Question

When ethanol is treated with benzene diazonium chloride it forms:
A. Arenes
B. Methane
C. Amines
D. Ethyl alcohol

Answer 1

Hint: A type of organic reaction in which an external nucleophile replaces or substitutes a nucleophile present in the compound is known as a nucleophilic substitution reaction. In the reaction, the group which leaves the compound after substitution is known as the leaving group and the compound on which reaction takes place is known as substrate.

Complete answer:
In organic chemistry, arenes are the aromatic hydrocarbons which are cyclic unsaturated compounds which consist of strikingly different chemical properties as compared to conjugated alkenes or polyenes and thus categorized as a separate class of hydrocarbons. The arenes and substituted arenes are highly stabilized by resonance. The simplest member of arene is benzene whose molecular formula is $C_6H_6$ and is structurally represented as follows:

Preparation of benzene from benzene diazonium chloride:
When benzene diazonium chloride reacts with ethanol it forms benzene and acetaldehyde along with the removal of nitrogen gas and hydrogen chloride. It is a single step nucleophilic substitution reaction which proceeds as follows:

The mechanism for the reaction involves a single step which is as follows:
Benzene diazonium chloride is not a very stable compound, so when it is treated with an alcohol the hydrogen atom present on the carbon adjacent to alcohol group attacks and formation of stable arene takes place along with the formation of respective aldehyde. The reaction mechanism for reaction of ethanol with benzene diazonium chloride is shown as follows:

Hence, on reaction of ethanol with benzene diazonium chloride, an arene is formed.
And hence option A is the correct answer.

Note:
It is important to note that benzene can alternatively be formed from benzene diazonium chloride by reacting it with hypophosphorous acid in the presence of water. In the reaction, benzene and phosphorus acid along with the removal of nitrogen gas and hydrogen chloride. It is also a single step reaction which proceeds as follows: