Origin of PYX thermal stability investigation with calorimetric and spectroscopic methods

Abstract

2,6-Bis(picrylamino)-3,5-dinitropyridine (PYX) is a highly thermostable explosive. The examination of its thermal decomposition was conducted, and kinetic parameters of the decomposition reaction were determined. Their values for the initial conversion degree (α = 0.02) and hermetic conditions are aEa = 261 ± 11 kJ mol−1, logA = 18.09. Volatile semi-products are formed during PYX thermal decomposition, which influence kinetic parameters of the decomposition reaction. That is why hermetic pans should be used for this analysis. The maximum safe temperature, i.e., T = 246 °C, was calculated on the basis of ADT24 method. Analysis of results obtained during spectroscopic analysis of PYX indicates that there are three main reasons of the compound stability. Strong hydrogen bonds between oxygen atoms in nitro groups and aromatic C–H and N–H protons are confirmed by analysis of IR and 1H NMR spectra. Large couplings in PYX carbon skeleton which stabilize the molecule are detected on the basis of FWHM of 13C NMR peaks. The stability of the analyzed compound is enhanced by the lack of carbon with sp3 hybridization.