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Titolo:
Micellar effect on the reaction of chromium(VI) oxidation of D-fructose inthe presence and absence of picolinic acid in aqueous media: a kinetic study
Autore:
Das, AK; Roy, A; Saha, B; Mohanty, RK; Das, M;
Indirizzi:
Visva Bharati Univ, Dept Chem, Santiniketan 731235, W Bengal, India Visva Bharati Univ Santiniketan W Bengal India 731235 35, W Bengal, India
Titolo Testata:
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
fascicolo: 6, volume: 14, anno: 2001,
pagine: 333 - 342
SICI:
0894-3230(200106)14:6<333:MEOTRO>2.0.ZU;2-8
Fonte:
ISI
Lingua:
ENG
Soggetto:
D-MANNOSE; PERCHLORIC-ACID; CHROMIC-ACID; CATALYZED OXIDATION; ELECTRON-TRANSFER; L-RHAMNOSE; D-GLUCOSE; MECHANISM; SURFACTANTS; MONOSACCHARIDES;
Keywords:
kinetics; oxidation; catalysis; D-fructose; chromium(VI); picolinic acid; surfactants;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
56
Recensione:
Indirizzi per estratti:
Indirizzo: Das, AK Visva Bharati Univ, Dept Chem, Santiniketan 731235, W Bengal, India Visva Bharati Univ Santiniketan W Bengal India 731235 ngal, India
Citazione:
A.K. Das et al., "Micellar effect on the reaction of chromium(VI) oxidation of D-fructose inthe presence and absence of picolinic acid in aqueous media: a kinetic study", J PHYS ORG, 14(6), 2001, pp. 333-342

Abstract

The kinetics and mechanism of the Cr(VI) oxidation of D-fructose in the presence and absence of picolinic acid (PA) in aqueous acid media were studied under the conditions [D-fructose]T much greater than [Cr(VI)](T) at different temperatures. Under the kinetic conditions, the monomeric species of Cr(VI) was found to be kinetically active in the absence of PA whereas in the PA-catalysed path, the Cr(VI)-PA complex was considered to be the active oxidant. In this path, the Cr(VI)-PA complex undergoes a nucleophilic attack by the substrate to form a ternary complex which subsequently experiencesa redox decomposition through glycol splitting leading to the lactone of C-4-aldonic acid along with formaldehyde and the Cr(TV)-PA complex. The primary product formaldehyde undergoes further oxidation tin part) to form formic acid. Then the Cr(IV)-PA complex participates further in the oxidation of D-fructose and ultimately is converted into the inert Cr(III)-PA complex. In the uncatalysed path, the Cr(VI)-substrate ester experiences an acid-catalysed redox decomposition (2e transfer) in the rate-determining step giving rise to the products. The uncatalysed path shows a second-order dependence on [H+] whereas the PA catalysed path shows a fractional order in [H+]. Both paths show a first-order dependence on [D-fructose]T and [Cr(VI)](T). The PA-catalysed path is first order in [PA](T). All these patterns remain unaltered in the presence of externally added surfactants. The effects of acationic surfactant, N-cetylpyridinium chloride (CPC), and an anionic surfactant, sodium dodecyl sulfate (SDS), on both the uncatalysed and PA-catalysed paths were studied. CPC inhibits both the uncatalysed and PA-catalysed paths whereas SDS catalyses the reactions. The observed micellar effects are explained by considering a distribution pattern of the reactants between the micellar and aqueous phases. The applicability of different kinetic models, e.g. the pseudo-phase ion-exchange model, the Menger-Portnoy model andthe Piszkiewicz cooperative model, was tested to explain the observed micellar effects. The effect of [surfactant](T) on the activation parameters was explored to rationalize the micellar effect. Copyright (C) 2001 John Wiley & Sons, Ltd.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 13/12/17 alle ore 23:36:02