PREPARATION OF DISULFIDES FROM THIOLS USING HYPERVALENT IODINE(III)

Abstract

Disulfides are important compounds for peptide synthesis and use as vulcanizing agents for rubber and elastomers. Traditionally, the preparation of disulfides involves the use of toxic oxidizing agents. In this work, we develop the synthesis of disulfide from thiols using hypervalent iodine (III) which is commercially available, inexpensive and less toxic. We screen type of hypervalent iodine (III), amount of hypervalent iodine (III) and solvents for oxidation of thiols 1a to disulfide 2a under monitoring by HPLC. Under the optimized condition which is the use of (diacetoxyiodo)benzene (DIB) in i-PrOH for 5 minute at room temperature, 13 thiols are convert into the corresponding disulfides 75-95 %yields. Importantly, the reaction can be performed in an open-flask reaction in undried solvent. In addition, we prepare the polystyrene-supported (diacetoxyiodo)benzene (PS-DIB) from iodination of polystyrene by I2/I2O5 followed by oxidation with either Ac2O/H2O2 or NaBO3.4H2O. Structure of prepared PS-DIB is confirmed by FTIR spectroscopy and the loading of the diacetoxyiodo group on polystyrene is determined by traditional iodometric titration giving value of 1.26-2.00 mmol/g. Under the optimized condition, 11 disulfides are successfully prepared in good to high yields (55-100 %). Moreover, PS-DIB can be regenerated by oxidization with NaBO3.4H2O and reused for oxidation of thiol without losing its performance.