JPH09169694A - Method for producing aromatic carboxylic acid - Google Patents

Abstract

(57) Abstract: An improved method for producing an aromatic carboxylic acid by oxidizing an aromatic compound having an alkyl group with molecular oxygen in an aqueous medium is provided. A compound in which a transition metal is incorporated in a heteropolyacid skeleton having a defective structural site is used as a catalyst, and the structure of the heteropolyacid anion can be stably maintained.
The reaction is carried out in an aqueous buffer solution of H 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD [0001] The present invention oxidizes an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent to produce an aromatic carboxylic acid industrially useful as a resin raw material, a raw material for medical and agricultural chemicals, and the like. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, as a method for industrially producing an aromatic carboxylic acid, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent is used as a heavy metal compound such as cobalt or manganese and bromine or A method of oxidizing in a liquid phase using a lower alkanoic acid such as acetic acid as a solvent in the presence of a catalyst composed of a bromine compound is practiced. However, in this method, a lower alkanoic acid such as acetic acid used as a solvent is consumed in a considerable amount due to combustion or the like, so that there is a problem that the manufacturing cost becomes high.

In order to solve such a problem, a method of using water as a solvent instead of lower alkanoic acid has been proposed (Japanese Patent Publication No. 39-13921 and Japanese Patent Laid-Open No. 58/1983).
-85840, JP-A-60-18403, etc.), the reaction rate is slow and not practical. Therefore, a method using ruthenium oxide as a catalyst (JP-A-3-130247), a method using a heavy metal and a bromine compound as a catalyst, and a heteropolyacid such as silicotungstic acid and phosphomolybdic acid as a co-catalyst (JP-A-2-200656), etc. A method for improving the above with a water solvent has been proposed. However, the above-mentioned improvement method has not yet reached the stage of practical use, and further improvement is desired. The present inventors, as an improvement of the water solvent method,
We proposed a method using a compound with a transition metal incorporated in a heteropolyacid skeleton with a defective structural site as a catalyst.
(Japanese Patent Application No. 6-190633)

[0004]

However, it was found that the method of Japanese Patent Application No. 6-190633 described above also has a problem that the catalytic activity decreases as the reaction progresses. Therefore, the present invention is intended to provide a method for producing an aromatic carboxylic acid while maintaining an increased catalytic activity for a long time.

[0005]

According to the present invention, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent is oxidized with molecular oxygen in an aqueous medium to produce an aromatic carboxylic acid. In the method described above, a compound in which a transition metal is incorporated in a heteropolyacid skeleton having a deficient structure site is used as a catalyst, and the reaction is carried out in a buffered aqueous solution at a pH at which the heteropolyacid anion structure can be stably maintained, thereby increasing the Is maintained for a long time, and the target aromatic carboxylic acid can be obtained in high yield.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail. In the present invention, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent is used as a raw material. The number of carbon atoms of the alkyl substituent is usually 1 to 8
However, preferred are methyl group, ethyl group and n-
An alkyl group having 1 to 3 carbon atoms such as propyl group and i-propyl group. The carbon number of the partially oxidized alkyl group is usually about 1-8. Examples of such a partially oxidized alkyl group include a formyl group, a carboxyl group and a hydroxyalkyl group. The aromatic compound as a raw material may have two or more of these substituents. When it has a plurality of substituents, the substituents may be the same or different. The aromatic nucleus of the aromatic compound includes not only a single ring such as a benzene ring but also a polycyclic aromatic nucleus such as a naphthalene ring.

Some of the aromatic compounds having an alkyl substituent or a partially oxidized alkyl substituent used as a raw material in the present invention are toluene, isopropylbenzene, 4,4'-dimethylbiphenyl, o-, m-. ，
Or an aromatic compound substituted with an alkyl group such as p-xylene, o-, m-, or p-diisopropylbenzene, pseudocumene (1,2,4-trimethylbenzene), and 2,6-dimethylnaphthalene; benzaldehyde,
Formyl group-substituted aromatic compounds such as o-, m-, or p-tolualdehyde, 2,4-dimethylbenzaldehyde, 2,4,5-trimethylbenzaldehyde, 2,6-diformylnaphthalene, and 1-formylnaphthalene. An aromatic compound substituted with a hydroxyalkyl group such as benzyl alcohol; a compound substituted with a formyl group and a carboxyl group such as o-, m-, or p-toluic acid, o-, m-, or p-carboxybenzaldehyde, or These mixtures etc. are mentioned.

In the present invention, a compound in which a transition metal is incorporated into a heteropolyacid skeleton having a defective structural site is used as a catalyst. As the transition metal, those selected from the elements of the groups 5 to 10 are usually used, and preferred are V of the group 5, Cr, Mo and W of the group 6, Mn of the group 7 and Mn of the group 8. Fe and Ru of the group, Co and Rh of the group 9, and Pd of the group 10. The periodic table of elements is based on the revised IUPAC Nomenclature of Inorganic Chemistry (1989). These transition metals are described, for example, in R. Neumanm et al., J. Am. Chem. Soc., 112 (1960) 602.
By the method described in 5, it can be incorporated into a heteropolyacid skeleton having a defective structural site. In addition to providing the reaction system as a heteropolyacid compound catalyst incorporating a pre-determined transition metal, a transition metal salt such as chloride and a deficient heteropolyacid compound are separately supplied to the reaction system to cause transition in the reaction system. It is also possible to form heteropolyacid compounds incorporating metals.

Examples of the heteropolyacid skeleton having this defective structure site include those represented by the following general formulas (1) to (3). Defect-type hexametallate ion (M ₅ O ₁₈ ) ⁿ -... (1) Defect-type keguin-type polyion ion (Y ₁ M ₁₁ O ₃₉ ) ⁿ -... (2) Deletion-type Dawson-type polyacid ion (Y ₂ M ₁₇ O ₆₁ ) ⁿ -... (3) (In these formulas, M represents molybdenum or tungsten, Y represents silicon, phosphorus or germanium. N represents a positive integer, but its value is usually 1 to There is no particular limitation on the cation of the compound in which the transition metal is incorporated in the heteropolyacid skeleton having these defective structural sites,
For example, an alkali metal ion such as a proton, sodium ion, or potassium ion, or an alkyl group having 1 to 20 carbon atoms.
And a tetraalkylammonium cation.

The catalyst is usually present in the reaction medium in the range of 10 to 100,000.
It is present at 0 ppm, preferably 100 to 5000 ppm. In order to stabilize the heteropolyacid compound catalyst incorporating these transition metals, a deficient heteropolyacid compound may coexist with the catalyst. The coexisting amount of heteropolyacid compound containing a transition metal is
It is usually 0.01 to 10 times equivalent, preferably 0.1 to 5 times equivalent. The oxidation reaction of the aromatic compound according to the present invention is carried out in an aqueous medium, and as the aqueous medium, water or a solution containing water as a main component is used.

In the present invention, a pH buffer is present in this aqueous medium to stabilize the heteropolyacid anion of the catalyst. The stability of heteropolyacids in aqueous media depends on their p
Depends on H. According to the knowledge of the present inventors, a compound having a transition metal incorporated in a heteropolyacid skeleton having a defective structural site is used as a catalyst to cause a decrease in catalytic activity when an aromatic carboxylic acid is produced in an aqueous medium. At least some
It is considered that the structure of the heteropolyacid compound changes due to the influence of the pH of the aqueous medium during the reaction.
Therefore, it is considered that a decrease in catalytic activity can be prevented by adding a pH buffer to the aqueous medium to carry out the reaction in a pH range in which the structure of the heteropolyacid anion of the catalyst is stably maintained.

The stable pH range of the heteropolyacid anion in the aqueous medium varies considerably even with the same type of heteropolyacid when the constituent elements are different. Therefore, in carrying out the present invention, it is necessary to select a pH buffering agent to be added to the aqueous medium, depending on the heteropolyacid anion of the catalyst used. However, since the stable pH region of the heteropolyacid anion can be determined from the measurement of its decomposition rate, the difference in the stable pH region depending on the heteropolyacid does not hinder the practice of the present invention (P. Souchay “ Ions Mineraux Condenses ”(Masson & Cie, Paris,
1969)). Examples of pH regions that can be stably used for some of the defective Keggin-type polyion ions are as follows.

[0013]

[Table 1] Normal use range Suitable range Optimal range [SiW ₁₁ O ₃₉ ] ^7- <8.2 <8.0 <7.8 [PW ₁₁ O ₃₉ ] ^7- <7.2 <7.0 <6. 8 [PMo ₁₁ O ₃₉ ] ^7- <5.2 <5.0 <4.8 [GeMo ₁₁ O ₃₉ ] ^8- <4.7 <4.5 <4.3 As a pH buffering agent, inorganic salts are usually used. Is used, and it is preferable to use phosphate, carbonate, borate and the like. The reaction uses a heteropolyacid skeleton having a defective structural site with a transition metal incorporated as a catalyst, and p
It can be carried out according to a conventional method except that the H buffer is present. The weight ratio of the aqueous medium and the aromatic compound as the reaction raw material is usually selected from the range of 1: 1 to 100: 1. As oxygen as an oxidant, air is usually used, but oxygen-enriched air or conversely diluted with an inert gas such as nitrogen can also be used. If desired, oxygen gas or a gas obtained by diluting it with nitrogen or the like can be used. These molecular oxygen-containing gases are usually continuously blown into the reaction system.

The reaction temperature is usually 100 to 300 ° C., preferably 150 to 230 ° C., and the reaction pressure is not lower than the pressure at which the liquid phase can be retained in the reactor at that reaction temperature, usually atmospheric pressure to 100 atm (0.1-10MP
a), preferably 10 to 80 atm (1 to 8 MPa). The reaction time is usually selected in the range of 0.1 to 8 hours, preferably 1 to 5 hours. Separation and purification of the aromatic carboxylic acid obtained according to the present invention is carried out by a conventional method such as filtration, centrifugation or distillation. The solution containing the catalyst after separating the product can be reused in the reaction.

[0015]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. Example 1 a reflux condenser, a titanium autoclave 500ml equipped with a stirrer, 0.57M-H ₃ BO ₃ buffer (pH =
5.1) 150 ml and p-xylene 10.35 g were charged. A defect type potassium silicotungstic acid K ₅ SiRu (H ₂ O) W ₁₁ O ₃₉ having Ru incorporated therein has a Ru concentration of 16
It was added so as to be 56 ppm. After replacing the inside of the autoclave with nitrogen, the temperature was raised to 200 ° C by heating. 200 ° C
At that point, pressurize air and pressurize at 60 atm.
Air was continuously supplied for 2 hours at a rate of Nl / Hr. The reactor was then cooled, the contents removed and the product filtered off. The obtained product was analyzed by high performance liquid chromatography and gas chromatography. As a result, the conversion of p-xylene was 94%, and the charged p
-63% yield of terephthalic acid based on xylene, p-
The yield of toluic acid was 9%. The main by-product was CO ₂ produced by combustion.

Example 2 0.57M-H ₃ BO ₃ buffer solution (pH = 5.1) was added to 0.2%.
The reaction was carried out in the same manner as in Example 1 except that the buffer solution was changed to 57M-potassium dihydrogen phosphate buffer (pH = 4.6). As a result, the conversion rate of p-xylene was 92%, and
-60% yield of terephthalic acid based on xylene, p-
The yield of toluic acid was 10%. The main by-product was CO ₂ produced by combustion.

Example 3 0.57M-H ₃ BO ₃ buffer solution (pH = 5.1) was added to 0.2%.
The reaction was carried out in the same manner as in Example 1 except that the 057M-phosphate buffer solution (pH = 2.3) was used. As a result, p-
The conversion rate of xylene was 90%, the yield of terephthalic acid with respect to the charged p-xylene was 55%, and the yield of p-toluic acid was 11%. The main by-product was CO ₂ produced by combustion.

Comparative Example 1 A reaction was carried out in the same manner as in Example 1 except that 150 ml of water was used as the solvent without using the 0.57M-H ₃ BO ₃ buffer solution (pH = 5.1). As a result, the conversion rate of p-xylene was 87%, the yield of terephthalic acid with respect to the charged p-xylene was 51%, and the yield of p-toluic acid was 13%.
Met. The main by-product is C generated by combustion.
It was O _2.

Claims (4)

[Claims] 1. A method for producing an aromatic carboxylic acid by oxidizing an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent with molecular oxygen in an aqueous medium to provide a heteropolyone having a defective structural site. A method for producing an aromatic carboxylic acid, which comprises using a compound having a transition metal incorporated in an acid skeleton as a catalyst and performing the reaction in a buffered aqueous solution having a pH capable of maintaining a stable structure of the heteropolyacid anion. 2. A heteropolyacid skeleton having a deficient structure site is represented by the following general formulas (1) to (3); deficient hexametallate ion (M ₅ O ₁₈ ) ⁿ -... (1) deficient Keggin type Polyacid ion (YM ₁₁ O ₃₉ ) ⁿ -... (2) Defective Dawson type polyacid ion (Y ₂ M ₁₇ O ₆₁ ) ⁿ -... (3) (In these formulas, M represents molybdenum or tungsten, Y represents silicon, phosphorus or germanium, and n represents a positive integer.) The process for producing an aromatic carboxylic acid according to claim 1, wherein 3. The method for producing an aromatic carboxylic acid according to claim 1, wherein the transition metal is selected from Group 5 to 10 elements. 4. The aromatic carboxylic acid according to claim 1, wherein the buffered aqueous solution dissolves at least one inorganic salt consisting of a phosphate, a carbonate and a borate. Manufacturing method.