Liquid Phase Aerobic Oxidation of Cinnamyl Alcohol to Cinnamaldehyde: Effect of Different Solvents

摘要

Background: Cinnamaldehyde is a valuable raw material in food, perfumery, agrochemical and pharmaceutical industries. Initially, manganate and di-chromate ions were used as catalysts for oxidation of cinnamyl alcohols to cinnamaldehyde. But there are several limitations with these methods. Therefore, research is needed to replace the existing method with one which is more practical and feasible for industries. Method: Support material (Zirconia or Titania) was synthesized by ammonolysis, while supported catalysts (0.01%Pt/ZrO2, 0.01%Pd/ZrO2, 0.01%Pt/TiO2, 0.01%Pd/TiO2) were prepared by incipient wetness technique. The samples were characterized by different physicochemical techniques like Scanning Electron Microscopy (SEM), X- ray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDX), and used for the oxidation of cinnamyl alcohol in a batch type reactor. The products were analyzed by GC (PerkinElmer Clarus 580) equipped with FID and column (rtx@-Wax 30m, 0.5mm ID, 0.5nm), using n-nonane as internal standard Results: The catalysts were tested for the liquid phase oxidation of cinnamyl alcohol to cinnamaldehyde. The effect of various reaction conditions as well as of different solvents on the % conversion was investigated. The maximum conversion of cinnamyl alcohol obtained was 74% with a 71.6% selectivity for cinnamaldehyde in cyclohexane as a solvent under a flow of oxygen gas as oxidant. The catalytic abilities of the catalysts were found to be in the order: 0.01%Pt/ZrO2>0.01%Pd/ZrO2>0.01%Pt/TiO2>0.01%Pd/TiO2. The activation energy viz 17.8 kJ/mole, revealed that the reaction is diffusion controlled. Conclusion: In this study, the catalysts (0.01%Pt/ZrO2, 0.01%Pd/ZrO2, 0.01%Pt/TiO2 and 0.01%Pd/TiO2) were synthesized, and evaluated for the oxidation of cinnamyl alcohol to cinnamaldehyde. Although, high catalytic activity was noticed in cyclohexane, but high selectivity was found to occur in toluene. Based on the study, 0.01% Pt/Zr02 is a promising catalyst for the oxidation of cinnamyl alcohol to cinnamldehyde in toluene.