| Autor: |
Das, T. N., Huie, R. E., Neta, P., Padmaja, S. |
| Zdroj: |
The Journal of Physical Chemistry - Part A; July 8, 1999, Vol. 103 Issue: 27 p5221-5226, 6p |
| Abstrakt: |
Formation and reactions of the ·SH/·S- and HSSH·-/HSS·2- radicals in aqueous solutions have been studied by excimer laser flash photolysis and by pulse radiolysis. Acidic H2S solutions can be photolyzed with 193 nm laser pulses and produce a transient species with λmax at 240 nm, ascribed to the ·SH/·S- radical. Solutions of SH- can be photolyzed also with 248 nm laser pulses to produce the ·SH/·S- radical. The same radical is formed by oxidation of SH- ions with SO4·- and CO3·- radicals. At pH > 5, ·SH/·S- reacts with SH- (kf = 4 × 109 L mol-1 s-1, kr = 5 × 105 s-1) to form HSSH·-/HSS·2-, with λmax at 380 nm. Both ·SH/·S- and HSSH·-/HSS·2- react rapidly with O2; the former produces SO2·- (k = 5 × 109 L mol-1 s-1), and the latter produces O2·- (k = 4 × 108 L mol-1 s-1). Both radicals react with olefinic compounds. The monomeric radical oxidizes Fe(CN)64-, SO32-, ClO2-, and chlorpromazine. The dimeric radical is a weaker oxidant toward ferrocyanide but reduces N-methylpyridinium compounds. The reduction potential for the dimeric radical at pH 7 was determined from one-electron transfer equilibria with Mo(CN)83- and with the 4-methoxyaniline radical cation and found to be 0.69 V vs NHE. From the equilibrium constant K = [HSS·2-]/[SH-][·S-] = 8 × 103 L mol-1, the reduction potential for (·S-,H+/SH-) is calculated to be 0.92 V. |
| Databáze: |
Supplemental Index |
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