N, N-Dimethylaniline ( DMA) is an organic compound, a substituted derivative of aniline. It is a tertiary amine, featuring a dimethylamino group attached to a phenyl group. This oily liquid is colourless when pure, but commercial samples are often yellow. It is an important precursor to dyes such as crystal violet.
Preparation
DMA was first reported in 1850 by the German chemist A. W. Hofmann, who prepared it by heating aniline and
iodomethane:
[Watts, Henry, A Dictionary of Chemistry and the Allied Branches of Other Sciences, Part 2, (London, England: Longmans, Green, and Co., 1881), Methylanilines, p. 1306][In 1850, August Hofmann announced his synthesis of methylaniline:
However, in 1877, the Swiss chemist Alfred Kern (1850–1893) contended that Hofmann's reaction produced only dimethylaniline, not methylaniline:
Hofmann found that acetic anhydride reacted only with methylaniline, not with dimethylaniline, and was thus able to show that his reaction produced both the mono- and di-methylated forms of aniline:
]
- C6H5NH2 + 2 CH3I → C6H5N(CH3)2 + 2 hydrogen iodide
DMA is produced industrially by
alkylation of
aniline with
methanol in the presence of an acid catalyst:
[Kahl, Thomas et al. (2007) "Aniline" in Ullmann's Encyclopedia of Industrial Chemistry. John Wiley & Sons: New York. ]
- C6H5NH2 + 2 methanol → C6H5N(CH3)2 + 2 H2O
Similarly, it is also prepared using
dimethyl ether as the methylating agent.
Reactions
Dimethylaniline undergoes many of the reactions expected for an aniline, being weakly basic and reactive toward electrophiles.
It is nitration to produce tetryl, a derivative with four nitro compound groups which was once used as explosive. In acidic solution, the initial nitration gives 3-nitrodimethylaniline.[.] It reacts with n-Butyllithium to give the 2-lithio derivative. Electrophilic methylating agents like dimethyl sulfate attack the amine to give the quaternary ammonium salt:
- C6H5N(CH3)2 +(CH3O)2SO2 → C6H5N(CH3)3CH3OSO3
Diethylaniline and dimethylaniline are both used as acid-absorbing bases.
Applications
DMA is a key precursor to commercially important triarylmethane dyes such as
malachite green and
crystal violet.
[Gessner, Thomas and Mayer, Udo (2002) "Triarylmethane and Diarylmethane Dyes" in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim.] DMA serves as a promoter in the curing of polyester and vinyl ester resins.
[ General Info on DMA (N,N-Dimethylaniline), Composites Australia] DMA is also used as a precursor to other organic compounds. A study of the in vitro metabolism of
N,N-dimethylaniline using guinea pig and rabbit preparations and GLC techniques has confirmed
N-demethylation and
N-oxidation as metabolic pathways, and has also established ring hydroxylation as a metabolic route.
