Thermally-Controlled Formation of Crystalline Hexachlorobenzene, Hexachloroethane, and Anhydrous Chromium Chloride

Abstract

The high-temperature preparation of purple crystalline anhydrous chromium chloride (CrC13) by passing CC14 vapors over green Cr2O3 powder in an inert atmosphere is an instructive experiment in the inorganic chemistry laboratory. A systematic investigation of this synthesis (using a carefully calibrated tube furnace, X-ray powder diffraction, infrared spectroscopy, and gas chromatography) revealed that the products formed as a consequence of the pyrolysis of CC14 are sensitive to the reaction temperature . When Crz03 is present, the formation of CrC13 dominates at temperatures between 600°C and 800°C; at temperatures above 900°C, CsCls forms preferentially (presumably from the linking of the C-C1 free radicals produced by the pyrolysis) as the unreacted metal oxide is sintered to form eskolaite. In the absence of C1-203, the pyrolysis products are crystalline hexachloroethane (C2Cls) at 600°C and needle-shaped crystals of hexachlorobenzene at temperatures above 900°C .