Author: Kelly-Anne Stark
Stark, Kelly-Anne, 2022 Analysis of the Nitrate Ester Explosives- Xylitol Pentanitrate and Erythritol Tetranitrate, Flinders University, College of Science and Engineering
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Nitrate ester explosives, such as nitroglycerin (NG) and pentaerythritol tetranitrate (PETN), have been used by Defence for decades. Recently, there has been an increased interest in the nitrate esters erythritol tetranitrate (ETN) and xylitol pentanitrate (XPN) by terrorists, amateur experimentalists, and the defence industry. Despite this interest, XPN was not well characterised in the academic literature.
Crystalline XPN was prepared by slow evaporation and subjected to single crystal x-ray diffraction to obtain a crystal structure. XPN crystalises in the centrosymmetric monoclinic space group P21/n. The density of XPN calculated from the crystal structure is 1.852 g.cm-1 and the calculated heat of formation is -500.48 kJ.mol-1. These values were entered into the computer program Cheetah 7.0 to determine the theoretical explosive performance of XPN. The calculated detonation pressure and velocity of detonation were determined to be 32.6 GPa and 8.780 km.s-1, respectively, which are comparable to the theoretical performances of ETN, PETN and cyclotrimethylene trinitramine (RDX). Sensitiveness testing showed that XPN is a primary explosive that is significantly more sensitive to impact and friction than PETN.
Analytical characterisation data were also collected to provide forensic scientists, first responders and Defence with reference data for XPN. GC-MS, LC-MS, NMR, and vibrational spectroscopy data were obtained. Vibrational spectroscopy displayed characteristic vibrations that are expected for a nitrate ester, with XPN able to be differentiated from ETN. High field strength NMR was able to differentiate XPN from ETN, and benchtop NMR, while unable to resolve all peaks, was also able to differentiate XPN from ETN, PETN and NG. Using direct-MS, diagnostic chloride and nitrate adduct ions were measured for XPN and UPLC was successful in separating XPN from ETN, PETN and NG. Cold-EI GC-MS provided spectra that were unique to each nitrate ester explosive, however, the results were inconsistent due to the likely thermal degradation of the molecules. As such, UPLC is recommended for the identification of XPN over GC-MS, however, for in-field detection, Raman and IR spectroscopy are desirable.
The chemical degradation of rigorously purified ETN was investigated at 60, 80 and 100 °C. ETN was found to be stable at 60 °C for up to 28 days, whereas no ETN was detected at 28 days at 80 °C and no ETN was detected at 14 days at 100 °C. The presence of acid vapour increased the rate of degradation with no observable ETN at 14, 7 and 2 days at 60, 80 and 100 °C, respectively, whereas at 40 °C, ETN exposed to acid vapour was stable for the 28 day trial period. Stabilisation studies involving 0.2 % w/w of DPA or EC were conducted at 80 and 100 °C. There was no significant difference between the stabilised and unstabilised ETN samples at these temperatures.
Keywords: Xylitol pentanitrate, Erythritol tetranitrate, Analysis, Mass spectrometry, Raman, NMR, Infrared, Sensitivity, Gas chromatography, Liquid chromatography, Nitrate esters, Explosives
Subject: Chemistry thesis
Thesis type: Doctor of Philosophy
Completed: 2022
School: College of Science and Engineering
Supervisor: Professor Paul Kirkbride