How Unstable are Thiosulfoxides? An ab Initio MO Study of Various Disulfanes RSSR (R = H, Me, Pr, All), Their Branched Isomers R2SS, and the Related Transition States1,2

Ab initio MO calculations at the MP2/6-311G** level of theory show that the thiosulfoxide H2SS is 143 kJ mol-1 less stable than the disulfane HSSH, separated by an activation barrier of 210 kJ mol-1. Using much higher levels of theory, these results are only slighty changed, proving the suitability...

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Bibliographic Details
Published in:Journal of the American Chemical Society 1997-02, Vol.119 (8), p.1990-1996
Main Authors: Steudel, Ralf, Drozdova, Yana, Miaskiewicz, Karol, Hertwig, Roland H, Koch, Wolfram
Format: Article
Language:English
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Summary:Ab initio MO calculations at the MP2/6-311G** level of theory show that the thiosulfoxide H2SS is 143 kJ mol-1 less stable than the disulfane HSSH, separated by an activation barrier of 210 kJ mol-1. Using much higher levels of theory, these results are only slighty changed, proving the suitability of the economical MP2/6-311G** scheme for the present purpose. At the same level Me2SS is 84 kJ mol-1 less stable than MeSSMe, with the transition state lying 340 kJ mol-1 above MeSSMe. Thermal isomerization of HSSH or MeSSMe can therefore be excluded, and H2SS and Me2SS should be kinetically stable toward unimolecular isomerization at low temperatures. Vibrational wavenumbers for H2SS and Me2SS are given. The allyl methyl thiosulfoxide MeAllSS is 83 kJ mol-1 less stable than the disulfane MeSSAll, but isomerization of the latter requires only 110 kJ mol-1. The corresponding RSSR and R2SS structures for R = Pr and All have been calculated at the HF/6-31G* level. The bimolecular decomposition of dimethyl thiosulfoxide to dimethyl sulfide and S2 is exothermic but spin-forbidden in the case of triplet S2, and endothermic but spin-allowed when singlet S2 is formed. The reactions of Me2SS with sulfur molecules S x (x > 2) to give Me2S and S x +1 are exothermic.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja9624026