Kinetics and mechanism of the conversion of a coordinated thiol to a coordinated disulfide by the one-equivalent oxidants neptunium(VI) and cobalt(III) in aqueous perchloric acid
Reaction of excess (2-mercaptoethylamine-N,S)bis(ethylenediamine)cobalt(III), I, with the 1-equiv oxidant Np(VI) (or Co/sup 3 +/(aq)) in aqueous perchloric acid media is shown to lead to (2-aminoethyl-N 2-ammonioethyl disulfide-S/sup 1/) bis(ethylenediamine)cobalt(III), II, according to the stoichiometry 5H/sup +/ + 2I + Np(VI) ..-->.. II + Co/sup 2 +/(aq) + Np(V) + 2enH/sub 2//sup 2 +/. This reaction follows the rate law -d(I)/dt = k'' (I) (oxidant). For Np(VI) as oxidant k'' is independent of (H/sup +/); at 25/sup 0/C, ..mu.. = 1.00 M (LiClO/sub 4/), k'' = k/sub 0/ = 2842 +- 15 M/sup -1/ s/sup -1/, ..delta..H/sub 0/* = 7.57 +- 0.08 kcal/mol, and ..delta..S/sub 0/* = -17.4 +- 0.3 eu. For Co/sup 3 +/(aq) as oxidant, k'' = k/sub 0/ + k/sub -1/(H/sup +/)/sup -1/ where the inverse acid path is taken to reflect oxidation by CoOH/sup 2 +/(aq); at 25/sup 0/C, ..mu.. = 1.00 M (LiClO/sub 4/), k/sub 0/ = 933 +- 32 M/sup -1/ s/sup -1/, k/sub -1/ = 1152 +- 22 s/sup -1/, ..delta..H/sub 0/* = 12.5 +- 0.7 kcal/mol, ..delta..H*/sub -1/ = 18.0 +- 0.4 kcal/mol, ..delta..S/sub 0/*= -3.1 +- 2.4 eu, and ..delta..S*/sub -1/ = 15.8 +- 1.2 eu. It is proposed that the conversion of I to II proceeds by initial 1-equiv oxidation of the coordinated thiol, reaction of the resultant coordinated thiol radical (RS.) with additional I to form a relatively stable radical ion dimer (RSSR./sup -/), and then internal electron transfer within the dimer to yield Co/sup 2 +/(aq) and II which contains a coordinated disulfide. The possible generality of this mechanism and its relevance to biological metal-thiol-disulfide interactions are noted.
- Research Organization:
- Argonne National Lab., IL
- OSTI ID:
- 7355063
- Journal Information:
- Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 15:7; ISSN INOCA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACTINIDE COMPOUNDS
CATIONS
CHARGED PARTICLES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COBALT COMPLEXES
COBALT COMPOUNDS
COMPLEXES
DISULFIDES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
IONS
KINETICS
NEPTUNIUM COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXIDATION
PERCHLORIC ACID
REACTION KINETICS
THIOLS
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
TRANSURANIUM COMPOUNDS