Vanadium tetrachloride
# Vanadium tetrachloride

Vanadium tetrachloride is the inorganic compound with the formula $VCl_4.$ This reddish-brown liquid serves as a useful reagent for the preparation of other vanadium compounds.

## Synthesis, bonding, basic properties

With one more valence electron than diamagnetic $TiCl_4,$ $VCl_4$ is a paramagnetic liquid. It is one of only a few paramagnetic compounds that is liquid at room temperature.

$VCl_4$ is prepared by chlorination of vanadium metal. $VCl_5$ does not form in this reaction; $Cl_2$ lacks the oxidizing power to attack $VCl_4.$ $VCl_5$ can however be prepared indirectly from $VF_5$ at −78 °C.

## Reactions

Consistent with its high oxidizing power, $VCl_4$ reacts with HBr at -50 °C to produce $VBr_3.$ The reaction proceeds via $VBr_4,$ which releases $Br_2$ during warming to room temperature.

    2 $VCl_4$ + 8 HBr → 2 $VBr_3$ + 8 HCl + $Br_2$

$VCl_4$ forms adducts with many donor ligands, for example, $VCl_4(THF)_2.$

It is the precursor to vanadocene dichloride.

### Organic chemistry

In organic synthesis, $VCl_4$ is used for the oxidative coupling of phenols. For example, it converts phenol into a mixture of 4,4'-, 2,4'-, and 2,2'-biphenols:

    2 $C_6H_5OH$ + 2 $VCl_4$ → $HOC_6H_4–C_6H_4OH$ + 2 $VCl_3$ + 2 HCl

## Applications

$VCl_4$ 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.

## Safety considerations

$VCl_4$ is a volatile, aggressive oxidant that readily hydrolyzes to release HCl.

