The Hofmann rearrangement is an organic reaction used to convert a primary amide to a primary amine using a halogen, base, water, and heat. The reaction begins with deprotonation of the amide by the base to form an anion which then attacks the halogen to form a N-haloamide. A second deprotonation by the base provides an anion that rearranges to an isocyanate intermediate and releases a halide anion. The isocyanate is then attacked by water which after a series of proton transfer step results in a zwitterionic intermediate, containing an ammonium cation and a carboxylate anion. Thermal conditions result in the explosion of carbon dioxide gas and quenching of the ammonium cation to the amine product.
Hofmann, A. W. Ber. Dtsch. Chem. Ges. 1881, 14, 2725–2736.