Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—VIII

Five polymorphic organic compounds which exhibited from three to seven modifications were examined. Because of enantiotropy, the commercial forms of three of the compounds did not consist of the modification with the highest melting point: These were 4-hydroxy-3,5-dimethoxybenzoic acid (4 modifications), 3-pyridylacetic acid (4 modifications) and 2,4,5-triaminopyrimidine (4 modifications). In contrast, 2-amino-2-cyanoacetamide (3 modifications) and [([(4-methylphenyl)sulphonyl]oxy)imino]propanedinitrile (7 modifications) were present in the highest melting form in the commercial products. A further 32 compounds (most of which had only two modifications) were examined and are reported without detailed results; six of them were enantiotropic.