Question

An alkyl bromide \( X (\mathrm{C}_5\mathrm{H}_{11}\mathrm{Br}) \) undergoes hydrolysis in a two-step mechanism. 
\( X \) is converted to a Grignard reagent and then reacted with \( \mathrm{CO}_2 \) in dry ether followed by acidification to give \( Y \).
What is \( Y \)?

• A.
• B.
• C.
• D.

Hint:

Grignard reagents react with $ CO}_2 $ to form carboxylates, which can be converted to carboxylic acids upon acidification.

Answer 1

The Correct Option is B

Step 1: Known Information. 
The starting compound is an alkyl bromide, \( X = \text{C}_5\text{H}_{11}\text{Br} \).
The reaction involves the following steps:
1. Conversion of \( X \) to a Grignard reagent.
2. Reaction of the Grignard reagent with \( \text{CO}_2 \).
3. Acidification to form the final product \( Y \).
Step 2: Conversion to Grignard Reagent.
The alkyl bromide \( \text{C}_5\text{H}_{11}\text{Br} \) reacts with magnesium metal in diethyl ether to form a Grignard reagent: $$ \text{C}_5\text{H}_{11}\text{Br} + \text{Mg} \rightarrow \text{C}_5\text{H}_{11}\text{MgBr} $$ The Grignard reagent is \( \text{C}_5\text{H}_{11}\text{MgBr} \).
Step 3: Reaction with Carbon Dioxide. 
The Grignard reagent \( \text{C}_5\text{H}_{11}\text{MgBr} \) reacts with carbon dioxide (\( \text{CO}_2 \)) in dry ether to form a carboxylic acid derivative: $$ \text{C}_5\text{H}_{11}\text{MgBr} + \text{CO}_2 \rightarrow \text{C}_5\text{H}_{11}\text{COOMgBr} $$ This intermediate is a magnesium salt of a carboxylic acid.
Step 4: Acidification. 
Upon acidification (e.g., with dilute acid), the magnesium salt is converted into the corresponding carboxylic acid: $$ \text{C}_5\text{H}_{11}\text{COOMgBr} + \text{H}^+ \rightarrow \text{C}_5\text{H}_{11}\text{COOH} $$ The final product \( Y \) is a carboxylic acid with the same carbon chain as the original alkyl bromide.
Step 5: Identify the Structure of \( Y \). 
The structure of \( X \) is given as \( \text{C}_5\text{H}_{11}\text{Br} \), which implies that \( X \) is a primary, secondary, or tertiary alkyl bromide.
However, the problem does not specify the exact structure of \( X \). Based on the options provided, we need to identify the correct carboxylic acid structure.
From the options:
1. \( \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{COOH} \)
2. \( \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{COOH} \)
3. \( \text{CH}_3\text{CH}_2\text{CH}(\text{CH}_3)\text{CH}_2\text{COOH} \)
4. \( \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{COOH} \)
The correct structure must match the general formula \( \text{C}_5\text{H}_{11}\text{COOH} \). Among the options, the correct structure is: $$ \boxed{\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{COOH}} $$