N-Monobenzoylation (acetylation, arylsulfonation), N-, C- di- and N-, C-, O- tribenzoylation of 5H(chloro, nitro)-2-methyl(ethyl)benzimidazoles

The interaction of 2-methyl(ethyl)-5H(chloro, nitro)benzimidazoles with benzoyl (acetyl) chloride, and p-toluenesulfonyl chloride in the presence of triethylamine in tetrahydrofuran or chloroform was studied. It was found that the reaction proceeds in three stages with the formation of N-monobenzoyl (acetyl, p-toluenesulfonyl), N-, C-dibenzoyl- and N-, C-, O-tribenzoyl benzimidazoles depending on the ratio of reagents, the nature of the substituent in the aromatic ring, α-methylene group, and acid chlorides. It was revealed that in the case of acetyl, p-toluenesulfonyl chloride reaction is stopped at the first stage with formation of N-monoacetyl (p-toluenesulfonyl) derivatives. The method for HPLC analysis for separation, identification and determination of the ratio of obtained compounds was developed. It was found that 1-acetyl (benzoyl)-2-methylbenzimidazoles were decomposed at the standing. The crystalline form of 1-acetyl-2-methylbenzimidazole is decomposed to the 2-methylbenzimidazole: 25% (7 days), 50% (15 days), 100% (30 days) and decomposition of 1-benzoyl-2-methylbenzimidazole to the 2-methylbenzimidazole (50%) occurs within 2 months.