Method for producing esters

Abstract

To produce an ester that allows effective use of an alkane, particularly a gaseous alkane.SOLUTION: According to a method for producing an ester, from an alkane represented by the general formula R1H and an aldehyde represented by the general formula R2CHO, oxygen sources are supplied, to produce an ester represented by the general formula R2COOR1 in the presence of a metal salt (M(L)m / n). (R1 is a C1-C20 open-chain or cyclic hydrocarbon group, R2 is a C1-C30 open-chain or cyclic hydrocarbon group. M is a metal element of Groups 8-12, L constitutes a counterion of the metal element ion, m denotes a valence of the metal element ion, and n denotes a valence of the counterion.)SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an ester, which can effectively utilize an alkane, particularly a gaseous alkane. [Background technology]

[0002] Currently, in order to establish a future industrial base that can utilize a variety of natural carbon resources in a balanced manner, there is a demand for technology to convert alkane gas resources, including methane, into useful chemical products and energy in unprecedented ways.

[0003] In particular, the main components of natural gas and shale gas are said to be gaseous alkanes at room temperature. Among them, methane released from agriculture and livestock farming has a global warming potential 25 times that of carbon dioxide, so utilizing it plays an important role in aiming for a decarbonized society.

[0004] Therefore, if it becomes possible to easily convert alkane gas resources, such as methane contained in abundant reserves of natural gas, into chemical products and energy using unprecedented technology, it will enable modern society to escape from the problem of dependence on oil and reduce carbon dioxide emissions, and this will be the basis for a technology that will make a major contribution to mitigating global warming.

[0005] However, the process of directly converting alkane gas resources such as methane into chemical products is difficult, and the synthesis gas (CO + H 2 Currently, indirect processes such as going through a third-party supplier are used.

[0006] As part of the utilization of alkane gas resources, a method is required to oxidize alkanes and convert them into esters, etc. Known methods for synthesizing esters include Fischer's esterification, which involves dehydration and condensation of acetic acid and ethanol in the presence of sulfuric acid as a catalyst, a method for converting acetaldehyde into ethyl acetate using a base catalyst, and a direct synthesis method from ethylene and acetic acid. However, no method was known that uses alkanes, which are the main components of natural gas.

[0007] When introducing a functional group into an alkane, a method of introducing the functional group by oxidation or the like has been considered, but problems such as combustion of the raw material or product under high temperature conditions have been pointed out, and reactions under mild conditions are being sought. For example, a method is known in which the CH group of an alkane is activated and oxidized under mild temperature conditions using a catalyst, and although this method can activate and oxidize secondary and tertiary CH groups and CH groups at the benzyl position, it is known that it cannot activate and oxidize the CH group of an alkyl group of a primary alkane, which is useful when using resources such as natural gas. (Non-Patent Document 1).

[0008] Regarding alcohols and ketones obtained by oxidation of alkanes, Patent Document 1 discloses a method for oxidizing alkanes with oxygen, in which the alkanes are reacted in the presence of aldehydes, a copper catalyst, and a nitrogen-containing compound. Patent Document 1 discloses a wide variety of alkanes, and the nitrogen-containing compounds disclosed are nitriles, aromatic amines, and tertiary amines. However, there is no suggestion about producing esters, and there is no suggestion at all about synthesizing esters using lower alkanes such as methane and ethane. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2002-30008 A [Non-patent literature]

[0010] [Non-Patent Document 1] Yukiko Hayashi, Naruyoshi Komiya, Ken Suzuki, Shun-Ichi Murahashi, Tetrahedron Letters, 54 (2013), 2706-2709. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention aims to produce an ester that can effectively utilize alkanes, particularly gaseous alkanes, and in particular to provide a method for constructing an ester by oxidizing alkanes having a primary alkyl group. [Means for solving the problem]

[0012] Means for Solving the Problems The present inventors have conducted intensive research to solve the above problems, and as a result have found that esters can be efficiently produced by using a specific catalyst in combination with specific reaction conditions, thereby completing the present invention. [1] General formula R 1 and an alkane represented by H. General formula R 2 From an aldehyde represented by CHO, Supply an oxygen source and a metal salt (M(L) m / n ) in the presence of a compound of the general formula R 2 COOR 1 To produce an ester represented by the formula: Method for producing esters. (R 1 is a C1-C20 linear or cyclic hydrocarbon group, R 2 is a C1-C30 chain or cyclic hydrocarbon group. M represents a metal element of Groups 8 to 12, and L constitutes a counter ion for the metal element ion, and is a carboxylate ion, halogen ion, nitrate ion, sulfate ion, or ClO 4 - , B.P.h. 4 - , P.F. 6- where m represents the valence of the metal element ion and n represents the valence of the counter ion. [2] The method for producing an ester according to [1], wherein the alkane is methane, ethane, propane, or butane. [3] The method for producing an ester according to [1] or [2], wherein the ester is produced in the presence of water and / or one or more organic compounds selected from nitrogen-containing compounds and halogenated hydrocarbons as a solvent. [4] Metal salts (M(L) m / n ) wherein M is at least one selected from iron, nickel, and ruthenium. [5] Metal salts (M(L) m / n ), where L is a C1-C20 carboxylate ion, a halogen ion, a nitrate ion, a sulfate ion, a perchlorate ion, or BP 4 - , P.F. 6 - A method for producing an ester of [1] to [4], wherein the ester is a metal salt selected from the group consisting of [6] The method for producing an ester according to any one of [1] to [5], wherein the organic compound is a nitrile or a chloroalkane. [7] The method for producing an ester according to any one of [1] to [6], wherein when water and the organic compound are used together as a solvent, the mass ratio of water:organic compound is 0.01:100 to 100:0.01. [8] The method for producing an ester according to any one of [1] to [7] above, wherein the alkane is methane or ethane. [9] R 2 CHO R 2 The method for producing an ester according to any one of [1] to [8] above, wherein the linear or cyclic C1 to C30 hydrocarbon group is linear or cyclic.

[10] The alkane is R 3 CH 3 It is expressed as R 3 is a linear, chain, or cyclic aliphatic hydrocarbon having a carbon number of C0 to C19. Effect of the Invention

[0013] According to the present invention, gaseous alkanes, which are the main components of natural gas and shale gas, can be converted into esters. The reaction conditions can also be milder than those of conventional ester synthesis methods. Gaseous alkanes are greenhouse gases generated in agriculture and livestock farming, but according to the present invention, they can be effectively utilized as various chemical products, which can be effective as a measure to prevent global warming. Furthermore, because the reaction conditions are mild, the plant can be installed in small and medium-sized facilities. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a conceptual diagram showing an example of a reaction mechanism of the present invention. [Diagram 2] FIG. 1 shows a gas chromatograph mass spectrometry chart of the product obtained when an ester was produced using ethane in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiment of the invention will be specifically described. First, the raw materials used in the present invention will be described. Reactant (1) Alkane In the present invention, the alkane is represented by the general formula R 1 H(R 1 is a C1 to C20 linear or cyclic hydrocarbon group). 3 CH 3 It can be expressed as R 3 are aliphatic hydrocarbons with carbon numbers ranging from C0 to C19, which may be linear, branched, or cyclic, and are characterized by having one or more functional groups that can be identified as methyl, ethyl, n-propyl, or n-butyl groups.

[0016] Examples of chain alkanes include methane, ethane, propane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, etc. Examples of branched alkanes include 2-methylpropane, 2-methylheptane, 2,3-dimethylhexane, 2,3,4-trimethylpentane, etc.

[0017] Examples of cyclic alkanes include cyclohexane, cyclopentane, cyclooctane, cycloheptane, and cyclododecane. In the present invention, it is preferable to use alkanes that are gaseous at room temperature, such as methane, ethane, propane, and butane.

[0018] These alkanes are known to be contained in natural resources such as natural gas, and in gases produced in the agricultural and livestock industries, but according to the present invention, these gases can be used in their gaseous state. Of these, methane or ethane is more preferable for exerting the effects of the present invention.

[0019] (2) Aldehydes The aldehyde may be represented by the general formula R 2 CHO(R 2 is a C1 to C30 linear or cyclic aliphatic hydrocarbon group or aromatic hydrocarbon group, which may further have a ring structure) is used.

[0020] The aldehydes used in the present invention may be aliphatic aldehydes or aromatic aldehydes, and specific examples thereof include aliphatic aldehydes such as acetaldehyde, propionaldehyde, n-butylaldehyde, isobutyraldehyde, n-valeraldehyde, isovaleraldehyde, pivalaldehyde, n-hexylaldehyde, n-heptylaldehyde, n-octylaldehyde, n-nonylaldehyde, and n-decylaldehyde, substituted or unsubstituted aromatic aldehydes such as benzaldehyde, p-chlorobenzaldehyde, m-chlorobenzaldehyde, m-cyanobenzaldehyde, p-tolualdehyde, and p-methoxybenzaldehyde, and mixtures thereof.

[0021] Of these, C2 to C30 aldehydes are preferred, and of these, propionaldehyde is most preferred. The amount of aldehyde used is appropriately selected depending on the amount of ester produced, but if the amount is an equivalent amount, an equivalent amount of ester can be produced. Usually, the amount is in the range of 0.1 to 1000 mol %, preferably 1 to 400 mol % based on the alkane, but is not particularly limited.

[0022] (3) Metal salts The metal salt used in the present invention is used as a catalyst in the reaction for synthesizing an ester from an alkane and an aldehyde.

[0023] Metal salts include M(L) m / n where M represents a metal element of Groups 8 to 12, L constitutes a counter ion for the metal element ion, and is a carboxylate ion having a carbon number of C1 to C20, a halogen ion, a nitrate ion, a sulfate ion, or ClO 4 - , B.P.h. 4 -, P.F. 6 - where m represents the valence of the metal element ion, and n represents the valence of the counter ion.

[0024] M represents a metal element of Groups 8 to 12. Specific examples include Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Os, Ir, Pt, and Au, and among these, Fe, Ni, Cu, and Ru are preferred.

[0025] In order for the metal salt used in the present invention to exhibit catalytic activity, differences in the metal valence, coordination number, coordination structure, counter anion, etc. greatly affect the catalytic activity. Furthermore, the activity also changes significantly depending on the combination of the metal and its counter ion and the structure of the counter ion.

[0026] In the present invention, since an ester is synthesized by adding an aldehyde to an alkane and using oxygen as an oxidizing agent, a redox reaction occurs between the substrate, raw material, and the metal of the metal salt, so it is preferable that the metal has a valence that easily changes in the reaction system. For example, in the case of copper, known copper metal salts and copper powder can be used as copper metal salts, but there are three types of valence, divalent, monovalent, and zero valent, and they are appropriately selected depending on the type of alkane or aldehyde used in the reaction and the solvent system. Depending on the solvent system, the stability and existence state change depending on the presence or absence of solvation, so they are selected taking these into consideration. L may become a radical and move during the reaction. Examples of L include carboxylic acids having aliphatic or aromatic hydrocarbons with carbon numbers C1 to C20, and among them, Cu(OAc) which is easy to obtain and handle and has high reactivity is preferable. 2 nH 2 O is preferably used. The following known compounds can be used as the copper metal salt. Specifically, Cu(OAc) 2 nH 2 O, Cu(OAc), CuCl, CuCl 2 nH 2 O, CuBr, CuBr 2 , CuSO 4 nH 2 O, Cu(NO 3 ) 2 nH 2 O, Cu(ClO 4 ) 2 , etc. The amount of the metal salt used is not particularly limited, but is usually in the range of 0.000001 to 200 mol %, preferably 0.00001 to 5 mol %, based on the alkane.

[0027] (4) Oxygen source The oxygen used in this reaction may be any of (a) oxygen gas, (b) air (composed of 20% oxygen, 78% nitrogen, 1% carbon dioxide, etc.), or (c) a mixture of oxygen gas and an inert gas such as nitrogen. The gas pressure may be reduced or increased, but an oxygen pressure of 1 atmosphere is also possible.

[0028] (5) Solvent In the reaction used in the present invention, it is preferable to use water and / or an organic compound as a solvent. As the organic compound, it is preferable to use a nitrogen-containing compound and a halogenated alkane in order to synthesize an ester.

[0029] As the organic solvent for the nitrogen-containing compound, nitriles can be used. As the nitriles, conventionally known ones can be used regardless of whether they are aliphatic or aromatic nitriles. Specific examples of aliphatic nitriles include acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, trimethylacetonitrile, hexanenitrile, 4-methylvaleronitrile, heptanenitrile, octanenitrile, undecanenitrile, decanenitrile, stearonitrile, cyclohexanecarbonitrile, cyclopentanecarbonitrile, and the like, and aliphatic dinitriles include malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, and azelanitrile. Examples of aromatic nitriles include benzonitrile, o-, m-, and p-phthalonitrile.

[0030] The halogenated alkane may be any halide in which hydrogen in the alkane is replaced with a halogen, such as fluoride, chloride, bromide, or iodide. Among these, methylene chloride, chloroform, dichloroethane, etc. are preferably used in the present invention.

[0031] Water and organic compounds may be added as solvents for the aldehydes and metal salts added. The amount of these to be used is not particularly limited, but it is usually 0.01 to 100 mol %, preferably 0.1 to 10 mol %, based on the alkane.

[0032] When both nitriles and halogenated alkanes are used, the reaction mixture does not need to contain water. However, if water is not contained, the reaction yield may be low, and the aldehydes may be consumed, leading to decomposition of the nitriles or promotion of oxidation of the aldehydes or the halogenated alkane.

[0033] Moreover, if the amount of water is too much, the oxidation reaction hardly progresses, so it is desirable to add water to the nitriles in a molar ratio (nitrile / water) of 0.01 / 100 to 1000 / 0.01, preferably 0.1 / 10 to 10 / 0.1.

[0034] Method for producing esters In the present invention, the alkane and the aldehyde are reacted in the presence of the metal salt by supplying an oxygen source to the alkane and the aldehyde to form a compound of the general formula R 2 COOR 1 In this step, water or an organic compound may be introduced, if necessary.

[0035] Although the reaction mechanism is unclear, for example, methane is used as the alkane, acetaldehyde is used as the aldehyde, and Cu(OAc) is used as the catalyst. 2 nH 2 One possible mechanism for the use of O is shown in Figure 1.

[0036] For example, acetaldehyde is a divalent copper salt (Cu(OAc) 2) produces an acyl radical. First, acetaldehyde, which is also used as a solvent in the reaction system, reduces the copper(II) salt to become a copper(I) salt, and acetic acid, which was the counter ion, is released into the solvent. However, hydrogen is removed from the aldehyde produced during the oxidation, and the acetaldehyde with the hydrogen removed becomes a radical aldehyde. In the case of copper(I) salt, the oxygen fed into the reaction system is oxidized with molecular oxygen to produce so-called oxyradical active species. This oxyradical active species further reacts with a radical aldehyde to produce peracetic acid, and this reaction occurs instantly. At this time, the monovalent copper is oxidized to a divalent copper, and copper active species of peracetic acid are produced on the copper. This copper peracetic acid active species removes a hydrogen atom from an alkane (methane in the figure, but ethane is similar), and it is thought that this stage is a concerted process of OO cleavage and CH cleavage. Next, Cu(II)-OR (R is a methyl or ethyl group derived from the substrate) exchanges ligands with the acetic acid that was removed from the copper in the first step, regenerating the alcohol product and copper acetate. This is followed by recombination of the ligands to produce methyl alcohol, which then reacts with acetaldehyde in the presence of oxygen to produce a hemiacetal, which is then oxidized to produce an ester. This mechanism is an example of the case where a copper metal salt is used, but the inventors believe that metallic oxyradical active species are one of the important active species for carrying out this reaction.

[0037] The reaction temperature is usually in the range of 0° C. to 150° C., and preferably about 25° C. to 80° C. The reaction proceeds even at room temperature, such as about 20° C. In the present invention, the reaction is preferably carried out under pressurized conditions, and a pressurized reaction apparatus such as an autoclave is preferably used. The pressurized conditions may be from normal pressure to 10 atmospheres (1 MPa), and for example, a method can be adopted in which the autoclave is connected to an apparatus that performs nitrogen replacement at 8 atmospheres and constantly supplies oxygen at 1 atmosphere from the start of the reaction throughout the reaction. EXAMPLES

[0038] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0039] (High pressure reactor) The reactor used was a high-pressure reactor TS-31H (manufactured by Taiyo Systems Co., Ltd.) equipped with an LC-20AT liquid delivery unit (manufactured by Shimadzu Corporation). (Gas Chromatography-Mass Spectrometry: GC-MS) The products were sampled and analyzed using a Shimadzu GCMS-QP2010 Plus. A RESTEK Rtx-VMS column (30 m × 0.25 mm) was used for chromatography. After sampling with an autosampler, the products were automatically injected. Detection was performed using a mass spectrometer.

[0040] Example 1 Copper acetate (20 μmol, 3.64 mg) was dissolved in 40 mL of acetonitrile, and 100 μL of the solution (Cu(OAc) 2 = 0.050 μmol, 9.1 μg), acetonitrile (5.0 mL), and dichloromethane (6.0 mL) were added, and the inside of the vessel was pressurized to 4.0 MPa with a mixed gas of ethane / oxygen (= 3 / 1). After the inside of the vessel was pressurized, propionaldehyde (2.0 mmol, 144 μL) dissolved in acetonitrile (4 mL) was added, and the reaction was started at 25°C. The reaction solution was sampled at regular intervals, processed using a silica gel column, and the reaction products were identified by GC-MS. The GC-MS chart is shown in Figure 2. In addition, a calibration curve for each product was created and quantified. The results are shown in Table 1. In Example 1, it was found that the following reaction occurred to obtain an ester.

[0041] [ka]

[0042] [Table 1]

[0043] Example 2 The ester was produced in the same manner as in Example 1, except that methane was used instead of ethane. The results are shown in Table 1.

[0044] [ka]

[0045] [Table 2]

[0046] (Reference example 1) The same procedure as in Example 1 was carried out except that ethanol was used instead of ethane. The results are shown in Table 3.

[0047] (Reference example 2) The same procedure as in Comparative Example 1 was carried out except that acetic acid was used instead of propynaldehyde in Reference Example 1. The results are shown in Table 3.

[0048] [ka]

[0049] [Table 3]

[0050] In the above example, when ethanol was used as a substrate, an ester was produced, but when a carboxylic acid was used, an ester was not produced. This can be considered to mean that ethanol may be one of the reaction intermediates of the present invention, but that a carboxylic acid does not exist in the reaction pathway.

[0051] Comparative Example 1 The same procedure as in Example 1 was carried out except that cyclohexane was used instead of ethane, but no ester was produced.

Claims

1. General formula R 1 A chain alkane represented by H; General formula R 2 From an aldehyde represented by CHO, By providing an oxygen source, a compound of the general formula R is prepared in the presence of copper acetate. 2 COOR 1 To produce an ester represented by the formula: Method for producing esters. (R 1 is a C1 to C20 chain hydrocarbon group, R 2 is a C1 to C30 linear or cyclic hydrocarbon group.

2. A method for producing an ester as described in claim 1, characterized in that the chain alkane is methane, ethane, propane, or butane.

3. 3. The method for producing an ester according to claim 1 or 2, wherein the ester is produced in the presence of water and / or one or more organic compounds selected from a nitrogen-containing compound and a halogenated hydrocarbon as a solvent.

4. 4. The method for producing an ester according to claim 3, wherein the organic compounds are nitriles and chloroalkanes.

5. The method for producing an ester according to claim 3 or 4, wherein when water and the organic compound are used together as a solvent, the mass ratio of water:organic compound is 0.01:100 to 100:0.01.

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