Question

In the following sequence of reaction,

Answer 1

Benzene

Answer 2

The sequence of reactions involves the reaction of 1,4-dibromocyclohex-2-ene with dimethylamine, followed by Hofmann elimination.

1. 1,4-dibromocyclohex-2-ene reacts with dimethylamine ($\text{CH}_3\text{-NH-CH}_3$) via nucleophilic substitution of one bromine atom to form (1-(dimethylamino)cyclohex-2-en-4-yl)bromide (A).
2. Heating (A) with $\text{KOH}$ causes intramolecular elimination of $\text{HBr}$ to form 1-(dimethylamino)cyclohexa-2,4-diene (B).
3. Reaction of the tertiary amine (B) with methyl iodide ($\text{CH}_3\text{I}$) leads to the formation of the quaternary ammonium iodide (1-(trimethylammonium)cyclohexa-2,4-diene) iodide (C).
4. Heating the quaternary ammonium hydroxide (formed from (C) and $\text{KOH}$) causes Hofmann elimination, leading to the formation of benzene (D) and trimethylamine ($\text{N(CH}_3\text{)}_3$). The elimination occurs by removing a proton from C6, forming a double bond between C1 and C6, which results in the formation of the stable aromatic ring of benzene.