Question

Which of the following compound has the highest rate of decarboxylation?

• A. ${\mathrm{CH}}_3\mathrm{COOH}$
• B. ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}$
• C. ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2\mathrm{COOH}$
• D. ${\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{COOH}$

Answer 1

The correct option is D

${\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{COOH}$

Explanation for the correct option:

(D) ${\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{COOH}$

• ${\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{COOH}$ is a $\mathrm{\beta }$-keto acid.
• $\mathrm{\beta }$-keto acid is a molecule containing a ketone on the $\mathrm{\beta }$-carbon of a carboxylic acid.
• “Decarboxylation of a $\mathrm{\beta }$-keto acid involves an enol intermediate that is formed by an internal proton transfer from the carboxylic acid group to the carbonyl oxygen atom of the ketone.”
• The enol is transformed into the corresponding ketone spontaneously.
• The chemical reaction for ${\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{COOH}$ is given below:

Explanation for incorrect options

All other acids are primary carboxylic acids and do not undergo decarboxylation easily. Thus options A, B, and C are incorrect.

Hence, the correct option is D i.e. ${\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{COOH}$.