Disulfides represent significant molecular and structural features in various biologically active compounds and fine chemicals. Therefore, the development of mild, efficient and sustainable methods to access disulfides is of great importance. Here, we describe the development of a mild metal‐free photocatalytic aerobic oxidation of thiols to disulfides using Eosin Y and visible‐light irradiation. A continuous flow procedure was developed to accelerate the photocatalytic process, enabling the preparation of disulfides with high purity in a timeframe of minutes. The mildness and applicability of our method was exemplified by the flow synthesis of the cyclic peptide hormone, oxytocin, requiring only a 200 s reaction time and an efficient one‐pot batch protocol for the preparation of the therapeutic thiuram disulfide, disulfiram.magnified image

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The photocatalytic aerobic oxidation of thiols to disulfides was investigated in a photomicroreactor. The base in this protocol allows to activate the photocatalyst and to facilitate a proton‐coupled electron transfer. On this basis, a mechanism was postulated for the photocatalytic aerobic oxidation. The photon/energy efficiency of the photomicroreactor is described. By varying the power supply, the effect of the photon flux on the yield of the photocatalytic process could be demonstrated. The effective photoelectric transformation efficiency was rather low, which indicated that sufficient cooling is required to dissipate non‐productive energy. Under optimal reaction conditions, the photonic efficiency substantially increased compared to batch reactors and other photomicroreactors. This could be attributed to the similar dimensions of the capillary photomicroreactor and the light‐emitting diode light source, which minimizes energy losses due to unfocused light irradiation.

Metal-Free Photocatalytic Aerobic Oxidation of Thiols to Disulfides in Batch and Continuous-Flow. -The batch conditions are also applied to prepare anti--alcoholism agent disulfiram (VII) (Antabuse) in a one-pot process. -(TALLA, A.; DRIESSEN, B.; STRAATHOF, N. J. W.; MILROY, L.-G.; BRUNSVELD, L.; HESSEL, V.; NOEL*, T.; Adv. Synth. Catal. 357 (2015) 10, 2180-2186, http://dx.doi.org/10.1002/adsc.201401010 ; Dep. Chem. Eng., Eindhoven Univ. Technol., NL-5612 AZ Eindhoven, Neth.; Eng.) -M. Tismer 47-093

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