Kinetics and mechanisms of the oxidation of ascorbic acid and benzene diols by nickel(III)tetraazamacrocycles in aqueous perchloric acid

1983 ◽  
Vol 61 (6) ◽  
pp. 1120-1125 ◽  
Author(s):  
A. McAuley ◽  
T. Oswald ◽  
R. I. Haines
Keyword(s):  
Ascorbic Acid ◽  
Perchloric Acid ◽  
Rate Constants ◽  
Cross Correlation ◽  
Outer Sphere ◽  
Transfer Reactions ◽  
Aqueous Perchloric Acid ◽  
Kinetics Of Reaction ◽  
Kinetics Of ◽  
Sphere Mechanism

The kinetics of reaction of ascorbic acid, hydroquinone, and catechol (H2A) with nickel(III) macrocycles (NiL3+) (L = cyclam, meso-(5,12)-7,7,14,14-Me6-14-ane-1,4,8,11-N4 (tet-a), and rac-(5,14)-7,7,12,12-Me6-14-ane-1,4,8,11-N4 (tet-c):[Formula: see text]have been investigated in aqueous perchloric acid solutions using the stopped-flow technique. The data are consistent with a rate-determining one-electron transfer reactions:[Formula: see text]followed by a rapid oxidation of the radical formed. In the reaction with ascorbic acid, for Ni(cyclam)3+, k1 = 250 M−1 s−1 (25 °C), k4Ka = 680 s−1; Ni(tet-c)3+, k1 = 2.52 × 103 M−1 s−1, k4Ka = 1.06 × 104 s−1; and Ni(tet-a)3+, k1 = 2.85 × 103 M−1 s−1 (21.95 °C), k4Ka = 1.26 × 104 s−1. With catechol, k1 = 6.98 × 102 M−1 s−1, 1.73 × 104 M−1 s−1, and 3.3 × 104 M−1 s−1 respectively in reactions with Ni(cyclam)3+, Ni(tet-c)3+, and Ni(tet-a)3+. With hydroquinone, k1 = 1.09 × 104 M−1s−1 (Ni(cyclam)3+) and 2.49 × 105 M−1 s−1 (20.9 °C) (Ni(tet-c)3+). The reactions are considered to take place via an outer-sphere mechanism and rate constants are discussed in terms of the Marcus cross correlation. Use has been made of predicted rate constants to identify reaction pathways in the hydrogen-ion dependent systems.

Electrode kinetics of Eu3+/Eu2+ reaction by cyclic voltammetry

1982 ◽  
Vol 47 (7) ◽  
pp. 1773-1779 ◽  
Author(s):  
T. P. Radhakrishnan ◽  
A. K. Sundaram
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Outer Sphere ◽  
Electrode Reaction ◽  
Transfer Reactions ◽  
Cyclic Voltammetric ◽  
Edta Solution ◽  
Kinetics Of ◽  
Activated Complex ◽  
Good Agreement

The paper is a detailed study of the cyclic voltammetric behaviour of Eu3+ at HMDE in molar solutions of KCl, KBr, KI, KSCN and in 0.1M-EDTA solution with an indigenously built equipment. The computed values of the rate constants at various scan rates show good agreement with those reported by other electrochemical methods. In addition, the results indicate participation of a bridged activated complex in the electron-transfer step, the rate constants showing the trend SCN- > I- > Br- > Cl- usually observed for bridging order of these anions in homogeneous electron-transfer reactions. The results for Eu-EDTA system, however, indicate involvement of an outer sphere activated complex in the electrode reaction.

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

1985 ◽  
Vol 63 (6) ◽  
pp. 1198-1203 ◽  
Author(s):  
A. McAuley ◽  
Lee Spencer ◽  
P. R. West
Keyword(s):  
Electron Transfer ◽  
Ascorbic Acid ◽  
Exchange Rate ◽  
Rate Constants ◽  
Outer Sphere ◽  
Kinetics And Mechanism ◽  
Hydrogen Ion ◽  
Transfer Reactions ◽  
Radical Ions ◽  
Electron Transfer Reactions

The reactions of the outer-sphere electron transfer reagent, Ni(9-aneN3)23+, (bis(1,4,7-triazacyclononane)nickel(III) ion) with ascorbic acid, hydroquinone, catechol, and resorcinol have been investigated. The absence of any proton related equilibria with the oxidant provides a means of ascribing the observed inverse hydrogen ion dependences to reactions of the dissociated ascorbate or quinolate ions, (HA−). The data are consistent with the rate-determining one-electron transfer reactions:[Formula: see text]followed by rapid oxidation of the radical ions formed. In the reaction with ascorbic acid, k1 ~ 0 and k2 (T = 25° C) = 5.2 × 106 M−1 s−1 (ΔH≠ = 10.1 ± 2.5 kcal mol−1, ΔS≠ = 5.7 ± 5.1 cal mol−1 K−1). For hydroquinone, catechol, and resorcinol, k1 = 2.9 × 103, 2.8 × 102, and ~0 M−1 s−1and k2 = 6.9 × 109, 4.1 × 109, and 2.8 × 108 M−1 s−1, respectively. These data have been combined with those from other similar reactions leading, by use of a Marcus correlation, to self-exchange rate constants for the HAsc−/HAsc• couple of 3.5 × 105 M−1 s−1 and for the H2Quin0/+ and H2cat0/+ systems of 5 × 107 and 2 × 107 M−1 s−1, respectively. The importance of the effect of bond-reorganisation on electron transfer is discussed.

Cinétique d'oxydation de la cyclohexanedione-1,2 par l'ion thallique

1969 ◽  
Vol 47 (19) ◽  
pp. 3539-3544 ◽  
Author(s):  
R. Favier ◽  
M. Zador
Keyword(s):  
Perchloric Acid ◽  
Rate Constants ◽  
Activation Parameters ◽  
Chloride Ions ◽  
Acid Solutions ◽  
Rate Expression ◽  
Aqueous Perchloric Acid ◽  
Kinetics Of

The kinetics of thallic ion oxidation of 1,2-cyclohexanedione in aqueous perchloric acid solutions lead to the rate expression[Formula: see text]The importance of traces of chloride ions has been shown. Rate constants and activation parameters has been determined and are discussed.

Kinetics of the oxidation of iron(II) by cerium(IV) in aqueous perchloric acid

1965 ◽  
Vol 61 ◽  
pp. 689 ◽  
Author(s):  
M. G. Adamson ◽  
F. S. Dainton ◽  
P. Glentworth
Keyword(s):  
Perchloric Acid ◽  
Aqueous Perchloric Acid ◽  
Kinetics Of
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