Example 2: 202 parts of 5-nitroimidazole were dissolved in 600 parts of 90% formic acid, followed by the addition of 250 parts of dimethyl sulfate. The reaction mixture was heated and kept for 6 hours. Upon completion of the reaction, the formic acid was removed by vacuum distillation. To the residue was added 420 parts of water and the mixture was cooled to 0°C to 5°C. The unreacted 5-nitroimidazole (60 parts) was separated by centrifugation. The pH of the mixture was adjusted to 10 using a 25% aqueous ammonia solution and the precipitate was precipitated at 0 °C to 5 °C. One hundred and thirty parts of 1-methyl-5-nitroimidazole were finally obtained with a melting point of 58°C to 60°C and a yield of 82% of the theoretical value (based on 4(5)-nitroimidazole).
