Trimethylborane
Encyclopedia
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. CAS number is 593-90-8. Molecular weight is 55.914. The heat of vapourisation is 25.6 kJ/mol.
The strongest line in the infrared spectrum is at 1330 cm-1 followed by lines at 3010 1185 cm-1.
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 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
: (NH3):B(CH3)3.
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
.
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
.
Vapour pressure is given by log P = 6.1385+1.75 log T - 1393.3/T - 0.007735 T. T is temperature in Kelvin. CAS number is 593-90-8. Molecular weight is 55.914. The heat of vapourisation is 25.6 kJ/mol.
Properties
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.
Preparation
Trimethylborane was first made by Stock and Zeidler. Their method of preparation combined boron trichlorideBoron trichloride
Boron trichloride is a chemical compound with the formula BCl3. This colorless gas is a valuable reagent in organic synthesis. It is also dangerously reactive.-Production and properties:Boron reacts with halogens to give the corresponding trihalides...
gas with dimethylzinc
Dimethylzinc
Dimethylzinc, also known as Zinc methyl, DMZ, or DMZn is a colorless mobile liquid Zn2, formed by the action of methyl iodide on zinc at elevated temperature or on zinc sodium alloy....
. 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
Trimethylaluminium
Trimethylaluminium is the chemical compound with the formula Al26, abbreviated as Al2Me6, 2 or the abbreviation TMA. This pyrophoric, colorless liquid is an industrially important organoaluminium compound...
in hexane
Hexane
Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures...
with boron tribromide
Boron tribromide
Boron tribromide, BBr3, is a colorless, fuming liquid compound containing boron and bromine. It is usually made by heating boron trioxide with carbon in the presence of bromine: this generates free boron which reacts vigorously with the bromine...
in dibutyl ether
Dibutyl ether
Dibutyl ether is a colourless, neutral, readily flammable liquid of low volatility with a characteristic odour. It is insoluble in water, but miscible with most common organic solvents...
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
Boron trifluoride
Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...
in ether to methyl magnesium iodide.
Reactions
Trimethylborane spontaneously ignites in air if the concentration is high enough. It burns with a green flame producing soot.Trimethylborane is a strong Lewis acid
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
. 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
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
: (NH3):B(CH3)3.
Trimethylborane reacts with diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
to disproportionate to form monomethyldiborane and dimethyldiborane: (CH3)BH2.BH3 and (CH3)2BH.BH3.
It reacts as a gas with trimethylphosphine
Trimethylphosphine
Trimethylphosphine is the organophosphorus compound with the formula P3, commonly abbreviated PMe3. This colorless liquid has a strongly unpleasant odour, which is characteristic of alkylphosphines. It is a pyramidal molecule with C3v symmetry, similar to ammonia and phosphine . As a ligand, its...
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
Trimethylarsine
Trimethylarsine is the chemical compound with the formula 3As, commonly abbreviated AsMe3 or TMAs. This organic derivative of arsine has been used as a source of arsenic in microelectronics industry, a building block to other organoarsenic compounds, and serves as a ligand in coordination...
or trimethylstibine
Trimethylstibine
Trimethylstibine is a chemical compound with the formula Sb3. It is a colorless pyrophoric and toxic liquid. It is produced by anaerobic bacteria in antimony-rich soils....
.
Methyl lithium reacting with the Trimethylborane produces a tetramethylborate salt: LiB(CH3)4. The tetramethylborate ion has a negative charge and is isoelectronic
Isoelectronicity
Two or more molecular entities are described as being isoelectronic with each other if they have the same number of electrons or a similar electron configuration and the same structure , regardless of the nature of the elements involved.The term valence isoelectronic is used when these molecular...
with neopentane
Neopentane
Neopentane, also called dimethylpropane, is a double-branched-chain alkane with five carbon atoms. Neopentane is an extremely flammable gas at room temperature and pressure which can condense into a highly volatile liquid on a cold day, in an ice bath, or when compressed to a higher...
.