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Amine alkylation ( amino-dehalogenation) is a type of between an and or an . 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{H-\!\!\overset{\displaystyle R1 \atop |}{\underset
\ce{->} \underbrace\ce{:\!\!\!\!\overset{\displaystyle R1 \atop
{\underset
_{\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:
\ce{->
\underbrace{\underbrace{R3-\overset{\displaystyle R1 \atop
{\underset{| \atop \displaystyle R2}{N+}}\!\!-R4}__{quaternay\ ammonium\ salt} }

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 .Organic Syntheses, Coll. Vol. 6, p.75 (1988); Vol. 53, p.13 (1973). Link Another example is found in the derivatization of .Org. Synth. 2008, 85, 10-14 Link Industrially, is produced by alkylation of ammonia with 1,2-dichloroethane.


Aniline and related aryl derivatives
Traditionally, aryl amination is difficult reaction which usually requires "activated" aryl halides, such as those with strong electron-withdrawing groups such as nitro groups ortho or para to the halogen atom.Organic Chemistry 4th Ed. Morrison & Boyd. For the arylation of amines with unactivated aryl halides, the Buchwald-Hartwig reaction is useful. In this process, palladium complexes serve as catalysts.J. F. Hartwig, "Organotransition Metal Chemistry: From Bonding to Catalysis" University Science Books, 2010. .


Alkylation using alcohols
Industrially, most alkylations are typically conducted using alcohols, not alkyl halides. Alcohols are less expensive than alkyl halides and their alkylation does not produce salts, the disposal of which can be problematic. Key to the alkylation of alcohols is the use of catalysts that render the hydroxyl group a good leaving group. The largest scale N-alkylation is the production of the methylamines from ammonia and , resulting in approximately 500,000 tons/y of , , and . The reaction is poorly selective, requiring separation of the three products. Many other industrially significant alkyl amines are produced, again on a large scale, from the alcohols. are another class of halide-free N-alkylating agents, useful in the production of .


Alternative alkylation methods
For laboratory use, the N-alkylation reaction is often unselective. A variety of alternative methods have been developed, such as the Delépine reaction, which uses . The Gabriel synthesis, involving the use of an equivalent to NH2, only applies to primary alkyl halides.

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