Boron trichloride
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| Boron trichloride | |
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| General | |
| Systematic name | Boron trichloride |
| Other names | Boron(III) chloride |
| Molecular formula | BCl3 |
| Molar mass | 117.17 g/mol |
| Appearance | Colorless gas, fumes in air |
| CAS number | [10294-34-5] |
| Properties | |
| Density and phase | 1.43 g/ml (O °C) |
| Solubility in water | decomp. |
| Melting point | −107.3 °C |
| Boiling point | 12.5 °C |
| Structure | |
| Molecular shape | Trigonal planar (D3h) |
| Bond length | 173 pm (B–Cl) |
| Dipole moment | zero |
| Hazards | |
| MSDS | External MSDS |
| EU classification | Very toxic (T+) |
| NFPA 704 | |
| R-phrases | R14, R26/28, R34 |
| S-phrases | SS1/2, S9, S26, S28, S36/37/39, S45 |
| Flash point | Non-flammable |
| RTECS number | ED1925000 |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions | Boron trifluoride Boron tribromide Boron triiodide |
| Other cations | Aluminium chloride Gallium chloride |
| Related compounds | Boron oxide Carbon tetrachloride |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references |
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Boron trichloride is the chemical compound with the formula BCl3. This colorless gas is a valuable reagent in organic synthesis. It is also dangerously reactive.
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[edit] Production and properties
Boron reacts with the halogens to give the corresponding trihalides. Boron trichloride is, however, produced by direct chlorination of boron oxide and carbon at 500 °C.
- B2O3 + 3 C + 3 Cl2 → 2 BCl3 + 3 CO
The synthesis is analogous to the Kroll process for the conversion of titanium dioxide to titanium tetrachloride.
BCl3 readily forms adducts with tertiary amines, phosphines, ethers, thioethers, and halide ions. For example, BCl3S(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)2SBCl3
(CH3)2S + BCl3
When boron trichloride is passed at low pressure through devices delivering an electric discharge, diboron tetrachloride,[1] Cl2B-BCl2, and tetraboron tetrachloride, formula B4Cl4, are formed. Colourless iboron tetrachloride (m.p. -93 °C) decomposes 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; the compounds with formulas B8Cl8 and B9Cl9 are known to contain closed cages of boron atoms.
The mixed aryl and alkyl boron chlorides are also of interest. Phenylboron dichloride is commercially available. Such species can be prepare by the reaction of BCl3 with organotin reagents:
- 2 BCl3 + R4Sn → 2 RBCl2 + R2SnCl2
[edit] 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 aluminum, 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 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 compounds.
BCl3 is used as a reagent in the synthesis of organic compounds. Like the corresponding bromide, it cleaves C-O bonds in ethers.[2]
[edit] Safety
BCl3 is an aggressive reagent that releases hydrogen chloride upon exposure to moisture or alcohols. The dimethylsulfide adduct is safer to use, when possible.
[edit] References
- ^ Wartik, T.; Rosenberg, R.; Fox, W. B. "Diboron tetrachloride" Inorganic Syntheses 1967, volume X, pages 118-126.
- ^ 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.
- W. Gerrard and M. F. Lappert (1958). "Reactions Of Boron Trichloride With Organic Compounds". Chemical Reviews 58: 1081 - 1111. DOI:10.1021/cr50024a003.
- D. R. Martin (1944). "Coordination compounds of boron trichloride. I - A review". Chemical Reviews 34: 461-473. DOI:10.1021/cr60109a005.
- Kabalka GW, Wu ZZ, Ju YH (2003). "The use of organoboron chlorides and bromides in organic synthesis". Journal of Organometallic Chemistry 680: 12-22. DOI:10.1016/S0022-328X(03)00209-2.
