Chapter 20 Carboxylic Acids and their derivatives Part 3- Chemistry free study material by TEACHING CARE online tuition and coaching classes

 

 

 

 

 

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

• Kolbe Schmidt reaction

 

 

ONa

 

CO₂

125°C, Pressure

OCOONa

Rearrangement

OH

COONa           Dil. HCl

COOH

 

 

Sodium phenoxide

Sodium phenyl carbonate

Sodium salicylate

Salicylic acid

 

 

It is a commercial method. The reaction yields both o- and p- isomers. Salicylic acid is more volatile and separated by steam distillation.

• Reimer-Tiemann reaction

 

 

4

OH + CCl

+  KOH

Heat

OH COOK

Dil. HCl                                         OH

COOH

 

 

• From benzene derivatives

 

 

 

(a)

 

 

 

(b)

Cl COOH

o-Chlorobenzoic acid

 

 

SO₃K COOH

o-Sulphobenzoic acid

Fuse with

NaOH

 

 

 

 

Fuse with

KOH

OH COOH

 

 

OH COOH

 

 

 

(c)

 

 

 

(d)

 

 

 

(e)

OH          + CH₂OH

Salicyl alcohol

 

 

OH         +

CH₃

o-Cresol

 

 

NH₂ COOH

Anthranilic acid

[O]

 

 

 

[O]

Chromic acid

 

 

 

 

PbO/NaOH

 

 

 

 

 

 

 

NaNO₂/HCl

0°C

OH COOH

 

 

OH COOH

 

 

N₂Cl COOH

 

 

 

 

 

 

 

 

 

 

 

 

H₂O

heat

 

 

 

 

 

 

 

OH COOH

 

 

 

(2)  Physical properties

• It is a colourless needle shaped crystalline compound.
• Its p. is 156°C.
• It is sparingly soluble in cold water but readily soluble in hot water, alcohol, ether and
• It is steam
• It is poisonous in However, its derivative used in medicine internally and externally as antipyretic and antiseptic.

(3)  Chemical properties

• Reaction with Na₂CO₃, NaHCO₃ or NaOH

O

||

 

 

Salicylic acid

C – OH OH

COO^– Na⁺

Aq. Na₂CO₃                                                         Aq. NaOH

OH

Mono sodium salicylate

COONa

 

ONa

Disodium salicylate

 

• Reaction with alcohols or phenols

OH

+   CH₃OH

 

 

HCl(gas)

OH

+ H₂O

 

COOH

Salicylic acid

COOCH₃

Methyl salicylate

 

 

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

+    C H OH

OH

POCl₃

 

 

 

Salicylic acid

6    5

COOH

COOC₆H₅

Phenyl salicylate (salol)

 

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.

• Decarboxylation

COOH

 

D

 

OH

Salicylic acid

OH

Phenol

+    CO₂

 

 

 

• Acetylation

 

Salicylic acid

 

OH COOH

 

+   ClCOCH₃

 

Acetyl chloride

 

 

 

Pyridine

 

 

 

 

 

 

Aspirin

 

OCOCH₃ COOH

 

(Acetyl salicylic acid)

 

Note : ® Aspirin is a white solid, melting point 135°C. It is used as antipyretic and pain killer (analgesic action).

 

 

 

• Reaction with ferric chloride solution

OH

 

 

 

 

Salicylic acid

 

• Reaction with PCl₅

COOH

FeCl₃

Solution

Violet colouration

 

 

Salicylic acid

 

• Bromination

OH COOH

Cl

PCl₅

COCl

o-Chlorobenzoyl chloride

 

OH

 

 

Salicylic acid

OH COOH

Br₂ water

Br                     Br

 

 

Br

 

2,4,6,–Tribromophenol

 

 

• Nitration

 

Salicylic acid

OH COOH

 

 

 

Fuming HNO₃

 

O₂N

 

 

 

 

NO₂

 

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

 

 

 

 

 

 

Benzene-1,2-dicarboxylic acid (Phthalic acid)

 

(1)  Methods of preparation

COOH

 

Benzene-1,3-dicarboxylic acid (Isophthalic acid)

 

CH₃

COOH

Benzene-1,4-dicarboxylic acid (Terphthalic acid)

 

[O]                               CH₃

 

 

 

• COOH

 

• By the oxidation of o-xylene :

 

o-Xylene

CH₃

KMnO₄

COOH

o-Toluic acid

COOH

Phthalic acid

 

• From naphthalene (Industrial method) : It is known as aerial

 

 

 

 

 

 

 

 

Naphthalene

Fuming H₂SO₄ HgSO₄,300°C

CO    O CO

Phthalic anhydride

COONa COONa

COOH COOH

 

 

(2)  Physical properties

• It is colourless crystalline
• Its melting point is not sharp (195–213°C).
• It is sparingly soluble in cold water but soluble in hot water, alcohol, ether, benzene

(3)  Chemical properties

 

 

 

NaOH                                               COONa

COOH

Acid salt

 

C2H5OH                                                           COOC₂H₅ COOH

Ethyl hydrogen phathalate

COONa COONa

Disodium phthalate

 

2   5

C H OH                                         COOC2H5 COOC₂H₅

Ethyl phthalate

 

 

 

PCl5                                                                                                  COCl

COCl

Phthaloyl chloride

 

 

 

COOH COOH

Phthalic acid

NH₃

COONH₄ COONH₄

Amm. phthalate

CONH₂       

CONH₂

Phthalamide

 

 

heat                                CO        O

 

– H₂O

 

 

 

Soda lime heat

 

 

 

Hg (CH₃COO)₂

CO

Phthalic anhydride

 

 

 

 

Benzene

 

COO COO

 

 

 

 

 

Hg           heat                                  CO Hg

CO

CO         NH

Phthalimide

 

 

 

 

 

 

O

 

 

 

• Uses : It is used in the manufacture of plastics, dyes and other compounds such as phthalic anhydride, phthalimide, anthraquinone and fluorescein