Pathways of nitrosobenzene reduction by thiols in alcoholic media

The biologically important reaction of nitrosobenzenes with thiols has been investigated in 2-propanol solution at room temperature, experimental cond itions which allow for the detection and characterization of key intermedia tes. Final stable products of such complex reactions include azoxybenzenes and anilines, formed in relative proportions and at a rate which depend on the reagents initial molar ratio. A detailed description of the reaction of 4-chloronitrosobenzene with benzenethiol in a-propanol was achieved by mea ns of H-1 NMR in situ analysis. The reaction is initiated by rapid and quan titative coupling of the two reagents into a covalent adduct, an N-hydroxys ulfenamide (N(OH)S), which decays to N-(4-chlorophenyl)hydroxylamine. This second intermediate is then converted via competing paths to 4,4'-dichloroa zoxybenzene and to N-(4-chlorophenyl)benzenesulfenamide (4-ClC6H4NHSPh), wh ich in turn decays to 4-chloroaniline. Interestingly, sulfinamides (ArNHS(O )R), major products of the reaction in aqueous media, do not form in 2-prop anol.