Baaklini Grace, Schindler Manon, Yuan Lina, Jores Clément De Saint, Sanselme Morgane, Couvrat Nicolas, Clevers Simon, Négrier Philippe, Mondieig Denise, Dupray Valérie, Cartigny Yohann, Gbabode Gabin, Coquerel Gerard
Laboratoire Sciences et Méthodes Séparatives UR3233, Université Rouen Normandie, Normandie Université, F-76000 Rouen, France.
LOMA, UMR 5798, Université Bordeaux, 351 Cours de la Libération, F-33400 Talence, France.
Molecules. 2023 Oct 12;28(20):7061. doi: 10.3390/molecules28207061.
It is shown that the presence of hundreds of ppm of water in 1,3-dimethylurea (DMU) powder led to the large depression of the transition temperature between the two enantiotropically related polymorphic forms of DMU (Form II → Form I) from 58 °C to 25 °C, thus explaining the reported discrepancies on this temperature of transition. Importantly, this case study shows that thermodynamics (through the construction of the DMU-water temperature-composition phase diagram) rather than kinetics is responsible for this significant temperature drop. Furthermore, this work also highlights the existence of a monohydrate of DMU that has never been reported before with a non-congruent fusion at 8 °C. Interestingly, its crystal structure, determined from X-ray powder diffraction data at sub-ambient temperature, consists of a DMU-water hydrogen bonded network totally excluding homo-molecular hydrogen bonds (whereas present in forms I and II of DMU).
结果表明，1,3 - 二甲基脲（DMU）粉末中存在数百ppm的水会导致DMU两种对映变体多晶型（晶型II→晶型I）之间的转变温度大幅下降，从58°C降至25°C，从而解释了此前报道的该转变温度的差异。重要的是，该案例研究表明，是热力学（通过构建DMU - 水的温度 - 组成相图）而非动力学导致了这一显著的温度下降。此外，这项工作还突出了一种以前从未报道过的DMU一水合物的存在，其在8°C时发生非一致熔融。有趣的是，根据低于环境温度下的X射线粉末衍射数据确定的其晶体结构，由一个完全排除了同分子氢键（而在DMU的晶型I和晶型II中存在）的DMU - 水氢键网络组成。
