Chemistry:Trimethylborane

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Trimethylborane
Trimethylborane.png
Trimethylborane Ball and Stick.png
Trimethylborane Space Fill.png
Names
Preferred IUPAC name
Trimethylborane[1]
Other names
Trimethylborine
Trimethylboron
Identifiers
3D model (JSmol)
ChemSpider
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
Safety data sheet MSDS from Voltaix
GHS pictograms GHS02: Flammable GHS04: Compressed Gas GHS05: Corrosive
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
Tracking categories (test):

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 described in 1862 by Edward Frankland,[6] who also mentioned its adduct with ammonia.[7] Due to its dangerous nature the compound was no longer studied until 1921, when Alfred Stock and Friedrich Zeidler took advantage of the reaction between boron trichloride gas and dimethylzinc.[8] 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,[9] or adding boron trifluoride in ether to methyl magnesium iodide.[10]

Reactions

Trimethylborane spontaneously ignites in air if the concentration is high enough. It burns with a green flame producing soot.[11] 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.[12]

Trimethylborane is a strong Lewis acid. B(CH3)3 can form an adduct with ammonia: (NH3):B(CH3)3.[13] as well as other Lewis bases. The Lewis acid properties of B(CH3)3 have been analyzed by the ECW model yielding EA= 2.90 and CA= 3.60. When trimethylborane forms an adduct with trimethylamine, steric repulsion between the methyl groups on the B and N results. The ECW model can provide a measure of this steric effect.

Trimethylborane reacts with water and chlorine at room temperature. It also reacts with grease but not with teflon or glass.[5]

Trimethylborane reacts with diborane to disproportionate to form methyldiborane 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.[10]

Methyl lithium reacting with the Trimethylborane produces a tetramethylborate salt: LiB(CH3)4.[14] 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.[15] For this use it has to be very pure.[13] It is also used in chemical vapour deposition where boron and carbon need to be deposited together.

References

  1. ↑ IUPAC Chemical Nomenclature and Structure Representation Division (2013). "P-6". in Favre, Henri A.; Powell, Warren H.. Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. IUPAC–RSC. ISBN 978-0-85404-182-4. https://pubs.rsc.org/en/Content/eBook/978-0-85404-182-4. . p. 974.
  2. ↑ Graner, G.; Hirota E.; Iijima T.; Kuchitsu K.; Ramsay, D. A.; Vogt, J.; Vogt, N. (2001). Molecules and Radicals. Landolt-Börnstein - Group II. 25C: Molecules containing three or four carbon atoms. p. 1370. doi:10.1007/10688787_381. ISBN 978-3-540-66774-2. 
  3. ↑ See MSDS
  4. ↑ 4.0 4.1 "Trimethylborane" (2009) at the Online Chemical Dictionary. .
  5. ↑ 5.0 5.1 5.2 Ginsberg, Alvin P., ed (1990). "Trimethylborane". Inorganic Syntheses 27: 339. 
  6. ↑ Frankland, Edward (1862). "Ueber eine neue Reihe organischer Verbindungen, welche Bor enthalten". Justus Liebigs Ann. Chem. 124: 129–157. doi:10.1002/jlac.18621240102. 
  7. ↑ Nishiyabu R.; Kubo Y.; James, T. D.; Fossey, J. S. (2011). "Boronic acid building blocks: tools for self assembly". Chem. Commun. 47 (4): 1124–1150. doi:10.1039/C0CC02921A. PMID 21113558. 
  8. ↑ Stock, A.; Zeidler, F. (1921). "Zur Kenntnis des Bormethyls und Boräthyls". Ber. Dtsch. Chem. Ges. A/B 54 (3): 531–541. doi:10.1002/cber.19210540321. https://zenodo.org/record/1426689. 
  9. ↑ Köster, Roland; Binger, Paul; Dahlhoff, Wilhelm V. (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. 
  10. ↑ 10.0 10.1 Mente, Donald Charles (May 1975). The Reactions of Trimethyl Group Va Lewis Bases with Simple Boron Lewis Acids (PDF) (PhD thesis). Texas Tech. Archived from the original (PDF) on 2011-08-15. Retrieved 2010-09-23.
  11. ↑ Ellern, Herbert (1968). Military and Civilian Pyrotechnics. Chemical Publishing Company. p. 24. ISBN 9780820603643. https://archive.org/details/militarycivilian00elle. 
  12. ↑ 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. 
  13. ↑ 13.0 13.1 Ross, Gaylon S. (2 October 1961). "Preparation of High Purity Trimethylborane". Journal of Research of the National Bureau of Standards Section A 66 (1). http://nvl.nist.gov/pub/nistpubs/jres/066/1/V66.N01.A06.pdf. Retrieved 22 September 2010. 
  14. ↑ Georg Wittig in 1958
  15. ↑ Ferguson, G. A. Jr; Jablonski, F. E. (2004-12-29). "Electron Mobility in Boron Trimethyl" (in en). Review of Scientific Instruments 28 (11): 893. doi:10.1063/1.1715757. ISSN 0034-6748. https://aip.scitation.org/doi/abs/10.1063/1.1715757. 



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