Salt forms of Amides: protonation and polymorphism of Carbamazepine and Cytenamide

Buist, A.R., Kennedy, A.R., Shankland, K. ORCID: https://orcid.org/0000-0001-6566-0155, Shankland, N. and Spillman, M. (2013) Salt forms of Amides: protonation and polymorphism of Carbamazepine and Cytenamide. Crystal Growth & Design, 13 (11). pp. 5121-5127. ISSN 1528-7483 doi: 10.1021/cg401341y

Abstract/Summary

In situ generation of HCl or HBr in alcohol leads to O-protonation of the amide group of carbamazepine. Six salt phases have been produced using this method and their crystal structures determined by single crystal diffraction. A new polymorph of carbamazepine hydrochloride is described as are two polymorphs of carbamazepine hydrobromide. All are protonated at the amide O atom to give RC(OH)NH2 cations. Prolonged exposure to air results in addition of water to the solid salt forms. Such hydration of carbamazepine hydrobromide simply gives a monohydrated phase, but similar treatment of the equivalent hydrochloride results in partial loss of HCl and the transfer of the remaining proton from the amide group to water to give [carbamazepine][H3O]0.5[Cl]0.5·H2O. A similar hydronium chloride species is the only product isolated after reaction of the carbamazepine analogue cytenamide with HCl generated in methanol.