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Amine alkylation ( amino-dehalogenation) 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 less so industrially, where alcohols are often preferred alkylating agents.
| \ce{->} \underbrace\ce{:\!\!\!\!\overset{\displaystyle R1 \atop |
_{\begin{matrix}
\atop \text{amine}} \\
\ce{(secondary \atop or\ tertiary)}
When the amine is a tertiary amine the reaction product is a quaternary ammonium salt in the Menshutkin reaction:
\underbrace{\underbrace{R3-\overset{\displaystyle R1 \atop |
Amines and ammonia are generally sufficiently nucleophilic to undergo direct alkylation, often under mild conditions. The reactions are complicated by the tendency of the product (a primary amine or a secondary amine) to 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. Organic Chemistry John McMurry 2nd Ed. Therefore, for laboratory purposes, N-alkylation is often limited to the synthesis of tertiary amines. An exception is the amination of alpha-halo carboxylic acids that do permit synthesis of primary amines with ammonia.Organic Syntheses, Coll. Vol. 1, p.48 (1941); Vol. 4, p.3 (1925). Link Intramolecular reactions of haloamines X-(CH2) n-NH2 give cyclic , and .
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,Organic Syntheses, Coll. Vol. 1, p.102 (1941); Vol. 8, p.38 (1928). Link 1-benzylindole,Organic Syntheses, Coll. Vol. 6, p.104 (1988); Vol. 54, p.58 (1974). LinkOrganic Syntheses, Coll. Vol. 6, p.106 (1988); Vol. 54, p.60 (1974). Link and azetidine.Organic Syntheses, Coll. Vol. 6, p.75 (1988); Vol. 53, p.13 (1973). Link Another example is found in the derivatization of cyclen.Org. Synth. 2008, 85, 10-14 Link Industrially, ethylenediamine is produced by alkylation of ammonia with 1,2-dichloroethane.
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