GB741380A - Process for the production of aromatic dicarboxylic acids - Google Patents

Abstract

A process for the production of aromatic dicarboxylic acids comprises heating a halogeno-methyl-alkyl benzene in aqueous suspension in the presence of a base the concentration of which is from about 1 per cent to about 50 per cent and oxygen, or an oxygen-containing gas, preferably under elevated pressure from about 20 to about 250 atmospheres, and is characterized by oxidizing in the presence of an oxidation catalyst. Halogenomethyl - alkyl benzenes mentioned include 1 - chloro - methyl - 4 - methyl benzene, 1-chloromethyl - 2 - methyl benzene, 1 - bromomethyl - 4 - methyl benzene, 1 - bromomethyl - 2 - methyl benzene, 1 - chloromethyl-4 - ethyl benzene, 1 - chloromethyl - 4 - n-propyl benzene, 1 - chloromethyl - 4 - isopropyl - benzene, 1 - bromomethyl - 4 - isopropyl benzene and 1-chloromethyl-4-amyl benzene. Mixtures of these starting materials may be employed, e.g. 1-chloromethyl-4-methyl benzene and 1-chloromethyl-2-methyl benzene may be oxidized and the phthalic and terephthalic acids separated. Oxidation catalysts mentioned include the oxides and/or salts of heavy metals such as silver oxide, cobalt oxide, copper oxide, manganese or lead oxide or peroxide or naphthenates or stearates of cobalt or manganese or mixtures of such materials. Bases mentioned are sodium, potassium or calcium hydroxide solution. The process may be carried out continuously. Oxalic and carbonic acids are produced as byproducts and sufficient excess of base is preferably employed to yield an alkaline mixture on completion of the reaction. In examples: terephthalic acid containing some p-toluic acid is produced by treating 1-chloromethyl-4-methyl-benzene with air in the presence of caustic soda solution, lead oxide and lead peroxide at elevated temperature and pressure and acidifying the reaction product (1); in a similar process 1-chloromethyl-4-ethyl benzene, produced by reacting formaldehyde and ethyl benzene in the presence of hydrochloric acid, is employed as starting material (2); and in a similar process a mixture of 1-chloromethyl-4-and 2-methyl benzenes is employed as starting material, terephthalic acid is precipitated on acidification of the reaction mixture and filtered off and phthalic acid is extracted from the filtrate with ether whilst p-toluic acid is produced as a by-product.