Polymer and micellar catalysis in d-fructose oxidation by imidazolium fluorochromate: A kinetic and mechanistic study

Abstract

This work investigated the oxidation of d-fructose using imidazolium fluorochromate (IFC) as an oxidant and analyzed how sodium dodecyl sulfate (SDS) and polyethylene glycol (PEG-400) affected the reaction kinetics. The process exhibited a unit-order dependence on IFC, d-fructose, and perchloric acid concentration. Perchloric acid was the primary source of hydrogen ions in the reaction mixture. The stoichiometry of the reaction indicated that 3 mol of d-fructose requires 4 mol of IFC. Acrylonitrile, a radical-generating species, did not impact the reaction rate, indicating the absence of a free radical intermediate. The reaction rate decreases as the Mn (II) ions concentration increases, suggesting the involvement of Cr (IV) species in the reaction. The dielectric value of the reaction medium (D) had an inverse effect on the rate, and the outcomes were consistent with the Amis (log k1 and 1/D) and Kirkwood plots (log k1 and (D-1/2D+1)), indicating the presence of dipole-dipole interactions in the process. SDS and PEG-400 catalyzed the reaction. The reaction showed significant catalysis before reaching the critical micelle concentration (CMC). However, the observed rate constants stabilized at higher SDS concentrations exceeding the CMC. Piszkiewicz's cooperativity model was employed to describe the surfactant catalysis, while the Benesi-Hildebrand equation was utilized to explain polymer catalysis. The activation parameters are ΔH† = 44.3 ± 1.3 kJ mol−1, and ΔS† = −133.4 ± 4.3 J K−1 mol−1. The products of the reaction have been identified by spectral analysis as d-arabinoniclactone and formic acid. The formation of an ester complex followed by its decomposition was proposed as the rate-limiting step in the proposed mechanistic reaction pathway.