Boron trifluoride 1647344 221103110 2008-06-23T01:51:31Z DOI bot 6652755 Citation maintenance. Initiated by [[User:Fconaway|Fconaway]]. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{Chembox new | Name = Boron trifluoride | ImageFileL1 = Boron-trifluoride-2D.png <!-- | ImageSizeL1 = 150px --> | ImageNameL1 = Boron trifluoride in 2D | ImageFileR1 = Boron-trifluoride-3D-vdW.png <!-- | ImageSizeR1 = 150px --> | ImageNameR1 = Boron trifluoride in 3D | Section1 = {{Chembox Identifiers | CASNo = 7637-07-2 | UNNumber = ''Compressed: ''[[List of UN Numbers 1001 to 1100|1008]].<br/>''Complex with acetic acid: ''[[List of UN Numbers 1701 to 1800|1742]].<br/>''Complex with propionic acid: ''[[List of UN Numbers 1701 to 1800|1743]].<br/>''Boron trifuoride diethyl etherate: ''[[List of UN Numbers 2601 to 2700|2604]].<br/>''Boron trifluoride dimethyl etherate: ''[[List of UN Numbers 2901 to 3000|2965]].<br/>''Boron trifluoride dihydrate: ''[[List of UN Numbers 2801 to 2900|2851]]. }} | Section2 = {{Chembox Properties | Formula = BF<sub>3</sub> | MolarMass = 67.8062 g mol<sup>−1</sup> | Density = 2.178 g dm<sup>−3</sup> | Solvent = other solvents | SolubleOther = decomposes | MeltingPt = −126°C | BoilingPt = −100.3°C}} }} '''Boron trifluoride''' is the [[chemical compound]] with the [[chemical formula|formula]] BF<sub>3</sub>. 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== Unlike the aluminium trihalides, the boron trihalides are all monomeric. They do undergo rapid reversible dimerization as indicated by the high rate of the halide exchange reactions: :BF<sub>3</sub> + BCl<sub>3</sub> → BF<sub>2</sub>Cl + BCl<sub>2</sub>F Because of the facility of this exchange process, the mixed halides cannot be obtained in pure form. The geometry of a [[molecule]] of BF<sub>3</sub> is described as [[trigonal planar]]. The D<sub>3h</sub> [[symmetry group|symmetry]] conforms with the prediction of [[VSEPR theory]]. Although featuring three polar covalent bonds, the molecule has no dipole moment by virtue of its high symmetry. Although [[isoelectronic]] with carbonate, CO<sub>3</sub><sup>2−</sup>, BF<sub>3</sub> is commonly referred to as " [[electron deficiency|electron deficient]]," a description that is reinforced by its [[exothermic]] reactivity toward [[Lewis base]]s. In the boron trihalides, BX<sub>3</sub>, the length of the B-F bonds (1.30 Å) is shorter than would be expected for single bonds,<ref name = greenwood>Greenwood, N. N.; A. Earnshaw (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.</ref> and this shortness may indicate stronger B-X [[pi bond|π-bonding]] in the fluoride. A facile explanation invokes the symmetry-allowed overlap of a p orbital on the boron atom with the in-phase combination of the three similarly oriented p orbitals on fluorine atoms.<ref name = greenwood/> ==Synthesis== BF<sub>3</sub> is manufactured by the reaction of boron oxides with [[hydrogen fluoride]]: :B<sub>2</sub>O<sub>3</sub> + 6 HF → 2 BF<sub>3</sub> + 3 H<sub>2</sub>O Typically the HF is produced in situ from sulfuric acid and [[fluorite]] (CaF<sub>2</sub>).<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref> On a laboratory scale, BF<sub>3</sub> is produced by the thermal decomposition of diazonium salts:<ref>{{OrgSynth | author = Flood, D. T. | title = Fluorobenzene | collvol = 2 | collvolpages = 295 | prep = CV2P0295}}</ref> :PhN<sub>2</sub>BF<sub>4</sub> → [[Fluorobenzene|PhF]] + BF<sub>3</sub> + [[nitrogen|N<sub>2</sub>]] ==Lewis acidity and related reactions== Boron trifluoride is a versatile Lewis acid that forms [[adduct]]s with such [[Lewis base]]s as [[fluoride]] and [[ether]]s: :[[Caesium fluoride|CsF]] + BF<sub>3</sub> → CsBF<sub>4</sub> :[[Diethyl ether|O(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>]] + BF<sub>3</sub> → BF<sub>3</sub>O(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub> [[Tetrafluoroborate]] [[salt]]s are commonly employed as [[non-coordinating anion]]s. The adduct with diethyl ether is a conveniently handled [[liquid]] and consequently is a widely encountered as a laboratory source of BF<sub>3</sub>. ====Comparative Lewis acidity==== All three lighter boron trihalides, BX<sub>3</sub> (X = F, Cl, Br) form stable adducts with common Lewis bases. Their relative Lewis acidities can be evaluated in terms of the relative exothermicities of the adduct-forming reaction. Such measurements have revealed the following sequence for the Lewis acidity: :BF<sub>3</sub>< BCl<sub>3</sub>< BBr<sub>3</sub> (strongest Lewis acid) This trend commonly attributed to the degree of [[pi bond|π-bonding]] in the planar boron trihalide that would be lost upon pyramidalization of the BX<sub>3</sub> molecule.<ref>Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. (1999). Advanced Inorganic Chemistry (6th Edn.) New York: Wiley-Interscience. ISBN 0-471-19957-5.</ref> which follows this trend: :BF<sub>3</sub> > BCl<sub>3</sub> > BBr<sub>3</sub> (most easily pyramidalized) The criteria for evaluating the relative strength of [[pi bond|π-bonding]] are not clear, however.<ref name = greenwood/><br /> One of the suggestion is that F atom is small compared to I atom, the lone pair electron in P<sub>z</sub> of F readily and easily donated and overlapped to empty P<sub>z</sub> orbital of boron. As a result, the back donation of F is greater than that of I. In an alternative explanation, the low Lewis acidity for BF<sub>3</sub> is attributed to the relative weakness of the bond in the adducts F<sub>3</sub>B-L.<ref>''Group V Chalcogenide Complexes of Boron Trihalides'' Boorman, P. M.; Potts, D. Canadian. Journal of Chemistry (Rev. can. chim.) volume 52, (1974) pp 2016-2020</ref><ref>{{cite journal | author = T. Brinck, J. S. Murray and P. Politzer | title = A computational analysis of the bonding in boron trifluoride and boron trichloride and their complexes with ammonia | year = 1993 | journal = [[Inorg. Chem.]] | volume = 32 | issue = 12 | pages = 2622–2625 | doi = 10.1021/ic00064a008}}</ref> ====Hydrolysis==== Boron trifluoride reacts with water to give [[boric acid]],and [[fluoroboric acid]]: and [HF] The reaction commences with the formation of the aquo adduct, H<sub>2</sub>O-BF<sub>3</sub>, which then loses HF: :4 BF<sub>3</sub> + 3 H<sub>2</sub>O → 3 HBF<sub>4</sub> + "B(OH)<sub>3</sub>" The heavier trihalides do not undergo analogous reactions, possibly the lower stability of the tetrahedral ions BX<sub>4</sub><sup>-</sup> (X = Cl, Br). Because of the high acidity of fluoroboric acid, the fluoroborate ion can be used to isolate particularly electrophilic cations, such as [[diazonium]] ions, that are otherwise difficult to isolate as solids. ==Handling== 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 [[polyamide]]s. [[Polytetrafluoroethylene]], [[polychlorotrifluoroethylene]], [[polyvinylidene fluoride]], and [[polypropylene]] show satisfactory resistance. The [[grease (lubricant)#Laboratory grease|grease]] used in the equipment should be [[fluorocarbon]] based, as boron trifluoride reacts with the hydrocarbon-based ones.<ref>{{cite web | publisher = [[Air Liquide]] | url = http://encyclopedia.airliquide.com/encyclopedia.asp?GasID=68 | work = Gas Encyclopedia | title = Boron trifluoride}}</ref> ==Uses== * applied as [[dopant]] in [[ion implantation]] * [[p-type semiconductor|p-type]] dopant for [[epitaxial]]ly grown [[silicon]] * initiates [[polymerisation]] reactions of [[saturation (chemistry)|unsaturated]] [[chemical compounds|compounds]]. Example [[polyether]]s * as a catalyst in some [[isomerization]], [[alkylation]], [[esterification]], [[Condensation reaction|condensation]], [[Mukaiyama aldol addition]], and other reactions. * used in sensitive [[neutron]] detectors {{Sectstub|date=May 2008}} ==References== <references/> ==External links== * http://www.osha.gov/dts/chemicalsampling/data/CH_221700.html * http://www.cdc.gov/niosh/ipcsneng/neng0231.html *[http://www.npi.gov.au/database/substance-info/profiles/15.html National Pollutant Inventory - Boron and compounds fact sheet] *[http://www.npi.gov.au/database/substance-info/profiles/44.html National Pollutant Inventory - Fluoride and compounds fact sheet] [[Category:Fluorides]] [[Category:Boron compounds]] [[Category:Nonmetal halides]] [[cs:Fluorid boritý]] [[de:Bortrifluorid]] [[fr:Trifluorure de bore]] [[nl:Boortrifluoride]] [[ja:三フッ化ホウ素]] [[zh:三氟化硼]]