This work reports on the crystal structures of two dioxane solvates of paracetamol that are true polymorphs. The high temperature phase is an orthorhombic form, space group Pbca, Z = 8, a = 12.6078(3) î.., b = 12.1129(2) î.., c = 13.4138(3) î.., V = 2048.52(7) î..3, (at 295 K) and the low temperature form is monoclinic, space group P21/c, Z = 4, a = 12.325(6) î.., b = 11.965(4) î.., c = 13.384(6) î.., = 92.01°, V = 1972.6(14)î..3 (at 123 K). The structures of these polymorphs are described as is the interrelationship between the two structures. In addition to the structural interrelationship, it is shown that the two forms undergo a reversible phase transformation. Desolvation of either form generates the stable monoclinic phase of paracetamol.
Vrcelj, R. M., Clark, N. I. B., Kennedy, A. R., Sheen, D. B., Shepherd, E. E. A., & Sherwood, J. N. (2003). Two new paracetamol / dioxane solvates - a system exhibiting a reversible solid state phase transformation. Journal of Pharmaceutical Sciences, 92(10), 2069-2073. https://doi.org/10.1002/jps.10477