PROCESS FOR PREVENTING BLACKENING OF PHTHALIC ACID

摘要

PROCESS FOR PREVENTING BLACKENING OF PHTHALIC ACID In the production of phthalic acid by oxidizing, in a liquid phase, tolualdehyde with molecular oxygen or a gas containing molecular oxygen in the presence of heavy metal salt containing a Mn salt, especially both Mn and Co salts, and a bromine compound, using a lower aliphatic monocarboxylic acid as a reaction solvent, blackening of phthalic acid is effectively prevented by conducting the oxidation of tolualdehyde in the presence of an alkylbenzene in an amount satisfying the following formula (1); M ? -0.15A2 + 15A + 40 ............. (1) wherein M is the Mn atom concentration in ppm by weight on the basis of the reaction solution, and A is the amount in % by weight of the alkylbenzene added on the basis of the total of tolualdehyde and said alkylbenzene, and is in a range of from more than 0 to 50 inclusive.