Question

Formic acid reacts with \(PCl_5\) to form

• A. methyl chloride
• B. acetyl chloride
• C. formyl chloride
• D. carbon monoxide and hydrogen chloride

Hint:

Formic acid is also unique in that it can act as a reducing agent and can be oxidized by mild oxidizing agents like Tollen's reagent.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Formic acid (HCOOH) is unique because it has a hydrogen atom directly attached to the carboxyl group.
Step 2: Detailed Explanation:
When \(PCl_5\) reacts with carboxylic acids, it generally replaces the -OH group with -Cl to form an acyl chloride (\(RCOCl\)). However, formic acid, being the simplest carboxylic acid, behaves differently. The initial product, formyl chloride (HCOCl), is unstable and decomposes immediately at room temperature to carbon monoxide (CO) and hydrogen chloride (HCl). The overall reaction is: \[ HCOOH + PCl_5 \rightarrow CO + 2HCl + POCl_3 \]
Step 3: Final Answer:
Formic acid reacts with \(PCl_5\) to give CO and HCl, option (D).