Selective and Efficient Detoxification of Sulfur Mustard Gas Analogues with H₂O₂ Using Bioinspired Mo and W Dithiolene Catalysts

Efficient and selective decomposition of chemical warfare agents (CWAs) is required to cope with threats from accidental or intentional releases from stockpiles. One of the most stockpiled CWAs is sulfur mustard (SM) gas. The most effective way to detoxify stockpiled SM is to oxidize the thioether functionality to its benign sulfoxide (SMO) state. However, overoxidation to the corresponding sulfone (SMO2), itself a potent toxin, should be avoided. Thus, catalysts for SM detoxification must be precisely tuned to promote the sluggish oxidation of SM while avoiding overoxidation of SMO to SMO2. In this study, Mo and W dithiolene catalysts, [MO2(dithiolene)2]2– (M = Mo or W), inspired by the active site structures of oxotransferase enzymes such as DMSO reductase were used as catalysts for oxidation of the SM research analogue, 2-chloroethyl ethyl sulfide (CEES), with aqueous H2O2 as an oxidant. Under optimized conditions, [WO2(mnt)2]2– and [MoO2(bdt)2]2– (mnt = maleonitriledithiolate, bdt = 1,2-benzenedithiolate) were found to promote selective CEES oxidation to sulfoxide CEESO without overoxidation to sulfone CEESO2 in as little as 5–15 min with catalyst loadings as low as 0.015 mol %. The W (pre)catalyst was also found to be reusable without measurable loss of activity. Experimental and computational studies indicate the involvement of η2-peroxo species, [M(O)(η2-O2)(dithiolene)2]2–, as the active oxidants formed in situ. Overall, the bioinspired catalysts in this study are shown to be promising candidates for developing convenient, inexpensive, efficient, and selective mustard gas detoxification technologies.