Synthesis of Pseudoionones by Aldol Condensation of Citral with Acetone on Li-Modified MgO Catalysts

Abstract

The liquid-phase synthesis of pseudoionones by aldol condensation of citral with acetone was studied on MgO samples containing between 0.13 and 2.6 wt. % of Li+. The Li+ addition to MgO up to about 0.5% increased the density of strong O2-basic sites, but increasing the Li+ amount further diminished the sample basicity. Formation of pseudoionones increased with the sample basicity: the higher the density of strong basic sites the higher the pseudoionone yields. Thus, Li-MgO samples containing the highest density of O2-sites were the most active catalysts for producing pseudoionones. Introduction Pseudoionones (PS) are valuable intermediate compounds for the synthesis of α and β-ionones, which are widely used as pharmaceuticals and fragrances. In particular, βionone is the preferred reactant for different synthesis processes leading to vitamin A (1). Pseudoionones are commercially produced via the aldol condensation of citral with acetone in a liquid-phase process involving the use of diluted bases, such as NaOH, Ba(OH)2, LiOH, which pose problems of high toxicity, corrosion, and spent base disposal (2). The consecutive cyclization of pseudoionones to yield α and βionones is catalyzed by strong liquid acids. The two-step process for ionone synthesis is depicted in equation (1).