Mechano-enzymatic and deep eutectic solvent (DES) mediated sulfoxidation reactions: a comparison study†

The oxidation of sulfide substrates into sulfoxides is a common reaction in organic chemistry, and it has found broad applications in the synthesis of drugs, chemicals and materials. Many sulfoxidation catalytic methods, including photo-, organo- and biocatalytic methods, have been developed to date with the aim to make such transformation more sustainable and in line with the principles of green chemistry. This work describes the development and green assessment of three sulfoxidation methodologies that combine biocatalysis with mechanochemistry and the use of deep eutectic solvents (DESs). A new mechano-enzymatic method where sulfoxides are prepared under mechanochemical conditions with CALB biocatalyst, UHP and AcOEt was first developed, followed by a mechanochemical method requiring only lactic acid (LacOH) and UHP. Finally, a DES-mediated method where sulfoxides are generated by the reaction of UHP with LacOH-based DES media was developed. All three methodologies afforded sulfoxide products selectively with high yields. A comparison of the green metrics revealed that the mechano and the mechano-enzymatic methods show the best green profile in terms of E-factor and RME parameters.