Nitroglycerine (or nitroglycerin, also called trinitroglycerin), C3H5(NO2)3 is a commonly known high explosive. Liquid at normal temperature and pressures, it is used in construction and demolition and is a component of dynamite.
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.
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.
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.
In medicine, nitroglycerin is used as a heart medication. Another name for nitroglycerin, commonly used in a medical context is glyceryl trinitrate, which more accurately reflects the chemical structure of nitroglycerin:
CH2-NO2 | CH-NO2 | CH2NO2
The principal action of nitroglycerin is vasodilatation, that is,
widening of blood vessels. The main effects of nitroglycerin in episodes of angina pectoris are
- chest pain subsides
- blood pressure decreases
- heart rate increases
See also: nitric acid; physiology