 | |||
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| Names | |||
|---|---|---|---|
| Preferred IUPAC name Trimethylborane[1] | |||
| Other names Trimethylborine Trimethylboron | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChemSpider |
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| ECHA InfoCard | 100.008.926 | ||
| EC Number |
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| 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 | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards | Spontaneously flammable in air; causes burns | ||
| GHS labelling: | |||
  | |||
| Danger | |||
| H220,H250,H280,H314 | |||
| P210,P222,P260,P264,P301+P330+P331,P302+P334,P303+P361+P353,P304+P340,P305+P351+P338,P310,P321,P363,P370+P378,P377,P381,P403,P405,P410+P403,P422,P501 | |||
| Flash point | Not applicable, pyrophoric gas | ||
| −40 °C (−40 °F; 233 K)[4] | |||
| Safety data sheet (SDS) | MSDS fromVoltaix | ||
| Related compounds | |||
Related compounds | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Trimethylborane (TMB) is a toxic,pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representingmethyl).
As a liquid it is colourless. The strongest line in theinfrared 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 bylogP = 6.1385 + 1.75 logT − 1393.3/T − 0.007735T, whereT is temperature inkelvins.[5] Molecular weight is 55.914. The heat of vapourisation is 25.6 kJ/mol.[4]
Trimethylborane was first described in 1862 byEdward Frankland,[6] who also mentioned its adduct with ammonia.[7] Due to its dangerous nature the compound was no longer studied until 1921, whenAlfred Stock and Friedrich Zeidler took advantage of the reaction betweenboron trichloride gas anddimethylzinc.[8] Although the substance can be prepared usingGrignard reagents the output is contaminated by unwanted products from the solvent. Trimethylborane can be made on a small scale with a 98% yield by reactingtrimethylaluminium inhexane withboron tribromide indibutyl ether as a solvent.[5] Yet other methods are reactingtributyl borate with trimethylaluminium chloride, or potassium tetrafluoroborate with trimethylaluminium,[9] or addingboron trifluoride in ether tomethyl magnesium iodide.[10]
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 strongLewis acid. B(CH3)3 can form an adduct withammonia: (NH3):B(CH3)3.[13] as well as other Lewis bases. The Lewis acid properties of B(CH3)3 have been analyzed by theECW model yielding EA= 2.90 and CA= 3.60. When trimethylborane forms an adduct withtrimethylamine, 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 withteflon or glass.[5]
Trimethylborane reacts withdiborane to disproportionate to formmethyldiborane anddimethyldiborane: (CH3)BH2.BH3 and (CH3)2BH.BH3.
It reacts as a gas withtrimethylphosphine 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 withtrimethylarsine ortrimethylstibine.[10]
Methyl lithium reacting with the Trimethylborane produces a tetramethylborate salt: LiB(CH3)4.[14] The tetramethylborate ion has a negative charge and isisoelectronic withneopentane,tetramethylsilane, and thetetramethylammonium cation.
Trimethylborane has been used as a neutron counter.[15] For this use it has to be very pure.[13] It is also used inchemical vapour deposition where boron and carbon need to be deposited together.
