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Studies in nickel(IV) chemistry. Kinetics of electron transfer from dimethyl sulfoxide to oxohydroxonickel(IV) in aqueous acid medium
Author(s) -
Neogi G.,
Acharya S.,
Panda R. K.,
Ramaswamy D.
Publication year - 1983
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550151002
Subject(s) - chemistry , protonation , reaction rate constant , aqueous solution , intramolecular force , dimethyl sulfoxide , electron transfer , kinetics , nickel , sulfoxide , medicinal chemistry , decomposition , inorganic chemistry , stereochemistry , organic chemistry , ion , physics , quantum mechanics
The kinetics of decomposition of “oxohydroxonickel(IV)” [Ni(IV)] with concomitant intramolecular electron transfer to produce hexaaquanickel(II) and dioxygen in aqueous acid solutions show pseudo‐first‐order dissappearance of the Ni(IV). The pseudo‐first‐order rate constants for the acid decomposition ( k ad ) satisfy\documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm ad}} = k_{\rm d} {\rm K}_{{\rm MH}} [{\rm H}^ +]/(1 + {\rm K}_{{\rm MH}} [{\rm H}^ +])$$\end{document}where K MH and k d refer to the equilibrium protonation constant and the decomposition constant of the protonated species of the Ni(IV) respectively. The values of K MH and k d in aqueous medium at 45°C and μ = 2.0 M are 25.5 ± 1 M −1 and (1.7 ± 0.1) × 10 −5 s −1 , respectively. The kinetics of the intermolecular electron transfer from dimethyl sulfoxide (DMSO) to the Ni(IV), producing Ni(H 2 O) 6 2+ and dimethyl sulfone as products, have been investigated by monitoring the formation of Ni(H 2 O) 6 2+ . The pseudo‐first‐order rate constants for the electron transfer k obs are linearly dependent on [DMSO] 0 or [H + ], attaining limiting values at higher relative [DMSO] 0 or [H + ], in accordance with\documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \frac{{[{\rm DMSO}]_0 }}{{1 + K_{{\rm MH}} [{\rm H}^ +]}}\left({\frac{{k_{1{\rm x}} K_{1{\rm c}} }}{{1 + K_{1{\rm c}} [{\rm DMSO}]_0 }} + \frac{{k_{2{\rm x}} K_{2{\rm c}} }}{{1 + K_{2{\rm c}} [{\rm DMSO}]_0 }}} \right)$$\end{document}where K 1 c and K 2 c represent the formation constants of the precursors involving DMSO and the unprotonated and one‐protonated Ni(IV) species, respectively, and k 1 x and k 2 x are the corresponding decomposition rate constants of the precursors. The values of K 2 c and k 2 x are (2.3 ± 0.1) × 10 4 M −1 and 19 ± 1 s −1 , respectively, at 45°C and μ = 1.0 M . Results are interpreted in terms of probable mechanisms involving (1) a rate‐determining decomposition of the protonated Ni(IV) followed by rapid product formation steps, and (2) precursor complex formation between DMSO and the unprotonated or the protonated species of the Ni(IV) followed by rate‐determining decomposition with electron transfer.