Boron trichloride

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Boron trichloride
Boron trichloride Boron-trichloride-2D.png
Boron trichloride
Boron trichloride Boron-trichloride-3D-vdW.png
Boron trichloride
Names
IUPAC name
Boron trichloride
Other names
Boron(III) chloride
Trichloroborane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.586 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-658-4
PubChem CID
RTECS number
  • ED1925000
UNII
  • InChI=1S/B.3ClH/h;3*1H/q+3;;;/p-3 Yes check.svgY
    Key: PYQQLJUXVKZOPJ-UHFFFAOYSA-K Yes check.svgY
  • InChI=1/B.3ClH/h;3*1H/q+3;;;/p-3
    Key: PYQQLJUXVKZOPJ-DFZHHIFOAV
  • ClB(Cl)Cl
Properties
BCl3
Molar mass 117.17 g/mol
AppearanceColorless gas,
fumes in air
Density 1.326 g/cm3
Melting point −107.3 °C (−161.1 °F; 165.8 K)
Boiling point 12.6 °C (54.7 °F; 285.8 K) [1]
hydrolysis
Solubility soluble in CCl4, ethanol
-59.9·10−6 cm3/mol
1.00139
Structure
Trigonal planar (D3h)
zero
Thermochemistry
107 J/mol K
Std molar
entropy
(S298)
206 J/mol K
-427 kJ/mol
-387.2 kJ/mol
Hazards [2]
Occupational safety and health (OHS/OSH):
Main hazards
May be fatal if swallowed or if inhaled
Causes serious burns to eyes, skin, mouth, lungs, etc.
Contact with water gives HCl
GHS labelling:
GHS-pictogram-exclam.svg GHS-pictogram-skull.svg GHS-pictogram-acid.svg
Danger
H300, H314, H330 [note 1]
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
4
0
2
W
Flash point Non-flammable
Safety data sheet (SDS) ICSC 0616
Related compounds
Other anions
Boron trifluoride
Boron tribromide
Boron triiodide
Other cations
Aluminium trichloride
Gallium trichloride
Related compounds
Boron trioxide
Carbon tetrachloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Boron trichloride is the inorganic compound with the formula BCl3. This colorless gas is a reagent in organic synthesis. It is highly reactive towards water.

Contents

Production and structure

Boron reacts with halogens to give the corresponding trihalides. Boron trichloride is, however, produced industrially by chlorination of boron oxide and carbon at 501 °C.

B2O3 + 3 C + 3 Cl2 → 2 BCl3 + 3 CO

The carbothermic reaction is analogous to the Kroll process for the conversion of titanium dioxide to titanium tetrachloride. One consequence of this synthesis route is that samples of boron trichloride are often contaminated with phosgene. [3]

In the laboratory BCl3 can be prepared by treating with AlCl3 with BF3, a halide exchange reaction. [4]

BCl3 is a trigonal planar molecule like the other boron trihalides. The B-Cl bond length is 175 pm. A degree of π-bonding has been proposed to explain the short B Cl distance, although there is some debate as to its extent. [4] BCl3 does not dimerize, although NMR studies of mixtures of boron trihalides shows the presence of mixed halides. The absence of dimerisation contrasts with the tendencies of AlCl3 and GaCl3, which form dimers or polymers with 4 or 6 coordinate metal centres.

Reactions

BCl3 hydrolyzes readily to give hydrochloric acid and boric acid:

BCl3 + 3 H2O → B(OH)3 + 3 HCl

Alcohols behave analogously giving the borate esters, e.g. trimethyl borate.

Ammonia forms a Lewis adduct with boron trichloride. NH3-BCl3-adduct-bond-lengthening-2D.png
Ammonia forms a Lewis adduct with boron trichloride.

As a strong Lewis acid, BCl3 forms adducts with tertiary amines, phosphines, ethers, thioethers, and halide ions. [5] Adduct formation is often accompanied by an increase in B-Cl bond length. BCl3•S(CH3)2 (CAS# 5523-19-3) is often employed as a conveniently handled source of BCl3 because this solid (m.p. 88-90 °C) releases BCl3:

(CH3)2S·BCl3 ⇌ (CH3)2S + BCl3

The mixed aryl and alkyl boron chlorides are also of known. Phenylboron dichloride is commercially available. Such species can be prepared by the redistribution reaction of BCl3 with organotin reagents:

2 BCl3 + R4Sn → 2 RBCl2 + R2SnCl2

Reduction

Reduction of BCl3 to elemental boron is conducted commercially in the laboratory, when boron trichloride can be converted to diboron tetrachloride by heating with copper metal: [6]

2 BCl3 + 2 Cu → B2Cl4 + 2 CuCl

B4Cl4 can also be prepared in this way. Colourless diboron tetrachloride (m.p. -93 °C) is a planar molecule in the solid, (similar to dinitrogen tetroxide, but in the gas phase the structure is staggered. [4] It decomposes (disproportionates) at room temperatures to give a series of monochlorides having the general formula (BCl)n, in which n may be 8, 9, 10, or 11.

n B2Cl4 → BnCln + n BCl3

The compounds with formulas B8Cl8 and B9Cl9 are known to contain closed cages of boron atoms.

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. Aluminium 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 BCl3. It has been used in the field of high energy fuels and rocket propellants as a source of boron to raise BTU value. BCl3 is also used in plasma etching in semiconductor manufacturing. This gas etches metal oxides by formation of a volatile BOClx and MxOyClz compounds.

BCl3 is used as a reagent in the synthesis of organic compounds. Like the corresponding bromide, it cleaves C-O bonds in ethers. [1] [7]

Safety

BCl3 is an aggressive reagent that can form hydrogen chloride upon exposure to moisture or alcohols. The dimethyl sulfide adduct (BCl3SMe2), which is a solid, is much safer to use, [8] when possible, but H2O will destroy the BCl3 portion while leaving dimethyl sulfide in solution.

See also

Related Research Articles

<span class="mw-page-title-main">Diborane</span> Chemical compound

Diborane(6), commonly known as diborane, is the chemical compound with the formula B2H6. It is a highly toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Given its simple formula, borane is a fundamental boron compound. It has attracted wide attention for its electronic structure. Several of its derivatives are useful reagents.

<span class="mw-page-title-main">Titanium tetrachloride</span> Inorganic chemical compound

Titanium tetrachloride is the inorganic compound with the formula TiCl4. It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. TiCl4 is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4", as a phonetic representation of the symbols of its molecular formula.

<span class="mw-page-title-main">Aluminium chloride</span> Chemical compound

Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms a hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are colourless crystals, but samples are often contaminated with iron(III) chloride, giving them a yellow colour.

Boron trifluoride is the inorganic compound with the formula BF3. This pungent, colourless, and toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.

<span class="mw-page-title-main">Triphenylphosphine</span> Chemical compound

Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to PPh3 or Ph3P. It is versatile compound that is widely used as a reagent in organic synthesis and as a ligand for transition metal complexes, including ones that serve as catalysts in organometallic chemistry. PPh3 exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether.

<span class="mw-page-title-main">Organotin chemistry</span> Branch of organic chemistry

Organotin chemistry is the scientific study of the synthesis and properties of organotin compounds or stannanes, which are organometallic compounds containing tin–carbon bonds. The first organotin compound was diethyltin diiodide, discovered by Edward Frankland in 1849. The area grew rapidly in the 1900s, especially after the discovery of the Grignard reagents, which are useful for producing Sn–C bonds. The area remains rich with many applications in industry and continuing activity in the research laboratory.

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<span class="mw-page-title-main">Indium(III) chloride</span> Chemical compound

Indium(III) chloride is the chemical compound with the formula InCl3 which forms a tetrahydrate. This salt is a white, flaky solid with applications in organic synthesis as a Lewis acid. It is also the most available soluble derivative of indium. This is one of three known indium chlorides.

<span class="mw-page-title-main">Aluminium hydride</span> Chemical compound

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<span class="mw-page-title-main">Gallium(III) chloride</span> Chemical compound

Gallium(III) chloride is an inorganic chemical compound with the formula GaCl3 which forms a monohydrate, GaCl3·H2O. Solid gallium(III) chloride is a deliquescent white solid and exists as a dimer with the formula Ga2Cl6. It is colourless and soluble in virtually all solvents, even alkanes, which is truly unusual for a metal halide. It is the main precursor to most derivatives of gallium and a reagent in organic synthesis.

<span class="mw-page-title-main">Organotitanium chemistry</span>

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<span class="mw-page-title-main">Diboron tetrachloride</span> Chemical compound

Diboron tetrachloride is a chemical compound with the formula B2Cl4. It is a colorless liquid.

<span class="mw-page-title-main">Aluminium compounds</span>

Aluminium (British and IUPAC spellings) or aluminum (North American spelling) combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heavier group 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances. Furthermore, as Al3+ is a small and highly charged cation, it is strongly polarizing and aluminium compounds tend towards covalency; this behaviour is similar to that of beryllium (Be2+), an example of a diagonal relationship. However, unlike all other post-transition metals, the underlying core under aluminium's valence shell is that of the preceding noble gas, whereas for gallium and indium it is that of the preceding noble gas plus a filled d-subshell, and for thallium and nihonium it is that of the preceding noble gas plus filled d- and f-subshells. Hence, aluminium does not suffer the effects of incomplete shielding of valence electrons by inner electrons from the nucleus that its heavier congeners do. Aluminium's electropositive behavior, high affinity for oxygen, and highly negative standard electrode potential are all more similar to those of scandium, yttrium, lanthanum, and actinium, which have ds2 configurations of three valence electrons outside a noble gas core: aluminium is the most electropositive metal in its group. Aluminium also bears minor similarities to the metalloid boron in the same group; AlX3 compounds are valence isoelectronic to BX3 compounds (they have the same valence electronic structure), and both behave as Lewis acids and readily form adducts. Additionally, one of the main motifs of boron chemistry is regular icosahedral structures, and aluminium forms an important part of many icosahedral quasicrystal alloys, including the Al–Zn–Mg class.

Niobium(III) chloride also known as niobium trichloride is a compound of niobium and chlorine. The binary phase NbCl3 is not well characterized but many adducts are known.

Manganese(III) chloride is the hypothetical inorganic compound with the formula MnCl3.

Gallium compounds are compounds containing the element gallium. These compounds are found primarily in the +3 oxidation state. The +1 oxidation state is also found in some compounds, although it is less common than it is for gallium's heavier congeners indium and thallium. For example, the very stable GaCl2 contains both gallium(I) and gallium(III) and can be formulated as GaIGaIIICl4; in contrast, the monochloride is unstable above 0 °C, disproportionating into elemental gallium and gallium(III) chloride. Compounds containing Ga–Ga bonds are true gallium(II) compounds, such as GaS (which can be formulated as Ga24+(S2−)2) and the dioxan complex Ga2Cl4(C4H8O2)2. There are also compounds of gallium with negative oxidation states, ranging from -5 to -1, most of these compounds being magnesium gallides (MgxGay).

<span class="mw-page-title-main">Tetrahalodiboranes</span> Class of diboron compounds

Tetrahalodiboranes are a class of diboron compounds with the formula B2X4. These compounds were first discovered in the 1920s, but, after some interest in the middle of the 20th century, were largely ignored in research. Compared to other diboron compounds, tetrahalodiboranes are fairly unstable and historically have been difficult to prepare; thus, their use in synthetic chemistry is largely unexplored, and research on tetrahalodiboranes has stemmed from fundamental interest in their reactivity. Recently, there has been a resurgence in interest in tetrahalodiboranes, particularly in diboron tetrafluoride as a reagent to promote doping of silicon with B+ for use in semiconductor devices.

References

  1. 1 2 Yamamoto, Y.; Miyaura, N. (2004). "Boron Trichloride". In Paquette, L. (ed.). Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons. doi:10.1002/047084289X.rb245.pub2. ISBN   0-471-93623-5.
  2. Index no. 005-002-00-5 of Annex VI, Part 3, to Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006. Official Journal of the European Union L353, 31 December 2008, pp. 1–1355at p 341.
  3. Brotherton, Robert J.; Weber, C. Joseph; Guibert, Clarence R.; Little, John L. (2000). "Boron Compounds". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a04_309. ISBN   978-3-527-30385-4.
  4. 1 2 3 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  5. Gerrard, W.; Lappert, M. F. (1958). "Reactions Of Boron Trichloride With Organic Compounds". Chemical Reviews . 58 (6): 1081–1111. doi:10.1021/cr50024a003.
  6. Wartik, T.; Rosenberg, R.; Fox, W. B. (1967). "Diboron Tetrachloride". Inorganic Syntheses. Vol. 10. pp. 118–125. doi:10.1002/9780470132418.ch18. ISBN   978-0-470-13241-8.
  7. Shun Okaya; Keiichiro Okuyama; Kentaro Okano; Hidetoshi Tokuyama (2016). "Trichloroboron-promoted Deprotection of Phenolic Benzyl Ether Using Pentamethylbenzene as a Non Lewis-Basic Cation Scavenger". Org. Synth. 93: 63–74. doi: 10.15227/orgsyn.093.0063 .
  8. Williard, Paul G.; Fryhle, Craig B. (1980). "Boron trihalide-methyl sulfide complexes as convenient reagents for dealkylation of aryl ethers". Tetrahedron Letters. 21 (39): 3731. doi:10.1016/0040-4039(80)80164-X.

Notes

  1. Within the European Union, the following additional hazard statement (EUH014) must also be displayed on labelling: Reacts violently with water.

Further reading