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Pentaborane(9)

January 01, 1970

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).

Pentaborane(9)
Names
IUPAC name
Pentaborane(9)
Other names
Pentaborane, pentaboron nonahydride, stable pentaborane
Identifiers
  • 19624-22-7 Y
3D model (JSmol)
  • Interactive image
ChEBI
  • CHEBI:33591
ChemSpider
  • 24765156 Y
ECHA InfoCard 100.039.253
EC Number
  • 243-194-4
26757
RTECS number
  • RY8925000
UNII
  • P1F0BN763J Y
UN number 1380
  • DTXSID10880057
  • InChI=1S/B5H9/c6-1-5-2(6)8-4(5)9-3(5)7-1/h1-5H Y
    Key: USBVLEBZPMQADS-UHFFFAOYSA-N Y
  • InChI=1/B5H9/c6-2-1-3(2,6)5(1,8-3)4(1,2,7-2)9-5/h1-5H
    Key: XPIBKKWNZBDJNI-UHFFFAOYAS
  • [H]1[BH]2[H][BH]3[BH]24[BH]1[H][BH]4[H]3
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)
Health 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g. nitroglycerinSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
4
4
4
W
Flash point 30 °C (86 °F; 303 K)
Explosive limits 0.42%-?[1]
Lethal dose or concentration (LD, LC):
<50 mg/kg[3]
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).
N verify (what is YN ?)

Structure, synthesis, properties edit

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]

5 B3H7Br− → 3 B5H9 + 5 Br− + 4 H2

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.

Reactions edit

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.

History of its use as a fuel edit

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]

Safety edit

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]

See also edit

References edit

  1. ^ a b c d e f NIOSH Pocket Guide to Chemical Hazards. "#0481". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ DeQuasie, Andrew. The Green Flame. Chapter 4. at the WayBack Machine.
  3. ^ Pentaborane chemical and safety data
  4. ^ "Pentaborane". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. ^ . Archived from the original on 17 February 2015. Retrieved 13 March 2015.
  6. ^ Stock, A. (1933). The Hydrides of Boron and Silicon. New York: Cornell University Press. ISBN 0-8014-0412-6.
  7. ^ Miller, V. R.; Ryschkewitsch, G. E. (1974). Pentaborane(9) (B5H9). Inorganic Syntheses. Vol. 15. pp. 118–122. doi:10.1002/9780470132463.ch26. ISBN 9780470132463.
  8. ^ Hrostowski, Henry J.; Myers, Rollie J. (29 December 2004). "The Microwave Spectra, Structure, and Dipole Moment of Stable Pentaborane". The Journal of Chemical Physics. 22 (2): 262. doi:10.1063/1.1740048. ISSN 0021-9606.
  9. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  10. ^ . Encyclopedia Astronautica. Archived from the original on 8 August 2007. Retrieved 11 August 2007.
  11. ^ . Encyclopedia Astronautica. Archived from the original on 26 August 2002. Retrieved 11 August 2007.
  12. ^ McDonald, G. (13 November 1957). "Thermal Stability of a Commercial Propyl Pentaborane (HEF-2) in the range 147 to 190 °C" (PDF). National Advisory Committee for Aeronautics.
  13. ^ ""Dragon Slayer" neutralizes super fuel" (PDF). Engineer Update. 25 (2). U.S. Army Corps of Engineers. February 2001.
  14. ^ CDC – NIOSH Pocket Guide to Chemical Hazards
  15. ^ Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)

January 01, 1970
pentaborane, inorganic, compound, with, formula, b5h9, most, common, boron, hydride, clusters, although, highly, reactive, compound, because, high, reactivity, with, oxygen, once, evaluated, rocket, fuel, like, many, smaller, boron, hydrides, pentaborane, colo. 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 Pentaborane 9 Names IUPAC name Pentaborane 9 Other names Pentaborane pentaboron nonahydride stable pentaborane Identifiers CAS Number 19624 22 7 Y 3D model JSmol Interactive image ChEBI CHEBI 33591 ChemSpider 24765156 Y ECHA InfoCard 100 039 253 EC Number 243 194 4 Gmelin Reference 26757 RTECS number RY8925000 UNII P1F0BN763J Y UN number 1380 CompTox Dashboard EPA DTXSID10880057 InChI InChI 1S B5H9 c6 1 5 2 6 8 4 5 9 3 5 7 1 h1 5H YKey USBVLEBZPMQADS UHFFFAOYSA N YInChI 1 B5H9 c6 2 1 3 2 6 5 1 8 3 4 1 2 7 2 9 5 h1 5HKey XPIBKKWNZBDJNI UHFFFAOYAS SMILES H 1 BH 2 H BH 3 BH 24 BH 1 H BH 4 H 3 Properties Chemical formula 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 Solubility in water 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 444W Flash point 30 C 86 F 303 K Explosive limits 0 42 1 Lethal dose or concentration LD LC LD50 median dose lt 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 Point group C4v Dipole moment 2 13 D Except where otherwise noted data are given for materials in their standard state at 25 C 77 F 100 kPa N verify what is Y N Infobox references Contents 1 Structure synthesis properties 2 Reactions 3 History of its use as a fuel 4 Safety 5 See also 6 ReferencesStructure synthesis properties editIts 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 5 B3H7Br 3 B5H9 5 Br 4 H2 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 Reactions editThe 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 History of its use as a fuel editPentaborane 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 Safety editAs 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 See also editZip fuelReferences edit a b c d e f NIOSH Pocket Guide to Chemical Hazards 0481 National Institute for Occupational Safety and Health NIOSH DeQuasie Andrew The Green Flame Chapter 4 Excerpted and archived at the WayBack Machine Pentaborane chemical and safety data Pentaborane Immediately Dangerous to Life or Health Concentrations IDLH National Institute for Occupational Safety and Health NIOSH NFPA Hazard Rating Information for Common Chemicals Archived from the original on 17 February 2015 Retrieved 13 March 2015 Stock A 1933 The Hydrides of Boron and Silicon New York Cornell University Press ISBN 0 8014 0412 6 Miller V R Ryschkewitsch G E 1974 Pentaborane 9 B5H9 Inorganic Syntheses Vol 15 pp 118 122 doi 10 1002 9780470132463 ch26 ISBN 9780470132463 Hrostowski Henry J Myers Rollie J 29 December 2004 The Microwave Spectra Structure and Dipole Moment of Stable Pentaborane The Journal of Chemical Physics 22 2 262 doi 10 1063 1 1740048 ISSN 0021 9606 Greenwood Norman N Earnshaw Alan 1997 Chemistry of the Elements 2nd ed Butterworth Heinemann ISBN 978 0 08 037941 8 N2O4 Pentaborane Encyclopedia Astronautica Archived from the original on 8 August 2007 Retrieved 11 August 2007 RD 270M Encyclopedia Astronautica Archived from the original on 26 August 2002 Retrieved 11 August 2007 McDonald G 13 November 1957 Thermal Stability of a Commercial Propyl Pentaborane HEF 2 in the range 147 to 190 C PDF National Advisory Committee for Aeronautics Dragon Slayer neutralizes super fuel PDF Engineer Update 25 2 U S Army Corps of Engineers February 2001 CDC NIOSH Pocket Guide to Chemical Hazards Documentation for Immediately Dangerous To Life or Health Concentrations IDLHs Retrieved from https en wikipedia org w index php title Pentaborane 9 amp oldid 1219441458, wikipedia, wiki, book, books, library,

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