Green Synthesis of Veratraldehyde Using Potassium Promoted Lanthanum-Magnesium Mixed Oxide Catalyst

Article abstract of DOI:10.1021/acs.oprd.7b00127

Veratraldehyde is an important chemical used in perfumery, agrochemical, and pharmaceutical industries. Current processes of manufacture of veratraldehyde use homogeneous catalysts, which make them highly polluting, creating problems of disposal of effluents and product purity. In the current work, veratraldehyde was synthesized from O-alkylation of vanillin with an environmentally benign reagent, dimethyl carbonate. A series of potassium loaded La₂O₃-MgO were prepared by the incipient wetness impregnation method, and their performance was evaluated vis-à-vis MgO, La₂O₃, La₂O₃-MgO, and a series of 1-4 wt % K/La₂O₃-MgO. All catalysts were characterized by different techniques, such as N₂ adsorption/desorption, XRD, TGA-DSC, FT-IR, CO₂-TPD, and SEM techniques. The effect of different loadings (1-4 wt %) of potassium on La₂O₃-MgO was studied, among which 2 wt % K/La₂O₃-MgO showed the best activity and selectivity due to high dispersion of potassium and high basicity in comparison with the rest. The activity of 2 wt % K/La₂O₃-MgO in O-methylation of vanillin with dimethyl carbonate (DMC) was closely associated with basicity. Various parameters were studied to achieve the maximum yield of the desired product. The maximum conversion was found with catalyst loading of 0.03 g/cm³ and mole ratio of vanillin and DMC of 1:15 at 160 °C in 2 h. The reaction follows pseudo-first-order kinetics for the O-methylation of vanillin. The energy of activation was found to be 13.5 kcal/mol. Scale-up was done using the kinetic model to observe that the process could be scaled up using the process parameters. The overall process is clean and green.