JP2024077640A - Method for producing benzoxazine compound - Google Patents

Abstract

To provide a production method that can produce a benzoxazine compound with high purity and high yield even when using raw materials poorly soluble in aromatic hydrocarbon solvents.SOLUTION: A method for producing a benzoxazine compound represented by the general formula (1) includes the step of reacting a bisphenol compound, a formaldehyde, and an aminothiol compound in the presence of a C3-8 aliphatic ester solvent. (R1: H, a C1-C6 alkyl. R2: a C1-C10 divalent hydrocarbon. X: a single bond, O, S, SO2, CO, formula (1a) or formula (1b)). (R3, R4: H, a C1-C10 alkyl, a C1-C10 alkyl halide, a C6-C12 aryl, or R3 and R4 bonding together to form a C5-C20 cycloalkylidene. Ar1, Ar2: a C6-C12 aryl (* representing a bonding position)).SELECTED DRAWING: None

Description

The present invention relates to a method for producing a benzoxazine compound. More specifically, the present invention relates to a method for producing a benzoxazine compound obtained using a bisphenol compound, an amine having a thiol group, and a formaldehyde compound as raw materials.

Benzoxazine compounds are compounds synthesized by reacting phenols, amines, and formaldehyde, and are known as thermosetting resin raw materials that harden by ring-opening polymerization of the benzoxazine ring when heated without producing volatile by-products. They are used as raw materials for molded articles that can be used as materials for insulating substrates, liquid crystal alignment agents, resin compositions for semiconductor encapsulation, and the like.
On the other hand, the curing temperature of benzoxazine compounds is generally relatively high, and in order to lower the polymerization temperature, catalysts, polymerization accelerators, and highly reactive benzoxazine compounds have been developed in recent years. Among the highly reactive benzoxazine compounds, for example, a hydroxyl-functional benzoxazine composition having a hydroxyl group introduced into the structure has been reported (Patent Document 1).

JP 2011-530570 A

In general, aromatic hydrocarbon solvents such as toluene are considered to be suitable as solvents for synthesizing these functional benzoxazine compounds. However, as in the comparative example described below, when using raw materials that are insoluble or poorly soluble in the solvent (e.g., 4,4'-dihydroxybiphenyl, etc.), the reaction does not proceed, and it is necessary to significantly increase the reaction temperature and time, resulting in a significant decrease in the purity of the product.
An object of the present invention is to provide a production method by which a benzoxazine compound can be obtained in high yield even when a bisphenol compound that is poorly soluble in aromatic hydrocarbon solvents is used as a raw material.

As a result of intensive research into solving the above-mentioned problems, the inventors discovered that by using an aliphatic ester solvent that exhibits superior solubility for poorly soluble raw material compounds compared to aromatic hydrocarbon solvents such as toluene, benzoxazine compounds can be obtained from these raw materials in high yields, and thus completed the present invention.

The present invention is as follows.
1. A method for producing a benzoxazine compound represented by general formula (1), comprising a reaction step of reacting a bisphenol compound represented by general formula (2), a formaldehyde compound, and an aminothiol compound represented by general formula (3) in the presence of an aliphatic ester solvent having 3 to 8 carbon atoms.
(In the formula, each R ₁ independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, each R ₂ independently represents a divalent hydrocarbon group having 1 to 10 carbon atoms, and X represents a single bond, an oxygen atom, a sulfur atom, a sulfonyl group, a carbonyl group, a divalent group represented by general formula (1a) or a divalent group represented by general formula (1b).)
(In general formulas (1a) and (1b), _R3 and _R4 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms; _R3 and _R4 may be bonded to each other to form a cycloalkylidene group having 5 to 20 carbon atoms as a whole; _Ar1 and _Ar2 each independently represent an aryl group having 6 to 12 carbon atoms; and * indicates the bonding position.)
(In the formula, R ₁ and X are defined as in general formula (1).)
(In the formula, _R2 is defined as in general formula (1).)
2. The method according to 1., wherein X in the general formulae (1) and (2) is a single bond, a sulfonyl group, or a divalent group represented by the general formula (1b).
3. The method according to 1. or 2., wherein R ₂ in the general formulae (1) and (3) is a linear or branched alkylene group having 1 to 10 carbon atoms or an alkylene group containing a cyclic alkane.
4. The method according to 1., wherein the reaction temperature in the reaction step is in the range of 30 to 80° C.

The method for producing a benzoxazine compound of the present invention is extremely useful because it can produce a benzoxazine compound in improved yield even when a bisphenol compound that has low solubility in aromatic hydrocarbon solvents is used as a raw material.

The method for producing a benzoxazine compound represented by the general formula (1) of the present invention is a method including a reaction step of reacting a bisphenol compound represented by the general formula (2), a formaldehyde compound, and an aminothiol compound represented by the general formula (3) in the presence of an aliphatic ester solvent having 3 to 8 carbon atoms. In this reaction, the reaction formula when formaldehyde is used as the formaldehyde compound is as follows.
(In the formula, R ₁ , R ₂ and X are defined as in general formula (1).)

<Benzoxazine compound represented by general formula (1)>
R ₁ in general formula (1) is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 carbon atom (methyl group), and particularly preferably a hydrogen atom. When R ₁ is not a hydrogen atom, the bonding position is preferably the ortho position on the benzene ring with respect to the oxygen atom of the benzoxazine ring.
R ₂ in the general formula (1) is a divalent group having 1 to 10 carbon atoms. Specific examples thereof include linear or branched alkylene groups having 1 to 10 carbon atoms, such as methylene group, ethylene group, propane-1,2-diyl group, propane-1,3-diyl group, butane-1,4-diyl group, pentane-1,5-diyl group, hexane-1,6-diyl group, cyclohexane-1,3-diyl group, and cyclohexane-1,4-diyl group, or alkylene groups containing a cyclic alkane; alkylidene groups having 1 to 10 carbon atoms, such as ethylidene group, propylidene group, isopropylidene group, butylidene group, cyclopentylidene group, and cyclohexylidene group; phenylene group; and divalent groups having 1 to 10 carbon atoms containing a benzene ring, such as groups represented by the following formulas.
(In the formula, * indicates the bond position.)
Among these, _R2 is preferably a linear or branched alkylene group having 1 to 10 carbon atoms, an alkylene group containing a cyclic alkane, or an alkylidene group having 1 to 10 carbon atoms, more preferably a linear or branched alkylene group having 1 to 10 carbon atoms or an alkylene group containing a cyclic alkane, still more preferably a linear or branched alkylene group having 1 to 6 carbon atoms or an alkylene group containing a cyclic alkane, and particularly preferably a linear or branched alkylene group having 1 to 4 carbon atoms.

X in the general formula (1) represents a single bond, an oxygen atom, a sulfur atom, a sulfonyl group, a carbonyl group, a divalent group represented by the general formula (1a) or a divalent group represented by (1b). Among them, the raw material bisphenol compound corresponding to the benzoxazine compound when it is a single bond, a sulfonyl group, or a divalent group represented by (1b) is difficult to dissolve in an aromatic hydrocarbon solvent, and it is difficult to synthesize the benzoxazine compound using an aromatic hydrocarbon solvent in the reaction. However, according to the production method of the present invention, the benzoxazine compound can be produced with an improved yield, which is preferable from the viewpoint of higher usefulness.
When X in general formula (1) is general formula (1a), more preferable _R3 and _R4 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and further preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a trifluoromethyl group, or an aryl group having 6 to 8 carbon atoms.
_R3 and _R4 may be bonded to each other to form a cycloalkylidene group having 5 to 20 carbon atoms as a whole, in which case the cured product obtained by using this benzoxazine compound has excellent heat resistance. The cycloalkylidene group having 5 to 20 carbon atoms may contain an alkyl group as a branched chain. The cycloalkylidene group preferably has 5 to 15 carbon atoms, more preferably has 6 to 12 carbon atoms, and particularly preferably has 6 to 9 carbon atoms.
Specific examples of the cycloalkylidene group include a cyclopentylidene group (5 carbon atoms), a cyclohexylidene group (6 carbon atoms), a 3-methylcyclohexylidene group (7 carbon atoms), a 4-methylcyclohexylidene group (7 carbon atoms), a 3,3,5-trimethylcyclohexylidene group (9 carbon atoms), a cycloheptylidene group (7 carbon atoms), a bicyclo[2.2.1]heptane-2,2-diyl group (7 carbon atoms), a 1,7,7-trimethylbicyclo[2.2.1]heptane-2,2-diyl group (10 carbon atoms), a 4,7,7-trimethylbicyclo[2.2.1]heptane-2,2-diyl group (10 carbon atoms), a tricyclo[5.2.1.0 ^2,6 ]decane-8,8-diyl group (10 carbon atoms), 2,2-adamantylidene group (10 carbon atoms), cyclododecanylidene group (12 carbon atoms), etc. are preferred. Cyclohexylidene group (6 carbon atoms), 3-methylcyclohexylidene group (7 carbon atoms), 4-methylcyclohexylidene group (7 carbon atoms), 3,3,5-trimethylcyclohexylidene group (9 carbon atoms), cyclododecanylidene group (12 carbon atoms) are more preferred. Cyclohexylidene group (6 carbon atoms), 3,3,5-trimethylcyclohexylidene group (9 carbon atoms), cyclododecanylidene group (12 carbon atoms) are more preferred. Cyclohexylidene group (6 carbon atoms), 3,3,5-trimethylcyclohexylidene group (9 carbon atoms), cyclododecanylidene group (12 carbon atoms) are particularly preferred.
When X in formula (1) is formula (1b), preferred Ar ₁ and Ar ₂ are each independently a benzene ring or a naphthalene ring, and more preferably both Ar ₁ and Ar ₂ are benzene rings. For example, when both Ar ₁ and Ar ₂ are benzene rings, the group represented by formula (1b) is a fluorenylidene group.
The bonding positions of X in the general formula (1) and the two benzoxazine rings are preferably the ortho or para positions on the benzene ring relative to the oxygen atom of the benzoxazine ring.

(Aliphatic ester solvent)
As the aliphatic ester solvent having 3 to 8 carbon atoms used in the production method of the present invention, an acetate ester solvent having 3 to 8 carbon atoms is preferred, an acetate ester solvent having 3 to 6 carbon atoms is more preferred, an acetate ester solvent having 4 to 6 carbon atoms is even more preferred, and an acetate ester solvent having 6 carbon atoms is particularly preferred. Specific examples of the aliphatic ester solvent having 3 to 8 carbon atoms include methyl acetate, ethyl acetate, propyl acetate (n-propyl acetate, isopropyl acetate), butyl acetate (n-butyl acetate, isobutyl acetate, sec-butyl acetate, t-butyl acetate), and hexyl acetate (n-hexyl acetate, etc.). Among these, butyl acetate is preferred, and among butyl acetates, n-butyl acetate is particularly preferred. Note that the chemical formula of butyl acetate is C ₆ H ₁₂ O ₂ , and therefore corresponds to an aliphatic ester solvent having 6 carbon atoms. The aliphatic ester solvent can be used alone or in combination of two or more thereof, and it is preferable to use only one type. The amount of the aliphatic ester solvent used is preferably 1.5 to 5 times by weight, more preferably 2 to 4 times by weight, and even more preferably 2.5 to 3 times by weight, relative to the amount of the bisphenol compound represented by formula (2).

(Bisphenol compound represented by general formula (2))
The definitions and preferred embodiments of _R1 and X in the bisphenol compound represented by the general formula (2) are the same as those in the general formula (1).
Specific examples of the bisphenol compound represented by the general formula (2) include bisphenol F (bis(2-hydroxyphenyl)methane, 2-hydroxyphenyl-4-hydroxyphenylmethane, bis(4-hydroxyphenyl)methane), bisphenol E (1,1-bis(4-hydroxyphenyl)ethane), bisphenol A (2,2-bis(4-hydroxyphenyl)propane), bisphenol C (2,2-bis(4-hydroxy-3-methylphenyl)propane), 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-dihydroxybiphenyl (hereinafter referred to as "BP"), 4,4'-dihydroxy-3,3'-dimethylbiphenyl, bis(4-hydroxyphenyl)ether, 4, Examples of the 4'-dihydroxybenzophenone include bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfide, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,1-bis(4-hydroxyphenyl)-1-naphthylethan, 2,2-bis(4-hydroxyphenyl)hexafluoropropane, bisphenol Z (1,1-bis(4-hydroxyphenyl)cyclohexane), bisphenol TMC (1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane), 1,1-bis(4-hydroxyphenyl)cyclododecane, 2,2-bis(4-hydroxyphenyl)adamantane, and 9,9-bis(4-hydroxy-3-methylphenyl)fluorene.
Among these, 4,4'-dihydroxybiphenyl (hereinafter referred to as "BP"), 4,4'-dihydroxy-3,3'-dimethylbiphenyl, bis(4-hydroxyphenyl)sulfone, 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, and the like are difficult to dissolve in aromatic hydrocarbon solvents, and it is difficult to synthesize benzoxazine compounds using aromatic hydrocarbon solvents in reactions. However, according to the production method of the present invention, they can be produced with an improved yield, and are therefore preferred from the viewpoint of high usefulness.

(Aminothiol compound represented by general formula (3))
The definition and preferred embodiments of _R2 in the aminothiol compound represented by the general formula (3) are the same as those in the general formula (1).
Specific examples of the aminothiol compound represented by the general formula (3) include 2-aminoethanethiol, 3-amino-1-propanethiol, 2-amino-1-methylethanethiol, 2-amino-2-methylethanethiol, 5-amino-1-pentanethiol, 6-amino-1-hexanethiol, 2-aminothiophenol, 3-aminothiophenol, 4-aminothiophenol, 4-aminobenzylmercaptan, etc. Among these, 2-aminoethanethiol, 3-amino-1-propanethiol, 2-amino-1-methylethanethiol, 2-amino-2-methylethanethiol, 5-amino-1-pentanethiol, and 6-amino-1-hexanethiol are preferred, 2-aminoethanethiol, 3-amino-1-propanethiol, and 2-amino-1-methylethanethiol are more preferred, and 2-aminoethanethiol is particularly preferred.
The amount of the aminothiol compound represented by the general formula (3) used is preferably in the range of 2.0 to 10.0 mol, more preferably in the range of 2.0 to 8.0 mol, even more preferably in the range of 2.0 to 6.0 mol, and particularly preferably in the range of 2.0 to 3.0 mol, relative to 1 mol of the bisphenol compound represented by the general formula (2).

(Formaldehyde)
Specific examples of formaldehydes include aqueous formaldehyde solutions, 1,3,5-trioxane, and paraformaldehyde.
The amount of formaldehyde used is preferably in the range of 4.0 to 20.0 mol, more preferably in the range of 4.0 to 16.0 mol, even more preferably in the range of 4.0 to 12.0 mol, and particularly preferably in the range of 4.0 to 8.0 mol, relative to 1 mol of the bisphenol compound represented by the general formula (2).

(catalyst)
In the present invention, a catalyst for promoting the reaction is not particularly necessary, but an acid catalyst or a base catalyst can be used as necessary. In this case, examples of acid catalysts that can be used include concentrated hydrochloric acid, hydrochloric acid gas, trifluoroacetic acid, methanesulfonic acid, p-toluenesulfonic acid, benzoic acid, and mixtures thereof, and examples of base catalysts that can be used include sodium hydroxide, sodium carbonate, triethylamine, triethanolamine, and mixtures thereof. Among these, p-toluenesulfonic acid and sodium hydroxide are preferred, and sodium hydroxide is more preferred.
The amount of the catalyst used is preferably in the range of 1 to 3 moles, more preferably in the range of 1 to 2 moles, and even more preferably in the range of 1 to 1.5 moles, relative to 1 mole of the aminothiol compound represented by general formula (3).

(Reaction conditions and methods)
The reaction temperature is preferably in the range of 30 to 80°C, more preferably in the range of 40 to 80°C, and even more preferably in the range of 50 to 70°C.
The reaction may be carried out under normal pressure, or under increased or reduced pressure.
There is no limitation on the method of mixing the raw materials, bisphenol compound represented by general formula (1), formaldehydes, and amine compound represented by general formula (2). For example, (i) a method of mixing an amine compound represented by general formula (2) with a mixture containing a bisphenol compound represented by general formula (1) and formaldehydes to carry out a reaction, (ii) a method of mixing a bisphenol compound represented by general formula (1) with a mixture containing formaldehydes and an amine compound represented by general formula (2), etc. can be mentioned. These mixtures may contain the above-mentioned solvents and catalysts, and there is no limitation on the method of mixing the catalyst, but it is preferable to mix the catalyst before mixing the amine compound represented by general formula (2).
In the production method of the present invention, there is no limitation on the method for mixing the remaining raw materials with the raw material mixture. However, from the viewpoint of reaction selectivity and suppressing the production of high molecular weight components as by-products, it is preferable to mix the raw materials continuously or intermittently rather than mixing them all at once.
The reaction may include a procedure for removing water derived from the raw materials or water generated during the reaction from the system. The procedure for removing the generated water from the reaction solution is not particularly limited, and the water can be removed by azeotropically distilling the generated water with the solvent system in the reaction solution. The generated water can be removed from the reaction system by using, for example, a pressure-equalizing dropping funnel equipped with a cock, a Dimroth condenser, a Dean-Stark apparatus, or the like.

(Post-processing operations)
After completion of the reaction, the reaction mixture obtained in the reaction step can be used to obtain the benzoxazine compound represented by general formula (1) from the mixture by a known method.
For example, the reaction-finished mixture obtained in the reaction step may be washed in a washing step with water or an alkaline aqueous solution in which sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, or the like is dissolved in water. After washing with the alkaline aqueous solution, it is preferable to wash with water so that the alkali does not remain in the reaction liquid. As a more specific operation, for example, it is preferable to add about 80 parts by weight of pure water to 100 parts by weight of the reaction mixture after the reaction is finished, stir for about 30 minutes, leave it, and then separate the organic layer and the aqueous layer once or a plurality of times. It is more preferable to end the washing with water by confirming that the pH of the aqueous layer separated after washing is in the range of 7 to 8.
The solution obtained by the reaction step may contain salts and unreacted paraformaldehyde, and a filtration step may be carried out to remove these by filtration.
The reaction mixture obtained in the reaction step or the reaction mixture that has been subjected to the washing step and/or filtration step can be subjected to a solvent distillation step in which the solvent is distilled off.
In addition, a crystallization step can be carried out by adding a solvent to the reaction mixture or the reaction mixture from which the solvent has been distilled off to obtain crystals. The obtained crystals can be filtered to obtain a powder or granular target product. The benzoxazine compound extracted by the above method can be made into a high-purity product by ordinary purification means such as washing with a solvent or water or recrystallization.
In addition, when carrying out the above-mentioned reaction step, washing step, filtration step, solvent distillation step, crystallization step, and other usual purification means, it is preferable to carry out the steps in an inert gas atmosphere such as nitrogen or argon, or in an atmosphere with less oxygen than air, in order to suppress oxidation, deterioration, coloration, and the like due to the influence of oxygen.

The present invention will now be described more specifically with reference to examples.
<Analysis method>
1. Confirmation of remaining amount of raw material compound (liquid chromatography: LC)
Apparatus: Prominence UFLC (liquid chromatography) manufactured by Shimadzu Corporation
Pump: LC-20AD
Column oven: CTO-20A
Detector: SPD-20A
Column: HALO C18 (inner diameter 3 mm, length 75 mm)
Oven temperature: 50°C
Flow rate: 0.7 mL/min
Mobile phase: (A) 0.2% by volume acetic acid aqueous solution, (B) tetrahydrofuran Gradient conditions: (A) vol.%
Method: 20% (0 min) → 40% (10 min) → 60% (20 min) → 100% (37 min) → 100% (40 min)
Sample injection volume: 10 μL
Detection wavelength: 280 nm
2. Reaction solution composition and purity analysis (gel permeation chromatography: GPC)
The purity of each synthesized benzoxazine compound was expressed as the area percentage value of the benzoxazine compound by this analysis.
Apparatus: HLC-8320/Tosoh Corporation Detector: Differential refractometer (RI)
[Measurement condition]
Flow rate: 1 mL/min
Eluent: tetrahydrofuran Temperature: 40°C
Wavelength: 254 nm
Measurement sample: 1 g of the benzoxazine compound-containing composition was diluted 200 times with tetrahydrofuran.
3. Confirmation of the chemical structure of the target compound ( ^1H -NMR)
Apparatus: Fourier transform nuclear magnetic resonance AVANCE III HD 400 (manufactured by BRUKER)
The measurement sample was dissolved in deuterated chloroform, and the ¹ H-NMR spectrum was measured.

Example 1
After adding 231 g (2.0 mol) of cysteamine hydrochloride to a 2 L four-neck flask, 165 g (2.0 mol) of 48% NaOH aqueous solution was added slowly over 5 minutes while stirring and checking the temperature rise. After that, after confirming that the pH of the aqueous layer was 9 to 10, 140 g (4.3 mol) of paraformaldehyde (purity: 92%) was added in small portions over 30 minutes. At this time, it was confirmed that the temperature of the reaction system rose from 30°C to 42°C. Then, the mixture was air-cooled while stirring, and after confirming that the temperature had dropped to 30°C, stirring was performed at 30°C for 1 hour. Then, 508 g of butyl acetate (2.8 times the weight of BP) and 184 g of BP were added to the flask. Then, the liquid temperature was raised to 60°C and the reaction was performed for 7 hours, and the reaction liquid was analyzed by the above LC. As a result, the residual rate of BP was calculated from the BP calibration curve and was 6.4% (same below). Therefore, the reaction was continued for an additional 5 hours at 70° C., but the residual rate of BP was 1.1%, and since the raw material had been almost consumed, the reaction was terminated.
After lowering the liquid temperature in the flask to 40°C, 400g of pure water was added to wash the organic layer of the reaction-terminated liquid, and the mixture was stirred for 30 minutes and then allowed to stand. After confirming the separation of the organic layer and the aqueous layer, the aqueous layer was removed. This washing operation was performed four times, and it was confirmed that the pH of the aqueous layer was 7 to 8. The solvent was then removed by distillation at 60°C under reduced pressure. Butyl acetate was added so that the solid content of the distillation residue after distillation became a varnish containing 15% by weight, and 291g of a yellow varnish was obtained. The yield of the benzoxazine compound represented by the following formula (A), which is the target compound, was 64% based on the BP used. The purity of the obtained benzoxazine compound was 64 area% as a result of GPC analysis by the above method.
The results of ¹ H-NMR analysis revealed that the benzoxazine compound represented by formula (A) was obtained.
¹ H-NMR analysis (400 MHz, solvent: CDCl ₃ , standard substance: tetramethylsilane)
3.00-3.17 (8H,m), 3.81-4.06 (8H,m), 4.84-4.86 (1H,br), 6.84-7.39 (6H,m).

Comparative Example 1 (Test Example 1 using an aromatic hydrocarbon solvent)
After adding 5.0 g (0.043 mol) of cysteamine hydrochloride to a 100 mL test tube, 3.5 g (0.042 mol) of 48% NaOH aqueous solution was slowly added while stirring. After that, it was confirmed that the pH of the aqueous layer was about 9 to 10, and 3.0 g (0.090 mol) of paraformaldehyde (purity: 92%) was added in small portions over 30 minutes. At this time, it was confirmed that the temperature of the reaction system rose from 30°C to 35°C. Then, it was air-cooled while stirring, and after it was confirmed that the temperature had dropped to 30°C, it was stirred at 30°C for 1 hour. Then, 11.0 g of toluene (2.8 times the weight of BP) and 4.0 g of BP were added to the test tube. Then, the liquid temperature was raised to 60°C, and the reaction was carried out for 7 hours. As a result of the analysis of the reaction liquid by the above LC, the residual rate of BP was 93.3%. Therefore, the reaction was continued for an additional 5 hours at 70°C, and the reaction solution was analyzed by LC as described above. As a result, the residual rate of BP had decreased to 80.6%. When the reaction was continued for an additional 5 hours, the residual rate of BP was 80.4%. Since there was almost no further consumption of BP, the reaction was terminated.

Comparative Example 2 (Test Example 2 using an aromatic hydrocarbon solvent)
After adding 5.0 g (0.043 mol) of cysteamine hydrochloride to a 100 mL test tube, 3.5 g (0.042 mol) of 48% NaOH aqueous solution was slowly added while stirring. After that, it was confirmed that the pH of the aqueous layer was about 9 to 10, and 3.0 g (0.090 mol) of paraformaldehyde (purity: 92%) was added in small portions over 30 minutes. At this time, it was confirmed that the temperature of the reaction system rose from 30°C to 35°C. Then, it was air-cooled while stirring, and after it was confirmed that the temperature had dropped to 30°C, it was stirred at 30°C for 1 hour. Then, 11.0 g of toluene (2.8 times the weight of BP) was added to the test tube, and 4.0 g of BP was added. After that, the liquid temperature in the test tube was raised to 100°C and the reaction was carried out for 3 hours, and a gel-like compound was generated, and the reaction liquid could not be analyzed by the above LC, and the benzoxazine compound represented by the desired formula (A) could not be obtained.

The consumption rates of BP, a raw material compound, from the start of the reaction in the above Example 1 and Comparative Example 1 are shown in Table 1 below. The consumption rate of BP is calculated by subtracting the remaining rate calculated from the calibration curve from 100%.

As shown in Table 1, in Example 1, which is a specific example of the present invention, BP is efficiently consumed and the reaction proceeds by using butyl acetate as a reaction solvent, whereas in Comparative Example 1, when toluene is used as a reaction solvent, the consumption rate of BP is low and the reaction stops midway.
In addition, in Comparative Example 2, the reaction temperature was set too high, which is thought to have caused the target benzoxazine to undergo a heat-induced hardening reaction, resulting in a gel-like compound. This experimental data demonstrated that it is difficult to dissolve BP and advance the reaction by increasing the reaction temperature.
From these facts, it has become clear that in a production method of a benzoxazine compound using a raw material that is insoluble or poorly soluble in an aromatic hydrocarbon solvent, such as 4,4'-dihydroxybiphenyl, by employing an aliphatic ester solvent as a reaction solvent, the reaction can be carried out more quickly without increasing the reaction temperature, and the benzoxazine compound can be obtained in a higher yield.

Claims (4)

A method for producing a benzoxazine compound represented by general formula (1), comprising a reaction step of reacting a bisphenol compound represented by general formula (2), a formaldehyde compound, and an aminothiol compound represented by general formula (3) in the presence of an aliphatic ester solvent having 3 to 8 carbon atoms.
(In the formula, each R ₁ independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, each R ₂ independently represents a divalent hydrocarbon group having 1 to 10 carbon atoms, and X represents a single bond, an oxygen atom, a sulfur atom, a sulfonyl group, a carbonyl group, a divalent group represented by general formula (1a) or a divalent group represented by general formula (1b).)
(In general formulas (1a) and (1b), _R3 and _R4 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms; _R3 and _R4 may be bonded to each other to form a cycloalkylidene group having 5 to 20 carbon atoms as a whole; _Ar1 and _Ar2 each independently represent an aryl group having 6 to 12 carbon atoms; and * indicates the bonding position.)
(In the formula, R ₁ and X are defined as in general formula (1).)
(In the formula, _R2 is defined as in general formula (1).) The method according to claim 1, wherein X in the general formulas (1) and (2) is a single bond, a sulfonyl group, or a divalent group represented by the general formula (1b). The method according to claim 1 or 2, wherein R ₂ in the general formulas (1) and (3) is a linear or branched alkylene group having 1 to 10 carbon atoms or an alkylene group containing a cyclic alkane. The method according to claim 1, wherein the reaction temperature in the reaction step is in the range of 30 to 80°C.