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.