Organocatalytic sulfoxidation in micellar systems containing amphiphilic flavinium salts using hydrogen peroxide as a terminal oxidant

Amphiphilic flavinium salt [10-dodecyl-5-ethyl-3,7,8-trimethylisoalloxazinium perchlorate (1b)], solubilized in micelles of sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium chloride (CTAC), hexadecyltrimethylammonium nitrate (CTANO3) or Brij 35, catalyzes the chemoselective oxidation of thioanisole (2) to its corresponding sulfoxide 4. The sulfoxidation rates observed in micelles in the presence of 1b exceeded, in most instances, those of the reactions catalyzed by its hydrophilic homologue [5-ethyl-3,7,8,10-tetramethylisoalloxazinium perchlorate (1a)] in homogeneous solutions. Reaction rates were strongly dependent on the type of micellar matrix and on the pH value. The highest acceleration rate was found in SDS micelles at pH 4.4 (TOF = 3 × 103 h−1). In our experiments, micelles favoured the catalytic process rather than the non-catalyzed reaction, this effect being especially pronounced in cationic micelles, for which the non-catalyzed reaction was markedly suppressed. The ratio vcat/v0vcat/v0 of the catalyzed and non-catalyzed reaction rates was almost 40 in CTANO3, while in homogeneous solution its value did not exceed 7.

Amphiphilic flavinium salt 1b solubilized in various types of micelles catalyzes the chemoselective oxidation of thioanisole (2) to sulfoxide 4. Reaction rates strongly depended on the type of micellar matrix and on the pH value. In our experiments, micelles favoured the catalytic process rather than the non-catalyzed reaction. This effect was especially pronounced in cationic micelles, for which the non-catalyzed reaction was markedly suppressed.Figure optionsDownload as PowerPoint slide