JP7750140B2 - Method for producing (meth)acrylic acid ester - Google Patents

Description

The present invention relates to a method for producing (meth)acrylic acid esters.

Mono(meth)acrylic acid esters of dihydroxybenzophenone derivatives are useful as monomers for obtaining lens materials and resist materials.
As a method for producing a mono(meth)acrylic acid ester of a dihydroxybenzophenone derivative, Non-Patent Document 1 describes a method in which 2,4-dihydroxybenzophenone is reacted with 1.5 moles of acrylic acid chloride and 1 mole of triethylamine in acetone.

Non-Patent Document 2 describes a method in which 2,4-dihydroxybenzophenone is reacted with 1 mole of acrylic acid chloride and 1.6 moles of triethylamine in tetrahydrofuran.
Patent Document 1 describes a method in which 2,4-dihydroxybenzophenone is mixed with tetrahydrofuran using 4-(dimethylamino)pyridine as a catalyst, and methacrylic anhydride is added dropwise to the mixture under ice cooling.

BioResources, 11(1), 373; 2016 Macromolecules, 53(11), 4465; 2020

JP 2015-18107 A

However, the methods described in Non-Patent Documents 1 and 2 use excessive amounts of raw materials, and also produce a large amount of triethylamine hydrochloride, which requires complicated purification procedures such as solvent substitution to obtain a highly pure product.
Furthermore, since a large amount of solvent is used and the reaction is carried out while cooling, it cannot be said to be an industrially suitable production method.

The method described in Patent Document 1 requires the use of highly toxic 4-(dimethylamino)pyridine and a large amount of solvent. It also requires complicated procedures, such as adding methacrylic anhydride while cooling. Furthermore, it requires an industrially disadvantageous purification method, such as silica gel column chromatography, to remove impurities.
Furthermore, according to the investigations of the present inventors, it has been found that in this method, in addition to the di(meth)acrylate, a compound is produced in which the carboxy group of (meth)acrylic acid is added to the unsaturated bond of the methacryloyl group or acryloyl group of the (meth)acrylic acid ester by Michael addition.

In view of the above circumstances, an objective of the present invention is to provide a method for producing a (meth)acrylic acid ester that can efficiently produce a mono(meth)acrylic acid ester of a dihydroxybenzophenone derivative.

In order to achieve the above object, the present invention employs the following configuration.
[1] A method for producing a (meth)acrylic acid ester represented by the following formula (2), comprising a step of reacting an alcohol represented by the following formula (1) with (meth)acrylic anhydride in the presence of a compound of at least one metal selected from metals of Group 1 of the periodic table and metals of Group 2 of the periodic table:
(In the formula (1), ^R1 and ^R2 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms.)
(In the formula (2), ^R1 and ^R2 are the same as ^R1 and ^R2 in the formula (1), respectively, and ^R3 represents a hydrogen atom or a methyl group.)
[2] The method for producing a (meth)acrylic acid ester according to [1], wherein the metal is at least one selected from the group consisting of lithium, sodium, magnesium, potassium, calcium, strontium, and barium.
[3] The method for producing a (meth)acrylic acid ester according to [1] or [2], wherein the compound of the metal is at least one selected from the group consisting of an oxide, hydroxide, carbonate, hydrogencarbonate, chloride, and organic acid salt of the metal.
[4] The method for producing a (meth)acrylic acid ester according to [3], wherein the compound of the metal is a (meth)acrylic acid salt of the metal.
[5] The method for producing a (meth)acrylic acid ester according to any one of [1] to [4], in which the reaction is carried out using a solvent.
[6] The method for producing a (meth)acrylic acid ester according to [5], wherein the amount of the solvent used is not more than twice the mass ratio of the alcohol represented by the formula (1).
[7] The method for producing a (meth)acrylic acid ester according to any one of [1] to [6], wherein the reaction is carried out at 0°C to 130°C.
[8] The method for producing a (meth)acrylic acid ester according to any one of [1] to [7], wherein the alcohol represented by the formula (1) is reacted with (meth)acrylic anhydride in an amount of 1 to 1.5 times by molar ratio.
[9] The method for producing a (meth)acrylic acid ester according to any one of [1] to [8], wherein the obtained (meth)acrylic acid ester is recovered by crystallization.

The method for producing a (meth)acrylic acid ester of the present invention makes it possible to efficiently obtain a mono(meth)acrylic acid ester of a dihydroxybenzophenone derivative.

As used in the specification and claims, the following terms have the following definitions:
"(Meth)acrylic acid" means a compound selected from "acrylic acid" and "methacrylic acid".
"(Meth)acrylic anhydride" means a compound selected from "acrylic anhydride" and "methacrylic anhydride".
The term "(meth)acrylic acid ester" refers to a compound selected from "acrylic acid ester" and "methacrylic acid ester".
"Di(meth)acrylate" means a compound selected from "diacrylate" and "dimethacrylate".
The term "Michael adduct" refers to a compound in which a carboxy group of (meth)acrylic acid is added to the unsaturated bond of the methacryloyl group or acryloyl group of a (meth)acrylic acid ester represented by formula (2) by Michael addition.

<Reaction step>
The method for producing a (meth)acrylic acid ester of the present invention includes a step of reacting an alcohol represented by the following formula (1) with (meth)acrylic anhydride.

(In the formula (1), ^R1 and ^R2 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms.)

(In the formula (2), ^R1 and ^R2 are the same as ^R1 and ^R2 in the formula (1), respectively, and ^R3 represents a hydrogen atom or a methyl group.)

From the viewpoint of corrosiveness, R ¹ and R ² are preferably a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms, and from the viewpoint of reaction rate and stability, a hydrogen atom or a methyl group is more preferable. ^{R 1} and R ² may be the same or different.
As the alcohol represented by formula (1), 2,4-dihydroxybenzophenone is most preferred in terms of reaction rate and stability.

The amount of (meth)acrylic anhydride used is preferably 0.5 to 5 times the amount of the alcohol represented by formula (1) in molar ratio. From the perspective of the (meth)acrylic acid ester yield based on the alcohol, this molar ratio is preferably 0.9 or more, more preferably 1 or more, and even more preferably 1.1 or more. Furthermore, from the perspective of reducing the processing load of the remaining (meth)acrylic anhydride at the end of the reaction, this molar ratio is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1.3 or less.

[Metal compounds]
In the method for producing a (meth)acrylic acid ester of the present invention, the alcohol represented by the formula (1) is reacted with (meth)acrylic anhydride in the presence of a compound of at least one metal selected from the group consisting of metals in Group 1 and metals in Group 2 of the periodic table.

The at least one metal selected from the metals of Group 1 of the periodic table and the metals of Group 2 of the periodic table is preferably at least one metal selected from the group consisting of lithium, sodium, magnesium, potassium, calcium, strontium, and barium.
Among these, at least one selected from lithium, magnesium, and calcium is preferred because good catalytic activity can be obtained.

Examples of metal compounds include oxides, hydroxides, salts with inorganic acids, salts with organic acids, and complex salts of at least one metal selected from metals in Group 1 and Group 2 of the periodic table.
Examples of salts with inorganic acids include carbonates, hydrogen carbonates, sulfates, chlorides, nitrates, phosphates, and borates.
Examples of the salts with organic acids include acetates, (meth)acrylates, and benzoates.
Examples of the complex salt include acetylacetonate and cyclopentadienyl complexes.

The metal compound is preferably at least one selected from the group consisting of oxides, hydroxides, carbonates, bicarbonates, chlorides, and organic acid salts of the metals, as this provides good catalytic activity, and more preferably at least one selected from the group consisting of oxides, hydroxides, carbonates, bicarbonates, and organic acid salts of the metals, as this does not contain halogens that may corrode equipment or containers.
The (meth)acrylates of the above metals are most preferred because they produce fewer by-products.

The metal compound may be a compound that can be mixed in a reaction system to obtain a compound of the metal, specifically, a metal, a metal compound, an acid, a base, or the like, which is added to the reaction system and acts as a compound of the metal in the reaction system.
The metal compound may be completely or partially dissolved in the reaction system.

The metal compounds may be used alone or in combination of two or more.
The method for charging the metal compound into the reactor may include charging the entire amount into the reactor at first, or charging a portion of the compound into the reactor at first and then feeding the remainder later.
The amount of the metal compound used is preferably 0.0001 to 0.5 times the amount of the alcohol represented by formula (1) in terms of molar ratio. From the viewpoint of smoothly proceeding with the reaction, the molar ratio is preferably 0.001 times or more, and more preferably 0.01 times or more. On the other hand, from the viewpoint of removing the metal compound and suppressing side reactions, the molar ratio is preferably 0.03 times or less, and more preferably 0.02 times or less.

[solvent]
A solvent can be used in the reaction between the alcohol represented by formula (1) and (meth)acrylic anhydride. Examples of the solvent that can be used include aliphatic hydrocarbons such as hexane, heptane, pentane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ethers such as diethyl ether, diisopropyl ether, methyl tert-butyl ether, and tetrahydrofuran; and ketones such as acetone, methyl ethyl ketone, diisopropyl ketone, and methyl isobutyl ketone. Two or more of these solvents may be mixed and used.

When a solvent is used, the amount of the solvent used is preferably 10 times or less by mass relative to the alcohol represented by formula (1). From the viewpoints of reaction rate and purification load, the amount of the solvent used is preferably 2 times or less by mass relative to the alcohol, and more preferably 0.6 times or less.
In order to dissolve the alcohol and allow the reaction to proceed smoothly, the amount of the solvent used is preferably 0.001 times or more, more preferably 0.01 times or more, by mass ratio relative to the amount of the alcohol.
According to the production method of the present invention, since the alcohol is partially dissolved in the (meth)acrylic anhydride, it is possible to produce the (meth)acrylic acid ester represented by formula (2) without using a solvent. Furthermore, even when a solvent is used, it is possible to use only a small amount of the solvent.

[Polymerization inhibitor]
In the present invention, a polymerization inhibitor can be used. The polymerization inhibitor is introduced into the reactor, but it can also be introduced into the piping, the top of the reflux cooling tower, or somewhere along the tower.
Examples of the polymerization inhibitor include quinone-based polymerization inhibitors such as hydroquinone, hydroquinone monomethyl ether, and benzoquinone; alkylphenol-based polymerization inhibitors such as 2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol, 2-tert-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, and 2,4,6-tri-tert-butylphenol; alkylated diphenylamine, N,N'-diphenyl-p-phenylenediamine, and phenylenediamine; Examples of the polymerization inhibitor include amine-based polymerization inhibitors such as ethiazine, hindered amine-based polymerization inhibitors such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, and 4-acetamino-2,2,6,6-tetramethylpiperidine-N-oxyl, and copper dithiocarbamate-based polymerization inhibitors such as metallic copper, copper sulfate, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, and copper dibutyldithiocarbamate.

These polymerization inhibitors may be used alone or in combination of two or more. The amount of polymerization inhibitor added will depend on the type and conditions, but it is preferable to use it in the range of 0.1 to 10,000 ppm by mass relative to the reaction liquid. Furthermore, bubbling an oxygen-containing gas through the reaction liquid may improve the polymerization inhibition effect.

[Reaction conditions, etc.]
The reaction temperature for reacting the alcohol represented by formula (1) with the (meth)acrylic anhydride can be in the range of 0 to 130° C. In order to ensure smooth progress of the reaction, the reaction temperature is preferably 20° C. or higher, and more preferably 40° C. or higher. On the other hand, in order to suppress polymerization and side reactions, the reaction temperature is preferably 120° C. or lower, more preferably 110° C. or lower, and even more preferably 100° C. or lower.

The reaction time can be determined appropriately based on the charge ratio and reaction temperature, but is preferably 0.5 to 48 hours. The time required for the conversion of the alcohol represented by formula (1) to reach 70% or more is preferred, and the time required for the conversion to reach 90% or more is even more preferred. From the standpoint of productivity, the reaction time is preferably 18 hours or less, more preferably 12 hours or less, and even more preferably 8 hours or less.

There is no particular limitation on the method for charging the raw materials into the reactor before the reaction, and examples thereof include the following methods.
1) A method in which the alcohol represented by formula (1) and (meth)acrylic anhydride are charged in their entirety at once.
2) A method in which either the alcohol represented by formula (1) or (meth)acrylic anhydride is charged in its entirety into a reactor, and the other is subsequently charged.
3) A method in which the entire amount of either the alcohol represented by formula (1) or (meth)acrylic anhydride is charged into a reactor, and a portion of the other is charged.
4) A method in which both the alcohol represented by formula (1) and (meth)acrylic anhydride are partially charged.

Furthermore, other raw materials such as metal compounds, polymerization inhibitors, and solvents may be charged in their entirety or in part into the reactor before the reaction.
With respect to the raw materials partially charged into the reactor before the reaction, the remainder may be fed either in portions or continuously after the start of the reaction.

Reaction methods include, for example, a batch system in which all raw materials are charged into a single reactor and the reaction is completed; a continuous system in which raw materials are continuously supplied into a reactor and the reaction is carried out continuously; and a circulation system in which a reactor and a blending tank are provided and the raw materials are reacted in the reactor while circulating between the reactor and the blending tank. The reaction may be carried out while recovering the by-product (meth)acrylic acid. The pressure may be reduced, atmospheric, or increased.

<Recovery and refinement>
After completion of the reaction, the reaction solution can be subjected to treatment such as distillation, treatment with an adsorbent, concentration, crystallization, washing, etc. to remove compounds of the metals used in the reaction and remaining (meth)acrylic anhydride, and the (meth)acrylic acid ester represented by formula (2) can be recovered and purified.

[Removal of (meth)acrylic anhydride]
When (meth)acrylic anhydride remains after the reaction is completed, it is also preferable to add a compound that reacts with (meth)acrylic anhydride to the reaction solution to convert the (meth)acrylic anhydride into a compound that is easy to remove, and then carry out treatment such as distillation, extraction, washing, etc. Examples of the compound that reacts with (meth)acrylic anhydride include water, alcohol, basic substances, and acidic substances.

When water or alcohol is added, (meth)acrylic anhydride can be converted to (meth)acrylic acid ester or (meth)acrylic acid.
Examples of the alcohol include straight-chain or branched-chain aliphatic alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol; unsaturated alcohols such as allyl alcohol; cyclic alcohols such as cyclopentanol and cyclohexanol; aromatic alcohols such as phenol and benzyl alcohol; and polyhydric alcohols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and glycerin.

Among these alcohols, alcohols having 4 or less carbon atoms are preferred, and methyl alcohol or ethyl alcohol is more preferred, from the viewpoint of removing the produced (meth)acrylic acid ester.
The treatment temperature when reacting with an alcohol is preferably 0 to 100° C. From the viewpoint of shortening the treatment time, the treatment temperature is more preferably 20° C. or higher, and even more preferably 40° C. or higher. On the other hand, from the viewpoint of suppressing polymerization and side reactions, the treatment temperature is preferably 100° C. or lower, and more preferably 80° C. or lower.

When a basic substance or an acidic substance, or an aqueous solution thereof, is added, (meth)acrylic anhydride can be converted into (meth)acrylic acid or a salt of (meth)acrylic acid.
Examples of basic substances include hydroxides of metals in Group 1 of the periodic table, such as sodium hydroxide and potassium hydroxide; hydroxides of metals in Group 2 of the periodic table, such as calcium hydroxide and magnesium hydroxide; carbonates of metals in Group 1 of the periodic table, such as sodium carbonate and potassium carbonate; carbonates of metals in Group 2 of the periodic table, such as calcium carbonate and magnesium carbonate; bicarbonates of metals in Group 1 of the periodic table, such as sodium bicarbonate and potassium bicarbonate; bicarbonates of metals in Group 2 of the periodic table, such as calcium bicarbonate and magnesium bicarbonate; and organic bases, such as pyridine and triethylamine. It is also possible to use two or more of these basic substances in combination.

Examples of acidic substances include inorganic acids such as sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrochloric acid, and heteropolyacids, and organic acids such as acetic acid, methanesulfonic acid, paratoluenesulfonic acid, and camphorsulfonic acid. It is also possible to use two or more of these acidic substances in combination.

When using a basic substance or an acidic substance, the treatment temperature is preferably 0 to 100°C. From the perspective of shortening the treatment time, the treatment temperature is more preferably 10°C or higher, and even more preferably 20°C or higher. On the other hand, from the perspective of suppressing polymerization and side reactions, the treatment temperature is more preferably 80°C or lower, and even more preferably 60°C or lower.

A solvent inert to the reaction can also be used in the treatment of converting (meth)acrylic anhydride into a compound that is easily removed using water, an alcohol, a basic substance, an acidic substance, etc. Examples of the inert solvent include the same solvents as those listed as usable in the reaction of the alcohol represented by formula (1) with (meth)acrylic anhydride.
The amount of solvent used in the treatment for converting the compound into one that is easily removable is preferably 0.1 to 50 times by mass relative to the amount of the (meth)acrylic acid ester of formula (2) obtained.

The treatment time for converting (meth)acrylic anhydride into a compound that is easily removed using water, alcohol, a basic substance, an acidic substance, or the like can be 0.01 to 48 hours. To ensure sufficient removal of (meth)acrylic anhydride, the treatment time is preferably 0.1 hour or more, and more preferably 0.2 hour or more. To suppress polymerization and side reactions, the treatment time is preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 6 hours or less.

The removal of (meth)acrylic anhydride or a compound obtained by previously converting (meth)acrylic anhydride into an easily removable compound, such as by distillation, extraction, or washing, may be carried out either before or after removing the metal compound.

[distillation]
Examples of methods for purifying the (meth)acrylic acid ester represented by formula (2) by distillation include simple distillation and distillation using a multi-stage distillation column (rectification column).
The distillation column may be, for example, a packed column using packings made of stainless steel, glass, ceramic, or the like having the shape of Raschig rings, Lessing rings, Dixon packings, Paul rings, saddles, Sulzer packings, or the like; or a plate column such as a perforated plate column or a bubble cap column.

The distillation tower and reactor may be connected in any of the following ways: the distillation tower is connected to the top of the reactor; the distillation tower is connected to the top of a separate vessel connected to the reactor; or the reactor is connected to any position between the top and bottom of the distillation tower. In any of these connection types, there may be one or more paths between the reactor and the distillation tower, and a device such as a heat exchanger may be interposed along the way.

Distillation can be performed using an internal reflux method that does not use a reflux condenser, or a method that uses a reflux condenser to control the reflux ratio. Distillation can be carried out under reduced pressure at a temperature range of 10 to 250°C. To prevent polymerization and side reactions, the distillation temperature is preferably 200°C or lower, and more preferably 150°C or lower. To maintain a sufficient amount of steam, the distillation temperature is preferably 40°C or higher, and more preferably 60°C or higher.

[Adsorbent treatment]
The amount of impurities can be reduced by contacting the reaction solution with an adsorbent, such as by column chromatography or by suspending the adsorbent to adsorb the impurities and then separating the adsorbent.

Adsorbents include activated clay, hydrotalcites, porous polymers, ion exchange resins (cation exchange resins or anion exchange resins), activated carbon, adsorption resins, silica gel, silica-alumina-based adsorbents, alumina gel, activated alumina, silicon dioxide, and zeolites.

The amount of adsorbent used is preferably 0.05 to 20% by mass relative to the mass of the (meth)acrylic acid ester represented by formula (2). 0.5 to 10% by mass is particularly preferred. If the amount is too small, the impurity reduction effect will not be sufficient, and if the amount is too large, the total amount of (meth)acrylic acid ester represented by formula (2) adsorbed onto the adsorbent will increase, resulting in loss due to adsorption of the (meth)acrylic acid ester represented by formula (2) and a heavy load when separating the adsorbent by filtration or other means.

The temperature at which the reaction liquid and adsorbent are brought into contact is not particularly limited, but can be between 0 and 100°C. To prevent side reactions during treatment, the temperature at which the reaction liquid and adsorbent are brought into contact is preferably 60°C or lower, and particularly 40°C or lower. The time for which the reaction liquid and adsorbent are brought into contact varies depending on the type of adsorbent and the amount used, but is preferably between 1 and 120 minutes, and more preferably between 3 and 60 minutes.

After the adsorption treatment with the adsorbent, the reaction liquid containing the (meth)acrylic acid ester represented by formula (2) can be separated from the adsorbent by a method such as filtration.
Examples of the filter include membrane filters made of fluororesin such as polytetrafluoroethylene.

When the reaction solution is brought into contact with the adsorbent, it is also preferable to add a solvent to the reaction solution in advance.
As the solvent, among those listed as solvents usable in the reaction of the alcohol represented by formula (1) with (meth)acrylic anhydride, toluene, methyl tert-butyl ether, tetrahydrofuran, acetone, methyl ethyl ketone, methyl isobutyl ketone, etc. These solvents may be used in combination of two or more.

[Crystallization]
Examples of methods for crystallizing the (meth)acrylic acid ester represented by formula (2) include a method of dissolving the ester in a solvent and then lowering the temperature of the solution to precipitate crystals, a method of concentrating the solution to precipitate crystals, and a method of adding a solvent in which the ester has low solubility to a solution of the (meth)acrylic acid ester represented by formula (2).
The obtained crystals can be recovered by a known method such as centrifugation, pressure filtration, vacuum filtration, or gravity filtration.

As a solvent for dissolving the (meth)acrylic acid ester represented by formula (2), among those listed as solvents usable for the reaction of the alcohol represented by formula (1) with (meth)acrylic anhydride, toluene, methyl tert-butyl ether, tetrahydrofuran, acetone, methyl ethyl ketone, methyl isobutyl ketone, etc. These solvents may be used in combination of two or more.
The amount of the solvent used to dissolve the (meth)acrylic acid ester represented by formula (2) is preferably 0.1 to 30 times, more preferably 0.5 to 5 times, in mass ratio, relative to the amount of the (meth)acrylic acid ester represented by formula (2).

As a solvent having low solubility to be added to the solution of the (meth)acrylic acid ester represented by formula (2), among those listed as solvents usable in the reaction of the alcohol represented by formula (1) with (meth)acrylic anhydride, hexane, heptane, pentane, cyclohexane, etc. These solvents may be used in combination of two or more.
The amount of the solvent having low solubility is preferably 2 to 200 times, more preferably 4 to 100 times, in mass ratio, the amount of the solvent in which the (meth)acrylic acid ester represented by formula (2) is dissolved.

[Cleaning]
The (meth)acrylic acid ester represented by formula (2) recovered by distillation, treatment with an adsorbent, crystallization, etc. may be washed with water, an aqueous solution of a salt such as sodium chloride or sodium sulfate, or an aqueous solution of a basic substance. Furthermore, the (meth)acrylic acid ester may be washed with water or an aqueous solution of an acidic substance before being washed with the aqueous solution of a basic substance.

Washing can remove water-soluble impurities.
As the basic substance and acidic substance used for washing, the same basic substances and acidic substances as those exemplified as the basic substances and acidic substances that can be used to convert (meth)acrylic anhydride into (meth)acrylic acid or a salt of (meth)acrylic acid can be used.

Washing may be performed once or multiple times. Furthermore, multiple washes using aqueous solutions of different basic substances may also be performed. After washing with a basic substance, it is preferable to wash with water to remove any basic substances remaining in the organic layer. The water used for washing is preferably distilled water or pure water deionized using an ion exchange resin or the like.

When the (meth)acrylic acid ester represented by formula (2) is washed with water or an aqueous solution, it is also preferable to add a solvent in advance.
As the solvent, among those listed as solvents usable for the reaction of the alcohol represented by formula (1) with the (meth)acrylic anhydride, a solvent that is poorly soluble in water but easily dissolves the (meth)acrylic acid ester represented by formula (2) can be used. Specifically, a solvent that dissolves 20 g or less in 100 g of water can be preferably used.
Examples of the solvent that dissolves 20 g or less in 100 g of water include hexane, heptane, pentane, cyclohexane, toluene, xylene, diethyl ether, diisopropyl ether, methyl tert-butyl ether, methyl isobutyl ketone, etc. Two or more of these solvents may be mixed and used.

When washing with water or an aqueous solution, the amount of solvent added in advance is preferably 0.1 to 30 times, and more preferably 0.5 to 5 times, the mass ratio of the (meth)acrylic acid ester represented by formula (2). If the amount of solvent is too small, the (meth)acrylic acid ester represented by formula (2) may migrate into the water or aqueous solution used for washing. Furthermore, if the amount of solvent is too large, a larger reactor will be required, and the time and energy required for concentration will increase.

[Action and effect]
Examples of by-products that may be produced by a side reaction when the alcohol represented by formula (1) is reacted with (meth)acrylic anhydride include a dimethacrylate represented by the following formula (3) and a Michael adduct represented by the following formula (4).
According to the method for producing a (meth)acrylic acid ester of the present invention, such side reactions are suppressed, and the (meth)acrylic acid ester represented by formula (2) can be efficiently obtained.

(In the formulas (3) and (4), ^R1 and ^R2 are the same as ^R1 and ^R2 in the formula (1), respectively, and ^R3 is the same as ^R3 in the formula (2).)

The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention.

The abbreviations and abbreviations used in the present examples are as follows:
MAOMA: Manufactured by Aldrich Co., Ltd., distilled and purified methacrylic anhydride.
DHBP: 2,4-dihydroxybenzophenone, manufactured by Tokyo Chemical Industry Co., Ltd.
MIBK: Methyl isobutyl ketone, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
THF: tetrahydrofuran, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
BHT: 2,6-di-tert-butyl-4-methylphenol, manufactured by Tokyo Chemical Industry Co., Ltd.
DMAP: 4-(dimethylamino)pyridine, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
HMBP: 2-hydroxy-4-(methacryloyloxy)benzophenone.
DMBP: 2,4-dimethacryloyloxybenzophenone.
Michael adduct: A Michael adduct in which methacrylic acid is added to the methacryloyl group of HMBP.

The reaction solution was analyzed by liquid chromatography (hereinafter referred to as HPLC). HPLC analysis was performed by dissolving a sample in acetonitrile under the following conditions.
Column: ODS-3V
Carrier: acetonitrile/10 mM phosphate buffer = 4/6
The 10 mM phosphate buffer solution was prepared by dissolving 0.78 g of sodium dihydrogen phosphate dihydrate in 1 L of ultrapure water and adjusting the pH to 2.6 using approximately 0.34 ml of 85% phosphoric acid.
・Flow rate: 1ml/min
Sample injection volume: 5 μl
・Temperature: 40℃
Detection wavelength: 254 nm

The yield of each component was determined by the calibration curve method from the HPLC peak area of the liquid after the reaction, and is a value based on the amount (mol) of the raw material DHBP charged as the standard (100 mol%).
The DHBP conversion rate was calculated by the following formula.
DHBP conversion rate (mol%) = 100 - DHBP residual rate (mol%)

[Example 1]
A five-neck flask equipped with a reflux condenser was charged with 18.5 g (0.12 mol) of MAOMA, 21.4 g (0.1 mol) of DHBP, 0.40 g (0.01 mol) of heavy magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 6.4 g of MIBK, and 10 mg of BHT, and the mixture was heated in an oil bath to react at 70° C. for 2 hours. The analysis results of the liquid after the reaction are shown in Table 1.

[Examples 2 to 9]
The same procedure as in Example 1 was carried out except that the heavy magnesium oxide in Example 1 was changed to 0.01 mol of the metal compound shown in Table 1. The liquid after the reaction was analyzed and the results are shown in Table 1.

[Example 10]
The same procedure as in Example 1 was carried out except that the amount of MAOMA was changed to 15.1 g (0.10 mol). The liquid after the reaction was analyzed and the results are shown in Table 1.

[Example 11]
A five-neck flask equipped with a reflux condenser was charged with 20.0 g (0.13 mol) of MAOMA, 21.4 g (0.1 mol) of DHBP, 0.40 g (0.01 mol) of heavy magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 20 g of MIBK, and 10 mg of BHT, and the mixture was heated in an oil bath to react at 60° C. for 4 hours. The analysis results of the liquid after the reaction are shown in Table 1.

[Example 12]
In a five-neck flask equipped with a reflux condenser, 18.5 g (0.12 mol) of MAOMA, 21.4 g (0.1 mol) of DHBP, 0.40 g (0.01 mol) of heavy magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 10 mg of BHT were placed, and the mixture was heated in an oil bath to react at 80° C. for 2 hours. The analysis results of the liquid after the reaction are shown in Table 1.

[Comparative Example 1]
A five-neck flask equipped with a reflux condenser was charged with 21.4 g (0.1 mol) of DHBP, 0.66 g (0.0054 mol) of DMAP, 53.7 g of THF, and 10 mg of BHT. While cooling in an ice bath, 15.4 g (0.1 mol) of MAOMA was added dropwise. After the dropwise addition, the mixture was allowed to react at room temperature for 5 hours. The analysis results of the reaction mixture are shown in Table 1.

[Comparative Example 2]
The same procedure as in Example 1 was carried out except that the heavy magnesium oxide was changed to 1.22 g (0.01 mol) of DMAP. The liquid after the reaction was analyzed and the results are shown in Table 1.

[Comparative Example 3]
The same operation as in Comparative Example 1 was carried out except that the amount of MAOMA was changed to 17.0 g (0.11 mol). The results of analysis of the liquid after the reaction are shown in Table 1.

As shown in Table 1, in all of the Examples, the DHBP conversion rate and HMBP yield were high, and the amount of by-products was small.
In Example 10, in which DHBP and an equimolar amount of MAOMA were reacted, the DHBP conversion rate was less than 100 mol%. In contrast, in other examples in which a slightly excess amount of MAOMA was reacted with DHBP, the DHBP conversion rate was 100 mol%. From this, it was confirmed that in order to increase the DHBP conversion rate, it is advantageous to react a slightly excess amount of MAOMA with DHBP.

On the other hand, in the comparative examples using DMAP, the DHBP conversion rate and HMBP yield were poor, and a large amount of by-products were produced. In particular, the results of Comparative Example 2, which did not employ the operation of adding MAOMA dropwise while cooling, were poor.
In Comparative Example 3, in which a slightly excess amount of MAOMA was reacted with DHBP compared to Comparative Example 1 in which DHBP was reacted with an equimolar amount of MAOMA, the DHBP conversion rate was higher, but the HMBP yield was actually lower.

Claims (8)

A method for producing a (meth)acrylic acid ester represented by the following formula (2), comprising a step of reacting an alcohol represented by the following formula (1) with (meth)acrylic anhydride in the presence of a compound of at least one metal selected from the group consisting of lithium, sodium, magnesium, potassium, calcium, strontium, and barium:
(In the formula (1), ^R1 and ^R2 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms.)
(In the formula (2), ^R1 and ^R2 are the same as ^R1 and ^R2 in the formula (1), respectively, and ^R3 represents a hydrogen atom or a methyl group.) 2. The method for producing a (meth)acrylic acid ester according to claim 1 , wherein the metal compound is at least one selected from the group consisting of an oxide, hydroxide, carbonate, hydrogencarbonate, chloride, and organic acid salt of the metal. The method for producing a (meth)acrylic acid ester according to claim 2 , wherein the compound of the metal is a (meth)acrylic acid salt of the metal. The method for producing a (meth)acrylic acid ester according to any one of claims 1 to 3 , wherein the reaction is carried out using a solvent. The method for producing a (meth)acrylic acid ester according to claim 4 , wherein the amount of the solvent used is equal to or less than two times by mass the amount of the alcohol represented by formula (1). The method for producing a (meth)acrylic acid ester according to any one of claims 1 to 5 , wherein the reaction is carried out at a temperature of 0°C to 130°C. The method for producing a (meth)acrylic acid ester according to any one of claims 1 to 6 , wherein the alcohol represented by formula (1) is reacted with (meth)acrylic anhydride in an amount of 1 to 1.5 times by molar ratio. The method for producing a (meth)acrylic acid ester according to any one of claims 1 to 7 , wherein the obtained (meth)acrylic acid ester is recovered by crystallization.