Optical resolution mechanism in an optically active solvent or cosolute in an equilibrium state

Abstract

By crystallization of ΔΛ-[Co(aet)(en)₂][ClO₄]₂ in the presence of Δ-Na[Co(edta)]·3H₂O or Na₂(D-tart)·2H₂O [aet = 2-aminoethanethiolate(1–), en = ethylenediamine, edta = ethylenediaminetetraacetate(4–) and D-tart =(RR)-tartrate(2–)] the Δ-aet complex always appears as the first crop. The mechanism can be best explained by use of a ternary solubility isotherm: a shift of the eutectic point on the central racemic line into the optically active region is caused by the active cosolute (or solvent); the larger the shift the higher is the percentage resolution. This isotherm has also clarified that the solubility difference between the enantiomers in the binary system is not relevant to the optical resolution. This resolution mechanism is applicable to conglomerates with rapid racemization rates.