Question

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

Answer 1

The given two reactions are two most important name reactions. We know that the carbylamine reaction is a reaction of amines. It is also known as Hofmann isocyanide synthesis. Sandmeyer reaction is a reaction of diazonium salts.

Complete step by step answer:
Let us look the reaction one by one:
We already know that carbylamine reaction is the reaction of amines. The essential reactants for these reactions are potassium hydroxide as a base, chloroform and an amine. In the first step, the chloroform is dehydrohalogenation using the potassium hydroxide base and forms an intermediate called dichlorocarbene. This intermediate is highly reactive. The electrophilic dichlorocarbene will attack the nucleophilic nitrogen of the primary amine. Then the elimination of hydrochloric acid takes place which leads to the formation of isonitrile. This carbylamine reaction can be used for the test for the presence of primary amine.
$\begin{aligned} & \text{KOH + CHC}{{\text{l}}_{3}}\text{ }\to \text{ :CHC}{{\text{l}}_{2}} \\\ & \text{R}-\text{N}{{\text{H}}_{2}}\text{ + :CHC}{{\text{l}}_{2}}\text{ }\to \text{ RNC + 3}{{\text{H}}_{2}}\text{O + 3KCl} \\\ \end{aligned}$

The Sandmeyer reaction is used for the synthesis of aryl halides from aryl diazonium salts. This is a type of substitution reaction. Catalysts used for this reaction are copper salts like chloride, bromide, or iodide. This reaction can be used for the transformations including hydroxylation, trifluoromethylation, halogenation in benzenes.
$PhN_{2}^{+}C{{l}^{-}}\xrightarrow[-{{N}_{2}}]{CuCl}\text{ }Ph-Cl+HCl$

Note: You may have a doubt that how the carbylamine reaction can be used for the test since it has no specific colouration or precipitation. The reason is the final product formed is an isocyanide. The isocyanides formed have a foul smell, so we can use this carbylamine reaction for the test of presence of a primary amine.