Thermal decomposition of the chloride and nitrate adducts of pentaerythritol tetranitrate in air at ambient pressure using a cross flow design tandem ion mobility spectrometry

Abstract

The thermal decomposition of the chloride adduct of pentaerythritol tetranitrate (PETN) has been studied with a new cross-flow sample introduction, dual shutter, ion mobility spectrometer. Chloride anions, produced in an ion source, react with PETN introduced by a nebulizer into a flow of heated gas orthogonal to the drift gas flow. This cross-flow procedure allows PETN introduction from solution at drift gas temperatures where the PETN∙Cl¯ intensity is sufficiently intense and stable to allow characterization of its thermal decomposition kinetics. Dual shutter operation allows the selection of PETN∙Cl¯ for observation of its thermal decomposition in the electrostatic drift field. In this adduct, Cl¯ displaces NO3¯ in an SN2 reaction with an activation energy of 80 ± 7 kJ mol-1 over the temperature range 145 °C–165 °C. At temperatures above 165 °C, decomposition occurs before ion selection, resulting in the release of NO3¯ and PETN∙NO3¯ becomes the sole adduct ion. PETN∙NO3¯ decomposes over the temperature range 175 °C–200 °C with an activation energy of 92 ± 8 kJ mol-1. Density functional calculations are used to interpret the results.