my-server
← Wiki Redirected from Vanadium oxychloride

Vanadium oxytrichloride

Vanadium oxytrichloride is the inorganic compound with the formula VOCl<sub>3</sub>. 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.

Properties

VOCl<sub>3</sub> is a vanadium compound with vanadium in the +5 oxidation state 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. VOCl<sub>3</sub> is highly reactive toward water and evolves HCl upon standing. It is soluble in nonpolar solvents such as benzene, CH<sub>2</sub>Cl<sub>2</sub>, and hexane. In some aspects, the chemical properties of VOCl<sub>3</sub> and POCl<sub>3</sub> are similar. One distinction is that VOCl<sub>3</sub> is a strong oxidizing agent, whereas the phosphorus compound is not. Neat VOCl<sub>3</sub> is the usual chemical shift standard for <sup>51</sup>V NMR spectroscopy.

Preparation

VOCl<sub>3</sub> arises by the chlorination of V<sub>2</sub>O<sub>5</sub>. The reaction proceeds near 600&nbsp;°C:

3 Cl<sub>2</sub> + V<sub>2</sub>O<sub>5</sub> → 2 VOCl<sub>3</sub> + 1.5 O<sub>2</sub>

Heating an intimate (well-blended with tiny particles) mixture of V<sub>2</sub>O<sub>5</sub>, chlorine, and carbon at 200–400&nbsp;°C also gives VOCl<sub>3</sub>. In this case the carbon serves as a deoxygenation agent akin to its use in the chloride process for the manufacturing of TiCl<sub>4</sub> from TiO<sub>2</sub>.

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

3 Cl<sub>2</sub> + V<sub>2</sub>O<sub>2</sub> → 2 VOCl<sub>3</sub>

A more typical laboratory synthesis involves the chlorination of V<sub>2</sub>O<sub>5</sub> using SOCl<sub>2</sub>.

V<sub>2</sub>O<sub>5</sub> + 3 SOCl<sub>2</sub> → 2 VOCl<sub>3</sub> + 3 SO<sub>2</sub>

Reactions

Hydrolysis and alcoholysis

VOCl<sub>3</sub> quickly hydrolyzes resulting in vanadium pentoxide and hydrochloric acid. An intermediate in this process is VO<sub>2</sub>Cl:

2 VOCl<sub>3</sub> + 3 H<sub>2</sub>O → V<sub>2</sub>O<sub>5</sub> + 6 HCl

VOCl<sub>3</sub> reacts with alcohols especially in the presence of a proton-acceptor to give alkoxides, as illustrated by this synthesis of vanadyl isopropoxide:

VOCl<sub>3</sub> + 3 HOCH(CH<sub>3</sub>)<sub>2</sub> → VO(OCH(CH<sub>3</sub>)<sub>2</sub>)<sub>3</sub> + 3 HCl

Interconversions to other V-O-Cl compounds

VOCl<sub>3</sub> is also used in the synthesis of vanadium oxydichloride.

V<sub>2</sub>O<sub>5</sub> + 3 VCl<sub>3</sub> + VOCl<sub>3</sub> → 6 VOCl<sub>2</sub>

VO<sub>2</sub>Cl can be prepared by an unusual reaction involving Cl<sub>2</sub>O.

VOCl<sub>3</sub> + Cl<sub>2</sub>O → VO<sub>2</sub>Cl + 2 Cl<sub>2</sub>

At >180&nbsp;°C, VO<sub>2</sub>Cl decomposes to V<sub>2</sub>O<sub>5</sub> and VOCl<sub>3</sub>. Similarly, VOCl<sub>2</sub> also decomposes to give VOCl<sub>3</sub>, together with VOCl.

Adduct formation

VOCl<sub>3</sub> is strongly Lewis acidic, as demonstrated by its tendency to form adducts with various bases such as acetonitrile and amines. In forming the adducts, vanadium changes from four-coordinate tetrahedral geometry to six-coordinate octahedral geometry:

VOCl<sub>3</sub> + 2 H<sub>2</sub>NEt → VOCl<sub>3</sub>(H<sub>2</sub>NEt)<sub>2</sub>

Organic chemistry

VOCl<sub>3</sub> is a catalyst or precatalyst in production of ethylene-propylene rubbers (EPDM). In organic synthesis, it has been used for oxidative coupling of phenols and anisoles.

References