Boron trichloride

Boron trichloride
Boron trichloride	Boron trichloride
Names
	IUPAC name Boron trichloride
	Other names Boron(III) chloride; Trichloroborane
Identifiers
CAS Number	10294-34-5 ;
3D model (JSmol)	Interactive image;
ChemSpider	23480 ;
ECHA InfoCard	100.030.586
EC Number	233-658-4;
PubChem CID	25135;
RTECS number	ED1925000;
UNII	K748471RAG ;
CompTox Dashboard (EPA)	DTXSID2041676 ;
	InChI InChI=1S/B.3ClH/h;31H/q+3;;;/p-3 Key: PYQQLJUXVKZOPJ-UHFFFAOYSA-K ; InChI=1/B.3ClH/h;31H/q+3;;;/p-3 Key: PYQQLJUXVKZOPJ-DFZHHIFOAV;
	SMILES ClB(Cl)Cl;
Properties
Chemical formula	BCl3
Molar mass	117.17 g/mol
Appearance	Colorless 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)
Solubility in water	hydrolysis
Solubility	soluble in CCl4, ethanol
Magnetic susceptibility (χ)	-59.9·10−6 cm3/mol
Refractive index (nD)	1.00139
Structure
Molecular shape	Trigonal planar (D3h)
Dipole moment	zero
Thermochemistry
Heat capacity (C)	107 J/mol K
Std molar; entropy (S⦵298)	206 J/mol K
Std enthalpy of; formation (ΔfH⦵298)	-427 kJ/mol
Gibbs free energy (ΔfG⦵)	-387.2 kJ/mol
Hazards
	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:
Pictograms
Signal word	Danger
Hazard statements	H300, H314, H330
NFPA 704 (fire diamond)	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). verify (what is ?) Infobox references

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.

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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.

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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.

Thumb — 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 → B_nCl_n + n BCl₃

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

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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 BOCl_x and M_xO_yCl_z 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]

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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.

List of highly toxic gases

[1]
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. 1–1355 at 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]
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.

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

Martin, D. R. (1944). "Coordination Compounds of Boron Trichloride. I. - A Review". Chemical Reviews. 34 (3): 461–473. doi:10.1021/cr60109a005.
Kabalka, G. W.; Wu, Z. Z.; Ju, Y. H. (2003). "The Use of Organoboron Chlorides and Bromides in Organic Synthesis". Journal of Organometallic Chemistry. 680 (1–2): 12–22. doi:10.1016/S0022-328X(03)00209-2.

International Chemical Safety Card 0616

[EROS-1] [1]
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] [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. 1–1355 at p 341.

[Brotherton-4] [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.

[greenwood-5] [4]
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[6] [5]
Gerrard, W.; Lappert, M. F. (1958). "Reactions Of Boron Trichloride With Organic Compounds". Chemical Reviews. 58 (6): 1081–1111. doi:10.1021/cr50024a003.

[7] [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.

[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.

[9] [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.

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

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Boron trichloride

Reduction

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Production and structure

Reactions

Uses

Safety

See also

References

Notes

Further reading

External links