JP2018115121A - Process for producing α-methylene-γ-butyrolactone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of producing α-methylene-γ-butyrolactone with high yield and high purity. SOLUTION: γ-Butyrolactone is reacted with an oxalate ester and an alcoholate to synthesize α-oxalyl-γ-butyrolactone enol salt, neutralized with an acid, and then α-oxalyl-γ-. An α-methylene-γ-butyrolactone is produced by reacting an enol salt of butyrolactone with formaldehyde or a precursor that generates formaldehyde and a carbonate. [Selection figure] None

Description

  The present invention relates to a method for producing α-methylene-γ-butyrolactone.

  Regarding a method for producing α-methylene-γ-butyrolactone or a related substance, Patent Document 1 discloses that a γ-butyrolactone derivative, an oxalate ester, and an alcoholate are reacted under heating to change the α-position of the lactone ring to alkyloxy. A method for producing an α-methylene-γ-butyrolactone derivative by reacting an aqueous formaldehyde solution and an aqueous potassium carbonate solution after obtaining a sodium salt (enol salt) of a zalylated oxalyl derivative, isolating the enol salt by filtration Is described.

Non-Patent Document 1 describes a method represented by the following scheme in which an alkyloxalyl group is introduced to activate the α-position of the lactone ring in a one-pot reaction, and then methyleneated with an aqueous formaldehyde solution.

  As described above, various production methods for α-methylene-γ-butyrolactone or related substances have been developed.

US 6531616

Agric. Biol. Chem. 1978, 42, 1585-1588

  However, also in Patent Document 1 and Non-Patent Document 1, in the method via an oxalyl derivative, a large amount of hardly soluble salt is produced as a by-product when methyleneating, so that the reaction solution becomes a slurry. For this reason, when extracting the target product, it is necessary to add a large amount of water in order to dissolve the salt. Even when extracting without dissolving the salt, it is very difficult to drain the slurry-like aqueous phase containing a large amount of salt from the reaction kettle, and it takes a long time, so the production efficiency is low. It becomes lower. These are major problems industrially, and are not always satisfactory as a practical industrial process that can be easily produced at low cost.

  Accordingly, an object of the present invention is to provide a method for producing high-purity α-methylene-γ-butyrolactone at a low cost, simply and in a high yield using a low-cost starting material and a general-purpose reactor. There is.

  As a result of intensive studies to solve the above problems, the present inventor has reacted a slurry-like aqueous phase containing a salt by carrying out a methyleneation step after neutralizing the base subjected to the oxalylation step. The inventors have found a method capable of producing α-methylene-γ-butyrolactone having a high yield and high purity by easily draining from the kettle, and have reached the present invention.

That is, the present invention provides (1) the following formula (I)
[In the formula (I), R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, or a cycloalkyl group having 5 to 10 carbon atoms. Represents an aryl group which may have a group or an alkyl substituent having 1 to 5 carbon atoms. ]
Γ-butyrolactone represented by the following formula (II)
[In Formula (II), R ⁵ may have a linear or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, or an alkyl substituent having 1 to 5 carbon atoms. Represents a good aryl group. ]
Oxalic acid ester represented by the following formula (III)
[In Formula (III), R ⁶ may have a linear or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, or an alkyl substituent having 1 to 5 carbon atoms. Represents a good aryl group. M represents an alkyl metal atom. ]
Is reacted with an alcoholate represented by the following formula (IV):

[In formula (IV), R ^{1 to} R ⁴ are the same as those in formula (I), R ⁵ is the same as in formula (II), and M is the same as those in formula (III). ]
An enol salt of α-oxalyl-γ-butyrolactone represented by
(2) The enol salt of α-oxalyl-γ-butyrolactone, formaldehyde or a precursor that generates formaldehyde, and carbonate are reacted to form the following formula (V):
Wherein ^(V), R 1 ~R ⁴ are the same as those in formula (I). ]
A process for producing α-methylene-γ-butyrolactone represented by the formula:
It is a manufacturing method of (alpha) -methylene-gamma-butyrolactone which has the process of neutralizing with an acid after the process of (1).

It is preferable that the equivalent of the acid used for neutralization is 0.1 to 3 with respect to γ-butyrolactone.
The acid used for neutralization is preferably hydrochloric acid or sulfuric acid.

  According to the present invention, α-methylene-γ-butyrolactone can be efficiently produced from an inexpensive raw material.

First, step (1) will be described.
The γ-butyrolactone represented by the formula (I) is “MARCH'S ADVANCED ORGANIC CHEMISTRY FIFTH EDITION”, page 484 (WILEY-INTERSCIENCE) Michael B. It can be produced by the method described in Smith, Jerry March.

R ¹ , R ² , R ³ and R ⁴ in the formulas (I), (IV) and (V) are each independently a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, A straight or branched alkyl group having 1 to 10 carbon atoms such as n-butyl group, iso-butyl group, t-butyl group and n-pentyl group, cyclohexane having 5 to 10 carbon atoms such as cyclopentyl group and cyclohexyl group. The aryl group which may have a C1-C5 alkyl substituent, such as an alkyl group, a phenyl group, a tolyl group, a xylyl group, can be mentioned. From the effect of improving the glass transition temperature (heat resistance) of a polymer obtained using α-methylene-γ-butyrolactone represented by the formula (V) as a raw material, a methyl group, an ethyl group, a propyl group, an isopropyl group, etc. The lower alkyl group is preferably, and the glass transition temperature of the polymer is specifically increased by having an alkyl group at the β-position.

R ⁵ in the formulas (II) and (IV) is a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a t-butyl group, an n-pentyl group, or the like. C1-C5 alkyl substitution such as linear or branched alkyl groups having 1 to 10 carbon atoms, cycloalkyl groups having 5 to 10 carbon atoms such as cyclopentyl groups and cyclohexyl groups, phenyl groups, tolyl groups and xylyl groups The aryl group which may have a group can be mentioned.

Examples of the oxalate ester in the formula (II) include oxalic acid dimethyl ester, oxalic acid diethyl ester, and oxalic acid diphenyl ester.
The amount of oxalate ester used is preferably 0.8 to 10 equivalents relative to γ-butyrolactone of formula (I), and more preferably 1 to 5 equivalents in view of reaction efficiency, production cost, etc. From the viewpoint of consuming the γ-butyrolactone and producing high-purity α-methylene-γ-butyrolactone in a high yield, 1 to 2 equivalents are more desirable. A small excess of oxalate can be removed during purification.

M in the formulas (III) and (IV) can include alkali metal atoms such as sodium and potassium.
R ⁶ in the formula (III) is linear or branched such as methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, t-butyl group, n-pentyl group, etc. Having a C1-C5 alkyl substituent such as a C1-C10 alkyl group, a cyclopentyl group, a cyclohexyl group, etc., a C5-C10 cycloalkyl group, a phenyl group, a tolyl group, a xylyl group, etc. An aryl group that may be used may be mentioned.

  Examples of the alcoholate in the formula (III) include alkali metal alcoholates (alkali metal alkoxides) such as sodium methylate, sodium ethylate, potassium methylate, potassium ethylate, potassium tert-butylate, and the like. Although it is easier to use a methanol solution of methylate or an ethanol solution of sodium ethylate, the alcoholate may be used in the form of powder.

  The amount of alcoholate used is preferably 0.8 to 10 equivalents relative to γ-butyrolactone of formula (I), and more preferably 1 to 5 equivalents in view of reaction efficiency, production cost, etc., and γ of formula (I) From the viewpoint of consuming high-yield α-methylene-γ-butyrolactone by consuming butyrolactone, 1 to 2 equivalents are more desirable.

  When using a methanol solution of sodium methylate or an ethanol solution of sodium ethylate, it is not necessary to add a solvent, but when adding a solvent or using a powdered material, methanol, ethanol, Alcohols such as i-propanol, n-butanol and t-butanol, esters such as ethyl acetate, butyl acetate and diethyl oxalate, diethyl ether, diisopropyl ether, t-butyl methyl ether, t-butyl ethyl ether, tetrahydrofuran , Ethers such as dioxane and cyclopentyl methyl ether, aromatic compounds such as toluene and xylene, alkanes such as pentane, hexane, heptane, octane and cyclohexane, halides such as chloroform and dichloromethane , Dimethyl sulfoxide, dimethylformamide, acetonitrile, polar solvent such as propionitrile can be used. These solvents may be used alone or in combination.

  If the solvent is not used, stirring may become difficult due to the slurry precipitated at the end of the reaction, and the entire reaction system may solidify. Therefore, the amount of the solvent is desirably 0.01 to 30 times the weight of the compound (I). In view of production cost, reaction yield, avoidance of breakage of the stirrer, etc., 0.1 to 10 times is more desirable, and 1 to 5 times is more desirable.

  The combination of the oxalate ester, the alcoholate and the solvent alcohol is arbitrary. In order not to complicate the reactants, the combination of oxalate ester, alcoholate and solvent can be, for example, dimethyl oxalate / sodium methylate / methanol, dimethyl oxalate / potassium methylate / methanol, diethyl oxalate. A combination of the same alcohols such as / sodium ethylate / ethanol is preferable.

However, considering the manufacturing cost, it is not always necessary to stick to this combination. For example, even when sodium methylate / methanol is used when diethyl oxalate is used, the ester of α-oxalyl-γ-butyrolactone represented by formula (IV) is only partially transesterified, and thereafter There is no support for this reaction.
The order in which γ-butyrolactone, oxalate ester, alcoholate and solvent are added may be arbitrary.

  Although the reaction temperature is not particularly limited, it is preferably 0 ° C. or higher and the boiling point of the solvent or lower, and γ-butyrolactone of formula (I) can be consumed to produce high-purity α-methylene-γ-butyrolactone in a high yield. It is preferably between −20 ° C. and 60 ° C., and more preferably between −10 ° C. and 50 ° C. from the viewpoint of reducing by-products.

  Although reaction time can be set arbitrarily, 0.1 to 100 hours are desirable. In consideration of reaction yield and work efficiency, 0.1 to 24 hours are desirable, and 0.5 to 5 hours are more desirable.

  After completion of the step (1), at least a part of the alcohol present in the system may be distilled off from the reaction solution containing the enol salt of α-oxalyl-γ-butyrolactone represented by the formula (IV), You may proceed to the next step without distilling off. When distilling off, it is preferable to distill off at least 50% of the alcohol present in the reaction system of the oxalylation step from the viewpoint of yield under reduced pressure. The degree of decompression here does not need to be particularly high, and may be a degree of decompression that can be achieved by a normal aspirator in the laboratory. Specifically, the degree of decompression may be 66.7 kPa (500 torr) or less.

  The temperature for distilling off the alcohol is preferably between −20 ° C. and 60 ° C., more preferably between 0 ° C. and 60 ° C., from the viewpoint of reducing by-products.

Next, neutralization after the step (1) will be described.
Examples of the acid to be added include inorganic acids, organic acids, inorganic acids, and mixtures of inorganic acids. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, phosphoric acid, boric acid and the like. Examples of the organic acid include formic acid, acetic acid, propionic acid, butyric acid, p-toluenesulfonic acid monohydrate, trifluoroacetic acid, benzoic acid, succinic acid, salicylic acid, terephthalic acid, and oxalic acid. In view of production cost, reaction yield, etc., hydrochloric acid and sulfuric acid are preferable.

  The amount of acid to be added is preferably 0.1 to 3 equivalents with respect to γ-butyrolactone used as a raw material represented by formula (I), and considering the improvement of the pot efficiency due to the increase of the aqueous phase due to neutralization. It is preferably 2 equivalents or less, and more preferably 0.6 equivalents or less from the viewpoint of cost due to the input amount of acid.

  The temperature at which the acid is added during neutralization is preferably below the boiling point of the solvent, and γ-butyrolactone of formula (I) is consumed to produce high-purity α-methylene-γ-butyrolactone in high yield. Since it can do, between -20 ° C and 60 ° C is preferred, and from a viewpoint which can reduce a by-product further, between -10 ° C-50 ° C is more preferred.

At the time of neutralization, the acid may be added after being dissolved in water alone, an organic solvent alone, or a mixed solvent of water and an organic solvent. Further, after adding the acid, water alone, an organic solvent alone, or a mixed solvent of water and an organic solvent may be added for dilution.
Although the time required for neutralization depends on the temperature, it is not particularly limited and can be arbitrarily set between 0.001 and 24 hours. However, in consideration of the stability of the product, it is between 0.01 and 10 hours. It is desirable to set.

Next, process (2) is demonstrated.
An oxalyl group can be converted into a methylene group by adding formaldehyde or a precursor that generates formaldehyde and a carbonate to the enol salt of α-oxalyl-γ-butyrolactone represented by the formula (IV).
As formaldehyde or a precursor that generates formaldehyde, for example, formaldehyde and its aqueous solution (formalin), paraformaldehyde, formal, trioxane, or the like that generates formaldehyde in the system, or an aqueous solution thereof is preferable. It is preferable to use an aqueous solution of formaldehyde.

  Although the amount of formaldehyde or a precursor that generates formaldehyde is not particularly limited, 0.8 to 10 equivalents are desirable with respect to γ-butyrolactone represented by the formula (I), and considering reaction efficiency, production cost, and the like, 0.9 to 5 equivalents are more desirable. From the viewpoint of consuming the γ-butyrolactone of the formula (I) to produce high-purity α-methylene-γ-butyrolactone in a high yield, 0.9 to 2 equivalents are preferable. More desirable.

  Examples of the carbonate used include lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, calcium carbonate, cesium carbonate and the like. In view of production cost, reaction yield, and the like, sodium carbonate and potassium carbonate are preferable.

The amount of carbonate can be arbitrarily set with respect to γ-butyrolactone represented by the formula (I), but is preferably 0.01 to 10 equivalents, and considering reaction efficiency, production cost, etc., 0.05 to 5 The equivalent is more desirable, and from the viewpoint of consuming the γ-butyrolactone of the formula (I) and producing high-purity α-methylene-γ-butyrolactone in a high yield, 0.1 to 3 equivalents are more desirable.
The carbonate may be added as it is, or a solution prepared in the aqueous solution may be added.

  The order in which formaldehyde or a precursor that generates formaldehyde and carbonate is added may be arbitrary. Formaldehyde or a precursor that generates formaldehyde may be added simultaneously with the carbonate, may be added after the carbonate, or may be added before the carbonate.

Although the reaction temperature is not particularly limited, it is preferably below the boiling point of the solvent, and γ-butyrolactone of formula (I) can be consumed to produce high-purity α-methylene-γ-butyrolactone in a high yield. Is preferably between -10 ° C and 50 ° C, considering that by-products can be further reduced and that the synthesized α-methylene-γ-butyrolactone is a compound that is easily polymerized. .
Although the reaction time depends on the reaction temperature, it is not particularly limited and is preferably 0.1 to 100 hours, preferably 0.1 to 24 hours in view of reaction yield and work efficiency, and 0.5 to 5 hours. It is desirable to set between.

  When a solvent is used in step (2), examples of the solvent include water alone, an organic solvent alone, and a mixed solvent of water and an organic solvent. The organic solvent may be a hydrophobic organic solvent or a hydrophilic solvent. As the hydrophobic organic solvent, the solvent used in step (1) may be used as it is, or a solvent may be further added as necessary. For example, water contained in an aqueous solution of formaldehyde or an aqueous solution in which a carbonate is dissolved can be used, but it may be added separately. Examples of the hydrophobic organic solvent include esters such as ethyl acetate, butyl acetate, and oxalic acid diethyl ester, ethers such as diethyl ether, diisopropyl ether, t-butyl methyl ether, t-butyl ethyl ether, and cyclopentyl methyl ether. Examples thereof include aromatic compounds such as toluene and xylene, alkanes such as pentane, hexane, heptane, octane and cyclohexane, and halides such as chloroform and dichloromethane. Examples of the hydrophilic solvent include alcohols such as methanol, ethanol, i-propanol, n-butanol, and t-butanol, polar solvents such as dimethyl sulfoxide, dimethylformamide, acetonitrile, and propionitrile, tetrahydrofuran, dioxane, and the like. . Water and organic solvents may be used alone or in combination.

  The amount of the solvent is desirably 0.01 to 30 times that of γ-butyrolactone represented by the formula (I), more desirably 0.1 to 10 times, and further desirably 1 to 5 times in consideration of the pot efficiency. Moreover, the mixing ratio in the case of using a mixed solvent of water and an organic solvent is arbitrary and is not particularly limited.

  After the reaction, salt precipitates in the reaction solution. This salt may be removed by filtration or the like as necessary, or may be directly transferred to the recovery step without being filtered. As a method for recovering the produced α-methylene-γ-butyrolactone from the filtrate, a method of extracting with a solvent and concentrating the extract is preferable. The solvent to be used is not particularly limited as long as it can dissolve α-methylene-γ-butyrolactone, but the hydrophobic organic solvent is preferable.

Then, purification operations, such as vacuum distillation and thin film distillation, can be performed on the concentrated residue to obtain a product. At that time, in order to prevent the polymerization of α-methylene-γ-butyrolactone, it is preferable that a polymerization inhibitor is present in the system. The type of the polymerization inhibitor is not particularly limited, and may be used alone or in combination of two or more.
The polymerization inhibitor may be added, for example, when the raw materials are charged before the reaction, or may be added to the reaction liquid in the step (2), may be added to the extract, or may be added before the distillation. good.

  Examples of the polymerization inhibitor include hydroquinone, p-methoxyphenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, tert-butyl-catechol, 2,6- Phenols such as di-tert-butyl-4-methylphenol, pentaerythritol, tetrakis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate), 2-sec-butyl-4,6-dinitrophenol Compound, N, N'-diisopropylparaphenylenediamine, N, N'-di-2-naphthylparaphenylenediamine, N-phenylene-N '-(1,3-dimethylbutyl) paraphenylenediamine, N, N'- Bis (1,4-dimethylphenyl) -paraphenylenediamine, N- (1,4 Amine compounds such as (dimethylphenyl) -N′-phenyl-paraphenylenediamine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-benzoyloxy-2,2,6,6 -N-oxyl compounds such as tetramethylpiperidine-N-oxyl and bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, copper, copper chloride (II), iron chloride And metal compounds such as (III).

  Although the usage-amount of a polymerization inhibitor should just be determined suitably, 10 ppm or more is preferable with respect to compound (III), and 50 ppm or more is more preferable in order to fully exhibit an effect. On the other hand, from the viewpoint of cost, the amount of the polymerization inhibitor used is preferably 10,000 ppm or less, and more preferably 5000 ppm or less.

  In addition, polymerization can be prevented by bubbling a molecular oxygen-containing gas such as air in the reaction solution. The amount of the molecular oxygen-containing gas such as air to be introduced can be appropriately set so as to obtain a desired polymerization preventing effect. For example, when air is used as the molecular oxygen-containing gas, it is preferable to perform bubbling at 0.5 to 3.0 ml / min with respect to 1 mol of the raw material used. It is particularly preferable from the viewpoint of amplification of the polymerization prevention effect that the polymerization inhibitor is present in the reaction liquid containing the compound (V) and the reaction is performed while introducing a molecular oxygen-containing gas such as air into the reaction liquid.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to an Example.
(Identification of product)
The measurement was performed with a nuclear magnetic resonance apparatus (1H-NMR). This measurement was performed by using a GSX-270 type FT-NMR manufactured by JEOL Ltd., putting a deuterated chloroform solution of about 5% by mass of the sample into a test tube having a diameter of 5 mmφ, a measurement temperature of 25 ° C., and an observation frequency of 270 MHz. In the single pulse mode, the integration was performed 16 times.

(Product purity analysis)
It was carried out by gas chromatography (GC). Shimadzu GC-2014 was used.

<Example 1>
“%” Other than the yield in the following description means “% by mass”.
[Synthesis of enol salt of α-alkyloxalyl-γ-butyrolactone]
A 28% sodium methoxide / methanol solution (24.69 g, 0.1280 mol, 1.35 eq) and toluene (25 g) were charged into a nitrogen-substituted three-necked flask equipped with a stirring blade linked to a three-one motor, and cooled with ice water. 18.70 g (0.1280 mol, 1.35 eq) of oxalic acid diethyl ester was added dropwise from a dropping funnel, and then 10.00 g (0.0948 mol) of β-methyl-γ-butyrolactone (hereinafter abbreviated as “MBL”). ) Was added dropwise over about 30 minutes. After completion of the dropwise addition, stirring was continued at room temperature for 2 hours to obtain a slurry-like reaction solution of α-ethyloxalyl-γ-butyrolactone enol salt.

[Neutralization]
The obtained enol salt was cooled with ice and neutralized by dropwise addition of 11.52 g (0.0389 mol, 0.40 eq) of 4N hydrochloric acid.

[Synthesis of α-methylene-γ-butyrolactone]
Subsequently, 7.69 g (0.0948 mol, 1.00 eq) of 37% formalin was added, and 69.87 g (0.1422 mol, 1.60 eq) of 30% aqueous potassium carbonate solution was added dropwise over about 30 minutes. After completion of the dropwise addition, stirring was continued at room temperature for 2 hours to obtain a slurry-like α-methylene-γ-butyrolactone reaction solution. The obtained α-methylene-γ-butyrolactone reaction solution was washed with 30 g of water and transferred to a 200 ml separatory funnel (Aswan Co., Ltd., Research Equipment General Catalog DLab skive type). It took 51 seconds to drain the aqueous phase containing the slurry salt and separated from the organic phase. The target product was extracted 3 times with 24.5 g of toluene from the slurry phase. Α-methylene-γ-butyrolactone in the combined organic phase was 8.50 g (yield 80%).

<Examples 2 to 11 and Comparative Example 1>
Table 1 summarizes the results of the synthesis performed in the same manner as in Example 1 except that the conditions described in Table 1 were changed.

Claims (3)

(1) The following formula (I)
[In the formula (I), R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, or a cycloalkyl group having 5 to 10 carbon atoms. Represents an aryl group which may have a group or an alkyl substituent having 1 to 5 carbon atoms. ]
Γ-butyrolactone represented by the following formula (II)
[In Formula (II), R ⁵ may have a linear or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, or an alkyl substituent having 1 to 5 carbon atoms. Represents a good aryl group. ]
Oxalic acid ester represented by the following formula (III)
[In Formula (III), R ⁶ may have a linear or branched alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, or an alkyl substituent having 1 to 5 carbon atoms. Represents a good aryl group. M represents an alkyl metal atom. ]
Is reacted with an alcoholate represented by the following formula (IV):
[In formula (IV), R ^{1 to} R ⁴ are the same as those in formula (I), R ⁵ is the same as in formula (II), and M is the same as those in formula (III). ]
An enol salt of α-oxalyl-γ-butyrolactone represented by
(2) The enol salt of α-oxalyl-γ-butyrolactone, formaldehyde or a precursor that generates formaldehyde, and carbonate are reacted to form the following formula (V):
Wherein ^(V), R 1 ~R ⁴ are the same as those in formula (I). ]
A process for producing α-methylene-γ-butyrolactone represented by the formula:
The manufacturing method of (alpha) -methylene-gamma-butyrolactone which has the process of neutralizing with an acid after the process of (1).   The method for producing α-methylene-γ-butyrolactone according to claim 1, wherein an equivalent of an acid used for neutralization is 0.1 to 3 with respect to γ-butyrolactone used as a raw material.   The method for producing α-methylene-γ-butyrolactone according to claim 2, wherein the acid used for neutralization is hydrochloric acid or sulfuric acid.