title: Reactions of aliphatic thiyl radicals in the solid state: photoisomerization of trans-4,5-dihydroxy-1,2-dithiacyclohexane and oxidation of dithiothreitol.
abstract: A description of free-radical reactions in the solid state is important for some processes causing long-term stability problems of natural and synthetic products. Recent studies revealed that, in the solid state, mercaptooctadecanethiyl radicals, C(18)H(37)S., do not abstract a hydrogen atom from mercaptooctadecane, C(18)H(37)SH, but yield perthiyl radicals, C(18)H(37)SS., via a net sulfur transfer (Faucitano et al. ChemPhysChem 2005, 6, 1100-1107). Here, we demonstrate that such a sulfur transfer is not a general phenomenon of thiyl-radical reactions in the solid state, providing experimental evidence for a solid-state hydrogen-transfer reaction between a dithiyl radical, generated through the photolysis of trans-4,5-dihydroxy-1,2-dithiacyclohexane (DTT(ox)), and dithiothreitol. The photolysis of crystalline solid deposits of DTT(ox) yields two isomers of 2,3-dihydroxy-1-mercaptotetrahydrothiophene with a combined quantum yield of Phi(F) = 0.39 +/- 0.02. This quantum yield was increased to Phi(F) = 0.87 +/- 0.13 when the solid deposits contained an additional dithiol, dl-1,4-dimercapto-2,3-butanediol (DTT), at a ratio of DTT/DTT(ox) = 10:1. This increase in quantum yield depended, in part, on the presence of oxygen but was independent of residual moisture in the solid samples. Mechanistically, the formation of 2,3-dihydroxy-1-mercaptotetrahydrothiophene can be rationalized by the H transfer from DTT to a photochemically formed dithiyl radical from DTT(ox), yielding 2 equiv of monothiyl radicals from DTT, followed by a series of radical transformations.
authors.affiliation: Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Avenue, Lawrence, KS 66047, USA.
authors.forename: Lorena B
authors.initials: LB
authors.lastname: Barrón
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Waterman
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Offerdahl
authors.forename: Eric
authors.initials: E
authors.lastname: Munson
authors.forename: Christian
authors.initials: C
authors.lastname: Schöneich
mesh_terms: D003510:Cyclohexanes / Q000737:chemistry*; D004229:Dithiothreitol / Q000737:chemistry*; D007536:Isomerism; D010084:Oxidation-Reduction; D010777:Photochemistry
chemical_list: C520773:4,5-dihydroxy-1,2-dithiacyclohexane; D003510:Cyclohexanes; D004229:Dithiothreitol