JPS6412257B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to naphthalene dicarboxylic acids, particularly 2,6
- A method for producing naphthalene dicarboxylic acid.

Naphthalene dicarboxylic acid is a compound useful as a polymer raw material, a dye intermediate, an industrial chemical, etc. Particularly in recent years, polyester produced from 2,6-naphthalene dicarboxylic acid and ethylene glycol has higher heat resistance and better heat resistance than polyethylene terephthalate.
Due to its excellent rigidity, it is attracting attention as a raw material for manufacturing films and fibers.

Conventional methods for producing 2,6-naphthalene dicarboxylic acid include naphthalene in which two chain alkyl groups containing 1 to 3 carbon atoms, such as methyl, ethyl, and isopropyl groups, are introduced into the naphthalene core through an alkylation reaction. The method mainly used is to separate 2,6-dialkylnaphthalene from a compound (hereinafter simply referred to as dialkylnaphthalene) and oxidize it to 2,6-naphthalene dicarboxylic acid.

However, in such a known method, it is extremely difficult to isolate the intermediate 2,6-dialkylnaphthalene, and it is not an economical method for producing 2,6-naphthalene dicarboxylic acid.

That is, when naphthalene is subjected to the above-mentioned normal alkylation reaction, chain alkyl groups are introduced into both the α-position and the β-position of the naphthalene nucleus, so dialkylnaphthalene becomes a mixture of many isomers, The content of 2,6-dialkylnaphthalene is low and generally remains below 20%. Since the boiling points of these dialkylnaphthalenes are close to each other, it is impossible to separate them by distillation, and the crystallinity of 2,6-dialkylnaphthalenes is not significantly different from other isomers. It is also difficult to crystallize and separate. Therefore, in order to isolate 2,6-dialkylnaphthalene, 2,6
- It was necessary to take complicated measures such as forming a complex between dialkylnaphthalene and nitrobenzoic acids, and then isolating and decomposing this complex.

The present inventors have discovered a dicarboxylic acid which can be derived from naphthalene at low cost, has a particularly high selectivity for 2,6-substituted isomers, is easy to separate from other by-product isomers, and can be oxidized to naphthalene dicarboxylic acid. As a result of intensive research to develop substituted naphthalene derivatives, it was discovered that dicyclohexylnaphthalene, especially 2,6-dicyclohexylnaphthalene, satisfies all of these conditions, and the present invention was achieved.

Therefore, the present invention is characterized by the selection of a specific compound as a starting material for the production of naphthalene dicarboxylic acid. That is, the present invention is a method for producing naphthalene dicarboxylic acid, which is characterized by oxidizing dicyclohexylnaphthalene. In particular, the features of the present invention are most effectively exhibited when 2,6-dicyclohexylnaphthalene is brought into contact with a molecular oxygen-containing gas in an acetic acid solvent in the presence of a catalyst containing cobalt and/or manganese and bromine. be done.

Incidentally, the present invention was made based on the discovery of the following fact.

(1) When naphthalene is reacted with a cyclohexanating agent such as chlorocyclohexane in the presence of a Friedel-Crafts catalyst such as aluminum chloride, the cyclohexyl group is selectively substituted at the β-position of the naphthalene nucleus, and the α-position is substituted with a cyclohexyl group. Not substantially replaced.

(2) As dicyclohexylnaphthalene produced by further cyclohexylation of β-cyclohexylnaphthalene, 2,6 isomers are the main products, and the amount of other isomers such as 2,7 isomers produced is relatively small.

(3) The target substance, 2,6-dicyclohexylnaphthalene, has a melting point of 151°C and good crystallinity, whereas the by-product, 2,7-dicyclohexylnaphthalene, has significantly poor crystallinity.

(4) When the dicyclohexylnaphthalene fraction (mixture of 2,6 and 2,7, etc.) obtained by distilling the cyclohexylation product of naphthalene is recrystallized using hexane or the like as a solvent, 2, Crystals of 6-dicyclohexylnaphthalene can be obtained.

(5) When 2,6-dicyclohexylnaphthalene is brought into contact with a molecular oxygen-containing gas in the presence of a catalyst containing cobalt and/or manganese and bromine in an acetic acid solvent, it is oxidized to 2,6-naphthalene dicarboxylic acid. .

The method of the present invention will be explained in more detail.

First, dicyclohexylnaphthalene, which is a starting material for the method of the present invention, is prepared. Dicyclohexylnaphthalene is obtained by cyclohexylating naphthalene.

Cyclohexylation of naphthalene involves reacting naphthalene with a cyclohexylating agent such as halogenated cyclohexane, cyclohexene, or cyclohexanol in the presence of a so-called Friedel-Crafts catalyst such as aluminum chloride using carbon disulfide or nitrobenzene as a solvent. Depends on how you do it.

The cyclohexylating agent is 2 for naphthalene.
It is appropriate to use about twice the molar amount, and Friedel-Crafts catalyst is 0.02 to 0.02 to naphthalene.
It is appropriate to use about 0.4 times the mole. The reaction temperature is also limited by the boiling point of the solvent used, but is preferably in the range of 0 to 100°C.

Note that it is of course possible to use β-monocyclohexylnaphthalene as a raw material instead of naphthalene. It is also possible to use tricyclohexylnaphthalene, which is a by-product in the cyclohexylation reaction of naphthalene, as a cyclohexylating agent, and to carry out a transcyclohexylation reaction between this and naphthalene or monocyclohexylnaphthalene.

The reaction mixture after the cyclohexylation reaction is
Mix with cold water to decompose the catalyst and separate the organic layer. At this time, if necessary, an organic solvent that is immiscible with water may be added to the reaction mixture to facilitate the liquid separation operation. The organic layer is thoroughly washed with aqueous alkaline solution and water, dehydrated and distilled. After distilling off the solvent, unreacted naphthalene, and monocyclohexylnaphthalene, a fraction consisting of dicyclohexylnaphthalene is obtained.

When this fraction is recrystallized using n-hexane or the like as a solvent, 2,6-dicyclohexylnaphthalene with a purity of 95% or more is obtained. 2,7 dicyclohexylnaphthalene etc. recovered from the mother liquor side are treated with a Friedel-Crafts catalyst to produce 2,7 dicyclohexylnaphthalene, etc.
It can be isomerized to 6-dicyclohexylnaphthalene.

In the present invention, the dicyclohexylnaphthalene thus obtained, in particular 2,6-dicyclohexylnaphthalene, is then contacted with a molecular oxygen-containing gas in the presence of an oxidation catalyst, preferably in an acetic acid solvent.
Oxidizes to the corresponding naphthalene dicarboxylic acid.

The solvent acetic acid is dicyclohexylnaphthalene 3
It is used at least twice its weight, preferably at least 10 times its weight.
Note that there is no particular problem even if water is present in the acetic acid in an amount of about 15% by weight or less.

A catalyst system consisting of cobalt and/or manganese and bromine is used as the oxidation catalyst, and these catalyst components are added in the form of the compounds shown below.

That is, cobalt compounds and manganese compounds can be used as long as they are soluble in acetic acid, but acetates, carbonates, hydroxides, bromides, etc. are particularly preferred.

As the bromine compound, inorganic bromine compounds such as bromine, hydrogen bromide, aluminum bromide, alkali metal bromides, cobalt bromide, and manganese bromide, and organic bromine compounds such as tetrabromoethane and bromoacetic acid can be used. Particularly preferred are hydrogen bromide, cobalt bromide, and manganese bromide.

The amount of cobalt compound and manganese compound used is preferably such that the total concentration of cobalt and manganese as metals is in the range of 200 to 3000 ppm relative to the solvent acetic acid. On the other hand, the amount of bromine compounds used is that the gram atomic weight of bromine atoms is greater than the total gram atomic weight of cobalt and manganese.
It is preferable to adjust the amount to about 0.5 to 2 times.

As the molecular oxygen-containing gas, pure oxygen or industrial exhaust gas can also be used, but from an industrial perspective, normal air is most suitable.

The reaction temperature is preferably 100 to 250°C, particularly 110 to 160°C. The reaction pressure is set so as to maintain the solvent acetic acid in a liquid phase at this temperature, and is suitably 10 to 30 atmospheres.

As the reaction method, any of a batch method, a semi-continuous method, and a continuous method may be employed, but a continuous method is preferable in order to stably obtain a product of good quality.

Since 2,6-naphthalene dicarboxylic acid produced by the oxidation reaction is poorly soluble in hot acetic acid, it can be separated from the solvent, catalyst, unreacted materials, by-products, etc. by solid-liquid separation of the reaction mixture. I can do it. The 2,6-naphthalene dicarboxylic acid thus obtained is further purified, if necessary, to obtain highly purified 2,6-naphthalene dicarboxylic acid.

The naphthalene dicarboxylic acid obtained by the method of the present invention can be used as a polymer raw material such as polyester or polyamide.
It can be widely used as a dye intermediate and other industrial chemicals.

The present invention will be specifically described below with reference to Examples.

Example Using a reactor equipped with a reflux condenser and a stirrer,
Add 25 parts of chlorocyclohexane to a mixture of 80 parts of carbon disulfide, 13.4 parts of naphthalene, and 28 parts of aluminum chloride.
part was added dropwise over 1 hour. During this time, hydrogen chloride gas was generated, and carbon disulfide was gently refluxed due to the heat of reaction. After completion of the dropwise addition, the mixture was heated under reflux for 30 minutes, cooled, and then poured into dilute hydrochloric acid to separate into an aqueous layer and an organic layer. The organic layer was washed with dilute alkali and then water, and the solvent was distilled off.

The residue was distilled under reduced pressure, followed by unreacted naphthalene, monocyclohexylnaphthalene, 195-205
11.8 parts of a fraction consisting mainly of dicyclohexylnaphthalene was obtained, distilled at a temperature of 0.9 mmHg. The main component of the can residue was tricyclohexylnaphthalene.

Dicyclohexylnaphthalene fraction is 2,6-
The main component was 2,6-dicyclohexyl and other isomers estimated to be 2,7 and 1,3 isomers, but by recrystallizing with n-hexane, 2,6-dicyclohexyl with a purity of over 95% was obtained. 3 parts of naphthalene were obtained.

2.5 parts of 2,6-dicyclohexylnaphthalene thus obtained were mixed with 0.27 parts of cobalt bromide hexahydrate, 0.13 parts of cobalt acetate tetrahydrate, and manganese acetate tetrahydrate.
0.33 parts of acetic acid and 100 parts of acetic acid were heated at 130° C. for 5 hours under a pressure of 20 atmospheres of air.

The cake obtained by filtering the reaction solution was washed with acetic acid,
One part of powdered solid was obtained. This IR spectrum is 2,
It was consistent with 6-naphthalene dicarboxylic acid.

Further, when esterified with methanol, a product was obtained whose IR spectrum, NMR spectrum, and gas chromatography retention time corresponded to 2,6-naphthalene dicarboxylic acid dimethyl ester.

Claims (1)

[Claims] 1. A method for producing naphthalene dicarboxylic acid, which comprises oxidizing dicyclohexylnaphthalene.