| Trimethylborane | |
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Trimethylborane |
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Other names
trimethylborine, trimethylboron |
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| Identifiers | |
| CAS number | 593-90-8 |
| ChemSpider | 62201 |
| EC number | 209-816-3 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | C3H9B |
| Molar mass | 55.92 g/mol |
| Appearance | Colorless gas or liquid |
| Density | 0.625 g/cm3 at -100 °C[1] |
| Melting point |
-161.5 °C, 112 K, -259 °F |
| Boiling point |
-20.2 °C, 253 K, -4 °F |
| Solubility in water | slight, Highly reactive |
| Structure | |
| Molecular shape | Δ |
| Hazards | |
| R-phrases | R17 R34[2] |
| S-phrases | S7 S23 S26 S36/37/39 S43 S45[2] |
| Main hazards | Spontaneously flammable in air; causes burns |
| Autoignition temperature |
-40 °C[2] |
| Related compounds | |
| Related compounds | triethylborane Diborane methylborane |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Trimethylborane is a toxic compound normally occurring as a gas that spontaneously catches fire in air. The formula is B(CH3)3, which can also be expressed as Me3B, with Me representing methyl. Its melting point is -161.5 °C and 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. T is temperature in Kelvin.[3] CAS number is 593-90-8.[4] Molecular weight is 55.914. The heat of vapourisation is 25.6 kJ/mol.[2]
Contents |
As a liquid it is colourless. The strongest line in the infrared spectrum is at 1330 cm-1 followed by lines at 3010 1185 cm-1.
Trimethylborane was first made by Stock and Zeidler. Their method of preparation combined boron trichloride gas with dimethylzinc.[3] 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.[3] Yet other methods are reacting tributyl borate with trimethylaluminium chloride, or potassium tetrafluoroborate with trimethylaluminium.[5] Yet another method is to add boron trifluoride in ether to methyl magnesium iodide.[6]
Trimethylborane spontaneously ignites in air if the concentration is high enough. It burns with a green flame producing soot.[7]
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.[3] Trimethylborane can form an adduct with ammonia: (NH3):B(CH3)3.[8]
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.[6]
Methyl lithium reacting with the Trimethylborane produces a tetramethylborate salt: LiB(CH3)4.[9] The tetramethylborate ion has a negative charge and is isoelectronic with neopentane.
Trimethylborane has been used as a neutron counter. For this use it has to be very pure.[8] It is also used in chemical vapour deposition where boron and carbon need to be deposited together.