Reduction potential of the sulfhydryl radical: Pulse radiolysis and laser flash photolysis studies of the formation and reactions of {sm_bullet}SH and HSSH{sm_bullet}{sup {minus}} in aqueous solutions
- National Inst. of Standards and Technology, Gaithersburg, MD (United States). Physical and Chemical Properties Div.
H{sub 2}S, which is a very toxic gas, has a large number of natural and anthropogenic sources, and the safe removal of this substance has been a matter of ongoing industrial concern. Formation and reactions of the {sm_bullet}SH/{sm_bullet}S{sup {minus}} and HSSH{sm_bullet}{sup {minus}}/HSS{sm_bullet}{sup 2{minus}} radicals in aqueous solutions have been studied by excimer laser flash photolysis and by pulse radiolysis. Acidic H{sub 2}S solutions can be photolyzed with 193 nm laser pulses and produce a transient species with {lambda}{sub max} at 240 nm, ascribed to the {sm_bullet}SH/{sm_bullet}S{sup {minus}} radical. Solutions of SH{sup {minus}} can be photolyzed also with 248 nm laser pulses to produce the {sm_bullet}SH/{sm_bullet}S{sup {minus}} reacts with SH{sup {minus}} ({kappa}{sub f} = 4 {times} 10{sup 9} L/mol s, {kappa}{sub r} = 5 {times} 10{sup 5} s{sup {minus}1}) to form HSSH{sm_bullet}{sup {minus}}/HSS{sm_bullet}{sup 2{minus}}, with {lambda}{sub max} at 380 nm. Both {sm_bullet}SH/{sm_bullet}S{sup {minus}} and HSSH{sm_bullet}{sup {minus}}/HSS{sm_bullet}{sup 2{minus}} react rapidly with O{sub 2}; the former produces SO{sub 2}{sm_bullet}{sup {minus}} ({kappa} = 5 {times} 10{sup 9} L/mol s), and the latter produces O{sub 2}{sm_bullet} ({kappa} = 4 {times} 10{sup 8} L/mol s). Both radicals react with olefinic compounds. The monomeric radical oxidizes Fe(CN){sub 6}{sup 4{minus}}, SO{sub 3}{sup 2{minus}}, ClO{sub 2}{sup {minus}}, 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){sub 8}{sup 3{minus}} and with the 4-methoxyaniline radical cation and found to be 0.69 V vs NHE. From the equilibrium constant K = [HSS{sm_bullet}{sup 2{minus}}]/[SH{sup {minus}}][{sm_bullet}S{sup {minus}}] = 8 {times} 10{sup 3} L/mol, the reduction potential for ({sm_bullet}S{sup {minus}},H{sup +}/SH{sup {minus}}) is calculated to be 0.92 V.
- OSTI ID:
- 682142
- Journal Information:
- Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 27 Vol. 103; ISSN 1089-5639; ISSN JPCAFH
- Country of Publication:
- United States
- Language:
- English
Similar Records
Kinetics of manganese(III) acetate in acetic acid: Generation of Mn(III) with Co(III), Ce(IV), and dibromide radicals; reactions of Mn(III) with Mn(II), Co(II), hydrogen bromide, and alkali bromides
Electron transfer and alkyl transfer with cobaloximes in aqueous solutions. Kinetic studies by pulse radiolysis