Note : Acetylene required for this purpose is obtained by action of water on calcium carbide.
CaC2 + 2H 2O → Ca(OH)2 + C2 H2
The yield is very good and the strength of acid prepared is 97%. The method is also quite cheap.
(c) By the action of CO on methyl alcohol : Methyl alcohol and carbon monoxide react together under a
pressure of 30 atmospheres and 200°C in presence of a catalyst cobalt octacarbonyl, Co2(CO)8 to form acetic acid.
CH3OH + CO Co2(CO)8 → CH 3 COOH
30atm200°C Acetic acid
Methyl alcohol
(2) Physical properties
(i) At ordinary temperature, acetic acid is a colourless, corrosive liquid with a sharp pungent odour of vinegar.
It has a sour taste.
(ii) Below 16.5°C, it solidifies as an icy mass, hence it is named glacial acetic acid.
(iii) It boils at 118°C. The high boiling point of acetic acid in comparison to alkanes, alkyl halides or alcohols of
nearly same molecular masses is due to more stronger hydrogen bonding between acid molecules. This also
explains dimer formation of acetic acid in vapour state.
(iv) It is miscible with water, alcohol and ether in all proportions.
(v) It is good solvent for phosphorus, sulphur, iodine and many organic compounds.
(3) Chemical properties : Acetic acid is a typical member of fatty acids. It shows all the general
characteristics of monocarboxylic acids.
Reaction chart of Acetic acid
Na CH3COONa
NaOH
NaHCO3 Sodium acetate
CH3COONa
CH3COONa+H2O+CO2↑
CH3COOH C2H5OH CH3COOC2H5
H2SO4
Acetic acid PCl3 or PCl5 Ethyl acetate
or SOCl2
CH3COCl
P2 O5
heat Acetyl chloride
(i) NH3 (CH3CO)2O
(ii) heat
Acetic anhydride
LiAlH4
CH3CONH2
NaOH+CaO
heat Acetamide
(i) CaCO3 CH3CH2OH
(ii) heat
Ethyl alcohol
(i) CaCO3
(ii) (HCOO)2 Ca, heat CH4
N3H Methane
Conc. H2SO4
CH3COCH3
(i) KOH
(ii) Electrolysis Acetone
(4) Uses : It is used, Cl2 red P CH3CHO Cl2 CHCl2COOH Cl2 CCl3COOH
heat P
Acetaldehyde Dichloro acetic acid P Trichloro acetic acid
CH3NH2
Methyl amine
CH3–CH3
Ethane
CH2ClCOOH
Chloroacetic acid
(i) As a solvent and a laboratory reagent.
(ii) As vinegar for table purpose and for manufacturing pickles.
(iii) In coagulation of rubber latex.
(iv) For making various organic compounds such as acetone, acetic anhydride, acetyl chloride, acetamide and esters.
(v) For making various useful metallic acetates, such as:
(a) Basic copper acetate which is used for making green paints.
(b) Al, Fe and Cr acetates which are used as mordants in dyeing.
(c) Lead tetra-acetate which is a good oxidising agent.
(d) Basic lead acetate which is used in the manufacture of white lead.
(e) Aluminium acetate which is used in the manufacture of water-proof fabrics.
(f) Alkali acetates which are used as diuretics.
(5) Tests
(i) Its aqueous solution turns blue litmus red.
(ii) Its aqueous solution gives effervescences with sodium bicarbonate.
(iii) The neutral solution of the acetic acid gives a wine red colour with neutral ferric chloride solution.
(iv) When heated with ethyl alcohol in presence of a small amount of concentrated sulphuric acid, it forms
ethyl acetate which has fruity smell.
(v) Acetic acid does not show reducing properties like formic acid, i.e., it does not reduce Tollen's reagent,
Fehling's solution and mercuric chloride.
Comparison of Formic Acid and Acetic Acid
Property Formic acid Acetic acid
1. Acidic nature,
(i) With electro- Forms salts, Hydrogen is evolved. Forms salts. Hydrogen is evolved.
positive metals
HCOOH + Na → HCOONa + 1 H2 CH 3 COOH + Na → CH 3 COONa + 1 H2
(ii) With bases 2 2
(iii) With Forms salts. Forms salts.
carbonates and
bicarbonates HCOOH + NaOH → HCOONa + H 2O CH3COOH + NaOH → CH3COONa + H 2O
Forms salts. Carbon dioxide is evolved.
Forms salts. Carbon dioxide is evolved.
HCOOH + NaHCO3 → HCOONa + H 2O + CO2 CH3COOH + NaHCO3 →
2. Ester formation Forms esters when treated with alcohols. CH 3COONa + H 2O + CO2
HCOOH + C2 H 5OH → HCOOC2 H 5 + H 2O
Forms esters when treated with
alcohols.
CH 3COOH + C2 H 5 OH H2SO4(conc.) →
3. Reaction with Forms formyl chloride which decomposes into CH 3COOC2 H 5 + H 2O
PCl5 CO and HCl. Forms acetyl chloride which is a stable
HCOOH + PCl5 → HCOCl(HCl + CO) + POCl3 + HCl compound.
4. Heating of CH 3COOH + PCl5 →
ammonium salt Forms formamide.
HCOONH 4 → HCONH 2 + H 2O CH 3COCl + POCl3 + HCl
Forms acetamide.
CH 3COONH 4 → CH 3CONH 2 + H 2O
5. Heating alone it decomposes into CO2 and H2 Unaffected
Unaffected
6. Heating with HCOOH → CO2 + H 2
conc. H2SO4 Forms mono, di or trichloro acetic
Decomposed into CO and H2O acids.
7. Reaction with
Cl2 in presence of HCOOH Conc. → CO + H2O Forms acetone.
red P (CH 3COO)2 Ca → CH 3COCH 3 + CaCO3
8 Action of heat H 2 SO4 Unaffected.
on salts,
(i) Calcium salt Unaffected Forms sodium carbonate and methane.
CH 3COONa + NaOH CaO →
Forms formaldehyde.
(HCOO)2 Ca → HCHO + CaCO3
(ii) Sodium salt Forms sodium oxalate.
(iii) Sodium salt 2HCOONa heat → COONa H2
with soda-lime |+
COONa
Forms sodium carbonate and H2.
HCOONa + NaOH CaO → Na2CO3 + H 2
9. Electrolysis of It evolves hydrogen. CH 4 + Na2CO3
sodium or It forms ethane.
potassium salt
10. On heating Unaffected Forms acetic anhydride.
with P2O5 2CH 3COOH P2O5 →(CH 3CO)2 O + H 2O
11. Reducing Gives silver mirror or black precipitate. Unaffected.
nature, HCOOH + Ag 2O → 2Ag + CO2 + H 2O
(i) Tollen's
reagent Gives red precipitate Unaffected.
(ii) Fehling's HCOOH + 2CuO → Cu2O + CO2 + H 2O Unaffected.
solution
Forms a white ppt. which changes to greyish Unaffected.
(iii) Mercuric black.
chloride HgCl 2 → Hg 2Cl 2 → 2Hg
(iv) Acidified Decolourises
KMnO4
12 Acid (neutral Greenish blue colour. Unaffected.
solution) +
NaHSO3 + Red colour which changes to brown ppt. on Wine red colour.
Sodium heating.
nitroprusside.
13 Acid (neutral
solution) +
neutral ferric
chloride
Interconversions
(1) Ascent of series : Conversion of formic acid into acetic acid.
HCOOH Ca(OH)2 →(HCOO)2 Ca heat → HCHO CH3MgBr → CH 3CH 2OMgBr H2O → CH 3CH 2OH
Formic acid Calcium formate Formaldehyde Addition product H+ Ethyl alcohol
[O] → CH 3CHO [O] → CH 3COOH
Acetaldehyde Acetic acid
HCHO H2 Ni → CH3OH HI → CH3 I KCN(Alc.) → CH3CN H2O → CH 3 COOH
Formaldehyde Methyl alcohol Methyl Methyl H+ Acetic acid
iodide cyanide
Arndt-Eistert homologation : This is a convenient method of converting an acid, RCOOH to RCH2COOH.
RCOOH SOCL2 → RCOCl CH2N2 → RCOCHN 2 EtOH → RCH 2 COOC 2 H 5 Hydrolysis → RCH 2COOH
Ag 2O
(2) Descent of series : Conversion of acetic acid into formic acid.
N3H → CH 3 NH 2 NaNO2HCl → CH 3OH [O] → HCHO [O] → HCOOH
H 2 SO4 Methyl amine Methyl alcohol Formaldehyde Formic acid
CH 3COOH NH3 → CH 3COONH 4 heat → CH 3CONH 2 Br2KOH → CH 3 NH 2
Acetic acid Amm. acetate Acetamide Methyl amine
NaOH → CH 3 COONa Sodalime → CH 4 Cl2 → CH 3 Cl AgOH → CH 3 OH [O] → HCHO [O] → HCOOH
Sodium acetate heat Methane hv Methyl Methyl alcohol Na2Cr2O7 +H2SO4 Formaldehyde Formic acid
chloride
(ACceHtic3CanOhy)d2riOde Conversion of Acetic acid into other organic compound
CH3 – CH3 Cl2 CH3 – CH2Cl AgOH CH3 – CH2OH [O] CH3 – CHO
hv
Ethane Ethyl chloride Ethyl alcohol Acetaldehyde
CH3CH2NH2 NH3
Ethyl amine
CH3 COCl
Electrolysis H2O CH3CH2COOH
KCN H+ Propionic acid
CH3CH2CH2NH2 [H] CH3CH2CN
LiAlH4
n-Propyl amine
CH3COONa Sodalime Cl2 CH3 Cl AgOH CH3OH [O] HCHO [O] HCOOH NaOH
hv
Sodium acetate CH4 Methyl chloride Methyl alcohol Formaldehyde Formic acid
Methane
COOH H2SO4 COONa heat HCOONa
| | Sodium formate
COOH COONa
Oxalic acid Sodium oxalate
CH3COOH Ca(OH)2 (CH3COO)2Ca heat CH3COCH3 H2/Ni CH3CHOHCH3 Alc.KOH CH3CH= CH2
Acetone Isopropyl alcohol Propene
Calcium acetate
I2 + NaOH 500°C Cl2
CHI3 HC ≡ CH ClCH2CH= CH2
Iodoform A acetylene Allyl chloride
PCl5 or SOCl2 CH3CONH2 Br2/KOH CH3NH2
Acetamide Methyl amine
NH3 P2O5 CH3CN [H] CH3CH2NH2
C2H5OH heat LiAlH4
Methyl cyanide Ethyl amine
CH3COCl CH3COOC2H5
Acetyl chloride Ethyl acetate
Rosenmund's CH3CHO HCN CH3CH OH H2O CH3CHOHCOOH
reduction CN H+
Acetaldehyde Cyanohydrin Lactic acid
Dicarboxylic Acids.
The acids containing two carboxylic groups are called dicarboxylic acids.
The saturated dicarboxylic acid are represented by the general formula Cn H 2n(COOH)2 where n = 0, 1, 2, 3 etc.
HO − C− (CH 2 )n − C− OH or HOOC(CH 2 )n COOH
|| ||
OO
According to IUPAC system, the suffix-dioic acid is added to the name of parent alkane, i.e. Alkane dioxic acid.
Formula Common name IUPAC name
HOOCCOOH Oxalic acid
HOOCCH2COOH Malonic acid Ethanedioic acid
1-3 Propanedioic
HOOCCH2CH2 Succinic acid acid
1,4-Butanedioic acid
COOH Glutaric acid 1,5-Pentanedioic
HOOC(CH2)3COOH Adipic acid acid
HOOC(CH2)4 COOH 1,6-Hexanedioic
acid
Oxalic Acid or Ethanedioic Acid
COOH or (COOH)2 or (C2 H 2O4 )
|
COOH
Oxalic acid is first member of dicarboxylic series.
It occurs as potassium hydrogen oxalate in the wood sorel, rhubarb and other plants of oxalis group and as
calcium oxalate in plants of rumex family.
It is found in the form of calcium oxalate in stony deposits in kidneys and bladdar in human body.
Oxalic acid present in tomatoes.
(1) Methods of Preparation
(i) By oxidation of ethylene glycol with acidified potassium dichromate
CH 2OH + 4[O] K2Cr2O7 → COOH + 2H 2O
| |
CH2OH H 2 SO4 COOH
Glycol
(ii) By hydrolysis of cyanogen with conc. hydrochloric acid : CN + 4 H 2O 2(HCl) → COOH + 2NH 4 Cl
| |
CN COOH
(iii) By heating sodium or potassium in a current of carbon dioxide at 360°C
2Na + 2CO2 heat → COONa
|
COONa
Sodium oxalate
(iv) Laboratory preparation : C12 H 22O11 + 18[O] HNO3 → 6 COOH + 5H 2O
|
Sucrose V2O5 COOH
Oxalic acid
(v) Industrial method : 2HCOONa 360°C → COONa + H 2
|
Sod. formate COONa
Sod. oxalate
Sodium formate is obtained by passing carbon monoxide over fine powdered of sodium hydroxide.
CO + NaOH 200°C → HCOONa
8 −10 atm
The sodium oxalate thus formed is dissolved in water and calcium hydroxide is added. The precipitate of
calcium oxalate is formed which is separated by filtration. It is decomposed with calculated quantity of dilute
sulphuric acid.
COONa COO
|+ Ca(OH)2 → | Ca + 2NaOH
COONa COO
Calcium oxalate
COO Ca H 2SO4 (dil.) COOH CaSO4
| + → | +
COO COOH Calcium sulphate
Oxalic acid (insoluble)
(soluble)
(2) Physical Properties
(i) It is a colourless crystalline solid. It consists of two molecules of water as water of crystallisation.
(ii) The hydrated form has the melting point 101.5°C while the anhydrous form melts at 190°C.
(iii) It is soluble in water and alcohol but insoluble in ether.
(iv) It is poisonous in nature. It affects the central nervous system.
(3) Chemical Properties
(i) Action of heat : It becomes anhydrous.
(COOH)2 2H2O 100−105°C →(COOH)2 + 2H2O
Hydrated oxalic Anhydrous
acid oxalic acid
(a) At 200°C, (COOH)2 + HCOOH + CO2
Formic acid
On further heating, formic acid also decomposes.
HCOOH → CO2 + H 2
(b) Heating with conc. H2SO4
COOH H2SO4 → CO + CO2 + H2O
|
COOH (conc.)
(ii) Acidic nature
Salt formation
COOH COOK KOH → COOK
| + KOH → | |
COOH COOK COOK
Oxalic acid Acid pot. oxalate Pot. oxalate
COOH 2NaHCO3 COONa 2CO2
|+ → |+ + 2H 2O
COOH COONa
Sod. oxalate
COOH Na 2 CO3 COONa
|+ → |+ H 2O + CO2
COOH COONa
(iii) Esterification
COOH C2H5OH → C| OOC2H5 C2H5OH → C|OOC2H5
| COOH
COOH COOC2 H 5
Ethyl hydrogen Ethyl oxalate
oxalate
(iv) Reaction with PCl5 : COOH COCl
|+ 2PCl 5 →| + 2POCl 3 + 2HCl
COOH COCl
Oxalyl
chloride
(v) Reaction with ammonia
COOH COONH 4 NH3 → COONH 4
|+ NH3 → | |
COOH COOH COONH4
Acid ammonium Amm. oxalate
oxalate
– H2O heat – 2H2O heat
C| ONH2 C| ONH2
COOH CONH2
Oxamic acid Oxamide
(vi) Oxidation : When oxalic acid is warmed with acidified KMnO4 .
2KMnO4 + 3H 2SO4 → K 2SO4 + 2MnSO4 + 3H 2O + 5[O]
COOH + [O] → 2CO2 + H 2O × 5
|COOH
COOH
2KMnO4 + 3 H 2 SO4 + 5 | → K 2 SO4 + 2MnSO4 + 10CO2 + 8H2O
Pot. permanganate COOH
(Purple)
Oxalic acid Colourless
Note : Oxalic acid decolourises the acidic KMnO4 solution.
(vii) Reaction with ethylene glycol
OH H O O
+
O=C CH2 heat O=C CH2
| OH H O | –H2O | |
CH2 CH2
O=C O=C
Oxalic acid Ethylene glycol O
Ethylene oxalate
(viii) Reduction : COOH 4H Zn → C| H2OH + H2O
|+ COOH
COOH H2SO4
Glycolic acid
It can also be reduced electrolytically using lead cathode into glycolic acid and glyoxalic acid.
COOH Electrolyticreduction → C|H 2OH + COOH + 2H2O
2| |
COOH 6[H] COOH CHO
Glycolic acid Glyoxalic acid
Carboxylic acids and their derivatives
(ix) Reaction with Glycerol : At 100° – 110°C, formic acid is formed. At 260°, allyl alcohol is formed.
(4) Uses : Oxalic acid (Polyprotic acid) is used,
(i) In the manufacture of carbon monoxide, formic acid and allyl alcohol.
(ii) As a laboratory reagent and as a standard substance in volumetric analysis.
(iii) In the form of antimony salt as a mordant in dyeing and calico printing.
(iv) In the manufacture of inks.
(v) For removing ink stains and rust stains and for bleaching straw, wood and leather.
(vi) In the form of ferrous potassium oxalate as developer in photography.
(5) Analytical test
(i) The aqueous solution turns blue litmus red.
(ii) The aqueous solution evolves effervescences with NaHCO3 .
(iii) The neutral solution gives a white precipitate with calcium chloride solution. It is insoluble in acetic acid.
H 2C2O4 NH4OH → (NH 4 )2 C2O4 CaCl2 → CaC2O4
Oxalic aicd Amm.oxalate Calcium oxalate
(iv) Oxalic acid decolourises hot potassium permanganate solution having dilute sulphuric acid.
(v) With hot conc. H 2SO4 , it evolves carbon monoxide which burns with blue flame.
Malonic Acid or Propane-1,3-Dioic Acid : CH 2 COOH or CH 2 (COOH)2 or (C3 H 4 O4 )
COOH
The acid occurs as calcium salt in sugar beet. It was so named because it was first obtained from malic acid
(hydroxy succinic acid) by oxidation.
(1) Methods of Preparation : From acetic acid
CH 3COOH Cl2 → CH 2ClCOOH KCN(Aq.) → CH 2CNCOOH H2OH+ → CH 2 COOH
Acetic acid P Chloroacetic acid Cyano acetic acid COOH
Malonic acid
(2) Physical Properties
(i) It is a white crystalline solid.
(ii) It's melting point is 135°C.
(iii) It is soluble in water and alcohol but sparingly soluble in ether.
(3) Chemical Properties
(i) Action of heat
(a) Heating at 150°C : CH 2 (COOH)2 → CH 3COOH + CO2
H OH
||
(b) Heating with P2O5 : = O P2O5 → O =C=C=C= O+ 2H2O
O = C − C− C
heat Carbon suboxide
||
OH H
(ii) Reaction with aldehyde : With aldehydes, α-β unsaturated acids are formed.
RCH = O+ H 2C COOH Pyridine → RCH = CHCOOH+ H2O + CO2
COOH
Aldehyde heat α -β unsaturated acid
(4) Uses : Its diethyl ester (malonic ester) is a valuable synthetic reagent for preparation of a variety of
carboxylic acids.
Succinic Acid or Butane-1,4-Dioic Acid : |CH2 −COOH or (CH 2 )2 (COOH)2 or (C4 H6O4 )
CH2 −COOH
It was first obtained by the distillation of yellow fossil, resin, amber and hence its name (Latin, Succinum = amber).
It is also formed in small amount during the fermentation of sugar.
(1) Methods of Preparation
(i) From ethylene : C||H2 Br2 → C|H2Br NaCN → C| H2CN H2OHCl → C|H2COOH
CH2 CH2Br CH2CN CH2COOH
Ethylene Ethylene Ethylene Succinic acid
bromide cyanide
(ii) From maleic acid [catalytic reduction]: CHCOOH H2 CH 2COOH
|| + Ni →|
CHCOOH heat CH2COOH
Note : This is an industrial method.
(iii) Reduction of tartaric acid or malic acid : CHOHCOOH HI → C| H2COOH ←HI CHOHCOOH
| P CH2COOH P |
CHOHCOOH Succinic acid CH2COOH
Tartaric acid Malic acid
(2) Physical properties
(i) It is a white crystalline solid. It melts at 188 o C
(ii) It is less soluble in water. It is comparatively more soluble in alcohol.
(3) Chemical Properties : Succinic acid gives the usual reactions of dicarboxylic acid, some important
reactions are :
(i) Action of heat : At 300°C
CH 2COOH 300°C → C| H 2CO O
|
CH2COOH (– H2O) CH2CO
Succinic acid Succinic anhydride
(ii) With ammonia : C|H2COOH CH 2COONH4 heat → |CH2CONH2 heat → CH 2CO NH
NH3 →| |
CH2COOH CH2COONH4 −H2O CH2CONH2 −NH3 CH2CO
Ammonium succinate Succinamide Succinimide
(iii) Reaction with Br2 : C|H2 −CO NH + Br2 NaOH → C| H2−CO N− Br + HBr
CH2 −CO 0°C CH2−CO
Succinimide N - bromosuccinimide
(N.B.S)
(iv) Reaction with ethylene glycol
HOOC − (CH 2 )2 − CO OH + H OCH 2 − CH 2O H + HO OC − (CH 2 )2 − CO OH + .......
– H2O
HOOC − (CH2)2 − CO − [−OCH2 − CH2O − OC − (CH2)2 − CO−]n − OH + H2O
Polyester
When sodium or potassium salt in aqueous solution is electrolysed, ethylene is obtained at anode.
(4) Uses : It finds use in volumetric analysis, medicine and in the manufacture of dyes, perfumes and polyester resins.
Adipic Acid or Hexane-1,6 –Dioic Acid : CH 2 −CH 2 −COOH or (CH 2 )4 (COOH)2 or (C6H10O4 )
|
CH2 −CH2 −COOH
It was first obtained by the oxidation of fats (Latin, adeps = fat.)
(1) Methods of Preparation
(i) From benzene
OH O
H2 O2 HNO3 HNO3 HOOC – (CH2)4 – COOH
Catalyst H3BO3, heat SeO3
Adipic acid
Benzene Cyclohexane Cyclohexanol Cyclohexanone
Note : It is an industrial method.
(ii) From tetrahydrofuran (THF)
C| H2 −|CH2 + 2CO + HOH → HOOC − (CH 2 )4 − COOH
CH2 CH2 Adipic acid
O
THF
(2) Physical Properties
(i) It is a white crystalline solid. Its melting point is 150°C.
(ii) It is fairly soluble in alcohol and ether but less soluble in water.
(3) Chemical Properties
It shows all the general reaction of dicarboxylic acids.
(i) Action of heat H2
H2C C
HOOC(CH2)4 COOH heat | C = O + CO2 + H2O
300°C
Adipic acid H2C
C
H2
Cyclopentanone
(ii) Formation of Nylon-66 [Reaction with hexa methylene diamine]
nH 2 N(CH 2 )6 NH 2 + nHO− C− (CH 2 )4 − C− OH
hexamethylene diamine
|| ||
adipic acid
O O
– nH2O
H HO O
| | || ||
− (− N − (CH2)6 − N − C− (CH2)4 − C −)n −
nylon-66
(4) Uses : It is used in the manufacture of several polymers.
Unsaturated Acids : When the double bond presents in the carbon chain of an acid is called unsaturated acid.
Example: CH 2 = CH − COOH+ H − C− COOH
||
Acrylic acid H −C−COOH
Maleic acid
Acrylic Acid or Prop-2-Enoic Acid : CH 2 = CH − COOH or (C3 H4 O2 )
(1) Methods of Preparation
CH2 CH2Br CH2Br CH2
|| | | ||
Br2 → HNO3 → Zn → H
(i) From allyl alcohol : C H C HBr C HBr C
| | [O] | heat |
CH2OH CH2OH COOH COOH
(ii) By oxidation of acrolein : CH 2 = CHCHO + [O] AgNO3 → CH 2 = CHCOOH
NH 4 OH
(iii) From propionic acid : CH 3CH 2COOH Br2P → CH 3 CHBrCOOH Alc.KOH → CH 2 = CHCOOH
Propionic acid
HVZ reaction α -Bromopropionic acid
(iv) By heating β-hydroxy propionic acid : C H 2 − CH 2 − COOH ZnCl2 → CH 2 = CH − COOH
heat, −H2O
|
OH
β -hydroxy propionic acid
(v) From vinyl cyanide
HC ≡ CH+ HCN Cu2Cl2HCl → CH 2 = CH − CN H + H2O → CH 2 = CH − COOH
Acetylene 90°C
Vinyl cyanide
(vi) From ethylene cyanohydrin
CH 2 − CH 2 +HCN → C H2− CH 2 − CN Conc.H2SO4 → CH 2 = CH − CN H + H2O → CH 2 = CHCOOH
O | heat −H2O
OH Vinyl cyanide
(acrylonitrile)
Ethylene oxide Ethylene cyanohydrin
Industrial method : This is a new method of its manufacture.
CH ≡ CH + CO + H 2O Ni(CO)4 → CH 2 = CHCOOH
(2) Physical Properties
It is colourless pungent smelling liquid. Its boiling point is 141°C.
It is miscible with water, alcohol and ether.
It shows properties of an alkene as well as of an acid.
(3) Chemical Properties
(i) With nascent hydrogen (Na and C2H5OH) : CH 2 = CHCOOH + 2[H] Ni → CH 3CH 2COOH
(ii) With halogens and halogen acids : Markownikoff's rule is not followed.
CH 2 = CHCOOH + Br2 CCl4 → CH 2 Br − CHBrCOOH
α ,β -Dibromopropionic acid
CH 2 = CHCOOH + HBr → BrCH 2 − CH 2COOH
β -Bromopropionic acid
(iii) Oxidation : In presence of dilute alkaline KMnO4.
CH 2 = CHCOOH + [O] + H 2O → CH 2OHCHOHCOOH
Glyceric acid
Note : On vigorous oxidation, oxalic acid is formed.
(iv) Salt formation : CH 2 = CHCOOH + KOH → CH 2 = CHCOOK + + H 2O
2CH 2 = CHCOOH + Na2CO3 → 2CH 2 = CHCOONa + + H 2O + CO2
Sodium acrylate
(v) Ester formation : CH 2 = CHCOOH + HOC2 H5 Conc.H2SO4 → CH 2 = CH − COOC2 H5
−H2O Ethyl acrylate
(vi) With PCl5 : CH 2 = CHCOOH + PCl5 → CH 2 = CH − COCl
Acryl chloride
(4) Uses : Its ester are used for making plastics such as Lucite and plexiglass.
Unsaturated Dicarboxylic Acids.
The molecular formula of the simplest unsaturated dicarboxylic acid is HOOC.CH = CH.COOH This formula,
however represents two chemical compounds, maleic acid and fumaric acid, which are geometrical isomers.
H − C− COOH HOOC − C− H
|| ||
H −C−COOH H −C−COOH
Cis-form (Maleic acid) Trans-form (Fumaric acid)
(1) Methods of Preparation of Maleic Acid
(i) By catalytic oxidation of 2-butene or benzene
CH −CH3 + 30 2 V2O5 → CHCOOH + 2H 2O
|| ||
CH −CH3 400°C CHCOOH
Maleic acid
2−Butene
C6 H6 + 9 O2 V2O5 → CH −CO O H2OH+ → CHCOOH
2 || ||
Benzene 400o C CH −CO CHCOOH
Maleic anhydride
(ii) From malic acid :
CH(OH)COOH heat → CHCOOH heat → CH −CO O NaOH → CH −COONa H + H2O → CH −COOH
| || || || ||
CH2COOH −H2O CHCOOH −H2O CH −CO boil CH−COONa CH −COOH
Malic acid Maleic acid Maleic anhydride Sodium salt Maleic acid
(Hydroxy succinic acid) (intermediate)
(2) Methods of Preparation of Fumaric Acid
(i) From maleic acid : H −C−COOH HCl → HOOC−C−H
|| ||
H−C−COOH boil
Maleic acid H −C−COOH
(ii) By oxidation of furfural with sodium chlorate
HC CH HOOC−C−H CO2
|| || + 4[O] NaClO3 → || +
C−CHO H −C−COOH
HC
O
(iii) By heating malic acid at about 150°C for long time
CH(OH)COOH HOOC−C−H
| heat → ||
CH2COOH 150°C, −H2O
H −C−COOH
Malic acid
(iv) By heating bromosuccinic acid with alcoholic potash : By heating bromosuccinic acid with
alcoholic potash.
C|H2COOH Alc.KOH → HOOC−C−H KBr 2O
|| + + H
CH.(Br)COOH H −C−COOH
(4) Physical Properties
(i) Both are colourless crystalline solids. Both are soluble in water.
(ii) The melting point of maleic acid (130.5°C) is lower than the melting point of fumaric acid (287°C).
(5) Chemical Properties
Chemically, both the acids give the reactions of alkenes and dibasic acids except that the maleic acid on
heating forms an anhydride while fumaric acid does not give anhydride.
CHCOOH heat → CHCO O+ H2O
|| ||
CHCOOH CHCO
Maleic acid Maleic anhydride
Both form succinic acid on reduction with sodium amalgam. They undergo addition reactions with bromine,
hydrobromic acid, water, etc. and form salts, esters and acid chlorides as usual. With alkaline KMnO4 solution, they
get oxidised to tartaric acid.
COOH COOH
|
H −C−OH H −C−COOH |
| ←Alk.KMnO4 || Br2water →
H −C−OH (Syn-addition) H −C−COOH (anti-addition) H −C− Br
| Maleic acid |
COOH (Cis)
Br − C− H
Tartaric acid |
(Meso) COOH
(Racemic mixture)
COOH ←Alk. KMnO4 H −C−COOH Br2water → COOH
|| (anti-addition)
| (Syn-addition) HOOC−C−H |
H −C−OH Fumaric acid (Trans) H −C− Br
| |
HO − C− H H − C− Br
| |
COOH COOH
Tartaric acid ((Meso)
(Racemic mixture)
Higher Fatty Acids.
Palmitic, stearic and oleic acids are found in natural fats and oils as glyceryl esters.
They have derived their names from the natural source from which they are prepared by hydrolysis with alkali.
Name of acids Source Molecular formula
Palmitic acid Palm oil, CH 3 (CH 2 )14 COOH
Stearic acid Stear (meaning CH 3 (CH 2 )16 COOH
tallow)
Oleic acid Olive oil. CH 3 (CH 2 )7 CH = CH(CH 2 )7 COOH
Palmitic and stearic acids are waxy colourless solids with melting points 64°C and 72°C, respectively. They
are insoluble in water but soluble in ethanol and ether. They find use in the manufacture of soaps and candles.
Soaps contain sodium or potassium salts of these higher fatty acids.
Oleic acid has low melting point, i.e., 16°C. It is insoluble in water but soluble in alcohol and ether. Besides the
reactions of acids, it also gives reactions of alkenes. Two aldehydes are formed on ozonolysis.
CH 3 (CH 2 )7 CH = CH(CH 2 )7 COOH (i)O3 → CH 3 (CH 2 )7 CHO + HOOC(CH 2 )7 CHO
(ii)Zn+ H2O
It is used for making soaps, lubricants and detergents.
(1) Difference between oils and fats : Oils and fats belong to the same chemical group, yet they are
different in their physical state.
(i) Oils are liquids at ordinary temperature (below 20°C) while fats are semi solids or solids (their melting
points are more than 20°C). A substance may be classed as fat in one season and oil in another season or the same
glyceride may be solid at a hill station and liquid in plains. Thus, this distinction is not well founded as the physical
state depends on climate and weather.
(ii) The difference in oils and fats is actually dependent on the nature of monocarboxylic acid present in the
glyceride. Oils contain large proportion of the glycerides of lower carboxylic acids, (e.g., butyric acid, caprylic acid
and caproic acid) and unsaturated fatty acids, (e.g., oleic, linoleic and linolenic acids) while fats contain a large
proportion of glycerides of higher saturated carboxylic acids, (e.g., palmitic, stearic acids).
Lard (fat of hogs) is a solid fat and its composition in terms of fatty acids produced on hydrolysis is
approximately 32% palmitic acid, 18% stearic acid, 45% oleic acid and 5% linolenic acid. Olive oil on the other
hand, contains 84% oleic acid, 4% linoleic acid, 9% palmitic acid and 3% stearic acid.
(2) Physical Properties of oils and Fats
(i) Fats are solids, whereas oils are liquids.
(ii) They are insoluble in water but soluble in ether, chloroform and benzene.
(iii) They have less specific gravity than water and consequently float on the surface when mixed with it.
(iv) Pure fats and oils are colourless, odourless and tasteless but natural fats and oils possess a characteristic
odour due to presence of other substances.
(v) They have specific melting points, specific gravity and refractive index hence they can be identified by
these oil constants.
(vi) Animal fats contain cholesterol, an unsaturated alcohol, whereas vegetable fats contains phytosterol.
(3) Chemical Properties : They give reactions of carbon-carbon double bonds and ester groups.
(i) Hydrolysis
(a) By superheated steam
CH2O COC17H35 CH2OH
| |
COC17 H 35 +3H2O → HOH + 3C17 H 35COOH
C HO COC17H35 C Stearic acid
|
| CH2OH
Tristearin Glycerol
CH2O
(b) Base hydrolysis [Saponification]
CH2OCOR CH2OH
||
C HOCOR + 3NaOH → C HOH + 3RCOONa
| | Salt fatty acid
CH2OCOR CH2OH (Soap)
Fat or oil Glycerol
(c) Enzyme hydrolysis : Enzyme like lipase, when added to an emulsion of fat in water, hydrolyses it into acid
and glycerol in about two or three days.
(ii) Hydrogenation : In the presence of finally divided nickel, the hydrogenation process is called hardening of oils.
O O
|| ||
CH 2O C(CH 2 )7 CH = CH(CH 2 )7 CH 3 CH 2O C C17 H 35
OO
|| ||
= CH(CH 2 )7 CH 3 +3H2 → CHO C17 H 35
CHO C(CH 2 )7 CH Ni,heat C
O O
|| ||
CH 2O C (CH 2 )7 CH = CH(CH 2 )7 CH 3 CH 2O C C17 H 35
Glyceryl trioleate or triolein (Liquid oil) Tristearin (A solid fat)
(iii) Hydrogenolysis [Reduction to alcohol]
O
||
CH 2 − O − C− C17 H 35
O CH2OH
|
|| 6H2 → 3C17 H 35CH 2OH
200atm C HOH + Octadecyl alcohol
CH − O − C− C17 H 35
|
CH2OH
O
||
CH 2 − O − C− C17 H 35
Tristearin
(iv) Drying : Certain oils, containing glycerides of unsaturated fatty acids having two or three double bonds
have the tendency of slowly absorbing oxygen from atmosphere and undergoing polymerisation to form hard
transparent coating. This process is known as drying and such oils are called drying oils. Unsaturated oils such as
linseed oil are, therefore, used as medium of paints and varnishes.
(v) Rancidification : On long storage in contact with air and moisture, oils and fats develop unpleasant
smell. The process is known as rancidification. It is believed that rancidification occurs due to hydrolysis-oxidation.
(4) Analysis of oils and fats
(i) Acid value : It indicates the amount of free acid present in the oil or fat. It is defined as the number of
milligrams of KOH required to neutralize the free acid present in one gram of the oil or fat. It is
determined by dissolving a weighed amount of oil or fat in alcohol and titrating it against a standard solution of
KOH using phenolphthalein as an indicator.
(ii) Saponification value : It is a measure of fatty acids present as esters in oils and fats. It is defined as the
number of milligrams of KOH required to saponify one gram of the oil or fat or number of milligrams of KOH
required to neutralize the free acids resulting from the hydrolysis of one gram of an oil or fat. It is determined by
refluxing a Saponification number of fat or oil = 168,000
M
M = molecular mass
(iii) Iodine value : Iodine value of a fat or oil is a measure of its degree of unsaturation. It is defined as the
number of grams of iodine taken up by 100 grams of fat or oil for saturation. For a saturated acid
glyceride, the iodine value is zero. Thus, the iodine value for a fat is low whereas for oil, it is high. As iodine does
not react readily, in actual practice, iodine monochloride is used. Iodine monochloride is known as Wij's reagent.
(iv) Reichert-Meissl value, (R/M value) : It indicates the amount of steam volatile fatty acids present in the
oil or fat. It is defined as the number of millilitres of 0.1 N KOH solution required to neutralize the
distillate of 5 grams of hydrolysed fat. It is determined by hydrolysing a known weighed amount (5 grams) of
the fat with alkali solution and the mixture is acidified with dilute sulphuric acid and steam distilled. The distillate is
cooled, filtered and titrated against 0.1 N KOH.
(5) Uses
(i) Many oils and fats are used as food material.
(ii) Oils and fats are used for the manufacture of glycerol, fatty acids, soaps, candles, vegetable ghee,
margarine, hair oils, etc.
(iii) Oils like linseed oil, tung oil, etc., are used for the manufacture of paints, varnish, etc.
(iv) Castor oil is used as purgative and codliver oil as a source of vitamins A and D. Almond oil is used in
pharmacy. Olive oil is also used as medicine.
(v) Oils are also used as lubricants and illuminants.
(6) Difference between vegetable oils and Mineral oils
Property Vegetable oils Minerals oils
1. Composition These are triesters of glycerol with higher These are hydrocarbons
fatty acids. (saturated). Kerosene oil–
2. Source Alkanes from C12 to C16.
Seeds root and fruits of plants. These occur inside earth in the
3. Hydrolysis form of petroleum.
Undergo hydrolysis with alkali. Form No hydrolysis occurs.
4. On adding NaOH and soap and glycerol.
phenolphthalein Decolourisation of pink colour occurs. No effect.
5. Burning
6. Hydrogenation Burns slowly Burn very readily.
No hydrogenation occurs.
Hydrogenation occurs in presence of
nickel catalyst. Solid glycerides (fats) are
formed.
(7) Soaps : Soaps are the metallic salts of higher fatty acids such as palmitic, stearic, oleic, etc. The sodium
and potassium salts are the common soaps which are soluble in water and used for cleansing purposes. Soaps of
other metals such as calcium, magnesium, zinc, chromium, lead, etc., are insoluble in water. These are not used for
cleansing purposes but for other purposes (lubricants, driers, adhesives, etc.)
Ordinary soaps (sodium and potassium) are the products of hydrolysis of oils and fats with sodium hydroxide
or potassium hydroxide. The oils and fats are mixed glycerides and thus soaps are mixtures of salts of
saturated and unsaturated long chain carboxylic acids containing 12 to 18 carbon atoms. This process
always yields glycerol as a byproduct.
CH2OCOR1 CH2OH R1COONa
| R2CO+ ONa
C HOCOR2 3 NaOH | R3CO+ ONa
+ → +
| C HOH
CH2OCOR3
Triglyceride |
CH2OH
Glycerol Soap
There are three methods for manufacture of soaps :
(i) The cold process
(ii) The hot process
(iii) Modern process
(8) Synthetic Detergents : The synthetic detergents or Syndets are substitutes of soaps. They have
cleansing power as good or better than ordinary soaps. Like soap, they contain both hydrophilic (water soluble) and
hydrophobic (oil-soluble) parts in the molecule.
C12 H 25 OSO3 Na C15 H 31 COONa
Hydrophobic Hydrophilic Hydrophobic Hydrophilic
part part p art part
Sodium lauryl sulphate (Detergent) Sodium palmitate (Soap)
Some of the detergents used these days are given below:
(i) Sodium alkyl sulphates : These are sodium salts of sulphuric acid esters of long chain aliphatic alcohols
containing usually 10 to 15 carbon atoms. The alcohols are obtained from oils or fats by hydrogenolysis.
CH 3 (CH 2 )10 CH 2 OH + HO SO3 H → CH 3 (CH 2 )10 CH 2OSO2OH NaOH → CH 3 (CH 2 )10 CH 2OSO2ONa
Lauryl alcohol Sulphuric acid Lauryl hydrogen sulphate Sodium lauryl sulphate (Detergent)
The other examples are sodium cetyl sulphate, C16 H33OSO2ONa and sodium stearyl sulphate,
CH 3 (CH 2 )16 CH 2OSO3 Na . Unlike ordinary soaps, they do not produce OH– ions on hydrolysis and thus can be
safely used for woollen garments.
(ii) Sodium alkyl benzene sulphonates : Sodium p-dodecyl benzene sulphonate acts as a good detergent.
It is most widely used since 1975.
CH3
|
CH 3 (CH 2 )9 CH == CH 2 + AlCl3 → CH 3 (CH 2 )9
1-Dodecene CH−
Benzene
2-Dodecyl benzene
CH3
|
(i)H2SO4 → CH 3 − (CH 2 )9 − − SO3 Na
(ii) NaOH CH−
Sodium dodecyl benzene sulphonate (S.D.S.)
These long chain alkyl benzene sulphonate (L.A.S.) are most widely used syndets.
(iii) Quaternary ammonium salts : Quaternary ammonium salts with long chain alkyl group have been
used as detergents, e.g., trimethyl stearyl ammonium bromide.
(CH3 )3 N Br
C18 H 37
(iv) Sulphonates with triethanol ammonium ion in place of sodium serve as highly soluble materials for liquid
detergents.
R− − O − SO− 2 N⊕ H(−CH 2 − CH 2OH)3
(v) Partially esterified polyhydroxy compounds also acts as detergents.
CH2OH
|
C17 H 35COOCH 2 C− CH 2O H
−
|
CH2OH
Pentaerythritol monostearate
Detergents are superior cleansing agents due to following properties.
(i) These can be used both in soft and hard waters as the calcium and magnesium ions present in hard water
form soluble salts with detergents. Ordinary soap cannot be used in hard water.
(ii) The aqueous solution of detergents are neutral. Hence these can be used for washing all types of fabrics
without any damage. The solution or ordinary soap is alkaline and thus cannot be used to wash delicate fabrics.
(9) Waxes : Waxes are the esters of higher fatty acids with higher monohydric alcohols. The acids and
alcohols commonly found in waxes are palmitic, cerotic acid (C25 H51COOH) , melissic acid (C30 H61COOH) and
cetyl alcohol (C16 H33OH) , ceryl alcohol (C26 H53OH) , myricyl alcohol (C30 H61OH) , etc.
Waxes are insoluble in water but are readily soluble in benzene, petroleum, carbon disulphide etc. Waxes on
hydrolysis with water yields higher fatty acids and higher monohydric alcohols.
C15 H 31COOC16 H 33 + H 2O → C15 H 31COOH+ C16 H 33OH
Cetyl palmitate Palmitic acid Cetyl alcohol
When hydrolysis is carried with caustic alkalies, soap and higher monohydric alcohols are formed.
C15 H31COOC16 H33 + NaOH → C16 H33OH + C15 H31COONa
Sodium palmitate (Soap)
The common waxes are:
(i) Bees wax, Myricyl palmitate, C15 H 31COOC30 H61
(ii) Spermaceti wax, Cetyl palmitate, C15 H 31COOC16 H 33
(iii) Carnauba wax, Myricyl cerotate, C25 H51COOC30 H61
Waxes are used in the manufacture of candles, polishes, inks, water proof coating and cosmetic preparations.
Waxes obtained from plants and animals are different than paraffin wax which is a petroleum product and a
mixture of higher hydrocarbons (20 to 30 carbon atoms). So paraffin wax is not an ester.
Candles are prepared by mixing paraffin wax (90%) with higher fatty acids like stearic and palmitic. The fatty
acids are added to paraffin wax as to give strength to candles. The mixture is melted and poured into metal tubes
containing streched threads. On cooling candles are obtained.
Substituted Carboxylic Acids.
The compounds formed by the replacement of one or more hydrogen atoms of the hydrocarbon chain part of
the carboxylic acids by atoms or groups such as X (halogen), OH or NH2, are referred to as substituted acids.
For example, CH 2ClCOOH ; CH 2OHCOOH ; CH 2 NH 2COOH
Chloroacetic acid Hydroxyacetic acid Aminoacetic acid
The position of the substituents on the carbon chain are indicated by Greek letters or numbers.
654321
C− C− C− C− C− C OOH
ε δ γ βα
For example, CH 3CHOHCOOH ; CH 3CHOHCH 2COOH
α -Hydroxypropionic acid β -Hydroxybutyric acid
2-Hydroxypropanoic acid 3-Hydroxybutanoic acid
Lactic Acid or α-hydroxy propionic acid or 2-hydroxy propanoic acid
It is the main constituent of sour milk. It is manufactured by fermentation of molasses by the micro-organism
(Bacterium acidi lactici-sour milk) in presence of CaCO3 .
(1) Method of Preparation
From acetaldehyde : CH 3CHO+ HCN → CH 3CH(OH)CN H2OH+ → CH 3CHOHCOOH
Acetaldehyde Cyanohydrin Lactic acid
(2) Physical Properties
It is a colourless syrupy liquid having a sour taste and smell.
It is hygroscopic and very soluble in water. It is optically active and exists in three distinct forms.
(3) Chemical Properties : It gives reactions of secondary alcoholic group and a carboxylic group.
Lactide CH3CHOHCOONa CH3CHO| COOH3
Sod. Lactate COOH
CO+H2O Heat
NaOH Acetyl lactic acid
Conc. H2SO4 CH3COCl
CH 3CHO + HCOOH Dil. H2SO4 CH 3CHOHCOOH CH 3CH 2COOH
Acetaldehyde Formic acid Heat 130°C Lactic Acid Propionic acid
KMnO4 PCl5 Fenton's reagent [O]
H2SO4 Fe2+/H2O2 or Ag2O
CH3CHO CH 3CHClCOCl CH3COCOOH
or Lactyl chloride Pyruvic acid
CH3COOH
(4) Uses : It is used in medicine as calcium and iron lactates, as mordant in dyeing, as acidulant in beverages
and candies, as a solvent (ethyl and butyl lactates) for cellulose nitrate.
Tartaric Acid. Or α,α'-Dihydroxy succinic acid or 2,3-Dihydroxy-Butane-1,4-Dioic acid
HO − C H − COOH
|
HO−CH −COOH
It is found as free or potassium salt in grapes, tamarind, and berries.
(1) Methods of Preparation
(i) Argol which separates as a crust during fermentation of grape juice is impure potassium hydrogen tartrate.
Argol is boiled with limewater. Calcium tartrate is precipitated which is filtered. The solution contains potassium
tartrate which is also precipitated by addition of CaCl2. The calcium salt is then decomposed with calculated
quantity of dilute H2SO4. The precipitate (CaSO4) is filtered and the filtrate on concentration gives the crystals of
tartaric acid.
CH(OH)COOK Ca(OH)2 CH(OH)COOK CH(OH)COO Ca
2| + |+ |
CH(OH)COOH → CH(OH)COOK CH(OH)COO
Pot.hydrogen tartrate Pot.tartrate (Filtrate) Calcium tartrate (ppt.)
CaCl2
-2KCl
CH(OH)COO CH(OH)COOH
| Ca H 2SO4 CaSO4 |
CH(OH)COO + → + CH(OH)COOH
Tartaric acid
(ii) Synthetic method
C + H2 Electric → CH ≡ CH H2 → CH 2 = CH 2 Br2 → CH 2 Br − CH 2 Br 2KCN → C| H2CN
arc Acetylene Ethylene Ethylene bromide CH2CN
Pd BaSO4
H2OH+ →|CH2COOH RedP → CHBrCOOH AgOH →|CHOHCOOH
Br2 |
CH2COOH CHBrCOOH CHOHCOOH
Succinic acid Tartaric acid
α ,α '-Dibromo succinic
acid
(iii) From glyoxal cyanohydrin : CHO HCN → CH(OH)CN CH(OH)COOH
| | H2OH+ → |
CHO CH(OH)CN CH(OH)COOH
Glyoxal Glyoxal cyanohydrin Tartaric acid
(2) Physical Properties : It is a colourless crystalline compound. It is soluble in water and alcohol but
insoluble in ether. It contains two asymmetric carbon atoms and thus shows optical isomerism (four forms). Natural
tartaric acid is the dextro variety. It contains two secondary alcoholic groups and two carboxylic groups.
Optical Isomerism in tartaric acid
COOH COOH COOH
| | |
H−C− OH HO−C− H H−C|− OH
| | H−C− OH
HO−C−H H− C− O H |
| |
COOH COOH COOH
d+ l-(Leavorotatory acid) Meso-Tartaric acid
Dextrorotatory Tartaric acid (Optical inactive)
Optical active
(i) d + Tartaric acid-Dextro-rotatory Optical active
(ii) l –Tartaric acid-Leavorotatory
(iii) Meso tartaric acid-optically inactive due to internal compensation.
(iv) Racemic tartaric acid (Equimolar mixture of d+, l–forms). Optically inactive due to external compensation
(3) Chemical Properties
CHCOOH With alkalies and alcohols,
|| it forms three series of salts
C|COOH
CAcHo2nCitOicOaHcid Heat, 150°C and esters, respectively
CH 2COOH CH 2 COOH
| |
C(OH)COOH CH3COCl |C(OCOCH3)COOH
| HCl
CH2COOH MCoHn2oCaOcOelyHderivative
Citric acid
Fuming H2SO4 Hl
heat reduction
CH 2COOH CH 2COOH
| |
CO
| CHCOOH
|
AceCtoHn2eCdOiaOrtHboxylic TCrHic2aCrbOaOllyHtic acid
acid
(4) Uses : It is used in carbonated beverages and effervescent tablets, in making baking powder (cream of
tartar) and mordant in dyeing (potassium hydrogen tartrate), in preparing Fehling's solution (sodium potassium
tartrate–Rochelle salt), in medicine as emetic, dyeing and calico-printing (tartar emetic-potassium antimonyl tartrate)
and silver mirroring.
(5) Tests
(i) When heated strongly, tartaric acid chars readily giving a smell of burnt sugar to produce free carbon and
pyruvic acid.
(ii) With AgNO3 : A neutral solution of tartaric acid gives a white ppt. which is soluble in ammonia. A silver
mirror is obtained on warming the ammonical silver nitrate solution (Tollen's reagent).
(iii) With Fenton's reagent : (H2O2 containing a little of ferrous salt) and caustic soda, It gives a violet colour.
(iv) With Resorcinol and conc. H2SO4 : It gives blue colour.
Citric Acid Or 2-Hydroxypropane Or 1,2,3-Tri Carboxylic Acid Or β-Hydroxy Tricarballylic Acid
It occurs in the juice of citrus fruits such as lemon, galgal, orange, lime, etc. Lemon juice contains 6-10% of
citric acid.
(1) Methods of Preparation
(i) By Fermentation : Citric acid is obtained by carrying fermentation of dilute solution of molasses with
micro-organism, Aspergillus nigar, at 26-28°C for 7 to 10 days. The resulting solution is neutralised with Ca(OH)2
to form insoluble precipitate, calcium citrate. It is decomposed by dilute H 2SO4 . The CaSO4 is filtered off and the
solution is concentrated under vacuum to get crystals of citric acid.
(ii) By Lemon juice : It is also obtained from lemon juice. The juice is boiled to coagulate proteins. From
clear solution, citric acid is obtained as calcium salt with Ca(OH)2 as described in the above method.
(iii) By synthetic method :
CH2OH CH2Cl CH2Cl CC|| H2ClOCNH KCN → CC|| H2CNOCNH CH2COOH
|
| HCl(g) → | dil. HNO3 → | HCN → H2OH+ → )COOH
heat [O] C(OH
C HOH CHOH CO |
CH2COOH
| | |
CH2OH (in acetic acid) CH2Cl CH2Cl
Glycerol CH2Cl CH2CN
(2) Physical Properties : It is a colourless crystalline compound. It possesses one water molecule as water of
crystallisation. It is soluble in water and alcohol but less soluble in ether. It is not optically active compound. It is
nontoxic in nature. It behaves as an alcohol and tribasic acid.
(3) Chemical Properties Pot. acid tartrate Potassium tartrate
CHOHCOOK CHOHCOOK
| and | C(OH)COOH
||
CHOHCOOH CHOHCOOK C(OH)COOH
Dihydroxy meleic acid
CH 3 COCOOH It forms two series of salts
Pyruvic acid [O] Fe 2+ /H2O2
Heat
Fenton' s reagent
C| HBrCOOH HBr C|HOHCOOH AgNO3 Tartronic acid + Sliver mirror
CHBrCOOH CHOHCOOH NH4OH (Test of tartaric acid)
α,α'−Dibromo succinic acid Tartaric acid
Fehling's solution CH(OH)COOH COOH
| [O] → |
HI Heat COOH K2Cr2O7/H2SO4 COOH
Complex formation
CH 2COOH CHOHCOOH Oxalic acid
| |
CH2COOH ←HI CH2COOH CH(OH)COOH COOH
Heat | [O] → |
Malic acid
Sucinic acid COOH COOH
Tartronic acid Oxalic acid
NaOOCCH − O O − HC − COONa
| |
NaOOCCH−O Cu
O − HC − COONa
(4) Uses : It finds use in making lemonades, as acidulant in food and soft drinks and makes the lemon sour,
as mordant in dyeing and calico printing. Ferric ammonium citrate, magnesium citrate (as an antacid and laxative),
sodium or potassium citrate are used in medicine. Ferric ammonium citrate finds use in making blue prints.
Aromatic Carboxylic Acids.
Aromatic acid contain one or more carboxyl group (COOH) attached directly to aromatic nucleus.
Examples
COOH COOH COOH
Benzoic acid CH3 COOH COOH COOH NO2
NH2
O-toluic acid COOH OH m-Nitro benzoic acid
Anthranilic acid
Phthalic acid Salicylic acid
Aromatic acid containing-COOH group in the side chain, they are considered as aryl substituted aliphatic acid.
Examples CH2COOH CH = CHCOOH
Phenyl acetic acid Cinnamic acid
The IUPAC names of the substituted acids are derived by prefixing the name of the substituent to the name of
parent acid i.e., benzoic acid and the position is indicated by an arabic numeral with the carbon atom carrying the
– COOH group being numbered as 1. For example,
COOH COOH COOH COOH
Benzoic acid CH3 OH NO2
2-Methylbenzoic acid 2-Hydroxybenzoic acid 3-Nitrobenzoic acid
(o-Toluic acid) (o-salicylic acid)
COOH COOH COOH
Br NH2 OCH3
4-Bromobenzoic acid 4-Aminobenzoic acid 4-Methoxy benzoic acid
(p-Anisic acid)
Benzoic Acid
(1) Methods of Preparation
(i) From oxidation of Benzyl alcohol [Laboratory method]
CH2OH CHO COOH
OO
Benzyl alcohol Benzaldehyde Benzoic acid
(ii) From hydrolysis of nitriles or cyanides COOH
CN + 2NH3
+ 2H2O H+ or OH–
Benzonitrile Benzoic acid
(iii) From Grignard reagent O COOH OH
|| + Mg I
MgI O C – OMgI
||
H+ , H2O
+C=O
Phenyl mag. iodide Addition product Benzoic acid
(iv) By hydrolysis of esters
C6 H5COOCH3 + H 2O H+orOH− → C6 H5COOH+ CH 3OH
Methyl benzoate Benzoic acid Methanol
(v) From trihalogen derivatives of hydrocarbons
CCl3 C(OH)3 COOH
+ 3KOH – 3 KCl + H2O
Benzotrichloride Unstable Benzoic acid
(vi) From benzene COCl
COOH
COCl2 H2 O/NaOH [Friedel-craft reaction]
AlCl3
(vii) From Toluene
H3C
COOH
[O], ∆
KMnO4/OH
or alkaline K2Cr2O7
Note : Chromic trioxide in glacial acetic acid or Co-Mn acetate can also be taken in place of alkaline KMnO4 .
(viii) From o-xylene [Industrial method]
CH3 [O] CO HOH COOH Soda COOH
CH3 V2O5 O COOH lime
CO
(ix) From naphthalene [Industrial method] COOH
COOH
Soda lime
COOH
(2) Physical Properties
(i) It is a white crystalline solid.
(ii) It has m.p. 394 K.
(iii) It is sparingly soluble in cold water but fairly soluble in hot water, alcohol and ether.
(iv) It has a faint aromatic odour and readily sublimes and is volatile in steam.
(3) Acidity of Aromatic Carboxylic Acid : Aromatic acid dissociates to give a carboxylate anion and proton.
C6 H5COOH ⇌ C6 H5CO O− + H +
Since the carboxylate anion (ArCO O− ) is resonance stabilised to a greater extent than the carboxylic acid
(ArCOOH).
O O− O O−
|| | + || |
Ar − C− OH ↔ Ar − C = O H Ar − C− O− ↔ Ar − C = O
Resonance in carboxylic acid Resonance in carboxylate anion
Non - equivalent structure and Equivalent structure and hence
hence less stable more stable
Effect of Substituents on Acidity : The overall influence of a substituent on acidity of substituted
benzoic acids is due to two factors.
(i) Inductive effect : If the substituent exerts–I effect, it increases the acidity of carboxylic acids, while if it
exerts + I effect it decreases the acidity. Inductive effect affects all positions, i.e., o–, m– and p–.
(ii) Resonance effect : Like inductive effect, if the resonance producing group exerts minus effect i.e., if it
withdraws electrons, it increases the strength of the benzoic acid. Similarly, if the group causes +R effect it decreases
the acidity of benzoic acid. However, remember that resonance effect affects only o- and p- positions. Thus if
resonance producing group is present in the m-position it will not exert its effect.
In case resonance and inductive effects both operate in the molecule, resonance effect being stronger
overpowers the inductive effect.
Thus on the above basis, the following order of acidity can be explained.
NO2 Cl OH
COOH COOH COOH COOH
p-Nitrobenzoic acid p-Chlorobenzoic acid Benzoic acid p-Hydroxybenzoic acid
– NO2 group exerts – Cl group exerts No other group – OH group exerts
– R and – I effects – I effects, + R + R and – I effects
NO2
Similarly : NO2 NO2 COOH
COOH
COOH
COOH
Acidity is only due to electron withdrawing inductive effect of the – NO2 group (resonance does not affect
the m-position) while in the p-isomer acidity is due to electron withdrawing inductive as well as resonance effect.
The acidity of the three isomers of hydroxybenzoic acids follows the following order.
OH OH COOH OH
COOH
– I effect COOH
+ M effect
COOH
Resonance effect cannot operate and hence only the acid-strengthening –I effect takes part with the result
m-hydroxybenzoic acid is stronger acid than benzoic acid. Like other substituted benzoic acid.
Acidic character among benzoic acids having different electron releasing group.
COOH COOH COOH COOH
> > CH3COOH > >
OCH3 OH NH2 CH3
(ii) Reactions of aromatic ring
(4) Chemical Properties :
(i) Reactions of carboxylic group
(i) Reactions of Carboxylic Group
(a) Reaction with metals
COOH COONa
+2 Na + H2
(b) Reaction with Alkalies Or NaHCO3 Or Na2CO3 : COONa
COOH + H2O
+ NaOH
or NaHCO3 or Na2CO3
(c) Formation of Esters :
Aromatic acid (benzoic acid) having no group in its ortho positions can be readily esterified with alcohol in
presence of a mineral acid. COOH COOC2H5 + H2O
+ C2H5OH
H+
In presence of ortho substituent the rate of esterification is greatly decreased due to steric effect.
The esterification of the various benzoic acids :
COOH COOH H3C COOH CH2COOH
CH3 CH3
CH3 H3C
;
Benzoic acid 2-Methylbenzoic acid 2, 6-Dimethylbenzoic acid 2,6-Dimethyl phenylacetic acid
The substituted phenylacetic acid is easily esterified because – COOH group is separated from benzene ring
by – CH2 – part.
The ortho-substituted benzoic acids can be easily esterified by treating the silver salt of the acid with alkyl
halides, i.e., COOH AgNO3 H3C COOAg H3C COOC2H5
H3C CH3 CH3 CH3
C2H5Br
This is due to the fact that in such cases the attack of the alkyl moiety of the alkyl halides is on the oxygen
atom of the – COOH group but not on the sterically hindered carbon atom.
(d) Formation of acid chloride
COOH COCl
+ PCl5 or SOCl2 + POCl3 + HCl
(e) Reaction with N3H [Schmidt reaction] Benzoyl Chloride
COOH H2SO4 NH2
+ N3H 50° C + CO2 + N2
Aniline
(f) Reaction with sodalime
COOH + CO2
NaOH + CaO Benzene
(g) Reaction with anhydride OO
COOH || ||
+ (CH3CO)2 O
C–O–C
∆
(h) Reduction COOH Benzoic anhydride
(i) Decarboxylation + LiAlH4
CH2OH
COOH MnO + H2O
+ HCOOH
∆ Benzyl alcohol
CHO
+CO2 + H2O
(j) Hunsdiecker reaction : C 6H5 COOAg + X2 in CCl4 → C6 H5 − X + CO 2 ↑ + AgX
heat Phenyl halide
Silver benzoate ( Br2 or Cl2 )
(ii) Reactions of Aromatic Ring
(a) Nitration COOH COOH
+ HNO3 H2SO4
m-nitrobenzoic aNciOd 2
(b) Sulphonation
COOH COOH
+ Fuming H2SO4 SO3H
(c) Chlorination
m-sulpho benzoic acid
COOH COOH
+ Cl2 Fecl3
Cl
m-chloro benzoic acid
(d) Reduction
COOH COOH
Na/amyl alcohol
Boil, 3H2
Cyclo hexanoic acid
(5) Uses : Benzoic acid is used,
(i) in medicine in the form of its salts especially as urinary antiseptic.
(ii) As sodium benzoate for preservation of food such as fruit juices, tomato ketchup, pickles etc.
(iii) In the preparation of aniline blue.
(iv) In treatment of skin diseases like eczema.
(6) General Tests
(i) Benzoic acid dissolves in hot water but separates out in the form of white shining flakes on cooling.
(ii) It evolves CO2 with sodium bicarbonate, i.e., it gives effervescence with sodium carbonate.
(iii) Neutral ferric chloride gives a buff coloured precipitate.
(iv) When warmed with ethyl alcohol and a little conc. H2SO4, a fragrant odour of ethyl benzoate is obtained.
(v) When heated strongly with soda lime, benzene vapours are evolved which are inflammable.
Cinnamic Acid [β-Phenyl acrylic acid]
CH = CH – COOH
(1) Methods of Preparation
(i) By Perkin's reaction C6 H5CHO + (CH 3CO)2 O CH3COONa → C6 H5CH = CHCOOH + CH3COOH
180°C
(ii) By Claisen condensation
C6 H 5 CHO + CH 3 COOC2 H 5 C2H5ONa' → C6 H 5 CH = CHCOOC2 H 5 H2O →
Ester H+
C6 H 5 CH = CHCOOH + C2 H 5 OH
(iii) By knoevenagel reaction
C6 H5CHO + CH 2 (COOH)2 NH3 → C6 H 5 CH = CHCOOH + CO2 + H2O
heat
(iv) Industrial method
C6 H5CHCl2 + H2CHCOONa 200°C → C6 H5CH = CHCOOH + NaCl + HCl
Benzal chloride Sodium acetate
(2) Physical Properties
(i) It is a white crystalline solid and its melting point 133°C.
(ii) It is very sparingly soluble in water.
(iii) It exhibits geometrical isomerism.
C6 H5 − C− H C6 H5 − C− H
|| ||
H − C − COOH HOOC−C−H
Trans - form Cis-form
(Cinnamic acid) (Allo cinnamic acid)
Cinnamic acid (stable form) occurs in nature both free and as esters in balsams and resins.
(3) Chemical Properties : It also gives reactions of benzene nucleus.
Oxidation C6H5CHO + C6H5COOH
CrO3
Benzaldehyde Benzoic acid
Reduction C6H5CH2CH2COOH
Na(Hg)/H2O
β-Phenyl propionic acid
Reduction C6H5CH2CH2CH2OH
LiAlH4 3-Phenyl propyl alcohol
– 10°C
C6H5CH = CHCH2OH
Cinnamyl alcohol
Soda lime C6H5CH = CH2
CH = CH – COOH distilled Styrene
Br2 C6H5CHBrCHBrCOOH
Dibromocinnamic acid
CH = CHCOOH CH = CHCOOH
NO2
Nitration +
Conc. HNO3/H2SO4
o-Nitrocinnamic acid NO2
p-Nitrocinnamic acid
PCl5 C6H5CH = CHCOCl
Cinnamyl chloride
C2H5OH C6H5CH = CHCOOC2H5
H+
Ethyl cinnamate
Carboxylic acids and their derivatives
Salicylic acid [O-Hydroxy benzoic acid]; OH
COOH
Salicylic acid is present in many essential oils in the form of esters. Oil of winter green is a methyl ester of
salicylic acid.
(1) Methods of preparation
(i) Kolbe Schmidt reaction
ONa CO2 OCOONa OH Dil. HCl OH
125°C, Pressure COONa COOH
Sodium Rearrangement
phenoxide Salicylic acid
Sodium phenyl Sodium salicylate
carbonate
It is a commercial method. The reaction yields both o- and p- isomers. Salicylic acid is more volatile and
separated by steam distillation.
(ii) Reimer-Tiemann reaction
OH + CCl4 + KOH Heat OH Dil. HCl OH
COOK COOH
(iii) From benzene derivatives
Cl Fuse with OH
(a) COOH NaOH COOH
o-Chlorobenzoic acid
(b) SO3K Fuse with OH
COOH KOH COOH
o-Sulphobenzoic acid OH
COOH
(c) OH + [O] Chromic
CH2OH acid OH
COOH
Salicyl alcohol
(d) OH + [O] PbO/NaOH
CH3
o-Cresol
(e) NH2 NaNO2/HCl N2Cl H2O OH
COOH 0°C COOH heat COOH
Anthranilic acid
(2) Physical properties
(i) It is a colourless needle shaped crystalline compound.
(ii) Its m.p. is 156°C.
(iii) It is sparingly soluble in cold water but readily soluble in hot water, alcohol, ether and chloroform.
(iv) It is steam volatile.
(v) It is poisonous in nature. However, its derivative used in medicine internally and externally as antipyretic
and antiseptic.
(3) Chemical properties
(i) Reaction with Na2CO3, NaHCO3 or NaOH
O
||
C – OH COO– Na+ COONa
ONa
Aq. Na2CO3 Aq. NaOH
OH OH
Salicylic acid Mono sodium salicylate Disodium salicylate
(ii) Reaction with alcohols or phenols OH
+ H2O
OH + CH3OH HCl(gas)
COOCH3
COOH
Methyl salicylate
Salicylic acid
Methyl salicylate is an oily liquid (oil of winter green) with pleasant material. It is also used in medicine in the
treatment of rheumatic pain and as a remedy for aches, sprains and bruises. It is used in perfumery and as a
flavouring. It is used for making of iodex.
OH POCl3 OH
+ C6H5OH
COOC6H5
COOH
Phenyl salicylate (salol)
Salicylic acid
Salol is a white solid m.pt. 43°C. It is a good internal antiseptic. It is used in making of toothpastes. Salol
absorbs ultraviolet light and its main use now is sun-screening agent and stabiliser of plastics.
(iii) Decarboxylation ∆ + CO2
COOH OH
OH Phenol
Salicylic acid
(iv) Acetylation
OH ClCOCH3 Pyridine OCOCH3
+
Acetyl chloride COOH
COOH
Aspirin
Salicylic acid (Acetyl salicylic acid)
Note : Aspirin is a white solid, melting point 135°C. It is used as antipyretic and pain killer (analgesic action).
(v) Reaction with ferric chloride solution
OH FeCl3 Violet colouration
COOH Solution
Salicylic acid
(vi) Reaction with PCl5 Cl
OH
PCl5
COOH
COCl
Salicylic acid
o-Chlorobenzoyl chloride
(vii) Bromination OH
Br Br
OH Br2 water
Br
COOH
2,4,6,-Tribromophenol
Salicylic acid
(viii) Nitration OH
COOH Fuming HNO3 O2N OH
NO2
Salicylic acid
NO2
2,4,6,-Trinitrophenol
Phthalic acid [1,2,-Benzene dicarboxylic acid]
COOH
COOH
There are three isomer (ortho, meta, para) of benzene dicarboxylic acid.
COOH COOH COOH
COOH
COOH
Benzene-1,2-dicarboxylic acid Benzene-1,3-dicarboxylic acid COOH
(Phthalic acid) (Isophthalic acid) Benzene-1,4-dicarboxylic acid
(Terphthalic acid)
(1) Methods of preparation CH3 [O] CH3 [O] COOH
(i) By the oxidation of o-xylene : CH3 KMnO4 COOH COOH
o-Xylene o-Toluic acid Phthalic acid
(ii) From naphthalene (Industrial method) : It is known as aerial oxidation.
Fuming H2SO4 CO O NaOH COONa COOH
HgSO4,300°C COONa COOH
CO
Naphthalene
Phthalic anhydride
(2) Physical properties
(i) It is colourless crystalline compound.
(ii) Its melting point is not sharp (195–213°C).
(iii) It is sparingly soluble in cold water but soluble in hot water, alcohol, ether, benzene etc.
(3) Chemical properties
NaOH COONa NaOH COONa
COOH
COONa
Acid salt
Disodium phthalate
C2H5OH COOC2H5 C2H5OH COOC2H5
COOH COOC2H5
Ethyl hydrogen phathalate Ethyl phthalate
PCl5 COCl
COCl
Phthaloyl chloride
COOH NH3 COONH4 heat CONH2
COOH
COONH4 – 2H2O CONH2
Phthalic acid
Amm. phthalate Phthalamide heat
– NH3
heat CO O CO
– H2O CO CO
NH
Phthalic anhydride Phthalimide
Soda lime
heat
Benzene
Hg (CH3COO)2 COO Hg heat CO O
COO Hg
(4) Uses : It is used in the manufacture of plastics, dyes and other compounds such as phthalic anhydride,
phthalimide, anthraquinone and fluorescein etc.
Carboxylic acids and their derivatives
Acid Derivatives.
The compounds which are obtained by replacing the − OH of the carboxylic group by other atoms or groups
such as X −, − NH2 , – OR and O − C− R are known as acid derivatives.
||
O
• R − C− group is common to all the derivatives and is known as acyl group and these derivatives are termed
||
O
as acyl compound.
• The important derivatives are given below :
Group replacing – OH Name Structure
Acyl halide O
X
Amide ||
(X = F, Cl, Br, I) ester
− NH 2 R − C− X
anhydride O
−OR′
||
−OOCR
R − C− NH2
O
||
R − C− OR′
(R′ may be R)
OO
|| ||
R − C− O − C− R
Reactivity
Acyl derivatives are characterised by nucleophilic substitution reactions.
R R Nu Nu
|
L C = O.. : + : Nu− .. : → R − C = O+ : L−
C − O..
L
Intermediate
O
||
(L = X, NH2,O − C− R or OR)
The relative reactivities of various acyl compounds have been found to be in the following order:
R OO OO
|| ||
C = O > R − C− O − C− R > R − C > R−C
X OR NH2
Out of acid halides, the acid chlorides are more important ones.
The overall order of reactivity can be accounted for in terms of the following three factors:
(i) Basicity of the leaving group (ii) Resonance effects and (iii) Inductive effects.
(i) Basicity of the leaving group : Weaker bases are good leaving groups. Hence, the acyl derivatives with
weaker bases as leaving groups are more reactive. Chloride ion is the weakest base while – NH2 is the strongest
base. Thus, acyl chlorides are most reactive and amides are least reactive.
(ii) Resonance effect : The leaving group in each case has an atom with lone pair of electrons adjacent to the
carbonyl group. The compound exists, therefore, as a resonance hybrid.
O O−
|| |
R−C ..←→ R − C
L L+
This makes the molecule more stable. The greater the stabilization, the smaller is the reactivity of the acyl compound.
However, acyl chlorides are least affected by resonance. Due to lower stabilization, the acid chlorides are more
reactive as the loss of − Cl is easier. Greater stabilization is achieved by resonance in esters and amides and thus,
they are less reactive.
(iii) Inductive effect : Higher the –I effect, more reactive is the acyl compound. Inductive effect of oxygen in
ester is greater than nitrogen in amide, hence ester is more reactive than an amide.
Acyl Halides
R−C O where R may be alkyl or aryl group.
Cl
Nomenclature: The common names as well as IUPAC names of the acid halides are derived by replacing ic
acid by yl halide.
Acyl chloride Common name IUPAC name
HCOCl Formyl chloride Methanoyl chloride
CH3COCl Acetyl chloride Ethanoyl chloride
CH3CH2COCl Propionyl chloride Propanoyl chloride
C6 H5COCl Benzoyl chloride
Benzoyl chloride
(1) Methods of Preparation
(i) From carboxylic acid : RCOOH + PCl5 → RCOCl + POCl3 + HCl
3RCOOH + PCl3 → 3RCOCl + H3 PO3
(ii) Industrial method : By distilling anhydrous sodium acetate
3CH 3COONa + PCl3 heat → 3CH 3COCl + Na3 PO3
2CH 3COONa+ POCl3 heat → 2CH 3COCl+ NaPO3 + NaCl
Sodium acetate Acetyl chloride
(CH3COO)2Ca+ SO2Cl2 heat → 2CH3COCl+ CaSO4
Calcium acetate Sulphuryl Acetyl chloride
chloride
(iii) With thionyl chloride : RCOOH + SOCl2 → RCOCl + SO2 + HCl
This is the best method because SO2 and HCl are gases and easily escape leaving behind acyl chloride.
(2) Physical properties : The lower acyl chloride are mobile, colourless liquid while the higher members are
coloured solids.
Acyl chloride have very pungent, irritating order and are strong lachrymators (tears gases)
The fume in air due to the formation of hydrochloric acid by hydrolysis.
They are readily soluble in most of the organic solvent. Acyl chloride don't form intermolecular hydrogen
bonding. Therefore, their boiling points are lower than those of their parent acids.
(3) Chemical properties
O O− O
|| | ||
R − − Cl + : Nu − →R− C − Cl → R − C + Cl −
C
||
Nu Nu
Cl − + H + → HCl
(i) Hydrolysis : CH3COCl+ HOH → CH3COOH+ HCl
Acetyl chloride Acetic acid
C6 H5COCl+ H2O → C6 H5COOH+ H2O
Benzoyl chloride Benzoic acid
(ii) Reaction with alcohols (alcoholysis)
CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl
Ethyl acetate
C6 H5COCl + C2 H 5 OH aq NaOHor → C6 H5COOC2 H5 + HCl
Pyridine Ethyl benzoate
Benzoyl chloride Ethyl alcohol
This reaction is called Schotten Baumann reaction.
(iii) Reaction with salts of carboxylic acid
OO
|| ||
CH 3 COCl + CH 3 COO − Na + Pyridine → CH 3 O − CH 3
C− C−
Acetic anhydride
(iv) Reaction with benzene (acylation) : This reaction is called friedel craft reaction.
COCH3
+ CH 3COCl Anhyd.AlCl3 → + HCl
Acetyl chloride Acetophenone
COC6H5
+ C6 H 5 COCl Anhyd.AlCl3 → + HCl
Benzoyl chloride Benzophenone
(v) Reaction with ammonia or amines : CH3COCl+ 2NH3 → CH3CONH2 + NH4Cl
Acetyl chloride Acetamide
C6H5COCl + 2NH3 → C6H5CONH2 + NH4Cl
Benzamide
However, acyl chlorides react with amines to form substituted amides.
O
||
CH3COCl + H 2 NC2 H5 → CH3 C− NH − C2 H5
N-Ethyl acetamide
CH3COCl + (C2H5 )2 NH → CH3CON(C2H5 )2 + HCl
N, N-Diethyl acetamide
(vi) Reduction : CH 3 COCl LiAlH4or → CH 3 CH 2OH
NaBH4
Ethanol (Primary alcohol)
CH3COCl + H2 Pd /BaSO4 → CH3CHO + HCl
This reaction is called Rosenmund reaction.
(vii) Reaction with organocadmium compounds (formation of ketones)
2CH3COCl + (CH3 )2 Cd → 2CH3COCH3 + CdCl2
Dimethyl Acetone
Cadmium
2C6 H5COCl + (CH3 )2 Cd → 2C6 H5COCH3 + CdCl2
Acetophenone
(viii) Reaction with diazomethane
OO O
|| 2C H 2 − N+ || C− H N+ ||
CH 3 − Cl + ≡ N → CH 3 − − ≡ N H2O → CH 3 CH 2 OH
C− Diazomethane C− (− N2) C−
Diazoacetone
(ix) Reaction with water : CH3COCl AgNO3/ H2O → CH3COOH + AgCl + HNO3
(x) Reaction with chlorine : CH3COCl + Cl2 RedP → Cl − CH2 − CO − Cl + HCl
Mono-α -chloroacetyl chloride
(xi) Reaction with Grignard reagent
CH3CO Cl + IMg CH3 → CH3COCH3 + Mg I
Methyl magnesium iodide Acetone Cl
(xii) Reaction with KCN : CH3COCl + KCN → CH3COCN H2O → CH3COCOOH
Acetyl cyanide Pyruvic acid
(xiii) Reaction with Salicylic acid
OH + ClOCCH 3 → OOCCH 3
COOH COOH + HCl
Salicylic Acetyl salicylic acid
acid (Aspirin)
(xiv) Reaction with ether : CH 3 COCl + C2 H5OC2 H5 ZnCl2 → CH 3COOC2 H 5 + C2 H5Cl
Diethyl ether anhy.
Ethyl acetate Ethyl chloride
(xv) Reaction with sodium peroxide (Peroxide formation)
O OO
|| N+ a O− − O− N+ a || ||
CH3C− O − O C CH + 2NaCl
2CH3 − C− Cl+ → Acetyl peroxide − − 3
Acetyl chloride
(xvi) Reaction with hydroxylamine and hydrazine
CH3COCl + H2 NOH → CH3CONHOH+ HCl
Hydroxyl Acetyl hydroxylamine
amine (hydroxamic acid)
CH3COCl + H2 NNH2 → CH3CONHNH2 + HCl
Hydrazine Acetyl hydrazine
(4) Uses
(i) As an acetylating agent.
(ii) In the estimation and determination of number of hydroxyl and amino groups.
(iii) In the preparation of acetaldehyde, acetic anhydride, acetamide, acetanilide, aspirin, acetophenone etc.
Acid Amides
R−C O where, R = −CH3 , − CH 2CH3 , − C6 H5
NH 2
Nomenclature
In common system, -i.c., acid is replaced by amide.
In IUPAC system, e of parent hydrocarbon is replaced by amide.
Acyl amides Common name IUPAC name
HCONH2 Formamide Methanamide
Acetamide Ethanamide
CH3CONH2 Propanamide
C2 H 5 CONH 2 Propionamide
C6 H5CONH 2 Benzamide Benzamide
The hydrogen atom of the acid may also be replaced by alkyl groups.
CH3CONHCH3 CH 3 CONHC2 H 5
N-Methyl ethanamide N -Ethyl ethanamide
(N-Methyl acetamide) (N -Ethyl acetamide)
Therefore, the acid amides are classified:
O O O
|| || ||
R − C− NH2 R − C− NHR′ R − C− NR2′
1o Amide 2o Amide 3o Amide
Similarly
O CONHCH 3 NHCOCH3 NHCOC6 H5
||
CH3 − C− NHCH3
N-Methylethanamide
(N-Methyl acetamide)
N-Methylbenzamide N - Phenylethanamide N-Phenyl benzamide
(Acetanilide) (Benzanilide)
O CH3 O CH3
|| | || |
H3 − C− N − CH3 CH3 − C− N − CH3
N-N-Dimethyl methanamide N,N-Dimethyl ethanamide
(N,N-Dimethyl formamide, DMF) (N,N-Dimethyl acetamide, DMA)
(1) Methods of preparation
(i) Ammonolysis of acid derivatives
CH3COCl + 2NH3 → CH3CONH2 + NH4Cl
Acetamide
(CH3CO)2 O + 2NH3 → CH3CONH2 + CH3COONH4
Acetamide Amm. acetate
C6 H5COCl+ NH3 → C6 H5CONH2 + HCl
Benzoyl chloride Benzamide
(ii) From ammonium salts of carboxylic acids (Laboratory Method)
CH3COONH4 Heat → CH3CONH2 + H2O
Acetamide
Note : Ammonium acetate is always heated in presence of glacial acetic acid to avoid the side product
( CH3COOH) .
(iii) By partial hydrolysis of alkyl cyanide : CH3C ≡ N Conc. HCl → CH3CONH 2
H2O / OH − Acetamide
(iv) By heating carboxylic acid and urea
H2N − C− NH 2 + R − C− OH heat → R − C− NH2 + CO2 + NH 3
|| || ||
OO O
Amide
(2) Physical properties
(i) Physical state : Formamide is a liquid while all other amides are solids.
(ii) Boiling points : Amides have high boiling points than the corresponding acids.
Acetic Acid Acetamide
b.p. 391 K b.p. 494 K
Benzoic acid Benzamide
b.p. 522 K b.p. 563 K
The higher boiling points of amides is because of intermolecular hydrogen bonding
HR HR HR
|| || ||
..........H − N − C = O.........H − N − C = O.........H − N − C = O
(iii) Solubility : The lower members of amide family are soluble in water due to the formation of hydrogen
bonds with water.
(3) Chemical properties
(i) Hydrolysis : CH3CONH2 + H2O Slowly → CH3COOH + NH3
CH3CONH2 + H2O + HCl Rapidly → CH3COOH + NH4Cl
CH3CONH2 + NaOH Farmore rapidly → CH3COONa + NH3
(ii) Amphoteric nature (Salt formation)
It shows feebly acidic as well as basic nature.
CH3CONH2 + HCl(conc.) → CH3CONH2.HCl
Acetamide hydrochloride
(only stable in aqueous solution)
2CH3CONH2 + HgO → (CH3CONH)2 Hg + H2O
Acetamide Mercuric Mercuric acetamide
Oxide
CH 3 CONH 2 + Na Ether → CH3CONHNa+ 1 H2
Sodium acetamide 2
(iii) Reduction : CH3CONH2 + 4[H] LiAlH4 → CH3CH2 NH2 + H2O
Acetamide Ethylamine
C6 H5CONH2 + 4[H] Na /C2H5OH → C6 H5CH2 NH2 + H2O
Benzamide Benzylamine
(iv) Dehydration: CH 3 CONH 2 P2O5 → CH3C ≡ N + H2O
Acetamide heat
Methyl cyanide
C6 H5CONH2 P2O5 → C6 H5 C≡N + H2O
Benzamide heat Phenyl
cyanide
C6 H5CONH2 SOCl2 → C6 H5C ≡ N
Phenyl cyanide
(v) Reaction with nitrous acid
CH3CONH2 + HONO NaNO2/ HCl → CH3COOH+ N2 + H2O
Acetic acid
C6 H5CONH2 + HONO NaNO2/ HCl → C6 H5COOH+ N2 + H2O
Benzoic acid
(vi) Hofmann bromamide reaction or Hofmann degradation : This is an important reaction for reducing a
carbon atom from a compound, i.e., − CONH2 is changed to − NH2 group.
CH 3 CONH 2 Br2 → CH3 NH2
Acetamide
NaOH or KOH Methyl amine (p-)
This reaction occurs is three steps:
O
||
CH3 − C− NH2 + Br2 + KOH → CH3CONHBr+ KBr + H2O
Acetobromamide
O
||
CH3 − C− NHBr2 + KOH → CH3 NCO + KBr + H2O
Methyl isocyanate
CH3 NCO + 2KOH → CH3 NH2 + K2CO3
Methyl amine
CH3CONH2 + Br2 + 4KOH → CH3 NH2 + 2KBr + K2CO3 + 2H2O
Mechanism: O .. KOH → O ..
|| || N−
R − C− NH2 + Br2 R Br KBr H2O
− C− | + +
H
N - Bromamide
R − O .. Br − O .. − + H2O
KOH → R N.. − Br K +
|| N− ||
C− | C−
H Unstable salt
O − O O
.. Br .. .. :R||
R − || N.. − K+ → R − || + KBr ; − N Rearrangement → O =C= N − R
N : C− (Intramolecular) Isocyanate
C− C−
Unstable Acetyl nitrene
(acyl nitrene)
R − N = C = O 2KOH → RNH2 + K2CO3
NH3/∆ COOH
CONH2 N3 (–HOD)
∆
COND2
2KOD/Br2 ∆ 2KOH/Br2.∆
ND2 + K2CO3 + HOD NH2 + 2HOD + K2CO3
Note : In this reaction a number of intermediates have been isolated; N-bromamides, RCONHBr; salts of
these bromamides [RCONBr−] K + ; Isocyanates, RNCO.
Nitrene rearranges to form isocyanate.
(vii) Action with alcohol : CH3CONH2 + CH3OH HCl → CH3COOCH 3 + NH4Cl
70o C methyl acetate
(viii) Reaction with grignard reagent
OMgBr
|
CH 3 − Mg − Br + CH 3 − CONH2 → CH 4 + CH 3 − CONH − MgBr CH3MgBr → CH3 − NH − MgBr
C−
|
CH3
OH O
NH 2 -NH3 →CH3
H2O/ H+ → CH | ||
Hydrolysis 3 CH 3
− C− − C−
|
CH3 Acetone
Unstable
(4) Uses
(i) In organic synthesis. The compounds like methyl cyanide, Methylamine and ethylamine can be prepared.
(ii) In leather tanning and paper industry.
(iii) As a wetting agent and as soldering flux.
Amides such as dimethyl formamide (DMF), dimethyl acetamide (DMA) are used as solvents for organic and
inorganic compounds.
Esters, R − C− OR
O||
These are the most important class of acid derivatives and are widely distributed in nature in plants, fruits and flowers.
Nomenclature : In common names and IUPAC system, change the suffix ic acid by ate.
Ester Common name IUPAC name
Methyl formate Methyl methanoate
HCOOCH3 Methyl acetate Methyl ethanoate
Ethyl acetate Ethyl ethanoate
CH3COOCH3 Phenyl acetate Phenyl ethanoate
CH 3COOC2 H 5 Ethyl α -methyl butyrate Ethyl 2-methylbutanoate
CH 3COOC6 H5
γ βα
CH 3CH 2C HCOOC2 H5
|
CH3
The name of some aromatic esters are given below :
COOCH3 COOC2 H 5 COOC2 H 5 OCOCH3
CH3
Methyl benzoate Ethyl benzoate Br 3-Methylphenyl ethanoate
Ethyl 4 - bromobenzoate
(1) Methods of preparation
(i) From carboxylic acid [Esterification] : Laboratory method.
OO
|| ||
R − OH + H OR′ H+
C− R − C− OR′+ H2O
Ester
CH3COOH+ CH2N2 Ether → CH3COOCH3 + N2
Acetic acid Diazomethane Methyl acetate
C6H5COOH+ CH2 N2 Ether → C6H5COOCH3 + N2
Benzoic acid Diazomethane Methyl benzoate
With diazomethane is the best method.
(ii) From acid chloride or acid anhydrides
CH3CO Cl+ H OC2 H5 → CH3COOC2 H5 + HCl
Acetyl chloride Ethyl alcohol Ethyl acetate
CH3CO O + CH3CH2OH → CH3COOCH2CH3 + CH3COOH
CH3CO Ethyl acetate
Ethyl alcohol
Acetic anhydride
C6 H5CO Cl + H OC2 H5 → C6 H5COOC2 H5 + HCl
Benzoyl chloride Ethyl alcohol Ethyl benzoate
(iii) From alkyl halide : C2H5Br + CH3COOAg → CH3COOC2H5 + AgBr
Ethyl bromide Silver acetate Ethyl acetate
(iv) From ether : CH3 − O − CH3 + CO BF3 → CH3COOCH3
Methoxy methane 350 K Methyl acetate
(v) From Tischenko reaction : CH 3 − C− H + O = C − CH 3 Al(OC2H5)3 → CH 3 − C − OC2 H 5
||
| ||
OH O
(2) Physical properties
(i) Physical state and smell : Esters are colourless liquids (or solids) with characteristic fruity smell. Flavours of
some of the esters are listed below :
Ester Flavour Ester Flavour
Amyl acetate Banana Isobutyl formate Raspberry
Benzyl acetate Jasmine Ethyl butyrate Pineapple
Amyl butyrate Apricot Octyl acetate Orange
(ii) Solubility : They are sparingly soluble in water but readily soluble in organic solvents such as alcohol, ether etc.
(iii) Boiling points : Their boiling points are lower than the corresponding acids because of the absence of
hydrogen bonding. i.e., ethyl acetate = 77.5oC.
(3) Chemical properties
(i) Hydrolysis : CH3COOC2 H5 + H 2O dil. acid CH3COOH + C2 H5OH
Ethyl acetate Acetic acid Ethyl alcohol
CH 3COOC2 H5 + NaOH CH 3COONa + C2 H5OH
Ethyl acetate Sod. acetate Ethyl alcohol
Hydrolysis of ester by alkalies (NaOH) is known as saponification and leads to the formation of soaps
Mechanism : It follows three steps :
Step I : The nucleophile, OH − ion from the alkali attacks the carboxyl carbon to form an intermediate.
O O−
|| |
CH 3 C OH − CH 3 C OC2 H5
− + → − −
| |
OC2H5 OH
Step II : The intermediate, then loses a molecule of ethoxide ion to form acetic acid as:
CH3 − C − O− O
+ O− C2H5
− OC2H5 → CH3 − C
OH OH
Step III : Ethoxide ion abstracts the acidic proton from acetic acid to form acetate ion.
OO
CH3 − C +−OC2H5 → CH3 − C + C2H5OH
OH O
Resonance stabilized
Note : This reaction is irreversible because a resonance stabilized carboxylate (acetate) ion is formed.
The acid hydrolysis of esters is reversible.
(ii) Reaction with ammonia (ammonolysis) : CH3CO OC2H5 + H NH2 → CH3CONH2 + C2H5OH
Ethyl acetate Acetamide
(iii) Reduction : CH 3 COOC2 H 5 + 4[H] LiAlH4 → 2C2 H 5 OH
or Na / C2H5OH
COOC2H5 LiAlH4 → CH2OH
+ 4H + C2H5OH
or Na / C2 H5OH
Ethyl benzoate Benzyl alcohol
Reduction in presence of Na / C2H5OH is known as Bouveault Blanc reduction.
The catalytic hydrogenation of ester is not easy and requires high temperature and pressure. The catalyst
most commonly used is a mixture of oxides known as copper chromate (CuO.CuCr2O4 ) .
O
||
R − OR′ + 2H2 CuO.CuCr2O4 → RCH 2OH + R′OH
C−
525K, 200 − 300atm
(iv) Reaction with PCl5 or SOCl2
CH3COOC2H5 + PCl5 → CH3COCl + C2H5Cl + POCl3
CH3COOC2H5 + SOCl2 → CH3COCl+ C2H5Cl + SO2
Acetyl chloride Ethyl chloride
C6 H5COOC2H5 + PCl5 → C6 H5COCl+ POCl3 + C2H5Cl
Ethyl benzoate Benzoyl chloride
(v) Reaction with alcohols : On refluxing ester undergoes exchange of alcohols residues.
R−C O + R′′OH H+ R−C O + R′OH
OR′ OR′′
(Excess)
CH 3COOC2 H5 + CH 3OH → CH 3COOCH3 + C2 H5OH
Ethyl acetate Methyl acetate
This reaction is known as alcoholysis or trans esterification.
(vi) Reaction with Grignard reagents
O OMgBr
|| CH 3 |
CH 3 CH3 MgBr C OC2 H
− C− OC2 H5 + → − − 5
|
Ethyl acetate CH3
O OMgBr O C2H5OMgBr
| | ||
3o alcohol : − CH 3 ←H+ CH 3 − − CH 3 ←CH3MgBr CH 3 − CH 3
CH3 − C H2O C C−
|
CH3 |
CH3
(vii) Claisen condensation
OO
|| ||
CH3 − OC2 H 5 + H − CH 2COOC2 H 5 C2H5O− Na+ → CH3 − C2 H 5 OH
C− C− CH2COOC2H5 +
Ethyl acetate (2 molecules) Ethyl acetoacetate
(β -ketoester)
(viii) Reaction with hydroxyl amine
OO
|| ||
CH 3 OC2H5 + H HNOH base → CH3 NHOH+ C2H5OH
− C− − C−
Ethyl acetate Hydroxyl Hydroxamic acid
amine
(ix) Reaction with hydrazine : CH3COOC2H5 + H2 NNH2 → CH3CONHNH2 + C2H5OH
Hydrazine Acid hydrazide
(x) Halogenation : CH3COOC2H5 + Br2 RedP → CH2BrCOOC2H5 + HBr
α −Bromoethyl acetate
(xi) Reaction with HI: CH3COOC2H5 + HI → CH3COOH+ C2H5OH
Acetic acid Ethyl alcohol
(4) Uses
(i) As a solvent for oils, fats, cellulose, resins etc.
(ii) In making artificial flavours and essences.
(iii) In the preparation of ethyl acetoacetate.
(5) General Tests
(i) It has sweet smell.
(ii) It is neutral towards litmus.
(iii) A pink colour is developed when one or two drops of phenolphthalein are added to dilute sodium hydroxide
solution. The pink colour is discharged when shaken or warmed with ethyl acetate.
(iv) Ethyl acetate on hydrolysis with caustic soda solution forms two compounds, sodium acetate and ethyl alcohol.
CH3COOC2H5 + NaOH → CH3COONa + C2H5OH
Acid Anhydride CH 3CO O or (CH3CO)2 O
CH 3CO
(1) Method of preparation
(i) From carboxylic acid
OO OO
|| || || ||
OH + H O − R Quartz tube → R R+ H 2O
R − C− C− Porcelain − C− O − C−
Acid anhydride
chips 1073 K
OO
|| ||
C6 H5CO OH + H OOCC6 H5 P4O10 → C6 H 5 H2O
heat − C− O − C− C6 H5 +
Benzoic anhydride
(ii) From carboxylic acid salt and acyl chloride [Laboratory method]
CH3COONa + CH3COCl Py → CH3COOCOCH3 + NaCl
Acetic anhydride
C6 H5COONa + C6 H5COCl Py → C6 H5COOCOC6 H5 + NaCl
Benzoic anhydride
(iii) From acetylene
CH + 2CH 3 COOH HgSO4 → CH 3 Distill → CH CHO + CH 3 CO O
heat CH 3 CO
||| | 3
CH(OOCCH3 )2
CH Acetic anhydride
(iv) From acetaldehyde : CH3CHO + O2 Cobalt → 2CH 3 − C− O − O − H → (CH3CO)2 O + H 2O
acetate ||
O
(2) Physical properties
(i) Physical state : Lower aliphatic anhydrides are colourless liquids with sharp irritating smell. The higher
members of the family as well as the aromatic acid anhydrides are solids in nature.
(ii) Solubility : They are generally insoluble in water but are soluble in the organic solvents such as ether,
acetone, alcohol, etc.
(iii) Boiling points : The boiling points of acid anhydrides are higher than those of carboxylic acids because of
the greater molecular size.
(3) Chemical Properties
OO
|| ||
(i) Hydrolysis : CH3 − C− O − C− CH3 + H2O → 2CH3COOH
Acetic anhydride Acetic acid
(ii) Action with ammonia : (CH3CO)2 O + 2NH3 → CH3CONH2 + CH3COONH4
Acetamide Amm. acetate
(iii) Acetylation : Acetic anhydride react with compound having active hydrogen.
(CH3CO)2 O + C2 H5OH → CH3COOC2 H5 + CH3COOH
Ethyl alcohol Ethyl acetate
(CH3CO)2 O + H 2 NC2 H5 → CH3CONHC2 H5 + CH3COOH
Ethyl amine N −Ethyl acetamide
(CH3CO)2 O + HN(C2 H5 )2 → CH3CON(C2 H5 )2 + CH3COOH
Diethylamine N, N −Diethyl acetamide
(CH3CO)2 O + H 2 NC6 H5 → CH3CONHC6 H5 + CH3COOH
Aniline Acetanilide
(CH3CO)2 O + OH OOCCH 3 + CH 3 COOH
COOH → COOH
Salicylic acid Acetyl salicylic
acid (Aspirin)
(iv) Action of dry HCl : (CH3CO)2 O + HCl → CH3COCl + CH3COOH
(v) Reaction with chlorine : (CH3CO)2 O + Cl2 → CH3COCl + CH2ClCOOH
Acetyl chloride Monochloroacetic
acid
(vi) Reaction with PCl5 : (CH3CO)2 O + PCl5 → 2CH3COCl + POCl3
(vii) Friedel craft's reaction : (CH3CO)2 O + C6 H6 AlCl3 → C6 H5COCH3 + CH3COOH
Benzene Acetophenone
(viii) Reaction with acetaldehyde : (CH3CO)2 O + CH3CHO → CH3CH(OOCCH3 )2
Acetaldehyde Ethylidene acetate
(ix) Reduction : (CH 3 CO)2 O LiAlH4 → CH3CH 2OH
Ether Ethyl alcohol
(x) Action with ether : CH3CO O.COCH3 + C2 H5 − O − C2 H5 → 2CH3COOC2 H5
Diethyl ether Ethyl acetate
(xi) Action with N2O5 : CH 3 COOCOCH 3 + N 2O5 → CH3 − C− O − N O
|| O
O
(4) Uses : Acetic anhydride is used
(i) as an acetylating agent.
(ii) For the detection and estimation of hydroxyl and amino group.
(iii) in the manufacture of cellulose acetate, aspirin, phenacetin, acetamide, acetophenone, etc.
Urea or Carbamide O = C NH 2
NH 2
Urea may be considered as diamide of an unstable and dibasic carbonic acid from which both the hydroxyl
groups have been replaced by − NH2 groups.
OH NH 2 NH 2
O=C −OH → O = C −OH → O = C
+ NH2 + NH2
OH OH NH 2
Carbonic acid Carbamic acid, Urea, diamide of
(Monoamide) carbonic acid or
carbamide
Urine in 1773 by Roulle and hence the name urea was given.
It was the first organic compound synthesised in the laboratory from inorganic material (by heating a mixture
of ammonium sulphate and potassium cyanate) by Wohler in 1828.
This preparation gave a death blow to Vital force theory.
It is the final decomposition product of protein's metabolism in man and mammals and is excreted along with urine.
Adults excrete about 30 grams of urea per day in the urine.
(1) Method of preparation
(i) From urine : Urine is treated with conc. nitric acid where crystals of urea nitrate CO(NH2)2.HNO3 are
obtained.
2CO(NH 2 )2 .HNO3 + BaCO3 → 2CO(NH 2 )2 + Ba(NO3 )2 + H 2O + CO2
Urea nitrate Urea
(ii) Laboratory preparation
(a) Wohler synthesis : 2KCNO + (NH4 )2 SO4 → 2NH4CNO + K 2 SO4
Potassium cyanate Ammonium sulphate Ammonium cyanate
NH 4 CNO Isomericchange → NH 2CONH 2
On heating Urea
Ammonium cyanate
The solid residue is extracted with alcohol and the extract evaporated when the crystals of urea are obtained.
It can be recrystalised from water.
(b) From phosgene or alkyl carbonate
O=C Cl 2 NH 3 → O = C NH 2 + 2HCl
Cl + NH 2
Carbonyl chloride Urea
(Phosgene)
O=C OC2 H 5 + 2 NH 3 → O = C NH 2 + 2C2 H5OH
OC2 H 5 NH 2
Ethyl carbonate Urea
(iii) Industrial method
(a) By partial hydrolysis of calcium cyanide
CaC2 + N2 heat → CaCN 2 + C
Calcium Calcium
Carbide cyanamide
The cyanamide is treated with dilute sulphuric acid at 40o C where partial hydrolysis occurs with the formation
of urea. CaCN 2 H2SO4 → H2 NCN H2O → H 2 NCONH 2
− CaSO4 (H2O2 )
Cyanamide (Urea)
or CaCN 2 + H2O + H2SO4 40oC → NH2CONH2 + CaSO4
(b) From carbon dioxide and ammonia
CO2 + 2 NH 3 150− 200oC → NH 2COONH 4 heat (140oC) → NH 2CONH 2
− H2O Urea
Ammonium carbamate
(2) Physical properties : Urea is a colourless, odourless crystalline solid. It melts at 132o C . It is very soluble in
water, less soluble in alcohol but insoluble in ether, chloroform.
Crystal structure: In solid urea, both nitrogen atoms are identical.
H2N NH 2 H 2 N+ NH 2 H2N N+ H 2
1.37 Å C ←→ C ←→ C
||
||
O O− O−
This indicates that C − N bond in urea has some double bond character.
(3) Chemical Properties
(i) Basic nature (Salt formation): It behaves as a weak monoacid base (Kb = 1.5 × 10−14 ) . It forms strong acid.
NH2CONH2 + HNO3(conc.) → NH2CONH2.HNO3
Urea nitrate
2NH2CONH2 + H2C2O4 → (NH2CONH2)2 H2C2O4
Oxalic acid Urea oxalate
Due to resonance stabilization of cation, the negatively charged oxygen atom is capable of coordination with one
proton.
H2N NH 2 H2 N+ NH 2 H2N N+ H2
C ←→ C ←→ C
|| | |
+ OH OH OH
Note : An aqueous solution of urea is neutral.
NH2 + H OH OH
(ii) Hydrolysis : O=C Aq.alkalior → O = C + 2NH3
acid OH Ammonia
NH2 + H OH
Urea Carbonic acid
CO2+↓H2O
NH2CONH2 + 2NaOH → 2NH3 + Na2CO3
An enzyme, urease, present in soyabean and soil also brings hydrolysis .
NH2CONH2 + 2H2O → (NH4 )2 CO3 → 2NH3 + CO2 + H2O
Ammonium carbonate
(iii) Action of heat : NH2CO NH2 + H HNCONH2 heat → NH2CONHCONH2 + NH3
(Two molecules of urea) Biuret
Urea is identified by the test known as biuret test. The biuret residue is dissolved in water and made alkaline with
a few drops of NaOH. When a drop of copper sulphate solution is added to the alkaline solution of biuret, a violet
colouration is produced.
when heated rapidly at 170o C , polymerisation takes place:
NH 2CONH 2 heat → NH 3 + HOCN (H − N = C = O) H
C
Cyanic acid
O=C C=O
3HOCN Polymerisation →(HOCN)3 or (H 3 N 3 C3 O3 ) or N– H
HN
C
(iv) Reaction with nitrous acid O
Cyanuric acid
O N OH
H2 N − CO − N H2 + 2HNO2 NaNO2+HCl → H2CO3 + 2N2 + 2H2O
Carbonic acid
HO N O
H2O↓+CO2
(v) Reaction with alkaline hypohalides
NaOH + Br2 → NaOBr + HBr
NH2CONH2 + 3NaBrO → N2 + 2H2O + CO2 + 3NaBr
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