Aldolization of butyraldehyde with formaldehyde over a commercial anion-exchange resin - kinetics and selectivity aspects

Butyraldehyde was aldolized with formaldehyde at 40-80 degrees C over an an ion-exchange resin catalyst in aqueous and methanolic solutions. The reacti on mixture was analyzed with gas and liquid chromatography as well as nucle ar magnetic resonance (NMR) spectroscopy. Two main products were detected: 2-ethyl-3-hydroxy-2-hydroxymethylpropanal (trimethylolpropane aldol) and 2- ethylpropenal (ethylacrolein). The molar ratio of the main products was dep endent on the formaldehyde-to-butyraldehyde ratio and the solvent compositi on but independent of the temperature. The yield of 2-ethyl-3-hydroxy-2-hyd roximethylpropanal increased with increasing formaldehyde-to-butyraldehyde ratio and with increasing water-to-methanol content of the reaction mixture . Besides the main reactions, self-condensation and acetalization of butyra ldehyde were detected as side reactions of minor importance. The self-conde nsation of butyraldehyde was suppressed in the presence of formaldehyde and the acetalization of butyraldehyde was minimized by the use of water as re action solvent. Rate equations were derived starting from molecular reactio n mechanisms and adsorption of formaldehyde on the catalyst structure. It t urned out that the rate equations can predict the distribution of the main products. (C) 2000 Elsevier Science B.V. All rights reserved.