Pentaerythritol tetranitrate

Pentaerythritol tetranitrate (PETN, also known as PENT, PENTA, TEN, corpent, penthrite, or rarely and primarily in German as nitropenta or pentrit)[2]  is one of the most powerful high explosives known, with a relative effectiveness factor (R.E. factor) of 1.66. In addition to being used as a plastic explosive,[3][4][5][6][7]  it is also used as a vasodilator drug to treat certain heart conditions.

The most common use of PETN is as an explosive with high brisance. It is more difficult to detonate than primary explosives, so dropping or igniting it will typically not cause an explosion (at atmospheric pressure it is difficult to ignite and burns relatively slowly), but is more sensitive to shock and friction than other high explosives such as TNT or tetryl.[8] Under certain conditions deflagration to detonation transition can occur.

It is rarely used alone, but primarily used in booster and bursting charges of small caliber ammunition, in upper charges of detonators in some land mines and shells, and as the explosive core of detonation cord.[9] PETN is the least stable of the common military explosives, but can be stored without significant deterioration for longer than nitroglycerin or nitrocellulose.[10] It is also used in exploding bridgewire detonators, either alone or with a subsequent booster charge. In spark detonators, PETN is used to avoid 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: 5810 kJ/kg (1390 kcal/kg)
    * 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 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)

PETN is used in a number of compositions. It is a major ingredient of the Semtex plastic explosive. It is also used as a component of pentolite, a 50/50 blend with TNT; a shaped charge of 8 oz of pentolite, used in the M9A1 (bazooka) rockets, can penetrate up to 5 inches of armor.[11] The XTX8003 extrudable explosive, used in the W68 and W76 nuclear warheads, is a mixture of 80% PETN and 20% of Sylgard 182, a silicone rubber.[12] It is often phlegmatized by addition of 5-40% of wax, or by polymers (producing polymer-bonded explosives); in this form it is used in some cannon shells up to 30mm caliber, though unsuitable for higher calibers. It is also used as a component of some gun propellants and solid rocket propellants. Nonphlegmatized PETN is stored and handled with approximately 10% water content.

PETN alone can not be cast as it explosively decomposes slightly above its melting point, but it can be mixed with other explosives to form castable mixtures.

PETN can be initiated by a laser. A pulse with duration of 25 nanoseconds and 0.5-4.2 joules of energy from a Q-switched ruby laser can initiate detonation of a PETN surface coated with a 100nm thick aluminium layer in less than half microsecond.

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 C and causes swelling of the samples.

Like other nitrate esters, the primary degradation mechanism is the loss of nitrogen dioxide; this reaction is autocatalytic. The subsequent step is loss of formaldehyde. Studies were performed on thermal decomposition of PETN.[13]

PETN has been replaced in many application by RDX, which is thermally more stable and has longer shelf life.[14]

PETN can be used in some ram accelerator types.[15]

PETN is practically insoluble in water (0.01 g/100 ml at 50°C), weakly soluble in common nonpolar solvents like aliphatic hydrocarbons 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). PETN forms eutectic mixtures with some liquid or molten aromatic nitro compounds, e.g. trinitrotoluene or tetryl. Due to its highly symmetrical structure 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° or above causes hydrolysis to dinitrate; presence of 0.1% nitric acid accelerates the reaction. Addition of TNT and other aromatic nitroderivates lowers thermal stability of PETN.

PETN is manufactured by numerous manufacturers as a powder, or together with nitrocellulose and plasticizer as thin plasticized sheets (e.g. Primasheet 1000 or Detasheet). Its residues are easily detectable in hair of people handling it.[16] The highest residue retention is on black hair; some residues remain present even after washing.[17]

Like the related explosive nitroglycerin (glyceryl trinitrate), PETN is also used medically as a vasodilator in the treatment of heart conditions. These drugs work by releasing the signaling gas nitric oxide in the body. The heart medicine Lentonitrat is nearly pure PETN.[18]

In the environment PETN undergoes biodegradation. Some bacteria denitrate PETN to trinitrate and then dinitrate, which is then further degraded.[11] PETN has low volatility and low solubility in water, therefore has low bioavailability for most organisms. Its toxicity is relatively low. Its transdermal absorption also seems to be low.[1] It poses threat for aquatic organism. It can be degraded to pentaerythritol by elementary iron.[19]

Replacement of the central carbon atom with silicon produces Si-PETN, which is extremely sensitive.[20][21]
[edit] Detection

Many technologies can be used to detect PETN, a number of which have been implemented in public screening applications, primarily for air travel. PETN is just one of a number of explosive chemicals typically of interest in that area, and it belongs to a family of common nitrate-based explosive chemicals which can often be detected by the same tests. One technology, detectors that test swabs wiped on passengers and their baggage for traces of explosives, is generally reserved for travelers who are thought to merit additional scrutiny. A second type of machine, whole-body imaging scanners that use radio-frequency electromagnetic waves or low intensity x rays to detect objects under clothing, was of limited availability because of cost, privacy groups' opposition, and industry concerns about bottlenecks.[22] This is, however, not an exhaustive list.

Monitoring of oral usage of the drug by patients has been performed by determination of plasma levels of several of its hydrolysis products, pentaerythritol dinitrate, pentaerythritol mononitrate and pentaerythritol, in plasma using gas chromatography-mass spectrometry.[23]
[edit] Production

PETN's preparation involves the nitration of pentaerythritol with a mixture of concentrated nitric and sulfuric acid. The preferred method of nitration is the ICI method, which utilizes concentrated nitric acid (98%+) alone, as mixed acid can create unstable sulfonated by-products.

    C(CH2OH)4 + 4 HNO3 → C(CH2ONO2)4 + 4 H2O

The pentaerythritol is poured into the concentrated acid, while the temperature is kept below 25 °C; PETN precipitates near the end of the reaction. The reaction mixture is poured into cold water, the precipitated fine white crystals are filtered and washed with sodium carbonate solution until alkaline reaction. Crude wet PETN is then dissolved in acetone with small amount of sodium carbonate, and in multiple steps diluted with water and heated up to 100 °C, while purified PETN is precipitated; acetone vapors are recycled. Recrystallized PETN can be phlegmatized with montan wax; water at 85°C, PETN, dye and wax are sequentially added into the phlegmatizer, mixed for about 10 minutes, then cooled to 70 °C and filtered, then washed with cold water and dried by warm air at 70 °C. Nonphlegmatized PETN, used for manufacture of explosive compositions, is stored and handled wet with about 10% water content.[24]

A thermally stabilized PETN can be prepared by dissolving PETN in a suitable solvent together with a stabilizer, e.g. polyvinylpyrrolidone, and precipitating it by pouring into rapidly stirred ethanol or water.
[edit] History and misuse

Penthrite was first synthesized in 1891 by German chemist Bernhard Tollens and P. Wiegand by nitration of pentaerythritol. In 1912, after being patented by the German government, the production of PETN started. PETN was used by the German Army in World War I.[25]

In 1983 the "Maison de France" house in Berlin was brought to a partial, almost total, collapse by the detonation of 24 kg of pentaerythritol tetranitrate by terrorist Johannes Weinrich.[26] In December 2001 al-Qaeda member Richard Reid used PETN in his unsuccessful attempt to blow up American Airlines Flight 63 from Paris to Miami.[27] He had intended to use the solid triacetone triperoxide (TATP) as a detonator.[8]