The secondary amide
1 reacts via its enolized form with phosphorus pentachloride to form the
oxonium ion 2. This produces a chloride ion which deprotonates the oxonium ion to form and
imine 3 and hydrogen chloride. These then react with one another to form an amine, with loss of the phosphorus chloride residue. The β-chloroimine
4 is unstable and undergoes internal elimination to a form a
nitrilium cation
5 which is cleaved by attack by chloride to form a nitrile
6a and a haloalkane
6b. ==See also==