Polymorphism of benzylthiouracil, an active pharmaceutical ingredient against hyperthyroidism

The crystal structures of dimorphic benzylthiouracil, a drug against hyperthyroidism, have been redetermined and the atom coordinates two independent molecules form I obtained for first time. dimorphism convincingly demonstrates conformational versatility benzylthiouracil molecule. It has established through calorimetric studies that low-temperature II transforms endothermically (?II?IH = 5.6(1.5) J g?1) into at 405.4(1.0) K. high-temperature melts 496.8(1.0) K (?I?LH 152.6(4.0) g?1). Crystallographic thermal expansion show is denser than I, leading to conclusion slope II-I equilibrium curve in pressure-temperature phase diagram positive. follows this corresponds case overall enantiotropic behaviour, which implies both solid phases possess their own stable region irrespective pressure. Moreover, clearly polymorph under ambient conditions.