Selectivity Engineering in One Pot Synthesis of Raspberry Ketone: Crossed Aldol Condensation of p‐Hydroxybenzaldehyde and Acetone and Hydrogenation over Novel Ni/Zn‐La Mixed Oxide

Abstract

AbstractRaspberry ketone, also called as rheosmin, is an important flavor compound used in perfumery and food industry. In the current work, it was synthesized from p‐hydroxybenzaldehyde (PHB) and acetone in one pot system. Crossed aldol condensation of p‐hydroxybenzaldehyde gave α,β‐unsaturated ketone, i. e. p‐hydroxybenzalacetone (PHBA) which was further reduced to obtain raspberry ketone. Mixed oxide catalysts of different combinations of Mg, La and Zn were prepared by three different methods such as hydrothermal, combustion and co‐precipitation. Among all Zn−La with mole ratio 3:1, synthesized by combustion method and glycine as fuel, gave the best results for selective synthesis of PHBA. For hydrogenation of PHBA, Ni, Cu and Pd metals were screened to find that 2% Ni/Zn3:La1 was the best catalyst for one‐pot synthesis of raspberry ketone. It showed excellent textural properties like high surface area (680 m2/g), activity and selectivity. The virgin and spent catalyst samples were fully characterized by SEM, TEM, TGA, FTIR, CO2 and NH3‐TPD and BET surface area analysis. It was stable, active and reused for 4 cycles. The kinetic model was developed separately for two different steps. The reaction is kinetically controlled with activation energy of 18.48 kcal/mol for crossed aldol condensation and 14.19 kcal/mol for hydrogenation step. It is an interesting example of process chemistry and engineering using a novel catalyst and process.