JP2011251927A - METHOD FOR PRODUCING α-ALKYL-SUBSTITUTED ESTER COMPOUND - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an α-alkyl-substituted ester in a high yield by reacting an ester compound with a dialkyl carbonate in the presence of a basic catalyst.SOLUTION: In the method for producing an α-alkyl-substituted ester such as α-methyl-γ-butyrolactone by reacting an ester compound such as γ-butyrolactone with a dialkyl carbonate such as dimethyl carbonate in the presence of a basic catalyst, a compound having an ether bond is allowed to exist in the reaction system. By allowing the compound having an ether bond to exist in the reaction system, the reaction efficiency between the ester compound and the dialkyl carbonate can be raised and the α-alkyl-substituted ester can be produced in a high yield.

Description

The present invention relates to a method for producing an α-alkyl-substituted ester by reacting an ester compound and dialkyl carbonate in the presence of a basic catalyst.
Specifically, the present invention relates to a method for producing an α-alkyl substituted ester such as α-methyl-γ-butyrolactone by reacting an ester compound such as γ-butyrolactone with a dialkyl carbonate such as dimethyl carbonate in the presence of a basic catalyst.

  Α-Methyl-γ-butyrolactone produced in the present invention is industrially extremely useful as an intermediate for producing 3-methyltetrahydrofuran, which is a monomer for producing polyether polyol, which is a raw material for producing highly functional elastic fibers. It is.

  Polyurethane resins using polytetramethylene ether glycol (hereinafter sometimes abbreviated as PTMG) obtained by ring-opening polymerization of tetrahydrofuran (hereinafter sometimes abbreviated as THF) have elastic properties, low temperature properties, Since it is excellent in mechanical properties such as hydrolyzability, it is widely used as elastic fibers and thermoplastic polyurethane elastomers. For the purpose of improving the mechanical properties of this polyurethane resin, a polyether polyol obtained by copolymerizing 3-methyltetrahydrofuran (hereinafter sometimes abbreviated as 3-MeTHF) in addition to THF is used as a urethane resin raw material. Things have been done. It is known that a polyurethane produced by using a polyether polyol obtained by copolymerizing THF and 3-MeTHF has improved mechanical properties as compared with the case of using polytetramethylene ether glycol (Japanese Patent Laid-Open No. Sho 63-63). No. 235320).

  While 3-MeTHF is a useful substance, since the difficulty of production is high, synthesis methods have been extensively studied, and many production methods have been proposed. Issues such as high calorific value, high load on production equipment such as the need for safety equipment because of the use of toxic substances as raw materials, problems such as high raw material costs and low selectivity in reactions There was a point.

  In view of the above-mentioned problems of the prior art, the present inventors use a raw material that is inexpensive and easily available, is excellent in safety, has a high yield, and can be industrially implemented with high purity 3-MeTHF. As a result of intensive studies to provide a production method, as a starting material, γ-butyrolactone (hereinafter sometimes abbreviated as GBL) was used as a starting material, and α-methyl-γ-butyrolactone (hereinafter referred to as “α”) was methylated at the α-position of GBL. And may be abbreviated as α-Me-GBL), and found that the above problem can be solved by producing 3-MeTHF, and using α-butyrolactone (GBL) as a raw material, the α-position of GBL It includes a step (1) for obtaining α-methyl-γ-butyrolactone (α-Me-GBL) by methylation and a step (2) for obtaining 3-methyltetrahydrofuran (3-MeTHF) from α-Me-GBL. About the manufacturing method of 3-methyltetrahydrofuran characterized by this, a patent application was filed prior to the present applicant (Japanese Patent Application No. 2010-33941, hereinafter referred to as a prior application).

  Specifically, in the method of the prior application, α-Me-GBL is produced by reacting GBL with dimethyl carbonate (hereinafter sometimes abbreviated as DMC) in the presence of potassium carbonate.

  A method for producing α-Me-GBL by reacting GBL and DMC in the presence of a basic catalyst such as potassium carbonate is also described in WO 02/10116 pamphlet.

JP-A-63-235320 Japanese Patent Application No. 2010-33941 WO 02/10116 pamphlet

  However, the reaction results in the conventional alkylation reaction were as follows: the reaction temperature was 215 ° C., the GBL conversion was about 70% when the reaction time was 7 hours, and the α-Me-GBL yield was about 60%. It was. For this reason, in order to construct an efficient industrialization process, it is desired to improve the conversion efficiency and yield, and shorten the reaction time to improve the production efficiency.

  An object of the present invention is to provide a method for efficiently producing an α-alkyl-substituted ester by reacting an ester compound and dialkyl carbonate in the presence of a basic catalyst.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have made a reaction system when an α-alkyl-substituted ester is produced by reacting an ester compound and a dialkyl carbonate in the presence of a basic catalyst. It has been found that the presence of a compound having an ether bond can shorten the reaction time and can also improve the yield of the α-alkyl-substituted ester.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] In a method for producing an α-alkyl-substituted ester by reacting an ester compound and a dialkyl carbonate in the presence of a basic catalyst, a compound having an ether bond is present in the reaction system. A method for producing an alkyl-substituted ester compound.

[2] The method for producing an α-alkyl-substituted ester compound according to [1], wherein the compound having an ether bond has 6 or more carbon atoms and 2 or more ether bonds.

[3] The method for producing an α-alkyl-substituted ester compound according to [1] or [2], wherein the compound having an ether bond has a substituent capable of coordinating or hydrogen bonding to a cation.

[4] The method for producing an α-alkyl-substituted ester compound according to [3], wherein the substituent capable of coordinating or hydrogen bonding to the cation is one or more selected from a hydroxyl group, an amino group, and an imino group.

[5] The α-alkyl-substituted ester according to any one of [1] to [3], wherein the compound having an ether bond is at least one selected from crown ether, polyalkylene glycol, and polyalkylene glycol dialkyl ether. Compound production method.

According to the present invention, when an α-alkyl-substituted ester is produced by reacting an ester compound and a dialkyl carbonate in the presence of a basic catalyst, a compound having an ether bond is present in the reaction system. Alkyl-substituted esters can be produced efficiently and in high yield.
According to the present invention, α-methyl-γ-butyrolactone, which is industrially extremely useful as an intermediate for producing 3-methyltetrahydrofuran as a monomer for producing a polyether polyol, which is a raw material for producing high-performance elastic fibers, It becomes possible to manufacture with a high yield, and this makes it possible to improve the production efficiency of 3-methyltetrahydrofuran and further polyether polyol.

  Hereinafter, embodiments of the method for producing an α-alkyl-substituted ester compound of the present invention will be described in detail.

  The method for producing an α-alkyl-substituted ester compound of the present invention is a method for producing an α-alkyl-substituted ester by reacting an ester compound and a dialkyl carbonate in the presence of a basic catalyst, in the presence of a compound having an ether bond. It is characterized by performing a reaction.

[Action mechanism]
In the present invention, the action mechanism of the effect that the reaction rate of the α-alkyl-substituted esterification reaction is improved by the presence of a compound having an ether bond in the reaction system is considered as follows.

That is, in the α-alkylation reaction according to the present invention, the α-position hydrogen atom of the ester compound is first extracted by a basic catalyst, and the reaction between the hydrogen atom-extracted portion and the dialkyl carbonate results in the intermediate carboalkoxy. Converted to a derivative. The intermediate is deprotonated again by a base present in the system (basic catalyst, alkoxide derived from dialkyl carbonate, etc.), and the resulting anion and dialkyl carbonate react to advance the alkylation of α position. .
The reaction between the α-alkylated intermediate and the alkoxide present in the system regenerates the dialkyl carbonate, and the intermediate passes through an α-alkyl-substituted ester in which the α-position is anionized with an alcohol. The α-alkyl-substituted ester, which is the target product, is obtained by the proton exchange reaction.

In this reaction process, if a cation is present near the anion from which the α-position hydrogen atom of the ester compound has been removed, the reactivity of the carbonyl group α-position anion due to cation-anion electrical neutralization or steric crowding of the cation. It is considered that the reaction between the ester compound and the dialkyl carbonate is inhibited.
Further, when an alkoxide anion acting as a base or a nucleophile can interact with a cation at each stage of the reaction, the negative charge of the anion is electrically neutralized by the cation positive charge and the reactivity is lowered.

  In such a reaction system, according to the present invention, the presence of a compound having an ether bond capable of interacting with a cation allows the anionic species at each stage of the reaction mechanism to interact electrostatically and sterically with the cation. As a result, it is estimated that the reactivity is improved and the reaction rate is also improved.

[Α-alkylation reaction]
The α-alkylation reaction of the ester compound in the present invention refers to a reaction in which an alkyl group is introduced into the α-position carbon of the ester compound. The alkyl group introduced here may have a substituent such as a hydroxyl group, and is preferably an alkyl group having no substituent.
Specifically, for example, the reaction is represented by the following reaction formula (1).

In the above reaction formula, R ₁ represents a hydrogen atom or a monovalent alkyl group having 10 or less carbon atoms, R ₂ represents a monovalent alkyl group having 10 or less carbon atoms, and R ₁ and R ₂ are bonded to each other to form a ring. May be formed. X and Y are each independently a monovalent alkyl group usually having 1 to 10 carbon atoms, and X and Y may be bonded to each other to form a ring. Preferably those which do not form a ring are preferred, more preferably a linear alkyl group, and even more preferably those wherein X and Y are the same.

More specifically, α-methylation using γ-butyrolactone (GBL) as the ester compound, dimethyl carbonate (DMC) as the dialkyl carbonate, and potassium carbonate (K ₂ CO ₃ ) as the basic catalyst. The reaction is represented by the following reaction formula (2) (Me is a methyl group).

[Ester compound]
In the present invention, the ester compound that is a raw material for α-alkylation is represented by R ₁ —CH ₂ —C (═O) —OR ₂ as described above, and R ₁ is a hydrogen atom or a monovalent having 10 or less carbon atoms. Alkyl group, preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. R ₂ is a monovalent alkyl group having 10 or less carbon atoms, preferably a monovalent alkyl group having 1 to 6 carbon atoms.
R ₁ and R ₂ may combine with each other to form a ring. In this case, the ring formed by combining R ₁ and R ₂ preferably has 3 to 10 carbon atoms, and the formed ring is a 4- to 8-membered ring having one oxygen atom. It is preferable.

  In this invention, it is preferable that the ester compound used as a raw material is (gamma) -butyrolactone from the industrial usefulness of the alpha-alkyl substituted ester manufactured.

  γ-Butyrolactone (GBL) is a conventionally known substance, and can be produced and used according to a known method, or a commercially available product can be obtained and used. GBL is a method obtained by oxidizing 1,4-butanediol with a Ru catalyst (Japanese Patent Laid-Open No. 2002-167380), a method obtained by partially reducing maleic anhydride with a Ni-Re catalyst (Japanese Patent Laid-Open No. 06-306069), Similarly, those obtained by a known method such as a method of partially reducing maleic anhydride with a Ni—Pd catalyst (Japanese Patent Laid-Open No. 06-321926) are used.

  The GBL used is preferably of high purity. That is, 4-hydroxybutyric acid generated by ring-opening of GBL is one of the impurities of GBL, but this causes a neutralization reaction with the basic catalyst used in the production method of the present invention and is used in the reaction. It is better to reduce as much as possible to reduce the active component of the catalyst.

[Dialkyl carbonate]
In the present invention, the dialkyl carbonate as the α-alkylating reagent is represented by XO—C (═O) —OY as described above, and X and Y are each independently a monovalent monovalent having 1 to 10 carbon atoms. An alkyl group, preferably a monovalent alkyl group having 1 to 6 carbon atoms, more preferably a monovalent linear alkyl group having 1 to 6 carbon atoms. More preferably, X and Y are the same.

X and Y may be bonded to each other to form a ring. When a ring is formed, the number of carbon atoms is not particularly limited, but is usually 1 or more and 10 or less, preferably 6 or less.
When a compound in which X and Y form a ring (hereinafter sometimes referred to as a cyclic carbonate) is used as a dialkyl carbonate in the present invention, an ω-hydroxyalkyl ester compound having a hydroxyalkyl group introduced therein can be obtained.
The dialkyl carbonate used in the present invention is preferably one having a monovalent alkyl group having 1 to 10 carbon atoms in which X and Y do not form a ring from the industrial utility, and more preferably. Are the same in X and Y.

  From the industrial usefulness and reactivity of the α-alkyl-substituted ester to be produced, the dialkyl carbonate is preferably dimethyl carbonate (DMC).

  Dimethyl carbonate (DMC) is a known compound, and can be produced and used according to a known method, or a commercially available product can be obtained and used.

  DMC has low toxicity, is easy to procure, and is available in industrial quantities. The DMC used for the production of α-Me-GBL is not particularly limited, but it is desirable to have a high purity. In particular, the smaller the water content and methanol content, the better.

  The amount of dialkyl carbonate used in the α-alkylation reaction in the present invention is not particularly limited, but is usually 1.0 mol, preferably the lower limit is the theoretical equivalent with respect to 1 mol of the ester compound. 1.2 mol, more preferably 1.5 mol. The upper limit is not particularly limited, but is usually 10.0 mol, preferably 5.0 mol, and more preferably 3.0 mol. If the upper limit is exceeded, the occupied capacity of the dialkyl carbonate with respect to the reactor volume increases, and the space production efficiency may decrease.

[Basic catalyst]
The basic catalyst used in the α-alkylation reaction in the present invention is not particularly limited, but alkali metals such as sodium and potassium; metal amides such as lithium diisopropylamide; amines; alkali metals and alkaline earths Metals such as metals, carbonates of transition metals, bicarbonates, carboxylates such as hydroxides and acetates, metal compounds such as oxides; metal alkoxides are used. In addition, heterogeneous basic catalysts such as alkali metal, alkaline earth metal complex oxides, and base-treated zeolites can also be used.

  Examples of the amines include chain aliphatic amines such as diisopropylamine, triethylamine, tributylamine, N, N-diisopropylethylamine, tetramethylenehexamine, and trioctylamine; 1,4-dimethylpiperazine, piperazine, piperidine, 1-benzylpiperidine, 1-methyl-2,2-dimethyl-6,6-dimethylpiperidine, DABCO (1,4-diazabicyclo [2.2.2] octane), DBU (1,8-diazabicyclo [5,4] , 0] -7-undecene), DBN (1,5-diazabicyclo [4,3,0] -5-undecene); aromatic amines such as triphenylamine; N, N -Benzylamines such as dimethylbenzylamine, N, N-phenyldibenzylamine; Pyridines such as lysine and 4-dimethylaminopyridine; imidazole, 1-methylimidazole, 1-ethylimidazole, 1-methyl-2-methylimidazole, 1-isobutyl-2-methylimidazole, 1-benzyl-2-methylimidazole 1-benzyl-2-phenylimidazole, 2-undecylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, TBZ (2,3- Dihydro-1H-pyrrolo [1,2-a] benzimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-dodecyl-2-methyl- Such imidazole compounds; Cycloalkenyl phosphine or trivalent phosphorus compounds such as triphenyl phosphite, phosphazene compounds, and the like.

  Of these, chain aliphatic amines, cyclic amines, and phosphazene compounds are preferred because of their strong basicity and easy deprotonation. As the chain aliphatic amines, chain aliphatic tertiary amines having a long alkyl chain such as trioctylamine are preferable in that they can be easily separated from the reaction product, and the cyclic amines are preferably Cyclic amines having an ene-imine structure such as DBU and DBN, which can increase the reaction activity by the formation of acyl intermediates, are preferred.

  Specific examples of the alkali metal compound include sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, cesium carbonate, lithium carbonate, sodium acetate, potassium acetate, cesium acetate. , Lithium acetate, sodium stearate, potassium stearate, cesium stearate, lithium stearate, sodium benzoate, potassium benzoate, cesium benzoate, lithium benzoate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, phosphoric acid Examples thereof include dilithium hydrogen, disodium phenylphosphate, disodium salt of bisphenol A, dipotassium salt, cesium salt, dilithium salt, sodium salt of phenol, potassium salt, cesium salt, and lithium salt.

  Examples of the alkaline earth metal compound include magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, magnesium bicarbonate, calcium bicarbonate, strontium bicarbonate, barium bicarbonate, magnesium carbonate, calcium carbonate, carbonate Examples include strontium, barium carbonate, magnesium acetate, calcium acetate, strontium acetate, barium acetate, magnesium stearate, calcium stearate, calcium benzoate, and magnesium phenyl phosphate.

  Examples of the metal alkoxide include sodium alkoxide such as sodium methoxide and sodium ethoxide, potassium alkoxide such as potassium t-butoxide, and the like.

  Examples of heterogeneous basic catalysts include calcium-barium-sodium oxide, calcium-barium-potassium oxide, calcium-barium-cesium oxide and other alkali metal-alkaline earth metal composite oxides, magnesium-calcium- Examples include alkaline earth metal composite oxides such as barium oxide, magnesium-strontium-barium oxide, and base-treated zeolite treated with sodium, potassium ions, and the like.

  Among these, alkali metal alkoxides, alkali metal hydroxides, and alkali metal carbonates are preferable in terms of high reactivity, and further sodium methoxide, potassium methoxide, potassium t-butoxide, sodium hydroxide, water Potassium oxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and cesium hydrogen carbonate are preferred. Furthermore, sodium methoxide and potassium carbonate are particularly preferred from the viewpoint of cost and availability.

  These basic catalysts may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  Although the usage-amount of these basic catalysts is not specifically limited, Usually, it is 5.0 mol or less with respect to 1 mol of ester compounds, Preferably it is 3.0 mol or less, More preferably, it is 1.0 mol or less. If the upper limit is exceeded, the production cost may increase and the stirring efficiency of the reactor contents may decrease. Moreover, it is 0.01 mol or more normally with respect to 1 mol of ester compounds, Preferably it is 0.1 mol or more, More preferably, it is 0.2 mol or more. If it is less than the lower limit, a practical reaction rate may not be obtained.

[Compound having an ether bond]
In the present invention, the compound having an ether bond present in the α-position alkylation reaction system preferably has 6 or more carbon atoms and 2 or more ether bonds.

  When the number of carbon atoms of the compound having an ether bond is less than 6, the above-described cation excretion action cannot be sufficiently obtained. In terms of cation excretion, this carbon number is preferably 8 or more, particularly 10 or more. The upper limit of the number of carbon atoms of the compound having an ether bond is not particularly limited, but the amount used in the case of maintaining the solubility of the compound having an ether bond in a dialkyl carbonate or ester compound and maintaining a constant ether / cation molar ratio. From the viewpoint of cost reduction in reduction and effective utilization of the reactor volume, it is usually 40 or less, and particularly preferably 30 or less.

  Similarly, when the number of ether bonds of the compound having an ether bond is less than 2, the above-described cation excretion action cannot be sufficiently obtained. In terms of cation excretion, the number of ether bonds is preferably 3 or more, particularly 5 or more. The upper limit of the number of ether bonds of a compound having an ether bond is not particularly limited, but the solubility of the compound having an ether bond in a dialkyl carbonate or an ester compound is maintained, and the use when the ether / cation molar ratio is constant is used. 20 or less, especially 15 or less are preferable from the viewpoint of cost reduction by reducing the amount and effective utilization of the reactor volume.

  The compound having an ether bond capable of coordinating or electrostatically interacting with the cation used in the present invention is preferably a compound having a substituent capable of coordinating or hydrogen bonding with the cation. It is preferable in terms of excretion action. Preferred examples of the substituent capable of coordinating or hydrogen bonding to the cation include a hydroxyl group, an amino group, and an imino group.

  In addition, the compound having an ether bond used in the present invention is preferably a compound having a functional group capable of strongly coordinating or electrostatically interacting with a cationic species for the purpose of enhancing the cation excretion action. Examples of the functional group that can strongly coordinate or electrostatically interact with the cationic species include a functional group having a lone electron pair such as a hydroxyl group, an amino group, and an imino group.

  Although it does not specifically limit as a compound which has an ether bond, Specifically, crown ether, polyalkylene glycol (carbon number of an alkylene group is 1-6), polyalkylene glycol dialkyl ether (carbon of an alkylene group). The number is 1-6, the carbon number of the alkyl group is 1-6), polyether polyamine, cyclodextrin and the like.

As the crown ether,
12-crown-4, benzo 12-crown-4, dibenzo 12-crown-4, cyclohexyl 12-crown-4, dicyclohexyl 12-crown-4, (2-hydroxyethyl) 12-crown-4, (3-hydroxy 12-crown ethers such as propyl) 12-crown-4, bis (2-hydroxyethyl) 12-crown-4, bis (3-hydroxypropyl) 12-crown-4;
15-crown-5, benzo 15-crown-5, dibenzo 15-crown-5, cyclohexyl 15-crown-5, dicyclohexyl 15-crown-5, (2-hydroxyethyl) 15-crown-5, (3-hydroxy 15-crown ethers such as propyl) 15-crown-5, bis (2-hydroxyethyl) 15-crown-5, bis (3-hydroxypropyl) 15-crown-5;
18-crown-6, benzo 18-crown-6, dibenzo 18-crown-6, cyclohexyl 18-crown-6, dicyclohexyl 18-crown-6, (2-hydroxyethyl) 18-crown-6, (3-hydroxy 18-crown ethers such as propyl) 18-crown-6, bis (2-hydroxyethyl) 18-crown-6, bis (3-hydroxypropyl) 18-crown-6;
Etc.

  These crown ethers are preferably used in consideration of the affinity with the cation used in the reaction. In other words, when a supramolecular complex is formed by interacting with a crown ether, an ion excretion effect is strongly expressed when the cation radius of the cation coincides with the ring inner diameter of the crown ether. In the reaction at the α-position of the ester, 15-crown ethers are preferably used when a sodium compound is used as the basic catalyst, and 18-crown ethers are used when a potassium compound is used as the basic catalyst. It is preferable. In addition, crown ether having a functional group capable of electrostatic interaction with a cation is also preferably used in order to improve the cation capturing ability of crown ether.

Examples of the polyalkylene glycol include pentaethylene glycol, hexaethylene glycol, tetrapropylene glycol, pentapropylene glycol, hexapropylene glycol and the like.
The polyalkylene glycol does not need to be a single component, and can be used as long as the number of carbon atoms and the number of ethers contained in the molecule are within the above-mentioned desirable ranges. The compounds contained therein are ethylene glycol having an average molecular weight of 300 (average carbon number 12.8, ether bond number 6.4), and propylene glycol having an average molecular weight 350 (average carbon number 17.7, ether bond number 5. 9) and the like.

  Examples of the polyalkylene glycol dialkyl ether include triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol dibutyl ether, tripropylene glycol dimethyl ether, tripropylene glycol dibutyl ether, tetrapropylene glycol dimethyl ether, tetratripropylene. Examples include glycol dibutyl ether, tris (tetramethylene glycol) dimethyl ether, and tetrakis (tetramethylene glycol) dimethyl ether.

  Polyether polyamines include tetraethylene glycol bis (α, ω-2-aminoethyl) ether, pentaethylene glycol bis (α, ω-2-aminoethyl) ether, 1- (2-methoxy-3-aminopropyl) Examples include tetraethylene glycol ether.

  Examples of cyclodextrins include α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin. Further, examples include per (2-aminoethyl) cyclodextrin, per (2,3-dihydroxypropyl) cyclodextrin, etc., when the hydroxyl groups of various cyclodextrins are bonded to a linking group having an ionic functional group.

  A compound having an ether bond is expected to increase the activity of a compound capable of strongly capturing a cation and reducing the electrostatic interaction between the cation and the ester or the alkoxide anion of the catalyst. From this point, it is considered that the degree of improvement in reaction activity can be compared with the complex formation constant of the compound having an ether bond and the cation used.

  When an alkali metal carbonate such as sodium carbonate or potassium carbonate is used as a basic catalyst, crown ethers having an inner diameter corresponding to the ionic radius have the largest complex formation constant, followed by long-chain polyalkylene glycol / long-chain poly Alkylene glycol amine, a long-chain polyalkylene glycol diether, and crown ethers are expected to be the compounds that provide the most improved activity, which is consistent with the results of the examples.

Polyalkylene glycols such as triethylene glycol, tetraethylene glycol, pentaethylene glycol, and polyethylene glycols having an average molecular weight of 250, 300, 400, and the like, which are mixtures thereof, are industrially easily available and suppress the additive cost. It is excellent in that point.
Further, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol dibutyl ether and the like are preferable as polyalkylene glycol alkyl ethers because they can be obtained at low cost.
Cyclodextrins can be used because they are available at low cost, and ammonium ions generated in the reaction system when bulky hydrophobic organic amines are used as catalysts compared to chain and cyclic ethers. It is excellent in that it is easy to capture.

  Of these compounds having an ether bond, crown ethers, polyalkylene glycols, and polyalkylene glycol alkyl ethers are preferred because they are excellent in terms of industry and performance.

Specific examples of the compound having an ether bond are further shown in the following structural formulas, but the present invention is not limited to the following.
In the following, Me represents a methyl group, Et represents an ethyl group, and Bu represents a butyl group.

  These compounds having an ether bond may be used singly or in combination of two or more.

  Although the usage-amount of the compound which has an ether bond is not specifically limited, It is 3 mol or less with respect to 1 mol of basic catalysts normally used for reaction, Preferably it is 2 mol or less, More preferably, it is 1 mol or less. Moreover, it is 0.01 mol or more normally with respect to 1 mol of basic catalysts, Preferably it is 0.05 mol or more, More preferably, it is 0.1 mol or more. If the upper limit is exceeded, the amount of the compound having an ether bond increases and the volumetric efficiency of the reactor decreases; excessive stirring power is required; a longer time is required for the separation step; Moreover, if it is less than the said minimum, a cation excretion effect | action is not enough and the improvement effect of the reaction rate obtained by adding the compound which has an ether bond may not be acquired.

Any method may be used when a compound having an ether bond is used in the reaction. For example, when charging the reaction, ester compound, dialkyl carbonate, a method of starting the reaction at the same time as the basic catalyst and starting the reaction, a method of dissolving in the raw materials used and adding it to the reactor as a solution, having an ether bond Examples include a method in which a compound alone is dissolved or suspended in a solvent and added to a reactor.
In addition, the compound having an ether bond may be added to the reactor at once in the amount used for the reaction, or may be divided and added to the reactor. For example, when the effect of improving the reaction rate is insufficient, it can be added in the middle of the reaction and added to the reactor. The simplest method is to add the entire amount at the start of the reaction and heat it together with other raw materials and catalyst species to cause the reaction.

[solvent]
The α-alkylation reaction according to the present invention can be performed in the absence of a solvent or using a solvent. When a solvent is used, the solvent to be used is not particularly limited as long as it does not affect the α-alkylation reaction, but an aromatic hydrocarbon solvent such as toluene and xylene, an aliphatic hydrocarbon solvent such as hexane and heptane. And ether solvents such as diethyl ether, monoethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, amide solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone are preferably used. It is done.

  Esters that do not have a hydrogen atom at the α-position of the carbonyl group and do not undergo an alkylation reaction can be used as a solvent. Examples thereof include benzoic acid esters and pivalic acid esters. Furthermore, any alcohol ester having the same alkyl group as the dialkyl carbonate to be used can be used because it does not cause cross alkylation.

These solvents may be used alone, or a plurality of arbitrary solvents may be mixed and used.
The reaction is preferably carried out without solvent.

[Additive]
When the α-alkylation reaction according to the present invention is performed, an appropriate additive other than the compound having an ether bond may be used.

[Reaction format]
As a form of the α-alkylation reaction according to the present invention, both a batch system and a continuous system can be adopted.

[Reaction conditions]
The temperature during the α-alkylation reaction in the present invention is not particularly limited, but is important for suppressing the progress of side reactions. The upper limit is usually 250 ° C., preferably 230 ° C., most preferably 220 ° C., and the lower limit is usually 170 ° C. or higher, preferably 190 ° C. or higher, more preferably 200 ° C. or higher. When the upper limit is exceeded, for example, in the case of the reaction of GBL and DMC, it is a reaction product of 4-alkoxide and DMC generated by the ring-opening reaction of the raw material GBL and the product α-Me-GBL 4 Side reactions may occur in which methyl (methoxycarboxy) butyrate, methyl 4- (methoxycarboxy) -2-methylbutyrate and methylation products methyl 4-methoxybutyrate and methyl 4-methoxy-2-methylbutyrate may occur. is there. If the amount is less than the lower limit, a practical reaction rate may not be obtained, or a by-product in which the GBL ring is opened, or a by-product in which two molecules are esterified and dimerized may be generated.

  The reaction time of the α-alkylation reaction in the present invention is not particularly limited, but the upper limit is usually 50 hours or less, preferably 30 hours or less, most preferably 20 hours or less, and the lower limit is usually 1 Time or more, preferably 2 hours or more, more preferably 3 hours or more. In the case where the upper limit is exceeded, for example, when GBL is used as a raw material, the ring-opening reaction of the GBL ring may proceed. On the other hand, when the lower limit is exceeded, a large amount of ester compound such as GBL as the raw material remains. There is.

In the α-position alkylation reaction in the present invention, CO ₂ is generated as the reaction proceeds. Since CO ₂ may poison the basic catalyst used in the reaction, the reaction may be carried out while removing CO ₂ from the system continuously or discontinuously. In this case, when the dialkyl carbonate of the α-alkylating agent is also removed at the same time as removing CO ₂ , the reaction can be continued by supplementing the removed dialkyl carbonate. Furthermore, a method may be adopted in which dialkyl carbonate vaporized while discharging CO ₂ generated by attaching a reflux pipe to the reactor and returning to the reaction system by refluxing may be adopted. Alternatively, a method of selectively removing CO ₂ using a separation membrane is also applicable. On the other hand, when the reaction is carried out without continuously removing CO ₂ , the reaction can be carried out using the reactor as a pressure vessel and accumulating the produced CO ₂ in the reactor.

[Post-processing]
After completion of the α-alkylation reaction according to the present invention, an α-alkyl-substituted ester can be obtained by ordinary post-treatment such as distillation and purification. For example, it can be obtained by distilling off dialkyl carbonate and by-produced alcohol used in excess under reduced pressure as it is, followed by distillation under reduced pressure to distill the α-alkyl-substituted ester. The compound having an ether bond added to the reaction system is separated from the α-alkyl-substituted ester during this distillation. Alternatively, the dialkyl carbonate and alcohol may be distilled off and then extracted using a solvent. Solvents that can be used in this case include ester solvents such as ethyl acetate, ether solvents such as diethyl ether, aromatic solvents such as toluene and xylene, halogenated aromatic solvents such as chlorobenzene, and halogens such as dichloromethane and chloroform. It is a system solvent, and preferably ethyl acetate, diethyl ether or toluene from the viewpoint of cost and availability. After solvent extraction, it can be purified by distilling off the solvent and distilling as necessary. In particular, when cyclic ester compounds such as GBL are used as raw materials, the diester carbonate and alcohol are further distilled off, and then an aqueous alkali solution is added to hydrolyze the by-produced oligoester and carbonate compound, followed by acids such as hydrochloric acid and sulfuric acid. Can be cyclized to α-Me-GBL and the like when the solution is made acidic. An extraction operation may be performed after this. In particular, when this reaction is performed when there are many by-products in the reaction, the yield of the target α-Me-GBL increases.

[Reaction results]
In the present invention, the conversion rate of the raw ester compound when carried out under the above reaction conditions is not particularly limited, but is usually 50% or more, preferably 70% or more, more preferably 80% or more.
The yield of the target α-alkyl-substituted ester is not particularly limited, but is usually 50% or more, preferably 70% or more, more preferably 80% or more.

  Further, the purity of the α-alkyl-substituted ester obtained is not particularly limited, but it is usually 80 mol% or more, preferably 90 mol% or more, more preferably, when analyzed by gas chromatography (GC) or the like. Although it is 95 mol% or more and there is no restriction | limiting in particular in an upper limit, Preferably it is 100 mol%.

  The main impurities contained in the α-alkyl-substituted ester obtained in this reaction are not particularly limited. For example, when DMC is used as the α-alkylating agent, methanol, DMC, 4- (Methoxycarboxy) -2-methyl-methyl butyrate, 4-methoxycarboxy-methyl butyrate, raw material ester compounds, oligoesters obtained by combining these compounds and the like. Although the content of the main impurities is not particularly limited, for example, GBL can be derived into THF, so even if such impurities are contained in an amount of about 20 mol%, the copolymer polyol raw material is used. It can be used for the next step as it is. However, the GBL content is preferably 10% by weight or less, more preferably 5% by weight or less in order to reduce the load of the subsequent purification step.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
In addition, the analysis conditions of the reaction product in the following examples and comparative examples are as follows.

<GC measurement conditions>
Device: GC-14 manufactured by Shimadzu Corporation
Column: GL Sciences capillary column TC-1701
Carrier: Helium gas Detector: FID
The analysis was performed by the internal standard substance addition method using tetraglyme.

[Example 1: Use of 18-crown-6]
The inside of the autoclave having an internal volume of 70 ml was replaced with nitrogen gas, and 2.62 g (19.0 mmol) of potassium carbonate and 2.05 g (7.8 mmol) of 18-crown-6 (6 ether bonds and 12 carbon atoms) were added. The inside of the reactor was again replaced with nitrogen gas. In a nitrogen gas atmosphere, 3.28 g (38.1 mmol) of γ-butyrolactone and 11.93 g (132 mmol) of dimethyl carbonate were added from the raw material inlet, and the mixture was heated and stirred at 215 ° C. in an electric furnace.
The conversion rate of γ-butyrolactone was 97%, and the yield of α-methyl-γ-butyrolactone was 70%, as determined by GC analysis of the recovered reaction solution when the reaction was completed by heating and stirring for 2 hours.
When the same reaction was carried out for 6 hours, the conversion rate of γ-butyrolactone was 100%, and the yield of α-methyl-γ-butyrolactone was 66%.

[Example 2: Use of tetraethylene glycol dimethyl ether]
The inside of the autoclave with an internal volume of 70 ml was replaced with nitrogen gas, and 2.62 g (19.0 mmol) of potassium carbonate and 2.05 g (7.8 mmol) of tetraethylene glycol dimethyl ether (5 ether bonds and 10 total carbon atoms) were added. The inside of the reactor was again replaced with nitrogen gas. In a nitrogen gas atmosphere, 3.28 g (38.1 mmol) of γ-butyrolactone and 11.93 g (132 mmol) of dimethyl carbonate were added from the raw material inlet, and the mixture was heated and stirred at 215 ° C. in an electric furnace.
The conversion rate of γ-butyrolactone was 85%, and the yield of α-methyl-γ-butyrolactone was 67%, as determined by GC analysis of the recovered reaction solution when the reaction was completed by heating and stirring for 2 hours.
When the same reaction was conducted for 6 hours, the conversion of γ-butyrolactone was 95%, and the yield of α-methyl-γ-butyrolactone was 57%.

[Example 3: Use of polyethylene glycol]
The inside of the autoclave having an internal volume of 70 ml was replaced with nitrogen gas, 1.77 g (12.8 mmol) of potassium carbonate, polyethylene glycol 300 (average molecular weight 300, average number of ether bonds 6.4, average total carbon number 12.8) 1 .29 g was added and the inside of the reactor was again replaced with nitrogen gas. In a nitrogen gas atmosphere, 3.70 g (43.0 mmol) of γ-butyrolactone and 11.61 g (129 mmol) of dimethyl carbonate were added from the raw material inlet, and the mixture was heated and stirred at 215 ° C. in an electric furnace.
The conversion rate of γ-butyrolactone was 92%, and the yield of α-methyl-γ-butyrolactone was 63%, as determined by GC analysis of the recovered reaction solution when the reaction was completed by heating and stirring for 2 hours.

[Comparative Example 1]
The inside of the autoclave having an internal volume of 70 ml was replaced with nitrogen gas, 2.61 g (19.0 mmol) of potassium carbonate was added thereto, and the inside of the reactor was again replaced with nitrogen gas. In a nitrogen gas atmosphere, 3.37 g (39.2 mmol) of γ-butyrolactone and 12.15 g (135 mmol) of dimethyl carbonate were added from the raw material inlet, and the mixture was heated and stirred at 215 ° C. in an electric furnace.
The conversion rate of γ-butyrolactone was 65%, and the yield of α-methyl-γ-butyrolactone was 36%, as determined by GC analysis of the recovered reaction solution when the reaction was completed by heating and stirring for 2 hours.
When the same reaction was conducted for 6 hours, the conversion of γ-butyrolactone was 95%, and the yield of α-methyl-γ-butyrolactone was 55%.

  From the above results, it can be seen that according to the present invention, an α-alkyl-substituted ester can be produced in a high yield by reacting an ester compound and a dialkyl carbonate in the presence of a basic catalyst.

Claims (5)

  An α-alkyl-substituted ester characterized in that a compound having an ether bond is present in a reaction system in a method for producing an α-alkyl-substituted ester by reacting an ester compound and a dialkyl carbonate in the presence of a basic catalyst. Compound production method.   The method for producing an α-alkyl-substituted ester compound according to claim 1, wherein the compound having an ether bond has 6 or more carbon atoms and 2 or more ether bonds.   The method for producing an α-alkyl-substituted ester compound according to claim 1 or 2, wherein the compound having an ether bond has a substituent capable of coordinating or hydrogen bonding to a cation.   The method for producing an α-alkyl-substituted ester compound according to claim 3, wherein the substituent capable of coordinating or hydrogen bonding to the cation is one or more selected from a hydroxyl group, an amino group, and an imino group.   The production of an α-alkyl-substituted ester compound according to any one of claims 1 to 3, wherein the compound having an ether bond is at least one selected from crown ether, polyalkylene glycol, and polyalkylene glycol dialkyl ether. Method.