A Study of the Pfeiffer Effect in Systems containing Trisoxalatometallate(III) Complexes and Cinchonine Hydrochloride

Abstract

The Pfeiffer effect was studied in systems containing cinchonine hydrochloride and trisoxalatometallate(II1) complexes of Al, Fe, Cr, Co, and Ir. The Pfeiffer rotatory dispersion curves of the Cr and Co complexes show Cotton effects analogous to that observed in the optical rotatory dispersion (0.r.d.) curves of the respective complexes. The source of the Pfeiffer effect in all these systems is attributed either to an association between the complex ion and the optically active species in solution alone, as in the case of the Ir(lI1) complex, or to a combination of this association and an "equilibrium shift" between the two enantiomers in solution in favor of one of them, as in the case of the other complexes under investigation.

The Pfeiffer effect with cinchoninium ion as a chiral environment substance

“…Similarity of the CD pattern which was developed 0020-1669/79/1318-1425S01.00/0 to that12 of resolved A-[Cr(ox)3]3" ion indicates that the chiral equilibrium of [Cr(ox)3]3" is shifted in favor of its A enantiomer; that is, the A enantiomer is enriched in the presence of cinchoH4" in agreement with the results reported earlier by other workers. [3][4][5][6] It is noteworthy in Figure 1 and Table I that the addition of dioxane and tetrahydrofuran (THF) enhances the Pfeiffer effect of the present system greatly, while other additives, dimethyl sulfoxide (Me2SO), 7V-methylacetamide (NMA), 7V,7V-dimethylacetamide (DMA), urea, and alcohols, have a diminishing or relatively small effect. Since dioxane and THF are almost nonpolar (their dielectric constant e = 2.2 and 7.4 at 25 °C, respectively13), electrostatically promoted association between [Cr(ox)3]3" and cinchoH4" is thought to be responsible for the enhanced Pfeiffer effect in these systems.…”