Enantiomer separations by capillary GC on modified gyclodextrins

Abstract

AbstractThree new chiral selectors, 6‐tert‐butyldimethylsilyl‐2,3‐diethyl‐a‐cyclodextrin, 6‐tert‐butyldimethylsilyl‐2,3‐diethyl‐ and dipropyl‐β‐cyclodextrin (TBDE‐α‐CD, TBDE‐β‐CD, TBDP‐β‐CD) were synthesized and tested as chiral stationary phases in capillary gas chromatography. TBDE‐β‐CD in particular showed a high enan‐tioselectivity for test chiral compounds due to good solubility in a polar polysiloxane (OV‐1701). Enantioselectivity obtained with TBDE‐β‐CD was compared with that of 6‐tert‐butyldimethylsilyl‐2,3‐di‐O‐methyl‐β‐cyclodextrin (TBDM‐β‐CD). Better enantiose‐lectivity was obtained with TBDE‐P‐CD than with TBDM‐β‐CD for the test chiral compounds studied. This is probably due to greater effect of the increased hydrophobicity of TBDE‐β‐CD which favors inclusion of the analytes than the effect of increased steric hindrance. With TBDP‐β‐CD the less polar lactones are well separated due most likely to increased hydrophobicity of the propyl groups while the more polar are not well resolved. For TBDP‐β‐CD it is likely that the unfavorable steric hindrance is predominant over the favorable hydrophobicity of the propyl groups, thus hindering the formation of inclusion complexes of the alcohols with TBDP‐β‐CD. TBDE‐α‐CD was also a valuable chiral selector for the separation of small chiral molecules such as simple secondary alcohols and nitro‐substituted alcohols.