Question

Complete the following reaction :

• A.

  

• B.

  

• C.
• D.
• E.

Hint:

When \(\text{H}_{2}\text{SO}_{4}\) and heat are mentioned together for a cyanohydrin, expect both the \(\text{CN} \rightarrow \text{COOH}\) conversion and \(\text{OH}\) removal to form a double bond.
Check the oxidation state: Nitriles always hydrolyze to acids, not aldehydes.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The reaction sequence starts from Cyclohexanone [A].

Step 1: Reaction with HCN.

Step 2: Reaction with concentrated \(\text{H}_{2}\text{SO}_{4}\) and heat.

Step 2: Detailed Explanation:
Reaction 1: Cyclohexanone (\([A]\)) reacts with \(\text{HCN}\) to form cyclohexanone cyanohydrin (\([B]\)).
The \(\text{CN}^{-}\) nucleophile attacks the carbonyl carbon, and \(\text{H}^{+}\) adds to the oxygen.
Structure of [B]: 1-hydroxycyclohexanecarbonitrile (a cyclohexane ring with an \(\text{OH}\) and a \(\text{CN}\) group on the same carbon).
Reaction 2: Treatment with concentrated \(\text{H}_{2}\text{SO}_{4}\) and heat causes two things:
1. Hydrolysis: The nitrile group (\(-\text{CN}\)) is hydrolyzed to a carboxylic acid group (\(-\text{COOH}\)).
2. Dehydration: The tertiary \(\text{OH}\) group is eliminated along with a neighboring hydrogen atom to form a double bond (\(\text{C}=\text{C}\)).
Because of the presence of heat and strong acid, dehydration is favorable, leading to an \(\alpha,\beta\)-unsaturated acid.
The final product [C] is Cyclohex-1-ene-1-carboxylic acid.

Step 3: Final Answer:
The final product [C] is cyclohex-1-ene-1-carboxylic acid, represented by option (A).