Transition Metal Chemistry p. 77 - 85 (2016)
Update date:2022-08-25
Topics:
Shanmugaprabha, Thangamariyappan
Selvakumar, Karuppaiah
Rajasekaran, Kasi
Sami, Ponnusamy
The kinetics of oxidation of 2-mercaptoethanol and 2-mercaptoethylamine by the heteropoly 11-tungsto-1- vanadophosphate anion, [PVVW11O40]4-, have been studied spectrophotometrically in aqueous perchloric acid at 25°C. EPR and optical studies show that [PVVW11O40]4- is reduced to the one-electron reduced heteropoly blue, [PVIVW11O40]5-, whilst the thiols are oxidized to the corresponding disulphides, RSSR. Spectrophotometric titrations show that the stoichiometry of both reactions is 1:1. At constant pH, the reactions show simple second-order kinetics with first-order dependence of rate on both [oxidant] and [thiol]. At constant [thiol], the rate of the reaction increases with increasing pH. Plots of kobs/[thiol]t versus 1/[H+] are linear with finite intercepts, showing that both the undissociated thiol (RSH) and thiolate ion (RS-) are reactive species. Generation of RS· from RSH proceeds via a separated-concerted proton-electron transfer mechanism. The reaction of thiolate ion is a simple outer-sphere electron transfer reaction. By applying the Marcus theory, the self-exchange rate constants for the couples HOCH2CH2S·/HOCH2CH2S- and H3N+CH2CH2S·/H3N+CH2CH2S- were evaluated as 3 × 109 and 2.2 × 108 M-1 s-1, respectively, at 25°C.
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Doi:10.1134/S1070328419080104
(2019)Doi:10.1021/jacs.8b10288
(2018)Doi:10.1039/c9nj04106k
(2020)Doi:10.1002/ejoc.201101807
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(2004)Doi:10.1021/ja01203a050
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