PREPARATION OF 1-METHYL-2,4,5-TRINITROIMIDAZOLE FROM DERIVATIVES OF 1-METHYLIMIDAZOLE AND ITS OXIDATION UNDER NITRATION CONDITIONS

Abstract

In this work, the nitration reactions of 1-methylimidazole and its nitro derivatives with a mixture of 98% HNO3 and 15% SO3 in H2SO4 were reinvestigated. 1-Methylimidazole, 1-methyl-4-nitroimidazole, 1-methyl-5-nitroimidazole, or 1-methyl-4,5-dinitroimidazole gave a mixture of 1-methyl-4,5-dinitroimidazole and 1-methyl-2,4,5-trinitroimidazole under the volume ratio of HNO3 to H2SO4 of 1:3 at 80°C temperature for 2.5 h, and the highest unisolated yield of 1-methyl-2,4,5-trinitroimidazole was 2.4%. 1-Methyl-2,4,5-trinitroimidazole was prepared from 1-methyl-2-nitroimidazole, 1-methyl-2,4-dinitroimidazole, or 1-methyl-2,5-dinitroimidazole under the same conditions, and the yields were 65, 76, and 82%, respectively. However, when the ratio of HNO3 to H2SO4 was 1:5 and reaction was carried out at 120°C for 2.5 h, only 1-methyl-4,5-dinitroimidazole was obtained from 1-methylimidazole, 1-methyl-4-nitroimidazole, or 1-methyl-5-nitroimidazole in yields 43, 64, and 81%, respectively. 1-Methyl-2-nitroimidazole, 1-methyl-2,4-dinitroimidazole, or 1-methyl-2,5-dinitroimidazole gave 1-methylimidazolidine-2,4,5-trione under the same conditions, the yields were 61, 63, and 65%, respectively.
Meanwhile, 1-methylimidazolidine-2,4,5-trione was obtained from 1-methyl-2,4,5-trinitroimidazole. Under strong nitration conditions, the nitro group at the C-2 position is a key substituent to promote oxidation of the imidazole ring. The possible reaction mechanism for the formation of 1-methylimidazolidine-2,4,5-trione from 1-methyl-2,4,5-trinitroimidazole is given. The products 1-methyl-2,4,5-trinitroimidazole and 1-methylimidazolidine-2,4,5-trione were characterized by IR spectroscopy, melting point, 1H and 13C NMR spectroscopy, and elemental analysis. The structure of 1-methylimidazolidine-2,4,5-trione was further confirmed by single crystal X-ray diffraction.