Condensation of glyceraldehyde acetonide with ethyl acetoacetate over Mg, Al-mixed oxides derived from hydrotalcites

Growing environmental concern is leading the chemical industry to develop clean technologies. α,β-unsaturated carbonyl compounds are important organic intermediates; however, their synthesis by the conventional routes requires several steps and produces toxic wastes. The catalytic behavior of Mg, Al-mixed oxides derived from hydrotalcites was studied using the Knoevenagel condensation between glyceraldehyde acetonide and ethyl acetoacetate producing the corresponding α,β-unsaturated carbonyl compound that is an important intermediate for fine chemicals. The influence of chemical composition of hydrotalcites and of activation procedure (calcination or calcination followed by rehydration) on the basic properties and on the catalytic performance was also investigated. All the catalysts were active for the studied reaction and 100% selective to the condensation product. The decrease in Al content in the Mg, Al-mixed oxides increased the conversion of glyceraldehyde acetonide and consequently the product yield. This trend reflects both the basic sites density as measured by TPD of CO2 and the mesoporous characteristics of the mixed oxides. The rehydration of the Mg, Al-mixed oxide also increased the conversion of glyceraldehyde acetonide without changing the selectivity. Although this activation procedure has decreased the basic sites density, it converted Lewis basic sites into Brönsted ones, which favored the condensation reaction under the studied conditions.