Nitroglycerin (NG) (alternative spelling nitroglycerine), also known astrinitroglycerol (TNG),nitro,glyceryl trinitrate (GTN), or1,2,3-trinitroxypropane, is a dense, colorless or pale yellow, oily, explosive liquid most commonly produced bynitratingglycerol withwhite fuming nitric acid under conditions appropriate to the formation of the nitric acidester. Chemically, the substance is anitrate ester rather than anitro compound, but the traditional name is retained. Discovered in 1846 byAscanio Sobrero,[4] nitroglycerin has been used as an active ingredient in the manufacture of explosives, namelydynamite, and as such it is employed in theconstruction,demolition, andmining industries. It is combined withnitrocellulose to form double-basedsmokeless powder, used as apropellant in artillery and firearms since the 1880s.
As is the case for many other explosives, nitroglycerin becomes more and more prone to exploding (i.e.,spontaneous decomposition) as the temperature is increased. Upon exposure to heat above 218 °C at sea-levelatmospheric pressure, nitroglycerin becomes extremely unstable and tends to explode. When placed in vacuum, it has anautoignition temperature of 270 °C instead.[5] With a melting point of 12.8 °C, the chemical is almost always encountered as a thick and viscous fluid, changing to a crystalline solid when frozen.[5][6] Although the pure compound itself is colorless, in practice the presence ofnitric oxide impurities left over during production tends to give it a slight yellowish tint.
Due to its high boiling point and consequently low vapor pressure (0.00026 mmHg at 20 °C),[5] pure nitroglycerin has practically no odor at room temperature, with a sweet and burning taste when ingested. Unintentional detonation may ensue when dropped, shaken, lit on fire, rapidly heated, exposed to sunlight and ozone, subjected to sparks and electrical discharges, or roughly handled.[7] Itssensitivity to exploding is responsible for numerous devastating industrial accidents throughout its history. The chemical's characteristic reactivity may be reduced through the addition of desensitizing agents, which makes it less likely to explode. Clay (diatomaceous earth) is an example of such an agent, forming dynamite, a much more easily handled composition. The addition of other desensitizing agents gives birth to the various formulations of dynamite.
Nitroglycerin was the first practical explosive produced that was stronger thanblack powder. It was synthesized by the ItalianchemistAscanio Sobrero in 1846, working underThéophile-Jules Pelouze at theUniversity of Turin.[10] Sobrero initially called his discovery "pyroglycerin" and warned vigorously against its use as an explosive.[11]
Nitroglycerin was adopted as a commercially useful explosive byAlfred Nobel, who experimented with safer ways to handle the dangerous compound after his younger brother,Emil Oskar Nobel, and several factory workers were killed in an explosion at the Nobels' armaments factory in 1864 inHeleneborg, Sweden.[12]
One year later, Nobel foundedAlfred Nobel and Company in Germany and built an isolated factory in the Krümmel hills ofGeesthacht nearHamburg. This business exported a liquid combination of nitroglycerin andgunpowder called "Blasting Oil", but this was extremely unstable and difficult to handle, as evidenced in numerous catastrophes.[13] The buildings of the Krümmel factory were destroyed twice.[14]
In April 1866, several crates of nitroglycerin were shipped toCalifornia, three of which were destined for theCentral Pacific Railroad, which planned to experiment with it as a blasting explosive to expedite the construction of the 1,659-foot-long (506 m)Summit Tunnel through theSierra Nevada Mountains. One of the remaining crates exploded, destroying aWells Fargo company office inSan Francisco and killing 15 people. This led to a complete ban on the transportation of liquid nitroglycerin in California. The on-site manufacture of nitroglycerin was thus required for the remaining hard-rockdrilling and blasting required for the completion of theFirst transcontinental railroad in North America.[15]
On Christmas Day 1867, an attempt to dispose of nine canisters of Blasting Oil that had been illegally stored at the White Swan Inn in the centre ofNewcastle upon Tyne resulted in an explosion on the Town Moor that killed eight people.
In June 1869, two one-ton wagons loaded with nitroglycerin, then known locally as Powder-Oil, exploded during transport while passing through the village ofCwm-y-glo in North Wales.[16] The explosion led to the loss of six lives, many injuries, and much damage to the village. Little trace was found of the two horses. The UK Government was so alarmed at the damage caused and what could have happened in a city location (these two tons were part of a larger load coming from Germany via Liverpool) that they soon passed the Nitro-Glycerine Act of 1869.[16] Liquid nitroglycerin was widely banned elsewhere, as well, and these legal restrictions led to Alfred Nobel and his company developing dynamite in 1867. This was made by mixing nitroglycerin withdiatomaceous earth (Kieselguhr in German) found in the Krümmel hills. Similar mixtures, such as "dualine" (1867), "lithofracteur" (1869), and "gelignite" (1875), were formed by mixing nitroglycerin with other inert absorbents, and many combinations were tried by other companies in attempts to get around Nobel's tightly held patents for dynamite.
Dynamite mixtures containingnitrocellulose, which increases the viscosity of the mix, are commonly known as "gelatins".
Following the discovery thatamyl nitrite helped alleviate chest pain, the physicianWilliam Murrell experimented with the use of nitroglycerin to alleviate angina pectoris and to reduce theblood pressure. He began treating his patients with small diluted doses of nitroglycerin in 1878, and this treatment was soon adopted into widespread use after Murrell published his results inThe Lancet in 1879.[17][18] A few months before he died in 1896, Alfred Nobel was prescribed nitroglycerin for this heart condition, writing to a friend: "Isn't it the irony of fate that I have been prescribed nitro-glycerin, to be taken internally! They call it Trinitrin, so as not to scare the chemist and the public."[19] The medical establishment also used the name "glyceryl trinitrate" for the same reason.
In its undiluted form, nitroglycerin is acontact explosive, meaning physical shock causes it to explode. If it has not been adequately purified during manufacture, it can degrade over time to even more unstable forms. This makes nitroglycerin highly dangerous to transport or use. In its undiluted form, it is one of the world's most powerful explosives, comparable to the more recently developedRDX andPETN.
Early in its history, liquid nitroglycerin was found to be "desensitized" by freezing it at a temperature below 45 to 55 °F (7 to 13 °C) depending on its purity.[20] Its sensitivity to shock while frozen is somewhat unpredictable: "It is more insensitive to the shock from afulminate cap or a rifle ball when in that condition but on the other hand it appears to be more liable to explode on breaking, crushing, tamping, etc."[21] Frozen nitroglycerin is much less energetic than liquid, and so must be thawed before use.[22] Thawing it out can be extremely sensitizing, especially if impurities are present or the warming is too rapid.[23]Ethylene glycol dinitrate or another polynitrate may be added to lower the melting point and thereby avoid the necessity of thawing frozen explosive.[24]
Chemically "desensitizing" nitroglycerin is possible to a point where it can be considered about as "safe" as modernhigh explosives, such as by the addition ofethanol,acetone, ordinitrotoluene.[25] The nitroglycerin may have to be extracted from the desensitizer chemical to restore its effectiveness before use, for example, by adding water to draw off ethanol used as a desensitizer.[25]
When nitroglycerin explodes, the products after cooling are given by:
4C3H5N3O9 → 12CO2 + 10H2O + 6N2 +O2
The heat released can be calculated from the heats of formation. Using −371 kJ/mol for the heat of formation of condensed phase nitroglycerin[26] gives 1414 kJ/mol released if forming water vapor, and 1524 if forming liquid water.
The detonation velocity of nitroglycerin is 7820 meters per second, which is about 113% the speed ofTNT. Accordingly, nitroglycerin is considered to be a high-brisance explosive, which is to say, it has excellent shattering ability. The heat liberated during detonation raises the temperature of the gaseous byproducts to about 5,000 °C (9,000 °F).[24] With a standard enthalpy of explosive decomposition of −1414 kJ/mol and a molecular weight of 227.0865 g/mol, nitroglycerin has a specific explosive energy density of 1.488 kilocalories per gram, or 6.23 kJ/g, making nitroglycerin 49% more energetic on a mass basis than the standard definitional value assigned to TNT (precisely 1 kcal/g).
The addition ofglycerol results in anexothermic reaction (i.e., heat is produced), as usual for mixed-acid nitrations. If the mixture becomes too hot, it results in a runaway reaction, a state of accelerated nitration accompanied by the destructiveoxidation of organic materials by the hotnitric acid and the release of poisonousnitrogen dioxide gas at high risk of an explosion. Thus, theglycerin mixture is added slowly to the reaction vessel containing the mixed acid (not acid to glycerin). The nitrator is cooled with cold water or some other coolant mixture and maintained throughout theglycerin addition at about 22 °C (72 °F), hot enough for esterification to occur at a fast rate but cold enough to avoid runaway reaction. The nitrator vessel, often constructed ofiron orlead and generally stirred withcompressed air, has an emergency trap door at its base, which hangs over a large pool of very cold water and into which the whole reaction mixture (called the charge) can be dumped to prevent an explosion, a process referred to as drowning. If the temperature of the charge exceeds about 30 °C (86 °F) (actual value varying by country) or brown fumes are seen in the nitrator's vent, then it is immediately drowned.
Nitroglycerin is an oily liquid that explodes when subjected to heat, shock, or flame. The main use of nitroglycerin, bytonnage, is in explosives such as dynamite and in propellants as an ingredient. However, its sensitivity has limited the usefulness of nitroglycerin as a military explosive; less sensitive explosives such asTNT,RDX, andHMX have largely replaced it in munitions.
Alfred Nobel developed the use of nitroglycerin as a blasting explosive by mixing nitroglycerin with inertabsorbents, particularly "Kieselguhr", ordiatomaceous earth. He named this explosive dynamite andpatented it in 1867.[32] It was supplied ready for use in the form of sticks, individually wrapped in greased waterproof paper. Dynamite and similar explosives were widely adopted forcivil engineering tasks, such as in drillinghighway andrailroadtunnels, formining, for clearing farmland of stumps, inquarrying, and indemolition work. Likewise,military engineers have used dynamite for construction and demolition work.
Nitroglycerin has been used in conjunction withhydraulic fracturing, a process used to recoveroil andgas fromshale formations. The technique involves displacing and detonating nitroglycerin in natural or hydraulically induced fracture systems, or displacing and detonating nitroglycerin in hydraulically induced fractures followed by wellbore shots using pelletizedTNT.[33]
Nitroglycerin has an advantage over some other high explosives in that, on detonation, it produces practically no visible smoke. Therefore, it is useful as an ingredient in the formulation of various kinds ofsmokeless powder.[34]
Alfred Nobel then developedballistite by combining nitroglycerin andguncotton. He patented it in 1887. Ballistite was adopted by several European governments as a military propellant. Italy was the first to adopt it. The British government and the Commonwealth governments adoptedcordite instead, which had been developed by SirFrederick Abel and SirJames Dewar of the United Kingdom in 1889. The original Cordite Mk I consisted of 58% nitroglycerin, 37% guncotton, and 5.0%petroleum jelly. Ballistite and cordite were both manufactured in the form of "cords".
Smokeless powders were originally developed using nitrocellulose as the sole explosive ingredient. Therefore, they were known as single-base propellants. A range of smokeless powders that contain both nitrocellulose and nitroglycerin, known as double-base propellants, was also developed. Smokeless powders were originally supplied only for military use, but they were also soon developed for civilian use and were quickly adopted for sports. Some are known as sporting powders. Triple-base propellants contain nitrocellulose, nitroglycerin, andnitroguanidine, but are reserved mainly for extremely high-caliber ammunition rounds such as those used in tank cannons andnaval artillery. Blasting gelatin, also known asgelignite, was invented by Nobel in 1875, using nitroglycerin,wood pulp, andsodium orpotassium nitrate. This was an early, low-cost, flexible explosive.
Inmedicine, nitroglycerin is probably most commonly prescribed forangina pectoris, a painful symptom ofischemic heart disease caused by inadequate flow of blood and oxygen to the heart, and as a potent antihypertensive agent. Nitroglycerin corrects the imbalance between the flow of oxygen and blood to the heart and the heart's energy demand.[35] There are many formulations on the market at different doses. At low doses, nitroglycerin dilates veins more than arteries, thereby reducingpreload (volume of blood in the heart after filling); this is thought to be its primary mechanism of action. By decreasing preload, the heart has less blood to pump, which decreases oxygen requirement since the heart does not have to work as hard. Additionally, having a smaller preload reduces the ventricular transmural pressure (pressure exerted on the walls of the heart), which decreases the compression of heart arteries to allow more blood to flow through the heart. At higher doses, it also dilates arteries, thereby reducingafterload (decreasing the pressure against which the heart must pump).[35] An improved ratio of myocardial oxygen demand to supply leads to the following therapeutic effects during episodes of angina pectoris: subsiding of chest pain, decrease ofblood pressure, increase of heart rate, andorthostatic hypotension. Patients experiencing angina when doing certain physical activities can often prevent symptoms by taking nitroglycerin 5 to 10 minutes before the activity. Overdoses may generatemethemoglobinemia.[36][37]
Nitroglycerin is available in tablets, ointment, solution forintravenous use,transdermal patches, or sprays administeredsublingually. Some forms of nitroglycerin last much longer in the body than others. Nitroglycerin, as well as the onset and duration of action of each form, is different. The sublingual or tablet spray of nitroglycerin has a two-minute onset and a twenty-five-minute duration of action. The oral formulation of nitroglycerin has a thirty-five-minute onset and a duration of action of 4–8 hours. The transdermal patch has an onset of thirty minutes and a duration of action of ten to twelve hours. Continuous exposure to nitrates has been shown to cause the body to stop responding normally to this medicine. Experts recommend that the patches be removed at night, allowing the body a few hours to restore its responsiveness to nitrates. Shorter-acting preparations of nitroglycerin can be used several times a day with less risk of developing tolerance.[38] Nitroglycerin was first used byWilliam Murrell to treat angina attacks in 1878, with the discovery published that same year.[18][39]
Infrequent exposure to high doses of nitroglycerin can cause severeheadaches known as "NG head" or "bang head". These headaches can be severe enough to incapacitate some people; however, humans develop atolerance to and dependence on nitroglycerin after long-term exposure. Although rare, withdrawal can be fatal;[40] symptoms include chest pain and other heart problems. These symptoms may be relieved with re-exposure to nitroglycerin or other suitable organic nitrates.[41]
For workers in nitroglycerin (NTG) manufacturing facilities, the effects of withdrawal sometimes include "Sunday heart attacks" in those experiencing regular nitroglycerin exposure in the workplace, leading to the development of tolerance for the venodilating effects. Over the weekend, the workers lost their tolerance, and when they were re-exposed on Monday, the drasticvasodilation produced afast heart rate, dizziness, and a headache. This is referred to as "Monday disease".[42][43]
"Quelle gocciole costituiscono il corpo nuovo di cui descriverò ora le proprietà, e che chiameròPiroglicerina." (Those drops constitute the new substance whose properties I will now describe, and which I will call "pyroglycerine".)[whose translation?]
^"Emil Nobel".NobelPrize.org. Archived fromthe original on 15 January 2009. Retrieved6 October 2008.
^Di Carlo, F. J. (1975). "Nitroglycerin Revisited: Chemistry, Biochemistry, Interactions".Drug Metabolism Reviews.4 (1):1–38.doi:10.3109/03602537508993747.PMID812687.
^Lewis, Richard J., Sr (15 March 2007).Hawley's Condensed Chemical Dictionary (15th ed.). United States: John Wiley & Sons, Inc. p. 897.ISBN978-0-471-76865-4.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Wexler, Philip (7 April 2014).Encyclopedia of Toxicology (3rd ed.). USA: Academic Press. p. 569.ISBN978-0123864543.
^Marsh, N.; Marsh, A. (2000). "A short history of nitroglycerine and nitric oxide in pharmacology and physiology".Clinical and Experimental Pharmacology and Physiology.27 (4):313–319.doi:10.1046/j.1440-1681.2000.03240.x.PMID10779131.S2CID12897126.
^Assembly of Life Sciences (U.S.) Advisory Center on Toxicology.Toxicological Reports. National Academies. p. 115. NAP:11288. Retrieved23 April 2013.
^"Nitroglycerine".NIOSH Pocket Guide to Chemical Hazards. CDC. Retrieved21 November 2015.
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