Investigation of a suitable metal catalytic system for the aldol reaction between acetophenone and benzaldehydes

Abstract

This study was aimed at finding an efficient metal ion catalytic system for the aldol reaction because waste generation in the conventional aldol reaction under standard condition is very high. The aldol reaction between aryl aldehydes (benzaldehyde, p-Br-, p-Me- and p-OMe- benzaldehydes) and ketones (acetone, cyclohexanone and acetophenone) was carried out with a catalytic amount of a metal salt (10% w/w) under refluxing conditions in different solvents. Of the metal salts used viz FeCl3, ZnCl2, TiO2 and AlCl3, FeCl3 performed as the best catalyst for the aldol reaction between para-tolualdehyde and acetophenone. Among the three solvents (EtOH/ H2O, CH2Cl2 and dioxane) examined, a mixture of EtOH and H2O was found to be the best solvent system. Several ligands viz ethylenediamine, PPh3, pyridine, aniline in different ratios were added to the reaction mixture to improve the yield of the aldol reaction catalysed by FeCl3. Among them ethylene diamine with FeCl3 in 1:3 ratio gave the best catalytic system. In addition, iron (III) catalysed aldol reactions carried out at 100 ̊C produced the best yields in 3 hours. Final products were analysed by thin layer chromatography and compared with authentic samples. In conclusion, 10% FeCl3, 30% ethylenediamine in EtOH/ H2O solvent system was found to be the optimum condition for the aldol reaction and the highest yield of 35% was obtained for the reaction between acetophenone and para-tolualdehyde under this new unconventional condition with little or no waste.