Investigations on the nature and redox properties of the transients formed on pulse radiolysis of aqueous solutions of 2-(phenylthio)ethanol

Abstract

The radical cation of 2-(phenylthio)ethanol (PTE)+, generated on reaction of specific one-electron oxidants Cl2-, Tl2+, SO4-, CCl3OO, Br2-, by pulse radiolysis in aqueous solutions of PTE exhibits absorption bands at 315 and 530 nm. Pulse radiolysis of PTE in 1,2-dichloroethane also produced a similar transient absorption spectrum. The hydroxyl radicals are observed to react with a bimolecular rate constant of 7.5×109 d mol-1 s-1 and form absorption bands at 300, 365 and 530 nm. While the 530 nm band decayed by first order kinetics with k=2.1×104 s-1, other bands showed mixed kinetics. O- reacts exclusively by H atom abstraction forming a transient absorption band in 290–330 nm region, H reacts both by H abstraction and H-adduct formation. Based on these studies, OH radicals are inferred to react by electron transfer, H abstraction and OH-adduct formation. The radical cation reacts with electron donors, I-, N3-, with a high rate constant value. In neutral solutions, eaq- reacts with a bimolecular rate constant of 7.1×108 d mol-1 s-1 and the transient absorption band at 360 nm (ε=1.4×103 d mol-1 cm-1) is assigned to H-adduct formed on protonation of radical anion (pKa=7.9). In basic solutions, the radical anion has very small absorption at 360 nm (ε=0.6×103 d mol-1 cm-1). The radical anion formed on reaction of eaq- with PTE at pH 12 is able to transfer an electron to MV2+ whereas at neutral pH, electron transfer is not possible. The reduction potential for the PTE/PTE- couple is determined to be -1.23 V.