Abstract
The number of crystal structures of diastereomeric salt pairs and especially of double salts is limited in the literature.
Highlights
Optical resolution via diastereomeric salt formation is the most simple and robust and the most frequently used method for enantiomer purification
In an optical resolution procedure via diastereomeric salt formation an optically active resolving agent is present beside the racemic mixture of the targeted compound
The low efficiency of the optical resolutions can be associated with the presence of the double salt during the optical resolution experiments (DOB-2 and DOB-4)
Summary
Optical resolution via diastereomeric salt formation is the most simple and robust and the most frequently used method for enantiomer purification. By analogy of the above, there is the possibility to obtain a crystalline salt that contains both enantiomers of the starting compound in 1 to 1 ratio and the resolving agent in optically pure form. Formation of such a so called double salt[6,7,8] is not so favoured by symmetry considerations, other factors may promote its formation. We found that practically there was no enantiomer discrimination in neither of the two chloromandelic acid resolutions with 1-cyclohexylethylamine resolving agent In both cases a double salt at 1 to 1 R- and S-chloromandelic acid ratio was found. Chloromandelate (DOB-4)] salts we uniquely have in hand two completed series, the structures of the two diastereomers and the double salt of an organic salt in both cases, all the three possible combinations of the molecular configurations were available for the comparison (Scheme 1)
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