JP6942346B2 - Method for producing cycloalkanol and cycloalkanone - Google Patents

Description

The present invention relates to a method for producing a mixture containing cycloalkanol and cycloalkanol by oxidation of cycloalkane.

The oxidation reaction of an organic compound is one of the most important and common reactions in synthetic organic chemistry, and various methods have been reported depending on the target organic compound. Among them, the oxidation reaction of cyclohexane occupies an important industrial position because it produces cyclohexanol and cyclohexanone, which are useful as synthetic intermediates in the production of nylons.

As one of the methods for oxidizing an organic compound, an insoluble solid catalyst, a soluble compound catalyst, and a method using molecular oxygen or air as an oxidizing agent are known. For example, Patent Document 1 describes that cycloalkanes such as cyclohexane are oxidized by contact with oxygen in the presence of an insoluble solid catalyst composed of a cobalt compound and a ruthenium compound. Patent Document 2 describes cycloalkane and cycloalkane by oxidizing cycloalkane in a two-phase system containing an aqueous solvent using molecular oxygen as an oxidizing agent in the presence of a nitrogen atom-containing compound catalyst having a solubility in water of a predetermined value or higher. It is described to produce oxidation products such as canon.

Further, as one of the oxidation methods for organic compounds, one using an electrolytic reaction is also known. For example, Non-Patent Document 1 describes cyclohexane trifluoroacetic acid (91%), which is obtained by electrolytically oxidizing cyclohexane in a dichloromethane solution containing 2.5 M trifluoroacetic acid and 0.05 M tetrabutylammonium hexafluorophosphate. It is described to produce cyclohexyl chloride (4%) and the like.

Further, as a method for producing cyclohexanol and cyclohexanone from cyclohexane by an electrolysis method, a method using an oxygen-active species produced by electrolysis of water has been proposed (for example, Patent Documents 3 and 4, Non-Patent Document 2). ..

On the other hand, although it is a system that does not utilize an electrolytic reaction, a method for producing cyclohexanol and cyclohexanone by oxidizing cyclohexane using a photocatalyst has been reported (for example, Non-Patent Document 3).

Further, although different from the method for producing cyclohexanol and cyclohexanone, in the method for producing hydrogen hydrogen by an electrochemical reaction of water, a production method and a production apparatus for irradiating a semiconductor photoelectrode with light to reduce a voltage have been proposed. (For example, Patent Document 5).

Japanese Unexamined Patent Publication No. 2004-2327 Japanese Patent No. 5197380 Special Fair 01-3955 Gazette CN1040323227B JP-A-2017-171554

Journal of the Chemical Society, Perkin Transactions 1, No. 6, pp. 610-613 (1976) International Journal of Electrochemical Science, Vol. 9, pp. 1547-1556 (2014) Catalysis Science & Technology, Volume 2, pp. 400-405 (2012)

The present inventor has examined the above-mentioned conventional techniques, but has recognized that each of them has the following problems.
Those using an insoluble solid catalyst or a soluble compound catalyst and molecular oxygen or air as an oxidant usually require harsh conditions such as high temperature and high pressure, and conversion of cyclohexane to suppress side reactions. There is a problem that the rate is greatly suppressed.
In an electrolytic reaction as described in Non-Patent Document 1, since activation is performed by electric energy, it is generally possible to carry out the reaction at normal temperature and pressure, and by controlling the applied electric energy. , The target product can be selectively obtained. However, when a metal electrode and a carbon electrode, which are widely used as anodes, are used, hydrocarbons are difficult to undergo an electrolytic reaction, and it is difficult to directly electrolyze cyclohexane to produce cyclohexanol and cyclohexanone. There is.
The method for producing cyclohexanol and cyclohexanone from cyclohexane using oxygen-active species produced by electrolysis of water uses an electrolytic solution having a water content of more than 70 mol%, and the oxygen-active species produced by electrolysis of water oxidizes cyclohexane. In addition to this, the produced cyclohexanol and cyclohexanone are further oxidized to increase the amount of by-products produced, it is difficult to uniformly mix the solution containing water with cyclohexane, and the concentration of cyclohexane is limited. There is a problem.
In a photocatalytic reaction using a photocatalyst without using an electrolytic reaction, activation is performed by light energy, so that the reaction can generally be carried out at normal temperature and pressure. However, there is a problem that the production rate of cyclohexanol and cyclohexanone is very slow and the practicality is poor.

The present invention is based on the present invention's recognition of the above-mentioned prior arts and their problems, and relatively efficiently produces cycloalkanol and cycloalkanene by electrolytic oxidation of cycloalkane. The challenge is to provide a new manufacturing method that can be used.

The present inventors perform electrolytic oxidation using a metal oxide electrode as an anode in a uniform electrolytic solution containing cycloalkane, supporting electrolyte, and organic solvent and having a low water content, under mild conditions and special. It has been found that cycloalkanol and cycloalkanone can be produced from cycloalkane without using a simple oxidizing agent.

That is, in the present invention, the supporting electrolyte and cycloalkane are uniformly mixed with an organic solvent, and cycloalkane is directly electrolytically oxidized in an electrolytic solution having a water content of 15 mol% or less. The present inventors have found that in the above-mentioned oxidation method, oxygen-active species produced by oxidation of water is not required in principle, and cycloalkanol and cycloalkanone can be selectively produced.
Further, the present inventors have found that the applied voltage required for the reaction can be significantly reduced by using a photoresponsive n-type semiconductor electrode as the metal oxide anode electrode and performing the same method under light irradiation. I found it.

で表されるシクロヘキサンであり、前記シクロアルカノール及びシクロアルカノンが、次の一般式（２）

で表されるシクロヘキサノール及びシクロヘキサノンである＜１＞〜＜６＞のいずれか１項に記載のシクロアルカノール及びシクロアルカノンの製造方法。 The present invention has been completed based on these findings, and is specifically characterized by the following.
<1> Cycloalkane and cycloalkane, which comprises electrolytically oxidizing cycloalkane using a metal oxide anode electrode in a uniform electrolytic solution containing cycloalkane, supporting electrolyte and an organic solvent and having a water content of 15 mol% or less. Method for producing cycloalkane.
<2> The metal oxide anode electrode has one or more conductive metal oxides selected from fluorine-doped tin oxide (FTO) and tin-doped indium oxide (ITO) on the surface. <1 > The method for producing cycloalkanol and cycloalkanone.
<3> The metal oxide anode electrode has an oxide of one or more metal elements selected from Si, Ti, Zr, Nb, Ta, and W on the surface. <1>. Cycloalkanol and cycloalkanone production method.
<4> The cycloalkanol according to <1>, wherein the metal oxide anode electrode has one or more photoresponsive n-type semiconductors selected from _{WO 3} , BiVO ₄ , and TiO _{2 on the surface.} And a method for producing cycloalkanone.
<5> The method for producing cycloalkanol and cycloalkanone according to <4>, which comprises irradiating the photoresponsive n-type semiconductor with light.
<6> The method for producing cycloalkanol and cycloalkanol according to any one of <1> to <5>, wherein the supporting electrolyte is nitric acid and the organic solvent is t-butyl alcohol.
<7> The cycloalkane is based on the following general formula (1).

Cyclohexane represented by, and the cycloalkanol and cycloalkanone are represented by the following general formula (2).

The method for producing cyclohexanol and cyclohexanone according to any one of <1> to <6>, which are cyclohexanol and cyclohexanone represented by.

According to the present invention, cyclohexanol and cyclohexanone such as cyclohexanol and cyclohexanone represented by a useful general formula (2) used as synthetic intermediates for nylons and the like can be produced relatively efficiently.

It is a figure which showed typically the electrolytic oxidation apparatus which concerns on embodiment for carrying out this invention. It is a figure which showed typically the photoelectrolytic oxidation apparatus which concerns on embodiment for carrying out this invention. It is a figure which showed typically the electrolytic oxidation reaction which concerns on the embodiment for carrying out this invention.

Hereinafter, a method for producing cyclohexanol and cyclohexanone such as cyclohexanol and cyclohexanone represented by the general formula (2) of the present invention will be described in detail based on embodiments and examples with reference to the drawings. The duplicate description will be omitted as appropriate.

The production of cycloalkanol and cycloalkanol such as cyclohexanol and cyclohexanone represented by the general formula (2) of the embodiment of the present invention shown in FIG. 1 includes a metal oxide anode electrode and a cathode electrode, and is provided with the general formula (1). ), And an electrolytic cell containing an electrolytic solution composed of an organic solvent in which a supporting electrolyte is dissolved. The metal oxide anode electrode and the cathode electrode are electrically connected via a DC power source to perform an electrolytic oxidation reaction. When the electrolytic oxidation reaction is carried out at a constant potential, a reference electrode is used in addition to the metal oxide anode electrode and the cathode electrode. The electrolytic cell may be a one-chamber type as shown in FIG. 1 or a two-chamber type having a diaphragm.

In the production of cycloalkanol and cycloalkanol such as cyclohexanol and cyclohexanone represented by the general formula (2) of the embodiment of the present invention shown in FIG. 2, a photoresponsive n-type semiconductor metal oxide anode electrode and a cathode electrode are used. It is carried out under light irradiation in an electrolytic cell containing an electrolytic solution composed of a cycloalkane such as cyclohexane represented by the general formula (1) and an organic solvent in which a supporting electrolyte is dissolved. Photoresponsive n-type semiconductor metal oxide The anode electrode and the cathode electrode are electrically connected via a DC power source to perform a photoelectrolytic oxidation reaction. When the electrolytic oxidation reaction is carried out at a constant potential, a reference electrode is used in addition to the photoresponsive n-type semiconductor metal oxide anode electrode and cathode electrode. The electrolytic cell may be a one-chamber type as shown in FIG. 2 or a two-chamber type having a diaphragm.

The cycloalkane used as a raw material in the present invention is usually a 3- to 12-membered ring (preferably a 3- to 10-membered ring, more preferably a 4- to 8-membered ring), and is, for example, cyclopropane, cyclobutane, cyclopentane, and the like. Cyclohexane, cyclooctane, cyclodecane, cyclododecane and the like can be mentioned, with cyclohexane being particularly preferable.
The cycloalkane may have a substituent as long as it does not inhibit the reaction. Examples of such a substituent include an alkyl group (for example, a methyl group, an ethyl group, an isopropyl group, etc.), a halogen atom, an oxo group, and the like.

In the following, a case where cyclohexanol and cyclohexanone are produced mainly by using cyclohexane as a cycloalkane will be described as an example.
In FIG. 3, cyclohexane represented by the general formula (1) is directly electrolytically oxidized on the metal oxide anode electrode to form an oxidation intermediate. When this oxidation intermediate reacts with molecular oxygen, cyclohexanol and cyclohexanone represented by the general formula (2) are produced.
The electrolytic oxidation reaction is preferably carried out under normal temperature and pressure from the viewpoint of economy, but it can also be carried out under heating at 100 ° C. or lower or under an appropriate pressure.

The molecular oxygen used in the reaction is sufficient to have a concentration at which oxygen in an atmosphere such as the atmosphere dissolves in the electrolytic solution, but in order to maintain the oxygen concentration in the electrolytic solution, oxygen is contained in the electrolytic solution. It is also possible to blow in the contained gas.
As in Comparative Example 4, when electrolysis was performed in a non-oxygen atmosphere such as a nitrogen atmosphere, cyclohexanol and cyclohexanone were hardly produced. Therefore, the present invention is as shown in FIG. , It is clear that it is based on the formation of an oxidation intermediate by the direct oxidation of cyclohexane and the reaction of this oxidation intermediate with molecular oxygen.
The atmosphere when the oxygen-containing gas is not blown into the electrolytic solution may be an oxygen-containing atmosphere such as the atmosphere.
In the present invention, an electrolytic solution having a low water content is used, and an oxygen-active species generated by electrolysis of water is not used. Therefore, it is greatly suppressed that the produced cyclohexanol or cyclohexanone is further oxidized to become a by-product. NS.

The metal oxide anode electrode of the present invention has a metal oxide on its surface. As the metal oxide, a conductive metal oxide such as FTO or ITO may be used, or a semiconductor metal oxide provided on the conductive base material may be used. Examples of the conductive base material used include a conductive glass base material such as FTO and ITO, and a metal base material. It is more preferable to use a conductive glass base material from the viewpoint of electrode stability and efficient production of cyclohexanol and cyclohexanone represented by the general formula (2). The shape of the conductive base material is not limited, but a plate-like material can be preferably used.

As the metal oxide provided on the conductive substrate, an oxide of one or more kinds of metal elements selected from Si, Ti, Zr, Nb, Ta, and W can be used, and an oxide of one or more kinds of metal elements can be used. Photoresponsive n-type semiconductors can also be used. Specifically, as the photoresponsive n-type semiconductor, those containing one or more elements selected from Bi, V, W, and Ti are preferable, and WO _{3 which exhibits visible light responsiveness and can be used stably.} Is particularly preferable.

The oxide provided in the conductive substrate of the present invention can be produced by various methods such as a thermal decomposition method, a mixed powder sintering method, an electrodeposition method, and a vapor deposition method such as sputtering. Above all, from the viewpoint of simple manufacturing method, it is preferable to manufacture by a thermal decomposition method. For example, the coating thermal decomposition method when the film is supported on the substrate in the form of a thin film will be described in detail in Examples. In this pyrolysis method, a solution containing an element (in some cases, a colloidal solution, a suspension, etc.) is well mixed to prepare a raw material solution, which is then calcined to prepare a carrier. The thermal decomposition method has an advantage that a uniform composition can be prepared because it is mixed with a solution. In particular, in the coating thermal decomposition method, which is a kind of thermal decomposition method, coating and firing are repeated when forming a thin film. There is also an advantage that a precise product can be manufactured by laminating. The thermal decomposition method used in the present invention may be any method as long as it is a method of mixing and firing a solution containing an element, and examples thereof include a sol-gel method, a complex polymerization method, and an organic metal decomposition method. Polymers and organic substances such as polyethylene glycol and ethyl cellulose may be added to the solution in order to control the viscosity of the solution and the porosity of the thin film.

The electrolytic solution used in the present invention is a uniform solution containing cycloalkane such as cyclohexane, a supporting electrolyte, and an organic solvent and having a water content of 15 mol% or less. The uniform electrolyte is (a) visually confirmed for transparency, and (b) confirmed by optical measurement (UV measurement, etc.) that there are no particles or droplets with a size of at least 350 nm or more. (Confirmation that it is not in the form of an emulsion).
The supporting electrolyte is not particularly limited, and any one that dissolves in an organic solvent and cycloalkane such as cyclohexane that can be represented by the general formula (1) can be used. Nitric acid is particularly preferable because it is soluble in an organic solvent or cyclohexane and the water content of the electrolytic solution can be 15 mol% or less.

The organic solvent of the electrolytic solution used in the present invention is not particularly limited as long as it dissolves cycloalkane such as cyclohexane represented by the general formula (1) and the supporting electrolyte, and t-butyl alcohol is particularly preferable.
The electrolytic solution used in the present invention is most preferably composed of cycloalkane, supporting electrolyte, organic solvent, and water content of 15 mol% or less, but a uniform solution having a water content of 15 mol% or less is obtained, and electrolytic oxidation of cycloalkane is performed. It is also permissible to contain some other components (for example, 10 mol% or less, preferably 5 mol% or less, more preferably 1 mol% or less) as long as it does not significantly interfere with the above.
When the electrolytic solution contains cyclohexane, t-butyl alcohol, and nitric acid having a concentration of 1 M, if the water content exceeds 15 mol%, it separates into two phases and does not form a uniform solution.

The cathode electrode material of the present invention is not limited, and examples thereof include platinum, gold, silver, palladium, and carbon. For efficiently producing cyclohexanol and cyclohexanone represented by the general formula (2). From the viewpoint, it is preferable to use platinum.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
An electrolytic solution (water content of about 12.7 mol%) was prepared by mixing 2 mL of concentrated nitrate (concentration 70%) as a supporting electrolyte, 12 mL of t-butyl alcohol as an organic solvent, and 18 mL of cyclohexane as a reaction substrate. An FTO electrode was installed at the anode of the one-chamber electrolytic cell, and a cathode electrode made of platinum was installed at the cathode, and these electrodes were electrically connected via a DC power supply potencio / galvanostat. The prepared electrolytic solution was injected into a one-chamber electrolytic cell, and an electric amount of 25 C was passed at a constant current of 2 mA under normal temperature and pressure.

After the electrolytic oxidation reaction, 200 μL of the electrolytic solution was collected, subjected to liquid separation treatment with diethyl ether and ion-exchanged water, and the organic layer was analyzed by gas chromatography. As a result, cyclohexanol represented by the general formula (2) was found to be 10. It was confirmed that 3 μmоl ・ h ^-1 and cyclohexanone were obtained at 26.5 μmоl ・ h ^-1.

(Comparative Example 1)
When the electrolytic oxidation reaction was carried out in the same manner as in Example 1 except that a carbon electrode was used as the anode, cyclohexanol and cyclohexanone were not obtained.

(Comparative Example 2)
When the electrolytic oxidation reaction was carried out in the same manner as in Example 1 except that a platinum electrode was used as the anode, cyclohexanol and cyclohexanone were not obtained.

(Example 2)
An oxide precursor coating solution of a metal selected from Si, Ti, Zr, Nb, Ta, and W (manufactured by High Purity Chemical Laboratory, EMOD coating type material) and ethyl cellulose as a thickener were dissolved. 400 μL of a solution consisting of butyl acetate (concentration of 0.04 M each) was spin-coated on the surface of the FTO conductive substrate at 500 rpm. This was air-fired at 550 ° C. to prepare various metal oxide anode electrodes on which metal oxides were laminated.

As shown in Table 1, it was confirmed that cyclohexane and cyclohexanol were obtained when the electrolytic oxidation reaction was carried out in the same manner as in Example 1 except that the oxide anode electrodes of each metal species were used.

(Example 3)
An aqueous solution of sodium tungstate prepared at 0.50 M was passed through a column packed with a strongly acidic cation exchange resin to prepare an aqueous solution of tungstic acid. The prepared tungstic acid aqueous solution and a solution consisting of polyethylene glycol as a thickener are distilled off with an evaporator, spin-coated on the surface of the FTO film of the conductive substrate, and then air-baked at 550 ° C. to form a WO ₃ film. It was created. _{The WO 3} visible light responsive optical anode electrode was prepared by appropriately repeating the above spin coating and air firing.

An electrolytic solution (water content of about 12.7 mol%) was prepared by mixing 2 mL of concentrated nitrate (concentration 70%) as a supporting electrolyte, 12 mL of t-butyl alcohol as an organic solvent, and 18 mL of cyclohexane as a reaction substrate. _{A WO 3} visible light responsive photoanode electrode was installed at the anode of the one-chamber electrolytic cell, and a cathode electrode made of platinum was installed at the cathode, and these electrodes were electrically connected via a DC power supply potentio / galvanostat. .. The prepared electrolytic solution was injected into a one-chamber electrolytic cell, irradiated with pseudo-sunlight (AM1.5) using a solar simulator under normal temperature and pressure, and an electric amount of 25C was passed at a constant current of 1 mA. Under light irradiation, the required applied voltage was reduced by about 2.1 V as compared with under light irradiation (under light irradiation: 0.7 V; under light non-irradiation: 2.8 V).

After the photoelectrolytic oxidation reaction, 200 μL of the electrolytic solution was collected, subjected to liquid separation treatment with diethyl ether and ion-exchanged water, and the organic layer was analyzed by gas chromatography. As a result, cyclohexanol represented by the general formula (2) was 4 It was confirmed that .9 μmоl ・ h ^-1 and cyclohexanone were obtained at 6.7 μmоl ・ h ^-1.

(Example 4)
When the photoelectrolytic oxidation reaction was carried out in the same manner as in Example 3 except that the _{TiO 2} photoanode electrode was used, cyclohexanol was obtained at ^{3.8 μmоl ・ h -1} and cyclohexanone was obtained at 9.7 μmоl ・ h ^-1. I confirmed that.

(Comparative Example 3)
When the reaction was carried out in the same manner as in Example 3 except that no current was applied, cyclohexanol and cyclohexanone were not obtained.

(Comparative Example 4)
When the electrolytic oxidation reaction was carried out in the same manner as in Example 1 except that the atmosphere of the electrolytic cell was changed to the atmosphere of nitrogen instead of the atmosphere of the atmosphere, the amounts of cyclohexanol and cyclohexanone produced were very small.

Since the present invention can suppress side reactions and relatively efficiently produce cyclohexanol and cyclohexanone such as cyclohexanol and cyclohexanone, it is an intermediate raw material for synthesizing various chemical products such as 6,6 nylon. It can be expected to be effectively used as a means of supply.

Claims (7)

Cycloalkane and cycloalkanone, which comprises electrolyzing cycloalkane using a metal oxide anode electrode in a homogeneous electrolyte containing cycloalkane, supporting electrolyte and organic solvent and having a water content of 15 mol% or less. Manufacturing method. The first aspect of claim 1, wherein the metal oxide anode electrode has one or more conductive metal oxides selected from fluorine-doped tin oxide (FTO) and tin-doped indium oxide (ITO) on the surface. Cycloalkanol and cycloalkanone production method. The cycloalkanol according to claim 1, wherein the metal oxide anode electrode has an oxide of one or more metal elements selected from Si, Ti, Zr, Nb, Ta, and W on the surface. And a method for producing cycloalkanone. The cycloalkanol and cycloall according to claim 1, wherein the metal oxide anode electrode has one or more photoresponsive n-type semiconductors selected from _{WO 3} , BiVO ₄ , and TiO _{2 on the surface.} How to make canon. The method for producing cycloalkanol and cycloalkanone according to claim 4, which comprises irradiating the photoresponsive n-type semiconductor with light. The method for producing cycloalkanol and cycloalkanol according to any one of claims 1 to 5, wherein the supporting electrolyte is nitric acid and the organic solvent is t-butyl alcohol. The cycloalkane is based on the following general formula (1).

Cyclohexane represented by, and the cycloalkanol and cycloalkanone are represented by the following general formula (2).

The method for producing cyclohexanol and cyclohexanone according to any one of claims 1 to 6, which is cyclohexanol and cyclohexanone represented by.

Images