Thermal stability of 3,4,5-trinitropyrazole and its ammonium salt

The thermal decomposition of trinitropyrazole (I) and its ammonium salt proceeds with a very strong self-acceleration, caused mainly by the catalytic action of the condensed products. The first-order rate constant for the initial stage k (1) describes the decomposition to a depth of conversion of 0.5% and is characterized by the following kinetic parameters E (kJ/mol) and log(A, s(-1)): 131.8 and 9.60 for the liquid phase and 116.0 and 8.57 for the solid state. The rate constant k (1) is smaller if the reaction occurs in nonpolar solvents and if I is methylated at position 1. All these data are interpreted in the framework of a mechanism according to which the reaction involves the oxidation by a nitro group of a neighboring carbon atom and proceeds through a highly polar cyclic transition state. Evaluation of the thermal stability of I is conducted using the method of a reference series composed of well-known regular HEs, which for the first time was implemented in terms of k (1). In the temperature range 20-80A degrees C, the stability of trinitropyrazole is close to that of nitroglycerin. Trinitropyrazole ammonium salt is severalfold more stable than trinitropyrazole itself.