Process for preparing 2,6-naphthalenedicarboxylic acid

#This invention relates to a process for preparing 2,6-naphthalenedicarboxylic acid and, more particularly to a process for preparing 2,6-naphthalenedicarboxylic acid which comprises oxidation reaction of 2,6-diisopropylnaphthalene or an oxidation product thereof with molecular oxygen in a solvent containing an aliphatic carboxylic acid in the presence of a catalyst composed of cobalt and manganese as heavy metals and a bromine compound.

#2,6-Naphthalenedicarboxylic acid is useful as a raw material for highly functional resins such as polyethylene naphthalate (PEN).

#Among various known processes for preparing 2,6-naphthalenedicarboxylic acid, a process comprising oxidation reaction of 2,6-dimethylnaphthalene as proposed in JP-A-49-42654 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") realizes reasonable yield but has difficulty in obtaining the starting material of high purity.

#The present invention is now illustrated in greater detail by way of Examples, but it should be understood that the present invention is not deemed to be limited thereto. All the yields are given by mol% based on the starting 2,6-diisopropylnaphthalene. The purity of 2,6-naphthalenedicarboxylic acid produced was determined by high performance liquid chromatography, expressed in percent area at UV 285 nm.

#In a 500 ml titanium-made autoclave equipped with a reflux condenser, a gas introducing pipe, a feed pump for a starting material, a back-pressure regulator, and an induction stirrer were charged 200 g of acetic acid, 9.35 g (37.5 mmol) of cobalt acetate tetrahydrate, 9.20 g (37.5 mmol) of manganese acetate tetrahydrate, 7.35 g (75.0 mmol) of ammonium bromide, and 5.93 g (75.0 mmol) of pyridine. After displacing the atmosphere with nitrogen, the inner pressure was adjusted to 30 kg/cm.sup.2 G with the back-pressure regulator. The inner temperature was raised to 200.degree. C., and air was fed therein at a rate of 3 to 4 Nl/min to keep the inner pressure at 30 kg/cm.sup.2 G (oxygen partial pressure: 6.5 kg/cm.sup.2).

#After the system became stable, 79.62 g (375 mmol) of 2,6-diisopropylnaphthalene was continuously fed over 4 hours. After completion of the feeding, air feeding was further continued for 1 hour while maintaining the system at 200.degree. C. and 30 kg/cm.sup.2 G.