Question

In the following sequence of reactions, \[ CH_3Br \xrightarrow{KCN} X \xrightarrow{H_3O^+} Y \xrightarrow{LiAlH_4 / \text{ether}} Z \] The final product \(Z\) is:

• A. acetone
  % option (B) methane
• B. acetaldehyde
• C. ethyl alcohol
• D. methane

Hint:

Nitrile → acid → alcohol is a common reaction chain.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This sequence involves nucleophilic substitution, followed by hydrolysis of a nitrile to a carboxylic acid, and finally the reduction of the acid to an alcohol.
Step 2: Key Formula or Approach:
1. Nucleophilic substitution: \(R-X + CN^{-} \rightarrow R-CN + X^{-}\)
2. Acidic hydrolysis: \(R-CN \xrightarrow{H_{3}O^{+}} R-COOH\)
3. Reduction: \(R-COOH \xrightarrow{LiAlH_{4}} R-CH_{2}OH\)
: Detailed Explanation:
1. Reaction 1: Methyl bromide reacts with \(KCN\) via \(S_{N}2\) mechanism.
\(CH_{3}-Br + KCN \rightarrow CH_{3}-CN (X) + KBr\)
\(X\) is Methyl cyanide (Acetonitrile).
2. Reaction 2: Complete hydrolysis of nitrile gives a carboxylic acid.
\(CH_{3}-CN \xrightarrow{H_{3}O^{+}} CH_{3}-COOH (Y)\)
\(Y\) is Ethanoic acid (Acetic acid).
3. Reaction 3: Lithium aluminium hydride is a strong reducing agent that converts acids to primary alcohols.
\(CH_{3}-COOH \xrightarrow{LiAlH_{4}} CH_{3}-CH_{2}OH (Z)\)
\(Z\) is Ethanol (Ethyl alcohol).
Step 3: Final Answer:
The final product \(Z\) is ethyl alcohol.