Question

The $- {\rm{COOH}}$ group in a carboxylic acid can be replaced by hydrogen atom by heating the acid with:
A. ${\rm{Zn}}$ and ${\rm{HCl}}$
B. ${{\rm{H}}_2}$ in the presence of nickel
C. sodalime
D. bromine and concentrated aqueous alkali

Answer 1

We know that removal of ${\rm{C}}{{\rm{O}}_{\rm{2}}}$ group from any organic compound is termed as decarboxylation. Various decarboxylating agents are used in chemical reactions to proceed that step. So it is clear that replacement of $- {\rm{COOH}}$ by ${\rm{H}}$ is actually leading to decarboxylation.

Complete step by step answer:
Decarboxylation is a reaction in which removal of a carboxyl group takes place in the form of carbon dioxide. This reaction is used to remove a carbon atom from an organic compound having a functional group.
Let us consider any carboxylic acid say acetic acid having formula ${\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}$. When it is treated with reducing agents such as ${\rm{Zn}}$ and ${\rm{HCl}}$ or ${{\rm{H}}_2}$ in the presence of nickel, it gets reduced to alcohols.
But we need to remove one carbon along with two oxygen atoms. This can be achieved by heating carboxylic acid in soda lime and doing decarboxylation. Sodalime is actually a mixture of sodium hydroxide and calcium oxide.

Thus, the correct option is C.

Note:
We know that carboxylic acids can be converted into alkanes having one less carbon atom using ${\rm{NaOH}} + {\rm{CaO}}$. This mixture is sodalime. This specific reaction is also referred to as decarboxylation and removal of one molecule of carbon dioxide takes place in this reaction.