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

摘要

The radical cation of 2-(phenylthio)ethanol (PTE)~(.+), generated on reaction of specific one-electron oxidants Cl_2~(.-), Tl~(2+), SO_4~(.-), CCl_3OO~., Br_2~(.-), 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 * 10~9 dm~3 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 * 10~4 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 atom 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~-, N_3~-, with a high rate constant value. In neutral solutions, e_(aq)~- reacts with a bimolecular rate constant of 7.1 * 10~8 dm~3 mol~(-1) s~(-1) and the transient absorption band at 360 nm (#epsilon# = 1.4 * 10~3 dm~3 mol~(-1) cm~(-1)) is assigned to H-adduct formed on protonation of radical anion (pK_a = 7.9). In basic solutions, the radical anion has very small absorption at 360 nm (#epsilon# = 0.6 * 10~3 dm~3 mol~(-1) cm~(-1)). The radical anion formed on reaction of e_(eq)~- with PTE at pH 12 is able to transfer an electron to MV~(2+) whereas at neutral pH, electron transfer is not possible. The reduction potential for the PTE/PTE~(.-) couple is determined to be -1.23 V.