Physical Organic Polarography

Zuman, P.

doi:10.1002/9780470171844.ch2

Cited by 17 publications

(5 citation statements)

References 14 publications

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“…The relatively slow conformational change required for 7a to cyclize may not be competitive with additional fast electron transfers from the radical cation intermediate, giving rise to polymers and other products and being responsible for the consumption of excessive charge. The difference in oxidation potential of ∼110 mV corre- sponds to lowering the activation barrier for formation of the radical cation by ∼2.2 kcal/mol . Similar effects have been observed both in small molecules and in DNA …”

supporting

confidence: 74%

Thegem-Dialkyl Effect in Electron Transfer Reactions: Rapid Synthesis of Seven-Membered Rings through an Electrochemical Annulation

Sperry

Wright

2005

J. Am. Chem. Soc.

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supporting

confidence: 74%

Thegem-Dialkyl Effect in Electron Transfer Reactions: Rapid Synthesis of Seven-Membered Rings through an Electrochemical Annulation

Sperry

Wright

2005

J. Am. Chem. Soc.

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“…parameters (data not shown). These small changes in the E p values of a given analyte are commonly observed in electrochemical studies …”

Section: Methodsmentioning

confidence: 67%

“…These small changes in the E p values of a given analyte are commonly observed in electrochemical studies. [39,52,53] ArN 2 + ions are known to react with OH À ions to give diazotates, [54] and the formation of these products may lead to significant changes in both the peak potential and peak currents of the voltammetric peaks of 16-ArN 2 + ions. For this reason, we investigated the effects of acidity on the voltammetric peaks obtained in emulsions.…”

Section: Determining K Obs Values In Octane/c 12 E 6 /Acidic Water Emmentioning

confidence: 99%

Effects of acidity and emulsifier concentration on the distribution of vitamin C in a model food emulsion

Pastoriza-Gallego

Losada‐Barreiro

2012

J of Physical Organic Chem

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We have analyzed the effects of acidity and emulsifier concentration on the distribution of ascorbic acid or vitamin C (VC) in a model emulsion prepared by mixing octane, acidic (HCl) water and the non‐ionic surfactant hexaethyleneglycol monododecyl ether (C12E6). VC is oil insoluble, and only the partition constant between the interfacial and aqueous regions (PWI) is needed to describe its distribution within the emulsion. The PWI values are calculated from the kinetic analyses of the variation of the observed rate constant (kobs) determined electrochemically for the reaction between the hydrophobic 4‐hexadecylbenzenediazonium (16‐ArN2+) ions and VC with the emulsifier concentration. The determined PWI values (PWI = 4–25) are low in comparison with those obtained for more hydrophobic antioxidants like vitamin E, and pH dependent, decreasing upon decreasing the acidity of the medium. These low values are reflected in the distribution of VC so that a large fraction (70%) is located in the aqueous region at low emulsifier concentrations. At a given pH, the %VC in the aqueous region decreases upon increasing the emulsifier concentration; meanwhile, at a given emulsifier concentration %VC increases upon lowering the acidity. The intrinsic rate constants in the interfacial region kI for the reaction between 16‐ArN2+ and VC have also been determined at different acidities. Their variation with the pH follows an upward bend curve, suggesting an inverse dependence of kI with the acidity of the medium, in keeping with the proposed mechanism for the reaction. The results may be of some interest to the food and pharmaceutical industries because of the extensive use of VC as antioxidant or preservative and because of the health benefits of VC. Copyright © 2012 John Wiley & Sons, Ltd.

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“…These small changes in the E p values of a given analyte are commonly observed in electrochemical studies. [40,55,56] The reactions of 16-ArN þ 2 with VC in emulsions were carried out as follows. Once the freshly prepared emulsion was thermostated and degassed in the electrochemical cell, an aliquot (50-100 ml) of a recently prepared aqueous acid VC solution was incorporated into the emulsion and the mixture was degassed again for another 3 min.…”

Section: Methodsmentioning

confidence: 99%

Kinetics and mechanism of the reaction between 4‐hexadecylbenzenediazonium ions and vitamin C in emulsions: further evidence of the formation of diazo ether intermediates in the course of the reaction

Pastoriza-Gallego¹,

Fernández-Alonso²,

Losada‐Barreiro³

et al. 2008

J of Physical Organic Chem

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The kinetics and mechanism of the reaction between hydrophobic 4-hexadecylarenediazonium ions, 16-ArN R 2 and vitamin C, VC, in a model emulsion prepared by mixing octane, acidic (HCl) water and the non-ionic surfactant hexaethyleneglycol monododecyl ether, C 12 E 6 , were investigated. Because emulsions are opaque, linear sweep voltammetry, LSV, was employed to monitor the reaction. Voltammograms of 16-ArN R 2 in emulsions show two reduction peaks as in aqueous systems. The half-life for the spontaneous decomposition of 16-ArN R 2 in the emulsion was estimated as t 1/2 ¼ 14.5 h at T ¼ 25 -C. Upon addition of VC to the system, the first reduction peak of 16-ArN R 2 disappears almost immediately and a new reduction peak is detected at E p ¼ S0.25 V. Electrochemical titration of 16-ArN R 2 shows that the new peak corresponds to the formation of a 1:1 adduct. The i P (E p ¼ S0.25 V) values can be linearly correlated with [16-ArN R 2 ] and the observed rate constants, k obs , were determined by fitting the (i p , t) data to the integrated first order equation. The variation of k obs with [VC] follows a saturation kinetics profile, consistent with the formation of an intermediate in a pre-equilibrium step. All the evidence is consistent with a reaction mechanism comprising two competitive pathways, the spontaneous D N R A N mechanism and the unimolecular decomposition of a transient diazo ether (DE) formed in a pre-equilibrium step. The data allowed estimations of the interfacial rate constant for the reaction between 16-ArN R 2 and VC S but did not allow the determination of the equilibrium constant for the DE formation.

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Physical Organic Polarography

Cited by 17 publications

References 14 publications

Thegem-Dialkyl Effect in Electron Transfer Reactions: Rapid Synthesis of Seven-Membered Rings through an Electrochemical Annulation

Thegem-Dialkyl Effect in Electron Transfer Reactions: Rapid Synthesis of Seven-Membered Rings through an Electrochemical Annulation

Effects of acidity and emulsifier concentration on the distribution of vitamin C in a model food emulsion

Kinetics and mechanism of the reaction between 4‐hexadecylbenzenediazonium ions and vitamin C in emulsions: further evidence of the formation of diazo ether intermediates in the course of the reaction

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