Chromium Chlorides

compounds of chromium and chlorine: CrCl₂, CrCl₃, and CrCl₄.

Chromous chloride, CrCl₂, is a white, hygroscopic crystalline compound, with a density of 2.75 g/cm³ and a melting point of 824°C. Its aqueous solutions are blue. Chromous chloride forms complexes with ammonia, hydrazine, dipyridyl, and other compounds. It is produced by the reduction of CrCl₃ by hydrogen at 700°C or by the reaction of hydrogen chloride with metallic chromium at 600°–700°C. It is used in chromometry.

Chromic chloride, CrCl₃, is a violet crystalline compound, with a density of 2.76 g/cm³ and a melting point of 1152°C. At 600°C, it sublimes in a stream of chlorine or decomposes in the absence of chlorine into chlorine and CrCl₂. It is soluble in water in the presence of reducing agents, such as Cr²⁺ and Fe²⁺. Chromic chloride is produced industrially by the high-temperature chlorination of chromium and ferrochrome, as well as of chrome ores, in the presence of charcoal with the separate condensation in the latter two cases of chromium chlorides and iron. It is used in the production of chromium by electrolytic or thermal reduction methods.

Chromium(IV) chloride, CrCl₄, is unstable in the solid state. It is formed in the gas phase upon heating CrCl₃ in an excess of chlorine.

Chromyl chloride, CrO₂Cl₂, is the most important chromium compound containing chlorine and oxygen. It is a dark-red liquid, with a density of 1.911 g/cm³, a melting point of –96.5°C, and a boiling point of 117°C. It oxidizes most organic compounds. Produced by the action of dry HCl on CrO₃, chromyl chloride is used as an oxidizing agent in organic synthesis, for example, in the production of alizarin, saccharin, and anthraquinonedyes.