Catalytic effect of alloxazinium and isoalloxazinium salts on oxidation of sulfides with hydrogen peroxide in micellar media
Three novel amphiphilic alloxazinium salts were prepared: 3-dodecyl-5-ethyl-7,8,10-trimethylisoalloxazinium perchlorate ( 1c ), 1-dodecyl-5-ethyl-3-methylalloxazinium perchlorate ( 2b ), and 3-dodecyl-5-ethyl-1-methylalloxazinium perchlorate ( 2c ). Their catalytic activity in thioanisole ( 3 ) oxidation with hydrogen peroxide was investigated in micelles of sodium dodecylsulfate (SDS), hexadecyltrimethylammonium nitrate (CTANO 3 ) and Brij 35. Reaction rates were strongly dependent on the catalyst structure, on the type of micelles, and on pH value. Alloxazinium salts 2 were more effective catalysts than isoalloxazinium salts 1 . Due to the contribution of micellar catalysis, the v cat / v 0 ratio of the catalyzed and non-catalyzed reaction rates was almost 80 with salt 2b solubilized in CTANO 3 micelles. Nevertheless, the highest acceleration was observed with non-amphiphilic 5-ethyl-1,3-dimethylalloxazinium perchlorate ( 2a ) in CTANO 3 micelles ( v cat / v 0 = 134). In this case, salt 2a presumably acts as a phase-transfer catalyst bringing hydrogen peroxide from the aqueous phase into the micelle interior. Synthetic applicability of the investigated catalytic systems was verified on semi-preparative scale.