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Nitroglycerin

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Nitroglycerine (also nitroglycerin, 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 used in construction and demolition[?]. It is also used medically as a vasodilator to treat heart conditions.

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 liquid Nitroglycerin may be "desensitized" by cooling to 40-50 degrees 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 may be considered approximately as "safe" as modern High Explosive formulations through the addition of apporoximately 10-30% Ethanol, Acetone, or, Dinitrotoluene(percentage varying with the desensitizing agent utilized). Desensitization requires extra effort to reconstitute the "pure" product. Failing this, it must be assumed desensitized Nitroglycerine will be substantially more difficult to detonate, possibly rendering it useless as an explosive for any given application.

(Nitroglycerin and any / all of the diluents mentioned will certainly "deflagrate", or burn. However, the incredible 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 which pre-ignites unshocked material, creating a fast-moving transition zone which [by virtue of the nature of the material]can detonate any fertile material it encounters, expanding in a never-ending cascade of hyper-instantaneous pressure-induced combustion building upon 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.

Table of contents

Properties

formula: CH2(ONO2)-CH(ONO2)-CH2(ONO2)
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.

It is used as an explosive in compositions called dynamite. Nitroglycerin is too sensitive to be used pure and needs other products to be stabilized.

Preparation

Nitroglycerin is prepared by nitration of glycerin. In the process, glycerin is slowly tipped into a mix of concentrated nitric and sulfuric acid. 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 making of nitroglycerin is obviously potentially very dangerous, because of the product's explosive nature. Do not attempt to make it yourself!

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 case is no exception. However, if the mixture becomes too hot, it will explode. 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 (ischaemic heart disease) in tablets, ointment or solution for intravenous use.

The principal action of nitroglycerin is vasodilatation[?], that is, widening of 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 which is not completely understood), and nitric oxide in turn is a well-known natural vasodilator.



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