An unusual resistance to alpha-bromination by arylacetyl compound: Studieson bromination of 2-acetylbenzimidazoles and their subsequent reactions with sulphur nucleophiles-synthesis of novel beta-kelosulphone derivatives ofbenzimidazoles.

Condensation of o-phenylenediamine with lactic acid under Phillips' conditi ons gave the known 2-(alpha-hydroxyethyl)benzimidazole 1 which on oxidation with acid dichromate furnishes 2-acetylbenzimidazole 2. Reaction of 2 with bromine in acetic acid at room temp. give a novel product 3 but not the ex pected 2-(alpha-bromoacetyl)benzimidazole 4. Rational explanation is offere d for this anamolous behaviour of 2. Compound 2 on alkylation, give I-alkyl derivatives which undergo smooth bromination with bromine in acetic acid t o give the corresponding 1-alkyl-2-(alpha-bromoacetyl)benzimidazoles. React ions of latter with sulphur nucleophiles such as PhS-, ArSO2- etc., resulti ng in substitution of bromine, lending to novel beta-ketosulphone derivativ es of benzimidazoles, are reported. Products have been characterised by IR, NMR (H-1 and C-13) and mass spectral data.