Polymorphism of Sulfathiazole

A combined approach of differential scanning calorimetry and hot-stage microscopy with image analysis in the investigation of sulfathiazole polymorphism

“…The peak resulted from a change in the optical properties of the crystals, as shown by the difference in the appearance of the highlighted crystals between (a) and (b) in Figure 7. The phenomenon was indicated by fluctuation in the HSM light intensity profile between 159.3˚C to a temperature slightly above 168.5˚C and it was probably due to a transformation of form III to form I, since the transformation was reported to occur in a temperature range of 150 to 170˚C [28]. The second peak at a maximum of 197.2˚C on the DSC thermogram corresponds to a melting peak of form II, whilst the third peak at a maximum of 202.5˚C corresponds to a melting peak of form I.…”

“…Different polymorphs were generated using methods available in the literature [28,32] as shown in Table 1. It is known that there are some inconsistencies in the enumeration of the sulfathiazole polymorphs in the literature [24,35].…”

“…It is known that there are some inconsistencies in the enumeration of the sulfathiazole polymorphs in the literature [24,35]. In this work, the enumeration of the polymorphs follows the convention proposed by Anwar and Chan and their co-researchers [25,28]. In order to further clarify the identity of the polymorphs, the Cambridge Structural Database (CSD) reference codes are quoted in the bracket.…”

“…At present, it has five known polymorphs that are well characterised and clearly described in the literature [24][25][26]. Although the polymorphism of sulfathiazole has been extensively and repeatedly investigated by various researchers [27][28][29][30], it remains difficult to produce a pure polymorph; most of the time, the desired polymorph contains impurities from at least one other form [31][32][33][34].…”

Formation, Physical Stability, and Quantification of Process-Induced Disorder in Cryomilled Samples of a Model Polymorphic Drug

“…34 The physicochemical properties of the five forms have been described in detail. [35][36][37][38][39][40] Relative thermodynamic stabilities at 0 K are generally accepted to follow the order of the densities of the structures, i.e. III ≈ IV > II > I > V, with form I being metastable at room temperature.…”