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  Wikipedia: Nitroglycerin

Wikipedia: Nitroglycerin
Nitroglycerin
From Wikipedia, the free encyclopedia.

Nitroglycerin (also nitroglycerine, trinitroglycerin, or glyceryl trinitrate) is a chemical compound, a heavy yellow poisonous oily explosive liquid obtained by nitrating glycerol. It is used in making explosives, specifically dynamite, and as such is used in construction and demolition. It is also used medically as a vasodilator to treat heart conditions.

Instability and desensitization

In its pure form, it is shock-sensitive (i.e., physical shock can cause it to explode) and degrades over time to even more unstable forms. This makes it highly dangerous to transport or use in its pure form.

Early in the history of this explosive it was discovered that liquid nitroglycerin can be "desensitized" by cooling to 40–50 °F, at which temperature it freezes, contracting upon solidification. However, later thawing can be extremely sensitizing, especially if impurities are present or if warming is too rapid. It is possible to chemically "desensitize" nitroglycerin to a point where it can be considered approximately as "safe" as modern High Explosive formulations, by the addition of approximately 10%–30% ethanol, acetone, or dinitrotoluene (percentage varys with the desensitizing agent used). Desensitization requires extra effort to reconstitute the "pure" product. Failing this, it must be assumed that desensitized nitroglycerine is substantially more difficult to detonate, possibly rendering it useless as an explosive for practical application.

What is detonation?

Nitroglycerin and any or all of the diluents mentioned above can certainly "deflagrate", or burn. However, the explosive power of nitroglycerin is derived not from burning, but from detonation, in which a shock propagates through a fuel-rich medium at greater than the speed of sound in that medium. In other words, the initial burn sets up a pressure gradient that pre-ignites unshocked material, creating a fast-moving transition zone, which (due to the nature of the material) can detonate any appropriate material it encounters, expanding in a never-ending cascade of hyper-instantaneous pressure-induced combustion building exponentially upon itself, quite unlike "deflagration", which generally relies solely upon available fuels independent of pressure and shock.

An explosion is essentially very fast combustion, and combustion requires fuel and oxidant. Nitroglycerin, as can be seen from its composition and structure (below), essentially contains both these components. If it is detonated under pressure, it explodes to form thousands of times its original volume in hot gas.

Properties

formula: CH2(ONO2)-CH(ONO2)-CH2(ONO2)
IUPAC Name: 1,2,3-Tris-nitrooxy-propane
colour: yellow but coulourless when pure
aspect: slightly oily liquid
density: 1.13 at 15 °C
melting point: 13.2 °C
molecular weight 227.0872
very sensitive to friction, shock, elevation of temperature, and sparks.

Preparation

Nitroglycerin is prepared by nitration of glycerin. In the process, glycerin is slowly tipped into a mix of concentrated nitric and sulfuric acids. The solution is slowly mixed. The temperature should never exceed 30 °C, otherwise there is a risk of explosion.

When the reaction is over, the mix is poured into a large amount of water. The nitroglycerin settles and is washed with water and sodium carbonate until it becomes neutral.

Manufacture

The industrial manufacturing process uses a 50:50 mixture of fuming sulphuric acid (fuming means it is very concentrated) and red fuming nitric acid. This produces nitronium ions in situ, which attack glycerin (also called glycerol) at its negatively charged oxygen atoms. The functional group NO2 is thus added, adding extra oxygen atoms to the flammable substance glycerin.

The use of strong acids almost always results in an exothermic reaction (i.e., heat is produced), and this reaction is no exception. However, if the mixture becomes too hot, it explodes. Thus, the acid mixture is added slowly to the reaction vessel containing the glycerin. The reaction vessel itself is cooled with ice-cold water or some other coolant mixture at about 0 °C. The vessel itself has an emergency trap door at its bottom, which hangs over a large pool of very cold water. If sensors in the mixture detect the temperature rising too rapidly, then the whole mixture can be dumped into the ice-cold water, which prevents an explosion if done in time.

Medical use

In medicine, nitroglycerin is used as a heart medication (under the trade names Nitrospan and Nitrostat). It is used as a medicine for angina pectoris (ischaemic heart disease) in tablets, ointment, or solution for intravenous use.

The principal action of nitroglycerin is vasodilation, that is, widening of the blood vessels. The main effects of nitroglycerin in episodes of angina pectoris are

These effects come about because nitroglycerin is converted to nitric oxide in the body (by a mechanism that is not completely understood), and nitric oxide in turn is a well-known natural vasodilator.

Terrorism

The Manila-based terrorist plot known as Project Bojinka called for the bombing of 11 airliners over the Pacific Ocean on January 21 and 22, 1995. Al Qaida agents were planned to plant liquid bombs, called "Mark II" "microbombs" on the aircraft. The device was inside Casio digital watches that contain nitroglycerin for the explosive and stabilizing that looked like cotton balls. Two 9 Volt batteries taken from children's toys were used to power light bulb filaments and to detonate the nitroglycerin. Trace amounts of sulphuric acid, nitrobenzene, silver azide, liquid acetone, and nitrate were present. The wiring was attached to the arm of the watch using a tiny space below the calculator. The alteration was so small that one could still wear the bomb as a watch.

This bomb was tested several times, first by Al-Qaida member Ramzi Yousef inside of a mall in Cebu City, then by cohort Wali Khan Amin Shah inside the Greenbelt Theatre in Manila on December 1, 1994.

The bomb also was tested on Philippine Airlines Flight 434 on December 11, 1994. He boarded the plane under an assumed name while hiding the batteries in the soles of his shoes. He assembled the bomb in the lavatory on the flight's Ninoy Aquino International Airport to Cebu leg. He stuck it under his seat and left the plane in Mactan-Cebu International Airport. The bomb exploded on the Cebu to New Tokyo International Airport (Narita, Japan), leg, killing a Japanese businessman and injuring 10. The plane made an emergency landing at Naha, Okinawa.

Project Bojinka was foiled on the night of January 6 and the morning of January 7, 1995, when Manila police found the plans and the bomb factory in Yousef's Manila apartment after a chemical fire occurred there.


  

From Wikipedia, the free encyclopedia. 
Modified by Geona