Studies in nickel(IV) chemistry. Part 4. Kinetics of the electron transfer from L-ascorbic acid to tris(dimethylglyoximato)nickelate(IV) in aqueous medium

Acharya, S.; Neogi, G.; Panda, R. K.; Ramaswamy, D.

doi:10.1039/dt9840001471

Cited by 16 publications

(5 citation statements)

References 4 publications

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“…The complex is inert to substitution but is sensitive to acid and protonates with a p K a of 10.8. , One-electron reduction at pH 12.4 yields the trivalent nickel complex, − although this complex differs from that formed via the one-electron oxidation of the divalent complex . There is also a report of a two-electron reduction in 1.5 M NaOH …”

Section: The Ni4+/2+ Or/and Ni4+/3+ Couplesmentioning

confidence: 99%

“…147 Redox reactions involving Ni IV are also subject to divalent metal ion catalysis. 203,204 Oxidations by [Ni IV (dmg) 3 ] 2of the two-electron reductant ascorbate 192 and the one-electron reductant [Fe(CN) 6 ] 4-205 have been investigated. Both reactions have as the rate-determining step the transfer of one electron from the reductant to Ni IV in an outer-sphere process to yield an undetected Ni III transient.…”

Section: The Ni 4+/2+ Or/and Ni 4+/3+ Couplesmentioning

confidence: 99%

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Redox Chemistry of Nickel Complexes in Aqueous Solutions

et al. 2005

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Section: The Ni4+/2+ Or/and Ni4+/3+ Couplesmentioning

confidence: 99%

Section: The Ni 4+/2+ Or/and Ni 4+/3+ Couplesmentioning

confidence: 99%

Redox Chemistry of Nickel Complexes in Aqueous Solutions

et al. 2005

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“…In most cases, the predominant reactive species is the ascorbate ion HA − , which is oxidized by electron transfer followed by deprotonation to give the ascorbyl radical (A •− ), which is then rapidly converted to dehydroascorbic acid (A). Oxidation by complexes of iron(III), − iridium(IV) and molybdenum(V), nickel(IV), , platinum(IV), , cobalt(III), , and ruthenium(III) − has been proposed to occur by outer-sphere electron transfer. Inner-sphere electron transfer has also been proposed for a number of substitution-labile oxidants. − Recently, the oxidation of 5,6-isopropylidene ascorbate by [Fe III (TPP)(Im)(ImH)] (TPP = tetraphenylporphyrin, ImH = 4-methylimidazole) in acetonitrile is shown to occur by a hydrogen atom transfer (HAT) mechanism …”

Section: Introductionmentioning

confidence: 99%

Kinetics and Mechanism of the Oxidation of Ascorbic Acid in Aqueous Solutions by a trans-Dioxoruthenium(VI) Complex

et al. 2008

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The oxidation of ascorbic acid (H(2)A) by a trans-dioxoruthenium(VI) species, trans-[Ru(VI)(tmc)(O)(2)](2+) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), has been studied in aqueous solutions under argon. The reaction occurs in two phases: trans-[Ru(VI)(tmc)(O)(2)](2+) + H(2)A --> trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + A, trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + H(2)A --> trans-[Ru(II)(tmc)(OH(2))(2)](2+) + A. Further reaction involving anation by H(2)A occurs, and the species [Ru(III)(tmc)(A(2-))(MeOH)](+) can be isolated upon aerial oxidation of the solution at the end of phase two. The rate laws for both phases are first-order in both Ru(VI) and H(2)A, with the second-order rate constants k(2) = (2.58 +/- 0.04) x 10(3) M(-1) s(-1) at pH = 1.19 and k(2)' = (1.90 +/- 0.03) M(-1) s(-1) at pH = 1.24, T = 298 K and I = 0.1 M for the first and second phase, respectively. Studies on the effects of acidity on k(2) and k(2)(') suggest that HA(-) is the kinetically active species. Kinetic studies have also been carried out in D(2)O, and the deuterium isotope effects for oxidation of HA(-) by Ru(VI) and Ru(IV) are 5.0 +/- 0.3 and 19.3 +/- 2.9, respectively, consistent with a hydrogen atom transfer (HAT) mechanism for both phases. A linear correlation between log(rate constants) for oxidation by Ru(VI) and the O-H bond dissociation energies of HA(-) and hydroquinones is obtained, which also supports a HAT mechanism.

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“…The majority of studies are reported involving the elucidation of the mechanism of electron transfer between ascorbic acid and one-electron oxidants (1,22). While significant inferences can be drawn from these studies, there remains a paucity of information pertaining to the mechanism in the presence of two-electron oxidants which are reported in few investigations (23)(24)(25)(26)(27) (28) and has a tendency to behave mostly as monomer under pre-equilibrated conditions. Efficient catalytic properties of ferrofluid (29) were reported recently in aqueous solution.…”

Section: Introductionmentioning

confidence: 97%