Oxidation of D-glucose in the presence of 2,2'-bipyridine by CrVI in aqueous micellar media: a kinetic study.
The kinetics of Cr(VI) oxidation of D-glucose to the corresponding lactone in the presence and absence of 2,2'-bipyridine (bipy) has been carried out under the conditions, [D-glucose](T) >> [Cr(VI)](T) at different temperatures in aqueous micellar media. The monomeric Cr(VI) species has been found to be kinetically active in the absence of bipy whereas in the bipy-catalysed path, the Cr(VI)-bipy complex has been found to be the active oxidant. In the bipy-catalysed path, the Cr(VI)-bipy complex undergoes nucleophilic attack by the substrate to form a ternary complex. The ternary complex spontaneously experiences a redox decomposition (through two-electron transfer) in the rate-determining step leading to the product lactone and Cr(IV)-bipy complex. The Cr(IV)-bipy complex then takes part in faster steps in the further oxidation of D-glucose and is ultimately converted into a Cr(III)-bipy complex. In the uncatalysed path, the Cr(VI)-substrate ester experiences acid catalysed redox decomposition (two-electron transfer) in the rate-determining step. The uncatalysed path shows a second order dependence on [H(+)] and a first order dependence on each of the reactants [D-glucose](T) and [Cr(VI)](T). In contrast, the bipy-catalysed path shows a first order dependence on each of the reactants [H(+)], [D-glucose](T) and [Cr(VI)](T). The bipy-catalysed path is first order in [bipy](T). These observations remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant, N-cetylpyridinium chloride (CPC) and anionic surfactant, sodium dodecyl sulfate (SDS) on both the uncatalysed and bipy-catalysed path has been studied. CPC inhibits both the uncatalysed and bipy-catalysed path, while SDS catalyses these reactions. The observed micellar effects have been explained by considering hydrophobic and electrostatic interactions between the surfactants and reactants.
Bayen
Ruhidas
R
Department of Chemistry, Visva-Bharati University, Santiniketan, India.
Islam
Monirul
M
Saha
Bidyut
B
Das
Asim K
AK
D015082:2,2'-Dipyridyl / Q000737:chemistry*; D002384:Catalysis; D002594:Cetylpyridinium / Q000737:chemistry; D002857:Chromium / Q000737:chemistry*; D005609:Free Radicals / Q000138:chemical synthesis; D005947:Glucose / Q000737:chemistry*; D007700:Kinetics; D008823:Micelles; D010084:Oxidation-Reduction; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry
D005609:Free Radicals; D008823:Micelles; D002857:Chromium; D012967:Sodium Dodecyl Sulfate; D015082:2,2'-Dipyridyl; D002594:Cetylpyridinium; D005947:Glucose