Preparation of a raspberry ketone precursor in the presence of rare earth oxide catalysts

Abstract

The raspberry precursor 4-(4-hydroxyphenyl)-but-3-ene-2-one which afterwards undergoes a catalytic hydrogenation to produce raspberry ketone was synthesized by aldol condensation of acetone and 4-hydroxybenzaldehyde over rare earth oxides as basic catalysts and supported rare earth oxides as acid–base bifunctional catalysts. Thereby, several rare earth metal oxides were tested in their neat form as well as supported on carriers with high surface areas such as alumina, titania, tetragonal zirconia and charcoal. The catalysts were characterized by XRD, BET, NH3/CO2-TPD and pyridine-FTIR. All experiments were carried out batch wise in 75ml autoclaves adjusting molar ratios of acetone and 4-hydroxybenz-aldehyde from 12:1 to 4:1, temperature range from 80 to 200°C and autogeneous pressures from 1 to 25bar. It could also be realized, that titania and alumina are no inert materials, but also highly active catalysts for this reaction. An experimental design program was used to optimize the reaction conditions as well as the conversion and selectivity. In addition the reaction was carried out in a fixed bed plug flow reactor to determine stability and robustness of the catalyst. The quality/contaminations of the starting material have a strong influence on the catalytic performance.