Catalysis of Organic..

Diez, Di Cosimo and Apesteguia 35540. Synthesis of Pseudoionones by AldolCondensation of Citral with Acetone on Li-Modified MgO CatalystsAbstractVerónica K. Díez, Juana I. Di Cosimo and Carlos R. ApesteguíaCatalysis Science and Engineering Research Group (GICIC ,Instituto de Investigaciones en Catálisis y Petroquímica (UNL-CONICET)Santiago del Estero 2654, (3000) Santa Fe, Argentinacapesteg@fiqus.unl.edu.arThe liquid-phase synthesis of pseudoionones by aldol condensation of citral withacetone 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 O 2- basicsites, but increasing the Li + amount further diminished the sample basicity.Formation of pseudoionones increased with the sample basicity: the higher thedensity of strong basic sites the higher the pseudoionone yields. Thus, Li-MgOsamples containing the highest density of O 2- sites were the most active catalysts forproducing pseudoionones.IntroductionPseudoionones (PS) are valuable intermediate compounds for the synthesis of α andβ-ionones, which are widely used as pharmaceuticals and fragrances. In particular, β-ionone is the preferred reactant for different synthesis processes leading to vitamin A(1). Pseudoionones are commercially produced via the aldol condensation of citralwith acetone in a liquid-phase process involving the use of diluted bases, such asNaOH, Ba(OH) 2 , LiOH, which pose problems of high toxicity, corrosion, and spentbase disposal (2). The consecutive cyclization of pseudoionones to yield α and β-ionones is catalyzed by strong liquid acids. The two-step process for iononesynthesis is depicted in equation (1).Increasing research work has been lately performed to find suitable andrecyclable solid catalysts for efficiently promoting the liquid-phase aldolcondensation of citral with acetone with the aim of developing an environmentallybenign process for producing pseudoionones. Climent et al. (3) showed that thereaction is poorly catalyzed by employing acid zeolites or bifunctional acid-basealuminophosphates (ALPO). In contrast, the use of solid bases such as MgO or Mg-Al mixed oxides may selectively produce pseudoionones (3,4). Other authors (5,6,7)have noted that Mg-Al hydrotalcites of Mg:Al ratio near 3 also form preferentiallypseudoionones, although the catalyst activity and selectivity are greatly affected by