Patent GB-820540-A (GB)
Title: Process for the preparation of aromatic and heterocyclic carboxylic acids
IPC: C07D333/38
Filed: 1957-10-01
Abstract: Catalyst compositions comprise a heavy metal or a compound thereof, if desired on a carrier, in conjunction with an alkali metal salt or other derivative of cyanic acid or of a polymer thereof (e.g. cyanuric acid, cyanamide or dicyandiamide).  A preferred composition is prepared by dissolving a heavy metal compound in a potassium cyanate melt.  Specified metals are Cd, Zn, Hg, Pb and Fe.ALSO:Salts of aromatic or heterocyclic carboxylic acids of aromatic character containing at least two carboxyl groups are prepared by heating an alkali or alkaline earth metal salt of a different aromatic or heterocyclic carboxylic acid of aromatic character in the presence of an alkali metal salt or other derivative of cyanic acid or of a polymer thereof with the exclusion of appreciable amounts of water and oxygen.  The salt thus obtained may be converted into the free acid, another salt or other derivatives. Temperatures of 250 DEG  to 500 DEG  C. or higher are mentioned.  Oxygen and water may be excluded by a protective gas or by effecting the reaction in a potassium cyanate melt.  Suitable polymers or derivatives of cyanic acid include cyanuric acid, cyanamide and dicyandiamide or potassium salts of the derivatives.  Acid binding agents may be present. Superatmospheric pressures may be used.  Numerous types of acid, the salts of which are stated to be suitable starting materials, include mono-, di- and polycarboxylic acids derived from aromatic and heterocyclic ring systems such as benzene, naphthalene, diphenyl, anthracene, terphenyl, diphenylmethane, benzophenone, pyridine, pyrazine, pyrimidine, pyridazine, a -pyran, furan, thiophene, thiazole, pyrazole, imidazole, quinoline, isoquinoline and indole. They may be substituted, e.g. by halogen or alkyl.  Mixtures, e.g. from the oxidation of crude xylene or coal may be used.  Instead of the salts, mixtures which form the salts on heating may be used, e.g. mixtures of the acid anhydrides with alkali metal carbonates.  The reaction is catalysed by heavy metals, e.g. Cd, Zn, Hg, Pb and Fe, and their compounds, e.g. the oxides and salts including complex salts and organometallic compounds.  Carriers and solid or liquid diluents may be present.  Reaction may be effected in a thin film. The reaction mixture or components thereof may be obtained in a finely-divided state by spray-drying an aqueous solution or suspension.  The catalyst may be dissolved in potassium cyanate and this melt added to the reaction mixture.  In examples: (1)-(24) terephthalic acid is prepared from potassium benzoate; catalysts used are cadmium fluoride, cadmium carbonate and lead fluoride; cyanic acid derivatives used are potassium cyanate, dipotassium cyanamide and tripotassium cyanurate; potassium carbonate or dipotassium oxalate is used as acid-binding agent; bentonite may be present; (25) to (28) terephthalic and isophthalic acids together with trimesic, trimellitic and benzoic acids are prepared from dipotassium orthophthalate in the presence of potassium cyanate and cadmium fluoride, cadmium carbonate or K2CdF2Cl2; (29) thiophene-2,5-dicarboxylic acid is prepared from potassium thiophene-2-carboxylate in the presence of potassium carbonate, potassium cyanate, cadmium oxide and a CO2 atmosphere; (30) dehydromucic acid is prepared from potassium pyromucate in the presence of potassium carbonate, cadmium fluoride and potassium cyanate in a CO2 atmosphere.