JPS5950754B2 - Method for producing dimethyl dicarboxylate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new industrial method for producing dimethyl dicarboxylate, and more specifically, by Kolbe electrocondensation reaction,
The present invention relates to a method for producing dimethyl dicarboxylate from monomethyl dicarboxylate in the presence of an alkali metal salt of monomethyl dicarboxylate in a methanol solvent.

Dimethyl dicarboxylate is extremely widely used as a raw material for perfumes, various polymers, plasticizers, etc., and dimethyl thapsinate and dimethyl octadecanoate are particularly useful as raw materials for macrocyclic musk perfumes.

Conventionally, methods for producing dicarboxylic acids and their esters include, for example, a method using cyclohexanone and olefin as raw materials and using Fenton's reagent, and a fermentation method to convert n-alkanes or monocarboxylic acids into dibasic acids using yeast. Various methods have been proposed.

However, all of these methods have problems such as extremely long reaction times, use of special reagents, and low yields, and are not necessarily satisfactory as industrial production methods. On the other hand, methods for producing dimethyl dicarboxylate by electrolytic condensation of monomethyl dicarboxylate include, for example, a method of electrolytically condensing adipic acid monoester and azelaic acid monoester, and these methods have been actively researched. has been carried out and various findings have been obtained.

That is, the method for producing dimethyl sebacate from monomethyl adipate was previously disclosed by the present inventors as an industrially implemented technique in JP-A-55-158285, JP-A-56-44782, etc. Furthermore, a method for producing thapsic acid diester from azelaic acid monoester is disclosed in Japanese Patent Publication No. 38-11116, Yukagaku, 12,669 (1963), and the like. By the way, when mononotyl dicarboxylate is electrolytically condensed in a batch manner to produce dimethyl dicarboxylate, the general formula HOOC(CH) is used.

) When a monomethyl dicarboxylate represented by NCOOCH is electrolytically condensed with n of 6 or more, a rapid voltage increase occurs in the latter half of the electrolytic condensation, making electrolysis impossible and unreacted monomethyl dicarboxylate. A large amount remains. If this monomethyl dicarboxylate exists in the electrolyte, the equipment for separating and recovering monomethyl dicarboxylate in the purification of dimethyl dicarboxylate in the subsequent process becomes complicated, and the monomethyl dicarboxylate is lost and the purity of the dimethyl dicarboxylate product decreases. There are problems such as causing In addition, in the method for producing thapsic acid diester disclosed in Japanese Patent Publication No. 38-11116, it is necessary to separate the anode chamber and the cathode chamber using a cation exchange membrane, and the water concentration in the anolyte is About 30-40
It is set to a value of weight %.

This method for producing thapsic acid diester has problems such as complicated equipment due to the use of a cation exchange membrane and extremely low current efficiency, making it difficult to manufacture industrially. As a production method, it is still not satisfactory. As a result of intensive research to provide an industrially advantageous method that can solve these various problems, the present inventors have succeeded in converting dimethyl sebacate from monomethyl adipate, which was previously proposed by the present inventors. Manufacture. Based on the conventional electrolytic method, monomethyl dicarboxylate is electrolytically condensed in batches for a certain period of time in a methanol solution containing this alkali metal salt, and then electrolytically condensed in the presence of monomethyl adipate, which makes electrolysis impossible. The inventors have discovered that the purpose can be achieved by preventing the rapid voltage increase, and have completed the present invention based on this knowledge. That is, the present invention involves electrolyzing monomethyl dicarboxylate represented by the general formula HOOC(CH2)NCOOCH3 (n in the formula is an integer of 6 to 9) batchwise for a certain period of time in a methanol solution containing this alkali metal salt. The present invention provides a method for producing dimethyl dicarboxylate, which is characterized by carrying out condensation and then electrolytic condensation in the presence of monomethyl adipate.

In the method of the present invention, monomethyl dicarboxylate used as a raw material has the general formula (1) HOOC(CH2)NCOO
CH3. ．． ．． ．． ．． ．． (I) (n in the formula is the same as above)
Suberic acid has the structure represented by
Monomethyl ester of azelaic acid, sebacic acid and undecaniic acid.

Preferred among these are monomethyl azelaate and monomethyl sebacate. As mentioned above, the method of the present invention is based on the electrolysis method previously proposed by the present inventors for producing dimethyl sebacate from monomethyl adipate. In order to prevent unreacted monomethyl dicarboxylate remaining due to the difficulty of continuing electrolysis, it is recommended to add monomethyl adipate to the electrolytic solution after electrolysis for a certain period of time, and continue electrolysis until monomethyl dicarboxylate is substantially eliminated. It is a feature.

This monomethyl adipate may be added to the electrolytic solution before the voltage rises and then electrolysis is performed, or it may be added after the voltage rises and electrolysis is performed again. Furthermore, it is preferable to add monomethyl adipate when the content of monomethyl dicarboxylate in the electrolytic solution is about 2% by weight or more, which is the content at the time when the voltage increases, and in particular, to increase the amount of the main product. In order to achieve this, the content of monomethyl dicarboxylate is preferably 2% by weight or more and 4% by weight or less. In the method of the present invention, the amount of monomethyl adipate added is preferably in the range of 2 to 8 times the mole of unreacted monomethyl dicarboxylate and its alkali metal salt,
More preferably 3 to 6 times the molar amount.

If the amount added is less than twice the mole, a rapid voltage increase will occur again, making it difficult to continue electrolysis and leaving unreacted monomethyl dicarboxylate. Moreover, at 8 times the mole or more, a large amount of dimethyl sebacate from monomethyl adipate other than the main product, and dimethyl dicarboxylate due to the cross Kolbe electrolysis reaction between monomethyl adipate and monomethyl dicarboxylate, which is a raw material, are produced. The solution in which electrolytic condensation is carried out in the method of the present invention is a methanol solution containing the raw materials monomethyl dicarboxylate and its neutralized salt, but the products dimethyl dicarboxylate, dimethyl sebacate,
It may also contain other by-products.

If the water content in this methanol solution is extremely low, the current and efficiency will be extremely poor, and if the water content exceeds 3.5% by weight, the selectivity and current efficiency will also be reduced. Therefore, in order to maintain high selectivity and current efficiency, it is preferable to maintain the water content in the range of 0.15 to 3.5% by weight. In the electrolytic condensation of the present invention, monomethyl dicarboxylate, which is a raw material, is heated until the voltage increases in the second half.
Alternatively, it may be carried out batchwise until the voltage rises, or it may be carried out continuously by maintaining the raw material monomethyl dicarboxylate at a constant concentration for a certain period of time, and then in the latter half when the voltage rises, or It may be done in batches until the temperature rises.

Furthermore, considering the separation and purification of the product in the subsequent process, electrolytic condensation after addition of monomethyl adipate should be carried out until the content of monomethyl dicarboxylate and monomethyl adipate in the electrolytic solution becomes 0.5% by weight or less. It is preferable to continue. In the present invention, the amount of monomethyl dicarboxylate charged during electrolytic condensation is preferably in the range of 10 to 50% by weight.

If the amount is higher than 50% by weight, the voltage will be high;
If it is less than % by weight, not only the volumetric efficiency decreases but also the current efficiency decreases. In the present invention, in order to increase the conductivity of the solution during electrolytic condensation, hydroxides, carbonates, bicarbonates, methylates, etc. of lithium, potassium, and sodium are used as neutralizing bases.
Ethylates or amines are used.

However, amines are oxidized at the anode, accelerating anode consumption, and using lithium compounds reduces current efficiency, so it is preferable to use sodium and potassium hydroxides, carbonates, bicarbonates, and methylates. . Further, the degree of neutralization (defined as the molar proportion of neutralizing acid with base) during charging of monomethyl dicarboxylate is preferably 2 to 50 mol%. If the degree of neutralization is less than 2 mol%, the voltage will be high, and if the concentration is higher than 50 mol%, the current efficiency will be low. The electrolytic cell used in the present invention may be one commonly used in organic electrolytic reactions, as long as it is capable of passing an electrolytic solution between the two electrodes at a high flow rate.

For example, an electrolytic cell has a cathode plate and an anode plate facing each other in parallel,
A polypropylene plate defining the electrode spacing is placed between the two electrodes. This polypropylene plate has an opening in the center so that the electrolyte can flow therethrough. The current-carrying area of the electrode is determined by the size of this opening, and the electrode spacing is determined by the thickness of this plate.

The electrolytic solution enters through a supply port provided in the electrolytic cell, undergoes a reaction while passing between the two electrodes, exits through an outlet port, and is circulated to the electrolyte tank. The electrode materials used in the electrolytic condensation of the present invention include platinum, rhodium, ruthenium,
Iridium or the like is used alone or in an alloy, and is usually used as a plating, and titanium, tantalum, etc. are used for the plating substrate.

Further, the cathode preferably has a low hydrogen overvoltage, but is not particularly limited, and platinum, iron, stainless steel, titanium, etc. can be used. The flow rate of the electrolytic solution in the electrolytic cell is preferably 1 to 4 m/sec.

If the flow rate is less than 1 m/sec, the current efficiency will be low, and if the flow rate is faster than 4 m/sec, the pressure loss within the electrolytic cell will increase.

The spacing between the electrodes is preferably 0.5 to 3 mm. If it is less than 0.5 mm, the pressure loss within the electrolytic cell will increase, and if it is wider than 3 mm, the voltage will increase.

The current density is preferably 5 to 40 A/Dm2, and 5 A/Dm
If it is less than ・, the current efficiency will be low. The temperature of the electrolyte is 45~
65°C is preferred. If the temperature is lower than 45° C., the current efficiency will be low and the voltage will be high, and in some cases, products will precipitate. Temperatures higher than 65°C are limited by the boiling point of the electrolyte.

After the electrolytic condensation is completed, the product can be purified and separated from the electrolytic solution by a conventional method. That is, after removing methanol from the electrolyte, it is directly separated into two oil-water layers, or
Alternatively, water can be added to separate the two layers, and highly purified dimethyl dicarboxylate can be obtained from the oil layer by distillation. The method of the present invention has the following advantages over conventional methods and various other proposed methods, and can be said to be an industrially extremely advantageous method.

That is, firstly, by applying the technology of the production method for dimethyl sebacate that the present inventors proposed earlier and electrolyzing monomethyl dicarboxylate for a certain period of time, adding monomethyl adipate and continuing electrolysis, dicarboxylic acid can be produced. Since monomethyl acid can be substantially eliminated, dimethyl dicarboxylate can be easily produced in the same manner as dimethyl sebacate. Second, the method of the present invention does not use any special chemicals or chemicals that pose safety problems. Thirdly, according to the method of the present invention, a desired product can be obtained with high current efficiency and high material yield. Fourthly,
By electrolytically condensing with the addition of monomethyl adipate, dimethyl dicarboxylate other than the main product such as dimethyl sebacate can be obtained, and these products can be used in fragrances as well as the main product dimethyl dicarboxylate. It is widely used as a raw material for various polymers, plasticizers, etc. It is a useful thing that can be used. EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way.

Example 1 Methanol was added to the electrolytic solution tank so that the concentrations of monomethyl azelaate, potassium salt of monomethyl azelaate, and water were 20% by weight, 2.64% by weight, and 3.0% by weight, respectively, and the amount of charged liquid was 1000 g. , potassium hydroxide,
Work in the order of monomethyl azelaate. and adjusted the liquid.

This adjusted solution was circulated to the electrolytic cell. Both poles of the electrolytic cell are 1.
It has a current-carrying area of 0cm x 100cm, and the cathode is 2m thick.
The anode is a 2 mm thick titanium plate plated with 4 microns of platinum. A polyethylene plate was placed to set the electrode spacing at 1 mm.

The electrolytic cell used had a liquid supply port and a liquid outlet. A liquid was flowed between the two electrodes at a flow rate of 2 m/Sec, and the current density was set to II.
Electrolysis was carried out at A/Dm2 while maintaining the temperature of the liquid at 48 to 52°C. Further, at the same time as the start of electrolysis, monomethyl azelaate was continuously added to the electrolyte tank at a rate of 56.0 g/Hr for 5 hours. After the addition, electrolysis was carried out while sampling the electrolytic solution and measuring the residual concentration of monomethyl azelaate using gas chromatograph Drough analysis. When the concentration reached 2.5% by weight, 172.9 g of monomethyl adipate was added at once. Add,
Subsequently, electrolysis was carried out while sampling the electrolytic solution and measuring the residual concentration of monomethyl azelaate and monomethyl adipate, and the electrolysis was terminated when the concentration reached 0.05% by weight. Electrolysis time from start to end is 1
The time was 1.83 hours, and the amount of liquid at the end was 1230 g. The electrolytic pressure varied from 9.5V to 8.0V, and from 8.3V to 8.0V when monomethyl adipate was added.
．． It rose to 9V. After the electrolysis was completed, each component of the electrolytic solution was measured by gas chromatography, and the concentrations of dimethyl thapsinate, dimethyl sebacate, and dimethyl brassylate were 22.14% by weight, 6.28% by weight, and 3% by weight, respectively.
．． It was 0.09% by weight.

The selectivity of each electrolytic condensation product is shown in Table 1, and the current efficiency is shown in Table 2.
Shown in the table. Note that the selectivity rate and current efficiency were calculated according to the following formula.

Selectivity of dimethyl thapsinate based on monomethyl azelaate Material yield of dimethyl brassylate based on monomethyl azelaate (based on monomethyl adipate) (Number of moles of monomethyl adipate consumed) Selectivity of dimethyl sebacate based on monomethyl adipate However, the composition ratio of the potassium salt of monomethyl azelaate and the potassium salt of monomethyl adipate at the end of electrolysis was the molar ratio of monomethyl azelaate and monomethyl adipate after the addition of monomethyl adipate.

In addition, the current efficiency is calculated based on the amount of electricity of 2 Farads.
It was calculated assuming that moles are produced. The same procedure was carried out in the following examples.

, Example 2 Monomethyl azelaate in Example 1 was replaced with monomethyl sebacate, and the same electrolysis apparatus as in Example 1 was used.

The concentration of monomethyl sebacate, potassium salt of monomethyl sebacate, and water in the charging solution is 20.0% by weight, respectively.
2.62% by weight, 3.2% by weight, and the amount of liquid to be charged is 10% by weight.
00g. The electrolysis conditions were also the same as in Example 1, and 59% of monomethyl sebacate was added to the electrolyte tank at the same time as the start of electrolysis.
．． It was added continuously for 5 hours at 0 g/Hr. Thereafter, the same operation as in Example 1 was carried out, and when the concentration of monomethyl sebacate reached 2.7% by weight, 190 g of monomethyl adipate was charged at once, and electrolysis was continued until the concentration of monomethyl sebacate and monomethyl adipate was 0.04% by weight. %, the electrolysis was completed. The electrolytic voltage changes from 10.2V to 8.6V,
Further, the voltage increased from 9.0 to 9.5V at the time when monomethyl adipate was added. The electrolysis time from the start to the end of electrolysis was 11.92 hours, and the amount of liquid at the end was 1261 g. As a result of gas chromatographic analysis of each component after the completion of electrolysis, the concentrations of dimethyl octadecanoate, dimethyl sebacate, and tetradecane dimethyl were 22.3% by weight, 6.88% by weight, and 3.19% by weight, respectively. It was in weight%. Table 3 shows the selectivity of each electrolytic condensation product, and Table 4 shows the current efficiency. Example 3 Concentrations of monomethyl azelate, potassium salt of monomethyl azelate, and water were 40% by weight and 5.28%, respectively.
It was charged into the same electrolytic apparatus as in Example 1 so that the amount was 1.0% by weight.

Claims (1)

[Scope of Claims] 1 Monomethyl dicarboxylate represented by the general formula HOOC(CH_2)_nCOOCH_3 (n in the formula is an integer of 6 to 9) is batchwise prepared for a certain period of time in a methanol solution containing the alkali metal salt. 1. A method for producing dimethyl dicarboxylate, which comprises electrolytically condensing the dimethyl dicarboxylate and then electrolytically condensing it in the presence of monomethyl adipate. 2. The method according to claim 1, wherein monomethyl adipate is added after electrolytic condensation is performed until the content of monomethyl dicarboxylate in the electrolytic solution is at least about 2% by weight. 3. The method according to claim 2, wherein monomethyl adipate is added after electrolytic condensation is performed until the content of monomethyl dicarboxylate is in the range of 2 to 4% by weight. 4. The method according to claim 2 or 3, wherein the amount of monomethyl adipate added is 2 to 8 times the molar amount of monomethyl dicarboxylate and its alkali metal salt. 5. The method according to claim 4, wherein the amount of monomethyl adipate added is 3 to 6 times the molar amount of monomethyl dicarboxylate and its alkali metal salt. 6. The method according to claim 1, wherein the monomethyl dicarboxylate is monomethyl azelaate and monomethyl sebacate. 7 The water content in the methanol solution in electrolytic condensation is set to 0.
2. A method according to claim 1, wherein the amount ranges from 15 to 3.5% by weight.