Effect of divalent cations on the basicity and catalytic performance of layered double hydroxide heterogeneous catalyst in microwave-assisted aldol-condensation of benzaldehyde with 1–heptanal

Abstract

In this study, we investigated the catalytic activity of bimetallic layered double hydroxide catalysts (M–Al–LDH) in the aldol condensation reaction between benzaldehyde (B) and 1–heptanal (H). Specifically, we used M–Al–LDH, where M represents magnesium (Mg), nickel (Ni), and zinc (Zn) with the same molar ratio of M/Al = 3, as heterogeneous basic catalysts for the aldol–condensation to produce jasminaldehyde (J). To prepare the M–Al–LDH catalysts, we employed the co-precipitation method using the nitrate precursors under a nitrogen atmosphere. Sodium hydroxide was used as the precipitating agent. The resulting solids were characterized using various techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA/DTA), and BET textural analysis, to study their structural properties. The performance of the catalysts was evaluated and compared in the aldol condensation reaction of benzaldehyde with 1–heptanal under solvent-free conditions, which were carried out in a microwave oven. We also investigated the influence of several reaction parameters on the conversion of 1–heptanal and the selectivity ratio (J/P) in detail to determine the optimal reaction conditions. The results obtained showed that the optimized Mg–Al–NO3 catalyst exhibited a higher conversion of 1–heptanal (99.7%) with a good selectivity ratio (J/P) of 4.00 compared to the other materials studied. Furthermore, the reaction proceeded rapidly in all cases, indicating the practicality of our protocol for the synthesis of jasminaldehyde.