Question

Which of the following carboxylic acids undergoes decarboxylation most easily on heating?
A.
B.
       

C.
 
D.

Answer 1

Hint : We know that a carboxylic acid has formula \[RCOOH\] where $R$ can be hydrogen benzene ring and hydrocarbon. Decarboxylation is a chemical reaction where removal of a carboxyl group takes place and releases carbon dioxide . Mostly decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. This reaction can be performed by heating carboxylic acid.

Complete step by step solution:
> Decarboxylation of any carboxylic acid depends upon the stability of carbanion. Carboxylic acids with beta keto systems are the most suitable carboxylic acid for the decarboxylation reaction. This is because the beta keto system stabilises the carbanion formation. $H - $ bonding makes decarboxylation reaction easy as it transfers acidic hydrogen into ketone oxygen, and eliminates carbon dioxide. Hence simple carboxylic acids which do not possess beta keto systems are harder to decarboxylate.
> We can identify $\beta - $ keto acid because these acids have ketone group at the second carbon from carbon from carboxylic acid. Here after observing all the options we got to know that the only option C i.e. $C{H_3}COC{H_2}COOH$ is $\beta - $ keto acid so it will go in decarboxylation easily on heating. The decarboxylation reaction of $C{H_3}COC{H_2}COOH$ on heating is given below;


Note : We have approached this reaction by finding the stability of carboxylic acid . We also know that carboxylic acid undergoes decarboxylation most easily on heating if it is $\beta - $ keto acid because it becomes less stable than simple carboxylic acid. Hence we have found after observing the options that the $\beta - $ keto acid is option C. We can find $\beta - $ keto acid as it has a keto group next second carbon from carboxylic acid.