic. However,
resins obtained from glycerol and phthalic acid are thermosetting polymers, due to the formation of cross-links by
the third –OH group present in glycerol.
(9) Thermosetting plastics are also called heat setting plastics whereas thermoplastics are called cold setting plastics.
(10) Latex is a colloidal dispersion of rubber in water. It is not a colloidal solution of isoprene in water or any
other solvent.
(11) Polymerisation of isoprene by free radical mechanism (in the presence of Na and heat) gives a product
which is different from natural rubber (Natural rubber is a polymer of isoprene). The synthetic product so obtained
is a mixture of cis and trans configurations and resembled Gutta percha. Gutta percha is a naturally occurring
polymer in plants. It is all trans-stereoisomer and is non-elastic.
(12) Terylene is a British name of Dacron.
(13) Co-polymer of vinyl chloride 90% and vinyl acetate 10% is called VINYON.
(14) Co-polymer of acrylonitrile 40% and vinyl chloride 60% is called DYNEL.
(15) Co-polymer of vinyl chloride and vinyledene chloride is called SARAN.
(16) Plasticizers cannot convert a thermosetting polymer into thermoplastic one. It converts a hard and brittle
plastic into soft and easily pliable one at room temperature.
(17) Free radical polymerisation of isoprene do not give Gutta percha (Gutta percha is a natural polymer). The
synthetic product so obtained resembles Gutta percha.
(18) Co-ordination polymerisation of isoprene gives a product similar to natural rubber.
(19) Latex is not a colloidal dispersion of isoprene in water.
Advance level information.
(1) Thermocol is polystyrene foamed with vapour of pentane.
(2) Cups used for hot drinks are made up of polystyrene. It does not become soft like other plastics at
temperatures near boiling point of water.
(3) A major development of co-ordination polymerisation is stereochemical control. Propene, for example,
could polymerise to any of the three different arrangements. Isotactic : with all methyl groups on one side of an
extended chain. Syndiotactic : with methyl groups alternating regularly from side to side. Atactic : with methyl
groups distributed at random. By proper choice of experimental conditions, i.e., temperature, pressure and catalyst,
each of these stereoisomeric propylene has been made.
(4) Addition polymers, generally, have only carbon atoms in their main chain. On the other hand,
condensation polymers, generally, have atoms other than carbon atoms, in their main chain.
(5) Polyurethanes : Polyurethanes are polymers obtained by the polymerisation of a urethane.
It is used for heat and sound insulation in the form of polyurethane foam. Mattresses, cushions and pillows
made out of polyurethane foam are washable and long lasting.
H
|
R − N − C− OR′
||
O
A urethane
(6) Epoxy resins : These are obtained by copolymerisation of epichlorohydrin and bisphenol-A. These resins
have good adhesive strength. These are used for making adhesives (Araldite, M-seal etc.) for making glass
reinforced plastic (fibre glass), for lamination, to impart crease resistance and shrinkage control to cotton, rayon and
for making anti-skid surface for highways.
(7) Polycarbonates : These are obtained by copolymerisation of diphenyl carbonate and bisphenol-A. It has
very high optical transparency, high impact strength over wide range of temperature. It is used for making bullet-
proof glass, baby-feed bottles, fridge containers, mixi jars etc.
(8) Thermoplastics are also called cold setting polymers. They are moulded when hot but set into the required
shape only on cooling. Thermosetting polymers are also called heat setting polymers. Such polymers are supplied in
the partially polymerised form. When put in a mould and heated they set into the required shape. They do not
require any cooling for setting.
(9) On long exposure to air and sun-light thermo-plastics becomes brittle. It is due to the evaporation of
plasticizer with time. The faint smell associated with various thermoplastics is due to slow evaporation of this
plasticizer.
(10) High density polyethene is a linear polymer. Carry bags made out of it are not so soft and make a
crackling sound when crushed in hands. You can easily tear them in one direction, but not at right angle to it.
Plastic twine is made out of such a polymer. They have very high tensile strength in one direction (along the
polymer chain) and a low tensile strength at right angle to it. Such carry bags are used to carry clothes, note-books
etc. Carry bags made of low density polyethene are soft, make no noise when crushed with hands, have same
tensile strength in all directions. Such carry bags are used to carry heavy objects (vegetables, fruits etc.)
(11) Kevlar is a nylon-polymer and is obtained by condensation copolymerization of terephthalic acid with
1, 4-diaminobenzene (p-phenylenediamine). The fibres of this polymer are so strong that they are used to make
bullet-proof vests.
(12) Lexan is a polycarbonate(polyester) and is prepared by condensation copolymerization of diethyl
carbonate and bisphenol A. It has unusually high impact strength and hence is used in making bullet-proof windows
and safety or crash helmits.
(13) Nomex is a polyamide made from m-phthalic acid and m-diaminobenzene. It is known for its fire-
resistant properties and is used in protective clothing for firefighters, astronauts and race car drivers.
(14) Ebonite is high sulphur (20-30 %S) rubber and is obtained by vulcanization of natural rubber.
(15) Rayon was originally called artificial silk but now the name rayon is given to all fibres obtained by
chemical treatment of cellulose. Thus, artificial silk is polysaccharide, i.e., cellulose derivative.
Stereochemical arrangement of polymers
(i) Isotactic (Same order) : When groups are arranged on one side of the chain. All y group i.e. on one side
and all Z groups on the opposite side of the chain. Y
YY
Z ZZ
(ii) Syndiotactic (Alternating order) : The Y and Z groups lie alternately on each side of the chain.
YZ Y
ZYZ
(iii) Atactic (Random order) : The Y and Z groups are arranged in a random fashion.
YZZ
Z ZY
Chemistry in action
Chemistry plays very important role in our every day life from the starting, it has been in the service of mankind.
Our daily needs of food, clothing, shelter, potable water, medicines etc. are in one or the other manner connected with
chemical compounds, processes and principles. We always owe a debt to chemists for their important contributions for
giving us life saving drugs, synthetic fibres, synthetic detergents, variety of cosmetics, preservatives for our food,
fertilizers, pesticides etc. There is no aspect of our life that is not affected by the developments in chemistry. Thus the
mankind owes much to chemistry because it has improved the quality of life.
Dyes.
Dye is a natural or synthetic colouring matter which is used in solution to stain materials especially fabrics. All
the coloured substances are not dyes. A coloured substance is termed as a dye if it fulfils the following conditions,
It must have a suitable colour.
It can be fixed on the fabric either directly or with the help of mordant.
When fixed it must be fast to light and washing, i.e., it must be resistant to the action of water, acids and
alkalies, particularly to alkalies as washing soda and soap have alkaline nature.
(1) Theory of Dyes : A dye consists of a chromophore group and a salt forming group called anchoric
group. In 1876, Otto witt put forth a theory as to correlate colour with molecular structure (constitution). The
theory is named 'The Chromophore Auxochrome Theory' and its main postulates are,
(i) The colour of the organic compounds is due to the presence of certain multiple bonded groups called
chromophores. Important chromophores are,
O OO
|| | || |
− N = N −; − N → O : ; − N = N −; C=O:; || || C=C ;
Azo Nitro O↓ ; − C = C− C = C−
Carbonyl C = S : ; − C− C−; Ethylenic Conjugated group
Thio carbonyl Dicarbonyl
Azoxy Quinonoid
[Chromophore-Greek word, Chroma = colour, Phorein = to bear].
The presence of chromophore is not necessarily sufficient for colour. To make a substance coloured, the
chromophore has to be conjugated with an extensive system of alternate single and double bonds as exists in
aromatic compounds.
The chromophore part of the coloured substance (dye) absorbs some wavelengths from white light and reflects
back the complementary colour. A coloured compound having a chromophore is known as chromogen.
(ii) Certain groups, while not producing colour themselves, when present along with a chromophore in an
organic substance, intensify the colour. Such colour assisting groups are called auxochromes (Greek word,
Auxanien = to increase; Chrome = colour), i.e. they make the colour deep and fast and fix the dye to the fabric.
The auxochromes are acidic or basic functional groups. The important auxochromes are,
Acidic : − OH − SO3 H − COOH
Sulphonic Carboxylic
Hydroxy
Basic : − NH2 − NHR − NR2
Amino
Alkylamino Dialkylamino
Example :
HSO3 N=N N(CH 3 )2
Auxochrome Chromophore
Chromogen
Examples : Chromophore Auxochrome
–N=N– – NH2
Dye
p-Aminoazobenzene O Error! Not a valid link.– OH
H2N (OrNan=ge)N –N O
Picric acid
OH
O2N NO2
NO2
(Yellow)
Alizarin OH
O OH
– OHError! Not a valid link.
O – N(CH3)2
(Purple solution in alkali)
Malachite green
C N+ (CH 3 )2 Cl
N(CH3)2
However, Otto witt chromophore-Auxochromo concept fails to explain the colour of certain dye stuffs like
indigo.
(2) Classification of Dyes : Dyes are classified to their chemical constitution or by their application to the
fibre.
(i) Classification of dyes according to their chemical structure
(a) Nitro and Nitroso dyes : These dyes contain nitro or nitroso groups as the chromophores and –OH as
auxochrome. A few example are,
O2N OH NO2 NO OH OH
OH NO NO2
NO2 1-Nitroso-2-naphthol 2-Nitroso-1-naphthol NO2
(Gambine-Y) (Gambine-R)
Picric acid Martius yellow
(2 : 4 : 6-Trinitrophenol) OH
NO2 NO
HO3S NaO3S OH
NO2 Naphthol green-B
Naphthol yellow-S
(b) Azo dyes : The azo dyes contain one or more azo groups – N=N–, as the chromophore. Azo dyes
constitute the largest and most important group of synthetic dyes. These can be prepared by diazotising an aromatic
amine and subsequent coupling with a suitable aromatic phenol or amine.
N = NCl + H NH 2 −HCl → N=N NH 2
30−40o C
p-Amino azobenzene (Aniline yellow)
N = NCl + H N(CH3 )2 → N=N N(CH3 )2
The important azo dyes are the following, p-Dimethyl amino azobenzene
(Butter yellow)
NH2
N=N NH2 , HO3S N=N N(CH 3 )2 ,
Methyl orange COOH
N=N NH 2 N=N N(CH 3 )2
NH2 Methyl red
Bismark brown NH2 NH2
N=N
N=N
SO3H Congo red SO3H
Azo dyes are highly coloured. Azo dyes can be further divided into acid, basic, direct, ingrain or developed
dyes, etc., on the basis of mode of application.
(c) Tri aryl methane dyes : In these dyes, the central carbon is bonded to three aromatic rings. One of which is
in the quinonoid form (the chromophore). Malachite green is the typical example of this class.
C N+ (CH3)2 C l
N(CH3)2
Malachite green
Rosaniline and crystal violet are other two important dyes of this class.
(d) Anthraquinone dyes : Para quinonoid chromophore is present in these anthracene type dyes. Alizarin is a
typical anthraquinone dye.
OH O OH
O2N NO2 OH
NO2 O
(Yellow) Alizarin
(e) Phthaleins : Products obtained by condensation of phthalic anhydride with phenols in presence of
dehydrating agents like conc. H2SO4 or anhydrous zinc chloride are called phthaleins.
OO
CO CO
CH C
OH
Phthalic O + OH Conc.
anhydride H H2SO4 →
120o C
− H 2O
Phenol OH OH
(2 molecules)
Phenolphthalein
The other important dyes of this class are,
O Br O
OH Br OH HgOH O O
Br Br
Br COOH
O OH
Br
O=C C O
COOH
Fluorescein OH Eosin Mercurochrome
(f) Indigo dyes : These dyes contain the carbonyl chromophore. Indigo is the oldest known dye.
OH
CN
C=C
NC
HO
Indigo (Dark blue crystalline powder)
Another indigo dye is royal blue in colour which is dibromo derivative of indigo. It is called Tyrian blue.
O H Br
C N
C=C
Br N C
HO
Note : Common 'Neel' used as a blueTiynriagnapgurepnlet in laundary to remove yellowish tint on white clothes or
in whitewashing is not indigo. It is ultramarine blue – an inorganic complex silicate of aluminium and
sodium with about 13% sulphur.
(ii) Classification of dyes according to their application
(a) Direct dyes : Direct dyes can be directly applied to the fibre, both animal and vegetable, by dipping in hot
aqueous solution of the dye. These dyes are most useful for those fabrics which can form hydrogen bonds, i.e., for
cotton, rayon, wool, silk and nylon. Martius yellow and congo red act as direct dyes. Examples : Marius yellow,
congo red.
(b) Acid dyes : These are usually salts of sulphonic acids and can be applied to wool, silk and nylon. The
presence of sulphonic acid group makes them water soluble. These dyes are applied from an acidic bath. The polar
acidic groups interact with the basic groups of the fabric. Orange-1 is an excellent acid dye.
Na +O3−S N=N OH
Orange-1 (Azo dye)
(c) Basic dyes : These are the hydrochlorides or zinc chloride salts of colour bases having basic groups. These
dyes react with anionic sites present on the fabric to attach themselves. These dyes colour fibres of nylons and
polyesters. Aniline yellow. Magenta (Rosaniline) and Malachite green are the examples of basic dyes.
Cl −− H2 N+ CH3
C NH2
MNagHen2ta
Note : Acid and basic dyes are actually direct dyes.
(d) Mordant dyes : These dyes have no natural affinity for the fabric and are applied to it with the help of
certain additional substances known as mordants. A mordant (Latin mordere = to bite) is any substance which can
be fixed to fabric and reacts with the dye to produce colours on fabric. Three types of mordants are commonly
used,
• Acidic mordants like tannic acid which are used with basic dyes. Fabric Mordant
• Basic mordants such as metallic hydroxides or albumin which are used OO OH
with acidic dyes. Al
• Metallic mordants like salts of aluminium, chromium, iron, tin, etc., OO
which are used with acidic dyes.
Actually the mordant forms an insoluble coordination compound O Alizarin
between the fabric and the dye and binds the two. Alizarin is a typical mordant
dye. It gives different colours depending on the metal ion used. For example, Coordination compound of Alizarin with Al3+
with Al 3+ , alizarin gives a rose red colour; with Ba2+ , a blue colour; with
Fe 3+ , a violet colour and with Cr 3− , a brownish red colour.
The process of mordant dyeing consists in impregnating the fabric with mordant in presence of wetting agent
followed by soaking of the fabric into the solution of dye.
(e) Vat dyes : These dyes are insoluble in water and cannot be applied directly. These dyes on reduction with
sodium hydrosulphite (NaHSO3 ) in a vat form a soluble compound which has great affinity for cotton and other
cellulose fibres. The cloth is soaked in the solution of a reduced dye and then hung in air or treated with oxidants
like perboric acid. As a result, the colourless compound is oxidised to insoluble dye which is now bound to the
fabric. The colourless and reduced state of the dye is called the Leuco base. The common examples of vat dyes are
indigo and tyrian purple. These are mostly used on cotton.
OH Reduction OH H
CN Oxidation CN
C=C CC
NC NC
HO H OH
Indigo Indigo-white, Leucobase
(Blue, water insoluble) (Colourless water insoluble)
(f) Ingrain dyes (developed dyes) : Ingrain dyes are those which are synthesised directly on the fabric.
Examples of this type are azo dyes. The fabric is immersed in the solution of coupling reagent (usually a phenol or
naphthol). Then it is dipped in the solution of suitable diazonium salt. Both react to form the dye whose molecules
are adsorbed on the surface of fabric. The ingrain dyeing is particularly suitable for cotton fabrics.
(g) Disperse dyes : These dyes are used to colour synthetic fabrics such as nylon, orlon, polyesters and
cellulose acetate which have tightly packed structures. The dyes are dispersed in a colloidal form in water. The fabric
is immersed in the colloidal dispersion of the dye when fine dye particles are trapped within the polymer structure of
the fabric. Examples of this type are monoazodye and anthraquinone dye.
Drugs and Chemotherapy.
Drugs may be a single chemical substance or a combination of two or more different substances. An ideal drug
should satisfy the following requirements,
When administrated to the ailing individual or host, its action should be localised at the site where it is desired to
act. In actual practice, there is no drug which behaves in this manner.
It should act on a system with efficiency and safety.
It should have minimum side effects.
It should not injure host tissues or physiological processes.
The cell should not acquire resistance to the drug after sometime.
Very few drugs satisfy all the above requirements. Each drug has an optimum dose, below which it has no
action and above this level it becomes a poison.
The term chemotherapy, which literally means chemical therapy or chemical treatment was coined in 1913 by
Paul Ehrlich, the father of modern chemotherapy. He defined chemotherapy as the use of chemicals
(drugs) to injure or destroy infections micro-organisms without causing any injury to the host.
Further growth of cancerous cells in the body is arrested by chemotherapy. Chemotherapy has developed into
a vast subject today and efforts are being continuously made to search new drugs as to free human beings from
various types of diseases. Chemicals (drugs) used in chemotherapy are usually classified according to their action.
(1) Antipyretic : Antipyretic is a drug which is responsible for lowering the temperature of feverish body. The
central nervous system, especially the hypothalamus, plays an important role in maintaining the balance between
the heat production and heat loss in order to regulate the body temperature. Hypothalamus is, thus, known as the
thermostat of the body.
The antipyretic drug helps to reset the thermostate at normal temperature. Heat production is not inhibited but
heat loss is increased by increased peripheral blood flow which increases the rate of perspiration. This causes body
to lose heat and subsequently lowers the body temperature.
Aspirin is an important antipyretic. The other antipyretics are phenacetin, O
paracetamol, novalgin and phenyl butazone. O C CH3
COOH
Aspirin should not be taken empty stomach. Some persons are allergic to aspirin.
The usual allergic reaction is rashes on skin, lowering of blood pressure, profuse Aspirin
sweating, intense thirst, nausea and vomitting. Calcium and sodium salts of aspirin are (Acetyl salicylic acid)
more soluble and less harmful.
The derivatives of p-aminophenol are used as antipyretic. The main limitation of these derivatives is that they
may act on red blood cells and thus, they may be harmful in moderate doses. The important derivatives are,
NHCOCH3 NHCOCH3 NHCOCH3
OC2H5 OH OCH3
Phenacetin Paracetamol Methacetin
(4-Ethoxy acetanilide) (4-Acetamidophenol) (4-Methoxy acetanilide)
Phenyl butazone is a pyrazolone derivative. Its structure is,
C6H5 C4H9 CH C O
C6H5N N CO or O C N C6H5
C C.C4H9 N
ONa C6H5
Phenyl butazone Butazolidine
It is highly toxic and hence not considered as a safe drug. Oxyphenyl butazone is less toxic and is used in
place of phenyl butazone.
(2) Analgesics : Drugs which relieve or decrease pain are termed analgesics. These are of two types,
(i) Narcotics : These are mainly opium and its products such as morphine, codeine and heroin. These
produce analgesia and sleep and in high doses cause unconsciousness. They are very potent drugs and their
chronic use leads to addiction.
(ii) Non-narcotics : These are the drugs which are not potent and do not cause addiction. Common drugs
are aspirin and analgin. These drugs also have antipyretic properties.
O C N N CH3
H–C C
CH3 CH2COCOl Na CH3
CHCOOH
Analgin
(CH3)2CH–CH2 CHCOOH ; NH ; H3CO Naproxen
CH3 Cl
Ibuprofen
Diclofenac
Sodium
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