2. Conversion into functional derivatives

(a) Conversion into acid chlorides

Examples:

Illustration 16:

Benzoyl chloride is prepared from benzoic acid by

(A) Cl₂,                         (B) SO₂Cl₂

(C) SOCl₂                          (D) Cl₂, H₂O

Solution:

(C)

(b) Conversion into esters

Conversion into Esters (Esterification):

Carboxylic acid on reacting with alcohols in presence of dehydrating agent (H₂SO₄ or dry HCl gas) gives esters. The reaction is known as esterification.

This reaction is reversible and the same catalyst, hydrogen ion, that catalyzes the forward reaction, esterification, necessarily catalyzes the reverse reaction hydrolysis.

The equilibrium is particularly unfavourable when phenols (ArOH) are used instead of alcohol; yet if water is removed during the reaction, phenolic esters [RCOOAr] are obtained in high yield.

The presence of bulky group near the site of reaction, whether in alcohol or in the acid, slows down esterification (as well as its reverse, hydrolysis).

Reactivity CH₃OH > 1° > 2° > 3°

In esterification HCOOH > CH₃COOH > RCH₂COOH > R₂CHCOOH > R₃CCOOH