Kinetics and mechanism of the oxidation of benzenediols and ascorbic acid by <i>bis</i>(1,4,7-triazacyciononane)nickel(III) in aqueous perchlorate media

McAuley, Alexander; Spencer, Liam; West, Paul R.

doi:10.1139/v85-204

Cited by 32 publications

(15 citation statements)

References 23 publications

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“…Possibility of outer-sphere electron transfer from H 2 Q to the diiron center is not an alternative mechanism as it leads to an exceedingly low value for the estimated one-electron self-exchange rate (k 11 =10 )18 dm 3 mol )1 s )1 ) for the {Fe 2 O} 4+ /{Fe 2 O} 3+ couple using Marcus equation k 12 =(k 11 k 22 K 12 ) 1/2 [30], where k 12 values are taken from Table 2, k 22 = self-exchange rate for the H 2 Q/H 2 Q + couple = 10 7 dm 3 mol )1 s )1 [31], K 12 =10 16 for reaction (10b).…”

Section: Reaction Pathmentioning

confidence: 99%

Mechanistic Studies on the Oxidation of Hydroquinone by an Oxo-bridged Diiron(III,III) Complex in Weakly Acidic Aqueous Media

Bhattacharyya

Mukhopadhyay

2006

Transition Met Chem

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The kinetics of oxidation of hydroquinone (H 2 Q) by a l-oxo-bridged diiron(III,III) complex, ½Fe 2 ðl-OÞ-ðphenÞ 4 ðH 2 OÞ 2 4þ (1) has been investigated in aqueous media at 25.0°C in presence of an excess of 1,10-phenanthroline (phen). The overall redox rate increases with increase in [H + ]. The title complex (1) and its conjugate bases, [Fe 2 ðl-OÞðphenÞ 4 ðH 2 OÞ(OH) 3þ (2) and [Fe 2 ðl-OÞðphenÞ 4 ðOHÞ 2 2þ (3), participate in the reaction with H 2 Q as the only kinetically reactive reducing species. Rate constants (in dm 3 mol )1 s )1 ) for the parallel reactions ð1Þ þ H 2 Q À! Products; ð2Þ þ H 2 Q À! Products and that for ð3Þ þ H 2 Q À! Products are, respectively, 500±40, 100±6 and 30±2. Substantial rate retardation in D 2 O media in comparison to that in H 2 O media suggests that electron transfer is coupled with proton movements in the rate-determining step.

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Section: Reaction Pathmentioning

confidence: 99%

Mechanistic Studies on the Oxidation of Hydroquinone by an Oxo-bridged Diiron(III,III) Complex in Weakly Acidic Aqueous Media

Bhattacharyya

Mukhopadhyay

2006

Transition Met Chem

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“…Previous kinetic reports [11,33,34] revealed that the rate increases due to either the dissociation of quinols or the presence of monohydroxy complex of Ni(III) species in the pH range 1.5-3.5. It has been reported that the [Ni III L 1 ] complex does not show dehydrogenation of macrocyclic ligand in basic solution [38].…”

Section: Hydroquinonementioning

confidence: 98%

“…Quinols have also been studied as reductants for IrCl 6 2- [25][26][27][28], V(V) [29], Np(VI) [30] and Mo(CN) 8 3- [31]. An extensive work has been carried out with substitution inert Ni(III) and Ni(IV) macrocyclic complexes as an oxidant [11,[32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Kinetics of oxidation of benzenediols by (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(III) in aqueous acidic media

Anuradha

Vijayaraghavan

2010

Reac Kinet Mech Cat

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The kinetics of the oxidation of hydroquinone (H 2 Q), catechol (H 2 cat) and substituted catechols with nickel(III) macrocycle [NiL 1 ] 3? (L 1 = 1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) has been studied spectrophotometrically in aqueous perchloric acid in the presence of sulfate. Over the pH range 1-2.6, and at higher sulfate concentration 0.05 \ [SO 42-] \ 0.2 mol dm -3 , the decomposition of [Ni III L 1 ] in the oxidation of benzenediols via [Ni III-L 1 (OH)(H 2 O)] is small. With hydroquinone, the rate constant is almost independent of the hydrogen ion concentration and with catechols, the involvement of catechol anion (Hcat -) has been considered. The rate constants for cross reactions are discussed in terms of the Marcus relationship.

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“…Oxidation of hydroquinone and catechol can proceed through ET-PT, PT-ET, s-CPET or HAT mechanisms, depending on the nature of oxidant, solvent, pH of the reaction medium, etc. Extensive kinetic studies on the oxidation of hydroquinone and catechol by a variety of transition metal complexes have been reported [8][9][10][11][12][13][14][15][16][17][18][19], including [Fe 2 (bby) 2 [17] proceeds through an ET-PT mechanism. With macrocyclic Ni(III) complexes, an s-CPET mechanism in which water acts as H ?…”

Section: Introductionmentioning

confidence: 99%

Proton-coupled electron transfer reactions: kinetic studies on the oxidation of dihydroxybenzenes by heteropoly 10-tungstodivanadophosphate in aqueous acidic medium

Shanmugaprabha¹,

Selvakumar²,

Vairalakshmi³

et al. 2015

Transition Met Chem

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Kinetic studies on the oxidation of hydroquinone and catechol by the heteropoly 10-tungstodivanadophosphate anion, [PV V V V W 10 O 40 ] 5-, have been carried out in aqueous acidic medium at 25°C by UV-visible spectrophotometry. The oxidation of hydroquinone shows simple second-order kinetics overall, with first-order dependence of the rate on both [oxidant] and [hydroquinone] at constant [H ? ]. For catechol oxidation, the order of the reaction with respect to [oxidant] is unity, while the order with respect to [catechol] is variable; this reaction shows Michaelis-Menten-type kinetics at constant [H ? ]. The rate of the reaction is insensitive to [H ?] in the pH range 1.2-1.7. Rate retardation for deuterated hydroquinone and catechol (C 6 H 4 (OD) 2 ) in D 2 O indicates breaking of the -OH bond in the rate-limiting step. Based on the observed kinetic isotope effect and calculated ground-state free energy change (DG 0 ) values, a hydrogen atom transfer mechanism is suggested for the reaction; i.e., in the ratelimiting step, one electron and one proton are transferred from the reductant to the oxidant in a concerted manner. Rates of oxidation of hydroquinone by this oxidant in neat acetonitrile at 25°C have also been measured. By applying the Marcus equation, the self-exchange rate constant of the oxidant (V V V IV OH/H Á ) in acetonitrile has been evaluated.

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Kinetics and mechanism of the oxidation of benzenediols and ascorbic acid by bis(1,4,7-triazacyciononane)nickel(III) in aqueous perchlorate media

Cited by 32 publications

References 23 publications

Mechanistic Studies on the Oxidation of Hydroquinone by an Oxo-bridged Diiron(III,III) Complex in Weakly Acidic Aqueous Media

Mechanistic Studies on the Oxidation of Hydroquinone by an Oxo-bridged Diiron(III,III) Complex in Weakly Acidic Aqueous Media

Kinetics of oxidation of benzenediols by (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(III) in aqueous acidic media

Proton-coupled electron transfer reactions: kinetic studies on the oxidation of dihydroxybenzenes by heteropoly 10-tungstodivanadophosphate in aqueous acidic medium

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