The reaction of alkyl hydropersulfides (RSSH, R = CH3 and tBu) with H2S in the gas phase and in aqueous solution

Abstract

The RSSH + H₂S → RSH + HSSH reaction has been suggested by numerous labs to be important in H₂S-mediated biological processes. Seven different mechanisms for this reaction (R = CH₃, as a model) have been studied using the DFT methods (M06-2X and ωB97X-D) with the Dunning aug-cc-pV(T+d)Z basis sets. The reaction of CH₃SSH with gas phase H₂S has a very high energy barrier (>45 kcal mol⁻¹), consistent with the available experimental observations. A series of substitution reactions R¹–S–S–H + ⁻S–R² (R¹ = Me, ^tBu, Ad, R² = H, S–Me, S–^tBu, S–Ad) have been studied. The regioselectivity is largely affected by the steric bulkiness of R¹, but is much less sensitive to R². Thus, when R¹ is Me, all ⁻S–R² favorably attack the internal S atom, leading to R¹–S–S–R². While for R¹ = ^tBu, Ad, all ⁻S–R² significantly prefer to attack the external S atom to form ⁻S–S–R². These results are in good agreement with the experimental observations.