Vanadium tetrachloride

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Vanadium tetrachloride
Vanadium tetrachloride
Identifiers
CAS number 7632-51-1 YesY
PubChem 24273
ChemSpider 19956660 YesY
RTECS number YW2625000
Jmol-3D images Image 1
Properties
Molecular formula VCl4
Molar mass 192.75 g/mol
Appearance bright red liquid, moisture sensitive
Density 1.816 g/cm3, liquid
Melting point −28 °C
Boiling point 154 °C
Solubility in water decomposes
Solubility in other solvents chlorocarbons, hydrochloric acid
Vapor pressure 7.9 Pa
Structure
Coordination
geometry
tetrahedral
Dipole moment 0 D
Hazards
EU Index Not listed
Main hazards oxidizer; hydrolyzes to release HCl
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Related compounds
Other anions vanadium tetrafluoride, vanadium disulfide, vanadium tetrabromide
Other cations titanium tetrachloride, chromium tetrachloride, niobium tetrachloride, tantalum tetrachloride
Related compounds vanadium trichloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Vanadium tetrachloride is the inorganic compound with the formula VCl4. This bright red liquid is a useful reagent for the preparation of other vanadium compounds.

Synthesis, bonding, basic properties[edit]

With one more valence electron than diamagnetic TiCl4, VCl4 is a paramagnetic liquid. It is one of only a few paramagnetic compounds that is liquid at room temperature.

VCl4 is prepared by chlorination of vanadium metal. VCl5 does not form; Cl2 lacks the oxidizing power to attack VCl4. In contrast, the heavier analogues NbCl5 and TaCl5 are stable and not particularly oxidizing. Of course, VF5 does exist, reflecting the increased oxidizing power of F2 vs Cl2. Indicative of its oxidizing power, VCl4 releases Cl2 at its boiling point (standard pressure) to afford vanadium(III) chloride.

Reactions[edit]

Consistent with its high oxidizing power, VCl4 reacts with HBr at -50 °C to produce VBr3. The reaction proceeds via VBr4, which releases Br2 during warming to room temperature.[1]

2 VCl4 + 8 HBr → 2 VBr3 + 8 HCl + Br2

VCl4 forms adducts with many donor ligands, for example, VCl4(THF)2.

It is the precursor to vanadocene dichloride.

Applications[edit]

VCl4 is a catalyst for the polymerization of alkenes, especially those useful in the rubber industry. The underlying technology is related to Ziegler-Natta catalysis, which involves the intermediacy of vanadium alkyls.

Organic chemistry[edit]

In organic synthesis, VCl4 is used to couple phenols. For example, it converts phenol into 4,4'-biphenol.[2] It is reduced to VCl
3
in the process.

2 C6H5OH + 2 VCl4 → HOC6H4–C6H4OH + 2 VCl3 + 2 HCl

This reaction highlights the oxidizing ability of VCl4, consistent with it being resistant to further oxidation by Cl2.

Safety considerations[edit]

VCl4 is a volatile, aggressive oxidant that readily hydrolyzes to release HCl.

References[edit]

  1. ^ Calderazzo, F.; Maichle-Mossmer, C.; Pampaloni, G. and Strähle, J. (1993). "Low-temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange". Dalton Transactions: 655–8. doi:10.1039/DT9930000655. 
  2. ^ M. K. O’Brien, B. Vanasse, “Vanadium(IV) Chloride” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York.