CrystEngComm 2018-04-08

Direct observation of α- to β-glycine transformation during ionic liquid mediated crystallization process

Liangfei Ouyang, Tengfei Zheng, Liang Shen

Index: 10.1039/C7CE02247F

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Abstract

The application of in situ powder X-ray diffraction (XRD) to monitor the polymorphic transformation and crystallization of glycine from ionic liquid-water system is introduced. We compared the polymorphic crystallization processes of glycine in the pure water, the hydrophilic ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4)- and hydrophobic 1-Butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6)-water system. In three cases, the mixture composed of the metastable α- and least stable β-glycine was entirely observed in the growth end under room temperature and 32% humidity, and the phase transformation of α- to β-form glycine was clearly observed through the variation of characteristic peaks 29.9° to 18.0 ° (2 theta) in the XRD patterns. In addition, the effect of ionic liquid [Bmin]PF6 as an anti-solvent on re-crystallization process of glycine from three commercialize brands were estimated. Also, the satisfactory reproducibility were obtained from glycine crystallization in the ionic liquid [Emim]BF4-water system for four independent experiments. Therefore, laboratory-based powder XRD can not only provide dynamic information about phase transformation in situ, but also be able to discover the unstable or transition state in the polymorphic design and control crystallization processes by adding ionic liquids or other additives.