Highly basic Mg/La mixed oxide (Mg/La MO) is an effective heterogeneous base, at room temperature for the one-pot Wittig reaction involving aldehyde, a-halo esters and triphenylphosphine to afford alpha,beta-unsaturated esters in good yields with high E-stereoselectivity. Mg/La mixed oxide was recovered quantitatively by simple filtration and reused. The basic properties of Mg/La mixed oxide have been compared to those of nanocrystalline magnesium oxide using the microcalorimetric adsorption of CO2. and the reactivity for Wittig reactions. Mg/La mixed oxide is a stronger base than magnesium oxide (MgO) but shows a much smaller number of sites. Hammett correlations have been determined for both bases and show that the reaction is base mediated, with values of rho = 1.7 for Mg/La mixed oxide, and 1.1 for nanocrystalline magnesium oxide, and a compensation effect can then be observed. (C) 2010 Elsevier B.V. All rights reserved.