Question

Ease of esterification of the following alcohols $C{H_3}C{H_2}OH$ (I), ${(C{H_3})_2}CHOH$(II) and ${(C{H_3})_3}COH$(III) with $HCOOH$is:
A. I < II < III
B. III < II < I
C. II < I < III
D. I = II = III

Answer 1

Here, we must keep in mind that in case of esterification of alcohol, there is cleavage of O-H bond. So, the reactivity of primary, secondary and tertiary alcohols will vary accordingly.

Complete step by step answer:
In the reactions involving cleavage of O-H bond, the oxygen atom is to take up the electron pair from the bond. The presence of alkyl group with +I (inductive) effect tends to increase the electron density around oxygen atom. Consequently, the bond cleavage in the O-H bond becomes difficult. Or, we can say that the alkyl group decreases the polarity of the O-H bond thereby making the release of H+ difficult. This adversely affects the reactivity of alcohol. Greater the number of alkyl groups present in the alcohol, lesser will be its reactivity. The ease of esterification of the following alcohols $C{H_3}C{H_2}OH$(I), ${(C{H_3})_2}CHOH$(II) and ${(C{H_3})_3}COH$(III) with $HCOOH$is III < II < I.

The correct answer is option B.

Additional Information: Reaction of alcohols with carboxylic acids will form esters and these reactions are known as esterification. In the esterification reaction O-H bond of alcohol will break and alcohol molecules act as nucleophiles while C-O bond of carboxylic acid will break in esterification. Oxygen atom of alcohol having lone pair of electrons and attack on carbonyl carbon of carboxylic acid molecule. Esterification reaction is catalysed by both acid and base. Esterification reactions are reversible in nature, reverse reaction is known hydrolysis of ester.

Note:
The same reactivity order holds true for acylation i.e. reaction of alcohols with acid chlorides and acid anhydrides.