Explain the mechanism of the Hofmann rearrangement when benzamide $C_{6} H_{5} CON H_{2}$ is treated with sodium hypochlorite ( $NaOCl$ ) and sodium hydroxide ( $NaOH$ ). Write the balanced overall chemical equation and name the organic product formed.

hard 5 marks Class 12 · Chemistry · Amines

Answer

Overall equation:

C_{6} H_{5} CON H_{2} + NaOCl + 2, NaOH \to C_{6} H_{5} N H_{2} + NaCl + N a_{2} C O_{3} + H_{2} O

. The organic product is aniline (phenylamine).

Step-by-step solution

Step 1: Generation of hypochlorite ion – NaOCl dissociates in water to give $OC l^{-}$ .
Step 2: The amide nitrogen attacks the electrophilic $OC l^{-}$ forming N‑chloro‑amide ( $C_{6} H_{5} C (= O) NClH$ ).
Step 3: In the strongly basic medium, the N‑chloro‑amide loses a proton to give the anionic N‑chloro‑amide ( $C_{6} H_{5} C (= O) NC l^{-}$ ).
Step 4: A second hydroxide ion abstracts a proton from the carbonyl carbon, producing a tetrahedral intermediate that collapses, expelling chloride ion and forming a nitrene‑like intermediate that rearranges to an isocyanate ( $C_{6} H_{5} NCO$ ).
Step 5: The isocyanate is rapidly hydrolyzed by water (present from NaOH) to give aniline and carbonic acid. The carbonic acid reacts with excess NaOH to give sodium carbonate ( $N a_{2} C O_{3}$ ).
Step 6: Combine all stoichiometric coefficients: one mole of benzamide reacts with one mole of NaOCl and two moles of NaOH to give one mole of aniline, one mole of NaCl, one mole of $N a_{2} C O_{3}$ , and one mole of water.
Step 7: Write the balanced overall equation: $C_{6} H_{5} CON H_{2} + NaOCl + 2, NaOH \to C_{6} H_{5} N H_{2} + NaCl + N a_{2} C O_{3} + H_{2} O$ .
Step 8: Identify the organic product – the amine formed is aniline, also called phenylamine.

Common mistake: Confusing the product with a carboxylic acid; the carbonyl carbon is lost as CO₂ (as carbonate), not retained in the product.

Concept tested: Hofmann rearrangement mechanism

Published 7 September 2026 · Last updated 16 September 2026 · How this solution was prepared and checked