Question

Explain the following reaction:
(a) Sandmeyer reaction
(b) Wurtz's Fitting reaction

Answer 1

• (a) Sandmeyer reaction $\to$
  

It is used to synthesize aryl halides from aryl diazonium salts. It is an example of a radical-nucleophilic aromatic substitution.

When a primary aromatic amine, dissolved or suspended in cold aqueous mineral acid, is treated with sodium nitrite, a diazonium salt is formed. Mixing the solution of freshly prepared diazonium salt with cuprous chloride or cuprous bromide results in the replacement of the diazonium group by $-Cl$ or $-Br$.

$C_6{H}_5-N{H}_2\underset{273-278K}{\overset{NaN{O}_2+HX}{\to }}{C_6{H}_5-N_2}^{+}{X}^{-}\{\begin{array}{cc}\stackrel{CuCl}{}& C_6{H}_5-Cl\\ \stackrel{CuBr}{}& C_6{H}_5-Br\\ \stackrel{CuCN}{\to }& C_6{H}_5-CN\end{array}$

• b) Wurtz's Fittig reaction $\to$
  

A mixture of an alkyl halide and aryl halide gives an alkylarene when treated with sodium in dry ether and is called Wurtz-Fittig reaction.

$C_6{H}_5-X+Na+R-X\stackrel{Ether}{\to }{C}_6{H}_5-R+NaX$