Discriminating interaction in the pfeiffer effect developed by L-tartaric acid and its derivatives

The Pfeiffer effect was examined on the systems of racemic [Co(phen)₃] Cl₂ with L-tartaric acid and with its derivatives, L-dimethyltartrate, L-diethyltartrate, L-dimethyldiacetyltartrate, and L-diacetyltartaric acid in water (phen = 1, 10-phenanthroline). It was found that the Pfeiffer effect is well developed when L-tartaric acid and its dimethyl- and diethylesters are employed as a chiral environment substance, but not when its diacetyl-derivatives are employed. This result indicates that the alcoholic OH groups of the chiral environment substances play an essential role in the chiral discrimination in these Pfeiffer systems. The NMR study on the corresponding [Zn(phen)₃]²⁺ systems suggests that L-tartaric acid attacks the complex along its C₃ axis, and that the discriminating interaction in the L-tartaric acid system is different from that in the L-dimethyl- and L-diethyltartrate systems.