Trimethylborane

Trimethylborane
Names
Preferred IUPAC name
Trimethylborane[1]
Other names
Trimethylborine
Trimethylboron
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.008.926
EC Number 209-816-3
Properties
C3H9B
Molar mass 55.92 g/mol
Appearance Colorless gas or liquid
Density 0.625 g/cm3 at −100 °C[3]
Melting point −161.5 °C (−258.7 °F; 111.6 K)
Boiling point −20.2 °C (−4.4 °F; 253.0 K)
Slight, highly reactive
Structure
Δ
Hazards
Main hazards Spontaneously flammable in air; causes burns
GHS pictograms
GHS signal word Danger
H220, H250, H280, H314
P210, P222, P260, P264, P280, P301+330+331, P302+334, P303+361+353, P304+340, P305+351+338, P310, P321, P363, P370+378, P377, P381, P403, P405, P410+403, P422, P501
Flash point Not applicable, pyrophoric gas
−40 °C (−40 °F; 233 K)[4]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl).

Properties

As a liquid it is colourless. The strongest line in the infrared spectrum is at 1330 cm−1 followed by lines at 3010 cm−1 and 1185 cm−1.

Its melting point is −161.5 °C, and its boiling point is −20.2 °C.

Vapour pressure is given by log P = 6.1385 + 1.75 log T − 1393.3/T − 0.007735 T, where T is temperature in kelvins.[5] Molecular weight is 55.914. The heat of vapourisation is 25.6 kJ/mol.[4]

Preparation

Trimethylborane was first made by Stock and Zeidler. Their method of preparation combined boron trichloride gas with dimethylzinc.[5] Although the substance can be prepared using Grignard reagents the output is contaminated by unwanted products from the solvent. Trimethylborane can be made on a small scale with a 98% yield by reacting trimethylaluminium in hexane with boron tribromide in dibutyl ether as a solvent.[5] Yet other methods are reacting tributyl borate with trimethylaluminium chloride, or potassium tetrafluoroborate with trimethylaluminium.[6] Yet another method is to add boron trifluoride in ether to methyl magnesium iodide.[7]

Reactions

Trimethylborane spontaneously ignites in air if the concentration is high enough. It burns with a green flame producing soot.[8] Slower oxidation with oxygen in a solvent or in the gas phase can produce dimethyltrioxadiboralane, which contains a ring of two boron and three oxygen atoms. However the major product is dimethylborylmethylperoxide, which rapidly decomposes to dimethoxymethylborane.[9]

Trimethylborane is a strong Lewis acid. It reacts with water and chlorine at room temperature. It also reacts with grease but not with Teflon or glass.[5] Trimethylborane can form an adduct with ammonia: (NH3):B(CH3)3.[10]

Trimethylborane reacts with diborane to disproportionate to form monomethyldiborane and dimethyldiborane: (CH3)BH2.BH3 and (CH3)2BH.BH3.

It reacts as a gas with trimethylphosphine to form a solid Lewis salt with a heat of formation of −41 kcal per mol. This adduct has a heat of sublimation of −24.6 kcal/mol. No reaction occurs with trimethylarsine or trimethylstibine.[7]

Methyl lithium reacting with the Trimethylborane produces a tetramethylborate salt: LiB(CH3)4.[11] The tetramethylborate ion has a negative charge and is isoelectronic with neopentane, tetramethylsilane, and the tetramethylammonium cation.

Use

Trimethylborane has been used as a neutron counter. For this use it has to be very pure.[10] It is also used in chemical vapour deposition where boron and carbon need to be deposited together.

References

  1. ↑ Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 974. doi:10.1039/9781849733069-00648. ISBN 978-0-85404-182-4.
  2. ↑ Graner, G., Hirota, E., Iijima, T., Kuchitsu, K., Ramsay, D. A., Vogt, J., Vogt, N.; Hirota; Iijima; Kuchitsu; Ramsay; Vogt; Vogt (2001). "C3H9B Trimethylborane". SpringerMaterials. Landolt-Börnstein - Group II Molecules and Radicals. 25C: 1. doi:10.1007/10688787_381. ISBN 3-540-66774-1.
  3. ↑ http://www.voltaix.com/images/doc/Msb000_TMB.pdf MSDS from Voltaix
  4. 1 2 Trimethylborane
  5. 1 2 3 4 William S. Rees, Jr. and al (1990). Alvin P. Ginsberg, ed. Trimethylborane. Inorganic Syntheses. 27. p. 339.
  6. ↑ Roland Koumlstera, Paul Bingera Wilhelm, V. Dahlhof; Binger; Dahlhoff (1973). "A Convenient Preparation of Trimethylborane and Triethylborane". Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry. 3 (4): 359–367. doi:10.1080/00945717308057281.
  7. 1 2 Donald Charles Mente (May 1975). "The Reactions of Trimethyl group Va Lewis Bases with simple Boron Lewis Acids" (PDF).
  8. ↑ Herbert Ellern (1968). "Military and Civilian Pyrotechnics". Chemical Publishing Company. p. 24. CiteSeerX 10.1.1.137.1104. Missing or empty |url= (help)
  9. ↑ Barton, Lawrence; Crump, John M.; Wheatley, Jeffrey B. (June 1974). "Trioxadiborolanes from the oxidation of methyldiborane". Journal of Organometallic Chemistry. 72 (1): C1–C3. doi:10.1016/s0022-328x(00)82027-6.
  10. 1 2 Gaylon S. Ross; et al. (2 October 1961). "Preparation of High Purity Trimethylborane" (PDF). Journal of Research of the National Bureau of Standards Section A. 66 (1).
  11. ↑ Georg Wittig in 1958
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