Method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane)

Abstract

The present invention provides a method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane), which comprises at least the following steps (1) to (3): (1) reacting at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, and then separating and extracting the generated liquid containing perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt by liquid separation operation; (2) separating the obtained liquid containing perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt by liquid separation operation; and (3) separating the obtained liquid containing perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt by liquid separation operation. (3) using the obtained solution or solid perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate alkaline earth metal salt to carry out a decarbonation reaction in a liquid phase system to produce perfluoro(2-methylene-4-methyl-1,3-dioxolane).

Description

Technical Field

[0001] The present invention relates to a method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane). Background Art

[0002] Perfluoro(2-methylene-4-methyl-1,3-dioxolane) is a compound used as a raw material for synthesizing poly[(perfluoro(2-methylene-4-methyl-1,3-dioxolane)] which is expected to be used as a resin for gas separation membranes, a transparent resin for optical fibers, and the like.

[0003] As methods for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane), there are known methods in which perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) is allowed to flow in a gaseous state over a sodium carbonate solid catalyst (Patent Document 1); a method in which 2-methoxycarbonyl-2-trifluoromethyl-4-methyl-1,3-dioxolane is fluorinated with fluorine gas, the ester is hydrolyzed with an aqueous potassium hydroxide solution to prepare a potassium salt, and the salt is dried to a solid, and then thermally decomposed to obtain perfluoro(2-methylene-4-methyl-1,3-dioxolane) (Patent Document 2); and a method in which a mixture of potassium perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate and potassium fluoride is separated in a solid form, dried, mixed with a bis(2-ethoxyethyl) ether solvent, and thermally decomposed to obtain perfluoro(2-methylene-4-methyl-1,3-dioxolane) (Non-Patent Document 1).

[0004] Patent Document 1: U.S. Patent No. 3308107

[0005] Patent Document 2: Japanese Patent No. 4776536

[0006] Non-patent document 1: F. Mikes, et al., Macromolecules 2005, 38, 4237-4245 Summary of the invention

[0007] The method described in Patent Document 1 requires a high temperature reaction of 295° C. and generates highly toxic fluorophosgene as a by-product, so it is difficult to implement on an industrial scale.

[0008] In addition, the method described in Patent Document 2 requires a reaction at a high temperature of 250° C. to 280° C. and is carried out in a solid phase system, so it is difficult to implement on an industrial scale.

[0009] On the other hand, in the method described in Non-Patent Document 1, the decarbonation reaction is a liquid phase system, and the reaction temperature is 130° C., which is relatively low. However, the target perfluoro(2-methylene-4-methyl-1,3-dioxolane) is obtained in the form of a mixture of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) as a by-product, and there is a problem that it is extremely difficult to separate the target product from the by-product by distillation.

[0010] In view of the above, one embodiment of the present invention provides a method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) which is easy to implement industrially, has a high yield, and is less likely to produce by-products that are difficult to separate.

[0011] Solutions to the problem

[0012] The present inventors have conducted intensive research on a method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) and have newly discovered that: after reacting at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product as a raw material with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, the generated perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl) is separated by a liquid separation operation. ) carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt is separated and extracted, and then one or more water content reduction treatments selected from water distillation and water adsorption are performed, and then used for decarbonation reaction in a liquid phase system, thereby suppressing the generation of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) which is difficult to separate, and perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be obtained with a high yield. In addition, the decarbonation reaction in the liquid phase system is easy to implement on an industrial scale.

[0013] That is, one embodiment of the present invention (hereinafter referred to as "embodiment A") is as follows.

[0014] [1] A method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane), comprising at least the following steps (1) to (3):

[0015] (1) reacting at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, and then separating and extracting a liquid containing the generated perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt by liquid separation operation;

[0016] (2) subjecting the obtained liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid to one or more water content reduction treatments selected from the group consisting of water distillation removal and water adsorption to obtain an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid in the form of a solution or a solid;

[0017] (3) Using the obtained solution or solid perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt, decarbonation reaction is carried out in a liquid phase system to produce perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0018] [2] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to [1], comprising:

[0019] In step (1), after separating and extracting the liquid containing the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid by liquid separation operation, the following step (4) is further performed.

[0020] (4) performing the following operation one or more times: further contacting the liquid containing perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt obtained in step (1) with water or water in which an inorganic salt is dissolved, followed by performing a liquid separation operation to separate and extract the liquid containing perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt again.

[0021] [3] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to [1] or [2], further comprising:

[0022] In step (1), at least one aprotic solvent C is added at least any one of before the reaction with the alkaline aqueous solution containing at least one cation selected from alkali metal ions and alkaline earth metal ions, after the reaction and after the liquid separation operation.

[0023] [4] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to [3], wherein

[0024] The aprotic solvent C is an ether solvent.

[0025] [5] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to [3] or [4], wherein

[0026] The aprotic solvent C is a glycol diether-based solvent.

[0027] [6] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of [3] to [5], wherein

[0028] The aprotic solvent C is diethylene glycol dimethyl ether.

[0029] [7] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of [1] to [6], wherein

[0030] The water content reduction treatment in step (2) includes distilling off water in the presence of one or more azeotropic solvents that form an azeotropic composition with water.

[0031] [8] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of [3] to [5], wherein

[0032] The water content reduction treatment in step (2) includes distilling off water in the presence of one or more azeotropic solvents that form an azeotropic composition with water and have a lower boiling point than the aprotic solvent C added in step (1).

[0033] [9] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to [7] or [8], wherein

[0034] The azeotropic solvent is one or more solvents selected from isopropyl alcohol and toluene.

[0035]

[10] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of [1] to [9], wherein

[0036] In the step (3), when the decarbonation reaction is carried out in a liquid phase system, the solvent contained in the liquid phase system contains a glycol diether-based solvent.

[0037] Another embodiment of the present invention (hereinafter referred to as "Aspect B") is as follows.

[0038]

[11] A method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane), the method comprising:

[0039] A reactive distillation step of continuously supplying a raw material liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid to a reactive distillation vessel to perform reactive distillation to produce perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0040]

[12] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to

[11] , wherein

[0041] The reactive distillation step further comprises:

[0042] A raw material solution of an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid dissolved in an aprotic solvent A is continuously supplied under reduced pressure to an aprotic solvent B heated in a reactive distillation vessel, and a reaction is performed while the generated perfluoro(2-methylene-4-methyl-1,3-dioxolane) is distilled out of the system.

[0043] The aprotic solvent B may be the same as or different from the aprotic solvent A and has a boiling point that is the same as or higher than that of the aprotic solvent A.

[0044]

[13] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to

[12] , wherein

[0045] The aprotic solvent A contains at least one ether solvent.

[0046]

[14] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to

[12] or

[13] , wherein

[0047] The aprotic solvent A contains at least one glycol diether-based solvent.

[0048]

[15] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of

[12] to

[14] , wherein

[0049] The aprotic solvent A contains diethylene glycol dimethyl ether.

[0050]

[16] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of

[12] to

[15] , wherein

[0051] The aprotic solvent B contains at least one alkane-based solvent.

[0052]

[17] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to

[16] , wherein

[0053] The aprotic solvent B contains liquid paraffin.

[0054]

[18] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of

[12] to

[15] , wherein

[0055] The aprotic solvent B contains at least one glycol diether-based solvent.

[0056]

[19] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to

[18] , wherein

[0057] The aprotic solvent B contains tetraethylene glycol dimethyl ether.

[0058]

[20] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of

[11] to

[19] , wherein

[0059] The raw material liquid contains perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid sodium salt.

[0060]

[21] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to any one of

[11] to

[20] , further comprising the following steps (1) and (2):

[0061] (1) reacting at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, and then separating and extracting a liquid containing the generated perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt by liquid separation operation;

[0062] (2) subjecting the obtained liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid to one or more water content reduction treatments selected from the group consisting of distillation removal of water and adsorption of water, thereby obtaining an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid in the form of a solution or a solid.

[0063] According to one embodiment of the present invention, there can be provided a method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) which is easy to implement industrially, has a high yield, and is less likely to produce by-products that are difficult to separate. DETAILED DESCRIPTION

[0064] Hereinafter, the embodiment A and the embodiment B will be described in more detail. Unless otherwise specified, the following descriptions related to the embodiment A can also be applied to the embodiment B, and the following descriptions related to the embodiment B can also be applied to the embodiment A.

[0065] [Method A]

[0066] Embodiment A relates to a method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane), which comprises at least the above steps (1) to (3).

[0067] Hereinafter, the above-mentioned production method will be described in more detail.

[0068] <Process (1)>

[0069] Perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) used as a raw material in step (1) is represented by Formula 1 below.

[0070] [Chemical formula 1]

[0071] (Formula 1)

[0072]

[0073] Perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) can be obtained by a method known in the literature. For example, as described in the publication of U.S. Patent No. 3308107 or Macromolecules 2005, 38, 4237-4245, by reacting a trifluoropyruvic acid fluoride monomer or a dimer thereof with hexafluoropropylene oxide in the presence of cesium fluoride, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) can be obtained. In addition, the hydrolyzate of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) is a product generated by the reaction of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) with water, and is usually obtained in the form of a mixture of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid (Formula 2 below) and hydrogen fluoride.

[0074] [Chemical formula 2]

[0075] (Formula 2)

[0076]

[0077] That is, in step (1), at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid (i.e., one or both) can be reacted with an alkaline aqueous solution containing one or more (i.e., only one or two or more) cations selected from alkali metal ions and alkaline earth metal ions.

[0078] In step (1), after reacting at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, the generated liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid is separated and extracted by a liquid separation operation. The liquid separation operation may also be referred to as a layer separation operation.

[0079] Here, the perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt may be represented by the following Formula 3. In Formula 3, M I Represents an alkali metal element. О and M I The bond of M represents a covalent bond or an ionic bond. In the case of an ionic bond, M I It should be noted that as a perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt, M IA perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt having the same kind of alkali metal element as represented by M I Two or more perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salts having different kinds of alkali metal elements.

[0080] [Chemical formula 3]

[0081] (Formula 3)

[0082]

[0083] The alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid can be represented by the following Formula 4 or Formula 5. In Formula 4 and Formula 5, M II Each independently represents an alkaline earth metal element. II The bond of M represents a covalent bond or an ionic bond. In the case of an ionic bond, M II M may represent an alkaline earth metal ion. II The bond with R represents an ionic bond. R represents a hydroxide ion (OH - ), bicarbonate ion (HCO3 - ), hydrogen sulfate ion (HSO4 - ), bisulfite ion (HSO3 - ), perchlorate ion (HClO4 - ) or halide ion. It should be noted that, as a perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt, one perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt having the same ion species represented by R can be generated, and two or more perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salts having different ion species represented by R can also be generated. In addition, as a perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt, M II A perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt having the same alkaline earth metal element as represented by M II Two or more perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salts having different kinds of alkaline earth metal elements.

[0084] [Chemical formula 4]

[0085] (Formula 4)

[0086]

[0087] [Chemical formula 5]

[0088] (Formula 5)

[0089]

[0090] As alkali metal ions, lithium ions, sodium ions, potassium ions, rubidium ions and cesium ions can be listed. In addition, as alkaline earth metal ions, beryllium ions, magnesium ions, calcium ions and the like can be listed. The alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions can be an aqueous solution prepared by dissolving one or more salts of these cations, such as hydroxides, carbonates, bicarbonates (also referred to as "bicarbonates"), and sulfites in water. The concentration of the above cations in the aqueous solution is, for example, 5 to 50% by weight in terms of the concentration of the salt. In addition, the amount of alkali metal ions used is, for example, in the range of 0.5 to 3 in terms of molar ratio relative to perfluoro (2,4-dimethyl-2-fluoroformyl-1,3-dioxolane), and the amount of alkaline earth metal ions used is, for example, in the range of 0.25 to 1.5 in terms of molar ratio relative to perfluoro (2,4-dimethyl-2-fluoroformyl-1,3-dioxolane).

[0091] R represents hydroxide ion (OH - ), bicarbonate ion (HCO3 - ), hydrogen sulfate ion (HSO4 - ), bisulfite ion (HSO3 - ), perchlorate ion (HClO4 - ) or halogen ions. Examples of halogen ions include fluoride ions (F - ), chloride ion (Cl - ), bromide ion (Br - ), iodide ion (I - )wait.

[0092] Among them, from the viewpoint of the availability and reactivity of the raw materials, R is preferably a hydroxide ion (OH - ) or bicarbonate ion (HCO3 - ).

[0093] Regarding the reaction temperature when at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolyzate is reacted with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, the temperature of the reaction solution is, for example, in the range of -10 to +50°C. Usually, at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolyzate is added successively, and the reaction is carried out while controlling the temperature, or an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions is added successively, and the reaction is carried out while controlling the temperature. Regarding the reaction time, for example, after the total amount of raw materials is mixed, the reaction is continued for 10 minutes to 1 hour, and then the separation operation is carried out after standing for 10 minutes to 1 hour.

[0094] The perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt generated by the above reaction is a salt, but due to the influence of fluorine atoms, there is a tendency to be difficult to dissolve in water. Therefore, the reaction solution after the reaction is usually separated into layers. The layer (organic layer) containing the perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt as the target of step (1) usually becomes the lower layer. It should be noted that, as described later, when a non-protonic solvent C is added, during the liquid separation operation, a layer (organic layer) containing a perfluoro (2,4-dimethyl-1,3-dioxolane-2-yl) carboxylic acid alkali metal salt or a perfluoro (2,4-dimethyl-1,3-dioxolane-2-yl) carboxylic acid alkaline earth metal salt as the target may become the upper layer. Alkali metal fluorides or alkaline earth metal fluorides generated as by-products are easily dissolved in the water layer side where the layer separation occurs with the organic layer containing the above-mentioned target. Some or all of these fluorides can be separated by liquid separation.

[0095] In addition, one or more aprotic solvents (referred to as "aprotic solvent C") may be added before, during, after, and after the liquid separation operation described below, reacting at least any one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product with the above-mentioned alkaline aqueous solution containing cations. By adding the aprotic solvent C, the separation and removal efficiency of the alkali metal fluoride or alkaline earth metal fluoride generated as a by-product can be improved, and the loss of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt to the water layer side can be reduced.

[0096] The aprotic solvent C is preferably an aprotic solvent that can dissolve an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid. Specifically, there can be mentioned ether solvents (ethers) such as diisopropyl ether, dibutyl ether, anisole, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; esters such as ethyl acetate, butyl acetate, and ethyl propionate; ketone solvents (ketones) such as methyl ethyl ketone, cyclohexanone, and acetophenone; amide solvents (amides) such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; nitrile solvents (nitriles) such as acetonitrile and propionitrile; aromatic hydrocarbon solvents (aromatic hydrocarbons) such as toluene and xylene; alkane solvents (alkanes) such as heptane and octane; and mixed solvents of two or more thereof. Among these, ether solvents are preferred from the viewpoint of solubility of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt, and more preferred are glycol diether solvents (glycol diethers) such as diethoxyethane and diethylene glycol dimethyl ether. The amount of the aprotic solvent C used can be generally set in the range of 0.5 to 5 times the weight ratio relative to the perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt.

[0097] Alternatively, the following step (4) may be performed after separating and extracting the liquid containing the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate by liquid separation operation.

[0098] (4) performing the following operation once or more times: contacting the liquid containing perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt obtained in step (1) with water or water in which an inorganic salt is dissolved, and then performing a liquid separation operation to separate and extract the liquid containing perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt. When the aprotic solvent C is added in step (1), the liquid containing the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate may be brought into contact with water or water in which an inorganic salt is dissolved in the presence of the aprotic solvent C. On the other hand, when the aprotic solvent C is not added in step (1), the liquid containing the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate may be brought into contact with water or water in which an inorganic salt is dissolved in the absence of the aprotic solvent C.

[0099] By carrying out step (4), the content of alkali metal fluoride or alkaline earth metal fluoride in the organic layer can be further reduced. As the inorganic salt here, in addition to the alkaline salts of hydroxides, carbonates, bicarbonates, and sulfites of alkali metals or alkaline earth metals, neutral salts such as chlorides, sulfates, and nitrates can also be used. Step (4) is also called a re-separation and extraction step. When implementing step (4), step (1), step (4) (re-separation and extraction step), and step (2) can be carried out in sequence.

[0100] <Process (2)>

[0101] In step (2), after step (1) or step (4), the liquid containing the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid is subjected to one or more water content reduction treatments selected from the group consisting of water distillation removal and water adsorption. Thus, a solution or solid perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt having a reduced water content compared to before the water content reduction treatment can be obtained. By step (1), as a liquid containing perfluoro (2,4-dimethyl -1,3-dioxolane -2-yl) carboxylic acid alkali metal salt or perfluoro (2,4-dimethyl -1,3-dioxolane -2-yl) carboxylic acid alkaline earth metal salt, a liquid with a low content of fluoride can be obtained. That is, a liquid with a low content of water bonded or interacting with the fluoride can be obtained. Therefore, by performing an operation that can be easily implemented industrially such as distillation and adsorption of water, the water content contained in perfluoro (2,4-dimethyl -1,3-dioxolane -2-yl) carboxylic acid alkali metal salt or perfluoro (2,4-dimethyl -1,3-dioxolane -2-yl) carboxylic acid alkaline earth metal salt can be reduced.

[0102] The removal of water by distillation is preferably carried out by distillation. The liquid temperature during distillation is, for example, 0 to 100°C, preferably 20 to 70°C, and it is usually efficient to carry out distillation under a reduced pressure of 0.1 kPa to 50 kPa. At this time, by the presence of one or more azeotropic solvents that form an azeotropic composition with water, the azeotropic composition containing water can be distilled off at a temperature lower than the boiling point of water. Therefore, it is not necessary to set a high vacuum, and the load on the device can be reduced. There is no particular limitation on the azeotropic solvent as long as it is a solvent that forms an azeotropic composition with water. n-Propanol, isopropanol, n-butanol, isobutanol, tert-butanol, tetrahydrofuran, 1,4-di ... Alkane, 1,2-dimethoxyethane, ethyl acetate, ethyl methyl ketone, acetonitrile, 1,2-dichloroethane, toluene, o-xylene, cyclohexane, etc. can be suitably used because the content of water in the azeotropic mixture is high, among which at least one of isopropanol and toluene is preferred. In addition, when the aprotic solvent C is added in step (1), the azeotropic solvent present in step (2) may be the same as or different from the aprotic solvent C. In this case, when the boiling point of the azeotropic solvent present in step (2) is lower than the boiling point of the aprotic solvent C added in step (1), it is easy to obtain the perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt obtained after distillation removal by azeotropy of water in the form of a solution containing the aprotic solvent C, and it can be used directly in step (3), so it is preferred.

[0103] In addition, as an adsorbent material for reducing the water content by adsorption removal, inorganic salts that can form hydrated salts such as anhydrous sodium sulfate, anhydrous magnesium sulfate, anhydrous calcium chloride, natural zeolite, synthetic zeolite and other physical adsorbent materials can be used, and these materials can also be used in combination in stages. As for the amount of adsorbent used, it is usually set to an amount that is 0.1 to 5 times the amount of water contained in the liquid containing perfluoro (2, 4-dimethyl-1, 3-dioxolan-2-yl) carboxylic acid alkali metal salt or perfluoro (2, 4-dimethyl-1, 3-dioxolan-2-yl) carboxylic acid alkaline earth metal salt obtained in step (1). As for the temperature when adsorption removal is performed, it can usually be carried out in an operating environment of normal pressure at an atmospheric temperature of 0 to 50 ° C, and the contact time with the adsorbent can usually be set in the range of 10 minutes to 24 hours.

[0104] <Step (3)>

[0105] In step (3), the solution or solid perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt obtained in step (2) is used to carry out a decarbonation reaction in a liquid phase system to produce perfluoro(2-methylene-4-methyl-1,3-dioxolane) as the target compound.

[0106] Here, perfluoro(2-methylene-4-methyl-1,3-dioxolane) may be represented by Formula 6 below.

[0107] [Chemical formula 6]

[0108] (Formula 6)

[0109]

[0110] In the case of obtaining a liquid perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt in step (2), the liquid can be directly used for decarbonation reaction, and a solvent can be added to react as needed. In addition, in the case of obtaining a solid perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt in step (2), a solvent can be used to dissolve or disperse the perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt, and decarbonation reaction can be carried out. Examples of the solvent used herein include ether solvents (ethers) such as diisopropyl ether, dibutyl ether, anisole, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; ester solvents (esters) such as ethyl acetate, butyl acetate, and ethyl propionate; ketone solvents (ketones) such as ethyl methyl ketone, cyclohexanone, and acetophenone; amide solvents (amides) such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; nitriles such as acetonitrile and propionitrile; aromatic hydrocarbon solvents (aromatic hydrocarbons) such as toluene and xylene; alkane solvents (alkanes) such as heptane and octane; and mixed solvents of two or more thereof. The solvents may be the same as or different from the aprotic solvent C added in step (1) or the azeotropic solvent present in step (2). From the viewpoint of the solubility of the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid and the yield of perfluoro(2-methylene-4-methyl-1,3-dioxolane), a glycol diether-based solvent (glycol diethers) can be preferably used.

[0111] The reaction temperature during the decarbonation reaction can be set to, for example, a range of 100°C to 200°C, preferably under a reduced pressure of 1 kPa to 90 kPa, while the generated perfluoro(2-methylene-4-methyl-1,3-dioxolane) is distilled off and the reaction is carried out. Alternatively, a solution of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal can be continuously added dropwise to a solvent heated to the same temperature range, while the generated perfluoro(2-methylene-4-methyl-1,3-dioxolane) is continuously distilled off and the reaction is carried out. The reaction time can generally be set to 0.5 hours to 24 hours. The perfluoro(2-methylene-4-methyl-1,3-dioxolane) distilled off during the reaction can be captured by a collector cooled to, for example, -20°C to -80°C. Alternatively, when a diaphragm pump is used for pressure reduction, the target perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be captured by cooling the pump outlet gas pressurized to above normal pressure to below the boiling point of perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0112] According to the embodiment A, perfluoro(2-methylene-4-methyl-1,3-dioxolane) having a low content of 2-hydro-perfluoro(2,4-dimethyl-1,3-dioxolane) as a by-product can be obtained. Therefore, the obtained perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be used as a synthetic raw material for poly[perfluoro(2-methylene-4-methyl-1,3-dioxolane)] as it is. Alternatively, it can be purified by precision distillation as needed.

[0113] [Method B]

[0114] The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to Embodiment B comprises a reaction distillation step of continuously supplying a raw material liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid to a reaction distillation vessel to perform reaction distillation to produce perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0115] Hereinafter, the above-mentioned production method will be described in more detail.

[0116] In the present invention and this specification, "reactive distillation" refers to a reaction form in which perfluoro(2-methylene-4-methyl-1,3-dioxolane) is distilled out of the reaction system while being generated. In the above-mentioned production method, the generation of perfluoro(2-methylene-4-methyl-1,3-dioxolane) by decarbonation reaction of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt is carried out in a liquid phase system, and therefore, it is easy to implement industrially. The reactive distillation is preferably carried out under reduced pressure. By carrying out the reactive distillation under reduced pressure, the distillation of perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be promoted, and as a result, perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be obtained with a better yield.

[0117] In the present invention and this specification, "continuously supplying" and "continuous supplying" are used in a meaning other than supplying the total amount of the component to be supplied at one time. For example, "continuously supplying" and "continuous supplying" include supplying by dripping the component to be supplied for a given time.

[0118] Regarding the target perfluoro(2-methylene-4-methyl-1,3-dioxolane), and the perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkali metal salt and perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid alkaline earth metal salt (hereinafter also referred to as “raw material metal salt”) contained in the raw material liquid, the above description related to Embodiment A can be referred to.

[0119] Examples of the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid include lithium salts, sodium salts, potassium salts, rubidium salts, and cesium salts.

[0120] Examples of the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid include beryllium salts, magnesium salts, and calcium salts.

[0121] From the viewpoint of industrial availability and reactivity, the raw material metal salt is preferably an alkali metal salt, and more preferably a sodium salt and a potassium salt.

[0122] The raw metal salt can be obtained, for example, by a method known in the literature. For example, as described in the publication of U.S. Patent No. 3308107 or Macromolecules 2005, 38, 4237-4245, the raw metal salt can be obtained by the following method, etc.: hydrolyzing the perfluoro (2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) obtained by reacting a trifluoropyruvic acid fluoride monomer or its dimer with hexafluoropropylene oxide in the presence of cesium fluoride, neutralizing with an alkali metal hydroxide, an alkali metal carbonate, an alkaline earth metal hydroxide or an alkaline earth metal carbonate, etc., and performing dehydration treatments such as heating under reduced pressure. Here, the raw metal salt contains an alkali metal fluoride or an alkaline earth metal fluoride as a byproduct during hydrolysis and neutralization in an equimolar amount or less.

[0123] Alternatively, one embodiment of Embodiment B may include obtaining the raw material metal salt through step (1) and step (2) included in Embodiment A. The details of step (1) and step (2) are as described above for Embodiment A.

[0124] In the above production method, it is preferred to carry out the reaction while adding the raw material metal salt dissolved in the aprotic solvent A to the heated aprotic solvent B under reduced pressure.

[0125] The aprotic solvent A is preferably an aprotic solvent that can dissolve the raw material metal salt. Specifically, ether solvents (ethers) such as diisopropyl ether, dibutyl ether, anisole, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, ester solvents (esters) such as ethyl acetate, butyl acetate, and ethyl propionate, ketone solvents (ketones) such as methyl ethyl ketone, cyclohexanone, and acetophenone, amide solvents (amides) such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone, nitrile solvents (nitriles) such as acetonitrile and propionitrile, aromatic hydrocarbon solvents (aromatic hydrocarbons) such as toluene and xylene, alkane solvents (alkanes) such as heptane and octane, and mixed solvents of two or more thereof. Among these, from the perspective of the solubility of the raw metal salt and the yield of perfluoro(2-methylene-4-methyl-1,3-dioxolane), it is preferred that the aprotic solvent A contains at least one ether solvent, and more preferably contains a glycol diether solvent (glycol diethers) such as diethoxyethane and diethylene glycol dimethyl ether. The amount of aprotic solvent A is preferably 0.5 to 5 times the weight ratio relative to the raw metal salt. In addition, the raw metal salt can be separated in the form of a solid and dissolved in the aprotic solvent A, or the aprotic solvent A can be added during the hydrolysis and / or neutralization of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane), and the solution can be subjected to azeotropic distillation and dehydration, etc. to obtain a solution for use.

[0126] The aprotic solvent B is the same as or different from the aprotic solvent A and is a solvent having a boiling point that is the same as or higher than that of the aprotic solvent A. The target perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be obtained by performing a decarbonation reaction of a raw metal salt. In order to allow the decarbonation reaction of the raw metal salt to react at a sufficient rate, it is desirable that the aprotic solvent B has a boiling point of 130° C. or higher. From this aspect, as preferred aprotic solvent B, ether solvents (ethers) such as dibutyl ether, diphenyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, ester solvents (esters) such as ethyl octanoate, diethyl malonate, and diethyl succinate, ketoester solvents (ketoesters) such as ethyl acetoacetate, ketone solvents (ketones) such as cyclohexanone, amide solvents (amides) such as dimethylacetamide and N-methylpyrrolidone, nitrile solvents (nitriles), aromatic hydrocarbon solvents (aromatic hydrocarbons) such as xylene and mesitylene, alkane solvents (alkanes) such as dodecane, decalin, and liquid paraffin, and mixed solvents of two or more thereof can be cited. Among these, from the aspect of the yield of perfluoro (2-methylene-4-methyl-1,3-dioxolane), the aprotic solvent B preferably contains one or more solvents selected from alkane solvents and glycol diether solvents. The amount of the aprotic solvent B used can be, for example, 0.2 to 5.0 times the amount of the raw material metal salt in terms of weight ratio.

[0127] Reaction distillation can be performed by continuously supplying a raw material liquid containing a raw material metal salt to a reaction distiller. The reaction distiller is not particularly limited as long as it is a device capable of supplying a raw material liquid, distilling and distilling a product (specifically, condensing by cooling), and decompressing the inside of the distiller as needed. Examples of the reaction distiller include a three-necked round-bottom flask equipped with a distiller (condenser and receiver), a reactor with a distillation device in a chemical plant, and the like.

[0128] Reaction distillation can be carried out, for example, under normal pressure or under reduced pressure, preferably under reduced pressure in the range of 1 kPa to 90 kPa. It is preferred to continuously supply the raw material liquid to the aprotic solvent B heated in the reaction vessel under reduced pressure. Here, the temperature of the aprotic solvent B in the reaction vessel is preferably in the temperature range of 100 to 200°C. There is no particular restriction on the supply rate of the raw material liquid to the reaction distillation vessel, but it is preferably a rate that can maintain the above temperature range. Usually, it can be set to 1 g / hr or more and 100 g / hr or less, preferably 10 g / hr or more and 60 g / hr or less, based on the weight / time conversion of the raw material metal salt per 1L reactor capacity. In addition, as needed, after the supply of the raw material liquid is completed, it can be further maintained under the same conditions for 0.5 hours to 4 hours to complete the distillation of the target perfluoro(2-methylene-4-methyl-1,3-dioxolane). The target product perfluoro(2-methylene-4-methyl-1,3-dioxolane) distilled by the reactive distillation can be captured by a collector cooled to, for example, -20°C to -80°C. Alternatively, when a diaphragm pump is used for decompression, the pump outlet gas pressurized to above normal pressure can be cooled to below the boiling point of perfluoro(2-methylene-4-methyl-1,3-dioxolane) to capture the target product perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0129] According to the embodiment B, as perfluoro(2-methylene-4-methyl-1,3-dioxolane) which is the target product distilled by reactive distillation, perfluoro(2-methylene-4-methyl-1,3-dioxolane) with a small amount of 2-hydro-perfluoro(2,4-dimethyl-1,3-dioxolane) mixed as a by-product can be obtained. Therefore, the product obtained by the above-mentioned production method can be used as a synthetic raw material for poly[perfluoro(2-methylene-4-methyl-1,3-dioxolane)] as it is, or can be used as a synthetic raw material for poly[perfluoro(2-methylene-4-methyl-1,3-dioxolane)] after purification by precision distillation as needed.

[0130] Example

[0131] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0132] The following equipment was used for the analysis.

[0133] 19 F-NMR: AVANCE II 400 manufactured by BRUKER.

[0134] <Reference Example 1>

[0135] Preparation of Perfluoro(2,4-Dimethyl-2-fluoroformyl-1,3-dioxolane)

[0136] In a 10L SUS316 autoclave equipped with a stirrer and having a pressure resistance of 8 MPa, the following trifluoropyruvic acid fluoride dimer (2222.4 g, pure component 1980.3 g, 6.88 mol), cesium fluoride (315.6 g, 2.08 mol) and diethylene glycol dimethyl ether (1338.8 g, 9.98 mol) were added, and the mixture was cooled to 0° C. on an ice bath. Subsequently, hexafluoropropylene oxide (2284.4 g, 13.76 mol) was added dropwise thereto over 2 hours, and the mixture was heated to 120° C. and reacted for 24 hours.

[0137] [Chemical formula 7]

[0138] Trifluoropyruvate fluoride dimer

[0139]

[0140] After the reaction was completed, the mixture was cooled to room temperature and separated to obtain crude perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (yellow liquid, 3047.4 g). 19 In the quantitative analysis of F-NMR, the target product, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) 2901.0 g (9.36 mol) was generated (yield 68% / trifluoropyruvic acid fluoride dimer basis). It should be noted that the target product was a mixture of two diastereomers, and the ratio was 6 / 4 (molar ratio).

[0141] 19 F-NMR (neat, 376 MHz) (Isomer 1) δ 23.63, -77.76 (d, J = 131.6 Hz), -80.13, -81.57, -83.56 (d, J = 135.4 Hz), -124.91. (Isomer 2) δ 23.16, -78.45 (d, J = 131.6 Hz), -80.37, -81.56, -84.05 (d, J = 139.1 Hz), -123.72.

[0142] [Chemical formula 8]

[0143] Perfluoro(2,4-dimethyl-2-fluorocarbonyl-1,3-dioxolane)

[0144]

[0145] <Reference Example 2>

[0146] Preparation of aqueous solution of potassium salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate

[0147] Potassium carbonate (659.8 g, 4.77 mol) and water (1400 mL) were added to a 10 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and dissolved while stirring, and then cooled to 0° C. on an ice bath. Next, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (1510.2 g, pure component 1450.5 g, 4.68 mol) prepared in Reference Example 1 was added dropwise over 2 hours while controlling heat release in the temperature range of 0 to 10° C., and then stirred for 1 hour in the same temperature range. After standing for 1 hour, the lower layer was separated and extracted by a liquid separation operation, and 2703 g (pure component 1602.2 g, 4.63 mol, yield 99%) of an aqueous solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt as the target was obtained.

[0148] <Reference Example 3>

[0149] Preparation of Perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic Acid Potassium Salt (Solid)

[0150] The potassium salt aqueous solution of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate (2304 g, pure component 1365.7 g, 3.95 mol) obtained in Reference Example 2 was added to a 3L flask, and concentrated under reduced pressure by an evaporator at a pressure of 13 kPa on a 60°C water bath, and then vacuum dried at the same temperature for 5 hours to obtain 1464.5 g of a white solid (pure component 1357.8 g, 3.92 mol, water content 0.45%).

[0151] 19 F-NMR (D2O, 376 MHz) (Isomer 1) δ -78.65 (dd, J = 233.1 Hz, 11.3 Hz), -81.26 (d, J = 11.3 Hz), -81.95, -84.44 (dd, J = 135.4 Hz, 11.3 Hz), -124.42 (m). (Isomer 2) δ -79.17 (dd, J = 135.4 Hz, 7.5 Hz), -81.49 (d, J = 15.0 Hz), -81.82, -84.57 (dd, J = 142.9 Hz, 7.5 Hz), -124.78 (m).

[0152] <Reference Example 4>

[0153] Preparation of aqueous perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid sodium salt

[0154] Sodium carbonate (51.10 g, 0.482 mol) and water (150 mL) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and stirred to form a suspension state, and then cooled to 0° C. on an ice bath.

[0155] Next, 152.36 g (pure component 145.00 g, 0.468 mol) of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) prepared in Reference Example 1 was added dropwise over 1 hour while controlling heat release in the temperature range of 0 to 10°C. Then, the mixture was further stirred for 1 hour in the same temperature range. After standing for 1 hour, the lower layer was separated and extracted by a liquid separation operation to obtain 259.72 g (pure component 146.74 g, 0.445 mol, yield 95%) of an aqueous solution of sodium salt of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate as the target product.

[0156] <Reference Example 5>

[0157] Preparation of magnesium salt of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate

[0158] Magnesium carbonate (40.64 g, 0.482 mol) and water (200 mL) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and a suspension was prepared while stirring, and then cooled to 0° C. on an ice bath.

[0159] Next, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (152.36 g, pure component 145.00 g, 0.468 mol) prepared in Reference Example 1 was added dropwise over 1 hour while controlling heat release in the temperature range of 0 to 10°C, and then stirred at the same temperature for 1 hour. After standing for 1 hour, the lower layer was separated and extracted by liquid separation operation to obtain 241.32 g (pure component 137.43 g, 0.215 mol, yield 92%) of an aqueous solution of bis[perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid] magnesium salt as the target.

[0160] [Examples and Comparative Examples Related to Form A]

[0161] <Example 1>

[0162] Step (1): Preparation of an aqueous solution of potassium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate

[0163] Potassium carbonate (65.65 g, 0.475 mol) and water (140 mL) were added to a 1L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and dissolved while stirring, and then cooled to 0°C on an ice bath. Next, the perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (150.8 g, pure component 143.6 g, 0.463 mol) prepared in Reference Example 1 was added dropwise to the above three-necked round-bottom flask over 1 hour while controlling heat release in the temperature range of 0 to 10°C, and then stirred for 1 hour in the same temperature range, and allowed to stand for 1 hour. The lower layer was separated and extracted by a liquid separation operation, and 268.3 g of an aqueous solution of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid potassium salt as the target was obtained. For the aqueous solution, trifluorotoluene was used as an internal standard substance. 19 Quantitative analysis by F-NMR revealed that the product contained 158.5 g (0.458 mol, yield 99%) of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt and 11.96 g (0.206 mol) of potassium fluoride.

[0164] Step (2): Preparation of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt (solid)

[0165] The potassium salt aqueous solution of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate (268.3 g, pure component 158.5 g, 0.458 mol) obtained in the above step (1) was added to a 500 mL flask, and concentrated under reduced pressure at 13 kPa by an evaporator on a water bath at 60°C, and then vacuum dried at the same temperature for 5 hours to obtain 170.2 g of a white solid (pure component 157.2 g, 30.454 mol, water content 0.43 wt%).

[0166] 19 F-NMR (D2O, 376 MHz) (Isomer 1) δ -78.65 (dd, J = 233.1 Hz, 11.3 Hz), -81.26 (d, J = 11.3 Hz), -81.95, -84.44 (dd, J = 135.4 Hz, 11.3 Hz), -124.42 (m). (Isomer 2) δ -79.17 (dd, J = 135.4 Hz, 7.5 Hz), -81.49 (d, J = 15.0 Hz), -81.82, -84.57 (dd, J = 142.9 Hz, 7.5 Hz), -124.78 (m).

[0167] Step (3): Synthesis of perfluoro(2-methylene-4-methyl-1,3-dioxolane)

[0168] In a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus with a cold collector (two stages at -20°C and -78°C), potassium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (170.2 g, pure component 157.2 g, 0.454 mol) and diethylene glycol dimethyl ether (255.3 g) prepared in the above step (2) were added. Under a reduced pressure of 30 kPa, the mixture was slowly heated to 130°C while stirring, and the reaction was carried out for 4 hours. After the reaction was completed, trifluorotoluene was used as an internal standard substance, and the reaction mixture was stirred for 4 hours. 19 F-NMR analysis of the product recovered in the cold collector confirmed the generation of 49.84 g (0.204 mol, 45% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 14.38 g (12% yield) of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane).

[0169] <Comparative Example 1>

[0170] In Example 1, steps (2) and (3) were carried out by the same operation as in Example 1, except that the liquid separation operation was not performed in step (1) and the whole amount of the reaction liquid was used.

[0171] That is, potassium carbonate (65.65 g, 0.475 mol) and water (140 mL) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and dissolved while stirring, and then cooled to 0° C. on an ice bath. Next, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (150.8 g, pure component 143.6 g, 0.463 mol) prepared in Reference Example 1 was added dropwise to the three-necked round-bottom flask over 1 hour while controlling heat release in a temperature range of 0 to 10° C., and the reaction solution was transferred to a 1 L flask, concentrated under reduced pressure at a pressure of 13 kPa by an evaporator on a 60° C. water bath, and then vacuum dried for 5 hours in the same temperature range to obtain 187.5 g of a white solid (pure component 158.5 g, 0.458 mol, water content 1.36 wt%). Next, a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus with a cooling collector (two stages at -20°C and 78°C) was added with potassium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (187.5 g, pure component 158.5 g, 0.458 mol) and diethylene glycol dimethyl ether (255.3 g). The mixture was slowly heated to 130°C while stirring under a reduced pressure of 30 kPa, and the reaction was carried out for 4 hours.

[0172] After the reaction, trifluorotoluene was used as an internal standard substance. 19F-NMR analysis of the product recovered in the cold collector confirmed the generation of 36.88 g (0.151 mol, 33% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 38.69 g (32% yield) of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane).

[0173] <Example 2>

[0174] (Method of adding aprotic solvent C (diethylene glycol dimethyl ether) in step (1))

[0175] Process (1):

[0176] Potassium carbonate (65.64 g, 0.475 mol) and water (153.3 g) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and after dissolving them while stirring, diethylene glycol dimethyl ether (321.4 g) was added and cooled to 0°C on an ice bath. Next, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (150.8 g, pure component 143.6 g, 0.463 mol) prepared in Reference Example 1 was dripped into the three-necked round-bottom flask over 1 hour while controlling heat release in the temperature range of 0 to 10°C, and then stirred for 1 hour in the same temperature range and allowed to stand for 1 hour. The upper layer was separated and extracted by liquid separation operation to obtain 582.8 g of a solution of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid potassium salt as the target. Trifluorotoluene was used as an internal standard substance and the solution was used 19 Quantitative analysis by F-NMR revealed that the product contained 159.4 g (0.461 mol, yield 100%) of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt and 1.72 g (0.030 mol) of potassium fluoride.

[0177] Step (2):

[0178] The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (582.8 g, pure component 159.4 g, 0.461 mol) obtained in step (1) was added to a 1 L flask equipped with a stirrer and a distillation apparatus, and the pressure was gradually reduced from 13 kPa to 1 kPa on an oil bath at 60°C while water and diethylene glycol dimethyl ether were distilled off to obtain a potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (386.9 g, pure component 154.7 g, 0.447 mol, water content 0.058 wt%).

[0179] Step (3):

[0180] The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (386.9 g, 154.7 g pure component, 0.447 mol) prepared in step (2) was added to a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus with a cold collector (two stages at -20°C and -78°C). The mixture was slowly heated to 130°C while stirring under a reduced pressure of 30 kPa, and the reaction was carried out for 4 hours. After the reaction was completed, trifluorotoluene was used as an internal standard substance. 19 F-NMR analysis of the product recovered in the cold collector confirmed the generation of 57.81 g (0.237 mol, 53% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 9.44 g (8% yield) of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane).

[0181] <Example 3>

[0182] (A method in which the organic layer is brought into contact with an inorganic salt aqueous solution (a 30 wt % potassium carbonate aqueous solution) and then the liquid is separated again in step (1))

[0183] Process (1):

[0184] Potassium carbonate (65.66 g, 0.475 mol) and water (153.1 g) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and dissolved while stirring, and then cooled to 0° C. on an ice bath. Next, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (150.8 g, pure component 143.6 g, 0.463 mol) prepared in Reference Example 1 was added dropwise to the three-necked round-bottom flask over 1 hour while controlling heat release in the temperature range of 0 to 10° C., and then stirred for 1 hour in the same temperature range, and after standing for 1 hour, the lower layer was separated and extracted by a liquid separation operation.

[0185] Step (4): Re-separation and extraction step

[0186] The lower layer after separation and extraction was added to a 1L flask again, and 150.4 g of diethylene glycol dimethyl ether and 30 wt% potassium carbonate aqueous solution (145.9 g) were added. After stirring for 1 hour, it was allowed to stand for 1 hour. The upper layer was separated and extracted by liquid separation operation to obtain 422.1 g of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid potassium salt solution. Trifluorotoluene was used as an internal standard substance to analyze the solution. 19 Quantitative analysis by F-NMR revealed that the product contained 158.5 g (0.458 mol, yield 99%) of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt and 0.95 g (0.016 mol) of potassium fluoride.

[0187] Step (2):

[0188] The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (422.1 g, pure component 158.5 g, 0.458 mol) obtained in step (1) was added to a 1 L flask equipped with a stirrer and a distillation apparatus, and water and diethylene glycol dimethyl ether were distilled off while the pressure was gradually reduced from 13 kPa to 1 kPa on an oil bath at 60°C. Then, 150.3 g of diethylene glycol was added again and distilled off under a reduced pressure of 1 kPa to obtain a potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (390.4 g, pure component 152.3 g, 0.440 mol, water content 0.046 wt%).

[0189] Step (3):

[0190] The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (390.4 g, 152.3 g pure component, 0.440 mol) prepared in step (2) was added to a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus with a cold collector (two stages at -20°C and -78°C). The mixture was slowly heated to 130°C while stirring under a reduced pressure of 30 kPa, and the reaction was carried out for 4 hours. After the reaction was completed, trifluorotoluene was used as an internal standard substance. 19 F-NMR analysis of the product recovered in the cold collector confirmed the generation of 59.05 g (0.242 mol, 55% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 8.13 g (7% yield) of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane).

[0191] <Example 4>

[0192] (A method in which an aprotic solvent C (diethylene glycol dimethyl ether) is added in step (1) and toluene is used as an azeotropic solvent in step (2))

[0193] Process (1):

[0194] Potassium carbonate (65.64 g, 0.475 mol) and water (153.3 g) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and after dissolving them while stirring, diethylene glycol dimethyl ether (150.1 g) was added and cooled to 0°C on an ice bath. Next, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (150.8 g, pure component 143.6 g, 0.463 mol) prepared in Reference Example 1 was dripped into the three-necked round-bottom flask over 1 hour while controlling heat release in the temperature range of 0 to 10°C, and then stirred for 1 hour in the same temperature range and allowed to stand for 1 hour. The upper layer was separated and extracted by liquid separation operation to obtain 418.4 g of a solution of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid potassium salt as the target. Trifluorotoluene was used as an internal standard substance and the solution was used 19 Quantitative analysis by F-NMR revealed that the product contained 159.9 g (0.462 mol, yield 100%) of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt and 1.87 g (0.032 mol) of potassium fluoride.

[0195] Step (2):

[0196] The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (418.4 g, pure component 159.9 g, 0.462 mol) obtained in step (1) was added to a 1 L flask equipped with a stirrer and a distillation apparatus, and the pressure was gradually reduced to 6 kPa on an oil bath at 50°C to distill off water. Then, toluene (150.2 g) was added, and the pressure was again increased to 6 kPa on a water bath at 50°C while distilling off an azeotropic mixture of water and toluene, thereby obtaining a potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (351.8 g, pure component 158.3 g, 0.457 mol, water content 0.058 wt%).

[0197] Step (3):

[0198] The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (351.8 g, pure component 158.3 g, 0.457 mol) prepared in step (2) was added to a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus with a cold collector (two stages at -20°C and -78°C). The mixture was slowly heated to 130°C while stirring under a reduced pressure of 30 kPa, and the reaction was carried out for 4 hours. After the reaction was completed, trifluorotoluene was used as an internal standard substance. 19F-NMR analysis of the product recovered in the cold collector confirmed the generation of 57.98 g (0.238 mol, 52% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 10.86 g (9% yield) of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane).

[0199] <Example 5>

[0200] (Method of continuously dropping a perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt solution in step (3))

[0201] Process (1):

[0202] Potassium carbonate (65.64 g, 0.475 mol) and water (153.3 g) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and after dissolving them while stirring, diethylene glycol dimethyl ether (320.5 g) was added, and the mixture was cooled to 0° C. on an ice bath. Next, perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (150.8 g, pure component 143.6 g, 0.463 mol) prepared in Reference Example 1 was added dropwise to the three-necked round-bottom flask over 1 hour while controlling heat release in the temperature range of 0 to 10° C., and then stirred for 1 hour in the same temperature range, and after standing for 1 hour, the upper layer was separated and extracted by a liquid separation operation, thereby obtaining 580.5 g of a solution of potassium salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate as the target product. Trifluorotoluene was used as an internal standard substance and the solution was used 19 Quantitative analysis by F-NMR revealed that the product contained 159.2 g (0.460 mol, yield 100%) of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt and 1.68 g (0.029 mol) of potassium fluoride.

[0203] Step (2):

[0204] The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (580.5 g, pure component 159.2 g, 0.460 mol) obtained in step (1) was added to a 1 L flask equipped with a stirrer and a distillation apparatus, and the pressure was gradually reduced to 13 kPa to 1 kPa on an oil bath at 60°C while water and diethylene glycol dimethyl ether were distilled off to obtain a potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (387.6 g, pure component 154.7 g, 0.447 mol, water content 0.052 wt%).

[0205] Step (3):

[0206] Liquid paraffin (Fuji Film Wako Pure Chemical Industries, Ltd., initial boiling point 300°C, 158 g) was placed in a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus with a cold collector (two stages at -20°C and -78°C), and heated to 130°C under a reduced pressure of 30 kPa while stirring. The potassium salt solution of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (386.9 g, pure component 154.7 g, 0.447 mol) prepared in step (2) was then added dropwise over 3 hours, and the mixture was further maintained under the same reduced pressure and temperature for 1 hour. After the reaction was completed, trifluorotoluene was used as an internal standard substance. 19 F-NMR analysis of the product recovered in the cold collector confirmed the generation of 85.07 g (0.349 mol, 78% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 4.72 g (4% yield) of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane).

[0207] <Example 6>

[0208] (Method using sodium salt as alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid)

[0209] Process (1):

[0210] Sodium carbonate (51.10 g, 0.482 mol) and water (150 mL) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and stirred to form a suspension state, and then cooled to 0° C. on an ice bath.

[0211] Next, 152.36 g (pure component 145.00 g, 0.468 mol) of perfluoro (2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) prepared in Reference Example 1 was added dropwise to the above three-necked round-bottom flask over 1 hour while controlling heat release in the temperature range of 0 to 10°C, and then stirred for 1 hour in the same temperature range. After standing for 1 hour, the lower layer was separated and extracted by liquid separation operation to obtain 259.72 g (pure component 146.74 g, 0.445 mol, yield 95%) of perfluoro (2,4-dimethyl-1,3-dioxolane-2-yl) carboxylic acid sodium salt solution as the target product. The sodium fluoride content was 4.56 g (0.109 mol).

[0212] Step (2):

[0213] Into a 1 L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus, 259.72 g (146.74 g, 0.445 mol) of the aqueous solution of sodium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate obtained in step (1) and diethylene glycol dimethyl ether (300 g) were added, and the mixture was heated to 60° C. on an oil bath, and while the degree of reduced pressure was gradually increased from 13 kPa to 1 kPa, water contained in the mixture was removed by azeotropic distillation with diethylene glycol dimethyl ether, thereby obtaining 320.60 g (target product content: 145.88 g, 0.442 mol, water content: 0.09 wt%) of a diethylene glycol dimethyl ether solution of sodium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate.

[0214] Step (3):

[0215] Liquid paraffin (Fuji Film Wako Pure Chemical Industries, Ltd., initial boiling point 300°C, 146 g) was placed in a 1L glass three-necked round-bottom flask equipped with a stirrer, a dropping funnel, and a distillation apparatus with a cooling collector (two stages at -20°C and -78°C). After heating to 135°C under a reduced pressure of 30 kPa while stirring, a diethylene glycol dimethyl ether solution (320.6 g) of the sodium salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid prepared in step (2) was added dropwise over 3 hours, and the mixture was further maintained under the same reduced pressure and temperature for 1 hour. After the reaction was completed, trifluorotoluene was used as an internal standard substance. 19 F-NMR analysis of the product (78.02 g) recovered in the cold collector confirmed the generation of 73.34 g (0.301 mol, 68% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane). It should be noted that the generation amount of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) was 4.55 g (3.9% yield).

[0216] <Example 7>

[0217] (Method of using magnesium salt as alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid)

[0218] Process (1):

[0219] Magnesium carbonate (40.64 g, 0.482 mol) and water (200 mL) were added to a 1 L glass three-necked round-bottom flask equipped with a stirrer and a dropping funnel, and a suspension was prepared while stirring, and then cooled to 0° C. on an ice bath.

[0220] Next, the perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) (152.36 g, pure component 145.00 g, 0.468 mol) prepared in Reference Example 1 was added dropwise to the above three-necked round-bottom flask over 1 hour while controlling heat release in the temperature range of 0 to 10°C, and then stirred for 1 hour in the same temperature range. After standing for 1 hour, the lower layer was separated and extracted by liquid separation operation to obtain 241.32 g (pure component 137.43 g, 0.215 mol, yield 92%) of aqueous bis[perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylic acid] magnesium salt solution as the target product. The magnesium fluoride content was 1.32 g (0.021 mol).

[0221] Step (2):

[0222] Into a 1 L three-necked glass round-bottom flask equipped with a stirrer and a distillation apparatus, 241.32 g (137.43 g, 0.215 mol, yield 92%) of the bis[perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid] magnesium salt solution obtained in step (1) and diethylene glycol dimethyl ether (300 g) were added, and the mixture was heated to 60° C. on an oil bath, and while the degree of reduced pressure was gradually increased from 13 kPa to 1 kPa, water contained in the mixture was removed by azeotropic distillation with diethylene glycol dimethyl ether, thereby obtaining 382.41 g (target product content 136.20 g, 0.213 mol, water content 0.07 wt%) of a diethylene glycol dimethyl ether solution of bis[perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid] magnesium salt.

[0223] Step (3):

[0224] Liquid paraffin (Fuji Film Wako Pure Chemical Industries, Ltd., initial boiling point 300°C, 136 g) was added to a 1L glass three-necked round-bottom flask equipped with a stirrer, a dropping funnel, and a distillation apparatus with a cold collector (two stages of -20°C and -78°C). After heating to 140°C while stirring under a reduced pressure of 30 kPa, the above-mentioned diethylene glycol dimethyl ether solution (382.4 g) of bis[perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid] magnesium salt was added dropwise over 3 hours, and the mixture was further maintained under the same reduced pressure and at the same temperature for 1 hour. After the reaction was completed, trifluorotoluene was used as an internal standard substance, and the reaction mixture was stirred at 40°C for 3 hours. 19 F-NMR analysis of the product (74.24 g) recovered in the cold collector confirmed the generation of 67.56 g (0.277 mol, 65% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane). It should be noted that the generation amount of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) was 4.50 g (4.0% yield).

[0225] In Examples 1 to 7, perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be obtained by decarbonation reaction in a liquid phase system that can be easily implemented on an industrial scale. By comparing Examples 1 to 7 with Comparative Example 1, it can be confirmed that in Examples 1 to 7, perfluoro(2-methylene-4-methyl-1,3-dioxolane) is obtained at a higher yield than in Comparative Example 1; and the generation of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) as a by-product can be suppressed.

[0226] [Examples and Comparative Examples Related to Form B]

[0227] <Example 8>

[0228] Synthesis of Perfluoro(2-Methylene-4-methyl-1,3-dioxolane)

[0229] In a 1L three-necked round-bottom flask, the potassium salt aqueous solution of perfluoro(2,4-dimethyl-1,3-dioxolane-2-yl)carboxylate (270 g, pure component 160.2 g, 0.463 mol), diethylene glycol dimethyl ether (320 g) and 30 wt% potassium carbonate aqueous solution (120 g) obtained in Reference Example 2 were added and stirred for 0.5 hour. After standing for 0.5 hour, the upper layer was separated and extracted from the reaction product separated into two layers by liquid separation operation.

[0230] Next, the upper layer after separation and extraction was added to a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus, and heated at 60°C on an oil bath. While gradually increasing the degree of reduced pressure from 13 kPa to 1 kPa, water and diethylene glycol dimethyl ether were azeotropically distilled off to obtain 411.5 g of a diethylene glycol dimethyl ether solution of potassium salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (target content 158.8 g, 0.459 mol, water content 0.06 wt%).

[0231] Next, liquid paraffin (Fuji Film and Wako Pure Chemical Industries, Ltd., initial boiling point 300°C, 159 g) was added to a 1L glass three-necked round-bottom flask equipped with a stirrer, a dropping funnel, and a distillation apparatus with a cold collector (two stages of -20°C and -78°C), and heated to 130°C while stirring under a reduced pressure of 30 kPa. Then, the above-mentioned diethylene glycol dimethyl ether solution (411.5 g) of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt was added dropwise over 3 hours, and the mixture was further kept at the same reduced pressure and temperature for 1 hour. After the reaction was completed, trifluorotoluene was used as an internal standard substance, and the reaction mixture was stirred at 40 °C for 1 hour. 19F-NMR analysis of the product (99.66 g) recovered to the cold collector confirmed the generation of 92.96 g (0.381 mol, 83% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane). It should be noted that the generation amount of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) was 3.64 g (3.0% yield).

[0232] The product recovered from the cold collector was added to a distillation apparatus equipped with a Kiriyama Pac10-stage distillation tower and a 200 mL round-bottom flask with a stirrer, and precision distillation was performed at a distribution ratio of 10 / 1 at normal pressure to obtain purified perfluoro(2-methylene-4-methyl-1,3-dioxolane) (boiling point 43-44°C, 76.2 g, purity 98.2%).

[0233] 19 F-NMR (CDCl3, 376MHz) δ -82.08 (m), -83.90 (dq, J=136.3Hz, 7.5Hz), -90.30 (dq, J=136. 3Hz, 5.0Hz), -126.78 (d, J=124.1Hz), -128.13 (dquin, J=124.1Hz, 1.0Hz), -130.48 (m).

[0234] <Example 9>

[0235] Synthesis of Perfluoro(2-Methylene-4-methyl-1,3-dioxolane)

[0236] Liquid paraffin (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd., initial boiling point 300°C, 159 g) was added to a 1L glass three-necked round-bottom flask equipped with a stirrer, a dropping funnel, and a distillation apparatus with a cold collector (two stages of -20°C and -78°C), and heated to 130°C while stirring under a reduced pressure of 30 kPa. Perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt (171.3 g, pure component 158.8 g, 0.459 mol) obtained in Reference Example 3 was dissolved in diethylene glycol dimethyl ether (238.2 g), and then it was added dropwise from the dropping funnel over 3 hours, and then maintained under the same reduced pressure and temperature for 1 hour. After the reaction was completed, trifluorotoluene was used as an internal standard substance, and the reaction mixture was stirred at room temperature for 1 hour. 19 F-NMR analysis of the product recovered in the cold collector confirmed the generation of 87.35 g (0.358 mol, 78% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane). It should be noted that the generation amount of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) was 4.12 g (3.4% yield).

[0237] <Comparative Example 2>

[0238] Synthesis of Perfluoro(2-Methylene-4-methyl-1,3-dioxolane)

[0239] In a 1L glass three-necked round-bottom flask equipped with a stirrer and a distillation apparatus with a cold collector (two stages at -20°C and -78°C), potassium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate (171.3 g, pure component 158.8 g, 0.459 mol) and diethylene glycol dimethyl ether (238.2 g) prepared in Reference Example 3 were added. Under a reduced pressure of 30 kPa, the mixture was slowly heated to 130°C while stirring, and the reaction was carried out for 4 hours. After the reaction was completed, trifluorotoluene was used as an internal standard substance, and the reaction was carried out by 19 The product recovered in the cold collector was analyzed by F-NMR, confirming the generation of 49.28 g (0.202 mol, 44% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 15.75 g (13% yield) of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane).

[0240] <Examples 10 to 15>

[0241] Synthesis of Perfluoro(2-Methylene-4-methyl-1,3-dioxolane)

[0242] The reaction was carried out in the same manner as in Example 9 except that the aprotic solvent A, the aprotic solvent B, and the reaction conditions were respectively those shown in Table 1. 19 F-NMR analysis The product recovered to the cold collector was analyzed to calculate the yields of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane), respectively.

[0243] [Table 1]

[0244]

[0245] Perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt: PPDD

[0246] Perfluoro(2-methylene-4-methyl-1,3-dioxolane): PMMD

[0247] 2-Hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane): PDHD

[0248] <Example 16>

[0249] Synthesis of Perfluoro(2-Methylene-4-methyl-1,3-dioxolane)

[0250] Into a 1L three-necked glass round-bottom flask equipped with a stirrer and a distillation apparatus were added 259.72 g (146.74 g, 0.445 mol) of the aqueous solution of sodium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate obtained in Reference Example 4 and diethylene glycol dimethyl ether (300 g), and the mixture was heated at 60°C on an oil bath. While gradually increasing the degree of reduced pressure from 13 kPa to 1 kPa, water and diethylene glycol dimethyl ether were removed by azeotropic distillation to obtain 320.60 g (target content 145.88 g, 0.442 mol) of diethylene glycol dimethyl ether solution of sodium perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylate. Next, a 1L glass three-necked round-bottom flask equipped with a stirrer, a dropping funnel, and a distillation apparatus with a cold collector (two stages of -20°C and -78°C) was added with liquid paraffin (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd., initial boiling point 300°C, 146 g), and heated to 135°C under a reduced pressure of 30 kPa while stirring, and then the above-mentioned diethylene glycol dimethyl ether solution (320.6 g) of sodium salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid was added dropwise over 3 hours, and further maintained at the same reduced pressure and temperature for 1 hour. After the reaction was completed, trifluorotoluene was used as an internal standard substance, and the reaction mixture was stirred at room temperature for 1 hour. 19 The product (78.02 g) recovered to the cold collector was analyzed by F-NMR, confirming the generation of 73.34 g (0.301 mol, 68% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane). It should be noted that the generation amount of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) was 4.55 g (3.9% yield).

[0251] <Example 17>

[0252] Synthesis of Perfluoro(2-Methylene-4-methyl-1,3-dioxolane)

[0253] Into a 1L three-necked glass round-bottom flask equipped with a stirrer and a distillation apparatus, 241.32 g (137.43 g, 0.215 mol) of the aqueous solution of magnesium bis[perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid] obtained in Reference Example 5 and diethylene glycol dimethyl ether (300 g) were added, and the mixture was heated to 60°C on an oil bath. While gradually increasing the degree of reduced pressure at a pressure of 13 kPa to 1 kPa, water and diethylene glycol dimethyl ether were azeotropically distilled off to obtain 382.41 g (target content 136.20 g, 0.213 mol) of magnesium bis[perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid] in diethylene glycol dimethyl ether.

[0254] Next, liquid paraffin (Fuji Film Wako Pure Chemical Industries, Ltd., initial boiling point 300°C, 136 g) was added to a 1L glass three-necked round-bottom flask equipped with a stirrer, a dropping funnel, and a distillation apparatus with a cold collector (two stages of -20°C and -78°C), and heated to 140°C while stirring under a reduced pressure of 30 kPa. The above-mentioned diethylene glycol dimethyl ether solution (382.4 g) of bis[perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid] magnesium salt was added dropwise over 3 hours, and the mixture was further maintained under the same reduced pressure and at the same temperature for 1 hour. After the reaction was completed, trifluorotoluene was used as an internal standard substance, and the reaction mixture was stirred at 40°C for 3 hours. 19 F-NMR analysis of the product (74.24 g) recovered to the cold collector confirmed the generation of 67.56 g (0.277 mol, 65% yield) of perfluoro(2-methylene-4-methyl-1,3-dioxolane). It should be noted that the generation amount of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) was 4.50 g (4.0% yield).

[0255] In Examples 8 to 17, perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be obtained by a decarbonation reaction in a liquid phase system that is easily implemented on an industrial scale. By comparing Examples 8 to 17 with Comparative Example 2, it can be confirmed that in Examples 8 to 17, perfluoro(2-methylene-4-methyl-1,3-dioxolane) can be obtained at a yield equal to or higher than that of Comparative Example 2 in which a decarbonation reaction in a solid phase system is performed; and the generation of 2-hydrogen-perfluoro(2,4-dimethyl-1,3-dioxolane) as a by-product can be suppressed to a yield equal to or lower than that of Comparative Example 2.

[0256] Through the various methods described above, it is possible to realize the industrial-scale implementation of perfluoro(2-methylene-4-methyl-1,3-dioxolane). The perfluoro(2-methylene-4-methyl-1,3-dioxolane) thus obtained can be used as a raw material for synthesizing poly[(perfluoro(2-methylene-4-methyl-1,3-dioxolane)] which is expected to be a resin for gas separation membranes and a transparent resin for optical fibers.

[0257] This application claims priority to Japanese Patent Application No. 2018-208937 filed on November 6, 2018 and Japanese Patent Application No. 2018-208938 filed on November 6, 2018, the entire contents of which are expressly cited herein as disclosed.

Claims

1. A method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane), the method comprising at least the following steps (1) to (3): (1) reacting at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, and separating and extracting a liquid containing the generated perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt by liquid separation operation, wherein the hydrolysis product of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) is a mixture of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid and hydrogen fluoride; (2) subjecting the obtained liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid to one or more water content reduction treatments selected from the group consisting of water distillation removal and water adsorption to obtain an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid in the form of a solution or a solid; (3) using the obtained solution or solid perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt to carry out a decarbonation reaction in a liquid phase system to produce perfluoro(2-methylene-4-methyl-1,3-dioxolane), and adding one or more aprotic solvents C in at least any one of before, after and after the liquid separation operation with the alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions in step (1), wherein the aprotic solvent C is at least one selected from diisopropyl ether, dibutyl ether, anisole, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, The solvent used in step (3) is at least one selected from diisopropyl ether, dibutyl ether, anisole, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

2. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 1, comprising: After the liquid containing the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid is separated and extracted by the liquid separation operation in step (1), the following step (4) is further performed. (4) performing the following operation one or more times: further contacting the liquid containing perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt obtained in step (1) with water or water in which an inorganic salt is dissolved, followed by performing a liquid separation operation to separate and extract the liquid containing perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt again.

3. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 1, wherein The aprotic solvent C is at least one selected from diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

4. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 1, wherein The aprotic solvent C is diethylene glycol dimethyl ether.

5. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 1, wherein The water content reduction treatment in step (2) includes distilling off water in the presence of one or more azeotropic solvents that form an azeotropic composition with water.

6. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 1, wherein The water content reduction treatment in step (2) includes distilling off water in the presence of one or more azeotropic solvents that form an azeotropic composition with water and have a boiling point lower than that of the aprotic solvent C added in step (1).

7. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 5 or 6, wherein The azeotropic solvent is one or more solvents selected from isopropyl alcohol and toluene.

8. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 1 or 2, wherein In the step (3), when the decarbonation reaction is carried out in a liquid phase system, the solvent contained in the liquid phase system contains a glycol diether-based solvent.

9. A method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane), the method comprising: A reactive distillation step of continuously supplying a raw material liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid to a reactive distillation device to perform reactive distillation to produce perfluoro(2-methylene-4-methyl-1,3-dioxolane), in, The reactive distillation step further comprises: A raw material solution of an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid dissolved in an aprotic solvent A is continuously supplied under reduced pressure to an aprotic solvent B heated in a reactive distillation vessel, and a reaction is performed while the generated perfluoro(2-methylene-4-methyl-1,3-dioxolane) is distilled out of the system. The aprotic solvent B is the same as or different from the aprotic solvent A and has a boiling point that is the same as or higher than that of the aprotic solvent A. The amount of the aprotic solvent A used is 0.5 to 5 times by weight, the amount of the aprotic solvent B used is 0.2 to 5.0 times by weight, the aprotic solvent B has a boiling point of 130° C. or higher, relative to the alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or the alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid, and the amount of the aprotic solvent A used is 0.5 to 5 times by weight, the amount of the aprotic solvent B used is 0.2 to 5.0 times by weight, and the aprotic solvent B has a boiling point of 130° C. or higher. The aprotic solvent A is at least one selected from diisopropyl ether, dibutyl ether, anisole, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, The aprotic solvent B is at least one selected from dibutyl ether, diphenyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dodecane, decalin, and liquid paraffin.

10. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 9, wherein The aprotic solvent A contains at least one selected from diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

11. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 9, wherein The aprotic solvent A contains diethylene glycol dimethyl ether.

12. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 9, wherein The aprotic solvent B contains at least one selected from dodecane, decalin, and liquid paraffin.

13. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 12, wherein The aprotic solvent B contains liquid paraffin.

14. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 9, wherein The aprotic solvent B contains at least one selected from the group consisting of dibutyl ether, diphenyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

15. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 14, wherein The aprotic solvent B contains tetraethylene glycol dimethyl ether.

16. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 9, wherein The raw material liquid contains perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid potassium salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid sodium salt.

17. The method for producing perfluoro(2-methylene-4-methyl-1,3-dioxolane) according to claim 9, further comprising the following steps (1) and (2): (1) reacting at least one of perfluoro(2,4-dimethyl-2-fluoroformyl-1,3-dioxolane) and its hydrolysis product with an alkaline aqueous solution containing one or more cations selected from alkali metal ions and alkaline earth metal ions, and then separating and extracting a liquid containing the generated perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkali metal salt or perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid alkaline earth metal salt by liquid separation operation; (2) subjecting the obtained liquid containing an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid to one or more water content reduction treatments selected from the group consisting of distillation removal of water and adsorption of water, thereby obtaining an alkali metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid or an alkaline earth metal salt of perfluoro(2,4-dimethyl-1,3-dioxolan-2-yl)carboxylic acid in the form of a solution or a solid.

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