TNT was first synthesized in 1863 by GermanchemistJulius Wilbrand[7] and was originally used as a yellow dye. Its potential as an explosive was not recognized for three decades, mainly because it was so much less sensitive than other explosives known at the time. Its explosive properties were discovered in 1891 by another German chemist, Carl Häussermann.[8] TNT can be safely poured when liquid into shell cases, and is so insensitive that in 1910 it was exempted from the UK'sExplosives Act 1875 and was not considered an explosive for the purposes of manufacture and storage.[9]
The German armed forces adopted it as a filling forartilleryshells in 1902. TNT-filledarmour-piercing shells would explode after they had penetrated the armour of Britishcapital ships, whereas the BritishLyddite-filled shells tended to explode upon striking armour, thus expending much of their energy outside the ship.[9] The British started replacing Lyddite with TNT in 1907.[10]
TheUnited States Navy continued fillingarmour-piercing shells withexplosive D after some other nations had switched to TNT, but began fillingnaval mines,bombs,depth charges, andtorpedo warheads with burster charges of crude grade B TNT with the color of brown sugar and requiring anexplosive booster charge of granular crystallized grade A TNT for detonation. High-explosive shells were filled with grade A TNT, which became preferred for other uses as industrial chemical capacity became available for removingxylene and similarhydrocarbons from the toluene feedstock and othernitrotolueneisomer byproducts from the nitrating reactions.[11]
Chunks of explosives-grade TNT
Trinitrotoluene melting at 81 °C (178 °F)
M795 artillery shells withfuzes fitted, labelled to indicate a filling of TNT
M107 artillery shells. All are labelled to indicate a filling of "Comp B" (mixture of TNT andRDX) and havefuzes fitted
A group ofM120 Rak mortar shells. The dark green shells on the left are stencilled to indicate a filling of TNT
Analysis of TNT production by branch of the German armed forces between 1941 and the first quarter of 1944, shown in thousands of tons per month
Detonation of the 500-ton TNT explosive charge as part ofOperation Sailor Hat in 1965. The passing blast-wave left a white water surface behind and a whitecondensation cloud is visible overhead.
In industry, TNT is produced in a three-step process. First,toluene isnitrated with a mixture ofsulfuric andnitric acid to producemononitrotoluene (MNT). The MNT is separated and then renitrated todinitrotoluene (DNT). In the final step, the DNT is nitrated to trinitrotoluene (TNT) using ananhydrous mixture of nitric acid andfuming sulfuric acid (oleum). Nitric acid is consumed by the manufacturing process, but the diluted sulfuric acid can be reconcentrated and reused.
After nitration, TNT can either be purified by crystallization from an organic solvent or stabilized by a process called sulfitation, where the crude TNT is treated with aqueoussodium sulfite solution to remove less stable isomers of TNT and other undesired reaction products. The rinse water from sulfitation is known asred water and is a significant pollutant and waste product of TNT manufacture.[12]
Control ofnitrogen oxides in feed nitric acid is very important because freenitrogen dioxide can result in oxidation of the methyl group of toluene. This reaction is highlyexothermic and carries with it the risk of a runaway reaction leading to an explosion.[citation needed]
In the laboratory, 2,4,6-trinitrotoluene is produced by a two-step process. A nitrating mixture of concentrated nitric and sulfuric acids is used to nitrate toluene to a mixture of mono- and di-nitrotoluene isomers, with careful cooling to maintain temperature. The nitrated toluenes are then separated, washed with dilutesodium bicarbonate to remove oxides of nitrogen, and then carefully nitrated with a mixture offuming nitric acid and sulfuric acid.[citation needed]
X-ray crystallography determined that each of the three planar nitro groups is substantially rotated out of the plane of the benzene ring.[13]
TNT is one of the most commonly used explosives for military, industrial, and mining applications. TNT has been used in oil and gasfracking (hydraulic fracturing) in shale formations. The technique involves displacing and detonatingnitroglycerin in hydraulically induced fractures followed by wellbore shots using pelletized TNT.[14]
TNT is valued partly because of its insensitivity to shock and friction, with reduced risk of accidentaldetonation compared to more sensitive explosives such asnitroglycerin. TNT melts at 80 °C (176 °F), far below the temperature at which it will spontaneously detonate, allowing it to be poured or safely combined with other explosives. TNT neither absorbs nor dissolves in water, which allows it to be used effectively in wet environments. To detonate, TNT must be triggered by a pressure wave from a starter explosive, called anexplosive booster.[15]
Although blocks of TNT are available in various sizes (e.g., 250 g, 500 g, 1,000 g), it is more commonly encountered insynergistic explosive blends comprising a variable percentage of TNT plus other ingredients. Examples of explosive blends containing TNT include:
Upondetonation, TNT undergoes a decomposition equivalent to the reaction
2 C7H5N3O6 → 3 N2 + 5 H2O + 12 CO + 2 C
plus some of the reactions
H2 + CO → H2O + C
and
2 CO → CO2 + C.
The reaction isexothermic but has a highactivation energy in the gas phase (~62 kcal/mol). The condensed phases (solid or liquid) show markedly lower activation energies of roughly 35 kcal/mol due to unique bimolecular decomposition routes at elevated densities.[23] Because of the production ofcarbon, TNT explosions have a sooty appearance. Because TNT has an excess of carbon, explosive mixtures with oxygen-rich compounds can yield more energy per kilogram than TNT alone. During the 20th centuryamatol, a mixture of TNT withammonium nitrate, was a widely used military explosive.[24]
TNT can be detonated with a high velocity initiator or by efficient concussion.[25] For many years, TNT used to be the reference point for the Figure of Insensitivity. TNT had a rating of exactly 100 on the "F of I" scale. The reference has since been changed to a more sensitive explosive calledRDX, which has an F of I rating of 80.[26]
The energy density of TNT is used as a reference point for many other explosives, including nuclear weapons, as their energy content is measured in equivalent tonnes (metric tons, t) of TNT. The energy used byNIST to define the equivalent is 4.184GJ/t or exactly 1kcal/g.[27]
For safety assessments, it has been stated that the detonation of TNT, depending on circumstances, can release 2.673–6.702 GJ/t.[28]
Theheat of combustion however is 14.5 GJ/t (14.5 MJ/kg or 4.027 kWh/kg), which requires that the carbon in TNT fully react with atmospheric oxygen, which does not occur in the initial event.[29]
For comparison,gunpowder contains 3 MJ/kg,dynamite contains 7.5 MJ/kg, andgasoline contains 47.2 MJ/kg (though gasoline requires anoxidant, so an optimized gasoline and O2 mixture contains 10.4 MJ/kg).[citation needed]
TNT is poisonous, and skin contact can cause skin irritation, causing the skin to turn a bright yellow-orange color. During theFirst World War, female munition workers who handled the chemical found that their skin turned bright yellow, which resulted in their acquiring the nickname "canary girls" or simply "canaries".[31]
People exposed to TNT over a prolonged period tend to experienceanemia and abnormalliver functions.Blood and liver effects,spleen enlargement and other harmful effects on theimmune system have also been found in animals that ingested or breathed trinitrotoluene. There is evidence that TNT adversely affects malefertility.[32] TNT is listed as a possible humancarcinogen, with carcinogenic effects demonstrated in animal experiments with rats, although effects upon humans so far amount to none (according to IRIS of March 15, 2000).[33] Consumption of TNT produces redurine through the presence of breakdown products and not blood as sometimes believed.[34]
Some military testing grounds are contaminated withwastewater from munitions programs, including contamination of surface andsubsurface waters which may be colored pink because of the presence of TNT. Such contamination, called "pink water", may be difficult and expensive toremedy.[citation needed]
TNT is prone toexudation ofdinitrotoluenes and other isomers of trinitrotoluene whenprojectiles containing TNT are stored at higher temperatures in warmer climates. Exudation of impurities leads to formation of pores and cracks (which in turn cause increased shock sensitivity). Migration of the exudated liquid into thefuze screw thread can formfire channels, increasing the risk of accidental detonation. Fuze malfunction can also result from the liquid migrating into the fuze mechanism.[35]Calcium silicate is mixed with TNT to mitigate the tendency towards exudation.[36]
Pink water andred water are two distinct types ofwastewater related to trinitrotoluene.[37] Pink water is produced from equipment washing processes aftermunitions filling ordemilitarization operations,[38][39] and as such is generally saturated with the maximum amount of TNT that will dissolve in water (about 150 parts per million (ppm).) However it has an indefinite composition that depends on the exact process; in particular, it may also containcyclotrimethylenetrinitramine (RDX) if the plant uses TNT/RDX mixtures, orHMX if TNT/HMX is used.Red water (also known as "Sellite water") is produced during the process used to purify the crude TNT. It has a complex composition containing more than a dozen aromatic compounds, but the principal components are inorganic salts (sodium sulfate,sodium sulfite,sodium nitrite andsodium nitrate) andsulfonatednitroaromatics.[citation needed]
Pink and red water are colorless at the time of generation; the color is produced byphotolytic reactions under the influence of sunlight. Despite the names, red and pink water are not necessarily different shades; the color depends mainly on the duration of solar exposure. If exposed long enough, "pink" water may turn various shades of pink, red, rusty orange, or black.[39][40]
Because of the toxicity of TNT, the discharge of pink water to the environment has been prohibited in the US and many other countries for decades, but ground contamination may exist in very old plants. However, RDX andtetryl contamination is usually considered more problematic, as TNT has very low soil mobility. Red water is significantly more toxic and as such it has always been considered hazardous waste. It has traditionally been disposed of by evaporation to dryness (as the toxic components are not volatile), followed by incineration. Much research has been conducted to develop better disposal processes.[citation needed]
Because of its suitability in munitions, TNTs toxicity has been characterized and reported. Residual TNT from manufacture, storage, and use can pollute water, soil, theatmosphere, and thebiosphere.[41]
The concentration of TNT in contaminated soil can reach 50 g/kg of soil, where the highest concentrations can be found on or near the surface. In September 2001, theUnited States Environmental Protection Agency (USEPA) declared TNT a pollutant whose removal is a priority.[42] The USEPA maintains that TNT levels in soil should not exceed 17.2 milligrams per kilogram of soil and 0.01 milligrams per litre of water.[43]
Dissolution is a measure of the rate that solid TNT in contact with water is dissolved. The relatively lowaqueous solubility of TNT causes solid particles to be continuously released to the environment over extended periods of time.[44] Studies have shown that TNT dissolves more slowly in saline water than in freshwater. However, when salinity is altered, TNT dissolves at the same speed.[45] Because TNT is moderately soluble in water, it can migrate through subsurface soil, and causegroundwater contamination.[46]
TNT and its transformation products are known to adsorb to surface soils and sediments, where they undergo reactive transformation or remained stored.[47] The movement or organic contaminants through soils is a function of their ability to associate with the mobile phase (water) and a stationary phase (soil). Materials that associate strongly with soils move slowly through soil. The association constant for TNT with soil is 2.7 to 11 L/kg of soil.[48] This means that TNT has a one- to tenfold tendency to adhere to soil particulates than not when introduced into the soil.[44]Hydrogen bonding andion exchange are two suggested mechanisms of adsorption between the nitro functional groups and soil colloids.
The adsorption of TNT is sensitive to soil type.[49]
Additional studies have shown that the mobility of TNT degradation products is likely to be lower "than TNT in subsurface environments where specific adsorption to clay minerals dominates the sorption process."[49] Thus, the mobility of TNT and its transformation products are dependent on the characteristics of the sorbent.[49] The mobility of TNT in groundwater and soil has been extrapolated from "sorption and desorptionisotherm models determined withhumic acids, in aquifer sediments, and soils".[49] From these models, it is predicted that TNT has a low retention and transports readily in the environment.[42]
Compared to other explosives, TNT has a higher association constant with soil, meaning it adheres more with soil than with water. Conversely, other explosives, such asRDX andHMX with low association constants (ranging from 0.06 to 7.3 L/kg and 0 to 1.6 L/kg respectively) can move more rapidly in water.[44]
The transformation of TNT is significantly enhanced under anaerobic conditions as well as under highly reducing conditions. TNT transformations in soils can occur both biologically and abiotically.[49]
An organism capable of the remediation of large amounts of TNT in soil has yet to be discovered.[50] Both wild and transgenic plants canphytoremediate explosives from soil and water.[51]
^Fairfield AP (1921).Naval Ordnance. Lord Baltimore Press. pp. 49–52.
^Urbanski T (1964).Chemistry and Technology of Explosives. Vol. 1. Pergamon Press. pp. 389–91.ISBN978-0-08-010238-2.{{cite book}}:ISBN / Date incompatibility (help)
^Ayoub K, van Hullebusch ED, Cassir M, Bermond A (2010). "Application of advanced oxidation processes for TNT removal: A review".J. Hazard. Mater.178 (1–3):10–28.doi:10.1016/j.jhazmat.2010.02.042.PMID20347218.
