Enantiomeric separation of amino alcohols by gas chromatography on a chiral stationary phase; influence of the perfluoroacylating reagent on the separation

✍ Scribed by Küsters, Ernst ;Portmann, Andrea

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 378 KB
• Volume: 17
• Category: Article
• ISSN: 0935-6304
• DOI: 10.1002/jhrc.1240170904

✦ Synopsis

Abstract

Racemic amino alcohols have been separated as perfluoroacylated derivatives by gas chromatography using either improved Chirasil‐Val or heptakis(2,6‐di‐O‐methyl‐3‐O‐pentyl)‐β‐cyclodextrin as stationary phase. Using Chirasil‐Val all the amino alcohols investigated were separated to baseline (α values between 1.03 and 1.08) whereas only a few amino alcohols were resolved on the modified cyclodextrin column. The enantioselectivity obtained on the latter phase was, however, significantly higher.

The separations were performed as trifluoroacetyl, pentafluoropropionyl, and heptafluorobutyryl derivatives and the chiral discrimination observed for the different derivatives was significantly different for both stationary phases.

In oder to obtain a better understanding of the separation mechanism, the Gibbs‐Helmholtz parameters Δ~(R,S)~Δ__H__° and Δ~(R,S)~Δ__S__° were determined. The most extraordinary result was obtained for the trifluoroacetyl derivative of allo‐threoninol. In addition to the order of elution of the enantiomers being the opposite of that for the other compounds, the separation seems to be entropy controlled (the sign Δ~(R,S)~Δ__H__° is positive), i.e. the separation improved at higher temperatures.