Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula
B(CH3)3 (which can also be written as Me3B, with Me representing
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
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. Molecular weight
is 55.914. The heat of vapourisation is 25.6 kJ/mol.
Trimethylborane was first made by Stock and Zeidler. Their method of
preparation combined boron trichloride gas with dimethylzinc.
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. Yet other methods are reacting tributyl borate
with trimethylaluminium chloride, or potassium tetrafluoroborate with
trimethylaluminium. Yet another method is to add boron trifluoride
in ether to methyl magnesium iodide.
Trimethylborane spontaneously ignites in air if the concentration is
high enough. It burns with a green flame producing soot. 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
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.
Trimethylborane can form an adduct with ammonia:
Trimethylborane reacts with diborane to disproportionate to form
monomethyldiborane and dimethyldiborane: (CH3)BH2.BH3 and
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.
Methyl lithium reacting with the
Trimethylborane produces a
tetramethylborate salt: LiB(CH3)4. The tetramethylborate ion has a
negative charge and is isoelectronic with neopentane,
tetramethylsilane, and the tetramethylammonium cation.
Trimethylborane has been used as a neutron counter. For this use it
has to be very pure. It is also used in chemical vapour deposition
where boron and carbon need to be deposited together.
^ Nomenclature of Organic Chemistry : IUPAC Recommendations and
Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of
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^ 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.
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^ http://www.voltaix.com/images/doc/Msb000_TMB.pdf MSDS from Voltaix
^ a b Trimethylborane
^ a b c d William S. Rees, Jr. and al (1990). Alvin P. Ginsberg, ed.
Trimethylborane. Inorganic Syntheses. 27. p. 339.
^ Roland Koumlstera, Paul Bingera Wilhelm, V. Dahlhof; Binger;
Dahlhoff (1973). "A Convenient Preparation of
Triethylborane". Synthesis and Reactivity in Inorganic and
Metal-Organic Chemistry. 3 (4): 359–367.
doi:10.1080/00945717308057281. CS1 maint: Multiple names: authors
^ a b Donald Charles Mente (May 1975). "The Reactions of Trimethyl
group Va Lewis Bases with simple Boron Lewis Acids" (PDF).
^ Herbert Ellern (1968). "Military and Civilian Pyrotechnics".
Chemical Publishing Company. p. 24.
CiteSeerX 10.1.1.137.1104 . Missing or empty url= (help)
^ Barton, Lawrence; Crump, John M.; Wheatley, Jeffrey B. (June 1974).
"Trioxadiborolanes from the oxidation of methyldiborane". Journal of
Organometallic Chemistry. 72 (1): C1–C3.
^ a b 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).
^ Georg Wi