PERSULFOXIDE AND THIADIOXIRANE INTERMEDIATES IN THE REACTION OF SULFIDES AND SINGLET OXYGEN

Structure and reactivity of intermediates in the reaction of sulfides and singlet oxygen have been studied in aprotic solvents. It is shown that sulfoxides and sulfones are the major products at the initial stage of reaction. While the sulfoxide formation is more sensitive to the electronic effect of substituents, the steric retardation is more significant for sulfone formation. The effect of additives also revealed the sharp contrast between the two reactions; sulfoxide formation is accelerated significantly by protic or coordinating solvents, but sulfone formation is never affected by additives. O-18-tracer experiments indicated that the two oxygen atoms in sulfones come from one oxygen molecule. The apparent activation energy for sulfone formation is positive in contrast to the sulfoxide case. These facts suggest that thiadioxirane intermediates are surely formed via a nonpolar reaction in competition with persulfoxide formation. It is also shown that persulfoxides are stabilized by coordinating solvents as well as by protic ones. The stability of thiadioxiranes is discussed on the basis of theoretical calculations.