Vapor pressures, mass spectra and thermal decomposition processes of bis(2,2-dintropropyl)acetat (BDNPA) and bis(2,2-dinitropropyl)formal (BDNPF)

Simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) and Fourier-transform ion cyclotron resonance (FTICR) instruments have been used to measure the mass spectra, measure vapor pressures and evaluate the thermal decomposition mechanism of bis(2,2-dinitropropyl)acetal (BDNPA) and bis(2,2-dinitropropyl)formal (BDNPF). The high mass accuracy FTICR mass spectra provide the chemical formulas of the ion fragments formed in the mass spectra of BDNPA, BDNPF and their decomposition products, and provide a basis for predicting possible structures of the ion fragments. The heat of vaporization (Delta H-vap) and vapor pressure at 25 degrees C are 93.01 +/- 0.38kJ/mol and 1.4532+0.40/-0.27mPa for BDNPA, and 84.77 +/- 0.88kJ/mol and 2.20+1.87/-1.07mPa for BDNPE STMBMS data support a nitro-nitrite (-NO2 -> -O-NO) rearrangement mechanism for both compounds. Upon rearrangement, both NO and NO2 are cleaved from the structure, thus producing a ketone radical. The nitro-nitrite rearrangement begins to occur at appreciable rates between 160 and 180 degrees C. Additional decomposition products include amines, imines and amides, as well as CO2 and H2O at higher temperatures. STMBMS mass loss data suggest the formation of a residue during the decomposition of BDNPA and BDNPE The major difference between the decomposition of the two compounds is the slower reaction rate of BDNPE We postulate that the less sterically hindered formal carbon of BDNPF subjects it to interactions with an intermediate, thus forming a complex and delaying its release. Methods to elucidate complex thermal decomposition mechanisms from STMBMS data are illustrated.