Abstract
The effect of various controlling factors on the polymorphic outcome of sodium dehydroacetate crystallization was investigated in this study. Cooling crystallization experiments of sodium dehydroacetate in water were conducted at different concentrations. The results revealed that the rate of supersaturation generation played a key role in the formation of the hydrates. At a high supersaturation generation rate, a new sodium dehydroacetate dihydrate needle form was obtained; on the contrary, a sodium dehydroacetate plate monohydrate was formed at a low supersaturation generation rate. Furthermore, the characterization and transformation behavior of these two hydrated forms were investigated with the combined use of microscopy, powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and dynamic vapor sorption (DVS). It was found that the new needle crystals were dihydrated and hollow, and they eventually transformed into sodium dehydroacetate monohydrate. In addition, the mechanism of formation of sodium dehydroacetate hydrates was discussed, and a process growth model of hollow crystals in cooling crystallization was proposed.
Highlights
The formation of polymorphs, solvates and hydrates is a prevalent phenomenon in the production of chemical compounds including active pharmaceutical ingredients [1,2]
As shown cooling rates were characterized by microscope, powder X-ray diffraction (PXRD), Raman, Fourier transform infrared (FTIR) and thermal gravimetric analysis (TGA)
The effects of the rate of supersaturation generation on DHA-S hydrate crystallization were investigated through cooling crystallization experiments
Summary
The formation of polymorphs, solvates and hydrates is a prevalent phenomenon in the production of chemical compounds including active pharmaceutical ingredients [1,2]. Different polymorphs of a chemical compound may exhibit different physicochemical properties such as solubility, melting point and density. Solvates and hydrates may impart different chemical and physical properties. Production of an unwanted hydrate will not satisfy the intended purpose or processing characteristics of the final product [2,3]. The use of seeding, structurally similar additives and different solvents have been widely adopted to induce polymorph formation. The rate of supersaturation generation usually plays a significant role in determining the polymorphic
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