One-Pot tandem catalysis: Green synthesis of β-pinene derivatives with MgO and mesoporous catalysts
Luis A. Gallego‐Villada, Edwin A. Alarcón, Felipe Bustamante, Aída Luz Villa
Abstract
Metal-modified heterogeneous catalysts based on mesoporous supports such as MCM-41 and SBA-15 were prepared and evaluated in the one-pot tandem transformation of β-pinene, along with MgO. This route involves epoxidation with H2O2 followed by the subsequent isomerization of the epoxide, yielding myrtanal as the major product; this aldehyde has wide-ranging applications as a fine chemical in fragrances, flavors, and as a precursor for pharmaceutical products. Several metals (Sn, Fe, Cu, Co) were anchored onto the supports by wetness impregnation methodology and the solids were thoroughly characterized using ICP/OES, XRD, N2 physisorption, TEM-EDX, pyridine-FTIR, NH3-TPD, and XPS techniques. Among these catalysts, Fe (5.07 wt%)/SBA-15 (FeS1) exhibited the highest yield to myrtanal (63 %) with a H2O2 efficiency of up to 60 %; this catalyst had a total acidity of 138 μmol g−1, a surface area of 496 m2 g−1, a pore volume of 0.96 cm3 g−1, and an acid site density of 0.28 μmol m−2. Myrtanal selectivity was also high with Sn-based catalysts, while it was poor with Cu-based materials and the null activity of Co catalysts. Total Lewis acidity and acid site density were identified as suitable kinetic descriptors of catalytic data, owing to their crucial role in the ring-opening of monoterpene epoxides. The most active catalyst showed reusability without considerable loss of substrate conversion or selectivity towards myrtanal. Additionally, no leaching of Fe was observed. Based on materials characterization and catalytic results, a plausible reaction pathway was proposed for the one-pot tandem transformation of β-pinene towards myrtanal.