Direct enantiomeric resolution of monoterpene hydrocarbons via reversed-phase high-performance liquid chromatography with an α-cyclodextrin bonded stationary phase

Abstract

Chiral recognition in liquid chromatography (LC) generally requires relatively strong interactions between the analyte and the chiral stationary phase, often in combination with steric interactions. Hence most LC enantiomeric separations favor compounds that have hydrogen bonding groups, aromatic rings, strong dipoles, possibilities for π-π or charge transfer interactions, etc. Compounds with little or no functionality are usually difficult to resolve by LC methods. Conversely gas chromatography (GC) has been very useful in resolving compounds with limited functionality, including hydrocarbons. In this sense GC has been very complementary to LC methodologies. In this work the enantiomeric separation of hydrocarbons by reversed-phase LC is described. It appears that chiral recognition results largely from “shape-selectivity” ( i.e., the tight fit of a hydrophobic moiety into a hydrophobic cavity) with few other substantial contributing interactions. Small amounts of methyl tert.-butyl ether greatly enhanced the separation efficiency. All commercial samples contain significant quantities of enantiomeric impurities.