Question

What products are obtained from the reaction of the following compounds with H₂CrO₄+ Δ?

a.

b.

c.

c.

Short answer

a.

b.

c.

Step-by-step solution

Characteristics of heating with chromic acid

Chromic acid is a very strong oxidizing agent which can oxidize alkyl benzene to carboxylic acids. It can also oxidize primary and secondary alcohols to carboxylic acids.Here all the reactions go through a radical intermediate.

Conversion of 1-ethyl-3-methylbenzene to benzene-1,3-dicarboxylic acid

(a) When 1-ethyl-3-methyl benzene is heated with chromic acid, each substitution in the benzene gets converted to carboxylic acids. At first position, ethyl group is oxidized to acid and at meta position, methyl group is also oxidized to carboxylic acid.

Synthesis of product (a)

Conversion of 1-butyl-3-(propan-2-yl)benzene to benzene-1,3-dicarboxylic acid

(b)

Similar to the above reaction, this compound also oxidizes completely to carboxylic acid. Both the substituents in first and third positions will oxidize into carboxylic acid. This indicates that the butyl group in the first position and the secondary alkyl group in third position also oxidize into carboxylic acid. The product formed is given below:

Synthesis of product (b)

Conversion of 1-tert-butyl-4-methyl benzene to 4-tert-butylbenzoic acid

Here, there is a difference as compared to other reactions given above. Only one substituent is oxidized to carboxylic acid. The tertiary alkyl group does not oxidize into acid because of steric hindrance. So the product formed is given below:

Synthesis of product (c)