Comparison of activity and selectivity of weakly basic anion-exchange catalysts for the aldolization of butyraldehyde with formaldehyde

Aldols are important intermediates in the production of polyols, which are raw material for lubricants, surface coatings, and synthetic resins. The activities and selectivities of gel-type and macroporous anion-exchange resin catalysts in the aldolization of butyraldehyde with formaldehyde in an aqueous environment were investigated at 60 °C. The experiments were carried out batchwise in a stirred glass reactor, and the reaction products were analyzed with high performance liquid chromatography. Two main products were observed, 2-ethyl-3-hydroxy-2-hydroxy-methylpropanal (trimethylolpropane aldol) and 2-ethyl-propenal (ethylacrolein). The product ratio was strongly dependent on the catalyst. The selectivity with respect to trimethylolpropane aldol varied within the range 2.7-7.3 for the catalysts investigated. Systematic kinetic experiments were carried out at 50-70 °C with the gel-type resin catalyst displaying the highest aldol selectivity. A kinetic model based on molecular mechanisms was able to describe the product distribution.