Choice of suitable micellar catalyst for 2,2′-bipyridine-promoted chromic acid oxidation of glycerol to glyceraldehyde in aqueous media at room temperature

Abstract

The micellar catalyzed 2,2′-bipyridine (bipy)-promoted oxidation of glycerol to glyceraldehyde by chromic acid is investigated under the criteria [glycerol]T ≫ [Cr(VI)]T at 30 °C. The critical micellar concentrations values of the three representative surfactants, N-cetylpyridinium chloride (CPC), sodium dodecyl sulphate (SDS), and TX-100, are determined by conductometric and spectrophotometric methods. The oxidized product glyceraldehyde is identified by 2,4-DNP test and FTIR spectral measurement. The pseudo-first-order rate constants (k obs, s−1) are calculated from the slope of plots of ln(A 450) versus time (t) which are linear. From these plots, the kinetic parameter k eff values are calculated and the k eff value of SDS-catalyzed bipy-promoted reaction path was found to be highest among all the combinations. In the bipy-promoted oxidation path, Cr(VI)–bipy complex is the main active oxidant which undergoes attack by the substrate to form the product. The active oxidant Cr(VI)–bipy complex reacts with glycerol to form a ternary complex which undergoes redox decomposition in a rate-limiting step. Here, the anionic surfactant SDS and the neutral surfactant TX-100 both catalyze the reaction in the presence of bipy, whereas the cationic surfactant CPC and neutral surfactant TX-100 inhibit the reaction in the absence of bipy. SDS is found to be the most suitable micellar catalyst for the bipy-promoted chromic acid oxidation of glycerol.