Attempts to explain the self-disproportionation observed in the partial sublimation of enantiomerically enriched carboxylic acids

On the Physical Basis of Asymmetry and Homochirality

“…116 In most cases the results correlate well with the ee of the eutectic composition, 114,117,118 although this interpretation is not a general rule and depends on both the substrate and experimental conditions. 118,119 Moreover, there is an interplay of thermodynamic (energy or stability of crystals) and kinetic features (e.g., crystal shape), at least with some fluorinated derivatives. 120 Although the term "resolution by sublimation" has been invoked, 113 it is obvious that separation of enantiomers cannot be achieved by sublimation; rather as correctly stated by Soloshonok, the process implies separation (or self-disproportionation) from the excess enantiomer by sublimation.…”

“…In a subsequent study dealing with amino acids, Feringa and coworkers obtained significant ees after sublimation; leucine with an initial 2% ee (an imbalance otherwise available via CPL photolysis) could be enriched up to 40% ee . In most cases the results correlate well with the ee of the eutectic composition, although this interpretation is not a general rule and depends on both the substrate and experimental conditions . Moreover, there is an interplay of thermodynamic (energy or stability of crystals) and kinetic features (e.g., crystal shape), at least with some fluorinated derivatives …”

Amino Acids in the Universe

“…For example, in the case of mandelic acid, this ee is of 45 %. If the starting material has a ee lower than 45 %, the partial sublimate will have a ee of 45 % and the residue will have a ee lower than the starting one up to reach 0 % [14,18]. In the opposite case, starting from a compound with a ee higher than the one of the euatmotic composition, the ee of the partial sublimate will be still 45 % but the ee of the residue will be enriched up to obtain a pure enantiomer.…”

“…So even starting from a sample with a small ee, the first sublimate will be 90 % enriched. However, only a small sample can be extracted by this way because the residue will reach quickly 0% ee [18]. It should be noted that only a starting mixture with a ee higher than the one of the euatmotic composition can give a pure enantiomer in the residue.…”

Optical Purifications via Self‐Disproportionation of Enantiomers by Achiral Chromatography: Case Study of a Series of α‐CF3‐containing Secondary Alcohols

“…1 Furthermore, it is generally accepted practice that the analytical data reported in the literature for chiral compounds are measured on samples as they are obtained by asymmetric reactions without further purification to enantiomerically pure state. In this context, one of the promising areas is the self-disproportionation of enantiomers (SDE) [3][4][5][6] demonstrating that optical purification of enantiomerically enriched compounds via separation of racemate from the excess enantiomer †7 can be achieved under achiral conditions of any type of phase-transition [8][9][10][11][12][13][14][15][16][17][18][19][20] or achiral chromatography. 2 Apparently, the major reason for reporting chiral compounds of various enantiomeric purities, is the painstaking, expensive and time-consuming efforts usually associated with the purification of enantiomerically enriched samples to optically pure form.…”