Stereoselective crystallization induced by traces of dissolved optically active impurities.

Isothermal crystallization of D,L-sodium-ammonium tartrate with traces of different impurities admixed shows that the added chiral contaminations produce a preferential crystallization of the tartrate isomer of same handedness. The critical lowest concentration of effective seeding agents is 0.1-0.5%. 1% optically active excess material induces 1.0-3.6% optical purity in the deposited crystals. An analysis of the relevant data reported so far gives similar figures in different crystallization systems. The relation of the results to the suggested lattice energy difference between enantiomers is discussed.