Regioselective Air Oxidation of Sulfides to O,S-Acetals in a Bubble Column

In this paper the use of a bubble column for a metal-free, selective oxidation of alpha-alkylthio-imines to O,S-acetals is presented. During the synthesis, which is straightforward to perform, the sulfides are oxidized to alpha-alkoxy- or, respectively, alpha-hydroxysulfide by adding activated carbon in the presence of atmospheric oxygen only. We show that the use of the bubble column, which is unusual on laboratory scale, improves the efficiency of the reaction in comparison to common laboratory techniques. As atmospheric oxygen alone is used for oxidation, this method is cost saving, environmentally friendly, and safe.