New Findings on the Crystal Polymorphism of Imepitoin

Scientific and industrial reasons dictate the study of the solid stateof imepitoin, a highly safe and tolerable anticonvulsant drug used inthe therapy of epileptic dogs that was approved in the Europe Union in2013. Our investigations allowed us to discover the existence of a newpolymorph of imepitoin, which finds itself in a monotropic relationshipwith the crystalline form (polymorph I) already known and present on themarket. This form (polymorph II), obtained by crystallization fromxylene, remains metastable under ambient conditions for at least 1 year.Both solid forms were characterized by thermal (DSC and TGA),spectroscopic (FT-IR and Raman), microscopic (SEM and HSM), anddiffractometric techniques. The thermodynamic relationship between thetwo polymorphs (monotropic) is such that it is not possible to study themelting of polymorph II, not even by adopting appropriate experimentalstrategies. Our measurements highlighted that the melting peak ofimepitoin actually also includes an onset of melt decomposition. The abinitio structure solution, obtained from synchrotron X-ray powderdiffraction data collected at room temperature, allowed us to determinethe crystal structure of the new polymorph (II). It crystallizes in themonoclinic crystal structure, P21/c space group (#14), with a =14.8687(6) & Aring;, b = 7.2434(2) & Aring;, c = 12.5592(4) & Aring;,beta = 107.5586(8)degrees, V = 1289.61(8) & Aring;3, and Z = 4.