Trinitrotoluene
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| Surname | Trinitrotoluene | |||||||||||||||||||||
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| Molecular formula | C 7 H 5 N 3 O 6 | |||||||||||||||||||||
| Brief description |
colorless to yellowish rhombohedral crystals or needles |
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| properties | ||||||||||||||||||||||
| Molar mass | 227.13 g mol −1 | |||||||||||||||||||||
| Physical state |
firmly |
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| density |
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| Melting point |
80.1 ° C |
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| boiling point |
Decomposition from 160 ° C |
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| solubility |
very bad in water (140 mg l −1 , 20 ° C) |
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| MAK |
Switzerland: 0.01 ml m −3 or 0.1 mg m −3 |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||||||||||||||
Trinitrotoluene ( TNT ), 2-methyl-1,3,5-trinitrobenzene according to the IUPAC nomenclature, is an explosive . The structural formula of the compound shows a benzene ring with a methyl group (-CH 3 ) and three ortho or para constant nitro group (-NO 2 ) as a substituent . The compound is formed by nitration of toluene by means of nitrating acid , a mixture of nitric and sulfuric acid .
First synthesized in 1863 by Julius Wilbrand (1839–1906) , the large-scale production of TNT began in 1901 in the German Empire . The TNT equivalent serves as a measure of the energy released in an explosion .
history
After the first presentation in 1863, the development of the synthesis by P. Hepp 1880 and the discovery of TNT as a suitable explosive by Karl Häussermann in 1889 the successful dynamite AG , formerly Alfred Nobel & Co. (DAG) first in 1901 at the factory Schlebusch large scale Production. Due to the military's need for TNT as a filling for grenades (first in the German Reich from 1902), numerous factories quickly emerged. At that time, however, the raw material toluene could only be produced in limited quantities, since one was dependent on the extraction of coal tar , a mixture of thousands of individual substances that is obtained during coke extraction . From today's perspective, however, this method is no longer economical because the proportion of toluene in coal tar is relatively low.
During the Second World War , TNT was again increasingly produced. So-called “sleep factories”, including the Tanne plant near Clausthal-Zellerfeld , were built before the war began, mostly with two systems, so that explosives could continue to be produced in the event of destruction or damage . The quantities produced had increased dramatically. The amount of TNT produced in the German Reich amounted to 18,000 tons per month, during the war a total of approx. 800,000 tons were produced. This increase was possible because the necessary starting material could now also be obtained from crude oil . In a two-stage process, the “German process”, the toluene was initially simply nitrated. The resulting mononitrotoluene (MNT) was purified from undesired by-products and nitrated again, whereby the desired crude TNT was produced via 2,4-dinitrotoluene (DNT). After washing and drying several times, it could be granulated and then processed. Security measures were neglected in order to ensure supplies at the front. Since TNT was considered non-toxic for a long time, the waste was only neutralized and allowed to flow into natural waters, where it was partly deposited in the form of sludge and damaged the environment as old armaments. Regarding the unknown toxicity , it is known that between 1911 and 1915, 279 munitions workers died from ingesting small amounts through the skin and respiratory tract. The two largest TNT production facilities in Germany during the Second World War were the Allendorf and Hessisch Lichtenau explosives factories .
Extraction and presentation
For the production of TNT, toluene can be nitrated with nitrating acid , a mixture of sulfuric and nitric acid. The former protonated due to their lower pK s -value (higher acid strength), the nitric acid. As a result, significantly more reactive electrophilic NO 2 + ions (also nitryl cation or nitronium ion ) are formed. The NO 2 + ions are the reactive molecules in the reaction mixture that enable electrophilic substitution on the aromatic.
The formation of trinitrotoluene takes place in stages. First, the mononitration of the toluene takes place, which takes place in the ortho or para position with 96% probability due to the inductive effect of the methyl group . The nitrotoluene now formed can be further nitrated by the strong electrophile NO 2 + until the maximum number of nitro groups is three in the molecule and trinitrotoluene is thus formed.
properties
Physical Properties
Trinitrotoluene can appear in two different modifications ( polymorphism ), which can be distinguished by their color. The stable, monoclinic form forms pale yellow, needle-shaped crystals that melt at 80.4 ° C. A metastable, orthorhombic shape forms orange crystals. When heated to 70 ° C, it converts to the monoclinic form. The compound is very sparingly soluble in water, moderately soluble in methanol (1%) and ethanol (3%), but readily soluble in ether , ethyl acetate (47%), acetone , benzene , toluene (55%) and pyridine . With its low melting point of 80.4 ° C, TNT can be melted in water vapor and poured into molds. The compound can be distilled in vacuo. According to Antoine, the vapor pressure function results according to log 10 (P) = A− (B / (T + C)) (P in bar, T in K) with A = 5.37280, B = 3209.208 and C = −24.437 in the temperature range from 503 K to 523 K. The connection can withstand continuous heating up to 140 ° C. Gas evolution begins above 160 ° C. From 240 ° C a deflagration occurs with strong soot development. TNT is toxic and can cause allergic reactions on contact with the skin. It gives the skin a bright yellow-orange color.
Explosion parameters
TNT is one of the best known, chemically homogeneous, i.e. consisting of only one component, explosives. Like all homogeneous explosives, TNT owes its explosiveness to internal chemical instability and the formation of much more stable, gaseous products during the explosion. The fuel required for the explosion (the reducing agent in the form of the carbon atoms) and the oxidizer (the oxidizing agent in the form of the nitro groups) are contained in the TNT molecule itself. Chemically speaking in the explosion of an intramolecular very fast and exothermic running redox reaction caused by a detonation starts. The resulting more stable and low-energy products are z. B. nitrogen , carbon dioxide, methane, carbon monoxide and hydrogen cyanide . The latter products can arise due to the insufficient oxygen content in the molecule.
If a sufficient amount of the substance was ignited at the beginning, the released energy maintains the reaction and the entire amount of substance reacts. The reaction takes place in a very fast, narrow reaction zone through which the substance runs like a wave . In the case of powerful explosives, the speed of this reaction zone reaches several thousand meters per second, i.e. it exceeds the internal speed of sound. The energy released and the formation of gases as reaction products lead to an extremely steep rise in pressure and temperature, which explains the effectiveness of explosive explosives.
Important safety parameters for the explosion behavior are:
- Heat of explosion : 3725 kJ kg −1 (H 2 O (l)) , 3612 kJ kg −1 (H 2 O (g))
- Normal gas volume : 975 l kg −1
- Detonation speed : 6900 m / s (density: 1.6 g / cm 3 )
- Lead block bulge : 30 cm 3 / g
- Deflagration point : 300 ° C
- Impact sensitivity : 15 Nm (1.5 kpm)
- Sensitivity to friction : no reaction up to 353 N (36 kp)
- Limit diameter in the steel sleeve test : 5 mm
use
TNT is still an important military explosive today. It is used militarily and commercially in mixtures as a safety explosive , which can only be detonated by initial ignition (for example by a detonator ). Cast TNT needed for safe ignition even a booster charge , called the booster . TNT alone will not explode in fire or heat; it just burns down. Due to its high production costs (around 20 times the commercial explosives), its main use is in the military sector (explosives especially in grenades , bombs and mines ).
The energy content in SI units is :
- 1 kg TNT ≙ 4.6 megajoules (4.6 10 6 joules). For comparison: firewood has a 3 to 4 times higher energy value.
The unit TNT equivalent used in connection with nuclear weapon explosions is based on the obsolete unit calorie and is defined by
- 1 kT (kilo ton TNT) ≙ 10 12 cal = 4.184 × 10 12 J.
- The units megaton and gigaton are defined analogously. The capitalization (symbol T ) is intended to prevent confusion with the mass unit ton (symbol lowercase t ).
Chemically related explosives
Individual evidence
- ↑ a b c d e f g h i Entry for CAS no. 118-96-7 in the GESTIS substance database of the IFA , accessed on December 23, 2013(JavaScript required) .
- ↑ a b J. Köhler, R. Meyer, A. Homburg: Explosivstoffe. Tenth, completely revised edition. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2008, ISBN 978-3-527-32009-7 .
- ↑ Entry on 2,4,6-trinitrotoluene in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- ↑ Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 118-96-7 or trinitrotoluene ), accessed on November 2, 2015.
- ^ J. Wilbrand: Note on trinitrotoluene. In: Annals of Chemistry and Pharmacy . Volume 128, 1863, pp. 178–179 ( limited preview in Google Book Search).
- ↑ a b c d e f g H. G. Gallagher, JN Sherwood: Polymorphism, twinning and morphology of crystals of 2,4,6-trinitrotoluene grown from solution. In: J. Chem. Soc., Faraday Trans. 92 (1996), pp. 2107-2116 ( doi : 10.1039 / FT9969202107 ).
- ↑ a b c R.M. Vrcelj, JN Sherwood, AR Kennedy, HG Gallagher, T. Gelbrich: Polymorphism in 2-4-6 Trinitrotoluene. In: Crystal Growth & Design 3 (6) (2003), pp. 1027-1032 ( doi : 10.1021 / cg0340704 ).
- ↑ Yu Maksimov: Steam Pressures of Nitroaromatic Compounds at Different Temperatures. In: Zh. Fiz. Khim. 42, pp. 2921-2925 (1968).
literature
- Richard Escales: Nitrogen Explosives. Survival Press 1915, Reprint 2003, ISBN 3-8330-0114-3 .
- Hans-Jürgen Quadbeck-Seeger among other things: chemistry records. People, markets, molecules. 2nd Edition. Wiley-VCH, Weinheim 1999, ISBN 3-527-29870-3 .
- ME Walsh, TF Jenkins, PS Schnitker, JW Elwell, MH Stutz: Evaluation of SW846 Method 8330 for characterization of sites contaminated with residues of high explosives. CRREL Report 93-5, US Army Cold Regions Research and Engineering Laboratory, Hanover, NH.
