Studies on synthesis of 2-acetylbenzimidazole and related benzimidazole derivatives

Condensation of o-phenylenediamine (1) with propanoic acid under Phillips' conditions gives 2-ethylbenzimidazole (2). Attempts to oxidise 2 to 2-acety lbenzimidazole (3) using H2O2, SeO2, KMnO4/acetone were unsuccessful, Conde nsation of 2 with benzaldehyde yields 2-(alpha-methylstyryl)benzimidazole ( 4) which on oxidation with KMnO4 gives benzimidazole-2-carboxylic acid (5) as the sole product. Reaction of 1 with pyruvic acid results in 3-methylben zo-1H-dihydropyrazine-2-one (7) rather than 3 as the major product, Treatme nt of 1 with formic acid gives the known compound benzimidazole (9) which w ith acetic anhydride in the presence of NaOAc does not yield 3. Reaction of 1 with lactic acid under Phillips' conditions gives 2-(alpha-hydroxyethyl) benzimidazole (10) which on oxidation with acid dichromate, however, yields 3. Studies on syntheses and spectral properties of related benzimidazoles are reported.