Hafnium compounds—continued

The bis(77-cyclopentadienyl)zirconium dichloride has been synthesized by a variety of routes and a variety of authors. It can be recovered from reaction systems of zirconium tetrachloride and sodium cyclopentadienide in tetrahydrofuran or ethyleneglycol dimethyl ether 89, 194, 343, 471) or with lithium cyclopentadienide 472) in place of the sodium compound. The hafnium compound was prepared in a similar manner 343, 471). In general, the residue obtained upon evaporation of the solvent is extracted with chloroform and the product from the extraction is recrystallized from benzene. The dichloride was also prepared 451) by the continuous recirculation of cyclopentadiene vapor through a bed of ZrCl2 at 270°-350°C. Another route to the chloride is the reaction of zirconium tetrachloride with cyclopentadienylmagnesium chloride 559) in benzene yet another involves the reaction of zirconium tetrachloride and cyclopentadiene in ethylamine as the solvent at room temperature 367). 

Zirconium and hafnium are separated by fractional distillation of the anhydrous tetrachlorides in a continuous molten solvent salt KCl—AlCl system at atmospheric pressure (56,57). Zirconium and hafnium tetrachlorides are soluble in KCl—AlCl without compound formation and are produced simultaneously. 

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