An ion mobility and theoretical study of the thermal decomposition of the adduct formed between ethylene glycol dinitrate and chloride

Abstract

An ion mobility spectrometer has been used to isolate and study the decomposition of the adduct formed between the chloride ion and ethylene glycol dinitrate (EGDN). Two shutter operation allows isolation of the adduct and observation of its decomposition to 2-chloroethyl nitrate (ClEN)+NO3− as it travels along the spectrometer drift region. The reaction is the expulsion of one of the NO3 groups of EGDN by Cl. The rate constants for the decomposition reaction measured over the temperature range 79–97°C give the Arrhenius parameters Ea=59.2±1.1kJmol−1 and ln A(s−1)=24.0±0.5. Ab initio calculations show that the reaction is a gas-phase SN2 reaction with a penta-coordinated carbon in the transition state between two stable intermediate ion-molecule complexes EGDN·Cl− and ClEN·NO3−. Calculation shows that NO2− reacts with EGDN in an analogous manner to Cl−, replacing one of the nitrate groups to form ethylene nitrate nitrite (ENN)+NO3−. The implication of these results for the ion chemistry of nitrate esters in the presence and absence of dopants over a range of temperatures is discussed.