JPH04116188A - Production of m-hydroxybenzyl alcohol - Google Patents

Abstract

PURPOSE:To simply separate a product from starting material and to increase current efficiency by supplying electric current for a period of time in which high current efficiency is maintained and adjusting a liq. mixture contg. unreacted starting material to a specified pH when electrolytic reduction of m-hydroxybenzoic acid is performed in an acidic aq. soln. CONSTITUTION:An electrolytic cell is divided into anode and cathode chambers and electrolytic reduction of m-hydroxybenzoic acid (m-HBA) is performed in an acidic aq. soln. in the cathode chamber to produce m-hydroxybenzyl alcohol (m-HBOH). At this time, electric current is supplied for a period of time in which high current efficiency is maintained, a liq. mixture contg. unreacted m-HBA is adjusted to pH6-8 by adding NaOH, Na2CO3 or other alkali and the m-HBOH is separated from the m-HBA. By this method, m-HBA can be separated from m-HBOH and recovered as salt and the quantity of electric current supplied for electrolysis can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to m-hydroxybenzyl alcohol (hereinafter referred to as 5
-Abbreviated as HBOH). More specifically, it relates to the separation of m-hydroxybenzoic acid (hereinafter abbreviated as +m-HBA) and m-HBOH.

m-HBOH is a compound useful as an intermediate for industrial medicines or agricultural chemicals, but at present it has not been industrially supplied by inexpensive production methods.

[Conventional technology]

Methods for synthesizing m-HBOH include fermentation using I-cresol as a raw material, ■ sodium, amalgam, NaBH4, and LiAe using hydroxybenzaldehyde as a raw material.
There are reduction reactions and hydrogenation reactions using Ha, etc., but they have not been put into practical use due to insufficient yields.Also, hydrogenation reactions are reactions at high temperatures and high pressures, and are not suitable for industrial production methods. There are various problems.

In addition, regarding the method using 5-HBA as a raw material, sodium amalgam and electrolytic reduction method (Beilstein 3
81752) has been proposed, but the yield was low and it could not be used as an industrial method.

The present inventors first investigated the production method of m-HBOH, and found a method in which m-HBA is electrolytically reduced in an aqueous solution or a water-soluble organic solvent (JP-A-6O-234987),
Furthermore, a method of adding a supporting electrolyte to the catholyte (Japanese Unexamined Patent Publication No. 6
We have already found a method to obtain +1-HBOH in high yield with 0-243293).

[YA problem that the invention attempts to solve]

The electrolytic reduction reaction of the present invention usually uses an electrolytic cell with separate positive and negative electrodes, and the reaction is carried out on the cathode side.However, in order to complete the electrolytic reduction reaction, the current efficiency decreases in the latter half when the substrate concentration decreases. Therefore, an amount of current approximately three times the theoretical amount of current (4Fr/mole) is required. That is, in order to carry out the present electrolytic reaction more effectively, it is necessary to reduce the amount of electrolytic current applied so as to stop electrolysis in the first half when the current efficiency is good.

An object of the present invention is to provide an efficient method for separating It-)IBft, an unreacted raw material, and m-)IBOH, a product, by reducing the amount of current applied.

[Means for Solving the Problems] The present inventors have conducted extensive studies to solve the above problems.

The theoretical amount of current for the electrolytic reduction reaction of m-HBA is 4 Fr/m
However, the relationship between the amount of current applied during actual electrolysis, the conversion rate of the reaction, and the current efficiency is as shown in Figure 1. That is, when the current flow amount is 2 Fr/+no+, the conversion rate is 50% and the current efficiency is 100%, but when the current flow amount is 4 Fr/n+ol, the conversion rate is increased to 70%, but the current efficiency decreases to 70%. When 7 Fr/mo1 current is applied, the conversion rate is 90
%, but the current efficiency is 50%. In this way, the relationship between the amount of current applied, the conversion rate, and the current efficiency has been clarified, and it has been found that it is essential to lower the conversion rate in order to improve the current efficiency.

Furthermore, by preparing a reaction mixture of m-HBA as a raw material and m-HBOH as a product in a pill, it is possible to reduce the amount of electrolytic current applied by separating and recovering m-HBA as a salt from m)IBOH. That is, the present invention involves electrolytically reducing 0l-1 (BA in an acidic aqueous solution in a cathode chamber using an electrolytic cell with separate anodes and cathodes,
When producing m-HBOII, after applying electricity for a period of time while maintaining the current efficiency, the mixed solution containing unreacted m-11BA is adjusted to pH 6 to 8, and the product and the starting material are separated. This is a method for producing m-HBOII.

The present invention will be explained in detail below.

The acidic aqueous solution used in the method of the present invention is not particularly limited as long as it is an acidic substance that is inactive to the electrolytic reduction reaction at the cathode. From the viewpoint of yield, sulfuric acid is a preferred mineral acid, and a 5-30% by weight aqueous sulfuric acid solution is usually used.

The concentration of m-HBA in acidic aqueous solution is usually 5 to 20% by weight.
It is. ii Electrolytic reduction reaction 20-70°C1 Preferably carried out at a temperature range of 40-60°C. Further, among the electrodes used in the electrolytic reduction reaction, the cathode material is one having a high hydrogen overvoltage, specifically, zinc, lead, cadmium, or mercury. There are no particular limitations on the anode as long as it is a normal electrode, but examples include lead, carbon, platinum, DSE (Dime
nsinally 5table Electrde)
etc. are used.

It is necessary to separate the anode chamber and cathode chamber of the electrolytic cell.

Examples of the material for the separating diaphragm include ion exchange membranes, asbestos, ceramics, and cinctate glass, but ion exchange membranes are preferably used.

In the electrolytic reduction reaction of the present invention, the current density is 5 to 30 A.
/dTat, preferably 10 to 2 OA/dm''.

That is, in the present invention, when m-HBA is electrolytically reduced in an acidic aqueous solution in a cathode chamber using an electrolytic cell in which an anode and a cathode are separated,
While maintaining high current efficiency, specifically current efficiency 50
% or more, preferably 70% or more, after passing the unreacted m-1 (mixture containing BA) to p
Separate the product and starting materials using HtWJr...-R
This is a method for producing BOH.

Specific embodiments of the present invention are as follows.

An electrolytic cell with isolated positive and negative electrodes is used, and a sulfuric acid aqueous solution of a predetermined concentration is charged to both electrodes. Heat the electrolytic cell to a predetermined temperature,
A constant DC current is applied. The raw material m-)18^ is added all at once, in portions, or continuously into the cathode chamber. Electricity is applied for a predetermined period of time to perform an electrolytic reduction reaction.

After energizing for a predetermined time, unreacted m-11BA and m − in the cathode chamber
For example, add an alkali such as sodium hydroxide or sodium hydrogen carbonate to an acidic mixture containing BOH to adjust the pH.
6 to 8, preferably pH 6, 5 to 7 Figure-2
As is clear from the pt1 curves of TI-HBA and m-IIBOH shown in , when the pH of the reaction mixture is less than 6, the distribution ratio of water and organic solvent in m-1(BA, m-HBOH becomes small). Extraction becomes difficult. In addition, when pl+ exceeds 8, m-HBOH and m-HBOH also form salts and dissolve in the aqueous layer, making separation difficult, which is not preferable.
-HBA is dissolved in the aqueous layer as a metal salt, and m-HBOH becomes free. m-118OH of the product in organic solvent
Extract. As a result, the salt of m-NBA is in the aqueous phase and +n
-1 (Boil can be separated into an organic phase. By making the aqueous phase acidic again, m-flBA can be recovered and used for the next electrolytic reduction reaction.

Moreover, m-HBOH can be obtained from the organic phase by distilling off the organic solvent.

〔Effect of the invention〕

m-HBA is electrolytically reduced in an acidic aqueous solution to produce m-IIBA.
In order to obtain this, it is necessary to apply an excessive amount of current compared to the theoretical amount of current, which leads to a decrease in current efficiency, which is a problem.

In the method of the present invention, after applying current within a period of high current efficiency, ff1-HBA and m-HBOH can be easily separated and recovered by preparing a pu of a mixed solution of unreacted raw materials and electrolytic components. It is industrially valuable.

〔Example] Hereinafter, the method of the present invention will be explained in detail with reference to Examples.

Example 1 Both electrodes have a solubility of 300 d, and an H-type cell isolated by Selemion (manufactured by Asahi Glass Co., Ltd.) CMV is used as a diaphragm, and 200 d of 10% sulfuric acid aqueous solution is charged into both electrode chambers, each serving as a cathode. 25c++1 lead plate, 25c as anode
J platinum plate was used. ! While keeping the solution cell at 60°C,
While applying a constant DC current of 4 A, 25 g of m-HBA was added to the cathode at a rate of 6.4 g/Hr using a microfeeder, and the entire amount of w-NBA was added in 3.9 hours.

After this, electrolysis was further continued for 1 hour (4.OFr/mo
le).

After electrolysis, the catholyte is extracted and replaced with 98% NaOH18,3
g was added to prepare p)l-7. Next, the mixture was extracted with ether, and after distilling off the ether, 16.7 g of crystals were obtained. As a result of CC analysis, the purity of m-HBOH was 98%, and the isolation yield was 73% (
As a result of HLC analysis of the extraction residue, the m-HBA conversion rate was 75% and the electrolytic current efficiency was 75%.

Example 2 200 d of 10% sulfuric acid aqueous solution was charged to both electrodes of an electrolytic cell similar to Example 1. A 25cJ lead plate was used as the cathode, and a 25c+a platinum plate was used as the anode. m-HBA2 while keeping the electrolytic cell at 50'C and applying 4A of DC current.
5g using a micro feeder at 6.4g/Hr
The total amount of m-NBA was added in 4.9 hours. After this, electrolysis was continued for another 1.1 hours (
5Fr/mole), after electrolysis, the catholyte is drained 9
Add 17.8g of 8% NaOH and pl! =7. Next, extract with ether, and after distilling off the ether, 17.9
Crystals of g were obtained. As a result of CC analysis, m-HBOH purity was 9.
7%, isolated yield 78% (98% based on consumed m-HBA)
), and as a result of HLC analysis of the extraction residue, m-
The HBA conversion rate was 80%, and the electrolysis current efficiency was 64%.

Comparative Example 1 Both electrodes have a solubility of 300 Inl, and an H-type cell isolated by Selemion (manufactured by Asahi Glass) CMV is used as a diaphragm, and a 10% sulfuric acid aqueous solution is charged into both electrode chambers at a rate of 200 Inl. 25cn lead plate as anode, 25cn as anode
ffl platinum plate was used. While maintaining the 1:1 solution cell at 60'C and applying 4A of DC current, m-HBA25
g using a microfeeder at 6.4 g/Hr
The total amount of m-)18M was added in 4.9 hours.

After this, electrolysis was further continued for 9.7 hours (12 Fr/
+note).

After electrolysis is complete, the catholyte is extracted and replaced with 98% NaOH16,7
g was added to neutralize to pH=7. Next, the mixture was extracted with ether, and after distilling off the ether, 21.3 g of crystals were obtained. As a result of CC analysis, m-HBO)I purity is 98%, isolation yield is 93%.
, 95% of the consumed steel HBA. Further, as a result of HLC analysis of the extraction residual liquid, the conversion rate of m-HBA was 98%, and the electrolytic current efficiency was 33%.

Comparative example 2 The same reaction as in Example 1 was carried out.

After the reaction was completed, the catholyte was extracted and 98% Na0I (16.7 g
was added to adjust the pH to 4. Next, extract with ether,
Ether was distilled off to obtain 18.8 g of crystals.

As a result of CC analysis, m-HBOI (87%, m-HBAI
I%, isolated yield was 73%, 97% based on consumed m-NBA. As a result of HLC analysis of the extraction residue, residual 5-H
BA was 4.2g.

Comparative example 3 The same reaction as in Example 2 was carried out.

After the reaction was completed, the catholyte was extracted and adjusted to pH 10 by adding 19.1 g of 98% NaOH. Next, extract with ether,
Ether was distilled off to obtain 16.1 g of crystals.

As a result of CC analysis, m4BOl (purity 99%, isolation yield 7
1%, and 89% relative to the consumed m-HB'A. As a result of HLC analysis of the extraction residue, 5 g of residual m-HBA, m-
HBO) was 11.6 g.

〔Effect of the invention〕

As is clear from the examples, in the production of m-HBOH by electrolytic reduction of m-HBA, the pHtFI of the electrolytic reaction solution
This method made it possible to separate unreacted an-HBA and m-HBOH. That is, prior to the present invention, an excessive amount of electric power exceeding the theoretical amount of current was required, and the current efficiency as an electrolytic reduction process was extremely low. However, pH1! Since an effective separation method has been established by manufacturing, it has become possible to improve current efficiency and improve volumetric efficiency by shortening reaction time.

[Brief explanation of drawings]

FIG. 1 shows the conversion rate and current efficiency of m-H'BA with respect to the amount of current applied.

Claims (1)

[Claims] 1. Electrolytic reduction reaction of m-hydroxybenzoic acid is carried out in an acidic aqueous solution in the cathode chamber using an electrolytic cell with separated anode and cathode, and m-
When producing hydroxybenzyl alcohol, after applying electricity for a period of time while maintaining high current efficiency, a mixed solution containing unreacted m-hydroxybenzoic acid is adjusted to pH 6 to 8, and m-
A method for producing m-hydroxybenzyl alcohol, which comprises separating hydroxybenzyl alcohol and m-hydroxybenzoic acid.