GB877109A - Process for the production of chromium hexacarbonyl - Google Patents

Abstract

Chromium hexacarbonyl is produced by reacting chromium or an organic chromium compound in which the chromium is linked to oxygen, nitrogen, or sulphur with carbon monoxide at a temperature of 80-200 DEG C. and a pressure of 10-400 atmos. in the presence of ammonia or an amine in the liquid state, a metal which is more electropositive than chromium or a hydride or alkyl hydride of said metal, and a halogen. The chromium may be in the form of a chromium-aluminium alloy. Chromium compounds specified are chromium acetate, 2-ethylhexanoate, acetlyacetonate, and ethyl xanthogenate, and trichlorotripyridine chromium. The carbon monoxide may be admixed with hydrogen. Amines specified are pyridine, quinoline, tri-ethylamine, and tributylamine. Electro-positive metals specified are zinc, magnesium and aluminium. Mixtures or alloys of two or more metals may be employed. The halogen may be introduced in the free state, e.g. as iodine, or as a compound, e.g. as chloroform, carbon tetrachloride, aluminium tribromide, copper chlorocarbonyl, or iron, cobalt, or nickel halide. It may alternatively be present in the chromium compound being reacted, e.g. trichloro tripyridine chromium. 0.1-2 molar per cent. of halogen or halogen compound may be employed. An inert liquid, e.g. toluene, isoctane, diethyl ether, a ketone or methyl alcohol may be present. Preformed chromium hexacarbonyl or another metal carbonyl, e.g. dicobalt octacarbonyl, or a metal salt, e.g. cobalt acetate, cobalt iodide, or mercuric chloride, capable of convertion into another metal carbonyl may be present as an accelerator. In a batch process using an autoclave, chromium hexacarbonyl may be recovered from the reaction product by steam distillation, optionally in the presence of added acid, e.g. hydrochloric acid to prevent foaming by extraction with diethyl ether, chloroform, carbon tetrachloride, or a hydrocarbon by subliming at 80-110 DEG C. in the presence of nitrogen, hydrogen, or carbon monoxide without separating the liquid phase, or by subliming at 75 DEG C. and 15 m.m. Hg after cooling to -40 DEG C. and separating the liquid phase. In a continuous process a solution or suspension may be passed down a reaction tower in countercurrent to carbon monoxide under pressure, the product gas being passed off overhead, cooled to remove chromium hexacarbonyl, and recycled after the addition of further carbon monoxide. Examples are given.