Structure-reactivity studies on (OH)-O-. radical reaction with substituteddialkyl sulfides

The results of the reaction of an (OH)-O-. radical with a number of functio nalized organic sulfides reported here demonstrate that the pH, the nature of the functional group and the chain length affect the nature of the (OH)- O-. radical reaction with sulfides. The transient absorption spectrum (lamb da(max) = 295 nm), formed on reaction of H-. atoms and (OH)-O-. radicals wi th an aqueous solution of 2-(methylthio)ethanol and 2-(ethylthio)ethanol is assigned to the alpha-thio radical. It decayed by second order kinetics wi th 2k = 5.2 x 10(9) dm(3) mol(-1) s(-1) and was quenched by oxygen. The tra nsient absorption spectra (lambda(max) = 480 and 500 nm respectively), obta ined on reaction with (OH)-O-. radicals (pH = 1), are assigned to a sulfur centered dimer radical cation. The variation of the transient absorbance wi th pH showed an inflection point at pH = 2.1. The reaction of (OH)-O-. radi cals (pH = 6) with 2,2'-thiodiethanoyl chloride showed the formation of alp ha-thio radicals (lambda(max) = 300 nm) and an OH-adduct (lambda = 350-380 nm), whereas in acidic solutions, the transient spectrum (lambda(max) = 340 nm, tau = 0.8 mu s) is assigned to an intra-molecular radical cation with a 4-membered ring configuration. The transient species (lambda(max) = 370 n m, tau = 17 mu s) formed on reaction of (OH)-O-. radicals with a 3,3'-thiod ipropionyl chloride is assigned to a 5-membered intra-molecular radical cat ion and remained independent of pH. The OH-adduct (lambda(max) = 350 nm, pH = 1 1) of 3,3'-thiodipropionamide is observed to undergo transformation to an intra-molecular radical cation (lambda(max) = 370 nm). The transformati on is not observed in acidic solutions and only an intra-molecular radical cation (lambda(max) = 370 nm) is observed immediately after the pulse. The contribution of alpha-thio radicals of 2,2'-thiodiethanamide decreased with pH, and in neutral solutions (OH)-O-. radicals are observed to react mainl y by (OH)-O-.-adduct formation whereas in acidic solutions (pH = 1), as int ra-molecular radical cation (lambda(max),, = 335 nm) with a 4-membered ring configuration is inferred to be the transient species.