Method for producing compound having reduced carbon-carbon double bond by reducing compound having homoallyl alcohol structure using flow-type solid polymer electrolytic device

Abstract

To provide a method for reducing a compound having a homoallyl alcohol structure in excellent yield and selectivity.SOLUTION: A method for producing a compound (B) having a reduced carbon-carbon double bond by reducing a compound (A) having a homoallyl alcohol structure, the method comprising a step of reducing the compound (A) using a flow-type solid polymer electrolyzer, wherein the carbon-carbon double bond is selectively reduced.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a compound in which a carbon-carbon double bond is reduced by reducing a compound having a homoallyl alcohol structure using a flow-through solid polymer electrolysis device. [Background technology]

[0002] In organic reaction processes, catalysts have often been used to reduce activation energy, but many processes require high temperatures as practical operating conditions. Generally, organic compounds decompose at high temperatures, turning into tar substances or causing side reactions. Therefore, prolonged reactions at high temperatures are undesirable, and can lead to reduced yields and selectivities. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Electrochimica Acta (2022), 417, 140264 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a method for reducing a compound having a homoallylic alcohol structure with excellent yield and selectivity. [Means for solving the problem]

[0005] The present inventors have found that the above problems can be solved by using a flow-through solid polymer electrolysis device, and have completed the present invention. That is, the present invention relates to the following [1] to [5]. [1] A method for producing a compound (B) in which a carbon-carbon double bond is reduced by reducing a compound (A) having a homoallylic alcohol structure, comprising the steps of: The method includes a step of reducing compound (A) using a flow-through solid polymer electrolysis device, A production method characterized by selective reduction of carbon-carbon double bonds. [2] The production method according to the above [1], wherein water is supplied as a hydrogen source in the step of reducing the compound (A) using a flow-type solid polymer electrolysis device. [3] The manufacturing method according to [1] or [2] above, wherein the solid polymer electrolyte membrane of the flow-through solid polymer electrolysis device is a proton exchange membrane. [4] The method according to any one of the above [1] to [3], wherein compound (A) is isopulegol and compound (B) is menthol. [5] The production method according to [4] above, wherein compound (A) contains at least two selected from the group consisting of normal-, neo-, iso-, and neoiso-isomers of isopulegol, and the ratio of normal menthol isomers in the obtained compound (B) is higher than the ratio of normal isomers of isopulegol in compound (A). [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram showing an example of a flow-through solid polymer electrolysis device. [Figure 2] FIG. 1 is a schematic diagram illustrating an example of a solid polymer electrolyte (SPE) electrolysis unit. DETAILED DESCRIPTION OF THE INVENTION

[0007] The method of the present invention for producing compound (B) having a reduced carbon-carbon double bond by reducing compound (A) having a homoallyl alcohol structure includes a step of reducing compound (A) using a flow-through solid polymer electrolysis apparatus. The compound (A) is represented by the following general formula: JPEG2026005324000001.jpg1830In the formula, R1 to R7 independently represent a hydrogen atom or a hydrocarbon group which may have a substituent, and R1 and R2, R1 and R3, R3 and R4, R3 and R6, and R5 and R7 may be bonded to each other to form a ring. Compound (A) is not particularly limited as long as it has a homoallyl alcohol structure, but examples thereof include isopulegol, but-3-en-1-ol (homoallyl alcohol), 3-methylbut-3-en-1-ol (isoprenol), 4-methylpent-4-en-2-ol, 2,3-dimethylbut-3-en-1-ol, 4,4-diphenylbut-3-en-1-ol, 4,8-dimethylnon-3-ene-1,8-diol, homogeraniol, homonerol, and homofarnesol, with isopulegol being preferred. Isopulegol may be any of the n-, neo-, neoiso-, and iso-isomers, or may be a mixture of any combination of these four isomers.

[0008] Compound (B) is a compound obtained by reducing only the carbon-carbon double bond at position 3 of compound (A). For example, when compound (A) is isopulegol, compound (B) is menthol. The compound (B) is represented by the following general formula: In the formula (1830), R1 to R7 independently represent a hydrogen atom or a hydrocarbon group which may have a substituent, and R1 and R2, R1 and R3, R3 and R4, R3 and R6, and R5 and R7 may be bonded to each other to form a ring. In addition, if the substituent has a carbon-carbon double bond, the carbon-carbon double bond may be reduced.

[0009] The method for producing compound (B) of the present invention includes a step of reducing compound (A) using a flow-type solid polymer electrolysis device. In the present invention, so-called organic electrolysis is performed using a flow-type solid polymer electrolysis device. The solid polymer electrolysis device is not particularly limited as long as it is a flow-type device. The use of a flow-type device facilitates reaction control. That is, the residence time in the electrolysis device can be controlled by setting the flow rate, and excessive reduction (hydrogenation) can be suppressed. This allows the carbon-carbon double bond of compound (A) to be selectively reduced. Furthermore, since an electrolyte is not required in the present invention, the product can be easily purified. Furthermore, the n-isomer ratio in compound (B) produced by the production method of the present invention can be higher than the n-isomer ratio in the substrate compound (A).

[0010] An example of a flow-through solid polymer electrolysis device used in the present invention is shown in Fig. 1. The flow-through solid polymer electrolysis device 10 comprises a solid polymer electrolyte (SPE) electrolysis unit 12, and a pair of separators 15 and 18 and end plates 16 and 19 that sandwich the SPE electrolysis unit 12. The solid polymer electrolyte (SPE) electrolysis unit 12 has a solid polymer electrolyte membrane 13 disposed between a cathode 14a and an anode 17a. The cathode 14a and the anode 17a are fixed by gaskets 14b and 17b, respectively (Fig. 2). A predetermined voltage is applied to the end plates 16 and 19 so that the potentials of the cathode 14a and the anode 17a are set to a predetermined potential. The current density is preferably 0 to 200 mA / cm. 2 The current density is in the range of 200mA / cm 2If the potential exceeds this range, excessive reduction (hydrogenation) may occur, such that the alcohol hydroxyl group is eliminated along with the carbon-carbon double bond of compound (A). The potential is preferably in the range of 0 to -3.0 V vs. NHE. If the potential exceeds -3.0 V vs. NHE, excessive reduction (hydrogenation) may occur, such that the alcohol hydroxyl group is eliminated along with the carbon-carbon double bond of compound (A). A reaction solvent containing a substrate (i.e., compound (A)) is supplied from substrate supply unit 11 via pipe 22, and an electrolyte containing a reducing agent is supplied from electrolyte supply unit 21 via pipe 25. The resulting compound (B) is recovered via pipe 23, and the electrolyte from which the protons have been consumed is recovered via pipe 24. In this example, since the reaction solvent and reaction water (electrolyte) are separated, there is no need to separate the reaction solvent and water after recovering compound (B).

[0011] The cathode contains at least one catalytic metal selected from the group consisting of Pt, Au, Ag, Pd, Rh, Ru, Fe, and Ni. Preferably, the cathode contains Pt. The catalytic metal is supported on a catalytic support made of an electron-conductive material. Supporting the catalytic metal on a catalytic support increases the surface area of ​​the cathode and inhibits aggregation of the catalytic metal. Examples of catalytic supports include porous carbon, porous metals, and porous metal oxides. Examples of porous carbon include carbon blacks such as Ketjen Black (registered trademark), acetylene black, furnace black, and Vulcan (registered trademark). Examples of porous metals include Pt black, Pd black, and fractal-precipitated Pt metal. Examples of porous metal oxides include oxides of Ti, Zr, Nb, Mo, Hf, Ta, and W. Porous metal compounds such as nitrides, carbides, oxynitrides, carbonitrides, and partially oxidized carbonitrides of metals such as Ti, Zr, Nb, Mo, Hf, Ta, and W can also be used for the catalyst support. The catalyst support carrying the catalyst metal is preferably coated with an ionomer, which improves the ionic conductivity of the cathode. When the solid polymer electrolyte membrane is a PEM, a proton-conductive ionomer is used. When the solid polymer electrolyte membrane 110 is an AEM, an anion-conductive ionomer is used. Examples of proton-conductive ionomers include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark). Examples of anion-conductive ionomers include polymers having a strongly basic group (e.g., a quaternary ammonium group, an imidazolium group), such as fumion (trademark) FAA-3. The cathode has a thickness of, for example, 1 to 100 μm. By setting the thickness of the cathode within this range, it is possible to suppress an increase in the resistance to proton migration. The anode contains at least one catalytic metal selected from the group consisting of, for example, Ru, Rh, Pd, Ir, Pt, and Au. The separator can be formed from, for example, carbon resin or a corrosion-resistant alloy such as a Cr-Ni-Fe, Cr-Ni-Mo-Fe, Cr-Mo-Nb-Ni, Cr-Mo-Fe-W-Ni, or Ti alloy.

[0012] The solid polymer electrolyte membrane used in the flow-through solid polymer electrolysis device is a proton exchange membrane (PEM), an anion exchange membrane (AEM), or the like. It selectively conducts protons or anions while preventing the mixing or diffusion of substances between the cathode and anode. The solid polymer electrolyte membrane also allows the water in the cathode to pass through. The proton exchange membrane (PEM) contains, for example, a perfluorosulfonic acid polymer. Examples of such polymers include Nafion (registered trademark) and Flemion (registered trademark). The anion exchange membrane (AEM) contains, for example, a polymer having a strong basic group such as a quaternary ammonium salt. Examples of such polymers include fumapem (trademark) FAA-3 and Neosepta (registered trademark) AHA. The solid polymer electrolyte membrane may be mixed with a reinforcing material such as porous PTFE (polytetrafluoroethylene). In the present invention, a proton exchange membrane is preferably used as the solid polymer electrolyte membrane. The thickness of the solid polymer electrolyte membrane is, for example, 5 to 300 μm.

[0013] As the reaction solvent, an alkane (cyclohexane, methylcyclohexane, hexane, etc.), an ether solvent (THF, CPME, etc.), or the like can be used. The hydrogen source used in reducing and hydrogenating compound (A) is not particularly limited, but examples thereof include water, etc. Using water as the hydrogen source makes the reaction a so-called green reaction. [Example]

[0014] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited thereto. Unless otherwise specified, "%" is by mass.

[0015] Example 1 1. Fabrication of Proton Exchange Membrane Electrolysis Unit A proton exchange membrane electrolysis unit having the configuration shown in FIG. 2 was fabricated as follows. First, a slurry was prepared as follows. Specifically, Pt / KB (manufactured by Tanaka Kikinzoku Kogyo, Pt loading: 46.1% by mass), in which platinum was supported as a catalytic metal on porous carbon (Ketjen Black (KB, registered trademark)) as a catalyst support, was weighed out. Subsequently, pure water, Nafion (registered trademark) ionomer solution (DE521, manufactured by DuPont), and 1-propanol were added to an 80 mL Teflon (registered trademark) container together with Pt / KB to prepare a dispersion. The amount of Nafion (registered trademark) added was set so that the weight ratio of carbon, the support for the carbon-supported metal catalyst (ionomer / carbon), was 0.8. Furthermore, the weight ratio of pure water to 1-propanol was set so that the weight ratio of the solvents contained in the resulting slurry was pure water:1-propanol = 1:99. Ten 2.5 mm diameter zirconia balls were placed in a Teflon (registered trademark) container and mixed for 20 minutes at 200 rpm using a pot mill to obtain a catalyst slurry. The slurry was applied to a 1 cm x 4 cm carbon paper (GDL39BB, manufactured by Siguracet Co., Ltd.), dried in an oven at 60°C for approximately 10 minutes, and then hot pressed at 120°C and 0.4 MPa for 1 minute. After hot pressing, the weight of the carbon paper was measured, and further slurry was applied as necessary. This process was repeated until the metal loading reached 0.5 mg / cm. 2 A DSE (registered trademark) oxygen evolving electrode (Y4585, manufactured by De Nora Permelec) was used as the cathode and anode, and a proton exchange membrane (Nafion (registered trademark) 117, manufactured by DuPont) was sandwiched between them to prepare a membrane electrode assembly (MEA). Finally, the cathode and anode stainless steel end plates, the cathode carbon separator, the anode titanium separator, the cathode and anode Teflon (registered trademark) gaskets, and the MEA described above were assembled as shown in Figure 2 and tightened with bolts to prepare a proton exchange membrane electrolysis unit. A torque wrench was used for tightening, and eight locations were tightened evenly with a force of 2.5 Nm. The size (length x width x thickness) of each component is shown below. Each end plate: 10.5cm x 12.5cm x 1.2cm Each separator: 6.5cm x 8.5cm x 1.3cm Each gasket: 6.5cm x 8.5cm x 0.16cm Cathode: 1.0cm x 4.0cm x 240μm Anode: 1.0cm x 4.0cm x 200μm Proton exchange membrane: 3.5cm x 10cm x 175μm

[0016] 2. Electrolysis Using the proton exchange membrane electrolysis unit prepared as described above, a menthol production apparatus (FIG. 1) was prepared as follows, and electrolysis was carried out. That is, a 1.0 M aqueous sulfuric acid solution was placed in the electrolyte supply part on the anode side and supplied to the anode at a flow rate of 5.0 mL / min using a Smoothflow pump (manufactured by Takumina Corporation). The solution was circulated between the anode and the electrolyte supply part. On the other hand, a 1.0 M solution of n-isopulegol (5 mL) dissolved in methylcyclohexane was supplied to the cathode substrate supply section at a flow rate of 2.0 mL / min using a Smoothflow pump, and the solution was circulated between the cathode and the substrate supply section. In this state, 50mA / cm 2 (The geometric area of ​​the electrode is 4 cm 2 Therefore, in this example, electrolysis was carried out up to 3.0 F / mol at a current of 200 mA (current application at 1 F / mol took about 40 minutes, and current application at 3.0 F / mol took about 120 minutes). The electrolysis was carried out under normal pressure, with the cathode and anode electrolysis sections both kept at 60°C by heaters. The electrolytic solution after the reaction was analyzed by gas chromatography (absolute calibration curve method), and the composition was found to be as follows (GC area %): n-Isopulegol 13.0% Menthol 87.0% (n:iso=100:0) Other 0%

[0017] <Example 2> Isopulegol A (n:neo:iso=94.4:1.3:4.3; GC area) was reduced under the conditions of Example 1. The reaction solution was analyzed by GC and found to have the following composition (GC area %). n-Isopulegol 17.7% Menthol 78.7% (n:iso=98.6:1.4) Other 3.6%

[0018] Example 3 Isopulegol B (purity 89.0%, n:neo:neoiso:iso=69.5:21.9:0.9:7.6; GC area) was reduced under the conditions of Example 1. The reaction solution was analyzed by GC and found to have the following composition (GC area): Isopulegol 19.6% (n:neo:iso=70.8:19.7:9.5) Menthol 59.6% (n:neo:neoiso:iso=85.9:6.4:2.0:5.7) Other 20.7%

[0019] <Comparative Example> Isopulegol B (1.54 g, purity 89.0%, n:neo:neoiso:iso = 69.5:21.9:0.9:7.6; GC area) and 5% Pd / C (hydrous, 15.4 mg, 1 wt%) were placed in a 50 mL stainless steel autoclave equipped with a magnetic stir bar and a glass inner tube, and the inside of the autoclave was purged with nitrogen. The inside of the autoclave was then purged with hydrogen gas to an internal pressure of 3.0 MPa, after which the reaction mixture was heated to 70 °C and stirred at 750 rpm for 3 hours. The reaction mixture was diluted with hexane (4 mL), the catalyst was filtered off, and the resulting solution was analyzed by GC, revealing the following composition (GC area). Isopulegol 0% Menthol 94.8% (n:neo:neoiso:iso=72.1:17.7:0:10.2) Other 5.2%

Claims

1. A method for producing a compound (B) in which a carbon-carbon double bond is reduced by reducing a compound (A) having a homoallylic alcohol structure, comprising the steps of: The method includes a step of reducing compound (A) using a flow-through solid polymer electrolysis device, A production method characterized by selective reduction of carbon-carbon double bonds.

2. 2. The method according to claim 1, wherein water is supplied as a hydrogen source in the step of reducing compound (A) using a flow-through solid polymer electrolysis device.

3. 2. The method according to claim 1, wherein the solid polymer electrolyte membrane of the flow-through solid polymer electrolytic device is a proton exchange membrane.

4. The method according to any one of claims 1 to 3, wherein compound (A) is isopulegol and compound (B) is menthol.

5. 5. The production method according to claim 4, wherein compound (A) contains at least two selected from the group consisting of normal-, neo-, iso-, and neoiso-isomers of isopulegol, and the ratio of normal menthol isomers in the obtained compound (B) is higher than the ratio of normal isomers of isopulegol in compound (A).

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