Finally, mixed solvent systems were evaluated to determine if the addition of a Category 1 solvent such as DMF led to an otherwise unreactive mixture can promote the trisulfide metathesis (S56-57). In mixtures of DMF and THF at room temperature, only trace S-S metathesis was observed when the volume of DMF was 25% or less. For higher proportions of DMF, the S-S metathesis reactivity was recovered. In mixtures of DMF and chlorobenzene, trace reaction was observed when only 5% of the solvent volume was DMF. However, at solvent compositions of 10% DMF and 90% chlorobenzene, S-S metathesis was observed in minutes at room temperature. Inhibition of trisulfide metathesis. We next turned our attention to potential inhibitors of the reaction that could, perhaps, provide mechanistic clues (S58-S77). For example, water was found to slow trisulfide metathesis in DMF and Category 1 solvents that otherwise promote rapid S-S exchange. First, the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) radical was added to the reaction as a potential radical scavenger or redox inhibitor. Indeed, S-S metathesis of dimethyl trisulfide and di-n-propyl trisulfide in DMF was inhibited by the addition of as little as 0.05 mol% TEMPO. While it was challenging to determine the fate of TEMPO, it was clear from electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopy that the radical of TEMPO was consumed in the reaction (S65 and S82-S83). Other radical scavengers such as 2,6-ditert-butyl-4-methylphenol (BHT) did not inhibit the reaction, so we tentatively attributed the TEMPO inhibition to a redox reaction, rather than trapping a putative radical intermediate. Next, it was found that 10 mol% 1,4-benzoquinone inhibited S-S metathesis, as did maleic anhydride and succinic anhydride. The trisulfide did not appear to form any detectable adduct with these inhibitors. This result potentially indicates that the inhibition proceeds by reaction of these electrophilic species with a reactive intermediate formed in low concentration. Electron paramagnetic resonance spectroscopy. The inhibition studies tentatively pointed to a reactive intermediate that is non-radical and quenched through a redox reaction with TEMPO or by reaction with electrophiles such as acids and anhydrides. Further evidence against radical intermediates in the metathesis reaction was provided by EPR spectroscopy (S78-S87). No significant signal for thiyl radicals was detected in solutions of dimethyl trisulfide in DMF. Similarly, no significant signal for thiyl radicals was detected in the crossover reaction mixture of dimethyl trisulfide and di-n-propyl trisulfide in DMF. Furthermore, the proradical spin trap 5,5-dimethyl-1pyrroline-N-oxide (DMPO) did not react with dimethyl trisulfide in DMF and no radicals were detected by EPR, providing further evidence against a radical mechanism.