Spontaneous Resolution of Chiral 3‑(2,3-Dimethylphenoxy)propane-1,2-diol under the Circumstances of an Unusual Diversity of Racemic Crystalline Modifications

Depending on the conditions of crystallization from solutions, racemic 3-(2,3-dimethylphenoxy)­propane-1,2-diol 1 forms three relatively stable crystalline modifications. Each of the crystalline forms, namely, two polymorphic racemic compounds and a racemic conglomerate, has been characterized by single-crystal X-ray diffraction. Two more metastable racemic compounds crystallized from the racemic melt have been found by differential scanning calorimetry method. Additional thermochemical investigations allowed to plot the dependence of the free Gibbs energy on temperature for all the phases found. With the help of slurrying experiments, the nature of the transitions between solid phases has been specified. It has been found that even a slight predominance of one of the enantiomers in almost racemic 1 samples ensures the crystallization of the conglomerate. The revealed features of rac-1 crystallization have been taken into account during the realization of its resolution into individual enantiomers by the entrainment procedure.