Transitions among five polymorphs of chlorpropamide near the melting point

Five polymorphs of chlorpropamide (alpha, beta, gamma, delta, and epsilon) were investigated near the melting point by using DSC. Structure of samples was tested by X-ray powder diffraction. Four first polymorphs were found to transform into epsilon-polymorph, which melts at T-m = 128 degrees C, Delta H-m= 24 kJ mol(-1). Enthalpy of the polymorph transitions ranges from +3 kJ mol(-1) for alpha -> epsilon to -0.8 kJ mol(-1) for beta -> epsilon. Structure of three first polymorphs was published elsewhere, and the structure of delta-polymorph is published for the first time. XRPD patterns for all polymorphs are reported, together with the atomic coordinates for the delta-polymorph.