Pulse radiolysis investigations on electron-transfer reactions in aqueous solutions of substituted alkyl sulfides

Abstract

The transient optical absorption band (A,,, = 345 nm, t+ = 4.0 ps, E = 2.6 x lo3 dm3 mo1-I ern-') formed on pulse radiolysis of N,O-saturated dilute neutral aqueous solutions of dimethyl 3,3'thiodipropionate (DTDP) is assigned to an 'OH-adduct. The rate constant for the reaction of 'OH radicals has been determined to be 1.4 x IO'O dm3 mol-' s-'. At higher solute concentrations the 'OH-adduct is converted to sulfur-centred dimer radical cations (A,,, = 510 nm, E = 4.9 x lo3 dm3 mol-I cm-', t+ = 14.0 ps). In acidic solutions, only dimer radical cations are formed. In neutral aqueous solutions of 3,3'-thiodipropanol (TDP) *OH radicals are able to bring about one-electron oxidation, forming intramolecular radical cations with p-orbital overlap between the oxidized sulfur and oxygen (Amax = 420 nm, t+ = 17 ps, E = 2.6 x lo3 dm3 mol-' cm-I). in acidic solutions, sulfur-centred dimer radical cations are formed (Amax = 51 0 nm, t+ = 12 ps, E = 6.3 x 1 O3 dm3 mol-' cm-'). In the presence of halide ions, the oxidized sulfur in DTDP and TDP stabilizes by formation of an >S.'.X type species. * 10%. Results and Discussion HydroxylRadical Reactions with DTDP.-Fig. l(a) shows the transient optical absorption spectrum obtained on pulse radiolysis of an N,O-saturated aqueous solution of DTDP (2.3 x lop4 mol dmP3, pH = 6.0, dose = 1.4 x 1017 eV cmP3 per pulse). It exhibits an absorption band with A, , , Paper 1/02825A

Spectral, Kinetic, and Redox Studies on the Transients Formed on Reaction of Hydroxyl Radicals with Thioanisole

“…Reaction of • OH Radicals in Acidic Solutions. It is known that OH-adducts of a number of organic compounds can undergo acid-catalyzed dehydration to form the solute radical cation. ,, But the nature of the transient spectrum and the formation and decay kinetics remained independent of pH in the range 1−11, suggesting that acid-catalyzed dehydration of OH-adducts is not taking place in this pH range. Depending upon the electron-donating/withdrawing power of the substituents, acid-catalyzed dehydration of OH-adducts is observed at different acid concentrations.…”

“…Depending upon the electron-donating/withdrawing power of the substituents, acid-catalyzed dehydration of OH-adducts is observed at different acid concentrations. In organic compounds containing highly electron withdrawing groups, it may take place in the presence of high acid concentration . In highly acidic solutions, HClO 4 ≥ 1 mol dm -3 , the yield of • H atoms would increase due to the reaction of e aq - with H + (e aq - + H + → • H + H 2 O).…”

“…Aerated aqueous solutions of KSCN was used for determining the dose delivered per pulse using G ε 500 = 21 520 dm 3 mol -1 cm -1 per 100 eV for the transient (SCN) 2 •- species and the dose per pulse was close to 15 Gy per pulse . All other experimental details are described elsewhere . The reaction of • OH radicals was carried out in N 2 O-saturated solutions where e aq - is quantitatively converted to • OH radicals (N 2 O + e aq - → N 2 + • OH + OH - ).…”

“…One-electron oxidation of alkyl sulfides (R 2 S) by • OH radicals and specific one- electron oxidants leads to the formation of the sulfur-centered radical cation (R 2 S •+ ). − The oxidized sulfur has a high tendency to coordinate with another sulfur or other heteroatoms (O, N, halogen) and form dimer radical cations absorbing in the 450−550 nm region. − The formation of the sulfur-centered dimer radical cation takes place via a complex reaction mechanism involving the OH-adduct and α-thio radical which absorb in the region 350−370 and 280−300 nm, respectively. , The reaction of • OH radicals with alkyl sulfides and substituted derivatives has been a subject of recent interest. − It has been shown that both the nature and the relative position of the substituent group with respect to sulfur play an important role in the formation of transient intermediate species. Such studies have also gained importance due to the formation of the sulfur-centered radical species as the possible intermediates in the biological systems with sulfur-containing compounds .…”

Rate constants of dichloride radical anion reactions with molecules of environmental interest in aqueous solution: a review

“…Sulfur radical cations show high tendency to be stabilized through three-electron bonded S ∴ X (X=O, S, N, Cl, Br, I) species. The k Cl2•- values of organic sulfide (R 1 R 2 S) reactions are in the 10 8– 10 9 M -1 s -1 range (Bonifacic and Asmus 1980 ; Mohan 1990 ; Mohan and Moorthy 1990a ; Mohan and Mittal 1991 , 1992 ; Maity et al 1994b ). In the experiments, Cl-adduct, R 1 R 2 S ∴ Cl, intermediates were observed.…”