JP7312399B2 - Method and apparatus for producing hydroxy acid - Google Patents

Description

The present invention relates to a method and apparatus for producing hydroxy acid.

Hydroxy acids represented by 3-hydroxypropionic acid (hereinafter also referred to as “3HP”) are compounds having a hydroxy group (hydroxyl group) and a carboxylic acid group in the same molecule, and are used in various applications. For example, 3HP is a very useful compound as a raw material for various chemical products such as acrylates.

Various studies have been conducted on methods for synthesizing hydroxy acids represented by 3HP. For example, as a method for synthesizing 3HP, a method of carrying out an oxidation reaction using 1,3-propanediol (hereinafter also referred to as "PDO") as a starting material is being studied. Generally, PDO is a compound having chemically equivalent hydroxy groups at both ends of an alkyl group having 3 carbon atoms, and it is quite difficult to oxidize only one of the hydroxy groups in terms of synthesis. Among them, Non-Patent Document 1 discloses a method of synthesizing 3HP from PDO by an oxidation reaction using hydrotalcite-supported gold-palladium nanoparticles as a catalyst.

M. Mohammad, S. Nishimura, K. Ebitani, AIP Conf. Proc. 2015, 1649, 58.

On the other hand, in the synthesis method of Non-Patent Document 1, it is necessary to constantly supply O ₂ gas, and the yield of 3HP is as low as 42%.

In view of the above circumstances, it is an object of the present invention to provide a method and an apparatus for producing a hydroxy acid that are suitably used in the reaction of oxidizing a diol to produce a hydroxy acid, have a high yield of the hydroxy acid in the reaction, and can be easily scaled up.

As a result of intensive studies on the above problems, the present inventors found that the above problems can be solved by applying a constant voltage based on a reference electrode to a metal particle-supported catalyst as a working electrode, and completed the present invention.

The method for producing a hydroxy acid according to the first aspect of the present invention for achieving the above object is to prepare an aqueous solution of a raw material having hydroxy groups at both ends of an organic compound or a reaction solution composed of a mixed solution of water and an organic solvent, and to immerse a working electrode, a counter electrode, and a reference electrode in the reaction solution, and energize the working electrode and the counter electrode for a predetermined period of time. A hydroxy acid is produced by oxidizing only a hydroxy group to form a carboxylic acid.

The method for producing a hydroxy acid according to the second aspect of the present invention is characterized in that, in the first aspect, the organic compound is an alkyl group having 2 to 8 carbon atoms or a compound having oxygen in the middle of the alkyl group.

A third aspect of the method for producing a hydroxy acid of the present invention is characterized in that, in the first or second aspect, a catalyst layer that assists the oxidation reaction is formed on the surface of the working electrode.

The method for producing a hydroxy acid according to the fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the predetermined time during which the working electrode and the counter electrode are energized is within the oxidation reaction possible time of the raw material in the reaction solution.

The apparatus for producing a hydroxy acid according to the first aspect of the present invention comprises: a reaction vessel for storing a reaction solution of raw materials having hydroxyl groups at both ends of an organic compound; a working electrode, a counter electrode and a reference electrode immersed in the reaction solution and energized; an energization time control unit for energizing the working electrode and the counter electrode for a predetermined time; It is characterized by

A hydroxy acid production apparatus according to a second aspect of the present invention is characterized in that, in the first aspect, a catalyst layer is formed on the surface of the working electrode to assist the oxidation reaction.

According to a third aspect of the present invention, there is provided an apparatus for producing a hydroxy acid according to the first or second aspect, wherein the energization time control unit sets the predetermined time for energizing the working electrode and the counter electrode to be within the oxidation reaction possible time of the raw material in the reaction solution.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method and an apparatus for producing a hydroxy acid that are suitably used in a reaction for producing a hydroxy acid by oxidizing a diol, have a high yield of the hydroxy acid in the reaction, and can be easily scaled up.

Schematic diagram showing one embodiment of the hydroxy acid production apparatus of the present invention Characteristic diagram showing CV measurement results of 1,3-propanediol Characteristic diagram showing CV measurement results of 1,3-propanediol when the pH of the reaction solution is changed Spectral diagram of mass spectrometry obtained in Example 1 Spectral diagram of mass spectrometry obtained in Example 2 Spectral diagram of mass spectrometry obtained in Example 3 Spectral diagram of mass spectrometry obtained in Example 4 Spectral diagram of mass spectrometry obtained in Example 5 Spectral diagram of mass spectrometry obtained in Example 6 Spectral diagram of mass spectrometry obtained in Example 7

The method and apparatus for producing a hydroxy acid according to the present invention will be described below with reference to FIGS. 1 to 10. FIG.

In this specification, the numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.

As shown in FIG. 1, one embodiment of the hydroxy acid production apparatus of the present invention comprises an energization control section 1, an energization time control section 2, and a reaction vessel 3. As shown in FIG. In the reaction container 3, three types of electrodes connected to the energization control unit 1 are immersed in the reaction solution 3a, and the oxidation reaction is started by applying a predetermined voltage from the energization control unit 1. As the three types of electrodes, a working electrode 4 carrying metal particles (not shown), a reference electrode 5 and a counter electrode 6 are used. The working electrode 4 has a metal particle-supported catalyst and an electrode material (both not shown). The metal particle-supported catalyst has metal particles containing noble metals including gold and platinum and a catalyst stabilizer, and a carrier containing carbon black that supports the metal particles (none of which is shown).

In the following, first, each component of the hydroxy acid production apparatus and its preparation method will be described in detail, and then the production method will be described in detail.

<<Energization control unit 1>>
The apparatus for producing hydroxy acid includes an electrification control unit 1 . The energization control unit 1 has a mechanism capable of controlling the voltage applied to the working electrode 4 based on the potential of the reference electrode 5 . Although it is not particularly limited as long as it is an energization control unit 1 having a circuit equipped with an operational amplifier, it is preferable that the reference electrode 5 can be controlled to -10 to +10 V, preferably -5 to +5 V, more preferably -2 to +2 V.

<<Energization time control unit 2>>
The hydroxy acid manufacturing apparatus includes an energization time control section 2 . The energization time control unit 2 functions as a monitor for grasping the oxidation reaction occurring on the working electrode 4 in real time and measuring the timing of reaction completion. The energization time control section 2 is normally connected in series in the middle of the circuit connecting the working electrode 4 and the counter electrode 6 . The energization time control unit 2 is not particularly limited as long as it can measure the current, but it is preferably one that can measure from 10 mA to 50 A.

<<reaction vessel 3>>
The hydroxy acid manufacturing apparatus includes a reaction vessel 3 . The reaction vessel 3 substantially acts as a reaction field for producing hydroxy acid. A reaction vessel 3 is filled with a reaction solution 3a, in which a working electrode 4, a reference electrode 5 and a counter electrode 6 are immersed. In order to increase the efficiency of the reaction, the reaction vessel 3 may be accompanied by a stirring device for stirring the reaction solution 3a. The material and shape of the reaction vessel 3 are not particularly limited as long as they do not hinder the production of hydroxy acid. For example, a resin or ceramic vessel or beaker is preferable.

<Connection method>
First, the working electrode 4 , the reference electrode 5 and the counter electrode 6 are immersed in the reaction solution 3 a in the reaction vessel 3 . After that, each electrode is connected to a predetermined terminal of the energization control section 1 . The energization time control section 2 is connected in series in a circuit connecting the working electrode 4 and the counter electrode 6 . The reaction solution 3a is stirred by the stirrer, and voltage is applied to the working electrode 4 by the energization controller 1, thereby starting the production of hydroxy acid.

<<Working electrode 4>>
The working electrode 4 of the present invention has a metal particle-supported catalyst and an electrode material. The metal particle-supported catalyst has metal particles containing noble metals including gold and platinum and a catalyst stabilizer, and a carrier containing carbon black that supports the metal particles.

Below, first, each element constituting the working electrode 4 will be described in detail, and then the manufacturing method thereof will be described in detail.

<Metal particle-supported catalyst>
(gold and platinum)
Metal particles include gold and platinum as noble metals.
The molar ratio of gold to platinum (gold:platinum) is not particularly limited, but it is preferably in the range of 99:1 to 1:99, more preferably in the range of 90:10 to 10:90, further preferably in the range of 90:10 to 20:80, even more preferably in the range of 90:10 to 30:70, in terms of higher yield and/or selectivity of the hydroxy acid (hereinafter simply referred to as "the point where the effects of the present invention are more excellent"). is particularly preferred, most preferably in the range of 80:20 to 75:35.

As a method for measuring the molar ratio of gold and platinum, for example, the metal particle-supported catalyst is treated with acid to elute gold and platinum, and gold ions and platinum ions in the eluate are quantified by high-frequency inductively coupled plasma (ICP) emission spectrometry.

(metal particles)
Although the average particle diameter of the metal particles contained in the metal particle-supported catalyst of the present invention is not particularly limited, it is preferably 1 to 10 nm, more preferably 1 to 5 nm, even more preferably 1 to 2 nm, from the viewpoint of better effects of the present invention.

The crystal structure of gold and platinum in the metal particles may be, for example, an alloy structure in which gold and platinum are arranged irregularly, a core-shell structure having platinum in the core layer and gold in the shell layer, or a core-shell structure having gold in the core layer and platinum in the shell layer. Any crystal structure shall be included in the metal particles of the present invention.

(catalyst stabilizer)
Metal particles include a catalyst stabilizer. The catalyst stabilizer acts as a protective agent that protects the precious metals contained in the metal particles. That is, catalyst stabilizers are often placed over the surface of noble metals, including gold and platinum.

A catalyst stabilizer means a hydrophilic polymer having a hydrophilic group in its main chain or side chain in its molecular structure.

The hydrophilic polymer compound can be selected from polyvinylpyrrolidone (PVP), polyvinyl alcohol, polyethyleneimine, polydiallyldimethylammonium chloride, polyacrylic acid, polysulfonic acid, and the like.

In particular, it is preferable to use polyvinylpyrrolidone (PVP) as the catalyst stabilizer, and the amount of adsorption to the carrier can be increased by making the content of the monomer number equal to or less than the total number of moles of the metal catalyst in the catalyst carrier. This is presumably because when the concentration of the catalyst stabilizer increases, the surface of the metal catalyst particles is densely covered with the catalyst stabilizer, and the hydrophobicity of the metal catalyst particles is reduced, so that the driving force for adsorption of the metal catalyst particles to the carbon particles, which also have hydrophobic surfaces, is lost.

(Carrier)
Carbon black is an example of the carrier that supports the metal particles. Carbon black used as a carrier is not particularly limited as long as it has electrical conductivity. Acetylene black and Vulcan XC-72 (VALCAN is a registered trademark of Gabot Corporation) can also be used, but Ketjenblack, which has a high specific surface area and high porosity, is more preferable.

<Metal particle-supported catalyst preparation method>
The method for producing the metal particle-supported catalyst is not particularly limited, but from the point of view of being able to efficiently produce the metal particle-supported catalyst, an embodiment including a step of obtaining a metal particle and a step of contacting the metal particle and carbon black to obtain a metal particle-supported catalyst.

The procedure of each step will be described in detail below.

(Metal particle forming step)
In this step, gold ions and platinum ions are reduced in the presence of PVP, which is a catalyst stabilizer, to produce noble metals including gold and platinum and metal particles including PVP.

Catalyst stabilizers are as described above.

Chloroauric acid is preferred as the source of gold ions used in this step. Moreover, chloroplatinic acid is preferable as a supply source of platinum ions.

In this step, the means for reducing gold ions and platinum ions in the presence of a catalyst stabilizer is preferably a reduction reaction by a NaBH ₄ reduction method. Besides NaBH ₄ , hydrazine, citric acid, ascorbic acid, ethanol and the like can also be used as the reducing agent. By reducing gold ions and platinum ions under the above conditions, precious metals including gold and platinum can be protected by the catalyst stabilizer.

In this step, the order of reducing gold ions and platinum ions is not particularly limited. For example, gold ions and platinum ions may be reduced simultaneously, or gold ions and platinum ions may be reduced separately, ie either gold ions or platinum ions are reduced and then the other ion is reduced sequentially. Generally, in the former case, an alloy structure in which gold and platinum are arranged irregularly can be formed, and in the latter case, core-shell noble metal particles composed of gold and platinum can be formed. Either case shall be included in this step.

By carrying out this step under the above conditions, it becomes possible to protect noble metals including gold and platinum with fine and uniform particle sizes by the amphoteric surfactant.

(Contact process)
This step is a step of bringing the metal particles into contact with a carrier containing carbon black to support the metal particles on the carrier to obtain a metal particle-supported catalyst.

The carbon black used in this step is as described above.

As used herein, "contacting" means, for example, but is not limited to, adding a component to another component. For example, a support containing carbon black may be added to a solution containing metal particles, or metal particles may be added to a solution containing a support containing carbon black. In this case, the order and speed of contacting each component can be appropriately set based on the chemical properties of the components used.

This step is preferably carried out in the presence of a solvent that substantially disperses the metal particles and the support containing carbon black. The solvent used in this step is preferably water.

In this step, the metal particles and the support containing carbon black are brought into contact with each other under room temperature conditions to obtain a mixture, thereby allowing the metal particles to be supported on the support. The contact time of the mixture is preferably 0.5 to 48 hours, more preferably 0.5 to 36 hours, and particularly preferably 0.5 to 24 hours. The metal particle-supported catalyst obtained by the above treatment can be separated by conventional means such as suction filtration.

The shape and dimensions of the metal particle-supported catalyst are not particularly limited. The shape of the metal particle-supported catalyst is not limited, but may be, for example, a fine particle shape or a powder shape, and any shape of the metal particle-supported catalyst can be used. A powdery form is particularly preferred.

<Electrode material>
The working electrode 4 contains an electrode material. The electrode material receives electrons generated by an oxidation reaction on the metal particle-supported catalyst and acts as a wiring that bypasses the electrons to the counter electrode 6 . Therefore, the metal particle-supported catalyst is often arranged on the surface of the electrode material so as to be in contact with the raw material in the reaction solution. The electrode material is not particularly limited as long as it is a material exhibiting conductivity, but it is preferable to use carbon paper or carbon cloth.

<Binder>
The working electrode contains a binder. The binder has the effect of bonding the metal particle-supported catalysts together and the metal particle-supported catalyst and the electrode material. As the binder, a polymer electrolyte having proton conductivity and a perfluoro-based proton exchange resin of a fluoroalkyl copolymer having a fluoroalkyl ether side chain and a perfluoroalkyl main chain is preferably used. Examples include Nafion (registered trademark) manufactured by DuPont, Aciplex (trade name) manufactured by Asahi Kasei, Flemion (registered trademark) manufactured by Asahi Glass, Gore-Select (registered trademark) manufactured by Japan Gore-Tex, etc. Partially fluorinated resins include polymers of trifluorostyrene sulfonic acid and those obtained by introducing sulfonic acid groups into polyvinylidene fluoride. There are also hydrocarbon-based proton-exchange resins such as styrene-divinylbenzene copolymers and polyimide-based resins into which sulfonic acid groups are introduced.

The metal particle-supported catalyst obtained in the above process functions as the working electrode 4 by dispersing it in a binder solution having a predetermined concentration, applying this dispersion to the electrode material, and drying it.

<<reference electrode 5>>
The hydroxyacid production apparatus includes a reference electrode 5 . Since the reaction is performed while controlling the voltage applied to the working electrode 4 during the production of hydroxy acid, it is necessary to know the voltage of the working electrode 4 accurately. A reference electrode 5 is used as a potential reference for this purpose. A necessary requirement for the reference electrode 5 is to exhibit a constant and stable potential over a long period of time. For that purpose, it is desirable not to pass the current through the reference electrode 5 . Examples of the reference electrode 5 include a standard hydrogen electrode, a reversible hydrogen electrode, a silver-silver chloride electrode, a calomel electrode, and a palladium/hydrogen electrode. For the production of hydroxyacids, Ag/AgCl reference electrodes are used because of their ease of use.

<<counter electrode 6>>
A reduction reaction occurs at the counter electrode 6 using the electrons generated at the working electrode 4 . A reduction reaction is probably occurring in which the hydrogen ions present in the reaction solution 3a are reduced to hydrogen. The material of the counter electrode 6 is basically not particularly limited as long as it is a substance exhibiting conductivity, and for example, platinum, stainless steel, titanium, and the like are used. Alternatively, an electrode coated with a catalyst that promotes the reduction reaction may be used.

<How to determine the boundary voltage>
The boundary voltage is determined by cyclic voltammetry (CV) measurement of the diol that is the raw material of the hydroxy acid to be produced. Prepare a working electrode 4 such as a glassy carbon electrode coated with a catalyst, a reference electrode 5 using Ag/AgCl or the like, and a counter electrode 6 such as a Pt wire, insert each electrode into a solution containing a diol, and then perform CV measurement. The reference electrode 5 is of the same type as that used in the hydroxyacid manufacturing apparatus. From the CV waveform obtained, it is first confirmed whether there is an oxidation peak indicating that the diol has been oxidized by the catalyst. If an oxidation peak is observed, confirm the voltage value at which the oxidation peak is reduced. This voltage value is the boundary voltage during the production of hydroxy acid. If no oxidation peak is observed, examine the conditions under which the target diol is oxidized by changing the pH and temperature of the solution containing the diol, the voltage scanning range, the type of catalyst used, and the like.

Here, taking 1,3-propanediol, which is a raw material of 3-hydroxy acid, as an example, CV measurement to determine the boundary voltage to be set in the hydroxy-acid production apparatus will be described (see FIG. 2). A glassy carbon electrode was used as the working electrode 4, and a catalyst in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was applied to the surface. A Ag/AgCl (saturated KCl) electrode was used as the reference electrode 5 and a platinum wire was used as the counter electrode 6 . Each electrode was immersed in a reaction solution (0.1 M 1,3-propanediol, 0.1 M NaOH), and a potentiostat was used to sweep the voltage between −0.8 and 0.6 V at a rate of 100 mV/s. As a result, as indicated by the solid line in FIG. 2, an oxidation peak was detected near −0.1 V indicating that 1,3-propanediol was oxidized. On the other hand, as indicated by the dashed line in FIG. 2, this oxidation peak was not observed in the reaction solution to which 1,3-propanediol was not added. Based on this CV measurement result, the boundary voltage was set to 0.3 V at which the oxidation peak of 1,3-propanediol was completely reduced. For other diols, the boundary voltage of the hydroxy acid production apparatus can be determined by confirming the boundary voltage value by CV measurement according to the above method.

<<Method for producing hydroxy acid>>
The apparatus for producing hydroxy acid described above can be suitably applied to a method for producing hydroxy acid. More specifically, the metal particle-supported catalyst or catalyst composition prepared as the working electrode 4 is suitably used for producing a hydroxy acid by oxidizing a diol having hydroxy groups at both ends of an organic compound. In this production method, only one hydroxy group in the diol is oxidized to a carboxylic acid group, producing a hydroxy acid having both a hydroxy group and a carboxylic acid group in the molecule.

First, the working electrode 4, the reference electrode 5, and the counter electrode 6 are immersed in the reaction solution 3a of the reaction vessel 3, and after each electrode is connected to a predetermined terminal of the energization control unit 1 in a predetermined manner, the energization control unit 1 applies a voltage to the working electrode 4, thereby starting the production of hydroxy acid. This set voltage uses the voltage value determined by the method of determining the boundary voltage. In the case of the example of FIG. 2, it is set to 0.3V. Further, the reaction solution 3a is always stirred by a stirring device during the reaction.

Below, first, the components used in this production method will be described in detail.

The metal particle-supported catalyst and catalyst composition are as described above.

The diol is not particularly limited as long as it is an organic compound having two hydroxy groups (hydroxyl groups), and includes diols having a lower limit of 2 or more carbon atoms and an upper limit of usually 10 or less, preferably 8 or less. It may also be an alkyl group having 2 to 8 carbon atoms or an organic compound having an oxygen in the middle of the alkyl group.

The method for producing a hydroxy acid of the present invention includes a step of producing a hydroxy acid by oxidizing one hydroxy group of a diol in the presence of the metal particle-supported catalyst or catalyst composition described above.

The amount relationship between the diol and the metal particle-supported catalyst is not particularly limited, and optimal conditions (concentration, reaction temperature, reaction time, reaction atmosphere, etc.) are appropriately selected depending on the type of diol used.

This step is preferably carried out in the presence of a solvent that substantially disperses or dissolves the diol. The solvent used in this step is not particularly limited as long as it does not inhibit the oxidation reaction of the diol, and any solvent commonly used in the art can be used. Examples of the solvent include, but are not limited to, water, acetone, acetonitrile, and THF, with water being preferred.

This step is preferably carried out under a basic pH of the solvent in which the diol is substantially dispersed or dissolved. The pH of the solvent used in this step is not particularly limited as long as it does not inhibit the oxidation reaction of the diol, and the pH range is preferably 7 or higher, more preferably 11 or higher.

As an example, FIG. 3 shows the CV measurement results for 1,3-propanediol at pH 6-12. From FIG. 3, it can be seen that the oxidation peak of 1,3-propanediol gradually increases from pH 10 to 12. On the other hand, at pH 9 or less (including pH 6), the current value hardly changed in the scanning range of -0.4 to 0.1 V, and propanediol oxidation reaction did not occur.

Examples of bases that can be used include inorganic bases such as sodium hydroxide and potassium hydroxide, organic bases such as pyridine, diethylamine and triethylamine, and alkali metal alkoxides such as sodium methoxide and sodium ethoxide.

The content of the base in the reaction solution 3a is not particularly limited, but is preferably 0.1 to 5.0M, more preferably 0.2 to 2.4M.

The procedure above produces a hydroxy acid. As mentioned above, a hydroxy acid is a compound having a hydroxy group and a carboxylic acid group in its molecule.

The catalyst composition of the present invention may optionally contain a solvent (eg, water or organic solvent).

Examples are shown below, but the present invention is not limited to these.

(Example 1)
A carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed as a working electrode 4 in a reaction solution (1.11 M sodium hydroxide, 0.37 M 1,3-propanediol) 3a, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.3 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. After reacting for 8 hours, about 1 mL of the reaction solution 3a was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter and subjected to a mass spectrometer (ESI-negative mode).

FIG. 4 shows the results of mass spectrometry. Deprotonated 3-hydroxypropanoic acid [90.08 g/mol] was detected as the main peak at m/z=89.0. As a result, it was found that 3-hydroxypropanoic acid [90.08 g/mol] was obtained from 1,3-propanediol [76.09 g/mol] in reaction solution 3a.

(Example 2)
A carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed as a working electrode 4 in a reaction solution (1M potassium hydroxide, 2 vol% 1,5-pentanediol) 3a, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.5 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. After reacting for 1 hour, about 1 mL of the reaction solution was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter and subjected to a mass spectrometer (ESI-negative mode).

FIG. 5 shows the results of mass spectrometry. Deprotonated 5-hydroxypentanoic acid [118.13 g/mol] was detected as the main peak at m/z=117.1. As a result, it was found that 5-hydroxypentanoic acid [118.13 g/mol] was obtained from 1,5-pentanediol [104.15 g/mol] in reaction solution 3a.

(Example 3)
A carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed as a working electrode 4 in a reaction solution (1M potassium hydroxide, 2 vol% 1,6-hexanediol) 3a, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.5 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. After reacting for 1 hour, about 1 mL of the reaction solution was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter and subjected to a mass spectrometer (ESI-negative mode).

FIG. 6 shows the results of mass spectrometry. Deprotonated 6-hydroxyhexanoic acid [132.16 g/mol] was detected as the main peak at m/z=131.1. As a result, it was found that 6-hydroxyhexanoic acid [132.16 g/mol] was obtained from 1,6-hexanediol [118.17 g/mol] in reaction solution 3a.

(Example 4)
A carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed as a working electrode 4 in a reaction solution (1M sodium hydroxide, 2 vol% 1,4-cyclohexanedimethanol) 3a, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.3 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. After reacting for 2 hours, about 1 mL of the reaction solution was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter and subjected to a mass spectrometer (ESI-negative mode).

FIG. 7 shows the results of mass spectrometry. Deprotonated 4-(hydroxymethyl)cyclohexanecarboxylic acid [158.19 g/mol] was detected as the main peak at m/z=157.1. As a result, it was found that 4-(hydroxymethyl)cyclohexanecarboxylic acid [158.19 g/mol] was obtained from 1,4-cyclohexanedimethanol [144.21 g/mol] in reaction solution 3a.

(Example 5)
A carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed in a reaction solution (1 M potassium hydroxide, 2 vol% ethylene glycol) 3a as a working electrode 4, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.3 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. After reacting for 1 hour, about 1 mL of the reaction solution was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter and subjected to a mass spectrometer (ESI-negative mode).

FIG. 8 shows the results of mass spectrometry. Deprotonated glycolic acid [76.05 g/mol] was detected as the main peak at m/z=75.1. As a result, it was found that glycolic acid [76.05 g/mol] was obtained from ethylene glycol [62.09 g/mol] in reaction solution 3a.

(Example 6)
A carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed as a working electrode 4 in a reaction solution (1M potassium hydroxide, 2 vol% triethylene glycol) 3a, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.5 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. After reacting for 1 hour, about 1 mL of the reaction solution was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter and subjected to a mass spectrometer (ESI-negative mode).

FIG. 9 shows the results of mass spectrometry. Deprotonated [2-(2-hydroxyethoxy)ethoxy]acetic acid [164.17 g/mol] was detected as the main peak at m/z=163.1. As a result, it was found that [2-(2-hydroxyethoxy)ethoxy]acetic acid [164.17 g/mol] was obtained from triethylene glycol [150.17 g/mol] in reaction solution 3a.

(Example 7)
A carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed as a working electrode 4 in a reaction solution (1M potassium hydroxide, 2 vol% tetraethylene glycol) 3a, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.5 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. After reacting for 1 hour, about 1 mL of the reaction solution was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter and subjected to a mass spectrometer (ESI-negative mode).

FIG. 10 shows the results of mass spectrometry. Deprotonated 2-[2-(2-hydroxyethoxy)ethoxy]acetic acid [208.23 g/mol] was detected as the main peak at m/z=207.23. As a result, 2-[2-(2-hydroxyethoxy)ethoxy]acetic acid [208.23 g/mol] was obtained from tetraethylene glycol [194.23 g/mol] in reaction solution 3a.

(Example 8) Reaction Yield: Ethylene Glycol Reaction solution (1 M potassium hydroxide, 10 mM ethylene glycol) 3a was soaked with a carbon cloth electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 as a working electrode 4, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also soaked. The working electrode 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.3 V was applied to the working electrode 4 as a boundary voltage with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. When the current value reached approximately 0 A, the voltage application to the electrodes was stopped, and about 1 mL of the reaction solution was sampled, and a cation exchange resin Amberlite IR120(H) (Sigma-Aldrich) was added to desalt the sample. Then, it was filtered with a syringe filter, and ethylene glycol and glycolic acid produced by its oxidation were quantified by HPLC.

Column: Rezex ROA-Organic Acid, 300 x 7.8 mm (Phenomenex)
Mobile phase: 0.005N sulfuric acid aqueous solution
Flow rate: 0.5 mL/min
Column temperature: 60℃
Detection: RI@40°C

Table 1 shows the quantitative results. As a result, glycolic acid in which one hydroxy group was converted to a carboxyl group was synthesized with a yield of 70.9% (average value).

(Example 10) Reaction yield: 1,3-propanediol In a reaction solution (0.558 M sodium hydroxide, 0.186 M 1,3-propanediol (PDO)) 3a, a carbon paper electrode in which AuPt (molar ratio 4:1) metal particles were supported on KB600 was immersed as a working electrode 4, and an Ag/AgCl electrode as a reference electrode 5 and a titanium mesh electrode as a counter electrode 6 were also immersed. The working 4, reference electrode 5, and counter electrode 6 were connected to predetermined terminals of the voltage controller. A voltage of 0.3 V was applied to the working electrode 4 with respect to the reference electrode 5 while stirring the reaction solution 3a at room temperature. Since a current was generated instantaneously after voltage application, the change in the current value was monitored over time to confirm the state of the oxidation reaction. The voltage application to the electrodes was stopped when the current value reached approximately 0A. The reaction solution was transferred to an eggplant flask while being filtered with a syringe filter, and after the solvent (water) was evaporated using an evaporator at 60° C. and 15 hPa, part of the precipitated solid was dissolved in D ₂ O and ¹ H-NMR spectrum analysis was performed. 3-hydroxy acid was quantified from the integral ratio of ¹ H spectra of 1,3-propanediol and 3-hydroxy acid (3HP) produced by its oxidation.

Table 2 shows the quantitative results. As a result, a 3-hydroxy acid in which one hydroxy group was converted to a carboxyl group was synthesized with a yield of 85.4% (average value).

It should be noted that the present invention is not limited to the above embodiments and examples, and can be modified in various ways as necessary.

1 energization controller 2 energization time controller 3 reaction vessel 4 working electrode 5 reference electrode 6 counter electrode

Claims (7)

A hydroxy acid is produced by preparing an aqueous solution of raw materials having hydroxy groups on both ends of an organic compound or a reaction solution consisting of a mixed solution of water and an organic solvent, and energizing the working electrode, counter electrode and reference electrode immersed in the reaction solution for a predetermined time, and applying a voltage of the working electrode with respect to the reference electrode at a voltage equal to or lower than a boundary voltage at which only one hydroxy group of the raw material is oxidized, thereby oxidizing only one hydroxy group of the raw material to carboxylic acid. A method for producing a hydroxy acid. 2. The method for producing a hydroxy acid according to claim 1, wherein the organic compound is an alkyl group having 2 to 8 carbon atoms or a compound having an oxygen in the middle of the alkyl group. 3. The method for producing a hydroxy acid according to claim 1, wherein a catalyst layer that assists the oxidation reaction is formed on the surface of the working electrode. 4. The method for producing a hydroxy acid according to any one of claims 1 to 3, wherein the predetermined time during which the working electrode and the counter electrode are energized is within the oxidation reaction time of the raw material in the reaction solution. a reaction vessel for storing a reaction solution of raw materials having hydroxyl groups on carbons at both ends of an organic compound;
a working electrode, a counter electrode and a reference electrode that are immersed in the reaction solution and energized;
An energization time control unit that energizes the working electrode and the counter electrode for a predetermined time, and an energization control unit that energizes the working electrode with respect to the reference electrode at a boundary voltage or less that oxidizes only one hydroxy group of the raw material to carboxylic acid. 6. The apparatus for producing hydroxy acid according to claim 5, wherein a catalyst layer for assisting the oxidation reaction is formed on the surface of the working electrode. 7. The apparatus for producing hydroxy acid according to claim 5 or 6, wherein the energization time control unit sets the predetermined time for energizing the working electrode and the counter electrode to be within the oxidation reaction time of the raw material in the reaction solution.

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