TNT

From Chempedia

From the battle field to the mountainside, trinitrotoluene has blasted its way into man’s greatest accomplishments and greatest failures. Here is a look at the fascinating force of TNT.

Chemical & Physical Properties of TNT:

2,4,6-Trinitrotoluene (TNT) is a pale yellow organic compound with a chemical formula of C₆H₂(NO₂)₃CH_3.¹ It is stable in its standard form, does not react with metals or absorb water, resists friction, and requires a detonator (alkali metals) to set it off. It is synthesized by nitrating toluene with a mixture of sulfuric and nitric acid to produce a waste acid. This waste acid is then used for the initial step of the reaction that proceeds in industrial use. TNT is mainly manufactured for for use as an explosive because it can rapidly change from a solid into an expanding gas. TNT has a melting point of 354K and explodes at a temperature higher than 240°C.² It density is 1.654g/cm³. Its specific combustion rate is 4.184MJ/kg. These properties make TNT meltable and easy to place in steam-heated vessels and able to be poured into casings with an array of compounds making it an important explosive.

History of TNT:

Trinitrotoluene (TNT) was invented in 1863 by a German chemist named Joseph Wilbrand. First used in 1905, in a war between Russia and Japan³, it was eventually produced in large quantities by the Germans in World War I. Because it was difficult to detonate the Germans were able to safely melt it and use it to fill artillery shells. This was an advantage, because the TNT filling gave their shells the ability to pierce armor.⁴ At that time these shells exploded at forces of approximately 2.25 million psi (pounds per square inch). TNT was later modified, and used in World War II. One of the modifications was a substance called RDX-TNT or cyclonite. This form explodes at about 4 million psi, and is the most commonly used explosive in the military.⁵ Before TNT, dynamite was the chief explosive. However, because it\’s main compound, nitroglycerin, was so sensitive to detonation, TNT took its place in military use.⁶

How TNT Works:

Trinitrotoluene is quite an explosive material. It can quickly destroy anything within its blast radius when detonated. Surprisingly TNT has less potential energy than even gasoline. Why is TNT less flammable than gasoline and other combustibles, yet much more explosive? There are two reasons which contribute to the answer of this question. The first is the extremely high reaction rate at which TNT converts into the stable products of CO, CO₂ and N₂ upon detonation.⁷ Here is the actual reaction:

These products all have very strong bonds which contributes to the great amount of energy released upon detonation, and consequently the rate at which it occurs. The detonation velocity of TNT is 6,940 m/s, and continuing our comparison to gasoline (in air) which is 0.34 m/s, it can be seen why TNT is more explosive. The second reason why TNT is so highly explosive is the actual physical construction of the molecule. The nitro groups are tightly packed, and are under high amounts of stress, so when the cluster of TNT is detonated it initiates a very fast chain reaction throughout the rest of the molecules. To show how greatly it expands after detonation, it is known that 1 gram of TNT produces 1 liter of gas.⁸ The final volume is 1000 times greater than the initial volume. Such a drastic increase in volume in such a short time, it is no longer a surprise why TNT is so highly combustible.

Uses of TNT:

Trinitrotoluene is produced for military weaponry and commercial use. The military uses TNT as a component in artillery, land mines and mortar shells. It can also be melted down and mixed with other explosives such as RDX and HMX to load into bombs.⁹ They also use TNT for demolition of ordnances that are unsafe to move and the destruction of old military compounds.¹⁰ The commercial use of TNT is limited because of it high restrictions and ability to be used as a weapon. Its main commercial purpose is for coal and mineral mining. Housing companies use TNT for controlled building demolitions and clearing land. TNT can also be used for under water mining of oil and other substances.¹¹ TNT is also mixed with other compounds in order to make a big explosion in large fire works.

Health & Environmental Impacts:

Although TNT may seem a viable source for a low cost explosive power, it poses great risks to the environment in which is it used and to those who are exposed to it. There are four main ways someone can become exposed: drinking contaminated water, breathing contaminated air, eating contaminated foods and eating contaminated soil. TNT can enter the environment through the manufacturing, processing, recycling or destruction of explosives. This solid chemical contaminates soil and ground water. Once the compound enters the water it breaks down further into smaller amounts which can then be absorbed by fish or plant life. The yellow odorless powder can also be absorbed directly into the skin and lead to headaches, anemia and skin irritation. TNT was used during World War I and the explosives were manufactured by workers in munitions plants. One serious health concern was skin irritation in the workers who handled TNT. Their skin actually turned bright yellow. For example, women were referred to as "canary girls".⁸ Anemia and abnormal liver function were also found to be the result of exposure and the longer the contact, the more serious the effects, including cataract development and possibly birth defects. The Environmental Protection Agency determined TNT to be a possible human carcinogen based on long term studies on urinary bladder tumor formations. Humans are not the only species that suffer from exposure to this chemical. In an attempt to control contamination to those involved with or exposed to the chemical, many governmental departments have designated rules for transportation and workplace exposure. "When shipped, the compound must be wet with at least 10% water by weight and it must be clearly labeled. The recommended exposure is 1.5 mg/m³ in workplace air for a 40hr week".¹² Researchers are also trying to find a way to clean up contaminated areas. One suggested treatment is the use of weeds. "Plants including stonewort, hornwort, and parrot feather, contain an enzyme called nitro-reductase that reacts with the nitro group on the TNT molecule. After the enzyme breaks the compound down into triaminotoluene, another enzyme called laccase oxidizes the triaminotoluene rapidly into biodegradable materials." ¹³This is one environmentally friendly way in which we are able to reduce the amount of contaminants. It is the hope of many that we will be able to clean up all of the contaminated areas, especially around military bases and in areas where the surrounding life is exposed, to prevent further damage.

¹ http://en.wikipedia.org/wiki/TNT_(explosive)

² http://www.britannica.com/eb/article-82388?tocId=82388

³ http://www.britannica.com/nobel/micro/200_74.html

⁴ http://trinitrotoluene.biography.ms/

⁵ http://www.tpub.com/content/combat/14110/css/14110_19.htm

⁶ See 3

⁷ http://www.ch.ic.ac.uk/vchemlib/mim/bristol/tnt/tnt_text.htm

⁸ http://www.nationmaster.com/encyclopedia/TNT-(explosive)

⁹ http://www.answers.com/topic/trinitrotoluene

¹⁰http://www.absoluteastronomy.com/encyclopedia/d/de/demolition.htm

¹¹http://www.epa.gov

¹²http://www.eco-usa.net/toxics/246tnt.shtml