JPH05310648A - Production of dialkyl dicarbonate - Google Patents

Abstract

PURPOSE:To provide a method for obtaining a high-purity dialkyl dicarbonate in good yield. CONSTITUTION:An alkali metallic salt of an alkyl carbonate with 3/100, preferably <=2/100 content of an alkali metallic alkoxide expressed in terms of a molar ratio to the alkali metallic salt of the alkyl carbonate, e.g. sodium t-butyl carbonate is made to react with an acid halide, e.g. p-toluenesulfonyl chloride in the presence of an aliphatic or an aromatic tertiary amine catalyst to afford the dialkyl dicarbonate of the formula (R<10> and R<11> are alkyl) with a low content of impurities, e.g. di-t-butyl carbonate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for industrially producing dialkyl dicarbonic acid esters.

[0002]

2. Description of the Related Art Dialkyl dicarbonate is a compound that has long been known as a food preservative.
Its importance as a protective agent for amino acids in peptide chemistry is increasing.

Conventionally, as a method of synthesizing dialkyl dicarbonate, a method of reacting an alkali metal carbonate of carbonic acid ester with an acid halide is known. The reaction mixture obtained by the reaction was washed with water to remove the by-product salt and then distilled to obtain the desired dialkyl dicarbonate.

[0004]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The inventors of the present invention have continued research on a method for producing a dialkyl dicarbonate with high yield and high purity. It was found that the carbonic acid dialkyl ester was by-produced when the reaction with the compound was carried out. The byproduct carbonic acid dialkyl ester reduces the purity of the intended dicarbonic acid dialkyl ester. Therefore, in order to remove the carbonic acid dialkyl ester produced as a by-product, when the dicarbonic acid dialkyl ester, which is the main product, is distilled, thermal decomposition of the dicarbonic acid dialkyl ester itself occurs, resulting in a problem that the yield is significantly reduced. there were.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, the present inventors have examined the formation mechanism of carbonic acid dialkyl ester in order to reduce it. As a result, the carbonic acid alkyl ester alkali metal salt as a raw material is produced from the corresponding alkali metal alkoxide, and therefore contains unreacted alkali metal alkoxide as an impurity. It was found that the carbonic acid dialkyl ester was by-produced by reacting with. Based on this finding,
By keeping the content of the alkali metal alkoxide which is an impurity in the carbonic acid alkyl ester alkali metal salt low, the dicarbonic acid dialkyl ester can be produced in a high yield, and
They have found that they can be produced with high purity, and have completed the present invention.

That is, the content of the alkali metal alkoxide contained in the alkyl carbonate ester alkali metal salt is
A method for producing a dialkyl dicarbonate ester, which comprises reacting an alkyl carbonate alkali metal salt having a molar ratio of 3/100 or less with respect to the alkyl carbonate alkali metal salt with an acid halide.

The alkali metal carbonate of carbonic acid ester in the present invention is represented by the following general formula.

[0008]

[Chemical 1]

(However, R ¹ is an alkyl group and M is an alkali metal.) Specific examples of the above-mentioned alkali metal carbonate alkyl carbonate include, for example, sodium methyl carbonate, sodium ethyl carbonate and sodium isopropyl carbonate. , Sodium isobutyl carbonate, sodium carbonate-
Examples thereof include t-butyl, sodium t-amyl carbonate, potassium methyl carbonate, ethyl ethyl carbonate, potassium isopropyl carbonate, isobutyl potassium carbonate, potassium t-butyl carbonate, potassium t-amyl carbonate and the like.

In the present invention, in order to obtain a dialkyl dicarbonate in a high yield and a high purity, the content of the alkali metal alkoxide contained in the starting material alkyl carbonate ester alkali metal salt is adjusted to carbonic acid. It is necessary that the molar ratio to the alkyl ester alkali metal salt is 3/100 or less. Further, the content of the alkali metal alkoxide is preferably low, and is preferably 2/100 or less, more preferably 1/100 or less with respect to the alkyl carbonate alkali metal salt, and most preferably contains no alkali metal alkoxide. preferable.

The carbonic acid alkyl ester alkali metal salt is
It is obtained by reacting the corresponding alkali metal alkoxide with carbon dioxide. The reaction method is not particularly limited, but the alkali metal alkoxide is dispersed in a solvent,
Examples thereof include a method of contacting gaseous carbon dioxide, a method of contacting finely powdered solid-state alkali metal alkoxide with gaseous carbon dioxide, and the like. In the method using a solvent, any solvent that does not react with an alkali metal alkoxide can be used without any limitation.

The method for obtaining an alkyl carbonate alkali metal salt of an alkali metal carbonate having an alkali metal alkoxide content of not more than the above-mentioned value is not particularly limited. , Reacting while analyzing the content of the alkali metal salt of carbonic acid ester produced and the unreacted alkali metal alkoxide, and continuing contact with gaseous carbon dioxide until the desired content of alkali metal alkoxide is obtained. A method etc. can be adopted. The reaction can be carried out under reduced pressure, normal pressure or increased pressure, but it is preferable to carry out the reaction in a closed system because the end point of the reaction can be easily seen from the amount of carbon dioxide used.

In this way, it is possible to obtain a carbonic acid alkyl ester alkali metal salt in which the content of the alkali metal alkoxide as an impurity is 3/100 or less in a molar ratio to the carbonic acid alkyl ester alkali metal salt. The alkyl ester alkali metal salt may be isolated by a known method, and may be used as it is depending on the case.

As the acid halide in the present invention, known ones can be used without any limitation, but aromatic sulfonyl halides are preferably used because they give the target compound in high yield. As the aromatic sulfonyl halide, a known compound having a halogenosulfone group bonded to an aromatic ring is used without any limitation. In particular, in the present invention, the following formula

[0015]

[Chemical 2]

An aromatic sulfonyl halide represented by the formula (wherein R ² and R ³ are a hydrogen atom, a halogen atom or an alkyl group, and X is a halogen atom) is preferably used.

Specific examples of aromatic sulfonyl halides that can be preferably used in the present invention are as follows. Benzenesulfonyl chloride, p-toluenesulfonyl chloride, 2,4-dimethylbenzenesulfonyl chloride, p-chlorobenzenesulfonyl chloride, 2,4-dichlorobenzenesulfonyl chloride, benzenesulfonyl bromide, p-toluenesulfonyl bromide, p-chlorobenzenesulfonyl bromide, etc. Can be mentioned.

The amount of the acid halide with respect to the alkyl carbonate alkali metal salt is usually 1 mol of the alkyl carbonate alkali metal salt because one molecule of the dicarbonic acid dialkyl ester is produced from 2 molecules of the alkyl carbonate ester alkali metal salt. Is selected in the range of 0.3 to 0.5 mol.

In the above reaction, it is preferable to use a catalyst in order to accelerate the reaction. Any known catalyst can be used without any limitation, but an aliphatic tertiary amine or an aromatic tertiary amine in which an aromatic ring is bonded to a nitrogen atom through an alkylene group is used in order to obtain a target compound in high yield. It is preferably used. In particular, in the present invention, the following formula

[0020]

[Chemical 3]

(Wherein R ⁴ and R ⁵ are the same or different alkyl groups, R ⁶ is an alkylene group, Y is a hydrogen atom, an alkoxy group, an alkylthio group, an aryl group, or

[0022]

[Chemical 4]

(Wherein R ⁷ and R ⁸ are a hydrogen atom or an alkyl group, at least one is an alkyl group, Z is O, S or> N—R ⁹ (wherein R ⁹ is a hydrogen atom or an alkyl group). A group), n is an integer of 1 or more, and m is 0 or 1.).

Aliphatic 3 which can be preferably used in the present invention
Specific examples of primary amines or aromatic tertiary amines having an aromatic ring bonded to a nitrogen atom via an alkylene group include:
Trimethylamine, N, N-dimethylbenzylamine,
N, N-diethylbenzylamine, N, N, N ', N'
-Tetramethylethylenediamine, N, N, N'N'-
Tetramethyl-1,3-propanediamine, N, N,
N'N'-tetramethyl-1,6-hexanediamine,
N, N, N'N'-tetraethyl-1,3-propanediamine, N, N, N'N'-tetraethyl-1,6-hexanediamine, N, N, N'N'-tetramethyl-
1,4-butanediamine, N, N, N'N'-tetramethyl-1,3-butanediamine, bis- [2- (N, N
-Dimethylamino) ethyl] ether, bis- [2-
(N, N-dimethylamino) propyl] ether, bis- [2- (N, N-dimethylamino) ethyl] sulfide, bis- [2- (N, N-dimethylamino) propyl]
Sulfide, 2- (N, N-dimethylamino) ethyl ethyl ether, 2- (N, N-dimethylamino) ethyl ethyl sulfide, bis- [2- (N, N-dimethylamino) ethyl] methylamine and the like. be able to.

Among aromatic tertiary amines represented by the above general formula or aromatic tertiary amines having an aromatic ring bonded to a nitrogen atom via an alkylene group, Y is an aryl group or

[0026]

[Chemical 5]

(Where R ⁷ and R ⁸ are hydrogen atoms or alkyl groups, at least one of which is an alkyl group), the yield of the target compound is particularly high. It is preferably used in the invention.

The amount of the above-mentioned aliphatic tertiary amine or aromatic tertiary amine having an aromatic ring bonded to a nitrogen atom through an alkylene group is not particularly limited, but in order to obtain a sufficient reaction rate. In addition, 0.01 to 20 mol%, and further 0.0
It is preferably in the range of 5 to 10 mol%.

In this reaction, in order to improve the dispersibility of the reaction solution, the concentration of the alkyl carbonate carbonate alkali metal salt is 3 to.
It is desirable to dilute with a solvent so as to be 60% by weight. The solvent used in this reaction is not particularly limited, and aromatic hydrocarbons such as benzene, toluene and xylene;
Ethers such as 4-dioxane and tetrahydrofuran;
Acetonitrile, methylpyrrolidone, N, N-dimethylformamide and the like are used. Further, an alcohol corresponding to the alkyl group in the starting material alkyl carbonate alkali metal salt can also be used. These organic solvents may be used alone or may be used as a mixed solvent of two or more kinds at all.

The reaction temperature in this reaction is not particularly limited, but if the temperature is too low, the reaction rate becomes small, and if the temperature is too high, the raw material and the target compound are decomposed, so that it is usually 0 to 100 ° C., preferably 20 to 80. It is preferable to carry out at ° C.

The reaction can be carried out under any of atmospheric pressure, pressurization and depressurization, and it is particularly preferable to carry out the reaction under pressurization of carbon dioxide gas in order to obtain a target compound in a high yield. Although the time required for the reaction varies depending on the reaction temperature and the type of solvent, a reaction time of 0.1 to 30 hours is usually sufficient.

In this way, it is possible to produce a reaction solution containing dicarbonic acid dialkyl ester with a small amount of by-products, particularly with a low content of carbonic acid dialkyl ester. Since this reaction liquid has a very small content of by-products, it is possible to minimize the loss due to decomposition of the dialkyl dicarbonate in the subsequent purification.

The reaction solution obtained is first treated to remove by-product salts. The method of removing the by-product salt is not particularly limited,
Examples thereof include a method by solvent extraction, a method by filtration, a method of desalting with an ion exchange membrane, and a method of washing with water.
These removal methods can be carried out either batchwise or continuously.

After removing the by-product salt in this manner, dialkyl dicarbonate ester is isolated. As the isolation method, a known method can be adopted without any limitation. Specifically, a crystallization method, a distillation method and the like can be mentioned.

The crystallization method is usually carried out by distilling off the solvent, cooling to a temperature below the freezing point of the dicarbonic acid dialkyl ester to crystallize the dicarbonic acid dialkyl ester, and separating the dicarbonic acid dialkyl ester crystallized by filtration or the like. By separating, a high-purity dicarbonic acid dialkyl ester is obtained. Pressure crystallization can also be carried out.

The method by distillation is not particularly limited, and for example, either a batch distillation method or a continuous distillation method can be used. Usually, after distilling off the solvent, a small amount of low-boiling component is distilled off and further concentrated to distill the main component dialkyl dicarbonate to obtain high-purity dialkyl dicarbonate. When the distillation temperature is too high, the decomposition amount of dialkyl dicarbonate increases, and when it is too low, a high vacuum is required.
It is carried out at 0 ° C, preferably 30 to 100 ° C. If the vacuum degree is too low, the boiling point of the dicarbonic acid dialkyl ester will be high, the decomposition amount of the dicarbonic acid dialkyl ester will increase, and if it is too high, the decompression device will be too large.
Usually, it is carried out in the range of 0.1 to 20 mmHg.

In this way, the following equation

[0038]

[Chemical 6]

(Note that R ¹⁰ and R ¹¹ are the same or different alkyl groups.) The dicarbonic acid dialkyl ester can be produced in high purity and in good yield.

[0040]

[Effect] According to the present invention, a highly pure dialkyl dicarbonic acid ester containing very few impurities can be obtained in good yield. Therefore, the method of the present invention is extremely useful industrially.

[0041]

EXAMPLES The present invention will be described below with reference to examples.
The invention is not limited to these examples.

Example 1 578.5 g (4.10 mol) of sodium t-butyl carbonate containing 0.006 mol of sodium t-butoxide was placed in an autoclave equipped with a stirrer, a thermometer and a gas inlet tube. Disperse in 1845 mL of toluene, add N, N,
N ', N'-tetramethylethylenediamine 4.83
g, N, N-dimethylformamide 217.0 g, p-
Add 363.5 g of toluenesulfonyl chloride and add 1
Carbon dioxide is press-fitted at Kg / cm ² · G, 40 to 45 ° C
It was made to react at the temperature of 6 hours. After the reaction, 1800 ml of water was added to dissolve the precipitated crystals, and the toluene layer and the water layer were separated. The toluene layer was further washed 3 times with 600 mL of water. When di-t-butyl dicarbonate and di-t-butyl carbonate in the toluene layer after washing with water were quantified, 382.5 g (1.75 mol, yield 85.5%) respectively,
It was 0.10 g (0.006 mol). The toluene layer was concentrated under reduced pressure to remove toluene, di-t-butyl carbonate was removed using a simple distillation apparatus, and di-t-butyl dicarbonate 378. 6 g
(Purity 99.4%, yield 84.1%, di-t-butyl carbonate content 0.02%) was obtained. Further by simple distillation, 3
Distilled at mmHg to give clear di-t-butyl dicarbonate 36
5.3 g (purity 99.7%, yield 81.4%, carbonic acid di-
t-butyl content 0.02%) was obtained.

Example 2 In the same manner as in Example 1, 378.6 g of di-t-butyl dicarbonate colored in light yellow (purity 99.4%, yield 8)
4.1%, di-t-butyl carbonate content 0.02%) was obtained. Further, by thin film distillation, distilling at 3 mmHg, 369.8 g of clear di-t-butyl dicarbonate (purity 99.
7%, yield 82.4%, di-t-butyl carbonate content 0.0
2%) was obtained.

Example 3 In the same manner as in Example 1, 382.5 g (1.75 mol, yield 85.5%) of di-t-butyl dicarbonate and di-t-butyl carbonate, respectively, were added. .10 g (0.006 mol)
A containing toluene layer was obtained. This toluene layer was concentrated under reduced pressure to remove toluene, and 390.4 g of di-t-butyl dicarbonate containing a small amount of solvent (purity 97.0%, yield 84.6%,
A di-t-butyl carbonate content of 0.14%) was obtained. This concentrated solution was allowed to stand in a constant temperature bath at 15 ° C. for 24 hours, and di-dicarbonic acid
The butyl was crystallized, the uncrystallized part was removed by decantation, and clear di-t-butyl dicarbonate 357.8.
g (purity 99.4%, yield 79.5%, di-t-butyl carbonate content 0.05%) was obtained.

Examples 4 to 6 and Comparative Examples 1 to 2 Using sodium t-butyl sodium carbonate containing sodium t-butoxide shown in Table 1, the same operation as in Example 1 was carried out, and di-t-dicarbonate was operated. -Butyl was synthesized. The results are shown in Table 1.
It was shown to.

[0046]

[Table 1]

Comparative Example 3 Dicarbonic acid di-carbonate was prepared in the same manner as in Example 2 except that 578.5 g (4.01 mol) of sodium t-butyl carbonate containing 0.17 mol of sodium t-butoxide was used. 342.4 g of t-butyl and di-t-butyl carbonate, respectively
(1.57 mol, yield 78.2%), 29.6 g (0.
A toluene layer containing 17 mol) was obtained. This toluene layer was concentrated under reduced pressure to remove toluene, and 372.1 g of di-t-butyl dicarbonate containing a small amount of solvent (purity 90.0%, yield 7
6.6%, di-t-butyl carbonate content 7.38%) was obtained. This concentrated solution was left to stand in a constant temperature bath at 15 ° C. for 24 hours to crystallize di-t-butyl dicarbonate, and the uncrystallized portion was removed by decantation to obtain 279.1 g of clear di-t-butyl carbonate. (Purity of 97.1%, yield of 61.9%, di-t-butyl carbonate content of 2.51%) was obtained.

Examples 7 to 10 Carbonic acid alkyl esters containing alkali metal alkoxides shown in Table 2 were used in the same manner as in Example 1 to synthesize dicarbonic acid dialkyl esters. The results are shown in Table 2.

[0049]

[Table 2]

Claims (1)

[Claims] 1. The content of the alkali metal alkoxide contained in the alkali metal carbonate ester is 3/10 in terms of the molar ratio to the alkali metal carbonate ester.
A process for producing a dialkyl dicarbonate ester, which comprises reacting an alkyl carbonate alkali metal salt of 0 or less with an acid halide.