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
IUPAC name
Boron trichloride
Other names
Boron(III) chloride
3D model (JSmol)
ECHA InfoCard 100.030.586 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-658-4
PubChem CID
RTECS number
  • ED1925000
  • InChI=1S/B.3ClH/h;3*1H/q+3;;;/p-3 Yes check.svgY
  • InChI=1/B.3ClH/h;3*1H/q+3;;;/p-3
  • ClB(Cl)Cl
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]
Solubility soluble in CCl4, ethanol
-59.9·10−6 cm3/mol
Trigonal planar (D3h)
107 J/mol K
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
H300, H314, H330 [note 1]
NFPA 704 (fire diamond)
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 toward water.


Production and structure

Boron reacts with halogens to give the corresponding trihalides. Boron trichloride is, however, produced industrially by direct 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. In the laboratory BF3 reacted with AlCl3 gives BCl3 via halogen exchange. [3] BCl3 is a trigonal planar molecule like the other boron trihalides, and has a bond length of 175pm.

A degree of π-bonding has been proposed to explain the short B Cl distance although there is some debate as to its extent. [3] It 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.


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. [4] 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 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: [5]

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. [3] It 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.


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 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. [1] [6]


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, [7] when possible, but H2O will destroy the BCl3 portion while leaving dimethyl sulfide in solution.

See also

Related Research Articles

Diborane Chemical compound

Diborane(6), generally known as diborane, is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a toxic, colorless and pyrophoric gas with a repulsively sweet odor. Synonyms include boroethane, boron hydride, and diboron hexahydride. Diborane is a key boron compound with a variety of applications. It has attracted wide attention for its electronic structure. Its derivatives are useful reagents.

Titanium tetrachloride 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" due to the phonetic resemblance of its molecular formula to the word.

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.

Phosphorus trichloride Chemical compound

Phosphorus trichloride is a inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic and reacts readily with water to release hydrogen chloride.

Triphenylphosphine 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 widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether.

Organotin chemistry Branch of organic chemistry

Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. 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.

Organoboron chemistry

Organoborane or organoboron compounds are chemical compounds of boron and carbon that are organic derivatives of BH3, for example trialkyl boranes. Organoboron chemistry or organoborane chemistry is the chemistry of these compounds.

Hafnium tetrachloride Chemical compound

Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.

Vanadium oxytrichloride Chemical compound

Vanadium oxytrichloride is the inorganic compound with the formula VOCl3. This yellow distillable liquid hydrolyzes readily in air. It is an oxidizing agent. It is used as a reagent in organic synthesis. Samples often appear red or orange owing to an impurity of vanadium tetrachloride.

Molybdenum(V) chloride Chemical compound

Molybdenum(V) chloride is the inorganic compound with the formula [MoCl5]2. This dark volatile solid is used in research to prepare other molybdenum compounds. It is moisture-sensitive and soluble in chlorinated solvents. Usually called molybdenum pentachloride, it is in fact a dimer with the formula Mo2Cl10.

Gallium trichloride Chemical compound

Gallium trichloride is the chemical compound with the formula GaCl3. Solid gallium trichloride 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.

Organotitanium compound

Organotitanium compounds in organometallic chemistry contain carbon-titanium chemical bonds. Organotitanium chemistry is the science of organotitanium compounds describing their physical properties, synthesis and reactions. They are reagents in organic chemistry and are involved in major industrial processes.

Organotellurium chemistry describes the synthesis and properties of chemical compounds containing a carbon-tellurium chemical bond. Organotellurium chemistry is a lightly studied area, in part because of the few applications.

Molybdenum tetrachloride Chemical compound

Molybdenum tetrachloride is the inorganic compound with the empirical formula MoCl4. The material exists as two polymorphs, both being dark-colored paramagnetic solids. These compounds are mainly of interest as precursors to other molybdenum complexes.

Zirconium(III) chloride Chemical compound

Zirconium(III) chloride is an inorganic compound with formula ZrCl3. It is a blue-black solid that is highly sensitive to air.

Trimethylborane Chemical compound

Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl).

Diboron tetrachloride Chemical compound

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

Tetrahydroxydiboron Chemical compound

Tetrahydroxydiboron is a chemical reagent which can be used to prepare boronic acids.

Aluminium compounds

Aluminium (or aluminum) 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.


  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   0471936235.
  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. OJEU L353, 31.12.2008, pp 1–1355at p 341.
  3. 1 2 3 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  4. Gerrard, W.; Lappert, M. F. (1958). "Reactions Of Boron Trichloride With Organic Compounds". Chemical Reviews . 58 (6): 1081–1111. doi:10.1021/cr50024a003.
  5. Wartik, T.; Rosenberg, R.; Fox, W. B. (1967). "Diboron Tetrachloride". Inorganic Syntheses. Vol. 10. pp. 118–125. doi:10.1002/9780470132418.ch18. ISBN   9780470132418.
  6. 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 .{{cite journal}}: CS1 maint: uses authors parameter (link)
  7. 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.


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

Further reading