Method for producing ammonia

Abstract

[Problem] To provide a method for manufacturing ammonia in which a molybdenum complex is used. [Solution] A method for manufacturing ammonia from nitrogen molecules in the presence of a reducing agent and a proton source, the molybdenum complex being a molybdenum complex represented by formula (1) (where R1 and R2 are independently a C3-6 alkyl group; X is an iodine atom, a bromine atom, or a chlorine atom; and R3 and R4 represent chlorine atoms), the reducing agent being a halide (II) of a lanthanoid metal, the proton source being alcohol or water, and the catalyst rotation frequency of the molybdenum complex exceeding 150.

Description

Technical Field

[0001] The present invention relates to a method for producing ammonia.

Background Art

[0002] In a method for producing ammonia from nitrogen molecules, there are reported examples of producing ammonia using a molybdenum complex as a catalyst and water as a proton source (Non-Patent Document 1). Furthermore, there are reported examples of producing ammonia using a molybdenum complex as a catalyst, samarium(II) iodide as a reducing agent, and alcohols or water as a proton source (Non-Patent Document 2).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a method for producing ammonia from nitrogen molecules, when a molybdenum complex is used as a catalyst, it is also an important required performance to be able to obtain ammonia immediately when necessary from the perspective of practical application. Therefore, a catalyst that can react at high speed from the initial stage of the reaction start is desired to achieve this performance.

[0005]

Means for Solving the Problems

[0006] In order to achieve the above object, the present inventors used various molybdenum complexes synthesized based on molecular design to improve the catalytic performance. As a result, a molybdenum complex with a turnover frequency (hereinafter abbreviated as TOF) [1 / min] exceeding 150, which is the amount of substance conversion performed by one molecule of the catalyst per unit time at the initial stage of the reaction start, was found, and the present invention was completed.

[0007] A catalyst with a high TOF generally means that the number of rotations of the catalyst is large even in a short reaction time. Therefore, an improvement in efficiency in the production of ammonia is expected, which is very beneficial.

[0008] That is, as a first aspect, the method for producing ammonia according to the present invention is a method for producing ammonia from nitrogen molecules in the presence of a molybdenum complex, a reducing agent, and a proton source, wherein the molybdenum complex has the formula (1):

Chemical formula

Advantages of the Invention

[0009] According to the method for producing ammonia of the present invention, by using a molybdenum complex capable of reacting at high speed, a method capable of efficiently producing ammonia from the initial stage of the start of the reaction is provided.

Embodiments for Carrying Out the Invention

[0010] In this specification, "n" represents normal, "s" represents secondary, and "t" represents tertiary.

[0011] "Me" represents a methyl group, "Et" represents an ethyl group, " t "Bu" represents a tertiary butyl group, "TMS" represents a trimethylsilyl group, and "thf" represents tetrahydrofuran.

[0012] Preferred embodiments of the method for producing ammonia of the present invention and the molybdenum complex represented by formula (1) used in the production method are shown below. Preferred embodiments of the method and apparatus for producing ammonia of the present invention are shown below.

[0013] In the molybdenum complex represented by formula (1), R 1 and R 2 each independently represents an alkyl group having 3 to 6 carbon atoms. Here, specific examples of the alkyl group having 3 to 6 carbon atoms include, for example, n-propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butyl group, n-pentyl group, isopentyl group, neopentyl group, t-pentyl group, 1,1-dimethylpropyl group, n-hexyl group, isohexyl group, and cyclohexyl group, etc., and the t-butyl group is preferred. X represents an iodine atom, a bromine atom or a chlorine atom. Here, X is preferably an iodine atom and a chlorine atom, and more preferably a chlorine atom. R 3 and R 4 represent a chlorine atom.

[0014] In the method for producing ammonia according to this embodiment, exposing to reduction conditions includes, for example, coexisting a reducing agent or supplying electrons by contacting with an electrode.

[0015] In the method for producing ammonia according to this embodiment, examples of the reducing agent include halides (II) of lanthanoid metals. Examples of lanthanoid metals include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, among which Sm is preferable. Examples of the halogen include chlorine, bromine, and iodine, among which iodine is preferable. As the halide (II) of lanthanoid metal, samarium (II) halide is preferable, and samarium (II) iodide is more preferable.

[0016] In the method for producing ammonia according to this embodiment, examples of the proton source include alcohol and water. As the alcohol to be used, glycol may be used, or ROH (R is a linear, cyclic, or branched alkyl group having 1 to 6 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, or a phenyl group which may have an alkyl group) may be used. Examples of glycol include ethylene glycol, propylene glycol, and diethylene glycol. Examples of ROH include linear or branched alkyl alcohols such as methanol, ethanol, propanol, isopropanol, n-butyl alcohol, s-butyl alcohol, isobutyl alcohol, and t-butyl alcohol; cyclic alkyl alcohols such as cyclopropanol, cyclopentanol, and cyclohexanol; fluorine atom-containing alcohols such as trifluoroethyl alcohol and tetrafluoroethyl alcohol; and phenol derivatives such as phenol, cresol, and xylenol. In the method for producing ammonia according to this embodiment, preferable proton sources are water and ethylene glycol, and water is more preferable.

[0017] In the method for producing ammonia according to the present embodiment, the production of ammonia from nitrogen molecules may be carried out in a solvent. The solvent is not particularly limited, and examples thereof include cyclic ether solvents, chain ether solvents, nitrile solvents, hydrocarbon solvents, and halogenated hydrocarbon solvents. Examples of cyclic ether solvents include tetrahydrofuran and 1,4-dioxane. Examples of chain ether solvents include diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, and cyclopentyl methyl ether. Examples of nitrile solvents include acetonitrile and propionitrile. Examples of hydrocarbon solvents include aromatic hydrocarbons such as toluene and o-xylene, and saturated hydrocarbons such as hexane, heptane, and petroleum ether. Examples of halogenated hydrocarbon solvents include dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene. In the method for producing ammonia according to the present embodiment, a preferred solvent is tetrahydrofuran. In the method for producing ammonia according to the present embodiment, when adding the molybdenum complex used as a catalyst, a preferred solvent is dichloromethane.

[0018] The yield of the produced ammonia can be measured by a known method. The quantification of ammonia in an aqueous sulfuric acid solution can be carried out, for example, using a known indophenol method (Analytical Chemistry, 1967, Vol. 39, pp. 971-974).

[0019] In the present invention, the performance of the molybdenum catalyst is represented by the turnover frequency. Here, the turnover frequency (also referred to as TOF) is the amount of substance conversion performed by one molecule of the catalyst per unit time.

[0020] In the present invention, the value of TOF obtained is greater than 150, more preferably greater than 200, and even more preferably greater than 250.

[0021] The time for ammonia production in the present invention is appropriately optimized according to the reaction equipment and other conditions. For example, when a 0.05 mmol / L solution of the molybdenum complex (1a) is used, the TOF can be estimated in 30 minutes.

[0022] It should be noted that the present invention is not limited to the above-described embodiments at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

Examples

[0023] The examples of the present invention will be described below. It should be noted that the following examples do not limit the present invention in any way.

[0024] [Experimental Example 1] Ammonia Production Molybdenum complex (1a) as a catalyst

Chemical formula

[0025] [Comparative Example 1] In Comparative Example 1, the molybdenum complex (1a) as the catalyst was changed to molybdenum complex (6). [Chemical formula] Except for using [molybdenum complex (6)], the same experimental operations as in Experimental Example 1 were performed to produce ammonia from nitrogen molecules. As a result, 4500 equivalents of ammonia were generated per catalyst (molybdenum complex). The turnover frequency (TOF) was 150 (1 / min). The molybdenum complex (6) used in Comparative Example 1 can be synthesized by the method described in Nature, 2019, Vol. 568(7753), pp. 536 - 540, a non - patent literature.

[0026] Comparing with the turnover frequency (TOF = 150 (1 / min)) of the prior art molybdenum complex (6) based on the above results, it was revealed that the molybdenum complex (1a) of the present invention has a TOF value of 267 (1 / min) or more, and is a catalyst that can react at high speed from the initial stage of the reaction start.

[0027] [Synthesis Example 1] The synthesis route of the molybdenum complex (1a) used as a catalyst is shown and explained below. [Chemical Formula]

[0028] Synthesis of Compound (2a) [Chemical Formula] The synthesis of compound (2a) is shown below. Di-tert-butylphosphine (2.25 g, 14.9 mmol) and paraformaldehyde (450 mg, 15.0 mmol) were added to a reaction vessel and stirred at 60 °C for 16 hours under a nitrogen atmosphere. Then, dichloroethane (150 mL) and 1,2-diamino-4,5-dichlorobenzene (1.07 g, 6.02 mmol) were added to the reaction vessel and stirred at 60 °C for 24 hours under a nitrogen atmosphere. Next, selenium (1.26 g, 16.0 mmol) was added and stirred at 20 - 25 °C (room temperature) for 24 hours under a nitrogen atmosphere. The reaction product was concentrated, and the obtained solid was separated by silica gel column chromatography (dichloromethane:hexane = 1 / 1). The recovered fraction was concentrated and dried under vacuum to isolate compound (2a) as a white solid in 2.58 g (3.97 mmol, 66% yield). Melting point = 195.4 - 196.5 °C 1 H NNR(CDCl3): δ 6.66 (s, 2H), 4.85 (br, 2H), 3.30 (d, J = 7.2 Hz, 4H), 1.42 (d, J = 15.2 Hz, 36H). 1313C NMR (CDCl3): δ 137.2 (s), 121.7 (s), 112.4 (s), 37.1 (d, J = 32.6 Hz), 34.6 (d, J = 40.3 Hz), 28.0 (s). 31 31P NMR (CDCl3): δ 79.7 (s with Se satellites, J = 706.1 Hz).

[0029] Synthesis of Compound (3a)

Chem.

[0030] Synthesis of Compound (4a)

Chem.

[0031] Synthesis of molybdenum complex (1a)

Chemical formula

Industrial Applicability

[0032] The present invention can be used in a method for producing ammonia.

Claims

Claim 1 A method for producing ammonia, which is a method for producing ammonia from nitrogen molecules in the presence of a molybdenum complex, a reducing agent, and a proton source, wherein the molybdenum complex is of formula (1): 【Chemical Formula 1】 (In formula (1), R １ and R ２ each independently represents an alkyl group having 3 to 6 carbon atoms, X is an iodine atom, a bromine atom, or a chlorine atom, R ３ and R ４ represents a chlorine atom.) and is a molybdenum complex represented by the reducing agent is a halide (II) of a lanthanoid metal, the proton source is an alcohol or water, the turnover frequency of the molybdenum complex exceeds 150, A method for producing ammonia. Claim 2 The method for producing ammonia according to claim 1, wherein the turnover frequency exceeds 250. Claim 3 The method for producing ammonia according to claim 1 or claim 2, wherein the turnover frequency can be obtained with a production time of 30 minutes.

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