Ionone synthesis on solid acid catalysts

VERÓNICA K. DÍEZ; CARLOS R. APESTEGUÍA; J. ISABEL DI COSIMO

Seúl, Corea del Sur

Congreso; 14th International Congress on Catalysis; 2008

Ionones (a, b and g isomers) are extensively used as pharmaceutical intermediates and fragrances. The b-ionone isomer is used in different synthesis processes leading to vitamin A, whereas a- and g-ionones are employed in perfume formulations. Ionones are commercially produced from citral via a two-step homogeneously-catalyzed process. In the first step, citral and acetone are contacted with diluted bases such as NaOH, Ba(OH)2, and LiOH to give pseudoionone (PS).  Then, the consecutive cyclization of PS to ionones is catalyzed by mineral acids. In this paper, the liquid-phase cyclization of PS to ionones was studied on solid acids combining Lewis and Brönsted acid sites, such as zeolite HBEA, Amberlyst 35W, SiO2-Al2O3, silica-supported heteropolyacids (HPA/SiO2) and Cs-HPA.  Amberlyst 35W and HPA/SiO2 were the most active catalysts showing that the reaction is preferentially promoted on strong Brönsted acid sites. In particular, 58.5 wt. % HPA/SiO2 yielded about 79 % ionones after 1.5 h of reaction at 383 K. This ionone yield is comparable to the best values reported in literature for the homogeneously-catalyzed reaction. The three ionone isomers were always obtained but the isomer distribution significantly changed with pseudoionone conversion, reaction time and temperature.