THERMAL TRANSFORMATION OF A CHIRAL, NON-RACEMIC EPOXIDE INTO A CONGLOMERATE - A CASE-STUDY

Formation of conglomerates is of general interest because they offer the possibility of enantiomeric separation by preferential crystallization. A surprising result was obtained for the chiral epoxide 1a,2,7,7a-tetrahydro-3-methoxynaphth-(2,3b)-oxirene, for which we have shown that the racemate crystals of a non racemic mixture can be easily transformed into a conglomerate by gentle heating and cooling within a defined temperature range. This transformation is not possible with the pure racemic mixture. Thus the enantiomeric excess seems to be the driving force for the conglomerate formation. Experiments have been carried out on analytical and preparative scale. Non racemic mixtures have been charaeterized by high pressure liquid chromatography on chiral stationary phase and crystal transformation has been monitored with differential scanning calorimetry (DSC) and infrared spectroscopy (IR).