Boron trifluoride
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| Boron trifluoride | |
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| Systematic name | Boron trifluoride |
| Molecular formula | BF3 |
| Molar mass | 67.8062 g mol−1 |
| Density | 2.178 g dm−3 |
| Relative density (air = 1) | 2.42 |
| Solubility (water) | decomposes |
| Melting point | −126°C |
| Boiling point | −100.3°C |
| CAS number | [7637-07-2] |
| Disclaimer and references | |
Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless, toxic gas forms white fumes in moist air. It is a valuable Lewis acid.
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[edit] Structure and chemistry
The molecule BF3 consists of boron and fluorine in a trigonal planar geometry. The BF3 molecule, although composed of highly polar covalent bonds, is nonpolar because of the boron atom's sp2 hybridisation which produce three symmetrical orbitals.
Boron is electron deficient and in chemical reactions, BF3 is a Lewis acid, for example reacting with fluorides to form tetrafluoroborate salts:
- CsF + BF3 → CsBF4
Boron trifluoride also forms acceptor compounds with such Lewis bases as ammonia and ethers. Boron trifluoride in the form of an adduct with diethyl ether can be conveniently handled as a liquid.
Unlike the other boron halides, when boron trifluoride reacts with water, it is decomposed to boric acid and fluoroboric acid (HBF4). The other halogens are too large to be able to form similar tetrahedral ions around the small boron atom. Because of the high acidity of fluoroboric acid, the fluoroborate ion can be used to isolate certain ions, such as diazonium ions, that are otherwise difficult to isolate. The decomposition of diazonium fluoroborates into an aryl fluoride, nitrogen and boron trifluoride is an important reaction in chemical laboratories, similar to the Sandmeyer reaction
[edit] Handling
Boron trifluoride is highly flammable and destructive to eyes and mucous membranes.
Boron trifluoride is corrosive. Suitable metals for equipment handling boron trifluoride include stainless steel, monel, and hastelloy. In presence of moisture it corrodes steel, including stainless steel. It reacts with polyamides. Polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, and polypropylene show satisfactory resistance. The grease used in the equipment should be fluorocarbon based, as boron trifluoride reacts with the hydrocarbon-based ones.[1]
[edit] Uses
- applied as dopant in ion implantation
- as a p-type dopant for epitaxially grown silicon
- initiates polymerisation reactions of unsaturated compounds. Example polyethers
- as a catalyst in some isomerization, alkylation, esterification, condensation, and other reactions.
- used in sensitive neutron detectors
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