Question

Explain the following reactions :
(a) Carbylamine reaction
(b) Sandmeyer reaction

Answer 1

(a) Carbylamine reaction:

Aliphatic/aromatic primary amines are heated with chloroform/alcoholic KOH to form foul-smelling alkyl isocyanides or carbylamines. This test is not given by secondary/tertiary amines.

$R-N{H}_2+CHC{l}_3+3KOH\stackrel{\Delta }{\to }R-NC+3KCl+3H_{2}O$
For example, ethylamine gives ethyl isocyanide.
$C_2{H}_5-N{H}_2+CHC{l}_3+3KOH\stackrel{\Delta }{\to }{C}_2{H}_5-NC+3KCl+3H_{2}O$

(b) Sandmeyer reaction:
It converts aryl diazonium salts to aryl halides. An aromatic amino group is substituted with a nucleophile (such as halide anions, cyanide, thiols, water, and others) via diazonium salt intermediate. The reaction is catalyzed by cuprous compounds.
$Ph{N}_2^{+}C{l}^{-}\underset{-N_2}{\overset{CuCl}{\to }}Ph-Cl$