Chirality-dependent sublimation of alpha-(trifluoromethyl)-lactic acid: Relative vapor pressures of racemic, eutectic, and enantiomerically pure forms, and vibrational spectroscopy of isolated (S,S) and (S,R) dimers

Abstract

A mass-spectrometric determination of the sublimation pressure diagram of alpha-(trifluoromethyl)-lactic acid as a function of its enantiomeric composition at 293 K shows that the racemic crystals have a 38 +/- 15% higher volatility than the enantiomerically pure crystals and the sublimation eutectic has a 55 +/- 10% higher vapor pressure. These data indicate a possibility for thermodynamically controlled enantiomeric enrichment of the residual material via sublimation of samples of higher than 35 +/- 10% ee. The vibrational spectroscopy of isolated (S,S) and (S,R) dimers in supersonic jets shows that chirality recognition effects are restricted to larger clusters. This is a consequence of the rigid planar carboxylic acid binding motif. (C) 2009 Elsevier B.V. All rights reserved.