Solid state thermochemical decomposition of neat 1,3,5,5-tetranitrohexahydropyrimidine (DNNC) and its DNNC-d6 perdeuterio-labeled analogue

The solid state thermochemical decomposition kinetics and activation energy of neat 1,3,5,5-tetranitrohexahydropyrimidine (DNNC) and its DNNC-d6 deuterium labeled analogue were obtained by isothermal differential scanning calorimetry (IDSC) at 142, 145, and 148 °C. Global rate constants and kinetic deuterium isotope effect (KDIE) data from the exothermic decomposition process suggest that homolytic CH bond rupture, in one or both types of chemically non-equivalent methylene (CH2) groups of the DNNC ring structure, constitutes the exothermic rate-controlling step. A DNNC-d6 energy of activation equal to 115 kJ/mol was determined for this initial autocatalytic exothermic energy release from which a 106 kJ/mol activation energy was calculated for unlabeled DNNC. This exothermic autocatalytic decomposition process follows an extended endothermic induction period for DNNC which shows a higher 128 kJ/mol activation energy during which a catalytic initiating species may form by a rate-controlling step different from CH bond rupture.