Patent Description:
Alcohol, carboxylic acid, and the like, which are of great use in terms of industrial application, are produced industrially by various kinds of methods. For example, as a method for producing methanol, a method of reacting carbon monoxide obtained by partial combustion of hydrocarbon with hydrogen gas at a high temperature and a high pressure is commonly used. Carbon monoxide and hydrogen gas, which are raw materials, can be produced, for example, by partial combustion of methane (natural gas), steam reforming, and the like. Also, alcohol, carboxylic acid, and the like are commonly produced by a biochemical method such as fermentation.

<CIT> describes a method for producing oxidation reaction product of a hydrocarbon or derivative thereof, and method of for producing oxidation reaction product of olefin. The methods involve a reaction system containing an organic phase, which organic phase contains a raw material and a chlorine dioxide radical.

<CIT> describes a production method for diol body. The method involves a reaction system including an organic phase, which organic phase contains a raw material and chlorine dioxide radicals.

Furthermore, in these years, for the effective use of natural gas such as shale gas, a method is proposed for producing an oxidation reaction product such as alcohol by oxidizing hydrocarbon contained in natural gas. As a method for producing an oxidation reaction product by a gas phase reaction, for example, there is a method for producing ethanol by oxidizing ethane with dinitrogen monoxide in the presence of an iron catalyst (Non Patent Literature <NUM>). As a method for producing an oxidation reaction product by a liquid phase reaction, there is a method for producing methanol by oxidizing methane by hydrogen peroxide in an acetonitrile solvent in the presence of an iron catalyst (Non Patent Literature <NUM>).

The production process of carbon monoxide by partial combustion of hydrocarbon, however, has a problem of spewing large amounts of carbon dioxide (greenhouse gas). Also, the production of an oxidation reaction product by a biochemical method such as fermentation has a problem of requiring great amounts of energy in fertilization, crop-dusting, harvesting, and transport in the process of cultivating raw material crops (e.g., maize), for example. Furthermore, these methods cannot produce alcohol, carboxylic acid, and the like using hydrocarbon as a raw material, and thus are not suitable for effective use of hydrocarbon contained in natural gas.

On the other hand, a method for producing an oxidation reaction product using hydrocarbon as a raw material can perform a reaction in an organic solvent. If this reaction can be performed in the aqueous phase, cost reduction can be expected.

With the foregoing in mind, it is an object of the present invention to provide a method that can produce an oxidation reaction product of a raw material that is at least one selected from the group consisting of methane, ethane, and propane in an aqueous phase.

In order to achieve the above object, the present invention provides a method for producing an oxidation reaction product including the step of: irradiating a reaction system with light in the presence of a raw material and a halogen oxide radical to react, wherein the raw material is at least one selected from the group consisting of methane, ethane, and propane, the reaction system is a reaction system containing an aqueous phase and being free from an organic phase, the aqueous phase contains the raw material and the halogen oxide radical, and in the reaction step, the raw material is oxidized by the light irradiation to produce an oxidation reaction product of the raw material.

In the following, the method for producing an oxidation reaction product of the present invention may simply be referred to as a "production method of the present invention". Advantageous Effects of Invention.

According to the production method of the present invention, using at least one selected from the group consisting of methane, ethane, and propane as a raw material, an oxidation reaction product of the raw material can be produced in an aqueous phase.

[<FIG> is an example of prediction based on the result of the density functional calculation by UCAM-B3LYP/<NUM>-<NUM>+G(d, p) def2TZV when a chlorine dioxide radical (ClO<NUM>•) is irradiated with light.

The present invention will be described below in more detail with reference to illustrative examples. The present invention, however, is by no means limited thereby.

In the reaction step of the production method of the present invention, for example, at least the aqueous phase may be irradiated with light.

In the production method of the present invention, for example, the halogen oxide radical may be a chlorine dioxide radical.

The production method of the present invention may further include the step of generating the halogen oxide radical, for example.

In the production method of the present invention, for example, a reaction system of the halogen oxide radical generation step may contain an aqueous phase, and in the halogen oxide radical generation step, the aqueous phase may contain a source of the halogen oxide radical and the halogen oxide radical may be generated from the source of the halogen oxide radical.

In the halogen oxide radical generation step of the production method of the present invention, for example, at least one of a Lewis acid or a Brønsted acid may be caused to act on the source of the halogen oxide radical to generate the halogen oxide radical.

In the production method of the present invention, for example, the halogen oxide radical may be a chlorine dioxide radical, and, in the halogen oxide radical generation step, the source of the chlorine dioxide radical may be chlorite ion (ClO<NUM>-).

In the reaction step of the production method of the present invention, for example, the reaction may be performed in a state where oxygen (O<NUM>) is present in the reaction system.

The production method of the present invention may be performed, for example, in an atmosphere having a temperature between -<NUM> and <NUM> and a pressure between <NUM> and <NUM> MPa. Furthermore, the production method of the present invention may be performed, for example, in an atmosphere having a temperatures between <NUM> and <NUM> and a pressure between <NUM> and <NUM> MPa or between <NUM> and <NUM> MPa.

In the production method of the present invention, the raw material is at least one selected from the group consisting of methane, ethane, and propane.

In the production method of the present invention, for example, the oxidation reaction product of the raw material may be at least one selected from the group consisting of alcohols, carboxylic acids, aldehydes, ketones, percarboxylic acids, and hydroperoxides.

In the production method of the present invention, when the hydrocarbon in the raw material is methane, for example, the oxidation reaction product may contain at least one of methanol, formic acid, formaldehyde, and methyl hydroperoxide.

In the production method of the present invention, when the hydrocarbon in the raw material is ethane, for example, the oxidation reaction product may contain at least one of ethanol, acetic acid, acetaldehyde, and ethyl hydroperoxide.

In the production method of the present invention, when the hydrocarbon in the raw material is propane, for example, the oxidation reaction product may contain at least one of <NUM>-propanol, <NUM>-propanol (isopropyl alcohol), propionic acid, propionaldehyde, acetone, and propyl hydroperoxide.

More specifically, the production method of the present invention can be performed, for example, as follows.

First, a raw material (substrate) is provided.

The raw material is at least one selected from the group consisting of methane, ethane, and propane.

Examples of the halogen oxide radical include an oxide radical of a halogen such as F<NUM>O• (oxygen difluoride radical), F<NUM>O<NUM>• (dioxygen difluoride radical), ClO<NUM>• (chlorine dioxide radical), BrO<NUM>• (bromic dioxide radical), and I<NUM>O<NUM>• (iodine oxide (V) radical). Of these, chlorine dioxide radicals are preferred from the viewpoint of cost, ease of handling, reactivity, safety, and the like. The halogen oxide radical may be generated from, for example, a source of the halogen oxide radical (radical generation source) as described below.

Next, the reaction system is provided. The reaction system is a reaction system containing an aqueous phase (may also be referred to as an "aqueous phase reaction system" hereinafter) as described above. The aqueous phase reaction system may be composed solely of the aqueous phase, or may contain other phases (e.g., a gas phase). The reaction system is free from an organic phase. In addition, the aqueous phase may be, for example, a phase in which bubbles are dispersed in water. The bubble is not particularly limited, and may be, for example, a hydrocarbon (e.g., a gas such as methane, ethane, or propane) which is the raw material, a source of the halogen oxide radical (e.g., chlorite HClO<NUM> or chlorite ion ClO<NUM>-), the halogen oxide radical (e.g., chlorine dioxide radical ClO<NUM>• ), another gas (e.g., oxygen gas O<NUM>), or two or more of them. The bubbles may be, for example, fine bubbles such as nano-bubbles (bubbles of nanometer size in diameter).

The aqueous phase contains the raw material and the halogen oxide radical. The halogen oxide radical may be generated from the source of the halogen oxide radical, for example, in the halogen oxide radical generation step described below. In this case, for example, the aqueous phase may contain the source of the halogen oxide radical. Further, for example, another aqueous phase containing the source of the halogen oxide radical may be provided.

The source of the halogen oxide radical is, for example, a compound containing oxygen and halogen, and can be halous acid (HXO<NUM>) or a salt thereof as a specific example. The salt of the halous acid is not particularly limited, and examples thereof include a metal salt, and examples of the metal salt include alkaline metal salts, alkaline earth metal salts, and rare earth salts. The source of the halogen oxide radical may be, for example, a compound containing oxygen, halogen, and a Group <NUM> element (e.g., at least one selected from the group consisting of H, Li, Na, K, Rb, and Cs), and can be, for example, the halous acid or an alkaline metal salt thereof. For the halogen oxide radical being the chlorine dioxide radical, the source thereof is not particularly limited and examples thereof include chlorous acid (HClO<NUM>) and salts thereof, and specific examples thereof include sodium chlorite (NaClO<NUM>), lithium chlorite (LiClO<NUM>), potassium chlorite (KClO<NUM>), magnesium chlorite (Mg(ClO<NUM>)<NUM>), and calcium chlorite (Ca(ClO<NUM>)<NUM>). Among them, from the viewpoint of cost, ease of handling, and the like, sodium chlorite (NaClO<NUM>) is preferred. Examples of the other sources include bromate such as sodium bromite and iodite such as sodium iodite.

In addition, the aqueous phase may further contain at least one of a Lewis acid and a Brønsted acid, for example. The aqueous phase contains, for example, the source of the halogen oxide radical (e.g., chlorite ion (ClO<NUM>-)) and a Bronsted acid. The aqueous phase is, for example, an aqueous phase in which the source of the halogen oxide radical (e.g., sodium chlorite (NaClO<NUM>)) and a Bronsted acid (e.g., hydrochloric acid) are dissolved in water. For example, in a state where the source of the halogen oxide radical and the Bronsted acid are dissolved in the aqueous phase, light irradiation (reaction step) to be described below may be started.

The aqueous phase can be produced by mixing the source of the halogen oxide radical and water, for example. Further, components other than the source of the halogen oxide radical and water may or may not be mixed as appropriate. Examples of such a component include the Lewis acid, the Brønsted acid, and the oxygen (O<NUM>).

In the aqueous phase, the concentration of the source of the halogen oxide radical is not particularly limited, and may be, for example, <NUM> mol/l or more and <NUM> mol/l or less. The concentration of the source of the halogen oxide radical may be, for example, a concentration converted into a chlorite ion (ClO<NUM>-) concentration in the case of chlorous acid or a salt thereof. The number of moles of the chlorite ion (ClO<NUM>-) may be, for example, <NUM>/<NUM> times or more of the number of moles of the raw material or <NUM> times or less.

Only one kind of each of the Lewis acid and Bronsted acid may be used, or a plurality of kinds of the Lewis acid and Bronsted acid may be used in combination. In addition, only one of the Lewis acid and the Brønsted acid may be used or both of them may be used in combination, or one substance may serve as both of the Lewis acid and the Brønsted acid. Note that, in the present invention, the "Lewis acid" refers to, for example, a substance which serves as a Lewis acid for the source of the halogen oxide radical.

The concentration of at least one of the Lewis acid and the Bronsted acid in the aqueous phase is not particularly limited, and can be set as appropriate according to, for example, the type of the raw material (substrate) and the target product (oxidation reaction product), and may be, for example, <NUM> mol/l or more and <NUM> mol/l or less.

The Lewis acid may be, for example, an organic substance or an inorganic substance. Examples of the organic substance include ammonium ions and organic acids (e.g., carboxylic acid). The inorganic substance may contain one or both of metal ions and non-metal ions. The metal ion may include one or both of a typical metal ion and a transition metal ion. The inorganic substance is, for example, at least one selected from the group consisting of alkaline earth metal ions (e.g., Ca<NUM>+), rare earth ions, Mg<NUM>+, Sc<NUM>+, Li+, Fe<NUM>+, Fe<NUM>+, Al<NUM>+, silicate ions, and borate ions. Examples of the alkaline earth metal ion include calcium, strontium, barium, and radium ions. Specific examples of alkaline earth metal ion include Ca<NUM>+, Sr<NUM>+, Ba<NUM>+, and Ra<NUM>+. Further, the "rare earth" is a generic term for a total of <NUM> elements including the two elements of scandium <NUM>Sc, yttrium <NUM>Y, and <NUM> elements (lanthanoid) from lanthanum <NUM>La to rutetium <NUM>Lu. Examples of the rare earth ion include trivalent cations corresponding to the <NUM> elements. Examples of the counter ion of the Lewis acid include trifluoromethanesulfonate ion (also referred to as CF<NUM>SO<NUM>- or OTf-), trifluoroacetate ion (CF<NUM>COO-), acetate ion, fluoride ion, chloride ion, bromide ion, iodide ion, sulfate ion, hydrogen sulfate ion, sulfite ion, nitrate ion, nitrite ion, phosphate ion, and phosphite ion. For example, the Lewis acid may be scandium triflate (Sc(OTf)<NUM>) or the like.

Further, the Lewis acid (including counter ion) may be at least one selected from the group consisting of AlCl<NUM>, AlMeCl<NUM>, AlMe<NUM>Cl, BF<NUM>, BPh<NUM>, BMe<NUM>, TiCl<NUM>, SiF<NUM>, and SiCl<NUM>, for example. It is to be noted that the "Ph" denotes a phenyl group and the "Me" denotes a methyl group.

The Lewis acidity of the Lewis acid is, for example, <NUM> eV or more, but is not limited thereto. The upper limit of the Lewis acidity is not particularly limited, and is, for example, <NUM> eV or less. Note that the Lewis acidity can be measured by the method described in<NPL>, <NPL>, or <NPL>, for example. Specifically, the Lewis acidity can be measured by the following method.

As to acetonitrile (MeCN) containing cobalt tetraphenylporphyrin, saturated O<NUM>, and an object whose Lewis acidity is to be measured (e.g., cations such as metals and represented by Mn+ in the chemical reaction formula (1a) below) in the chemical reaction formula (1a) below, the change in the ultraviolet-visible absorption spectrum at room temperature is measured. On the basis of the obtained reaction rate constant (kcat), the ΔE value (eV), which is an indicator of the Lewis acidity, can be calculated. The higher the kcat, the stronger the Lewis acidity. Furthermore, the Lewis acidity of an organic compound can be estimated from the energy level of the lowest unoccupied molecular orbital (LUMO) calculated by the quantum chemical calculation. The higher the value at the positive side, the stronger the Lewis acidity.

The Bronsted acid is not particularly limited and examples thereof include inorganic acids and organic acids, and specific examples thereof include trifluoromethanesulfonic acid, trifluoroacetic acid, acetic acid, hydrofluoric acid, hydrogen chloride, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfurous acid, nitric acid, nitrous acid, phosphoric acid, and phosphorous acid. The Bronsted acid has an acid dissociation constant pKa of, for example, <NUM> or less. The lower limit of the pKa is not particularly limited, and is, for example, -<NUM> or more.

As for the oxygen (O<NUM>), for example, oxygen may be dissolved by blowing air or oxygen gas into the water before or after adding the source of the halogen oxide radical, the Lewis acid, the Brønsted acid, the reaction substrate (raw material), and the like. At this time, for example, the water may be saturated with oxygen (O<NUM>). By allowing the aqueous phase to contain the oxygen (O<NUM>), for example, the oxidation reaction of the raw material (substrate), can further be promoted.

In the present invention, as described above, the Lewis acid, the Bronsted acid, the radical generation source, or the like may or may not be dissolved in the water in the aqueous phase. For example, the production method of the present invention may be performed in a state where the Lewis acid, the Bronsted acid, the radical generation source, or the like is dispersed or precipitated in the water.

Next, in the production method of the present invention, as described above, a halogen oxide radical generation step of generating the halogen oxide radical may be performed.

The halogen oxide radical generation step is not particularly limited. The halogen oxide radical generation step is described below mainly with reference to a case in which the halogen oxide radical is a chlorine dioxide radical by way of example. The halogen oxide radical generation step, however, is not limited thereto.

The halogen oxide radical generation step may be performed, for example, by dissolving the chlorine dioxide radical generation source (e.g., chlorite or a salt thereof) in water and allowing the resultant to stand still, thereby naturally generating chlorine dioxide radical from chlorite ion. At this time, for example, the presence of at least one of the Lewis acid and the Brønsted acid in the water further promotes the generation of chlorine dioxide radical. Further, for example, as described above, the chlorine dioxide radical may be generated by irradiating the aqueous phase with light. However, as described above, the chlorine dioxide radicals can be generated by simply allowing the aqueous phase to stand still without performing light irradiation.

The mechanism by which the chlorine dioxide radical is generated from the chlorite ion in water is presumed, for example, as in the Scheme <NUM> below. The Scheme <NUM> below, however, is an example of a presumed mechanism and does not limit the present invention in any way. The first (uppermost) reaction formula in the Scheme <NUM> below shows a disproportionation reaction of chlorite ion (ClO<NUM>), and it is considered that the presence of at least one of a Lewis acid and a Brønsted acid in water facilitates the movement of the equilibrium to the right. The second (middle) reaction formula in the Scheme <NUM> below shows a dimerization reaction, and hypochlorite ion (ClO-) generated in the first reaction formula reacts with chlorite ion to generate dichlorine dioxide (Cl<NUM>O<NUM>). It is considered that the greater the protons H+ in water, i.e., the more acidic, the easier the process is to proceed. The third (lowermost) reaction formula in the Scheme <NUM> below shows radical generation. In this reaction, the dichlorine dioxide generated in the second reaction formula reacts with a chlorite ion to produce a chlorine dioxide radical.

In the next step (reaction step), when the aqueous phase reaction system is used, for example, the chlorine dioxide radical may be generated in the aqueous phase reaction system, and then the aqueous phase reaction system may be subjected to the reaction step as it is.

Subsequently, the reaction step is performed. The reaction system used in the reaction step is an aqueous phase reaction system, as described above. The reaction step is described below mainly with reference to a case in which the halogen oxide radical is a chlorine dioxide radical by way of example. The reaction step can be performed in the same manner, for example, when the halogen oxide radical is other than chlorine dioxide radical.

First, prior to performing the reaction step, the raw material and the halogen oxide radical (e.g., chlorine dioxide radical) are caused to be contained in the aqueous phase. The raw material and the halogen oxide radical may be dissolved in the aqueous phase, for example, or may be dispersed, suspended, or the like in the aqueous phase.

Next, in the reaction step, for example, as described above, the aqueous phase is irradiated with light. The case in which chlorine dioxide radical (ClO<NUM>•) in the aqueous phase is irradiated with light is predicted to be as shown in <FIG>, for example. <FIG> shows the result of the density functional calculation by UCAM-B3LYP/<NUM>-<NUM>+G(d, p) def2TZV. The left side of <FIG> shows the state of chlorine dioxide radical (ClO<NUM>•) molecule before light irradiation, and the right side of <FIG> shows the state of chlorine dioxide radical (ClO<NUM>•) molecule after light irradiation. As shown in <FIG>, before light irradiation, two oxygen atoms O are each bound to chlorine atom Cl, and the bond length of Cl-O is <NUM>Å (<NUM>). On the other hand, after light irradiation, only one oxygen atom O is bound to the chlorine atom Cl, the bond length of Cl-O is <NUM>Å (<NUM>), and the other oxygen atom is bound to the one oxygen atom. Thus, it is considered that Cl-O bond is cleaved and chlorine radical (Cl•) and oxygen molecule (O<NUM>) are generated. <FIG>, however, is merely an example of the prediction of the calculation result and does not limit the present invention in any way.

It is considered that the reaction occurring in the reaction step is, for example, as follows. First, chlorite ions (ClO<NUM>-) in the aqueous layer (aqueous phase) react with acid to generate chlorine dioxide radicals (ClO<NUM>•). Next, the aqueous phase containing the chlorine dioxide radicals (ClO<NUM>•) is irradiated with light to give light energy hν (h is a Planck constant and ν is a frequency of light), whereby the chlorine dioxide radicals (ClO<NUM>•) in the aqueous phase are decomposed to generate chlorine radicals (Cl•) and an oxygen molecule (O<NUM>). Thus, the raw material (substrate) is oxidized to produce an oxidation reaction product (e.g., alcohol). For example, when the oxidation reaction product is water-soluble (e.g., water-soluble alcohol), it is dissolved in the aqueous phase. This description, however, is merely an example, and does not limit the present invention in any way. For example, the oxidation reaction product is not limited to a water-soluble alcohol, and may be any oxidation reaction product. For example, the oxidation reaction product may be non-water soluble.

In the reaction step, the wavelength of the irradiation light is not particularly limited, and may be, for example, <NUM> or more and <NUM> or less. The light irradiation time is not particularly limited, and may be, for example, <NUM> or more and <NUM> or less. The reaction temperature is not particularly limited, and may be, for example, <NUM> or more and <NUM> or less. The atmospheric pressure at the time of reaction is not particularly limited, and may be, for example, <NUM> MPa or more and <NUM> MPa or less. According to the present invention, for example, as described in the Examples to be described below, the reaction step or all the steps including the reaction step can be performed at ordinary temperature (room temperature) and a normal pressure (atmospheric pressure) without heating, pressurizing, depressurizing, or the like at all. It is to be noted that the "room temperature" is not particularly limited, and is, for example, <NUM> to <NUM>. Furthermore, according to the present invention, for example, as described in the Examples to be described below, the reaction step or all the steps including the reaction step can be performed in a normal-atmosphere environment without performing inert gas substitution or the like.

In the light irradiation, the light source is not particularly limited. For example, excitation can be performed easily by using visible light contained in natural light such as sunlight, for example. Further, for example, a light source such as a xenon lamp, a halogen lamp, a fluorescent lamp, or a mercury lamp may or may not be used as appropriate instead of or in addition to the natural light. Further, a filter for cutting wavelengths other than the necessary wavelengths may or may not be used as appropriate.

The mechanism by which ethanol is generated by an oxidation reaction of ethane is presumed, for example, as in the Scheme <NUM> below. The Scheme <NUM> below, however, is merely an example of a presumed mechanism and does not limit the present invention in any way. Specifically, as shown in <FIG>, chlorine dioxide radicals are decomposed by light irradiation to generate chlorine radicals (Cl•) and an oxygen molecule (O<NUM>). The chlorine radicals act as a hydrogen-withdrawing agent against ethane to generate ethyl radicals (CH<NUM>CH<NUM>•). Then, the oxygen molecule oxidizes the ethyl radical as shown in the Scheme <NUM>, thereby generating ethanol.

The reaction formula of the case where methanol and formic acid are generated by an oxidation reaction of methane using sodium chlorite is, for example, as the following Scheme <NUM>. It is to be noted, however, that the Scheme <NUM> is merely an example and the oxidation reaction of methane using the present invention is not limited thereto.

NaClO<NUM> + 2CH<NUM> → 2CH<NUM>OH + NaCl 3NaClO<NUM> + 2CH<NUM> → 2HCOOH + 3NaCl + H<NUM>O     Scheme <NUM>.

The mechanism by which methanol is generated by an oxidation reaction of methane is presumed, for example, as in the Scheme <NUM> below. The Scheme <NUM> below, however, is merely an example of a presumed mechanism and does not limit the present invention in any way. Specifically, in the same manner as in the case in which ethanol is generated from ethane, first, chlorine dioxide radicals are decomposed by light irradiation to generate chlorine radicals (Cl•) and an oxygen molecule (O<NUM>). The chlorine radicals act as a hydrogen-withdrawing agent against methane to generate methyl radicals (CH<NUM>•). Then, the oxygen molecule oxidizes the methyl radical as shown in the Scheme <NUM>, thereby generating methanol.

As an oxidation reaction of methane, for example, a reaction shown in Scheme <NUM> below is also conceivable. This, however, is also merely an example, and does not limit the present invention in any way.

In addition, in the present invention, the raw material (substrate) is not limited only to ethane or methane. The raw material is at least one selected from the group consisting of methane, ethane, and propane.

In the present invention, for example, as in the Scheme A below, the raw material may be represented by the following chemical formula (A1), and the oxidation reaction product thereof may be at least one of an alcohol represented by the following chemical formula (A2) and a carboxylic acid represented by the following chemical formula (A3). In the Scheme A, Rs are each a freely selected atom or atomic group, and may be, for example, a hydrogen atom or a hydrocarbon group (provided that the raw material is at least one selected from the group consisting of methane, ethane, and propane). Also, for example, in the Scheme A below, the oxidation reaction product may contain aldehyde in addition to or instead of at least one of alcohol and carboxylic acid.

In the Scheme A, when the raw material (substrate) (A1) is methane, for example, as in the Scheme A1 below, the oxidation reaction product may contain at least one of methanol and formic acid. In addition, when the raw material (substrate) (A1) is ethane, for example, as in the Scheme A2 below, the oxidation reaction product may contain at least one of ethanol and acetic acid. The Schemes A1 and A2, however, are merely examples, and the oxidation reaction of methane or ethane is not limited thereto in the production method of the present invention. <CHM>
<CHM>.

Further, for example, as in the Scheme B below, the raw material may be represented by the following chemical formula (B <NUM>), and the oxidation reaction product thereof may be at least one of an alcohol represented by the following chemical formula (B2) and a carbonyl compound represented by the following chemical formula (B3) (e.g., a ketone). In the Scheme B, Rs are each a freely selected atom or atomic group (provided that the raw material is at least one selected from the group consisting of methane, ethane, and propane). Rs may be identical to or different from each other.

In the production method of the present invention, the ratio between the obtained oxidation reaction products (e.g., the ratio between alcohol and carboxylic acid) can be adjusted by appropriately setting the reaction conditions.

Furthermore, in the production method of the present invention, the oxidation reaction product of the raw material (substrate) is not limited to the alcohol, carboxylic acid, aldehyde, ketone, or the like. In addition to or instead of them, for example, a chlorinated product or the like of the raw material (substrate) may be contained. For example, when the chlorine atom radical Cl• in the gas phase reaction of hydrocarbon is bimolecularly involved (e.g., gas phase reaction using chlorine gas Cl<NUM>), even in the presence of oxygen molecule O<NUM>, chlorination is presumed to occur preferentially. In the production method of the present invention, although chlorine atom radical Cl• and oxygen molecule O<NUM> are generated by decomposition of chlorine dioxide radical, since the reaction is performed in a liquid phase, chlorination of the substrate is suppressed, and the alcohol, carboxylic acid, aldehyde, ketone, and the like are presumed to be preferentially generated. These presumptions are merely examples, and do not limit the present invention in any way.

Furthermore, after the reaction step, the step of recovering the oxidation reaction product is performed as necessary. The recovery step is not particularly limited, and for example, a method similar to that of a common organic synthesis reaction may be used. Specifically, for example, a method such as extraction with an organic solvent, distillation, fractionation, or filtration may be used as appropriate to recover the oxidation reaction product from the reaction system. Furthermore, the recovered oxidation reaction product is isolated and purified as necessary. The method of isolating and purifying the recovered oxidation reaction product is not particularly limited, and can be performed as appropriate by distillation, filtration, or the like according to a common organic synthesis reaction.

According to the present invention, for example, by a very simple method of simply irradiating a chlorine dioxide radical aqueous solution with light, chlorine atom radical Cl• and oxygen molecule O<NUM> can be generated, thereby performing the oxidation reaction. Furthermore, by such a simple method, for example, the raw material can be converted into an oxidation reaction product efficiently even under very mild conditions such as ordinary temperature and normal pressure.

Furthermore, according to the present invention, the oxidation reaction product of the raw material can be obtained without using toxic heavy metal catalysts and the like. This allows the oxidation reaction product to be obtained efficiently by a method with very small burden to the environment in addition to the fact that the reaction can be performed under very mild conditions such as ordinary temperature and normal pressure as described above.

The production method of the present invention can be performed at low cost in a simple manner, for example. Specifically, for example, it is also possible to perform the reaction at room temperature and atmospheric pressure without requiring high temperature, high pressure, and the like. Therefore, for example, a reaction can be performed without requiring a special reaction vessel, a facility, or the like, and scale-up of the reaction volume is also easy. Further, for example, it is also possible to produce a halogen oxide radical using sodium chlorite or the like, which is excellent in safety and inexpensive, and to perform the reaction. According to the production method of the present invention, for example, methanol, formic acid, and the like widely used in the market can be produced at low cost and safely, so that the industrial utility value of the present invention is huge. The field of use of the present invention is not particularly limited, and the present invention is widely available, for example, in the same fields as the general fields of use of the oxidation reaction product of the aforementioned raw material. The production method of the present invention is available, for example, for fuel synthesis, synthesis of chemical raw materials, and the like.

Examples of the present invention will be described below in more detail. The present invention, however, is by no means limited thereby.

Heavy water (D<NUM>O) was placed in a <NUM>-volume glass vessel. In this D<NUM>O, <NUM> (mM denotes mmol/l; the same applies hereinafter) of methane (CH<NUM>), <NUM> of sodium chlorite (NaClO<NUM>), and <NUM> of oxygen gas (O<NUM>) were dissolved to prepare an aqueous solution (aqueous phase reaction system). The aqueous solution was irradiated with light using a <NUM> W Xe lamp for <NUM> hours at room temperature (about <NUM>) and at atmospheric pressure. In this way, the chlorine dioxide radical generation (halogen oxide radical generation step) from the sodium chlorite and the reaction of the methane and the chlorine dioxide radical (reaction step) were simultaneously performed. The reaction was tracked by <NUM>H NMR. After <NUM> hours of light irradiation, <NUM>H NMR confirmed the generation of methanol and formic acid, which are the oxidation reaction products of raw material (methane). The yield of the oxidation reaction product based on the raw material (methane) was calculated from the peak intensity of <NUM>H NMR, and it was found that methanol was <NUM>% and formic acid was <NUM>%.

Further, for comparison, when the experiment was performed for <NUM> hours in the same manner as in Example <NUM> except that light irradiation was not performed, no reaction (yield of oxidation reaction product was <NUM>%) occurred. Further, when light irradiation was performed for <NUM> hours under the same conditions as in Example <NUM> except that sodium chlorite (NaClO<NUM>) was not used, no reaction occurred.

Oxidization reaction of ethane was performed in an aqueous phase in the same manner as in Example <NUM> except that <NUM> of ethane (C<NUM>H<NUM>) was used instead of <NUM> of methane (CH<NUM>). After <NUM> hours of light irradiation, <NUM>H NMR confirmed the generation of ethanol and acetic acid, which are the oxidation reaction products of raw material (ethane). The yield of the oxidation reaction product based on the raw material (ethane) was calculated from the peak intensity of <NUM>H NMR, and it was found that ethanol was <NUM>% and acetic acid was <NUM>%.

Oxidization reaction of propane was performed in an aqueous phase in the same manner as in Example <NUM>, except that <NUM> of propane (C<NUM>H<NUM>) was used instead of <NUM> of methane (CH<NUM>). After <NUM> hours of light irradiation, <NUM>H NMR confirmed the generation of <NUM>-propanol (isopropyl alcohol), propionate, and acetone, which are the oxidation reaction products of raw material (propane). The yield of the oxidation reaction product based on the raw material (propane) was calculated from the peak intensity of <NUM>H NMR, and it was found that <NUM>-propanol was <NUM>%, propionic acid was <NUM>%, and acetone was <NUM>%.

As shown in Examples <NUM> to <NUM>, it was possible to efficiently produce an oxidation reaction product such as an alcohol, a carboxylic acid, a ketone, or the like from a hydrocarbon simply by light irradiation in a normal-atmosphere environment at ordinary temperature and a normal pressure. It is to be noted that, while a xenon lamp was used as a light source in the Examples, use of sunlight, LED, or the like as a light source achieves further energy saving and cost reduction.

Further, as shown in Examples <NUM> to <NUM>, according to the present invention, it is possible to efficiently obtain an oxidation reaction product having extremely high industrial utility value using a hydrocarbon as a raw material (substrate). For example, all of the methanol and formic acid obtained in Example <NUM> and the ethanol and acetic acid obtained in Example <NUM> are of great utility for various applications such as fuels, solvents, and raw materials of chemical products. In other words, the Examples demonstrated that the present invention has a huge value from the viewpoint of industrial application.

Claim 1:
A method for producing an oxidation reaction product comprising the step of:
irradiating a reaction system with light in a presence of a raw material and a halogen oxide radical to react, wherein
the raw material is at least one selected from the group consisting of methane, ethane, and propane,
the reaction system is a reaction system comprising an aqueous phase and being free from an organic phase,
the aqueous phase comprises the raw material and the halogen oxide radical, and
in the reaction step, the raw material is oxidized by the light irradiation to produce an oxidation reaction product of the raw material.