Insight into Structural Demand for Cold Crystallization of a Small Molecule. A Case Study for Schiff Base Compounds that Exhibit Prototropic Tautomerization
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- Iwase Katsunori
- DENSO CORPORATION
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- Toyama Yasuhiro
- DENSO CORPORATION
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- Yoshikawa Isao
- Institute of Industrial Science, The University of Tokyo
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- Yamamura Yasuhisa
- Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba
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- Saito Kazuya
- Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba
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- Houjou Hirohiko
- Institute of Industrial Science, The University of Tokyo
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Abstract
<p>To elucidate the relationship between prototropic tautomerism and the cold crystallization phenomenon, o-hydroxy aryl Schiff base compounds derived from three different toluidine isomers were examined. Comparing their thermal behavior, we confirmed that cold crystallization occurred to give a different crystalline phase compared to the initial state. To elucidate the mechanisms of the cold crystallization of the materials, their thermal, structural, and energetic properties were investigated. The DFT calculation of the molecules in their OH- and NH-forms suggested that the NH-form has higher molecular flexibility, which may prevent normal crystallization upon cooling, compared to the OH-form. Spectroscopic analyses implied that the molecules are present as a mixture of the OH- and NH-forms, and that they efficiently crystallize when a preferable OH/NH ratio is achieved. For this molecular system, we concluded that the equilibrium between NH- and OH-forms controls the supercooling of the liquid as well as nucleation and crystal growth.</p>
Journal
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- Bulletin of the Chemical Society of Japan
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Bulletin of the Chemical Society of Japan 91 (4), 669-677, 2018
The Chemical Society of Japan
