Mineral Catalysis of a Potentially Prebiotic Aldol Condensation
R.M. De Graaf*, J.Visscher, Y.Xu, G.Arrhenius and A.W.Schwartz

*Evolutionary Biology Research Group, Faculty of Science, University of Nijmegen, Postbut 9010, Nijmegen 6500 GL, The Netherlands

ABSTRACT

Minerals may have played a significant role in chemical evolution. In the course of investigating the chemistry of phosphonoacetaldehyde (PAL), an analogue of glycolaldehyde phosphate, we have observed a striking case of catalysis by the layered hydroxide mineral hydrotalcite ([Mg2Al(OH)6][Cl.nH2O]). In neutral or moderately basic aqueous solutions, PAL is unreactive even at a concentration of 0.1 M. In the presence of a large excess of NaOH (2M), the compound undergoes aldol condensation to produce a dimer containing a C3-C4 double-bond. In dilute neutral solutions and in the presence of the mineral, however, condensation takes place rapidly, to produce a dimer which is almost exclusively the C2-C3 unsaturated product.