NATURE OF 2-SIGMA/1-SIGMA-STAR 3-ELECTRON-BONDED CHLORINE ADDUCTS TO SULFOXIDES

Reaction of sulfoxide radical cations, R2SO.+, with chloride ions in acidic aqueous solutions (pH less-than-or-equal-to 6) leads to optically absorbing transient R2SO therefore Cl radicals, which are characterized by a sulfur-chlorine three-electron bond containing two bonding sigma-electrons and one antibonding sigma* electron. The same species is formed upon oxidation of sulfoxides by Cl2.-, although only with relatively low rate constants. The measured lambda-max are 390, 400, and 410 nm for the R2SO therefore Cl species with R = Me, Et, and n-Pr, respectively. Equilibrium constants for R2SO.+ + Cl- reversible R2SO therefore Cl have been determined to be 560, 600, and 575 M-1, for the same respective series of species (error limit +/- 20%). It is considered that our three-electron-bonded species is identical with an electronically not further specified chlorine-atom adduct to sulfoxide, R2SO(Cl)., observed earlier in sulfoxide-containing solutions of carbon tetrachloride and dichloromethane. The R2SO therefore Cl exhibit oxidizing properties and are shown to oxidize, for example, organic sulfides and disulfides (rate constants on the order of 10(8) M-1 s-1) or SCN-(rate constants on the order of 10(9) M-1 s-1). The optical and kinetic results are discussed in light of the electronic properties of the radical species.