Carbylamine reaction template

Base turns chloroform into dichlorocarbene; aniline adds to it, two molecules of HCl are lost and phenyl isocyanide forms. Only primary amines (two N–H) can do this.

Mechanism step by step

A primary amine, CHCl₃ and alcoholic KOH give a foul-smelling isocyanide

1. Deprotonation – Hydroxide removes the C–H proton of chloroform
2. Dichlorocarbene – CCl₃⁻ loses Cl⁻ (α-elimination)
3. Amine adds – The N lone pair fills the empty orbital of the carbene
4. Proton shift – H moves from N⁺ to C⁻
5. First HCl lost – Base removes N–H; C=N forms as Cl⁻ leaves
6. Second HCl lost – Base removes C–H, Cl⁻ leaves and the N lone pair makes the third bond

Key points

• Overall: RNH₂ + CHCl₃ + 3 KOH → RNC + 3 KCl + 3 H₂O.
• A test for primary amines (aliphatic or aromatic): the isocyanide has a very unpleasant smell.
• Secondary and tertiary amines lack the two N–H needed and give no isocyanide.
• Also called Hofmann’s isocyanide test. The same :CCl₂ appears in the Reimer–Tiemann reaction.

Drawn with 126 atoms, 20 arrows, 11 shapes – every one editable in MolDraw.

Sources

• Furniss et al., Vogel's Textbook of Practical Organic Chemistry, 5th ed., Longman 1989 Textbook
• Smith, March's Advanced Organic Chemistry, 8th ed., Wiley 2020 Textbook