Gas-phase reaction of methylamine and dimethylamine with sulfur trioxide was investigated. From a reaction mixture between methylamine and sulfur trioxide, N-methyl-sulfamate (1), N-methylimidodisulfate (2), N, N'-dimethylsulfamide (3) and sulfate (4) were isolated and identified by elemental analysis and by comparison of the infrared spectra with those of authentic samples. Quantitative analysis of reaction products showed that in the amine-excess region (Mr>5) (1) was a major product, while in the intermediate region (3≤Mr≤5) (2) predominated. In the sulfur trioxide-excess region (Mr<3) a colorless crystalline solid was formed which was readily hydrolyzed in humid air or on dissolving in water to form a large amount of sulfate. On the other hand, treatment of the solid with methylamine gave major amounts of (1) and (2), and minor amounts of (3) and (4). This result suggests that a “sulfur trioxide addition compound” would be formed in this region. In the case of dimethylamine, N, N'-dimethylsulfamate (5) was obtained exclusively (96% yield) in the amine-excess region, whereas both in the intermediate region and in the sulfur trioxide-excess region the yield of (5) decreased with decreasing molar ratio (Mr) of dimethylamine to sulfur trioxide and that of sulfate (6) increased. This result could best be explained in terms of the formation of “sulfur trioxide addition compound”. Supporting evidence for this assumption was obtained from infrared spectral data and the observation that the yield of (5) increased markedly when a reaction mixture in these regions was treated with dimethylamine. The expected tetramethylsulfamide (7) was not isolated.
The synthesis of N-substitude leuco auramine (1) by condensation of 4, 4'-bisdimethylamino benzhydrol (2) and aromatic amines (3), and the colored structure of (1) in acetic acid was investigated. (2) and (3) gave (1) in good yield without any catalyst in boiling ethanol. The absorption spectra of (1) in acetic acid was found to be quite similar to that of (2) in acetic acid.