LECTURE NOTE SK025 (ORGANIC) KMKt

NH3 Name Product Name
derivatives
NH2NHC6H5 phenyl C=NNHC6H5 phenyl
hydrazine hydrazone
O
|| semi O semi
NH2NHCNH2 || carbazone
carbazide C=NNHCNH2

Carbonyl reacts with hydrazine or phenylhydrazine
to form yellow orange precipitate.

67

iv) Oxidation

Oxidation Tollens Fehling Schiff
reactions
Differentiation test for aldehydes and ketones :

REMEMBER Strong
Oxiziding
agent : Can’t be
used as
KMnO4 / H+, ∆ Differentiation
K2Cr2O7 / H+, ∆ test

CrO3/H+

68

iv) Oxidation

Strong oxidizing agent Carboxylic Acid
RCOOH
Aldehyde

Mild oxidizing agent Carboxylate
Ion RCOO-
Tollens’,
Schiff,
Fehling’s and
Benedict’s solutions

Ketone resistant to oxidation

because they do not have hydrogen
attached to the carbonyl carbon atom.

69

General reaction : KMnO4 / H+ O
||
O ∆ R—C—OH
||
R—C—H Carboxylic acid

Aldehyde

Other strong oxidizing agents:

➢ Hot acidified K2Cr2O7 @
➢ Hot acidified Na2Cr2O7 @
➢ Acidified CrO3

70

Example : KMnO4 / H+ O
||
O ∆ CH3CH2—C—OH
||
CH2CH3—C—H propanoic acid

propanal

O K2Cr2O7 / H+ O
|| ||
—C—H ∆ —C—OH

cyclopentylmethanal Cyclopentylmethanoic acid

O KMnO4 / H+ Purple colour of
||
CH3 — C — CH3 ∆ acidified KMnO4
remains
Propanone

72

O
||
R — C — CH3

Reagent : excess I2 in NaOH(aq)

Observation : light yellow precipitate (CHI3)
is formed.

73

General reaction :

O O
|| ||
CH3—C—R excess I2 , NaOH R— C — O- + CHI3 (s)

Triiodomethane
(iodoform)

Example : O
O ||
|| H—C—O-
CH3—C—H + excess I2, OH- + CHI3

OBSERVATION: Light yellow precipitate (CHI3) formed. 74

Which structures show the formation of yellow
precipitate with excess iodine in NaOH?

1) 2) 3)

CH3 H O

H3C CH2 C O H3C CH2 C O C

4) 5) H3C CH3

H HO CH3 O
CH
CO C 6)

C

75

1) 2)

H3C CH2 CH3 H
C O 3)
C O H3C CH2 O

4) 5) CH3 C CH3

H HO H3C
CH
CO C 6)

O

C

76

Learning Outcomes:

9.3 Chemical Properties of Carbonyl Compounds

b) Explain the identification test for aldehyde
& ketone using:

i. 2,4-dinitrophenylhydrazine

(2,4-DNPH).

ii. Tollens’, Fehlings’ and Benedict’s

reagent

c) Differentiates between:

i. carbonyl & other compounds
ii. Aldehydes & ketone

Identification
Tests

1.Brady’s Test
2.Tollens’ Test
3.Fehlings’ Test

4.Benedict’s Test

78

Brady’s Test

Identification Test The presence of carbonyl group
Reagent :
2,4-DNPH (Brady’s reagent)
Observation:
H NO2 NO2
|
H—N-N

2,4-dinitrophenylhydrazine

Yellow @ Orange precipitate is formed.

79

1. Brady’s Test

Example :

CH3 HH NO2
| ||
CH3CH2—C O + H—N-N NO2 2,4-DNPH
|| Brady’s
|| reagent

CH3 H NO2 NO2 yellow @
|| orange
H2O + CH3CH2—C N-N precipitate

2-butanone-2,4-dinitrophenylhydrazone

80

2. Tollens’ Test (Silver Mirror Test)

Identification Test Differentiates aldehydes from ketones

Reagent : ➢ a mixture of aqueous silver nitrate
and aqueous ammonia @ Tollens’ reagent.
Product : ➢ Contains diamminosilver (I) ion,
Observation:
Ag(NH3)2+.

Carboxylate ion, RCOO- & silver, Ag(s)

Silver is deposited on the wall of the
test tube (Silver mirror)

81

General reaction :

O [Ag(NH3)2]+ OH- O + Ag
|| ||
R—C—H R—C—O- Silver
mirror
82

Aldehyde is oxidised to carboxylate ion.
Ag+ is reduced to Ag (silver)

Example :

O [Ag(NH3)2]+ OH- O
|| ||
CH3CH2—C—H CH3CH2—C—O-

propanal + Ag

O [Ag(NH3)2]+ OH- Silver mirror
||
—C—H O
||
phenylmethanal —C—O-

+ Ag

Silver mirror

83

3. Fehlings’ Test

Identification Test to distinguish aliphatic aldehydes from
aromatic aldehydes and ketones

Reagent : ➢ Cupric tartrate complex ion,
Cu2+ (complex)

➢ Show the blue colour solution.

Product : Carboxylate ion, RCOO- &
Observation: Copper (I) oxide, Cu2O(s)

Brick red precipitate is formed.

84

4. Benedict’s Test

Identification Test to distinguish aldehydes and ketones

Reagent : ➢ Cupric citrate complex ion,
Cu2+ (complex)
Product :
Observation: ➢ Show the blue colour solution.

Carboxylate ion, RCOO- &
Copper (I) oxide, Cu2O(s)

Brick red precipitate is formed.

85

General reaction : O Cu2O(s)
||
O R—C—O- + Brick-red
|| + 3H2O precipitate
R—C—H + 2Cu2+ + 5OH-
86
Blue

Aliphatic aldehyde is oxidised to carboxylate ion.
Copper (II) ion, Cu2+ is reduced to Copper (I) ion, Cu+.

Example :

CH3C||- H + 2Cu2+ + 5OH- CH3C||- O-
O O
Blue
+ Cu2O(s)

Brick-red
precipitate
+ 3H2O

OBSERVATION: Brick-red precipitate

ALDEHYDE Vs KETONE

Aldehydes are more Steric factor
reactive than ketone in Electronic factor
Nu- addition reaction:

Steric factor O
||
O R—C—R’
||
R—C—H  Two alkyl groups.
 Less positively charged
 Only one alkyl group.
 More positively charged of the carbonyl C.
of the carbonyl C.
 More steric effect.
 Less steric effect.
88

ALDEHYDE Vs KETONE

Electronic factor

Alkyl group, R = Electron O
Donating/Releasing ||
R—C—R’
O|| group
R—C—H

Aldehyde has only ONE electron
donating group.

Thus making the aldehyde
carbonyl group slightly more
electron-poor and electrophilic.

Refer : pg 832, Wade., Organic Chemistry, 17th Ed, Prentice Hall 89

Reduction of C=O

Selectivity of Reducing Agents
LiAlH4 - does not reduce C=C and C≡C
NaBH4 - does not reduce C=C , C≡C and C=O

in acid and esters

H2/Pt - reduce C=C, C≡C and C=O

Hence, NaBH4 is the best reducing agent for
reduction of simple ketone and aldehyde.

90

Learning Outcomes:
9.3 Chemical Properties of Carbonyl Compounds

d) Outline the synthesis of compounds
involving carbonyl compounds.

* Limit to maximum 4 steps only

Example :Outline the synthetic pathway of ethanal from
ethane

UV NaOH(aq) H3C CH2 PCC H3C CH
H3C CH3 + Cl2 OH CH2Cl2 O
H3C CH2

Cl

92

Edited by : Revised by :
SAHB, WRWL, NSR MPJ

Approved by :
ZA

93

CHAPTER 10.0

CARBOXYLIC ACIDS
AND

ITS DERIVATIVES

10.1 Write the
general
formula

10.2 10.0 : 10.5
Nomenclature Chemical
CARBOXYLIC ACIDS Properties
AND ITS

DERIVATIVES

10.3 Physical 10.4
Properties Preparation

10.1 Introduction
a) State the general formula of carboxylic acids : (C1)

OO

Ar C OH and R C OH

b) Give the name carboxyl compounds according to
the IUPAC nomenclature (C2)

c) State the common names of carboxylic acids with
parent chain ≤ C5 (C1)

d) Give the structural formulae of carboxyl
compounds (parent chain ≤ C10) (C2)

Introduction

O
C OH

Functional group: Carboxyl

GENERAL FORMULA
OF

CARBOXYLIC ACIDS

OO

R C OH Ar C OH

(R ≡ alkyl or H) (Ar ≡ aryl)

Also can be written : RCOOH or RCO2H

NOMENCLATURE
OF

CARBOXYLIC ACIDS

STRUCTURAL FORMULA IUPAC NAME
HCOOH Methanoic acid
CH3COOH Ethanoic acid
CH3CH2COOH Propanoic acid
CH3CH2CH2COOH Butanoic acid
CH3CH2CH2CH2COOH Pentanoic acid
CH3CH2CH2CH2CH2COOH Hexanoic acid
CH3CH2CH2CH2CH2CH2COOH Heptanoic acid
CH3CH2CH2CH2CH2CH2CH2COOH Octanoic acid
CH3CH2CH2CH2CH2CH2CH2CH2COOH Nonanoic acid
CH3CH2CH2CH2CH2CH2CH2CH2CH2COOH Decanoic acid

ALIPHATIC CARBOXYLIC ACID

According to IUPAC nomenclature, for carboxylic acids:

➢ Parent chain is the longest carbon atoms that contain the
carboxyl group.

➢ The chain is numbered starting from the carboxyl carbon
atom as C1.

CH3 O

CH3CH2CHCH2 C OH

5 4 32 1

➢ The carboxyl group is at the terminal.

One COOH – carboxyl group is at one end
Two COOH – carboxyl groups are at both ends

➢ Replace -e in the alkanes by ‘oic acid’ (eg: methanoic
acid).

CH3 O

CH3CH2CHCH2 C OH
54 32 1

3-methylpentanoic acid

➢ If two carboxyl groups present, add – dioic acid to the
name of parent alkane; alkanedioic acid.

O CH3 O

HO C CH2 CH CH2 CH2 C OH

12 3 4 56

65 4 3 21

3-methylhexanedioic acid

➢ The carboxyl group is given priority over other functional
groups.

➢ Other functional group is treated as substituents, if
present.

6 O

CH3

HO CH CH2 CH2 CH2 C OH

54 3 2 1

5-hydroxyhexanoic acid

➢ Carboxylic acid with double bond are named as x – alkenoic
acid [x = position of double bond]

O CH3

HO C CH2 CH CH CH CH3

1 23 4 5 6

5-methyl-3-hexenoic acid

1 4

HOOC COOH

23
CC

HH

cis-2-butenedioic acid

➢ A cyclic carboxylic acid is named as:
▪ cycloalkanecarboxylic acid
▪ cycloalkenecarboxylic acid

➢ The C atom which is attached to –COOH is numbered as C1

COOH COOH

1
62

5 3 cyclopentanecarboxylic acid

4 CH3

3-methyl-2-cyclohex-2-enecarboxylic acid

➢ A cyclic dicarboxylic acid is named as:
▪ 1,x – cycloalkanedicarboxylic acid
▪ 1,x – cycloalkenedicarboxylic acid

6

COOH

51

4

2 COOH

3

1,2-cyclohexanedicarboxylic acid

6

1 COOH

5

Cl 4 2 COOH

3

4-chloro-1,2-cyclohex-1-enedicarboxylic acid

AROMATIC CARBOXYLIC ACID

➢ When R is an aryl group, the parent name is benzoic
acid.

32

Cl 4 1 COOH

56

4-chlorobenzoic acid @
p-chlorobenzoic acid

➢ An aromatic dicarboxylic acid is named as
1,x-benzenedicarboxylic acid

HOOC 2
1
3
4 COOH

HOOC 56

4 1,3-benzenedicarboxylic acid
5
3 CH3

2

CH CH3

61

COOH

2-isopropyl-1,4-benzenedicarboxylic acid

Common names with parent chain ≤ C5

STRUCTURAL IUPAC NAME COMMON NAME
FORMULA
Methanoic acid Formic acid
HCOOH

CH3COOH Ethanoic acid Acetic acid
Propionic acid
CH3CH2COOH Propanoic acid
Butyric acid
CH3CH2CH2COOH Butanoic acid Valeric acid

CH3CH2CH2CH2COOH Pentanoic acid

Structure formulae with parent chain ≤ C10

STRUCTURAL FORMULA IUPAC NAME

HCOOH Methanoic acid

CH3COOH Ethanoic acid
CH3CH2COOH Propanoic acid
CH3CH2CH2COOH Butanoic acid
CH3CH2CH2CH2COOH Pentanoic acid
CH3CH2CH2CH2CH2COOH Hexanoic acid
CH3CH2CH2CH2CH2CH2COOH Heptanoic acid
CH3CH2CH2CH2CH2CH2CH2COOH Octanoic acid
CH3CH2CH2CH2CH2CH2CH2CH2COOH Nonanoic acid
CH3CH2CH2CH2CH2CH2CH2CH2CH2COOH Decanoic acid

10.2 Physical Properties of Carboxylic Acids

a) Explain the physical properties : (C2, C3 & C4)
i. Boiling point
ii. Solubility in water

BOILING POINT

➢ The boiling point of carboxylic Hydrogen bond
acid is higher than alcohol,
ketone or aldehyde of similar O HO
molecular weight.
RC CR
➢ It is due to carboxylic acids
molecule are arranged closely OH O
packed, as stable dimers, at
which the hydrogen bonds Hydrogen bond
formed between the molecules
are relatively strong. Dimerisation of Carboxylic Acid

➢ Thus, more energy is needed
to overcome the strong
hydrogen bonding, boiling
point increase.

Arrange the compounds in each set in order of increasing
boiling point and explain.
(a) CH3(CH2)5COOH, CH3(CH2)6CHO, CH3(CH2)6CH2OH

CH3(CH2)6CHO < CH3(CH2)6CH2OH < CH3(CH2)5COOH

✓ Octanal has the lowest boiling point because it only has weak van
der Waals forces between their molecules.

✓ 1-octanol and heptanoic acid have strong hydrogen bond between
their molecules.

✓ Boiling point of heptanoic acid is higher than 1-octanol because
heptanoic acid has the –COOH group that exists as stable dimers
through hydrogen bonds .

✓ The hydrogen bond of heptanoic acid is stronger than 1-octanol.

SOLUBILITY IN WATER

Hydrogen Bonds H

➢ Carboxylic acids are soluble O HO HO
in water due to the formation C
of hydrogen bond between RC H R
the water molecules and O
carboxylic acid molecules. OH O H

➢ The solubility of carboxylic acid in water is almost the same as alcohol.
➢ Simple carboxylic acids (C1-C5) are completely soluble in water.

➢ Aliphatic carboxylic acids with C > Hydrophilic area
5 are insoluble in water. As the
length of the hydrocarbon chain O
increases, hydrophobic area R C OH
increase, hydrogen bonding with
water molecule hardly formed thus Hydrophobic area
the solubility of the acid in water
decreases.

➢ Aromatic carboxylic acids are slightly soluble in water
due to the huge aromatic ring (large hydrophobic area).

large hydrophobic area

Cl COOH

➢ Dicarboxylic acids are relatively more soluble since

more hydrogen bonds can be formed with water

molecules.

H Hydrogen Bonds H

HO HO O HO
H H
C CH2 C 23
OH O OH OH

Hydrogen Bonds