JPS62127487A - Production of m-hydroxybenzyl alcohol - Google Patents

Abstract

PURPOSE:To produce m-hydroxybenzyl alcohol in a high yield by the electrolytic reduction of m-hydroxybenzoic acid in an acidic aqueous soln. by allowing m-hydroxybenzyl alcohol to always exist in the electrolytic soln. and carrying out the reaction at a specified temp. CONSTITUTION:When m-hydroxybenzoic acid is electrolytically reduced in an acidic aqueous soln. such as 10-20wt% aqueous H2SO4 soln. to produce m-hydroxybenzyl alcohol, m-hydroxybenzyl alcohol is cumulatively added during the reaction so that it always exists in the electrolytic soln. and the reaction is carried out at 20-70 deg.C, especially 30-60 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a useful compound of m-hydroxybenzyl alcohol, but at present it has not been commercially supplied by an inexpensive manufacturing method.

Synthesis methods for mHBOH include fermentation using m-cresol as a raw material, sodium amalgam using m-hydroxybenzaldehyde as a raw material, NILBH4, and LiAlH.
Although there are reductions using 4, etc. and hydrogen-based 10 reactions, they have not been put to practical use because the yields are insufficient. Further, the hydrogenation 111 reaction is a reaction at high temperature and high pressure, and there are various problems with industrial production methods.

Regarding the method using m-hydroxybenzoic acid (hereinafter abbreviated as mH]]A) as a raw material, sodium amalgam and electrolytic reduction method have been proposed (Bericht LfL 1
752 (1905)), but the yield was low and it could not be used as an industrial method.

Ming will do it.

Regarding the industrial production method of mHBOH, the present inventors have
After carrying out sharpening studies, we have previously discovered a method for obtaining 7nHBOH with high yield and high purity by electrolytic reduction of mHBA (Japanese Patent Application No. 59-90887, Japanese Patent Application No. 59-96639). These electrolytic reactions are batch reactions, but in order for the electrolytic reaction to proceed smoothly, the electrolyte must be uniformly dissolved.
It is necessary that no damage be caused to the electrode surface.

mHBA has low solubility in water, and it has been difficult to increase the substrate concentration. It is desirable to keep the substrate concentration at 10% or higher from the standpoint of industrial production efficiency and economic efficiency, but in order to dissolve mT (BA) in an aqueous solvent and achieve a concentration of 10% or higher, the temperature must be set at 90°C or higher. In addition, a method of increasing the concentration of mHBA by using a quaternary ammonium salt as a supporting electrolyte and increasing its compatibility with it, and a method of increasing the solubility of mHBA by using a water-soluble organic solvent.
There is a need for a method such as adding ester to A to increase its water solubility.

It was also found that when electrolyzing mHBA in a solution state, it is necessary to make the solution acidic, and the present inventors have previously proposed these methods.

However, if a supporting electrolyte or an organic solvent is used during the reaction, separation from the organic solvent or supporting electrolyte becomes complicated in order to isolate ml (BOH) after the completion of electrolysis, which increases costs.
Connects to p. Furthermore, in the method of increasing the solubility by raising the temperature, the decomposition rate of m HB A becomes faster as the temperature rises in an acidic aqueous solution, which is not preferable.

Figure 1 shows that the sulfuric acid concentration in the mHBA sulfuric acid aqueous solution is 5% by weight.
, 255% by weight, and the mHBA thermal decomposition rate after 5 hours.

As can be seen from the figure, for example, 1 (90% in 1 sulfuric acid aqueous solution)
When mHBA is dissolved at ℃, the decomposition proceeds at a rate of about 5 tons per hour, and although 4 to 5 hours are appropriate for the reaction, 20 to 25% of the total It turns out that decomposition cannot be ignored.

Furthermore, there was a problem with the heat resistance of the cation exchange membrane used in the diaphragm of the electrolytic cell, making electrolysis at high temperatures practically impossible.

In order to improve their luck, the present inventors conducted intensive studies on a method of electrolytic reduction by dissolving the substrate concentration by 1° or more in an acidic aqueous solution, and finally completed the present invention.

Figure 2 shows the solubility curve of mHBA at each temperature using an aqueous solution of mHBOH added to 100 g of water as a parameter. In the figure, the numbers in parentheses of each solubility curve indicate the weight of mHBOH added. Indicates the person in charge.

As can be seen from the figure, the solubility of mHBA becomes extremely high when, for example, 10 parts by weight of mHBOH is present, and the solubility is sufficient to allow mHBA decomposition to be carried out even at a relatively low temperature of 70° C. or lower.

Thus, although mHBA has low solubility in water,
mHBOH has high solubility in water, mHBO
When H is dissolved, the solubility of mHBA increases, so there is no need to add an organic solvent or supporting electrolyte to the electrolytic reduction reaction system, and the reaction can be carried out at a relatively low reaction temperature. For this purpose, it was realized that fiHBOH must always be present in the electrolytic solution subjected to the electrolytic reduction reaction, and the present invention was developed.

That is, in the present invention, when fiHBA is electrolytically reduced in an acidic aqueous solution, mHBO is always present in the electrolytic solution, and 2
This is a method for producing 1HBOH characterized in that it is carried out at a temperature of 0 to 70°C.

The present invention will be explained in detail below.

In the present invention, in order to always have mHBOH present in the electrolyte, mHBOH as a raw material must be added to mHBOH during the preparation stage.
A batch method may be used, in which mHBA is added and dissolved, and then mHBA is charged all at once.

However, there is a limit to the concentration of reaction substrates in the electrolyte.
As mHBOH gradually increases as the reaction progresses,
It is necessary to reduce the amount of mHBA used in the raw material, which reduces production efficiency. Furthermore, since the reaction time is long, mHBOH also tends to be slightly decomposed.

Therefore, in the present invention, it is desirable to adopt a semi-patch method in which mHBA to be consumed is added sequentially and cumulatively as the reaction progresses.

In addition, in the present invention, the acidic aqueous solution is not particularly limited as long as it is an acidic substance that is inert to the electrolytic reaction at the cathode, but mineral acids are preferably used in terms of cost, especially considering the material and yield characteristics. From this point of view, sulfuric acid is a preferred mineral acid. The concentration used is 5 to 30% by weight, preferably 10 to 20% by weight. When the sulfuric acid concentration is low, such as 5 parts by weight or less, the decomposition rate of mHBA is small, but the reaction rate is slow, and at high concentrations, such as 30 parts by weight or more, the reaction rate is fast, but the decomposition rate of mHBA is low. growing.

In the method of the present invention, it is not necessary to maintain the electrolytic reduction reaction temperature below 90°C, but 20 to 70°C, preferably 30°C.
Perform at a temperature of ~60'C. Further, electrolytic reduction with a substrate concentration of 10% or more is possible. mHBOH is present in the electrolyte, so when using the semi-patch method, mHBA
The addition rate can be determined by the consumption rate of mHBA, that is, the amount of current applied. The concentration of mHBA in the electrolyte is preferably maintained at 5% or less by cumulative addition, so that the electrolytic reaction proceeds smoothly and the total substrate concentration can be easily brought to 10% or more. I can do it.

However, if the concentration is too high, the viscosity will increase, which will adversely affect the current and the ion exchange membrane, so the final reaction substrate concentration is desirably 30 parts or less, usually 10 to 15 parts.

In addition, when the reaction temperature is below 20°C, mHB in the electrolyte
A is hardly dissolved, and for this purpose a large amount of mHBOH must be present, resulting in poor production efficiency. 70 again
If the temperature is higher than 0.degree. C., the decomposition rate of mHBA will be large and the yield of the target product will be poor.

In the present invention, the mHBA in the electrolytic solution does not necessarily have to be completely in an aqueous solution, and there is no problem even if it remains in the form of a slurry.
OH is appropriately determined based on the reaction temperature, acid concentration, mHBA solubility, and reaction substrate concentration.

Furthermore, in the method of the present invention, among the currents, materials having a high hydrogen overvoltage, specifically zinc, lead, cadmium, and mercury, are used as the cathode material. On the other hand, there are no particular limitations on the material used for the positive electrode, as long as it is a normal electrode material.

Although mHBOH is produced even in an electrolytic cell without a diaphragm, the yield of mHBOH relative to mHBA decreases because an oxidation reaction occurs even in a positive state. For this reason, it is particularly preferable to isolate the positive and negative chambers and the cathode chamber using a cation exchange membrane. As the material for the diaphragm, asbestos, ceramics, sintered glass, etc. can be used.

In the electrolytic reduction of the present invention, the current density is preferably 5 to
It is 30A/dm'. Theoretically, it is a four-electron reduction,
The current flow rate is 4Fr/mole, but the current efficiency is 50~
70%, so 5-8Fr/m is required to complete the reaction.
ole N, it is necessary to pass air volume.

As described above, the method of the present invention can also suppress thermal decomposition of mHBA by carrying out the process in the presence of mHBOI at an electrolyte temperature of 20 to 70°C, and more preferably by cumulatively adding mHBA depending on the reaction rate. The desired product can be obtained in high yield.Examples are shown below.

Example 1 Both electrode chambers had a capacity of 300 rnl, and an H-type electrolytic cell was used that was isolated with Selemion CMV (a cation exchange membrane manufactured by Asahi Glass ■) as a diaphragm.
200+n/each of sulfuric acid aqueous solution. 5 as cathode
0. A lead plate of ffl and a platinum plate of 5ocrI were used as an anode.

While maintaining the electrolytic cell at 30°C and applying a constant DC current of 6A, 25g of mHBA was added to the catholyte at a rate of 6g/hour using a microfeeder, and mHBA was added to the catholyte at a rate of 6g/hour in 4.2 hours.
HBA was added throughout Europe. After this, further electrolysis was carried out for 08 hours, 1
1! continued. (1,12Fr) After the electrolysis, liquid chromatography (HLC) analysis of the catholyte revealed that mH
BA was 0.1% and mHBOH was 9.9%. mH
The yield of BOH was 97.0%. Current efficiency 62.7.

Example 2 Using an electrolyzer similar to Example 1, 200 m of 20% sulfuric acid water was charged into both electrode chambers of the electrolytic cell, and while keeping the temperature at 6°C, a constant DC current of 12A was applied to mHBA 40.
21+1 L of the catholyte was added to the catholyte at a rate of 12 g/hour using a microfeeder, and constant current electrolysis was performed for 4 hours. (1,79Fr) After the electrolysis was completed, the HLC analysis result was mH as in Example 1.
BA O, 2%, mHBOH 15.6'ly.

Yield of mHBOH 95.4%. Current efficiency 61.8%.

Comparative Example 1 Using the same electrolytic cell as in Example 1, 200 mj of 15 ml of sulfuric acid aqueous solution was charged into both electrode chambers, the mouth temperature was set to 70°C, and m
HBA 259 was added to the catholyte. The catholyte was in the form of a slurry. This was subjected to constant current electrolysis at 5 A for 5 hours. (0,933Fr) After the electrolysis, the HLC analysis results were as in Example 1: mHBA 1.3%, mHBA
OH was 7.2%, and 2 others. Yield of fiHBOH 70.5%. Current efficiency: 54.8.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between solution temperature and mHBA decomposition rate after 5 hours in aqueous sulfuric acid solutions of mHBA at various concentrations. FIG. 2 shows solubility curves of mHBA at various temperatures in aqueous solutions of various concentrations added with mHBOH.

Claims (4)

[Claims] (1) Production of m-hydroxybenzyl alcohol, characterized in that when m-hydroxybenzoic acid is electrolytically reduced in an acidic aqueous solution, m-hydroxybenzyl alcohol is always present in the electrolytic solution, and the process is carried out at 20 to 70°C. Method. (2) Claim (1) states that m-hydroxybenzyl alcohol is present in the electrolytic solution by carrying out the reaction while cumulatively adding m-hydroxybenzoic acid as a raw material as the electrolytic reaction progresses. the method of. (3) The method according to claim (1), wherein the reaction temperature is 30 to 60°C. (4) The method according to claim (1), wherein the acidic aqueous solution is a 10 to 20% by weight sulfuric acid aqueous solution.