Pentaerythritol tetranitrate (PETN), also known as PENT, pentyl, TEN (tetraeritrit nitrate, primarily in Russian), corpent, or penthrite (or, rarely and primarily in German, as nitropenta), is an explosive material. It is the nitrate ester of pentaerythritol, and is structurally very similar to nitroglycerin. Penta refers to the five carbon atoms of the neopentane skeleton. PETN is a very powerful explosive material with a relative effectiveness factor of 1.66. When mixed with a plasticizer, PTNGR forms a plastic explosive. Along with RDX it is the main ingredient of Semtex. PETN is also used as a vasodilator drug to treat certain heart conditions, such as for management of angina.
History Pentaerythritol tetranitrate was first prepared and patented in 1894 by the explosives manufacturer Rheinisch-Westfälische Sprengstoff A.G. of Cologne, Germany. The production of PETN started in 1912, when the improved method of production was patented by the German government. PETN was used by the German Military in World War I. It was also used in the MG FF/M autocannons and many other weapon systems of the Luftwaffe in World War II.
Properties PETN is practically insoluble in water (0.01 g/100 mL at 50 °C), weakly soluble in common nonpolar solvents such as aliphatic hydrocarbons (like gasoline) or tetrachloromethane, but soluble in some other organic solvents, particularly in acetone (about 15 g/100 g of the solution at 20 °C, 55 g/100 g at 60 °C) and dimethylformamide (40 g/100 g of the solution at 40 °C, 70 g/100 g at 70 °C). It is a non-planar molecule that crystallizes in the space group P421c. PETN forms eutectic mixtures with some liquid or molten aromatic nitro compounds, e.g. trinitrotoluene (TNT) or tetryl. Due to the steric hindrance of the adjacent neopentyl-like moiety, PETN is resistant to attack by many chemical reagents; it does not hydrolyze in water at room temperature or in weaker alkaline aqueous solutions. Water at 100 °C or above causes hydrolysis to dinitrate; the presence of 0.1% nitric acid accelerates the reaction. The chemical stability of PETN is of interest, because of the presence of PETN in aging weapons. Neutron radiation degrades PETN, producing carbon dioxide and some pentaerythritol dinitrate and trinitrate. Gamma radiation increases the thermal decomposition sensitivity of PETN, lowers melting point by few degrees Celsius, and causes swelling of the samples. Like other nitrate esters, the primary degradation mechanism is the loss of nitrogen dioxide; this reaction is autocatalytic. Studies were performed on thermal decomposition of PETN. In the environment, PETN undergoes biodegradation. Some bacteria denitrate PETN to trinitrate and then dinitrate, which is then further degraded. PETN has low volatility and low solubility in water, and therefore has low bioavailability for most organisms. Its toxicity is relatively low, and its transdermal absorption also seems to be low. It poses a threat for aquatic organisms. It can be degraded to pentaerythritol by iron.
Production Production is by the reaction of pentaerythritol with concentrated nitric acid to form a precipitate which can be recrystallized from acetone to give processable crystals. Variations of a method first published in US Patent 2,370,437 by Acken and Vyverberg (1945 to Du Pont) form the basis of all current commercial production. PETN is manufactured by numerous manufacturers as a powder, or together with nitrocellulose and plasticizer as thin plasticized sheets (e.g. Primasheet 1000, Detasheet and Durasheet 1). PETN residues are easily detectable in hair of people handling it. The highest residue retention is on black hair; some residues remain even after washing.
Explosive use
The most common use of PETN is as an explosive with high brisance. It is a secondary explosive, meaning it is more difficult to detonate than primary explosives, so dropping or igniting it will typically not cause an explosion (at standard atmospheric pressure it is difficult to ignite and burns vigorously), but is more sensitive to shock and friction than other secondary explosives such as TNT or tetryl. Under certain conditions a deflagration to detonation transition can occur, just like that of ammonium nitrate. It is rarely used alone in military operations due to its limited stability, but is primarily used in the main charges of plastic explosives (such as C4) along with other explosives (especially RDX), booster and bursting charges of small caliber ammunition, in upper charges of detonators in some land mines and shells, as the explosive core of detonation cord. PETN is the least stable of the common military explosives, but can be stored without significant deterioration for longer than nitroglycerin or nitrocellulose. During World War II, PETN was most importantly used in exploding-bridgewire detonators for the atomic bombs. These exploding-bridgewire detonators gave more precise detonation compared to primacord. PETN was used for these detonators because it was safer than primary explosives like lead azide: while it was sensitive, it would not detonate below a threshold amount of energy. Exploding bridgewires containing PETN remain in use in current nuclear weapons. In spark detonators, PETN is used to avoid the need for primary explosives; the energy needed for a successful direct initiation of PETN by an electric spark ranges between 10–60 mJ. Its basic explosion characteristics are:
Explosion energy: 5,810 kJ/kg (1,390 kcal/kg), so 1 g of PETN has the energy of 1.24 g of TNT. PETN is approximately 7% denser than TNT, so by the same token, 1 cm3 of PETN has the energy of about 1.33 cm3 of TNT. Detonation velocity: 8350 m/s (1.73 g/cm3), 7910 m/s (1.62 g/cm3), 7420 m/s (1.5 g/cm3), 8500 m/s (pressed in a steel tube) Volume of gases produced: 790 dm3/kg (other value: 768 dm3/kg) Explosion temperature: 4230 °C Oxygen balance: −6.31 atom -g/kg Melting point: 141.3 °C (pure), 140–141 °C (technical) Trauzl lead block test: 523 cm3 (other values: 500 cm3 when sealed with sand, or 560 cm3 when sealed with water) Critical diameter (minimal diameter of a rod that can sustain detonation propagation): 0.9 mm for PETN at 1 g/cm3, smaller for higher densities (other value: 1.5 mm)
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