Paraben synthesis using trifluoromethanesulfonic acid immobilized on zirconium oxide as catalyst

MIRTA BLANCO; MARINA GORSD; LUIS PIZZIO

Ottawa, Canada

Conferencia; 3rd International IUPAC Conference on Green Chemistry; 2010

Parabens are preservatives in foods, and are synthesized by 4-hydroxybenzoic acid esterification with the corresponding alcohol catalyzed by acids. The heterogeneous catalysts avoid the use of mineral acids, which generate high amount of wastes. Trifluoromethanesulfonic acid (triflic acid) has a highly acidic nature, but has environmental disadvantages when used as homogeneous catalyst. An alternative is the triflic acid heterogeneization by immobilization on an adequate support. Here, triflic acid was immobilized on zirconium oxide (zirconia) obtained by sol-gel, using urea as pore-forming agent. After removing urea, the solid was calcined at 100, 205, 310 and 425 ºC for 24 h. The zirconias were impregnated with triflic acid, and then the weakly adsorbed acid was leached. Mainly mesoporous materials were obtained, whose specific surface area decreased with the temperature of the support thermal treatment. The same trend followed the amount of acid bonded to the support, due to the amount of OH groups to be protonated by the acid decreases by dehydroxylation during thermal treatment. The catalysts were thermally stable up to 250 ºC, exhibited strong acidity and the acid site number decreased with the triflic acid content. The catalytic activity in propyl paraben synthesis agreed well with the amount of acid bonded to the support, but diminished for the synthesis of different parabens in the order propyl > ethyl > methyl ester. The reaction proceeded selectively and the catalysts can be re-used with only a slight conversion decrease. Appropriate catalysts for paraben synthesis were prepared, thus contributing with the clean process field.