Effect of Solution Composition on Impurity Profile of the Crystallized Product in Oiling-Out Crystallization

Oiling-out is a unique phenomenon that the liquid phase is separated into two parts during crystallization. The emergence of new liquid phase changes the environment where crystals nucleate and grow, we call "mother phase," because target material and impurities become distributed to each phase according to their own particular distribution ratios. In our previous study on crystallization of an intermediate compound with impurities (denoted Imp-A, -B, and -C), we found that when oiling-out was formed, incorporation of Imp-C was inhibited, because Imp-C was distributed to the mother phase less than Imp-A and -B. In this study, we explored the effect of EtOH solution composition on impurity profile of the crystallized product in oiling-out crystallization, and found that the low content of Imp-B in the EtOH solution, the higher content of Imp-C in the crystallized product. Our finding revealed that not only oiling-out but also Imp-B played a key role in inhibiting the incorporation of Imp-C into the crystals.