Crystal engineering of polymorph appearance: the case of sulphathiazole

A combined modeling and experimental strategy has been applied to the problem of solvents and reaction byproducts influence on the appearance of sulphathiazole polymorphs from solution. In terms of developing a robust process for isolating polymorphs, a purely structural approach is limited since it neglects the role kinetics have in determining the appearance of polymorph structures. Ostwald recognized this (in 1899) when detailing his Rule of Stages. As does the lack of polymorph selectivity and the phenomena of disappearing polymorphs further highlight the issue of kinetics. Using the Polymorph Appearance Strategy (Scheme 1) our current work (Faraday Trans. 94(8) (1998) 1035; J. Pharm. 172 (1998) 169; Chem. Br. (1999) 44) aims to address some of these issues.