JPS5837397B2 - Method for producing n-valeric acid or its esters - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing n-valeric acid or its esters.

N-valeric acid and its esters are particularly important industrially as they are used as raw materials for various fragrances such as flavors.

As a conventional industrial method for producing n-valeric acid or its esters, a method is known in which n-valeric acid is produced by oxidation of n-pentyl alcohol or reduction of levulinic acid, and then esterified. Both methods have problems such as expensive raw materials, and cannot be called advantageous manufacturing methods.

As a result of intensive research aimed at establishing an industrially advantageous manufacturing method, the present inventors have found that a mixture of dimethyl sebacate, methyl allyl acetate, and methyl n-valerate can be obtained by electrolytically oxidizing monomethyl adipate. Then, methyl allyl acetate is converted to γ-valerolactone, and methyl n-valerate is once hydrolyzed to n-valeric acid, and then both are directly distilled or esterified.

- It was discovered that the two can be easily separated by converting to valeric acid ester, leading to the present invention.

That is, the present invention electrolytically oxidizes adipic acid monomethyl ester in the presence of its alkali metal salt in a methanol solvent, and obtains a mixture of methyl allyl acetate and methyl n-valerate by distillation from the obtained raw material. The mixture is treated with an acidic aqueous solution to obtain a mixture of γ-valerolactone and n-valeric acid, and then γ-valerolactone and n-valeric acid are separated by distillation, or the mixture is treated with alcohols using an acid catalyst. The process is characterized by converting n-valeric acid into n-valeric acid esters through treatment and then separating γ-valerolactone and n-valeric acid esters by distillation.

The electrolytic oxidation of monomethyl adipate in the present invention involves the electrolytic oxidation of monomethyl adipate in the presence of an alkali metal salt of monomethyl adipate produced by adding a neutralizing base to increase the conductivity of the electrolyte in methanol solvent. concentration to 0.1
Either by maintaining the concentration within the range of 5 to 3.0% by weight and carrying out batchwise until the raw material monomethyl adipate is substantially exhausted;
Alternatively, the process is carried out continuously while maintaining monomethyl adipate at a constant concentration, yielding dimethyl sebacate as the main raw material and a mixture of methyl allylacetate and methyl n-valerate as the by-product.

The concentration of monomethyl adipate is set at 10 to 60% by weight when electrolysis is carried out batchwise, and from 5 to 40% by weight when electrolysis is carried out continuously.
Set it to % by weight.

In both cases, if the concentration is above the upper limit, the voltage will be high and the current efficiency will be low, and if the concentration is below the lower limit, the current efficiency will be poor.

Lithium, sodium, potassium hydroxides, carbonates, bicarbonates, methylates, ethylates, etc. are used as neutralizing bases to increase the conductivity of the electrolyte solution, but sodium, potassium hydroxides, carbonates, Bicarbonates are preferred.

In addition, the degree of neutralization (the molar proportion of monomethyl adipate neutralized with a base) is set at 5 to 50 mol% when electrolysis is carried out batchwise, and when electrolysis is carried out continuously. In some cases, it is set to 10 to 60 mol%.

If the degree of neutralization is above the upper limit, the current efficiency will be poor, and if the degree of neutralization is below the lower limit, the voltage will be high.

It is necessary to maintain the water concentration in the electrolyte in the range of 0.15 to 3.0% by weight; if it is less than 0.15% by weight, the current efficiency will be extremely poor, and even if the concentration is higher than 30% by weight, the current will be low. Efficiency and material yield are lower.

The electrolytic cell may be one commonly used in organic electrolytic reactions, as long as it is capable of passing an electrolytic solution between 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.

As the electrode material, platinum, rhodium, ruthenium, iridium, etc. are used alone or in an alloy for the anode, and are usually used as plating, and titanium, tantalum, etc. are used for the plated 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 distance between the electrodes is preferably 0.5 to 3 m. If it is less than 0.5 mm, the pressure loss in 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/d, and 5 A/dmj
If it is less than that, the current efficiency will be low.

The temperature of the electrolytic solution is preferably 45 to 65°C.

If the temperature is below 45℃, the current efficiency will be low and the voltage will be high.
Temperatures higher than 65°C are limited by the boiling point of the electrolyte.

After removing methanol from the electrolytic solution obtained as described above, a mixture of methyl allylacetate and methyl n-valerate is obtained by distillation.

Since both are contained in approximately the same amount in the mixture and their boiling points are extremely close, it is extremely difficult to separate the two simply by distillation.

The treatment of the mixture of methyl allyl acetate and methyl n-valerate with an acidic aqueous solution in the present invention is aimed at converting methyl allyl acetate into γ-valerolactone, and at the same time, methyl n-valerate is hydrolyzed and n-valerate is converted into γ-valerolactone. - Converted to valeric acid.

As the acidic aqueous solution, aqueous solutions of sulfuric acid, p-toluenesulfonic acid, trifluoroacetic acid, halogenated halides, perchloric acid, etc. are used, but in general, a sulfuric acid aqueous solution may be used.

The sulfuric acid concentration used is 40 to 90% by weight.

At a concentration lower than 40% by weight, hydroxylation of methyl allylacetate to the double bond becomes difficult to occur, making it difficult to produce γ-valerolactone, and even at a concentration of 90% by weight, the yield becomes poor.

After treatment with an acidic aqueous solution, the sulfuric acid is neutralized with an alkali such as an aqueous sodium carbonate solution, the raw material is extracted and separated with a solvent such as chloroform, methylene chloride, benzene, etc., and the solvent is removed to obtain n-valeric acid and γ-valerolactone. Get a mixture.

Of course, after neutralizing the acidic aqueous solution, it is possible to directly separate the two layers to obtain a mixture of n-valeric acid and γ-valerolactone as an oil layer.

In the present invention, the difference in boiling point between n-valeric acid and γ-valerolactone from a mixture is about 20°C at normal pressure, and it is possible to separate them simply by distillation, but it is possible to separate them with high purity. Separation requires a considerable number of distillation stages.

On the other hand, a mixture of both is treated with an alcohol in the presence of an acid catalyst to convert n-valeric acid to n-valeric acid ester, which increases the difference in boiling point from γ-valerolactone and separates it by distillation. You may.

In this case, the acid catalyst may be a general esterification acid catalyst such as sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, etc., and the alcohol is one whose boiling point is not close to the boiling point of the produced n-valeric acid ester and the boiling point of gamma-valerolactone. Any solvent may be used, but methanol, ethanol, propanol, etc. are used.

As detailed above, the present invention provides a novel method for producing n-valeric acid or its esters, which is industrially extremely advantageous compared to conventional production methods, and has the following advantages: There is.

First, electrolytic oxidation of monomethyl adipate yields a mixture of methyl allyl acetate and methyl n-valerate, and at the same time dimethyl sebacate is obtained; rather, dimethyl sebacate is the main product, and moreover, it is plastic. agent,
It is an industrially extremely important substance that is widely used in lubricating oils, nylon 6, 10, etc.

In this way, the mixture of methyl allylacetate and methyl n-valerate can be positioned as a by-product of dimethyl sebacate, which is an extremely important substance industrially, and n-
It is extremely advantageous as a raw material for producing valeric acid.

Second, by treatment with an acidic aqueous solution of methyl allyl acetate and methyl n-valerate, γ-valerolactone can be obtained simultaneously with n-valeric acid, and this substance is used as a raw material for various fragrances, solvents, agricultural chemicals, etc. It is an industrially important substance.

Conventionally, γ-valerolactone has been produced by hydrogenation of levulinic acid or by reacting acrylic acid ester with ethanol in the presence of ditertiary butyl peroxide, but compared to these conventional methods, The method according to the invention is a very advantageous method.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 35.7% by weight of monomethyl adipate was added to the electrolyte solution.
Potassium salt of monomethyl adipate 5.0% by weight, water 1
．． Two volumes of methanol solution containing 8% by weight are added and circulated to the electrolytic cell.

Both electrodes of the electrolytic cell have a current-carrying area of 1.2αX 100 crn, the cathode is a titanium plate with a thickness of 2 mm, and the anode is a titanium plate with a thickness of 2 mm and plated with 2 micron platinum. The electrode spacing was defined by a polyethylene plate.

The electrolytic cell has an electrolyte supply inlet and an outlet, and the liquid is flowed between the two electrodes at a flow rate of 2.0 m/sec, with a current density of 10.
1 k/di, keeping the temperature of the liquid at 53-56°C.
Electrolysis was carried out for 3.5 hours.

The voltage varied from 7.5■ to 5.7■. The electrolytic solution after the completion of the electrolytic reaction was 1.78k9, and when the concentration of each portion was determined by gas chromatography, methyl allylacetate and methyl n-valerate were each 1.6% by weight, and dimethyl sebacate was 1.6% by weight. It was 23.0% by weight.

Next, after removing methanol from the electrolyte, 50 mmHg
A mixture of methyl allylacetate and methyl n-valerate was distilled off at 89°C under reduced pressure.

Next, the mixed solution 505' of methyl allyl acetate and methyl n-valerate was mixed with 100 g of a 50% by weight aqueous sulfuric acid solution and stirred at 90° C. for 2 hours.

Then, the mixture was cooled, and only the added sulfuric acid was neutralized with a 20% by weight aqueous sodium carbonate solution, and the product was extracted three times with 50 g of chloroform.

When the concentration of each component in 193 g of chloroform solution was determined by gas chromatography, the concentration of γ-valerolactone was 10.
4% by weight, and n-valeric acid was 11.5% by weight.

Next, after removing chloroform from the chloroform extract, the two were separated by distillation at normal pressure.

The boiling point of n-valeric acid was 186°C, and the boiling point of γ-valerolactone was 207°C.

Example 2 Using the same apparatus as in Example 1, 4% by weight of monomethyl adipate, 4.6% by weight of potassium salt of monomethyl adipate, 5% by weight of dimethyl sebacate, and 0.5% by weight of water were added to the electrolyte tank in advance. Add 2 kg of methanol solution containing IA/d 1 to 6. OA/di, and during electrolysis, while continuously adding insufficient monomethyl adipate and potassium hydroxide to keep the concentration of monomethyl adipate and potassium salt of monomethyl adipate constant in the electrolytic solution. The other raw materials were electrolyzed in the same manner as in Example 1 for 20 hours.

The electrolytic solution after the completion of the electrolytic reaction was 1.76 ky, and the concentrations of each portion were 4% by weight of monomethyl adipate, 4.6% by weight of potassium salt of monomethyl adipate, 26.0% by weight of dimethyl sehacate, The concentrations were 2.1% by weight of methyl allylacetate and 2.1% by weight of methyl n-valerate.

Next, in the same manner as in Example 1, a mixture of methyl allylacetate and methyl n-valerate was taken out.

Next, 50 g of a mixture of methyl allyl acetate and methyl n-valerate was mixed with 80 g of an 80% by weight sulfuric acid aqueous solution at 80°C.
The mixture was stirred for 1 hour, then cooled, and only the sulfuric acid was neutralized with a 10% by weight aqueous sodium carbonate solution.Then, the product was extracted with chloroform in the same manner as in Example 1, and after removing the chloroform, 500g of methanol and 50% by weight of methanol were added. % sulfuric acid 5g
was added and heated under reflux for 5 hours.

After the reaction was completed, the mixture was neutralized with 5% by weight sodium carbonate, methanol was removed, and the oil layer was separated by distillation at normal pressure.

21 g of methyl n-valerate were obtained at a boiling point of 130 DEG C., and 11 g of .gamma.-valerolactone were obtained at a boiling point of 105 DEG C./30 Hg.

Claims (1)

[Claims] 1. Monomethyl adipate is electrolytically oxidized in the presence of its alkali metal salt in a methanol solvent, and a mixture of methyl allylacetate and methyl n-valerate is obtained by distillation from the obtained raw material, The mixture is treated with an acidic aqueous solution to obtain γ
- obtaining a mixture of valerolactone and n-valeric acid,
γ-valerolactone and n-valeric acid are then separated by distillation, or the mixture is treated with alcohols in the presence of an acid catalyst to convert n-valerian [n-valeric acid esters] and then γ-valeric acid is converted to n-valeric acid esters by distillation. - A method for producing n-valeric acid or its esters, which comprises separating valerolactone and n-valeric acid esters. 2. The method according to claim 1, wherein the electrolytic oxidation is carried out while maintaining the water concentration in the electrolytic solution in the range of 0.15 to 3.0% by weight. 3. The method according to claim 1, wherein the treatment of the mixture of methyl allylacetate and methyl n-valerate with an acidic aqueous solution is carried out with an aqueous sulfuric acid solution. 4. The method according to claim 3, wherein the sulfuric acid concentration of the sulfuric acid aqueous solution is 40 to 90% by weight.