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Names | |
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IUPAC name Pentaborane(9) | |
Other names Pentaborane, pentaboron nonahydride, stable pentaborane | |
Identifiers | |
3D model (JSmol) | |
ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.039.253 |
EC Number |
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26757 | |
RTECS number |
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UNII | |
UN number | 1380 |
CompTox Dashboard (EPA) | |
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Properties | |
B5H9 | |
Molar mass | 63.12 g/mol |
Appearance | Colorless liquid |
Odor | pungent, like sour milk [1] |
Density | 0.618 g/mL |
Melting point | −46.8 °C (−52.2 °F; 226.3 K) |
Boiling point | 58.4 °C (137.1 °F; 331.5 K) [2] |
Reacts | |
Solubility | Benzene, Cyclohexane, and in other hydrocarbons |
Vapor pressure | 171 mmHg (20°C) [1] |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards | Extremely toxic, extremely flammable, can ignite spontaneously, corrosive |
NFPA 704 (fire diamond) | |
Flash point | 30 °C (86 °F; 303 K) |
Explosive limits | 0.42%-? [1] |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | <50 mg/kg [3] |
LC50 (median concentration) | 3 ppm (mouse, 4 hr) 6 ppm (rat, 4 hr) 3.4 ppm (mouse, 4 hr) 35 ppm (dog, 15 min) 244 ppm (monkey, 2 min) 67 ppm (rat, 5 min) 40 ppm (mouse, 5 min) 31 ppm (rat, 15 min) 19 ppm (mouse, 15 min) 15 ppm (rat, 30 min) 11 ppm (mouse, 30 min) 10 ppm (rat, 1 hr) 6 ppm (mouse, 1 hr) [4] |
NIOSH (US health exposure limits): | |
PEL (Permissible) | TWA 0.005 ppm (0.01 mg/m3) [1] |
REL (Recommended) | TWA 0.005 ppm (0.01 mg/m3) ST 0.015 ppm (0.03 mg/m3) [1] |
IDLH (Immediate danger) | 1 ppm [1] |
Structure | |
C4v | |
2.13 D | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Pentaborane(9) is an inorganic compound with the formula B5H9. It is one of the most common boron hydride clusters, although it is a highly reactive compound. Because of its high reactivity with oxygen, it was once evaluated as rocket or jet fuel. Like many of the smaller boron hydrides, pentaborane is colourless, diamagnetic, and volatile. It is related to pentaborane(11) (B5H11).
Its structure is that of five atoms of boron arranged in a square pyramid. Each boron has a terminal hydride ligand and four hydrides span the edges of the base of the pyramid. It is classified as a nido cage.
It was first prepared by Alfred Stock by pyrolysis of diborane at about 200 °C. [6] An improved synthesis starts from salts of octahydrotriborate (B3H−8), which is converted to the bromide B3H7Br− using HBr. Pyrolysis of this bromide gives pentaborane. [7]
In the U.S., pentaborane was produced on a commercial scale by Callery Chemical Company.
Above 150 °C, it decomposes, producing hydrogen. Unlike diborane, It is quite stable at room temperature if stored properly. It is much more stable in presence of water than diborane.
Pentaborane is a highly polar compound, with a dipole moment of 2.13 D. [8] It is soluble in hydrocarbons like benzene, and cyclohexane, and in greases including those used in lab equipment.
The chemistry of pentaborane is extensive. [9] Halogenation give the symmetrical derivatives B5H8X, which can be isomerised to place the halide on the base of the square pyramid. With strong bases such as alkyl lithium reagents, it can be deprotonated and the resulting lithium salts react with diverse electrophiles to give substituted derivatives. It is Lewis acidic, forming double adducts with two equivalents of trimethylphosphine. Pentaborane is used for the synthesis of other boron hydride clusters. It is also a precursor to metallaboranes. For example, it reacts with diiron nonacarbonyl to give B4H8Fe(CO)3.
Pentaborane was evaluated by both the U.S. and Russian armed services as a so-called "exotic fuel". Because simple boron compounds burn with a characteristic green flame, the nickname for this fuel in the U.S. industry was "Green Dragon". In terms of heat of combustion, pentaborane surpasses its equivalent carbon compounds because their self-linking element, carbon, weighs at least one atomic mass unit more than an atom of boron, and some boranes contain more hydrogen than the carbon equivalent. The ease of breaking the chemical bonds of the compound is also taken into consideration.
Interest in this substance began as a possible fuel for high-speed jets. The propellant mix that would produce the greatest specific impulse for a rocket motor is sometimes given as oxygen difluoride and pentaborane[ citation needed ]. During the early years of the space race and the missile gap, American rocket engineers thought they could more cheaply produce a rocket that would compete with the Soviets by using an existing first stage and putting an upper stage with an engine that produces thrust at a very high specific impulse atop it. So projects were begun to investigate this fuel.
This pentaborane was considered for use as a fuel by North American Aviation when the XB-70 Valkyrie was in the planning stages, but the aircraft ended up using hydrocarbon fuel instead. Pentaborane was also investigated to be used as a bipropellant with nitrogen tetroxide. [10] In the Soviet Union, Valentin Glushko used it for the experimental RD-270M rocket engine, under development between 1962 and 1970. [11]
Other boranes were evaluated as fuels, including propylpentaborane (BEF-2) and ethyldecaborane (REF-3). [12] Diborane and decaborane and their derivates were also investigated.
Problems with this fuel include its toxicity and its characteristic of bursting into flame on contact with the air. Furthermore, its exhaust (when used in a jet engine) would also be toxic.
The US destroyed its last stockpiles of "Green Dragon" in 2000, long after the pentaborane had been discarded as unworkable. The destruction procedure hydrolyzed the pentaborane with steam to yield hydrogen and a boric acid solution. The long delay occurred in part because there are no industrial plants consuming pentaborane as a feedstock. Instead, army engineers constructed a bespoke system, nicknamed the "Dragon Slayer". [13]
As one of the compounds that have a NFPA 704 (fire diamond) rating of 4 for every category, it is naturally extremely dangerous.
Above 30 °C it can form explosive concentration of vapors with air. Its vapors are heavier than air. It is pyrophoric—can ignite spontaneously in contact with air, when even slightly impure. It can also readily form shock sensitive explosive compounds, and reacts violently with some fire suppressants, notably with halocarbons and water. It is highly toxic and symptoms of lower-level exposure may occur with up to 48 hours delay. Its acute toxicity is comparable to some nerve agents.
Occupational exposure limits for pentaborane set by the Occupational Safety and Health Administration and National Institute for Occupational Safety and Health stand at 0.005 ppm (0.01 mg/m3) over an eight-hour time-weighted average, with a short-term exposure limit of 0.015 ppm (0.03 mg/m3). [14] The acute toxicity of pentaborane has caused it to be considered immediately dangerous to life and health, with a limit set at 1 ppm. [15]
Boron hydride clusters are compounds with the formula BxHy or related anions, where x ≥ 3. Many such cluster compounds are known. Common examples are those with 5, 10, and 12 boron atoms. Although they have few practical applications, the borane hydride clusters exhibit structures and bonding that differs strongly from the patterns seen in hydrocarbons. Hybrids of boranes and hydrocarbons, the carboranes are also well developed.
1,2-Dibromoethane, also known as ethylene dibromide (EDB), is an organobromine compound with the chemical formula C
2H
4Br
2. Although trace amounts occur naturally in the ocean, where it is probably formed by algae and kelp, substantial amounts are produced industrially. It is a dense colorless liquid with a faint, sweet odor, detectable at 10 ppm. It is a widely used and sometimes-controversial fumigant. The combustion of 1,2-dibromoethane produces hydrogen bromide gas that is significantly corrosive.
Diborane(6), commonly known as diborane, is the chemical compound with the formula B2H6. It is a highly toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Given its simple formula, borane is a fundamental boron compound. It has attracted wide attention for its electronic structure. Several of its derivatives are useful reagents.
Monomethylhydrazine (MMH) is a highly toxic, volatile hydrazine derivative with the chemical formula CH6N2. It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as nitrogen tetroxide and nitric acid. As a propellant, it is described in specification MIL-PRF-27404.
Cyclohexanol is the organic compound with the formula HOCH(CH2)5. The molecule is related to cyclohexane by replacement of one hydrogen atom by a hydroxyl group. This compound exists as a deliquescent colorless solid with a camphor-like odor, which, when very pure, melts near room temperature. Millions of tonnes are produced annually, mainly as a precursor to nylon.
Decaborane, also called decaborane(14), is the inorganic compound with the chemical formula B10H14. It is classified as a borane and more specifically a boron hydride cluster. This white crystalline compound is one of the principal boron hydride clusters, both as a reference structure and as a precursor to other boron hydrides. It is toxic and volatile, giving off a foul odor, like that of burnt rubber or chocolate.
Hexaborane, also called hexaborane(10) to distinguish it from hexaborane(12) (B6H12), is a boron hydride cluster with the formula B6H10. It is a colorless liquid that is unstable in air.
Stibine (IUPAC name: stibane) is a chemical compound with the formula SbH3. A pnictogen hydride, this colourless, highly toxic gas is the principal covalent hydride of antimony, and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 170.7 pm (1.707 Å). The smell of this compound from usual sources (like from reduction of antimony compounds) is reminiscent of arsine, id est garlic-like.
Heptachlor is an organochlorine compound that was used as an insecticide. Usually sold as a white or tan powder, heptachlor is one of the cyclodiene insecticides. In 1962, Rachel Carson's Silent Spring questioned the safety of heptachlor and other chlorinated insecticides. Due to its highly stable structure, heptachlor can persist in the environment for decades. In the United States, the Environmental Protection Agency has limited the sale of heptachlor products to the specific application of fire ant control in underground transformers. The amount that can be present in different foods is regulated.
Lithium hydride is an inorganic compound with the formula LiH. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not soluble but reactive with all protic organic solvents. It is soluble and nonreactive with certain molten salts such as lithium fluoride, lithium borohydride, and sodium hydride. With a molar mass of 7.95 g/mol, it is the lightest ionic compound.
Hydrogen selenide is an inorganic compound with the formula H2Se. This hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound with an exposure limit of 0.05 ppm over an 8-hour period. Even at extremely low concentrations, this compound has a very irritating smell resembling that of decayed horseradish or "leaking gas", but smells of rotten eggs at higher concentrations.
Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to around 40%. An estimated 270,000 tons were produced in 2005.
Nitrogen trifluoride is the inorganic compound with the formula. It is a colorless, non-flammable, toxic gas with a slightly musty odor. In contrast with ammonia, it is nonbasic. It finds increasing use within the manufacturing of flat-panel displays, photovoltaics, LEDs and other microelectronics. NF
3 is a greenhouse gas, with a global warming potential (GWP) 17,200 times greater than that of CO
2 when compared over a 100-year period.
2-Chloroethanol (also called ethylene chlorohydrin or glycol chlorohydrin) is an organic chemical compound with the chemical formula HOCH2CH2Cl and the simplest beta-halohydrin (chlorohydrin). This colorless liquid has a pleasant ether-like odor. It is miscible with water. The molecule is bifunctional, consisting of both an alkyl chloride and an alcohol functional group.
Boron compounds are compounds containing the element boron. In the most familiar compounds, boron has the formal oxidation state +3. These include oxides, sulfides, nitrides, and halides.
Perchloryl fluoride is a reactive gas with the chemical formula ClO
3F. It has a characteristic sweet odor that resembles gasoline and kerosene. It is toxic and is a powerful oxidizing and fluorinating agent. It is the acid fluoride of perchloric acid.
Bromochloromethane or methylene bromochloride and Halon 1011 is a mixed halomethane. It is a heavy low-viscosity liquid with refractive index 1.4808.
Dichlorofluoromethane or Freon 21 or R 21 is a halomethane or hydrochlorofluorocarbon with the formula CHCl2F. It is a colorless and odorless gas. It is produced by fluorination of chloroform using a catalyst such as antimony trifluoride:
Pentaborane(11) is inorganic compound with the chemical formula B5H11. It is an obscure boron hydride cluster, especially relative to the heavily studied pentaborane(9) (B5H9). With two more hydrogen atoms than nido-pentaborane(9), pentaborane(11) is classified as an arachno- cluster.
A borane is a compound with the formula BRxHy although examples include multi-boron derivatives. A large family of boron hydride clusters is also known. In addition to some applications in organic chemistry, the boranes have attracted much attention as they exhibit structures and bonding that differs strongly from the patterns seen in hydrocarbons. Hybrids of boranes and hydrocarbons, the carboranes, are also a well developed class of compounds.