Efficient Oxidation of Sulfides to Sulfoxides and of Thiols to Disulfides with Aqueous HIO3

Abstract

Oxidations of thiols to disulfides and of sulfides to sulfoxides under mild conditions in organic media are of practical importance for organic synthesis. Taking into account that thiols and sulfides are easily oxidizable and may thus be overoxidized, extensive studies have been carried out to develop methods for controlled oxidation of these compounds [1312]. The known oxidants are not free from disadvantages, including difficult accessibility [4, 8], methods of preparation [2, 8], long reaction time [5, 12], laborious treatment of the reaction mixture [4, 12], and high toxicity [1]. We have found that aqueous HIO3 may be very effective reagent for the transformation of thiols into disulfides, ensuring high yields of the products and requiring no organic solvent (Table 1). Aqueous HIO3 was also found to effectively oxidize sulfides to the corresponding sulfoxides. These reactions are carried out by heating the reactants on a steam bath, and sulfoxides are formed in excellent yields (Table 1). It should be noted that thiols and sulfides having double CIC bonds could not be oxidized with aqueous HIO3 with the same selectivity; therefore, this procedure cannot be recommended for oxidation of unsaturated thiols and sulfides. Table 2 compares the efficiency of the proposed procedure with some published results [7, 8, 11]. The oxidation of sulfides and thiols with aqueous HIO3 is superior to the other methods, for it utilizes cheap and accessible reagents, occurs under mild conditions, and ensures good yields and easy isolation of the products. A mixture of 1 mmol of thiol or sulfide and 0.25 g of aqueous HIO3 (54 wt %) was agitated at room ____________ * The original article was submitted in English. temperature using a magnetic stirrer or heated on a steam bath for a time specified in Table 1. The progress of the reaction was monitored by TLC or GLC. When the reaction was complete, 5 ml of CH2Cl2 and 0.5 g of Na2S2O3 were added, and the mixture was stirred for 15 min and filtered. The filtrate was dried over anhydrous MgSO4 and evaporated, and the residue was purified by column chromatography on silica gel. Reagents from Merck, Fluka, BDH, and Aldrich were used. The products were isolated and purified by chromatographic methods and were identified by comparing their physical properties (melting or boiling points and refractive indices) and IR and