On the melting temperatures of 3,6-diamino-9H-carbazole and 3,6-dinitro-9H-carbazole

This article records the diversely reported melting temperatures of 3,6-diamino-9H-carbazole (DAC) and 3,6-dinitro-9H-carbazole (DNC), and reports a reinvestigation on their melting phenomena, and associated specific observations. A rationalization of these reports has been attempted on the basis of IR spectroscopic, X-ray diffraction, thermal response, solubility behavior, and differential scanning calorimetric data on DAC and DNC. The data indicate that an exothermic inter-molecular deaminative self-condensation involving N₉H and NH₂ sets in prior to melting of DAC, which obscures the actual melting process. An extrapolated onset melting temperature of 241.0 °C and a peak temperature of 296.5 °C at zero heating rate have been assigned for DAC from DSC measurements. A possible structure of the polymeric self-condensation product is also presented. For DNC, a peak melting temperature of 296.5 ± 1.8 °C, but no onset melting temperature could be assigned.