Chapter 16.18, Problem 45P

Interpretation Introduction

Interpretation:

To state the drawbacks of the reaction of alkyl halide and ammonia to prepare primary amines.

Concept introduction:

The synthesis of primary amine can be done by using three different methods.

(1) In first method reaction of primary alkyl halide with ammonia is used as to prepare primary alkyl halide. This reaction is a nucleophilic substitution reaction in which ammonia molecule acts as a nucleophile and alkyl halide as the substrate. The products obtained after the reaction are mixture of primary, secondary and tertiary amines. Therefore, this method is not useful for the preparation of primary amines. The reaction equation is written as,

(2) The synthesis of primary amine is done by using phthalimide and primary alkyl halide in presence of hydroxide base. The important point for this reaction is the phthalimide group has only one hydrogen atom which is attached to nitrogen and can be replaced by alkyl group. Therefore, only one alkyl group can be substitued to the nitrogen atom and so only primary amine will form as the product. The general reaction equation is written as,

(3) The reaction of primary alkyl halide with azide ion forms alkyl azide which after catalytic hydrogenation reaction gives primary amine. This is the best method for the preparation of primary amines as the side product obtained is nitrogen gas which can be seperated from the primary amine easily. The reaction equation is written as,