Question

How will you prepare benzoic acid from benzene, with the help of Friedel-Craft reaction? Also, write any two chemical properties of Benzoic acid?

Answer 1

Benzoic acid can be prepared from the benzene with the help of the Friedel-Craft reaction. In the case of benzoic acid, the acyl group is substituted into the benzene ring. This reaction is also known as Friedel-Crafts acylation of Benzene.

Complete step by step answer:
The benzene ring is reacted with a mixture of carbonyl chloride $COC{l_2}$ and $AlC{l_3}$ (aluminum chloride) that acts as a catalyst. The product benzoyl chloride is formed.
The reaction is as follows:
${C_6}{H_6} + COC{l_2} \to {C_6}{H_5}COCl$
Or

This reaction is an example of an electrophilic substitution reaction. The electrophile is $ClC{O^ + }$ that is produced by the reaction of carbonyl chloride and aluminum chloride.
The reaction is as follows:
$COC{l_2} + AlC{l_3} \to ClC{O^ + } + AlC{l_4}^ -$
The electrophilic substitution mechanism is divided into 2 stages:
Stage 1 –

Stage 2 –

Now when this product is hydrolyzed in presence of HCl. benzoin acid is formed as follows,

Some chemical properties of benzoic acid are,
Benzoic acid can be converted into benzyl alcohol by treating it with lithium aluminum hydride.
The reaction is shown below,
${C_6}{H_5}COOH + LiAl{H_4} \to {C_6}{H_5}C{H_2}OH$
When benzoic acid reacts with thionyl chloride benzoyl chloride is formed as follows,
${C_6}{H_5}COOH + SOC{l_2}\xrightarrow{{pyridine}}{C_6}{H_5}COCl + S{O_2} + HCl$

Note: A student can get confused between acylation and alkylation. Alkylation is the transfer of an alkyl group from one compound to another.
To convert benzene to ethylbenzene there is a very well-known reaction which is the Friedel-Craft alkylation reaction. In presence of aq. $AlC{l_3}$ it reduces the nucleophilicity of the benzene ring by the formation of the cation of the benzene ring. the reaction is shown below,

A student can also get confused between electrophilic substitution and nucleophilic substitution. Electrophilic substitution involves the displacement of a functional group by an electrophile, i.e., hydrogen whereas nucleophilic substitution involves the attack of a positively charged atom by a nucleophile.