Question

Benzene can be obtained by heating either benzoic acid with X or phenol with Y. X and Y respectively are
A. Zinc dust and soda-lime
B. Soda-lime and zinc dust
C. Zinc dust and sodium hydroxide
D. Soda-lime and copper

Answer 1

Hint:We can convert the benzoic acid into benzene by decarboxylation. For this, a basic solution is required which can take protons of the carboxylic group and cause decarboxylation. The phenol can be converted into benzene by heating phenol with a good reducing agent.

Complete answer:
 We can get benzene from benzoic acid by decarboxylation. Decarboxylation means the removal of carbon dioxide.
Calcium oxide is known as soda-lime. Soda-lime works as a base that abstracts the acidic proton. The acidic hydrogen is the hydrogen attached to the carboxylic group of benzoic acid. After removing the proton, the carbon dioxide removes so, benzene gets a positive charge which is delocalized and this cation gets protonated by the solvent. Thus benzene forms.
The reaction is as follows:

The phenol can be converted into benzene by using the zinc dust. Phenol loses a proton to form phenoxide ion. The oxygen removes from this phenoxide ion forming a free radical on the benzene ring. The zinc ion with oxide ion forms zinc oxide and benzene radical joins with hydrogen radical to form benzene.
The reaction is as follows:

Benzene can be obtained by heating either benzoic acid with soda-lime (X) or phenol with Zinc dust (Y). X and Y are soda-lime and zinc dust respectively.

Therefore option (B) soda-lime and zinc dust, is correct.

Note:
Soda-lime is a mixture of sodium hydroxide and calcium oxide. The soda-lime solution is basic. We have to convert benzoic acid into benzene and phenol into benzene means benzoic acid and phenol both are getting reduced. Zinc dust is an excellent reducing agent which works at high temperatures. Zinc dust can be used to reduce almost all aromatic compounds.