Kinetic studies of liquid-phase acetal formation catalyzed by Keggin-type heteropolyacids

Various acetal formation reactions were examined by a Keggin-type heteropolyacid. The reaction kinetics of the acetal formation was also investigated through comparison of heteropolyacids with other acid catalysts in the reaction between cyclohexanone and 1,2-butandiol to produce cyclohexanone ethylethylene acetal. Tungstosilicic acid was found to have a superior catalytic activity compared to other acids. For several reactions between a carbonyl compound and a dialcohol, the reaction mixture was spontaneously separated into two liquid phases, a product phase and a catalyst phase, with high yields of acetal. The recovered catalyst phase was repeatedly applicable to the reaction for the formation of cyclohexanone ethylethylene acetal. The phase separation is concluded to be caused by exclusion of the product acetal from the catalyst phase. Although the catalytic activity was strongly depressed by water produced during the reaction, tungstosilicic acid was found to have a high resistance to water, compared to other acid catalysts.