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

The radical cation of 2-(phenylthio)ethanol (PTE)(.+), generated on reactio n of specific one-electron oxidants Cl-2(.-), Tl2+, SO4.-, CCl3OO., Br-2(.- ), by pulse radiolysis in aqueous solutions of PTE exhibits absorption band s at 315 and 530 nm. Pulse radiolysis of PTE in 1,2-dichloroethane also pro duced a similar transient absorption spectrum. The hydroxyl radicals are ob served to react with a bimolecular rate constant of 7.5 x 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 x 10(4) s(-1), other ban ds showed mixed kinetics. O.- reacts exclusively by H-. atom abstraction fo rming a transient absorption band in 290-330 nm region, H-. reacts both by H-. abstraction and H-adduct formation. Based on these studies, (OH)-O-. ra dicals are inferred to react by electron transfer, H-. abstraction and OH-a dduct formation. The radical cation reacts with electron donors, I-, N-3(-) , with a high rate constant value. In neutral solutions, e(aq)(-) reacts wi th a bimolecular rate constant of 7.1 x 10(8) dm(3) mol(-1) s(-1) and the t ransient absorption band at 360 nm (epsilon = 1.4 x 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 x 10(3) dm(3) mol(-1) cm(-1)). The radical anion form ed on reaction of e(aq)(-) with PTE at pH 12 is able to transfer an electro n to MV2+ whereas at neutral pH, electron transfer is not possible. The red uction potential for the PTE/PTE.- couple is determined to be -1.23 V.