MINERAL CATALYSIS OF A POTENTIALLY PREBIOTIC ALDOL CONDENSATION

Minerals may have played a significant role in chemical evolution. In the course of investigating the chemistry of phosphonoacetaldehyde (PA L), an analogue of glycolaldehyde phosphate, we have observed a striki ng case of catalysis by the layered hydroxide mineral hydrotalcite ([M g2Al(OH)(6)] [Cl.nH(2)O]). In neutral or moderately basic aqueous solu tions, PAL is unreactive even at a concentration of 0.1 M. In the pres ence of a large excess of NaOH (2 M), the compound undergoes aldol con densation to produce a dimer containing a C3-C4 double-bond. In dilute neutral solutions and in the presence of the mineral, however, conden sation takes place rapidly, to produce a dimer which is almost exclusi vely the C2-C3 unsaturated product.