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

A mass-spectrometric determination of the sublimation pressure diagram of α-(trifluoromethyl)-lactic acid as a function of its enantiomeric composition at 293 K shows that the racemic crystals have a 38±15%38±15% higher volatility than the enantiomerically pure crystals and the sublimation eutectic has a 55±10%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%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.

Do gas phase dimers play a role in the chirality-dependent sublimation of α-(trifluoromethyl)-lactic acid? We show that this is not the case and that thermodynamically controlled sublimation at low temperature exhibits the expected eutectic behavior typical for immiscible solids of enantiomerically pure and racemic crystals.Figure optionsDownload as PowerPoint slide