Citric acid oxidation by vanadium(V) in sulfuric acid medium: Kinetic and mechanistic study

Abstract

The citric acid oxidation by vanadium(V) in sulfuric acid medium at 303 K is reported. The reaction rate was determined spectrophotometrically by monitoring the formation of vanadium(IV) at 760 nm. The oxidation showed a first‐order dependence with respect to vanadium(V) concentration and fractional order with respect to citric acid concentrations, with no control and with constant ionic strength. The reaction is also first order with respect to sulfuric acid concentration with no control and of fractional order at constant ionic strength. The reaction rate is enhanced by an increase of ionic strength and increased by a decrease of the dielectric constant. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 566–572, 2000

Speciation in the aqueous H+/H2VO4–/H2O2/citrate system of biomedical interest

“…Considerable problems have been encountered in this system because, at [V] tot /[Cit] tot > 2, slowly decomposing decavanadates are formed and require up to 24 h to equilibrate. On the other hand, spontaneous vanadium reduction occurs to some extent with all ratios investigated, but increases as [V] tot /[Cit] tot and pH decrease, in accordance with kinetic studies in sulfuric acid medium 34 and similarly to the H + /H 2 VO 4 − /lactate system. 27 To approximate the extent of vanadium reduction over time and pH in the 0.150 M Na(Cl) medium, the total vanadium integral of the spectra has been taken for several solutions with [V] tot /[Cit] tot = 4.…”

Estudo do comportamento cinético de oxidação do ácido mandélico por Estudo do comportamento cinético de oxidação do ácido mandélico por vanádio(V) em meio de ácido sulfúrico: efeito da presença de CTAB

“…Devido às analogias entre as catálises micelar e enzimática, os substratos orgânicos têm sido oxidados na presença de surfactantes, para investigar a sua influência na velocidade de reação (DIN; MORSHED; KHAN, 2002;PANDEY;UPADHYAY, 2005). Estudos anteriores realizados por este grupo (ANDO et al, 2003;TAKASHIMA, 2000;TAKASHIMA;RONCONI, 1998;TAKASHIMA, 1995;CLEMENTIN;TAKASHIMA, 1993;TAKASHIMA, 1993) acerca da oxidação de α-hidroxiácidos por vanádio(V) em solução aquosa, têm mostrado que a estrutura e a natureza, tanto do substrato quanto do oxidante, a capacidade de oxidação do substrato, a força iônica da mistura de reação, além de outras condições experimentais, podem influenciar a cinética e o mecanismo de oxidação desses compostos. O vanádio(V) em solução ácida ocorre como íon pervanadila (VO 2 + ) e pode ser mais ou menos reativo dependendo da natureza do meio.…”