Vanadium tetrachloride

Vanadium tetrachloride
IUPAC name Vanadium tetrachloride Vanadium(IV) chloride
Identifiers
CAS number	7632-51-1 Y
PubChem	24273
ChemSpider	19956660 Y
RTECS number	YW2625000
Jmol-3D images	Image 1
SMILES [V+2].[V+2].[Cl-].[Cl-].[Cl-].[Cl-]
InChI InChI=1S/4ClH.2V/h4*1H;;/q;;;;2*+2/p-4 Y Key: UNUHYFVFMNJHJW-UHFFFAOYSA-J Y InChI=1/4ClH.2V/h4*1H;;/q;;;;2*+2/p-4 Key: UNUHYFVFMNJHJW-XBHQNQODAR
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
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	0 3 2 W
Related compounds
Other anions	vanadium tetrafluoride, vanadium disulfide, vanadium tetrabromide
Other cations	titanium tetrachloride, chromium tetrachloride, niobium tetrachloride, tantalum tetrachloride
Related compounds	vanadium trichloride
Y tetrachloride (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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

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

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

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

In organic synthesis, VCl₄ is used to couple phenols. For example, it converts phenol into 4,4'-biphenol.^[2] It is reduced to VCl₃ 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

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

References

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.