Patent GB-971575-A (GB)
Title: Process for the oxidation of precious metals
Inventor: HELDEN ROBERT VAN
IPC: C01G55/00
Filed: 1961-03-14
Abstract: Ir, Os, Pd, Pt, Rh and Ru, or lower valency compounds thereof, are oxidized to a higher valency state by introducing an oxygen-containing gas into a mixture of said metals or compounds, one or more mineral acids and/or aromatic sulphonic acids, and one or more redox systems, said mixture components being present in a substantially non-aqueous liquid medium containing one or more carboxylic acids.  Specified mineral acids are sulphuric, phosphoric and, the preferred, hydrochloric acids and preferred redox systems are the nitrogen-monoxide and dioxide system and a mixture of the nitrogen monoxide system and the basic iron acetate system.  The liquid medium is preferably for the major part composed of the carboxylic acid(s); suitable acids being those which are liquid at the oxidation temperature, which is usually between 0 DEG  and 150 DEG  C., preferably at ambient temperature (e.g. acetic and pivalic acids).  Other organic liquids having less than 1% degredation under the reaction conditions may also be present in said medium.  The invention is of particular interest in connection with the regeneration of precious metal salts from the reaction product of the process for preparing alkenyl esters of carboxylic acids by reacting salts of said metals, derived from mineral acids and/or aromatic sulphonic acids, with olefinically unsaturated hydrocarbons and metal, other than precious metal, salts of carboxylic acids (see Division C2).  Specification 969,018 also is referred to.ALSO:Precious metals, i.e. Ir.; Os.; Pd.; Pt.; Rh.; and Ru., or lower valency compounds thereof are oxidized to compounds of such metals or compounds in which the metals have a higher valency state than initially by introducing oxygen or an oxygen-containing gas into a mixture of said metals or compounds, one or more mineral acids and/or aromatic sulphonic acids, and one or more redox systems, said mixture components being present in a substantially non-aqueous liquid medium containing one or more carboxylic acids.  Specified mineral acids are sulphuric, phosphonic and, the preferred, hydrochloric acids and preferred redox systems are the nitrogen-monoxide and dioxide system and a mixture of the nitrogen monoxide system and the basic iron acetate system.  The liquid medium is preferably for the major part composed of the carboxylic acid(s); suitable acids being those which are liquid at the oxidation temperature, which is usually between 0 DEG  and 150 DEG C., preferably at ambient temperature (e.g. acetic and pivalic acids). Other organic liquids having less than 1% degredation under the reaction conditions may also be present in said medium. The invention is of particular interest in connection with the regeneration of precious metal salts from the reaction product of the process for preparing alkenyl esters of carboxylic acids by reacting salts of said metals, derived from mineral acids and/or aromatic sulphonic acids, with olefinically unsaturated hydrocarbons and metal, other than precious metal, salts of carboxylic acids in a substantially non-aqueous medium. The regeneration may be performed simultaneously with said process.  Specification 969,018 also is referred to.