A carboxylic acid ester is prepared commonly by reacting a carboxylic acid with excess of an alcohol in the presence of a small quantity of a strong acid such as conc. $\mathrm{H}_2 \mathrm{SO}_4$ as a catalyst. The reaction is reversible and generally the equilibrium constant for the esterification is close to 1 . As it is a reversible reaction, different methods are used to increase the yield of ester. It is established that the mechanism of esterification under such conditions involves initial protonation of the acid followed by the attack of the alcohol as a nucleophile.



The correct statement(s) is/are

• Correct answer
  A

  When esterification is carried out using molar ratio of acid and alcohol as 1:10, the yield of the ester with respect to the acid should be close to $90 \%$.
• B

  The function of conc. $\mathrm{H}_2 \mathrm{SO}_4$ is also to increase the free energy change of the reaction and thereby increasing the equilibrium constant.
• Correct answer
  C

  When an ester is heated with acidified water the protonation will be more favourable at the acyl oxygen atom than at the alkoxy oxygen atom.
• Correct answer
  D

  When butyl hexanoate is heated with a large excess of methanol in the presence of a small quantity of conc. $\mathrm{H}_2 \mathrm{SO}_4$, methyl hexanoate is the major product.

Hence, the correct answer is options: 'A', 'C', 'D'.