Van Arkel method

Titanium tetraiodide can be prepared by direct combination of the elements at 150—200°C it can be made by reaction of gaseous hydrogen iodide with a solution of titanium tetrachloride in a suitable solvent and it can be purified by vacuum sublimation at 200°C. In the van Arkel method for the preparation of pure titanium metal, the sublimed tetraiodide is decomposed on a tungsten or titanium filament held at ca 1300°C (152). There are frequent hterature references to its use as a catalyst, eg, for the production of ethylene glycol from acetylene (153). 

A classical example of this process is given by the van Arkel method for the preparation (purification) of several metals. If impure Cr, for instance, is contained together with a small quantity of iodine in a vacuum tube maintained at a temperature at which chromium iodide volatilizes, and a hot zone is created by means of, say, a W filament heated by an electric current, the following reaction will be observed ... 

The residue dissolves in water to a violet solution which soon evolves Ho and turns green. VIg, obtained by heating the tri-iodide at reduced pressure, has been used in the preparation of pure vanadium by the Van Arkel method. 

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See also in sourсe #XX -- [ ]

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