Structural similarity and similarity in thermal properties of the polymorphs: melting and crystallization from the melt
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Structural similarity and similarity in thermal properties of the polymorphs: melting and crystallization from the melt of tolbutamide and chlorpropamide T. N. Drebushchak1,2 · V. A. Drebushchak2,3 Received: 31 July 2019 / Accepted: 19 February 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The polymorphism of tolbutamide and chlorpropamide under melting/crystallization was investigated with using DSC and in situ X-ray powder diffraction. The asymmetry in thermal transformations was revealed for both substances. Under heating, all tolbutamide/chlorpropamide polymorphs transform into high-temperature IH/ε polymorph, which melts at 128 °C. The crystal structures of the high-temperature polymorphs, IH and ε, are very similar to each other in the unit cell parameters and in the arrangement of z-shaped infinite hydrogen-bonded ribbons. Under cooling, other polymorph crystallizes from the melt, V for tolbutamide and β for chlorpropamide, thus making easy the obtaining of these metastable polymorphs. The polymorphs of tolbutamide and chlorpropamide crystallized from their melts turned out to be also very similar to each other in their structures (space group, unit cell parameters, arrangement of π-shaped infinite hydrogen-bonded ribbons). Solid– solid transformation V ⇒ II in tolbutamide was detected both in samples stored under room conditions and those melted in capillaries, thus providing new easy way for II tolbutamide crystallization. In generalizing our results, one can expect that if evident similarity is found among the polymorphs of similar molecules in their crystal structure, the similarity in their thermal properties can be also found, and vice versa. Keywords Chlorpropamide · DSC · Polymorphism · Tolbutamide · X-ray diffraction
Introduction The polymorphism of molecular crystals remains a hot topic for several decades, and the polymorphism of active pharmaceutical ingredients (API) is of utmost importance [1–8]. There are two reasons for this empirical scientific and technological activity. First, the uncontrolled polymorphism of the ingredients and products generates the technological Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10973-020-09475-4) contains supplementary material, which is available to authorized users. * T. N. Drebushchak [email protected] 1
Institute of Solid State Chemistry and Mechanochemistry, SB RAS, Kutateladze, 18, Novosibirsk, Russia 630128
2
Novosibirsk State University, Pirogova, 2, Novosibirsk, Russia 630090
3
V.S. Sobolev Institute of Geology and Mineralogy, SB RAS, Pr. Ak. Koptyuga, 3, Novosibirsk, Russia 630090
problems in the pharmaceutical industry. Second, newly discovered polymorphs can possess better characteristics as compared with old traditional ones. The lack of uniformity and similarity among the crystallization conditions of polymorphs and their mutual transformations does not allow choosing any optimal strategy for revealing all possible polymorphs. Any omitted possible way of crys
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