Communication pubs.acs.org/OPRD
An Improved and Scalable Synthesis of Insensitive High Explosive 4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX) Mukesh B. Deshmukh, Amulrao U. Borse, Pramod P. Mahulikar, and Dipak S. Dalal* Department of Organic Chemistry, School of Chemical Sciences, North Maharashtra University, Umavi Nagar, Jalgaon, Maharashtra 425001, India S Supporting Information *
ABSTRACT: 4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX), a well-known nitramine category explosive, is much less sensitive to impact and friction stimuli as compared to the familiar explosives, RDX and HMX. TEX is currently produced on pilot plant scale and is being pursued as an insensitive explosive. Herein a newer, improved, efficient, and high yielding protocol is developed for the synthesis of TEX by using solid acidic silica sulfuric acid as an efficient and recyclable catalyst. Sequentially for process parameters optimization, a study was carried out with variation of catalyst loading, nitric acid, and mole ratio of reactants. The process scale-up is also achieved successfully.
1. INTRODUCTION Energetic materials play the significant role in weapon industries, aeronautics, and other high technological fields.1,2 In general, high performance of explosives is difficultly escorted by their high sensitivity toward external stimuli. Instead of resolving for a compromise between performance and sensitivity, efforts have been made to develop insensitive high explosives with appropriate consideration in context to the thermal stability of potential explosives.3 In other words, high performance, high thermal stability, and insensitivity toward external stimuli are the foremost goals for developing explosives and being vigorously pursued. The explosives with a wurtzitane ring system including nitramine functionalities have focused much interest in the synthesis and development of the most prominent and relatively new powerful explosives. The wellknown example of this class of explosives are 4,10-dinitro2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL20).4−11 A prominent resembling cage structure to CL-20 is 4,10dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo[5.5.0.0.5,903,11]dodecane, normally abbreviated as TEX (Figure 1). The four nitramine groups of CL-20 get replaced by ether bridges in TEX. Due to the existence of same isowurtzitane cage structure as present in CL-20, TEX preserves the very high density (ρ = 1.99 g/cm3) at ambient temperature. Nevertheless the absence of sterically necessitating nitramine groups diminishes its sensitivity significantly and establishes this, an interesting insensitive energetic material.12,13 Among the number of high energy materials endeavored, TEX determines a distinctive place with a combination of insensitivity, high performance, and © 2016 American Chemical Society
Figure 1. Molecular structures of (a) 4,10-dinitro-2,6,8,12-tetraoxa4,10-diazaisowurtzitane (TEX); (b) hexanitrohexaazaisowurtzitane (HNIW, CL-20); (c) 1,4-diformyl-2,3,5,6-tetrahydroxypiperazine (DFTHP).
density. It has excellent thermal stability as well as high detonation velocity (8665 m/s) and detonation pressure (370 kbar). This 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX), an illustrious caged nitramine, gaining interest in the field of high energy materials (HEMs).1,2,14 Owing to have combined properties of high energy, density, detonation pressure, and low sensitivity, the cage crystal molecules containing the nitro groups are important and widely used as energetic materials.15−21 In general, TEX is synthesized in a reaction by nitrolysis of hexa-substituted piperazine derivatives. It complies from the available literature that the 1,4-diformyl-2,3,5,6-tetrahydroxypiperazine (DFTHP) is most appropriate intermediate from which TEX is obtained in optimum yields. DFTHP is prepared in the base catalyzed condensation of aqueous glyoxal with formamide. The condensation is accomplished by dissolving formamide in 40% aqueous glyoxal solution in a molar ratio of 1:1 or 1:2, cooling to 0 °C, maintaining a pH of 8−10 by addition of a base. The earliest syntheses of DFTHP3,22−24 are performed by very long reaction times of 25−72 h, and the corresponding yields differ extensively from 28 to 81%. Received: March 3, 2016 Published: June 24, 2016 1363
DOI: 10.1021/acs.oprd.6b00066 Org. Process Res. Dev. 2016, 20, 1363−1369
Organic Process Research & Development
Communication
According to Gottlieb et al.,25 DFTHP was prepared by addition of a base (NaOH) to the glyoxal solution prior to introducing the formamide, such that the formamide get combined with a homogeneous basic solution. The rate of DFTHP formation was accelerated by maintaining the pH of the reaction mixture above 10. The temperature was maintained between 30−45 °C for 1 h to afford the yield of 80−85%. Jalovy et al.26 accounted a process for the preparation of DFTHP in which basic media was asserted by employing triethylamine and was added to a mixture of formamide and 40% aqueous glyoxal solution in a molar ratio of 1:1. The temperature was maintained between 40−45 °C for 2 h to afford the yield of 80%. As accounted in the literature, Ramakrishnan et al.27 reported the first method for the synthesis of TEX. In this method, a mixture of DFTHP with a glyoxal trimer was added to concentrated sulfuric acid, followed by dropwise addition of 100% nitric acid. The method afforded the product which was extremely contaminated with the unchanged glyoxal trimer as studied by the 1HNMR of the material formed which only contains less amount, i.e.,
