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| Names | |
|---|---|
| IUPAC name Boron trichloride | |
| Other names Boron(III) chloride Trichloroborane | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.030.586 |
| EC Number |
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| RTECS number |
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| UNII | |
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| Properties | |
| BCl3 | |
| Molar mass | 117.16 g·mol−1 |
| 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)[1] |
| hydrolysis | |
| Solubility | soluble inCCl4,ethanol |
| −59.8·10−6 cm3/mol | |
Refractive index (nD) | 1.00139 |
| Structure | |
| Trigonal planar (D3h) | |
| zero | |
| Thermochemistry | |
| 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[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: | |
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| Danger | |
| H300,H314,H330[note 1] | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Safety data sheet (SDS) | ICSC0616 |
| Related compounds | |
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Othercations | |
Related compounds | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Boron trichloride is theinorganic compound with the formula BCl3. This colorless gas is a reagent inorganic synthesis. It is highly reactive towards water.
Boron reacts withhalogens to give the corresponding trihalides. Boron trichloride is, however, produced industrially bychlorination ofboron oxide andcarbon at 501 °C.
Thecarbothermic reaction is analogous to theKroll 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 withphosgene.[3]
In the laboratory BCl3 can be prepared by treating with AlCl3 withBF3, 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 ofAlCl3 andGaCl3, which form dimers or polymers with 4 or 6 coordinate metal centres.
BCl3 hydrolyzes readily to give hydrochloric acid andboric acid:
Alcohols behave analogously giving the borate esters, e.g.trimethyl borate.
As a strongLewis acid, BCl3 formsadducts with tertiaryamines,phosphines,ethers,thioethers, andhalide 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:
The mixedaryl andalkyl boron chlorides are also of known.Phenylboron dichloride is commercially available. Such species can be prepared by theredistribution reaction of BCl3 with organotin reagents:
Reduction of BCl3 to elemental boron is conducted commercially in the laboratory, when boron trichloride can be converted todiboron tetrachloride by heating with copper metal:[6]
B4Cl4 can also be prepared in this way. Colourless diboron tetrachloride (m.p. −93 °C) is a planar molecule in the solid, (similar todinitrogen 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 whichn may be 8, 9, 10, or 11.
The compounds with formulas B8Cl8 and B9Cl9 are known to contain closed cages of boron atoms.
Boron trichloride is a starting material for the production of elemental boron. It is also used in therefining ofaluminium,magnesium, zinc, andcopper alloys to removenitrides,carbides, andoxides from molten metal. It has been used as a soldering flux for alloys of aluminium,iron,zinc,tungsten, andmonel. Aluminium castings can be improved by treating the melt with boron trichloride vapors. In the manufacture of electrical resistors, a uniform and lasting adhesivecarbon film can be put over aceramic 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 inplasma etching insemiconductor manufacturing. This gas etches metal oxides by formation of a volatile BOClx and MxOyClz compounds.
BCl3 is used as areagent in the synthesis of organic compounds. Like the corresponding bromide, it cleaves C-O bonds inethers.[1][7]
BCl3 is an aggressive reagent that can formhydrogen chloride upon exposure to moisture oralcohols. Thedimethyl 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.
