Chromatographic resolution of organic acids using the Kromasil-CHI-TBB chiral stationary phase

Abstract

Derivatives of racemic mandelic and tropic acids have been separated directly on a t-butylbenzoylated tartaric acid-based chiral stationary phase (CSP) (Kromasil-CHI-TBB) on both analytical and preparative scales. The resolution of the enantiomers of the model compound, rac-3-methoxytropic acid, was optimized by changing the nature and the composition of the mobile phase. The dominating interaction between the CSP and these hydroxy acids was found to be hydrogen-bonding. Consequently, retention of the analytes on the CSP decreased with increasing polarity of the mobile phase modifier. The separation of the enantiomers was strongly influenced by the π-donating and π-accepting ability of the aryl moiety, and strong electron-withdrawing substituents in the aryl group e.g.,—CF3 result in a loss of chiral recognition. However, the CSP can discriminate between the two enantiomers only when both the aryl moiety and the carboxylic function are directly bonded to the asymmetric carbon atom. The Kromasil-CHI-TBB column displays broad selectivity for the enantiomers of mandelic and tropic acid derivatives, which are relatively simple structures and not easily resolved. Even though the α-values are moderate, the high efficiency of the column facilitates the use of the CSP for the preparative scale chiral separation of a number of these compounds. Chirality 11:420–425, 1999. © 1999 Wiley-Liss, Inc.