Title: 2,4,6-Trinitrotoluene - A Useful Starting Compound in the Synthesis of Modern Energetic Compounds Authors: Mateusz Szala and Jesse J. Sabatini This manuscript has been accepted after peer review and appears as an Accepted Article online prior to editing, proofing, and formal publication of the final Version of Record (VoR). This work is currently citable by using the Digital Object Identifier (DOI) given below. The VoR will be published online in Early View as soon as possible and may be different to this Accepted Article as a result of editing. Readers should obtain the VoR from the journal website shown below when it is published to ensure accuracy of information. The authors are responsible for the content of this Accepted Article. To be cited as: Z. anorg. allg. Chem. 10.1002/zaac.201700414 Link to VoR: http://dx.doi.org/10.1002/zaac.201700414 Zeitschrift für anorganische und allgemeine Chemie 10.1002/zaac.201700414 REVIEW mechanical stimuli. The synthesis of a new energetic compound 2,4,6-Trinitrotoluene – A Useful with reduced sensitivity (e.g. NTO) requires the purchase or synthesis of precursors that are not energetic, and that have not been used in the synthesis of explosives. The application of Starting Compound In the readily available TNT to the synthesis of other energetic compounds–especially in explosives manufacturing plants–is a Synthesis of Modern Energetic very attractive solution mentioned in scientific literature. The aim of this paper is to examine the possibility of using TNT Compounds to produce new attractive explosive mixtures with desired properties that do not share TNT’s major downsides as a Mateusz Szala*[a], Jesse J. Sabatini [b] standalone ingredient. The most frequently mentioned disadvantages of TNT include its relatively high vapor pressure[6], Abstract: This review presents a history, properties, and its susceptibility to photolytic degradation[7] and its susceptibility environmental fate of 2,4,6-trinitrotoluene (TNT). Industrial to reactions in an alkaline environment[8]. methods of TNT production are discussed, as are several energetic derivatives of TNT. The performances and 1.1. Synthesis of TNT applications of these TNT derivatives are also described. Since the first synthesis of TNT by nitration of toluene by Wilbrandt in 1863[1], many methods of it synthesis from a variety of substrates were described. Tiemann synthesized TNT by 1. Introduction nitration of 2-nitrotoluene.[9] Jackson and Phinney obtained TNT by thermal decarboxylation of 2,4,6-trinitrophenyl acetic acid.[10] 2,4,6-trinitrotoluene (TNT) was first produced by Wilbrandt in Alfthan produced trinitrotoluene during nitration of 1-isopropyl-4- 1863[1], though its explosive properties were not immediately methylbenzene with mixed acid.[11] TNT was also obtained recognized due to its low sensitivity to mechanical stimuli and a through the nitration of dinitroanisole (DNAN) in 1935 by James.[12] 4-nitrotoluene was applied for synthesis of the title relatively high critical diameter. It can be assumed that TNT was [13] [2] compound by Titow. TNT was also obtained by methylation of first used for military purposes around the year 1900 , while 1,3,5-trinitrobenzene.[14] Technologists have worked on waste 2,4,6-trinitrophenol (picric acid) was still used on a massive minimalisation during the TNT synthesis, and some papers scale as a secondary explosive during WWI. Although picric acid report the concern of “red water” problem. Elimination of red was discovered approximately 100 years before TNT[3], its water formation from TNT manufacture, and improvements of widespread use largely ended with the close of WWI. TNT is still the regioselectivity in the nitration of toluene, have been [15] one of the most common secondary explosives that has been in published but efforts are still ongoing to address these shortcomings. nearly continuous use for 155 years. TNT was initially used in its Manuscript pure form, though it is now more popularly used with RDX to 1.2. Technology of TNT form Composition B, and as a component of melt-cast explosive compositions with a reduced sensitivity to unintentional initiation. Production of TNT on an industrial scale is carried out in The other ingredients of these latter kinds of compositions are periodic mode by stepwise introduction of nitro groups to toluene. also low sensitivity explosives such as 3-nitro-1,2,4-triazolone In almost all known industrial methods, the process is realized in three steps[16-19], though methods have also involved two step (NTO) or 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)[4]. Due to processes.[20] In each subsequent nitration step, the the mass production of TNT in many countries, its price is concentration of nitric and sulphuric acid increase, while the [5] relatively low ($5.50 per kg ). The low-cost and high purity of concentration of water decreases. Introduction of each nitro commercial TNT explains why this compound can be considered group onto the toluene ring requires higher temperatures in to be an attractive substrate for the synthesis of other explosives. excess of 100 oC. The available details of TNT production on the Currently, the use of secondary explosives for military industrial scale are presented in Table 1. purposes must meet increasingly stringent requirements Continuous methods of TNT synthesis have been developed in Great Britain[21], Germany[22], Sweden[23] and Sweden- concerning high heat resistance and low sensitivity to Norway.[24, 25] These methods consisted of the nitrator-separator system. Depending on plant conception, the installation can comprise up to eighteen units. Continuous methods applied for explosive synthesis are safer because reactor capacities are *[a] Dr. M. Szala smaller. At any moment during production, there is the risk of Department of Explosives hazardous material accumulation. The specific details of Military University of Technology Accepted contemporary continuous TNT plants are unpublished at this 2 Kaliskiego str, 00-908 Warsaw, Poland E-mail: [email protected] time. Nonetheless, for the aforementioned methods described to [b] Dr. Jesse J. Sabatini prepare TNT, the crude product is purified to remove nitric and U.S. Army Research Laboratory sulphuric acid, TNT non-symmetric isomers, and other side Energetics Technology Branch products such as tetranitromethane, and trinitrobenzene. Aberdeen Proving Ground, MD 21005 Removal of the by-products are realized by mixing the solid or molten crude TNT product with water, followed by filtration. The This article is protected by copyright. All rights reserved. Zeitschrift für anorganische und allgemeine Chemie 10.1002/zaac.201700414 REVIEW filtered solid then undergoes sulphitation to yield flakes of TNT, which are dried to obtain the pure product.[19, 22] Table 1. Conditions of TNT synthesis in industrial scale. Concentration, % Temperature, Method Step °C HNO3 H2SO4 H2O I 28 56 16 60 French, II 32 61 7 90 1925[16] III 49 49 2 105 British, I na na na 50 1914- II na na na na [17] 1918 III 79.5 17.8 2.7 66-100 17- I 27-28 54-55 40-50 19 USSR, II 23 67 10 80-105 1940[18] 17.5- 81.5- III - 115 18.5 82.5 I 28 56 16 34-40 German, II na na na 60-65 [19] 1945 6 III 24 70 96 SO3 Italian, I 28 60 12 75 Scheme 2. Representative examples of nucleophilic substitutions of TNT 1934[20] II 24 70 6 96 1.3. General reactivity of TNT 2. Synthesis of explosives from 2,4,6- trinitrotoluene Since the reactivity of TNT has been the subject of numerous theoretical and experimental research efforts,[26, 27] the reactivity of TNT will not be discussed further if the product of the reaction is not an explosive or does not have potentially useful properties. 2.1. 1,3,5-trinitrobenzene This review intentionally omits all compounds that are commonly known universal substrates in synthesis (e.g. picryl chloride). The oldest explosive synthesized from TNT was symmetrical The chemical reaction on each functional group of TNT leads to trinitrobenzene (TNB), first described in 1883 by Claus and the formation of compounds with a higher reaction potential than Becker.[33] Since then, many methods of TNB synthesis have pure TNT. For example, oxidation of the methyl functional group been identified, although these methods are based on the Manuscript of TNT (1) can lead to 2,4,6-trinitrobenzaldehyde (2) or 2,4,6- oxidation of the methyl group to the carboxyl group to afford 10, trinitrobenzoic acid (3), whereas reduction of TNT is possible, followed by thermal decarboxylation (Scheme 3).[34-37] Another thus converting the nitro groups to the amino derivatives 4 and 5 method for the preparation of TNB is a stepwise nitration of (Scheme 1). Protons at the 3- and 5-position of TNT may benzene, although this method is not used in practice due to the undergo vicarious nucleophilic substitution (VNS) to give 6, as harsh conditions required in successive nitration reactions. The shown in Scheme 2.[28] The nitro group may be substituted, for detonation parameters of TNB are slightly higher than those of instance, with the sulphide group to give 7.[29, 30] Use of Bronsted TNT. At a density of 1.60 g/cm3 the detonation velocity of TNB is bases allows for the α-deprotonation of the methyl group, which 7.3 km/s.[19] Unfortunately, the melting point of TNB is 122 ºC can then undergo nucleophilic substitution reactions to give 8.[31] and is thus too high to prepare standalone melt cast explosive The methyl group can also react with aromatic nitroso- compositions based on this temperature. compounds to yield imine-based materials, such as 9.[32] Scheme 3. Synthesis of 1,3,5-trinitrobenzene from TNT.