Liquid phase oxidation of para-chlorotoluene to para-chlorobenzaldehyde using vanadium silicate molecular sieves Original Research Article

Liquid phase oxidation of para-chlorotoluene (PCT) with aqueous H2O2 has been investigated in the presence of vanadium silicates, VS-1 (MFI) and VS-2 (MEL). Vanadium impregnated silicalite-1 (V/Si-1) and silicalite-2 (V/Si-2) were also included for comparison. Under identical conditions, VS-1 is considerably more active for PCT conversion than the others, however, VS-1 and VS-2 are found to be comparable for the selective formation of para-Chlorobenzaldehyde (p-CIBZD). The effect of reaction time, Si/V molar ratio, catalyst concentration, reaction temperature and H2O2/PCT molar ratio on the catalyst performance were examined in order to optimize the conversion of PCT and selectivity for p-CIBZD. The conversion of PCT using VS-1 is increased significantly with the increase in reaction time, catalyst concentration, reaction temperature and H2O2/PCT molar ratios, however, an increase in the Si/V molar ratio of VS-1 lowered the PCT conversion and increased slightly the selectivity for p-CIBZD. A selectivity of the order of >64.0% to p-CIBZD is obtained at 13.4 wt% conversion of PCT at 373 K. After the separation of the catalyst during the reaction from the reaction mixture, the product formation is not noticed. Recycling of the catalyst shows that the deactivation of the catalyst VS-1 is related to the stability of the vanadium ions in the framework of VS-1. The reaction pathway from PCT to p-CIBZD is thought to be via formation of para-chlorobenzyl alcohol (p-CIBZA) and proceeds probably through a homolytic mechanism.