Hofmann mustard oil reaction.

Explanation

### Step-by-Step Solution for Hofmann Mustard Oil Reaction

**Step 1: Understanding the Reactants**
- The Hofmann mustard oil reaction is primarily used to identify primary (1°), secondary (2°), and tertiary (3°) amines. The reaction involves a primary amine reacting with carbon disulfide (CS2) followed by mercuric chloride (HgCl2).

**Step 2: Reaction of Primary Amine with CS2**
- When a primary amine (R-NH2) reacts with carbon disulfide (CS2), the sulfur atom in CS2 acts as a nucleophile. The nitrogen atom of the amine donates a hydrogen atom to the sulfur, resulting in the formation of a thiourea intermediate.

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