Boron trichloride 3873319 224380336 2008-07-08T16:28:34Z 148.177.1.218 {{Chembox new | Name = Boron trichloride | ImageFile = Boron-trichloride-2D.png <!-- | ImageSize = 150px --> | ImageName = Boron trichloride | ImageFile1 = Boron-trichloride-3D-vdW.png <!-- | ImageSize1 = 150px --> | ImageName1 = Boron trichloride | IUPACName = Boron trichloride | OtherNames = Boron(III) chloride | Section1 = {{Chembox Identifiers | CASNo = 10294-34-5 | RTECS = ED1925000 }} | Section2 = {{Chembox Properties | Formula = BCl<sub>3</sub> | MolarMass = 117.17 g/mol | Appearance = Colorless gas,<br />fumes in air | Density = 1.43 g/ml (O °C) | Solubility = ''decomp.'' | MeltingPt = &minus;107.3 °C | BoilingPt = 12.5 °C }} | Section3 = {{Chembox Structure | MolShape = Trigonal planar (''D''<sub>3h</sub>) | Dipole = zero }} | Section7 = {{Chembox Hazards | ExternalMSDS = | EUClass = Very toxic ('''T+''') | RPhrases = {{R14}}, {{R26/28}}, {{R34}} | SPhrases = {{S1/2}}, {{S9}}, {{S26}}, {{S28}},<br />{{S36/37/39}}, {{S45}} | FlashPt = Non-flammable }} | Section8 = {{Chembox Related | OtherAnions = [[Boron trifluoride]]<br />[[Boron tribromide]]<br />[[Boron triiodide]] | OtherCations = [[Aluminium chloride]]<br />[[Gallium chloride]] | OtherCpds = [[Boron oxide]]<br />[[Carbon tetrachloride]] }} }} '''Boron trichloride''' is a [[chemical compound]] with the formula BCl<sub>3</sub>. 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. Boron trichloride is, however, produced industrially by direct [[chlorination]] of [[boron oxide]] and [[carbon]] at 500 °C. :B<sub>2</sub>O<sub>3</sub> + 3 C + 3 Cl<sub>2</sub> → 2 BCl<sub>3</sub> + 3 CO The synthesis is analogous to the [[Kroll process]] for the conversion of titanium dioxide to titanium tetrachloride. In the laboratory BF<sub>3</sub> reacted with AlCl<sub>3</sub> gives BCl<sub>3</sub> via halogen exchange.<ref name = greenwood>{{Greenwood&Earnshaw}}</ref> BCl<sub>3</sub> is a trigonal planar molecule like the other boron trihalides, and has a bond length of 175pm. It has a zero dipole moment because it is symmetric and therefore the dipole moments associated with the bonds cancel each other out. Boron trichloride does not form dimers, although there is some evidence that may indicate dimerisation at very low temperatures (20°K). NMR studies of mixtures of boron trihalides shows the presence of mixed halides which may indicate a four centre intermediate e.g a dimer. The absence of dimerisation contrasts with the other trihalides of group 13 which contain 4 or 6 coordinate metal centres, for example see [[aluminium trichloride|AlCl<sub>3</sub>]] and [[gallium trichloride|GaCl<sub>3</sub>]]. A degree of π-bonding has been proposed to explain the short B<nowiki>&minus;</nowiki> Cl distance although there is some debate as to its extent.<ref name = greenwood /> BCl<sub>3</sub> is a [[Lewis acid]] readily forming [[adduct]]s with tertiary [[amines]], [[phosphines]], [[ethers]], [[thioether]]s, and [[halide]] ions.<ref>{{cite journal| author = W. Gerrard and M. F. Lappert| title = Reactions Of Boron richloride With Organic Compounds| journal = [[Chemical Reviews]]| year = 1958| volume = 58| pages = 1081–1111| doi = 0.1021/cr50024a003}}</ref> For example, BCl<sub>3</sub>S(CH<sub>3</sub>)<sub>2</sub> (CAS# 5523-19-3) is often employed as a conveniently handled source of BCl<sub>3</sub> because this solid (m.p. 88-90 °C) releases BCl<sub>3</sub>: :(CH<sub>3</sub>)<sub>2</sub>SBCl<sub>3</sub><math>\overrightarrow{\leftarrow}</math> (CH<sub>3</sub>)<sub>2</sub>S + BCl<sub>3</sub> When boron trichloride is passed at low pressure through devices delivering an electric discharge, diboron tetrachloride,<ref>Wartik, T.; Rosenberg, R.; Fox, W. B. "Diboron tetrachloride" Inorganic Syntheses 1967, volume X, pages 118-126.</ref> Cl<sub>2</sub>B-BCl<sub>2</sub>, and tetraboron tetrachloride, formula B<sub>4</sub>Cl<sub>4</sub>, are formed. Colourless diboron tetrachloride (m.p. -93 °C) has a planar molecule in the solid, (similar to [[dinitrogen tetroxide]], but in the gas phase the structure is staggered<ref name = greenwood />. It decomposes at room temperatures to give a series of monochlorides having the general formula (BCl)<sub>''n''</sub>, in which ''n'' may be 8, 9, 10, or 11; the compounds with formulas B<sub>8</sub>Cl<sub>8</sub> and B<sub>9</sub>Cl<sub>9</sub> are known to contain closed cages of boron atoms. The mixed [[aryl]] and [[alkyl]] boron chlorides are also of interest. [[Phenyl]]boron dichloride is commercially available. Such species can be prepare by the reaction of BCl<sub>3</sub> with organotin reagents: :2 BCl<sub>3</sub> + R<sub>4</sub>Sn &rarr; 2 RBCl<sub>2</sub> + R<sub>2</sub>SnCl<sub>2</sub> ==Uses== Boron trichloride is a starting material for the production of elemental boron. It is also used in the [[refining]] of [[aluminium]], [[magnesium]], [[zinc]], and [[copper]] alloys to remove [[nitrides]], [[carbides]], and [[oxides]] from molten metal. It has been used as a soldering flux for alloys of aluminium, [[iron]], zinc, [[tungsten]], and [[monel]]. Aluminum castings can be improved by treating the melt with boron trichloride vapors. In the manufacture of electrical resistors, a uniform and lasting adhesive [[carbon film]] can be put over a [[ceramic]] base using BCl<sub>3</sub>. It has been used in the field of high energy fuels and rocket propellants as a source of boron to raise BTU value. BCl<sub>3</sub> is also used in [[plasma etching]] in [[semiconductor]] manufacturing. This gas etches metal oxides by formation of a volatile BOCl<sub>x</sub> compounds. BCl<sub>3</sub> is used as a [[reagent]] in the synthesis of organic compounds. Like the corresponding bromide, it cleaves C-O bonds in [[ether]]s.<ref> Yamamoto, Y.; Miyaura, N. "Boron Trichloride" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.</ref> ==Safety== BCl<sub>3</sub> is an aggressive reagent that releases [[hydrogen chloride]] upon exposure to moisture or [[alcohol]]s. The [[dimethyl sulfide]] adduct is safer to use, when possible. ==References== {{Reflist}} <div class="references-small"> *{{cite journal | author = D. R. Martin | title = Coordination compounds of boron trichloride. I - A review | journal = [[Chemical Reviews]] | year = 1944 | volume = 34 | pages = 461–473 | doi = 10.1021/cr60109a005}} * {{cite journal | author = Kabalka GW, Wu ZZ, Ju YH | title = The use of organoboron chlorides and bromides in organic synthesis | journal = Journal of Organometallic Chemistry | year = 2003 | volume = 680 | pages = 12–22 | doi = 10.1016/S0022-328X(03)00209-2}}<references /></div> ==External links== * {{ICSC|0616|06}} [[Category:Boron compounds]] [[Category:Chlorides]] [[Category:Nonmetal halides]] [[cs:Chlorid boritý]] [[fr:Trichlorure de bore]] [[pl:Chlorek boru]] [[zh:三氯化硼]]