Nitration of dimethylaniline

Nitration of dimethylaniline results in the oxidation of one of the methyl groups to the carboxyl group which is not strongly linked to nitrogen and is readily split off as carbon dioxide. Thus, as the nitration of dimethylaniline proceeds, gases consisting of NO and N02 (from the reduction of nitric acid) and of C02 (from the oxidized N-methyl group) are evolved abundantly. 

Indeed, all the above indicated intermediates with the exception of the hypothetical product (III) have been isolated from the reaction mass. 

The more recent work of Garkson, Holden and Malkin [4] shows, however, that the reaction proceeds somewhat differently. In fact, the dinitroderivative (II) which undergoes demethylation to the substance (IV) is formed first, and then the nitramine (VI) is isomerized (p. 5) to the trinitro derivative (V), before the latter is nitrated to tetryl  

The last step (V) to (1) is reversible if tetryl is dissolved in concentrated sulphuric acid and allowed to stand the N-nitro group is expelled and trinitromethylaniline (V) is formed (cf. p. 5). 

The empirical equation for the preparation of tetryl from dimethylaniline is as follows  

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Tetryl. In the manufacture of Tetryl, it is usual not to nitrate dime thy laniline directly, but to dissolve it first in coned sulfuric acid and then to nitrate the dimethylaniline sulfate so obtained. Direct nitration of dimethylaniline proceeds so violently that it can be carried out only under specialized conditions. Many years experience of Tetryl manufacture has shown that the ratio of sulfuric acid to dimethylaniline should not be lower than 3 1, since a smaller amount of sulfuric acid may be detrimental to the nitration process. However, the ratio of sulfuric acid to dimethylaniline must not be too high, otherwise Tetryl yield is decreased. Temp must be maintained between 20-45° to avoid sulfonation of the benzene ring. Care must be exercised not to leave any unreacted dimethylaniline prior to introduction of nitric acid, because of the potential violence of the dimethyl-aniline-nitric acid reaction. Consequently, continuous methods of prepn are to be preferred as they inherently minimize accumulation of unreacted dimethylaniline... 

It was discovered by Michler and Meyer in 1879 and was made by the nitration of dimethylaniline. One methyl group is oxidised and at the same time the benzene nucleus is nitrated in the 2, 4, 6-positions. The usual method of preparation from dimethylaniline is to dissolve 1 part of dimethylaniline in 14 to 15 parts of sulphuric acid to this solution about 9 parts are added of a mixed acid containing 67% of nitric acid and 16% of... 

Fig. 8. Flow diagram of plant for continuous nitration of dimethylaniline.

Inasmuch as the nitramines are the most important of the nitrated amines, it would be appropriate to say a few words about them. According to Backer(Ref 1) some nitramines were prepd as early as 1869 by GriessTbut they were not identified as such until much later when Zincke repeated some of Griess work. In 1877, Mertens of Holland prepd an explosive by nitration of dimethylaniline but he did not establish its structure. In 1883, van Romburgh, also of Holland, proved that the compd prepd by Mertens was a nitramine. 

The nitration of aniline in the presence of a large amount of strong sulfuric acid results wholly in the formation of m-nitro-aniline, but the similar nitration of dimethylaniline gives principally a mixture of the ortho- and para-derivatives. Mono-methylaniline stands between aniline and dimethylaniline in respect to the orienting effect of its amino group it yields a considerable amount of the m-nitro- compound—and dimethylaniline is preferred for the preparation of tetryl. Commercial dimethylaniline contains a certain amount of monomethylaniline, from which it is extremely difficult to free it, and this in the manufacture of tetryl is converted in part into 2,3,4,6-tetranitro-phenylmethylnitramine, or m-nitrotetryl, pale yellow, almost white, crystals from benzene, m.p. 146-147.087... 

Van Romburgh, Rec. trav. chim., 8, 274 (1889). Van Romburgh and Schepers, Versl. Kon. Akad. Wetenschapen, 22, 293 (1913), also prepared this substance by the nitration of dimethylaniline (in 20 times its weight of concentrated sulfuric acid). 

The two commercial methods of preparing Tetryl via nitration of dimethylaniline, or production of diriitromethylaniline and its subsequent nitration, were described under Nitration" in Vol 8, N71-L to N72-L. Because the first of these reactions involves the oxidation of a methyl group it is highly exothermic and great care must be exercised to control the reaction temp. The second process proceeds with less gas evolution than the first and is less likely to be violent. In the lab, high purity Tetryl can be obtained by nitrating dimethylaniline with nitric acid (not mixed acid) in the presence of inert solvents such as dichloromethane, chloroform or carbon tetrachloride (Ref 18)... 

Similarly the nitration of dimethylaniline yields p- nitroso derivative, which undergoes similar reactions, to form HCN. 

The safety limit of temperature depends on the chemical structure of the compound being nitrated. For exMnple, in the nitration of dinitrotoluene to trinitrotoluene or of phenol to picric acid, temperatures neM 120°C Mid over are considered dangerous. In the nitration of dimethylaniline to tetiyl, a temperature higher than 80°C must be considered dangerous. Esterification with nitric acid should be carried out at a temperature close to room temperature or lower. 

Dimethylaniline is widely used as an intermediate in the manufacture of dyes, rubber accelerators, explosives, and some medical products. Such important dyes as auramine, malachite green, methyl violet, crystal violet, and methylene blue are dmved from dimethylaniline. This compoimd also finds application in the preparation of quaternary alkylating compounds, such as are described under Oodeine. The explosive tetryl, which is tri-nitrophenylmethylnitramine, is manufactured by the nitration of dimethylaniline. 

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