Nitration of 4-nitroimidazole in acetic anhydride/glacial acetic acid gives 1,4-dinitroimidazole. The crystal and molecular structure of this compound have been determined by direct methods. Crystals are orthorhombic; P212121, a 5.853(3), b 9.591(8), c 10.392(5) � , V 583.4(7) � 3 , Dm 1 .76 g cm-1, Dc, 1 .80 g cm-1 (Z = 4); λ 0.71069 � ; T 173 K. The structure was refined to R = 0.048 for 926 reflections [I > 2 σ(1)]. Both 2-methyl-4-nitro- and 5-methyl-4-nitro-imidazoles N-nitrate under the same conditions. When heated in solution at 100-140�C 1,4-dinitro- and 2-methyl-1,4-dinitro-imidazoles rearrange to give C-nitro isomers and some denitration products, but 5(4)-methyl-1,4(5)-dinitroimidazole failed to give identifiable products.
Titration of bases and their salts with perchloric acid in acetic anhydride, glacial acetic acid and their mixture.