Thermal properties of dipicolinic acid and dipicolinic acid sodium salt NaH(COO)2C5H3N•H2(COO)2C5H3N•3H2O

Abstract

Pyridine-2,6-dicarboxylic acid (dipicolinic acid) are actively studied by scientists. Dicarboxylic acid can be used as a special biomarker of anthrax. The crystal structure of NaH(COO)2C5H3N•H2(COO)2C5H3N•3H2O (1) was redetermined from single crystal. In the structure of the sodium salt of dipicolinic acid, sodium is the central atom having two molecules of dipicolinic acid and three molecules of water as ligands. The dipicolinic anion coordinate sodium cation by both oxygens and one nitrogen atom. A network of hydrogen bonds connects water and dipicolinic acid molecules. Hydrogen bonds take part in the formation of building blocks and arranging them into chains which, in their turn, make up layers. The sodium salt of dipicolinic acid as well as its precursor – dipicolinic acid were studied by IR spectroscopy and simultaneous thermal analysis. According to thermal analysis dipicolinic acid is anhydrous substance, that decompose on melting at 252 °C forming only gaseous products, presumably CO2 and pyridine. Opposite to that, thermolysis of its sodium salt follow much more complicated way. According to thermogram the 1 has first stage of three water molecules removal at 105 °C. The measured mass loss is very close to expected mass loss. Heat of dehydratation reaction is 151 kJ/mole. On a further heating the sodium salt of dipicolinic acid was melted at 256 °C with large mass loss. The nature of products at 268 and 315 °C is hard to state. EDX elemental analysis of black residue after 700 °C state brutto-formula of “NaNC5O2” – Na cyanate or carbonate in glassy carbon matrix.