PURPOSE: To obtain the subject high-purity compound in simple operation by adding water, etc., to a reaction mixture prepared by oxidizing methylnaphthalene in the liquid phase with air, depositing and separating naphthalenecarboxylic acid and washing the separated crude naphthalenecarboxylic acid under specific conditions.
CONSTITUTION: Methylnaphthalene is oxidized with molecular O2 in the presence of a catalyst containing at least one heavy metal selected from Co and Mn and Br2 in a solvent containing acetic acid to provide a reaction mixture. Water or a hydrous liquid is then added to the above-mentioned reaction mixture to deposit and separate the naphthalenecarboxylic acid. The separated crude naphthalenecarboxylic acid is subsequently washed with water or a mixture solution thereof with a water-miscible solvent, such as acetic acid, at ≥70°C under ordinary pressure to recycle washings after the washing operation as part of the reaction solvent through the oxidative reaction step. Thereby, the objective compound of ≥99% purity, improved in hue and useful as a dye, pigment, photographic chemical, etc., is readily and efficiently obtained at a low cost without requiring special apparatuses, such as distilling or pressurizing apparatuses.
ITO IKUO
TAKEDA KYOICHI
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