Method for producing tetrabasic acid anhydride

Abstract

To provide a method for producing a tetrabasic acid anhydride that inhibits polymer formation and exhibits superior productivity.SOLUTION: The foregoing problem can be solved by a method for producing a tetrabasic acid anhydride that includes adding an acid anhydride group-containing monomer to a styrenic compound in the presence of oxygen and a polymerization inhibitor to synthesize the tetrabasic acid anhydride. It is preferable to use the polymerization inhibitor in an amount of 0.0001 pt.mass to 0.5 pt.mass relative to 100 pts.mass of the total of the styrenic compound and the acid anhydride group-containing monomer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a tetracarboxylic dianhydride derived from a styrene compound.

Background Art

[0002] Tetracarboxylic dianhydrides having two acid anhydride groups are used as raw materials for, for example, polyester resins, polyamide resins, polyimide resins, and photosensitive resins by utilizing the reactivity of the acid anhydride groups.

[0003] As a method for synthesizing a tetracarboxylic dianhydride using a styrene compound as a raw material, Patent Document 1 discloses a method for synthesizing a tetracarboxylic dianhydride using 2,6-di-tert-butyl-4-methylphenol under a nitrogen atmosphere. Patent Document 2 discloses a method for synthesizing a tetracarboxylic dianhydride using phenothiazine under a nitrogen atmosphere. Patent Document 3 discloses a method for synthesizing a tetracarboxylic dianhydride using phenothiazine under a nitric oxide atmosphere.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the production methods of Patent Documents 1 and 2, the polymerization inhibition of the styrene compound was insufficient, and polymers as by-products were generated. In Patent Document 2, the presence or absence of by-products was determined by liquid chromatography, but since the polymer remained at the entrance of the liquid chromatography column and did not pass through, it could not be detected. In addition, in the production method of Patent Document 3, due to the toxicity and corrosiveness of nitrogen monoxide, ordinary production equipment cannot be used, and safety equipment and corrosion-resistant reaction equipment are required, resulting in high costs and low productivity.

[0006] An object of the present invention is to provide a method for producing a tetracarboxylic dianhydride that suppresses the formation of a polymer of by-products and has good productivity.

Means for Solving the Problems

[0007] The method for producing a tetracarboxylic dianhydride of the present invention is a method of synthesizing by adding a monomer containing an acid anhydride group to a styrene-based compound in the presence of oxygen and a polymerization inhibitor.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a method for producing a tetracarboxylic dianhydride that suppresses the formation of a polymer and has good productivity.

Modes for Carrying Out the Invention

[0009] The terms used in this specification are defined. A monomer is a compound capable of radical polymerization.

[0010] The method for producing a tetracarboxylic dianhydride of the present invention (hereinafter referred to as this production method) synthesizes a tetracarboxylic dianhydride by adding a monomer containing an acid anhydride group to a styrene-based compound in the presence of oxygen and a polymerization inhibitor. In this production method, the presence of oxygen in addition to the polymerization inhibitor in the reaction system can suppress the polymerization of the styrene-based compound. As a result, it is difficult to form a polymer of by-products that were conventionally produced in large amounts. In addition, nitrogen monoxide is toxic and corrodes stainless steel production equipment, so special production equipment was required. However, oxygen is non-toxic compared to nitrogen monoxide and does not require special production equipment, so productivity is improved.

[0011] The styrene-based compound is a monomer having a styrene structure and capable of reacting with a monomer containing an acid anhydride group. Styrene compounds include, for example, styrene, α-methylstyrene, β-methylstyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, 4-methyl-1-isopropenylbenzene, 4-tert-butylstyrene, 4-tert-butyl-1-isopropenylbenzene, ortho-chlorostyrene, meta-chlorostyrene, para-chlorostyrene, ortho-fluorostyrene, meta-chlorostyrene, para-chlorostyrene, pentafluorostyrene, para-methoxystyrene, meta-butoxystyrene, para-butoxystyrene, 4-(1-ethoxyethoxy)styrene, para-vinylbenzoic acid, para-vinylbenzaldehyde, para-chloro-α-methylstyrene, para-fluoro-α-methylstyrene, para-tert-butyl-α-methylstyrene, 1,1-diphenylethylene, diphenylphosphinostyrene, 1,4-divinylbenzene, 1,3-divinylbenzene, 4-nitrostyrene, 4-aminostyrene, 4-vinylbiphenyl, 2,4,6-trimethylstyrene, trimethoxy(4-vinylphenyl)silane, 4-n-octylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, sodium styrene-4-sulfonate, 4-(chloromethyl)styrene, 4-acetoxystyrene, 4-(trifluoromethyl)styrene, and the like. Among these, styrene and α-methylstyrene are preferred in terms of reactivity.

[0012] The acid anhydride group-containing monomer is a compound that can be added to a styrene compound to form a tetrabasic acid anhydride. Examples of the acid anhydride group-containing monomer include maleic anhydride, citraconic anhydride, itaconic anhydride, 2,3-dimethylmaleic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, phenylmaleic anhydride, bromomaleic anhydride, cis-aconitic anhydride, and the like. Among these, maleic anhydride and itaconic anhydride are preferred in terms of reactivity.

[0013] The amount of the acid anhydride group-containing monomer used is preferably 1.5 to 10.0 moles, more preferably 1.5 to 3.0 moles, and even more preferably 2.0 to 2.5 moles, per 1 mole of the styrene compound. From the perspective of further suppressing the formation of by-product polymers, it is preferable that the acid anhydride group-containing monomer be present in excess of the styrenic compound during the reaction. The amount of the acid anhydride group-containing monomer used is preferably 2.0 to 10.0 moles, more preferably 2.5 to 5.0 moles, per mole of the styrenic compound.

[0014] This production method preferably involves, for example, dropping the styrenic compound into the acid anhydride group-containing monomer. This makes it easier to control the reaction temperature during synthesis. The dropping temperature is preferably from 25°C to 180°C, more preferably from 80°C to 150°C. The reaction rate improves at 25°C or higher. Also, it is easy to suppress the formation of by-product polymers at 180°C or lower.

[0015] Examples of the polymerization inhibitor include quinone compounds, catechol compounds, phenothiazine compounds, N-nitrosoamine compounds, etc. Examples of quinone compounds include methylhydroquinone, hydroquinone, benzylhydroquinone, di-tert-butylhydroquinone, benzoquinone, etc. Examples of catechol compounds include catechol, p-tert-butylcatechol, pyrogallol, etc. Examples of phenothiazine compounds include phenothiazine, benzophenothiazine, acetamidophenothiazine, etc. Examples of N-nitrosoamine compounds include N-nitrosodiphenylamine, N-nitrosodimethylamine, etc. Among these, quinone compounds and catechol compounds are preferable in terms of suppressing the formation of by-products, and methylhydroquinone and p-tert-butylcatechol are more preferable.

[0016] In one embodiment of this production method, the amount of the polymerization inhibitor used is preferably 0.005 parts by mass to 5 parts by mass, more preferably 0.01 parts by mass to 0.5 parts by mass, per 100 parts by mass of the total amount of the styrenic compound and the acid anhydride group-containing monomer. In other embodiments of this manufacturing method, the amount of polymerization inhibitor used is preferably 0.0001 to 0.5 parts by mass, more preferably 0.0001 to 0.1 parts by mass, per 100 parts by mass of the total amount of the styrenic compound and the monomer containing an acid anhydride group.

[0017] In this manufacturing method, oxygen can be supplied to the reaction site by introducing dry air into the reaction apparatus. Usually, oxygen derived from air exists in the reaction apparatus. However, since oxygen in the reaction solution is consumed as the addition reaction progresses, it is necessary to continuously supply oxygen to suppress the polymerization of the styrenic compound. Note that in this manufacturing method, oxygen may be introduced instead of air. The introduction may be carried out by supplying to the upper part of the reaction apparatus. More preferably, the introduction is carried out by bubbling dry air or oxygen into the reaction solution. Note that dry air is, for example, a gas obtained by passing air through a dehumidifying filter such as silica gel. The oxygen concentration in the reaction apparatus varies depending on the reaction solvent used. For example, in the case of cyclohexanone, the oxygen concentration may be 7.0% by volume or more. With an oxygen concentration of this level, oxygen is taken in to such an extent that the formation of polymers can be suppressed by stirring the reaction solution. On the other hand, care must be taken as the oxygen concentration must be outside the explosion limit range of the organic solvent used to avoid ignition due to static electricity. Also, the introduction flow rate of the dry air used in the present invention is more preferably 0.01 to 1.0 L / min per liter of the volume of the reaction apparatus.

[0018] In this manufacturing method, a solvent can be used. Examples of the solvent include aromatic solvents such as toluene, xylene, and mesitylene, aliphatic hydrocarbon solvents such as hexane, heptane, and cyclohexane, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, benzophenone, acetophenone, and cyclohexanone, and ester solvents such as ethyl acetate, butyl acetate, and isoamyl acetate. Among these, cyclohexanone and toluene are preferred. In this manufacturing method, for example, when adding an acid anhydride group-containing monomer to a styrene-based compound, if the styrene-based compound is dropped into the acid anhydride group-containing monomer, the amount of the solvent used is preferably 30% by mass or less, more preferably 10% by mass or less, based on the total amount of the styrene-based compound and the acid anhydride group-containing monomer. The lower limit of the solvent is 0%. The less the reaction solvent, the faster the reaction rate.

[0019] An example of this manufacturing method will be described. Note that the present invention is not limited to the following examples. Charge a stainless steel reaction apparatus with a styrene-based compound, an acid anhydride group-containing monomer, a polymerization inhibitor, and a reaction solvent, and stir well. Start introducing dry air into the reaction apparatus before and after the start of stirring, and stir well until oxygen is taken into the reaction solution. Then, raise the internal temperature and carry out an addition reaction at about 80°C to 130°C. The reaction time of the addition reaction is about 10 to 20 hours. The addition reaction is confirmed by gel permeation chromatography through sampling. The reaction end point is set at the time when the disappearance of the raw material styrene-based compound is confirmed. After confirming the reaction end point, take out the reaction solution, and then perform filtration to obtain a white crystalline tetracarboxylic dianhydride. Note that the introduction of dry air is carried out until the end of the addition reaction.

[0020] In this manufacturing method, the reaction temperature is more preferably 90°C to 120°C.

[0021] Another aspect of the manufacturing method of the tetracarboxylic dianhydride of the present invention will be described. A first step of adding an acid anhydride group-containing monomer to a styrene-based compound in the presence of oxygen and a polymerization inhibitor to obtain a tetracarboxylic dianhydride. Next, a second step of adding a poor solvent to precipitate crystals of the tetracarboxylic dianhydride. Next, a manufacturing method of a tetracarboxylic dianhydride is provided, which includes a third step of performing filtration to remove the unreacted acid anhydride group-containing monomer. In addition, it is preferable to use 0.0001 to 0.5 parts by mass of the polymerization inhibitor based on 100 parts by mass in total of the styrene-based compound and the acid anhydride group-containing monomer. When the production method of the other aspect is carried out, the amount of the polymerization inhibitor used can be reduced.

[0022] As described above, in the presence of oxygen and a polymerization inhibitor, in the first step of adding an acid anhydride group-containing monomer to a styrene-based compound to obtain a tetrabasic acid anhydride, the styrene-based compound and the acid anhydride group-containing monomer can be charged and reacted all at once. Alternatively, the styrene-based compound can be dropped and reacted in the acid anhydride group-containing monomer. In this production method, the latter method is preferable because the reaction temperature is easy to control.

[0023] The amount of the styrene-based compound used is preferably 0.3 times mole or less based on the acid anhydride-containing monomer. While 2 times mole of the acid anhydride-containing monomer reacts with the styrene-based compound, when the amount of the styrene-based compound used is 0.3 times mole or less based on the acid anhydride-containing monomer, the formation of by-product high molecular weight compounds can be further suppressed. Subsequent to the above first step, in the second step of adding a poor solvent to precipitate crystals of the tetrabasic acid anhydride, a solvent in which the solubility of the tetrabasic acid anhydride is low is preferable as the poor solvent. The poor solvent may be any solvent in which the solubility of the tetrabasic acid anhydride is low, and a solvent having a solubility of the tetrabasic acid anhydride in 100 g of the solvent at 25°C of 10 g or less is preferable. Examples of the poor solvent include hexane, heptane, toluene, xylene, and the like. In the third step of performing filtration to remove the unreacted acid anhydride group-containing monomer, suction filtration and pressure filtration are preferable. In filtration, filter media such as filter cloth and filter paper are used.

[0024] Various known filter media can be used as the filter medium. The filter medium can be roughly classified by material, structure, shape, and fineness of mesh (also referred to as filtration accuracy).

[0025] The material of the filter medium can be roughly classified into inorganic compounds, organic compounds, and paper. Inorganic compounds include, for example, metals such as titanium; alloys such as stainless steel and Hastelloy; metal oxides (ceramics) such as alumina, zirconia, and titanium oxide; silicon dioxide (glass) such as glass fiber, activated carbon, diatomaceous earth, etc. Organic compounds include, for example, polyethylene, polypropylene, polyester, polyolefin, polyethylene terephthalate, polytetrafluoroethylene, polyurethane, polyacrylonitrile, polyvinylidene fluoride, perfluoroalkoxy alkane, cellulose phenol resin, nylon, nylon 66, rayon, acetate, polyphenylene sulfide, polyethersulfone, polysulfone, cotton, wool, silk, etc. Filter paper can be used as the filter medium.

[0026] The structures of the filter media include mesh, powder (particles), fiber, etc. Mesh is a shape obtained by processing the filter medium into a fibrous form and weaving it regularly. Coarse particles are captured by utilizing the gaps between the fibers. Examples of the weaving methods include plain weave, twill weave, basket weave, twill basket weave, etc. Powder is a shape obtained by processing the filter medium into fine particles. The fine particles are densely packed, and coarse particles are captured by utilizing the gaps between the fine particles. Fiber is a shape obtained by processing the filter medium into a fibrous form and intertwining it irregularly. Coarse particles are captured by utilizing the gaps between the fibers. In addition to the above, there are also structures such as the phase inversion method in which a resin containing no solvent is formed into a thin film and microvoids are generated in the resin by evaporating the solvent, and the stretching method in which a resin with no voids is formed into a thin film and microvoids are generated by stretching, etc.

[0027] As the coarseness (filtration accuracy) of the filter medium, any filter medium can be selected within the range of 1 nm to 1 mm according to the size of the object.

[0028] The material of the filter medium is preferably, for example, polyethylene, polypropylene, polytetrafluoroethylene, or glass fiber. The structure of the filter material is preferably a fiber, a structure obtained by the phase conversion method, or a structure obtained by the stretching method.

[0029] The filtration temperature is preferably 55 to 80 °C, more preferably 60 to 75 °C. The filtration pressure is preferably 0.01 to 2.00 MPa, more preferably 0.02 to 1.00 MPa, and even more preferably 0.03 to 0.5 MPa.

[0030] The use of the tetracarboxylic dianhydride obtained by this production method is preferably for the synthesis and modification of various resins. Examples of such uses include raw materials such as polyester resins, polyamide resins, polyimide resins, and photosensitive resins.

[0031] [Examples of Embodiments] Examples of embodiments of the present invention are given below. The present invention is not limited thereto.

[0032] <1>A method for producing a tetracarboxylic dianhydride by adding a monomer containing an acid anhydride group to a styrene-based compound in the presence of oxygen and a polymerization inhibitor. <2>The method for producing a tetracarboxylic dianhydride according to <1>, wherein 0.0001 part by mass to 0.5 part by mass of the polymerization inhibitor is used based on 100 parts by mass in total of the styrene-based compound and the monomer containing an acid anhydride group. <3>The method for producing a tetracarboxylic dianhydride according to <1> or <2>, wherein the polymerization inhibitor is at least one selected from the group consisting of quinone-based compounds and catechol-based compounds. <4>A first step of obtaining a tetracarboxylic dianhydride by adding a monomer containing an acid anhydride group to a styrene-based compound in the presence of oxygen and a polymerization inhibitor Next, a second step of adding a poor solvent to precipitate crystals of the tetracarboxylic dianhydride Next, a method for producing a tetracarboxylic dianhydride, comprising a third step of performing filtration to remove the unreacted monomer containing an acid anhydride group <5>The method for producing a tetracarboxylic dianhydride according to <4>, wherein 0.0001 part by mass to 0.5 part by mass of the polymerization inhibitor is used based on 100 parts by mass in total of the styrene-based compound and the monomer containing an acid anhydride group. [Examples]

[0033] Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the examples. In addition, "parts" means "parts by mass" and "%" means "% by mass".

[0034] The obtained tetracarboxylic dianhydride was identified by 1H-NMR measurement and gel permeation chromatography (GPC) measurement.

[0035] (1H-NMR) 1H-NMR was measured by dissolving the sample in DMSO-d6 using UltraShield 400 (manufactured by Bruker).

[0036] (Gel Permeation Chromatography (GPC)) For GPC, HLC-8320GPC (manufactured by Tosoh Corporation) equipped with an RI / UV detector was used. Two separation columns were connected in series, and for both packing materials, "TSK-GEL SUPER HZM-N" was connected in a pair and used. The measurement was carried out under the conditions of an oven temperature of 40 °C, using a tetrahydrofuran (THF) solution as the eluent, and a flow rate of 0.35 ml / min. The sample was dissolved in THF to a concentration of 0.1% and 20 microliters was injected into the apparatus. All molecular weights are in terms of polystyrene conversion values.

[0037] (Gas Chromatography (GC)) 0.2 g of the sample was precisely weighed, 10 mL of acetonitrile was added, and ultrasonic treatment was performed for 15 minutes to prepare a solution. After filtering this solution with a 0.25 μm PTFE filter, it was analyzed by a gas chromatograph (manufactured by Shimadzu Corporation, GC-2025). The measurement conditions were as follows: DB-5MS (manufactured by Agilent Technologies) was used as the separation column, the injection temperature was 280 °C, the injection volume was 1 μL, and helium gas was used as the carrier gas.

[0038] (Example 1) Into a 2 L stainless steel (SUS) reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, 172.6 parts of styrene, 341.4 parts of maleic anhydride, 0.514 part of methylhydroquinone, and 256.5 parts of cyclohexanone were charged. Then, while blowing dry air at a flow rate of 200 mL / min, the mixture was heated and stirred at an internal temperature of 100 °C for 14 hours. After cooling to room temperature, the precipitated white crystals were filtered off, and the crystals were rinsed with 256.5 parts of cyclohexanone and 256.5 parts of toluene, followed by drying under reduced pressure at 80 °C for 3 hours to obtain a white crystalline product. When the obtained product was analyzed by 1H-NMR, GC, and GPC, it was confirmed that the product was the target tetracarboxylic dianhydride and there were no resin by-products. Also, no alteration such as corrosion spots or rust was observed on the SUS reaction vessel before and after the reaction, and it was confirmed that the vessel was in a state where it could be repeatedly used.

[0039] (Examples 2 - 10) Synthesis was carried out in the same manner as in Example 1 except that the raw materials used in Example 1 were changed to the raw materials and charged amounts described in Table 1 and the dry air flow rate, and tetracarboxylic dianhydrides of Examples 2 - 10 were obtained respectively. The obtained products are shown below. Note that the product synthesized in the comparative example is the same as that in Example 1.

[0040] [Chemical formula] JPEG2025100366000002.jpg58144JPEG2025100366000003.jpg63144

[0041] (Comparative Example 1) Into a 2 L SUS reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, 172.6 parts of styrene, 341.4 parts of maleic anhydride, 0.514 part of methylhydroquinone, and 256.5 parts of cyclohexanone were charged. Then, while blowing nitric oxide at a flow rate of 200 mL / min, the mixture was heated and stirred at an internal temperature of 100 °C for 14 hours. After cooling to room temperature, the precipitated white crystals were filtered off, and the crystals were rinsed with 256.5 parts of cyclohexanone and 256.5 parts of toluene, followed by drying under reduced pressure at 80 °C for 3 hours to obtain a white crystalline product. When the obtained product was analyzed by 1H-NMR, GC, and GPC, it was confirmed that the product was the target tetracarboxylic dianhydride and there were no by-products of the resin. On the other hand, significant corrosion and rusting were observed on the SUS reaction vessel before and after the reaction, and it was confirmed that the vessel could not be reused.

[0042] (Comparative Example 2) Into a 2 L SUS reaction vessel equipped with a thermometer, a condenser, and a stirrer, 172.6 parts of styrene, 341.4 parts of maleic anhydride, and 256.5 parts of cyclohexanone were charged. Then, while blowing nitrogen at a flow rate of 200 mL / min, the mixture was heated at an internal temperature of 100 °C for 1 hour, and the viscosity increased significantly. After cooling to room temperature, a resin gel-like product was obtained. When the obtained product was analyzed by 1H-NMR, GC, and GPC, it was confirmed that the product did not contain the target tetracarboxylic dianhydride and was a by-product of the resin. Also, no corrosion or rusting was observed on the SUS reaction vessel before and after the reaction, and it was confirmed that the vessel could be reused.

[0043] (Comparative Example 3) Into a 2 L stainless steel (SUS) reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, 172.6 parts of styrene, 341.4 parts of maleic anhydride, and 256.5 parts of cyclohexanone were charged. Then, while blowing dry air at a flow rate of 200 mL / min, the mixture was heated at an internal temperature of 100 °C for 1 hour, and the viscosity increased significantly. After cooling to room temperature, a resin gel-like product was obtained. When the obtained product was analyzed by 1H-NMR, GC, and GPC, it was confirmed that the product did not contain the target tetracarboxylic dianhydride and was a by-product of the resin. Also, no corrosion or rusting was observed on the SUS reaction vessel before and after the reaction, and it was confirmed that the vessel could be reused.

[0044] (Comparative Example 4) Into a 2 L reaction vessel made of SUS equipped with a thermometer, a condenser, and a stirrer, 172.6 parts of styrene, 341.4 parts of maleic anhydride, 256.5 parts of cyclohexanone, and 0.514 part of methylhydroquinone were charged. Then, while blowing nitrogen at a flow rate of 200 mL / min, it was heated at an internal temperature of 100 °C for 1 hour, and as a result, the viscosity increased significantly. After cooling to room temperature, a resin gel-like product was obtained. When the obtained product was analyzed by 1H-NMR, GC, and GPC, it was confirmed that the target tetracarboxylic dianhydride was not contained in the product and that it was a by-product of the resin. Also, no alteration such as corrosion spots or rust was observed on the SUS reaction vessel before and after the reaction, and it was confirmed that the vessel could be used repeatedly.

[0045]

Table 1

[0046] The symbols in the table are as follows. In the table, the amount of polymerization inhibitor used means the amount (parts) of the polymerization inhibitor used with respect to 100 parts of the total amount of the styrene-based compound and the acid anhydride group-containing monomer. Also, the blending amount of the monomers in the table indicates the blending amount (mol%) when the total amount of the styrene-based compound and the acid anhydride group-containing monomer is 100 mol%.

[0047] (Styrene-based compound) ·St: Styrene ·4TBSt: 4-tert-butylstyrene ·α-MSt: α-methylstyrene (Acid anhydride group-containing monomer) ·MA: Maleic anhydride ·IA: Itaconic anhydride ·CA: Citraconic anhydride (Polymerization inhibitor) ·MHQ: Methylhydroquinone ·TBC: p-tert-butylcatechol ·PTZ: Phenothiazine

[0048] (Evaluation of reactivity) The product obtained as a result of the reaction was analyzed by 1H-NMR, GC, and GPC, and the reactivity was evaluated at three levels. If the resin by-product was below the detection limit, it was evaluated as ○; if a very small amount of resin by-product was contained, it was evaluated as △; and if a large amount of resin by-product was contained, it was evaluated as ×.

[0049] (Evaluation of toxicity) The toxicity of the gas blown into the system during the reaction itself was evaluated at two levels. When the gas used in the reaction was dry air, since dry air itself has no toxicity, it was judged to have low toxicity and was evaluated as ○. On the other hand, when the gas used in the reaction was nitric oxide, since it is a gas extremely harmful to the human body, it was judged to have high toxicity and was evaluated as ×.

[0050] (Evaluation of productivity) For the industrialization of tetracarboxylic dianhydride, high productivity that allows general-purpose equipment to be repeatedly used is required. Therefore, in the examples, based on the presence or absence of deterioration such as corrosion spots and rust on the SUS reaction vessel before and after the reaction, the productivity was evaluated at two levels. After the reaction, if there were no deterioration such as corrosion spots and rust on the SUS reaction vessel and the vessel was in a state where it could be repeatedly used, it was evaluated as ○. On the other hand, if significant deterioration such as corrosion spots and rust was observed on the SUS reaction vessel after the reaction and the vessel could not be repeatedly used, it was evaluated as ×.

[0051]

Table 2

[0052] From the results in Table 2, it can be seen that this production method can suppress the formation of polymers and produce tetracarboxylic dianhydride with good productivity. On the other hand, in Comparative Example 1, although the reactivity was good, the use of toxic nitric oxide made the toxicity and productivity inappropriate. Also, in Comparative Examples 2 to 4, when either or both of dry air and the polymerization inhibitor were lacking, tetracarboxylic dianhydride could not be obtained and the reactivity was inappropriate.

[0053] (Example 11) Into a 2 L SUS reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, 406.2 parts of maleic anhydride, 0.257 parts of methylhydroquinone, and 15.6 parts of cyclohexanone were charged. Then, while blowing dry air at a flow rate of 200 mL / min, the internal temperature was raised to 140 °C, and 107.8 g of styrene was uniformly added dropwise over 6 hours. The reaction was terminated by heating and stirring at 140 °C for 2 hours. Next, after cooling to room temperature, 359.8 g of toluene was added, and the precipitated white crystals were filtered off to remove unreacted maleic anhydride. Then, the crystals were washed with 300 parts of toluene, and further dried under reduced pressure at 80 °C for 3 hours to obtain a white crystalline product. When the obtained product was analyzed by 1H-NMR, GC, and GPC, it was confirmed that the product was the target tetracarboxylic dianhydride and there were no resin by-products. Also, no deterioration such as corrosion spots or rust was observed on the SUS reaction vessel before and after the reaction, and it was confirmed that the vessel could be reused repeatedly.

[0054] (Examples 12 - 14, Comparative Example 5) Synthesis was carried out in the same manner as in Example 11, except that the raw materials used in Example 11 were changed to the raw materials and charged amounts described in Table 3, and the flow rate of dry air was changed, to obtain the tetracarboxylic dianhydrides of Examples 12 - 14 and Comparative Example 5, respectively.

[0055] [Table 3]

[0056] The symbols in the table are the same as those in Table 2.

[0057] (By-product content) Sampling was carried out at the end point of the synthesis of the tetracarboxylic dianhydride and quantified by gas chromatography to evaluate the polymer content of the by-products.

[0058] [Table 4]

[0059] From Tables 3 and 4, it was possible to verify numerically that, as described so far, the polymer of the by-product is less likely to be generated by the production method of the present invention.

Industrial Applicability

[0060] The method for producing a tetracarboxylic dianhydride of the present invention can be mainly used in the industrial production of tetracarboxylic dianhydrides as raw materials for alkyd resins, unsaturated polyester resins, polyamide resins, polyimide resins, and the like.

Claims

**Claim 1** A method for producing a tetrabasic acid anhydride by adding a monomer containing an acid anhydride group to a styrene-based compound in the presence of oxygen and a polymerization inhibitor. **Claim 2** The method for producing a tetrabasic acid anhydride according to claim 1, wherein 0.0001 to 0.5 parts by mass of the polymerization inhibitor is used based on 100 parts by mass in total of the styrene-based compound and the monomer containing an acid anhydride group. **Claim 3** The method for producing a tetrabasic acid anhydride according to claim 1 or 2, wherein the polymerization inhibitor is at least one selected from the group consisting of quinone-based compounds and catechol-based compounds. **Claim 4** A first step of obtaining a tetrabasic acid anhydride by adding a monomer containing an acid anhydride group to a styrene-based compound in the presence of oxygen and a polymerization inhibitor Next, a second step of adding a poor solvent to precipitate crystals of the tetrabasic acid anhydride Next, a method for producing a tetrabasic acid anhydride, comprising a third step of performing filtration to remove unreacted monomer containing an acid anhydride group **Claim 5** The method for producing a tetrabasic acid anhydride according to claim 4, wherein 0.0001 to 0.5 parts by mass of the polymerization inhibitor is used based on 100 parts by mass in total of the styrene-based compound and the monomer containing an acid anhydride group.

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