Vanadium oxytrichloride

Vanadium oxytrichloride
IUPAC name Vanadium trichloride oxide
Other names Vanadyl chloride Vanadyl trichloride
Identifiers
CAS number	7727-18-6 Y
PubChem	24410
RTECS number	YW2975000
Properties
Molecular formula	VOCl3
Molar mass	173.30 g/mol
Appearance	Yellow to brown liquid
Density	1.826 g/cm3, liquid
Melting point	-76.5 °C, 197 K, -106 °F
Boiling point	126.7 °C, 400 K, 260 °F
Solubility in water	Decomposes
Solubility in other solvents	chlorinated solvents
Vapor pressure	8.1 Pa (20 °C)
Structure
Molecular shape	Tetrahedral
Hazards
EU Index	Not listed
Main hazards	Toxic, hydrolysis to HCl
NFPA 704	1 3 3
LD50	140 mg/kg (oral in rats)
Related compounds
Related vanadium compounds	Vanadium(V) oxide Vanadium tetrachloride Vanadium oxytrifluoride
Related compounds	Phosphoryl chloride
Y oxytrichloride (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 oxytrichloride is the inorganic compound with the formula VOCl₃. This distillable liquid hydrolyzes readily in air and is a strong oxidant. It is used as a reagent in organic synthesis.^[1]

Properties

VOCl₃ is a vanadium(V) compound and as such is diamagnetic. It is tetrahedral with O-V-Cl bond angles of 111° and Cl-V-Cl bond angles of 108°. The V-O and V-Cl bond lengths are 157 and 214 pm, respectively. VOCl₃ is highly reactive toward water and evolves Cl₂ upon standing. It is soluble in nonpolar solvents such as benzene, CH₂Cl₂, and hexane. In some aspects, the chemical properties of VOCl₃ and POCl₃ are similar. One distinction is that VOCl₃ is a strong oxidizing agent, whereas the phosphorus compound is not.^[2]

Preparation

VOCl₃ is synthesized by the chlorination of V₂O₅. The reaction proceeds at ca. 600 °C:^[3]

3 Cl₂ + V₂O₅ → 2 VOCl₃ + 1.5 O₂

When the V₂O₅ is used as an intimate mixture with carbon, the synthesis proceeds at 200-400 °C; in this case the carbon serves as a deoxygenation agent akin to its use in the Kroll process for the manufacturing of TiCl₄ from TiO₂.

Vanadium(III) oxide can also be used as a precursor:

3 Cl₂ + V₂O₃ → 2 VOCl₃ + 0.5 O₂

A more typical laboratory synthesis involves the chlorination of V₂O₅ using SOCl₂.^[4]

V₂O₅ + 3 SOCl₂ → 2 VOCl₃ + 3 SO₂

Reactions

Hydrolysis and alcoholysis

Vanadium oxytrichloride quickly hydrolyzes resulting in vanadium pentoxide and hydrochloric acid. In the picture, orange V₂O₅ can be seen forming on the walls of the beaker. An intermediate in this process is VO₂Cl:

2 VOCl₃ + 3 H₂O → V₂O₅ + 6 HCl

VOCl₃ reacts with alcohols especially in the presence of a proton-acceptor (e.g. Et₃N) to give alkoxides:

VOCl₃ + 3 ROH → VO(OR)₃ + 3 HCl (R = Me, Ph, etc.)

Interconversions to other V-O-Cl compounds

VOCl₃ is also used in the synthesis of VOCl₂.

V₂O₅ + 3 VCl₃ + VOCl₃ → 6 VOCl₂

Dioxovanadium monochloride can be prepared by an unusual reaction involving Cl₂O.^[5]

VOCl₃ + Cl₂O → VO₂Cl + 2 Cl₂

At >180 °C, VO₂Cl decomposes to V₂O₅ and VOCl₃. Similarly, VOCl₂ also decomposes to give VOCl₃, together with VOCl.

Adduct formation

VOCl₃ is strongly Lewis acidic, as demonstrated by its tendency to form adducts with various bases such as MeCN and amines. In forming the adducts, vanadium changes from four-coordinate tetrahedral geometry to six-coordinate octahedral geometry:

VOCl₃ + 2 H₂NEt → VOCl₃(H₂NEt)₂

VOCl₃ in alkene polymerization

VOCl₃ is used as a catalyst or precatalytst in production of ethylene-propylene rubbers (EPDM).

References

1. ^ M. O'Brien, B. Vanasse (2001). Encyclopedia of Reagents for Organic Synthesis. 
2. ^ A. Earnshaw, N. Greenwood (1997). The Chemistry of the Elements - Second Edition. pp. 513–514. 
3. ^ A. Holleman, E. Wiberg (2001). Inorganic Chemistry. 
4. ^ S. Tyree (1967). Inorganic Syntheses Volume IX. p. 80. 
5. ^ H. Oppermann, "Gleichgewichte mit VOCl₃, VO₂Cl, VOCl₂" Zeitschrift für Anorganische und Allgemeine Chemie, vol. 331. 113-126 (1967)