Nitroglycerin
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.
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.
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.
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.
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.
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 vasodilation, that is,
widening of the blood vessels.
The main effects of nitroglycerin in episodes of angina pectoris are
Instability and desensitization
What is detonation?
Properties
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
Manufacture
The making of nitroglycerin is obviously potentially very dangerous, because of the product's explosive nature. Do not attempt to make it yourself!Medical use
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.
