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

Derivatives of racemic mandelic and tropic acids have been separated direct ly on a t-butylbenzoylated tartaric acid-based chiral stationary phase (CSP ) (Kromasil-CHI-TBB) on both analytical and preparative scales. The resolut ion 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 foun d to be hydrogen-bonding. Consequently, retention of the analytes on the CS P decreased with increasing polarity of the mobile phase modifier. The sepa ration of the enantiomers was strongly influenced by the pi-donating and pi -accepting ability of the aryl moiety, and strong electron-withdrawing subs tituents 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 b oth the aryl moiety and the carboxylic function are directly bonded to the asymmetric carbon atom. The Kromasil-CHI-TBB column displays broad selectiv ity for the enantiomers of mandelic and tropic acid derivatives, which are relatively simple structures and not easily resolved. Even though the alpha -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 thes e compounds. Chirality 11:420-425, 1999. (C) 1999 Wiley-Liss, Inc.