Polymorphism of POP and SOS III. Solvent crystallization of β 2 and β 1 polymorphs

Single crystals of β 1 and polycrystals of β 2 of POP and SOS were obtained from acetonitrile solution. The crystallization behavior of the two polymorphs was almost the same in POP and SOS; rapid cooling of the solution preferentially crystallized the metastable β 2 form, and the most stable β 1 form crystallized in a very low solute concentration at the expense of β 2 , via solution‐mediated transformation. The single crystal of β 2 revealed needle‐like irregular shape, whereas well‐defined slender rhombic shape was observed in β 1 . The solubilities of the β 1 forms of POP and SOS in tetradecane solution were precisely measured in a temperature range of 10∼20°C. This study showed that the solvent crystallization was the single way to grow the β 1 crystal, since melt‐cooling and melt‐mediated transformation did not crystallize β 1 both in POP and SOS.