Process for preventing blackening of phthalic acid

摘要

In the production of phthalic acid by oxidizing, in a liquid phase, tolualdehyde with molecular oxygen or a gas containing the 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, a 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