Self-Condensation of n-Butyraldehyde Over Solid Base Catalysts

The catalytic properties of various solid bases for self-condensation of n-butyraldehyde in liquid phase were studied to elucidate the factors governing the activity and selectivity. For alkaline earth oxide catalysts and γ-alumina catalyst, aldol condensation occurred, followed by Tishchenko-type cross-esterification of n-butyraldehyde with the dimer produced by the aldol condensation to form trimeric glycol ester. Alkali ion-modified alumina catalysts exhibited a high selectivity for the aldol condensation dimer, the trimeric glycol ester being formed tittle. Both basic and acidic sites on the surfaces of the alkaline earth oxides and γ-alumina were assumed to contribute to Tishchenko-type cross-esterification. The suppression of Tishchenko-type cross-esterification for alkali ion-modified alumina catalysts is due to the absence of acidic sites on the surfaces. The catalytic performances of alumina-supported magnesium oxide and alkali zeolite X were also examined. Alumina-supported magnesium oxide exhibited lower activity but higher selectivity to trimeric glycol ester than MgO. This catalytic feature was caused by the lower basicity and higher acidity on the surface of alumina-supported magnesium oxide as compared with MgO. The activity of alkali ion-exchanged zeolites was lowest among the catalysts examined in this study. The modification of zeolites with excess alkali ions improved the activity.