Amine alkylation

Amine alkylation (amino-de-halogenation) is a type of organic reaction between an alkyl halide and ammonia or an amine. The reaction is called nucleophilic aliphatic substitution (of the halide), and the reaction product is a higher substituted amine. The method is widely used in the laboratory, but is less important industrially, where alkyl halides are not preferred alkylating agents.

When the amine is a tertiary amine the reaction product is a quaternary ammonium salt in the Menshutkin reaction:

Amines and ammonia are generally sufficiently basic to undergo direct alkylation, often under mild conditions. The reactions are difficult to control because the reaction product (a primary amine or a secondary amine) are often more nucleophilic than the precursor and will thus preferentially react with the alkylating agent. For example, reaction of 1-bromooctane with ammonia yields almost equal amounts of the primary amine and the secondary amine. Therefore, for laboratory purposes, N-alkylation is often limited to the synthesis of tertiary amines. A notable exception is the reactivity of alpha-halo carboxylic acids that do permit synthesis of primary amines with ammonia.Intramolecular reactions of haloamines X-(CH₂)_n-NH₂ give cyclic aziridines, azetidines and pyrrolidines.

N-alkylation is a general and useful route to quaternary ammonium salts from tertiary amines, because overalkylation is not possible.

Examples of N-alkylation with alkyl halides are the syntheses of benzylaniline, 1-benzylindole, and azetidine. Another example is found in the derivatization of cyclen. Industrially, ethylenediamine is produced by alkylation of ammonia with 1,2-dichloroethane.

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