AQA A Level chemistry - A2 Unit 4: Section 3.4.7 Amines

3.4.7 Amines - Nucleophilic properties

Specification

Students should:

understand that the nucleophilic substitution reactions (including mechanism) of ammonia and amines with haloalkanes form primary, secondary, tertiary amines and quaternary ammonium salts; know that the latter can be used as cationic surfactants

Nucleophilic substitution of haloalkanes using ammonia

Ammonia reacts with haloalkanes by nucleophilic substitution to form amines.

nucleophilic substitution of a haloalkane by ammonia

The reaction can proceed further as the product also reacts with ammonia making secondary and then tertiary amines.

Even tertiary amines can react with haloalkanes forming quaternary salts:

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Cationic surfactants

Surfactants are compounds that lower the surface tension of a liquid, or that between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants.

A cationic surfactant is a structure with a positive charge. For a quaternary ammonium salt to act as a cationic surfactant, one of the alkyl groups is typically much larger than the other three. For example, cetrimonium bromide, (hexadecyltrimethylammonium bromide, CTAB, ((C₁₆H₃₃)N(CH₃)₃Br).

Cetrimonium ion

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