FT-IR study on the effect of solvents on polymorphic crystallization of organic compounds

FT-IR measurements of solutions of organic compounds, which have several polymorphs, were carried out to discuss the effects of solvents on polymorphic crystallization. DL-Methionine (DL-Met) and bisphenol A (BPA) were used as model compounds. For DL-Met, characteristic peaks of IR spectra of solutions after reaction crystallization with various acids agreed with those of obtained crystals. The difference of IR spectra between solutions indicates that molecular conformations of DL-Met have already changed in the solutions before crystallization and were affected by the acids used for the reaction crystallizations. In the case of BPA, IR spectra of solutions with various solvents were measured to examine the effects of solvents on polymorphic crystallization. Solutions with benzene and ethylbenzene showed similar characteristic peaks each other and form II crystals precipitated from benzene solutions while amorphous solid was obtained from ethylbenzene solutions. Form I crystallized from other solutions without characteristic peaks. From these results, FT-IR measurement of solutions was concluded to be a useful analytical method to examine the effect of solvents on selective crystallization of polymorphs.