A method for the direct oxidative carbonylation of methane to prepare acetic acid

Abstract

This invention discloses a method for the direct oxidative carbonylation of methane to prepare acetic acid. Specifically, this invention provides a catalytic method for the preparation of acetic acid from methane, comprising the following steps: under solvent conditions, in the presence of light, an iron catalyst, chloride ions, and an oxidant, methane and carbon monoxide undergo a methane oxidative carbonylation reaction to obtain acetic acid. This method utilizes readily available methane, carbon monoxide, and air (or oxygen), employs an iron catalyst, and achieves direct, efficient, and highly selective acetic acid production via a one-step photocatalytic reaction, demonstrating promising application prospects. The substrate scope of this invention is broad, applicable to a range of chain and cyclic alkanes.

Description

Technical Field

[0001] This invention relates to the field of visible light catalytic oxidation, and more specifically to a method for the direct oxidative carbonylation of methane to prepare acetic acid using an iron complex as a catalyst. Background Technology

[0002] Methane is a major component of natural gas and possesses substantial reserves globally, further enhanced by the discovery of methane hydrates and shale gas. Simultaneously, methane constitutes a significant proportion of landfill gases and oil extraction byproducts. As a clean and economical energy source, methane plays a vital role in global power generation and heating; however, its combustion process generates 20-25% of global carbon dioxide emissions. Furthermore, as a greenhouse gas with a stronger greenhouse effect than CO2, methane's environmental impact cannot be ignored. In remote oil extraction sites, due to technological and geographical limitations, large quantities of methane are not effectively utilized but are directly burned, consuming 3.5% of global methane production. In addition, methane is a cornerstone feedstock for the chemical industry. Currently, the conversion of methane into high-value-added chemicals often requires high-temperature and high-pressure conditions. Therefore, developing advanced catalytic technologies to achieve efficient methane conversion under milder conditions can not only reduce greenhouse gas emissions but also decrease the chemical industry's dependence on petroleum-based feedstocks, promoting the green transformation of the industry and providing technological support for environmental sustainability and sustained economic growth.

[0003] Acetic acid is a key chemical raw material widely used in the chemical, synthetic fiber, pharmaceutical, and rubber industries. Its production primarily relies on the methanol carbonylation reaction, which is typically produced from coal or natural gas through steam reforming. Downstream applications include compounds such as PTA, vinyl acetate, acetate esters, acetic anhydride, and chloroacetic acid, widely used in the chemical, synthetic fiber, pharmaceutical, and rubber industries. Global demand for acetic acid is steadily growing, projected to increase from 16.1 million tons in 2020 to 19.6 million tons in 2027, representing a compound annual growth rate of 3%. Industrially, the conversion of methane to acetic acid involves three steps: methane reforming to produce syngas, syngas conversion to methanol, and methanol carbonylation to synthesize acetic acid. This process requires stringent standards. Operating conditions, including high temperature and high pressure, lead to high energy consumption and equipment costs. Despite its widespread industrial application, alcohol carbonylation technology still faces challenges, including high energy consumption, expensive and easily deactivated precious metal catalysts, and increased complexity and cost in byproduct handling. Furthermore, the reactors require specialized materials to withstand high temperatures and pressures and resist feedstock corrosion, further increasing costs and maintenance difficulties. These factors limit the economic efficiency and environmental sustainability of this technology.

[0004] The aerobic carbonylation of methane is a direct route to convert readily available methane, carbon monoxide, and air (or oxygen) into high-value-added acetic acid. However, the chemical inertness of methane poses a significant challenge to this conversion process, as it readily undergoes over-oxidation under reaction conditions, generating non-target products such as methanol and formic acid. Therefore, achieving efficient activation of C1 compounds and precise control over product selectivity has long been a technical challenge in this field. In 1994, Sen and colleagues first reported the aerobic carbonylation of methane using RuCl3 as a catalyst, obtaining acetic acid at a relatively high temperature with a C2 / C1 selectivity of 2.7, a conversion number (TON) of only 38, and a reaction time as long as 14 days. Subsequently, research groups including Flytzani-Stephanopoulos, Tao, and Wang improved this process by applying it to a heterogeneous catalytic system, thereby improving catalytic efficiency. Nevertheless, due to the readily oxidizable nature of the Rh-CH3 intermediate, the C2 / C1 selectivity was not significantly improved. Compared with carbonylation techniques based on CX bond activation, the aerobic carbonylation of methane still faces significant challenges in improving selectivity, which further highlights the urgency of developing novel catalytic strategies. Summary of the Invention

[0005] This invention addresses the technical problems of existing methane oxidative carbonylation systems, which involve high temperatures, precious metal catalysts, and poor C2 / C1 selectivity. To this end, this invention provides a simple and efficient method for the direct oxidative carbonylation of methane to produce acetic acid. Starting with readily available methane, carbon monoxide, and air (or oxygen), and using an iron catalyst, acetic acid can be directly, efficiently, and selectively obtained through a one-step photocatalytic reaction, showing promising application prospects. This invention has a wide range of substrate applicability, suitable for a series of chain and cyclic alkanes.

[0006] The present invention solves the above-mentioned technical problems by adopting the following technical solution.

[0007] This invention provides a method for catalytically preparing acetic acid from methane, comprising the following steps: in a solvent... Under agent conditions, Under the influence of light, an iron catalyst, chloride ions, and an oxidant, methane and carbon monoxide... The methane is subjected to an oxidative carbonylation reaction to yield acetic acid;

[0008] The iron catalyst is selected from Et4NFeCl4, ferric chloride (FeCl3), ferric tribromide (FeBr3), ferric trifluoromethanesulfonate (Fe(OTf)3), ferrous trifluoromethanesulfonate (Fe(OTf)2), ferric trifluoroacetate (Fe(TFA)3), ferric sulfate (Fe2(SO4)3), ferric nitrate (Fe(NO3)3), ferric phosphate (FePO4), ferric tetrafluoroborate (Fe(BF4)3), ferric perchlorate (Fe(ClO4)3), and ferrous perchlorate (Fe(ClO4)3). 3) Ferric oxalate (Fe2(C2O4)3), Ferric acetylacetone (Fe(acac)3), Ferric p-benzenesulfonate (Fe(OTs)3), Ferric ammonium ethylenediaminetetraacetate (Fe(NH4)EDTA), Ferric sodium ethylenediaminetetraacetate (Fe(Na)EDTA), Ferric ethylenediaminetetraacetate (Fe4(EDTA)3), Ferrous chloride (FeCl2), Ferrous bromide (FeBr2), Ferrous sulfate (FeSO4), Ferrous oxalate (FeC2O4), Ferrous phosphate (Fe3(PO4)2) 4) Ferrous tetrafluoroborate (Fe(BF4)2), ferrous perchlorate (Fe(ClO4)2), ferrous acetate (Fe(CH3CO2)2), ferrous carbonate (FeCO3), iron complexes as shown in Formula I, iron complexes as shown in Formula II, iron complexes as shown in Formula III, iron complex 6, iron complex 7, iron complex 16 and iron complex 18, or one or more of these.

[0009]

[0010]

[0011] in:

[0012] Z can be F, Cl, Br, or I independently;

[0013] X 1 Independently N, O, or S;

[0014] R, R 1 and R 2 Independently for H and C 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl, -O-halogenated C 1-6 Alkyl, -COO-C 1-6 Alkyl, C 6-10 aryl, 5-10 heteroaryl, with one or more R a Replacement C 6-10 aryl or aryl with one or more R aThe substituted 5-10 heteroaryl group, wherein the heteroatoms in the 5-10 heteroaryl group are independently selected from one, two or three of N, O and S, and the number of heteroatoms is independently one, two or three.

[0015] R a Independently for C 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl or -O-halogenated C 1-6 alkyl.

[0016] In one implementation scheme, the C 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl, -O-halogenated C 1-6 Alkyl and -COO-C 1-6 C in alkyl 1-6 Alkyl groups are independently C 1-4 Alkyl groups, such as methyl, ethyl, n-propyl, isobutyl, n-butyl, isobutyl, sec-butyl, or tert-butyl.

[0017] In one implementation scheme, the C 6-10 aryl and one or more R a Replacement C 6-10 C in aryl 6-10 The aryl group can be phenyl or naphthyl, for example, phenyl.

[0018] In one implementation scheme, Z is Cl.

[0019] In one implementation scheme, R is independently C 6-10 aryl or aryl with one or more R a Replacement C 6-10 Aryl group, for example, R is independently phenyl,

[0020] In one implementation scheme, X 1 It can be either N or O.

[0021] In one implementation scheme, R 1 Independently H or C 1-6 Alkyl; for example, H or isopropyl.

[0022] In one implementation scheme, R 2 Independently for H and C 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl, -COO-C 1-6 Alkyl, C 6-10 aryl or aryl with one or more R a Replacement C 6-10Aryl groups; for example, H, -COO-CH3, -CF3, tert-butyl, methoxy, phenyl,

[0023] In one embodiment, the iron complex as shown in Formula I is any of the following iron complexes:

[0024]

[0025] In one embodiment, the iron complex as shown in Formula II is any of the following iron complexes:

[0026]

[0027] In one embodiment, the iron complex as shown in Formula III is any of the following iron complexes:

[0028]

[0029] In one embodiment, the iron catalyst is Et4NFeCl4, ferric chloride, ferrous chloride, ferric trifluoromethanesulfonate, ferrous trifluoromethanesulfonate, ferric perchlorate, ferrous perchlorate, ferrous tetrafluoroborate, ferric ammonium ethylenediaminetetraacetate, ferric sodium ethylenediaminetetraacetate, ferric ethylenediaminetetraacetate, iron complex as shown in Formula I, iron complex as shown in Formula II, iron complex as shown in Formula III, iron complex 6, iron complex 7, iron complex 16, or iron complex 18; preferably, the iron catalyst is Et4NFeCl4, ferric chloride, ferrous chloride, ferric trifluoromethanesulfonate, ferrous trifluoromethanesulfonate, ferric perchlorate, ferrous perchlorate, ferrous tetrafluoroborate, iron complex as shown in Formula I, iron complex as shown in Formula II, iron complex as shown in Formula III, iron complex 6, iron complex 7, iron complex 16, or iron complex 18; further preferably, the iron catalyst is

[0030]

[0031] In one embodiment, the molar ratio of the iron catalyst to the volume of the solvent is (0.001-1) μmol:1 mL, for example (0.001-0.5) μmol:1 mL, or for example 0.01 μmol:1 mL, 0.02 μmol:1 mL, 0.05 μmol:1 mL or 0.1 μmol:1 mL.

[0032] The solvent is a conventional solvent for such reactions in the art, such as one or more selected from water, hydrocarbon solvents, halogenated hydrocarbon solvents, alcohol solvents, nitrile solvents and acid solvents, such as one or more selected from water, alcohol solvents, nitrile solvents and acid solvents, or, for example, an alcohol solvent or a mixture of an alcohol solvent and water.

[0033] In one embodiment, the alcohol solvent is hexafluoroisopropanol, the nitrile solvent may be acetonitrile, and the acid solvent is acetic acid.

[0034] In one embodiment, the solvent is a mixture of an alcohol solvent and water, such as hexafluoroisopropanol and water.

[0035] In one embodiment, the volume ratio of water to alcohol solvent is (0-1):1, for example (0-0.1):1, or (0-0.03):1, or even 0.002:1, 0.0025:1, 0.005:1 or 0.02:1.

[0036] In one embodiment, the source of the chloride ions is selected from one or more of lithium chloride, ammonium chloride, magnesium chloride, calcium chloride, aluminum chloride, HCl, tetramethylammonium chloride, tetraethylammonium chloride, and pyridine hydrochloride, such as lithium chloride, ammonium chloride, magnesium chloride, calcium chloride, aluminum chloride, HCl, tetramethylammonium chloride, tetraethylammonium chloride, or pyridine hydrochloride.

[0037] In one embodiment, when the solvent includes water, the water and the source of the chloride ions participate in the methane oxidative carbonylation reaction in the form of a chloride-containing solution.

[0038] In one embodiment, the molar ratio of the chloride ions to the iron catalyst is (1-10000):1, for example (1-1000):1, or (1-600):1, or even 100:1, 125:1, 250:1, 300:1 or 500:1.

[0039] In one embodiment, the methane oxidative carbonylation reaction is carried out in a reaction vessel.

[0040] In one embodiment, the pressure range of the carbon monoxide is 1-150 bar, for example 5-120 bar, or for example 10 bar, 20 bar, 50 bar or 100 bar.

[0041] In one embodiment, the pressure range of the methane is 1-100 bar, for example 1-20 bar, or even 2 bar, 5 bar, or 10 bar.

[0042] In one embodiment, the oxidant is air, oxygen, hydrogen peroxide, or persulfate, such as air, or compressed air.

[0043] The amount of oxidant used is the conventional amount used in this type of reaction in the art. In one embodiment, the oxidant is air or oxygen, and the method of introducing the oxidant is a conventional method in this type of reaction in the art, such as introducing the oxidant by gas displacement, wherein the number of gas displacements is 3-5 times.

[0044] In one embodiment, the oxidant is air or oxygen, and the pressure range of the oxidant is 0.01-10 bar, for example 0.01-6 bar, or for example 1 bar, 2 bar or 5 bar.

[0045] In one embodiment, the light is ultraviolet light and / or visible light with a wavelength of 300nm-780nm, for example, light with a wavelength of 360nm-420nm.

[0046] The (highest) temperature of the methane oxidative carbonylation reaction varies depending on the boiling point of the solvent, in order to avoid the solvent from boiling. For example, the temperature of the methane oxidative carbonylation reaction is -10℃ to 100℃, or 20℃ to 70℃, such as 20℃, 25℃, 30℃, 40℃ or 60℃.

[0047] In one embodiment, the methane oxidative carbonylation reaction is carried out in a flowing photoreactor.

[0048] In one embodiment, the iron catalyst, chloride ions and the solvent participate in the reaction in the form of a mixed solution, the flow rate of the mixed solution being (0.1-5) mL / min, for example (0.5-3) mL / min, or for example 1 mL / min.

[0049] In one embodiment, the flow rate of the methane is (1-30) mL / min, for example (1-10) mL / min. For example, 2 mL / min.

[0050] In one embodiment, the flow ratio of carbon monoxide to methane is (1-30):1, for example (5-15):1, or even 5:1.

[0051] In one embodiment, the flow rate ratio of the oxidant to the methane is (0.1-5):1, for example (0.1-1):1, or for example 0.5:1.

[0052] In the methane oxidative carbonylation reaction, the progress of the reaction can be monitored using conventional methods in the art (e.g., GC-MS, GC-FID, or...). 1 The reaction is detected by ¹H-NMR, and the endpoint is generally set when the acetic acid production no longer increases. The reaction time can be 0.1-48 hours, for example, 30 minutes, 1 hour, 5 hours, 8 hours or 10 hours.

[0053] In one embodiment, the conversion number of the iron catalyst is above 1500, for example, 1500-35000.

[0054] In one embodiment, the reaction system of the methane oxidative carbonylation reaction consists of the following components: light, iron catalyst, chloride ions, oxidant, solvent, methane, and carbon monoxide.

[0055] In one embodiment, the methane oxidative carbonylation reaction comprises the following steps: at room temperature, the iron catalyst, the chloride ions and the solvent are mixed, and the methane, carbon monoxide and air (or oxygen) are introduced, and the mixture is stirred under irradiation with light of wavelength 360nm-420nm to obtain acetic acid.

[0056] The present invention provides the application of iron complexes of Formula I, Formula II, Formula III, 6, 7, 16 or 18 as described in any of the preceding claims as catalysts in the oxidative carbonylation reaction of methane.

[0057] This invention provides an iron complex or its crystal form, wherein the iron complex is any of the following compounds:

[0058]

[0059]

[0060] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0061] The reagents and raw materials used in this invention are all commercially available.

[0062] The significant advantages of this invention lie in the fact that the core of the photocatalyzed iron-based methane oxidative carbonylation technology is the direct conversion of methane into acetic acid using visible light and inexpensive iron resources, avoiding the high energy consumption and greenhouse gas emissions of traditional synthesis. Specifically, the preparation method of this application enables a one-step, highly selective conversion of methane and carbon monoxide into acetic acid under mild aerobic conditions, utilizing light energy and an economical iron-based catalyst. This method avoids the harsh conditions required by traditional processes, significantly improves the selectivity of C2 products, and reduces energy consumption and manufacturing costs. This method exhibits extremely high atom economy, producing only a small amount of byproducts. The low cost and high selectivity of the iron-based catalyst ensure high-purity acetic acid production and simplify the purification process. Furthermore, this technology can be combined with solar energy to promote the transformation of the chemical industry towards environmental protection, economy, and efficiency, reflecting the direction of green chemistry. Attached Figure Description

[0063] Figure 1An ellipsoidal diagram of the three-dimensional structure of iron complex 8 in Example 10.

[0064] Figure 2 An ellipsoidal diagram of the three-dimensional structure of iron complex 13 in Example 15.

[0065] Figure 3 An ellipsoidal diagram of the three-dimensional structure of iron complex 16 in Example 18.

[0066] Figure 4 An ellipsoidal diagram of the three-dimensional structure of iron complex 17 in Example 19.

[0067] Figure 5 This is a flow chart of the photoreaction process in the embodiment. Detailed Implementation

[0068] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0069] Tetraphenylporphyrin iron (catalyst 1) is commercially available, and its structural formula is as follows:

[0070]

[0071] The catalyst Et4NFeCl4 was prepared according to the references Ben Brahim, Kh.; Ben gzaiel, M.; Oueslati, A.; Gargouri, M. Electrical Conductivity and Vibrational Studies Induced Phase Transitions in [(C2H5)4N]FeCl4. RSC Adv. 2018, 8(71), 40676–40686.

[0072] Preparation Example 1: Preparation of Iron Complexes

[0073]

[0074] 4-Methoxybenzaldehyde (2.1 g, 15 mmol), pyrrole (1.0 g, 15 mmol), and propionic acid (75 mL) were added to a 250 mL flask. The resulting mixture was refluxed with stirring for 5 hours, cooled to room temperature, and then concentrated to remove the solvent. The resulting dark residue was dissolved in 50 mL of dichloromethane and washed successively with saturated sodium carbonate aqueous solution and water. The organic layer was separated, dried over anhydrous sodium sulfate, and evaporated to dryness. The resulting residue was purified by column chromatography (PE / DCM = 15:1, Rf = 0.3) to give pure 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin as a purple solid (0.41 g, 15%). 1 H NMR (400MHz, CDCl3) δ8.92 (s, 8H), 8.13 (d, J = 8.5Hz, 8H), 7.29 (d, J = 8.5Hz, 8H), 4.10 (s, 12H), -2.75 (s., 2H).

[0075] Add 0.23 g (0.32 mmol) of 5,10,15,20-tetra(4-methoxyphenyl)porphyrin and 100 mL of DMF solution to a 250 mL flask and heat to reflux. After the porphyrin is completely dissolved, add FeCl₂·4H₂O (519 mg, 3.2 mmol) in three batches over half an hour. After TLC confirms complete conversion of free porphyrin, concentrate to remove 50 mL of DMF. Cool to 60 °C and add 40 mL of 6 M HCl, after which solid precipitation begins. Continue stirring for 2 hours. Filter the solid and wash it with 3 M HCl until the filtrate is no longer green. Dry the solid under vacuum to obtain iron catalyst 2 (230 mg, 87% yield).

[0076] Preparation Example 2: Preparation of Iron Complex 3

[0077]

[0078] 2-Trifluoromethylbenzaldehyde (2.6 g, 15 mmol), pyrrole (1.0 g, 15 mmol), and propionic acid (75 mL) were added to a 250 mL flask. The resulting mixture was refluxed with stirring for 5 hours, cooled to room temperature, and then concentrated to remove the solvent. The resulting dark residue was dissolved in 50 mL of dichloromethane and washed successively with saturated sodium carbonate aqueous solution and water. The organic layer was separated, dried over anhydrous sodium sulfate, and evaporated to dryness. The resulting residue was purified by column chromatography (PE / DCM = 15:1, Rf = 0.3) to give pure 5,10,15,20-tetrakis(2-trifluoromethylphenyl)porphyrin as a purple solid (0.40 g, 12%). 1 H NMR (400MHz, CDCl3) δ8.51(s,8H),8.19-8.10(m,8H),7.94-7.79(m,8H),-2.74(br s.,2H).

[0079] Add 0.28 g (0.32 mmol) of 5,10,15,20-tetra(2-trifluoromethylphenyl)porphyrin and 100 mL of DMF solution to a 250 mL flask and heat to reflux. After the porphyrin is completely dissolved, add FeCl₂·4H₂O (519 mg, 3.2 mmol) in three batches over half an hour. After TLC confirms complete conversion of free porphyrin, concentrate to remove 50 mL of DMF. Cool to 60 °C and add 40 mL of 6 M HCl, after which solid precipitation begins; continue stirring for 2 hours. Filter the solid and wash with 3 M HCl until the filtrate is no longer green. Solid vacuum-dried iron catalyst 3 (260 mg, 84% yield)

[0080] Preparation Example 3: Preparation of Iron Complex 4

[0081]

[0082] 3,5-Di(trifluoromethyl)benzaldehyde (3.6 g, 15 mmol), pyrrole (1.0 g, 15 mmol), and propionic acid (75 mL) were added to a 250 mL flask. The resulting mixture was refluxed with stirring for 5 hours, cooled to room temperature, and then concentrated to remove the solvent. The resulting dark residue was dissolved in 50 mL of dichloromethane and washed successively with saturated sodium carbonate aqueous solution and water. The organic layer was separated, dried over anhydrous sodium sulfate, and evaporated to dryness. The resulting residue was purified by column chromatography (PE / DCM = 15:1, Rf = 0.4) to give pure 5,10,15,20-tetrakis(3,5-di(trifluoromethyl))porphyrin as a purple solid (0.74 g, 17%). 1 H NMR (400MHz, CDCl3) δ8.82(s,8H),8.70(s,8H),8.39(s,4H)-2.87(s.,2H).

[0083] Add 0.37 g (0.32 mmol) of 5,10,15,20-tetrakis(3,5-di(trifluoromethyl))porphyrin and 100 mL of DMF solution to a 250 mL flask and heat to reflux. After the porphyrin is completely dissolved, add FeCl₂·4H₂O (519 mg, 3.2 mmol) in three batches over half an hour. After TLC confirms complete conversion of free porphyrin, concentrate to remove 50 mL of DMF. Cool to 60 °C and add 40 mL of 6 M HCl. Solid precipitation begins, and stirring continues for 2 hours. Filter the solid and wash with 3 M HCl until the filtrate is no longer green. Solid vacuum-dried iron catalyst 4 (327 mg, 82% yield)

[0084] Preparation Example 4: Preparation of Iron Complex 5

[0085]

[0086] A solution of ligand (S,S)-2,6-bis(4-isopropyl-2-oxazolin-2-yl)pyridine (1.5 g, 5 mmol) in dichloromethane was added dropwise to a solution of FeCl3 (0.8 g, 5 mmol) in dichloromethane, and the mixture was stirred at room temperature for 6 h. After removing the solvent, 10 mL of n-hexane was added and stirred for half an hour to obtain a brown suspension. The solid was filtered, and the filter cake was washed with n-hexane and dried under vacuum to obtain a brown solid Fe(III) catalyst 5 (2.1 g, 91% yield).

[0087] Preparation Example 5: Preparation of Iron Complex 6

[0088]

[0089] The ligand 2,6-bis[1-(2,4,6-trimethylphenylimino)ethyl]pyridine was prepared according to the literature “Butschke, B.; Fillman, KL; Bendikov, T.; Shimon, LJW; Diskin-Posner, Y.; Leitus, G.; Gorelsky, SI; Neidig, ML; Milstein, D. How Innocent Are Potentially Redox Non-Innocent Ligands Electronic Structure and Metal Oxidation States in Iron-PNN Complexes as a Representative Case Study. Inorg. Chem. 2015, 54(10), 4909–4926. https: / / doi.org / 10.1021 / acs.inorgchem.5b00509.”

[0090] A solution of 10 mL of acetonitrile containing 490 mg (1.2 mmol) of ligand 2,6-bis[1-(2,4,6-trimethylphenylimino)ethyl]pyridine was added dropwise to a solution of 10 mL of acetonitrile containing 200 mg (1.2 mmol) of FeCl3, and the mixture was stirred at room temperature for 4 h. The solid was filtered off, and the filter cake was washed with acetonitrile until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 6 (217 mg, 31%) was obtained.

[0091] Preparation Example 6: Preparation of Iron Complex 7

[0092]

[0093] The ligand 4,4'-di-tert-butyl-2,2'-bipyridine (107 mg, 0.4 mmol) was dissolved in 10 mL of acetonitrile, and then added dropwise to 10 mL of FeCl3 (32 mg, 0.2 mmol) acetonitrile solution. The mixture was stirred at room temperature for 4 h to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with acetonitrile until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 7 (136 mg, 98%) was obtained.

[0094] Preparation Example 7: Preparation of Iron Complex 8 (Fe(terpy)Cl3)

[0095]

[0096] The ligand 2,2':6',2”-terpyridine (1.6 g, 7.2 mmol) was dissolved in 20 mL of acetonitrile, and then added dropwise to 10 mL of FeCl3 (1.2 g, 7.4 mmol) in acetonitrile. The mixture was stirred at room temperature for 4 h to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with acetonitrile until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 8 (2.5 g, 88% yield) was obtained. Single crystals of Fe(III) catalyst 8 were obtained by volatilization of the acetonitrile saturated solution of the complex at room temperature (single crystal data are shown in Table 1 below, and the single crystal structure ellipsoid diagram is shown in Figure 1 below). Figure 1 (As shown).

[0097] Table 1

[0098]

[0099]

[0100] Preparation Example 8: Preparation of Iron Complex 9

[0101]

[0102] The ligand 2,2':6',2"-terpyridine-4,4',4"-triethyl tricarboxylate {[2,2':6',2”-terpyridine]-4,4',4"-tricarboxylate} (81.4 mg, 0.2 mmol) was dissolved in 5 mL of chloroform, and then added dropwise to 10 mL of FeCl3 (32 mg, 0.2 mmol) in acetonitrile. The mixture was stirred at room temperature for 4 h to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with acetonitrile until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 9 (80 mg, 71%) was obtained.

[0103] Preparation Example 9: Preparation of Iron Complex 10

[0104]

[0105] Preparation of ligand 4,4',4”-tris(trifluoromethyl)-2,2':6',2”-terpyridine:

[0106]

[0107] Under nitrogen protection, 40 mL of anhydrous THF and n-BuLi (33.2 mL, 53.1 mmol, 1.6 M in hexane) were added to a 250 mL Schlenk flask. The flask was cooled to -78 °C, and 50 mL of anhydrous THF solution of 2-bromo-4-trifluoromethylpyridine (10 g, 44.2 mmol) was added dropwise. After stirring for 30 min, Bu3SnCl (17.3 g, 53.1 mmol) was added dropwise, and the flask was stirred at -78 °C for 1 h. The flask was allowed to warm to room temperature naturally, and stirring was continued for 2 h. The reaction was quenched by adding 10 mL of saturated ammonium chloride aqueous solution, and the mixture was concentrated under reduced pressure. The residue was extracted with DCM and separated. After drying and concentrating the organic phase, the residue was purified by neutral alumina column chromatography (pure PE, Rf = 0.9) to give 4-trifluoromethyl-2-tributyltin pyridine (17.8 g, 92% yield).

[0108] Under nitrogen protection, 4-trifluoromethyl-2-tributyltinylpyridine (17.0 g, 38.9 mmol), 2,6-dichloro-4-trifluoromethylpyridine (3.0 g, 13.9 mmol), Pd(PPh3)4 (1.6 g, 1.4 mmol), and 45 mL of toluene were added to a 100 mL Schlenk flask, and the mixture was heated to reflux overnight. After the reaction solution cooled to room temperature, EA, water, and diatomaceous earth were added. The mixture was filtered, separated, and the organic phase was dried and concentrated. The solution was then purified by column chromatography (PE / EA = 50:1, Rf = 0.7) to give a white solid 6-5a (4.2 g, 69% yield).

[0109] 1 H NMR (400MHz, CDCl3) δ8.92 (d, J = 4.8Hz, 2H), 8.80 (s, 4H), 7.69–7.59 (m, 2H);

[0110] 13 C NMR (101MHz, CDCl3) δ155.8, 155.8, 150.4, 141.0 (q, J = 34.3Hz), 139.7 (q, J = 34.3Hz), 122.9 (q, J=274.7Hz), 122.8 (q, J=274.7Hz), 120.1 (q, J=4.0Hz), 117.9 (q, J=4.0Hz), 117.0 (q, J=4.0Hz); 19 F NMR(376MHz, CDCl3)δ–64.73,–64.85; HRMS(ESI+)calcdfor C 18 H9F9N3 + (M+H) + 438.0647, found 438.0643.

[0111] The ligand 4,4',4”-tris(trifluoromethyl)-2,2':6',2”-terpyridine (87 mg, 0.2 mmol) was dissolved in 5 mL of chloroform, and then added dropwise to 10 mL of acetonitrile solution of FeCl3 (32 mg, 0.2 mmol). The mixture was stirred at room temperature for 4 h, and then 5 mL of diethyl ether was added to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with diethyl ether until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 10 (87 mg, 73%) was obtained.

[0112] Preparation Example 10: Preparation of Iron Complex 11

[0113]

[0114] The ligand 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine (80 mg, 0.2 mmol) was dissolved in 5 mL of chloroform, and then added dropwise to 10 mL of acetonitrile solution of FeCl3 (32 mg, 0.2 mmol). The mixture was stirred at room temperature for 4 h, and then 5 mL of diethyl ether was added to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with diethyl ether until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 11 (72 mg, 64%) was obtained.

[0115] Preparation Example 11: Preparation of Iron Complex 12

[0116]

[0117] Preparation of ligand 4,4',4”-trimethoxy-2,2':6',2”-terpyridine

[0118]

[0119] Under nitrogen protection, 60 mL of anhydrous THF, n-BuLi (18.3 mL, 29 mmol, 1.6 M in hexane), and i-PrMgBr (13.3 mL, 13.3 mmol, 1 M in THF) were added to a 250 mL Schlenk flask, and the mixture was cooled to -78 °C. 50 mL of anhydrous THF solution of 2-bromo-4-methoxypyridine (5 g, 27 mmol) was slowly added dropwise, and the mixture was stirred for 30 min. Then, Bu3SnCl (9.5 g, 29 mmol) was added dropwise, and stirring continued for 1 h. The mixture was allowed to cool naturally to room temperature and then stirred overnight. After the reaction was complete, 10 mL of saturated ammonium chloride aqueous solution was added to quench the reaction. The reaction solution was concentrated under reduced pressure, and the residue was extracted three times with DCM. The combined organic phases were dried and concentrated, and then purified by neutral alumina column chromatography (PE / EA = 10:1, Rf = 0.3) to give a colorless liquid 4-methoxy-2-tributyltin pyridine (7.0 g, 66% yield).

[0120] Under nitrogen protection, 4-methoxy-2-tributyltinylpyridine (7 g, 18 mmol), 2,6-dibromo-4-methoxypyridine (1.6 g, 6 mmol), Pd(PPh3)4 (0.7 g, 0.6 mmol), and 40 mL of toluene were added to a 100 mL Schlenk flask, and the mixture was heated under reflux overnight. After the reaction solution cooled to room temperature, EA, water, and diatomaceous earth were added, followed by filtration. The filtrate was separated, and the organic phase was dried and concentrated. The crude product was recrystallized from 100 mL of methanol to give a white solid (0.7 g, 36% yield).

[0121] 1 H NMR (400MHz, CDCl3) δ8.51(d,J=6.0Hz,2H),8.14(d,J=2.8Hz,2H),8.00(s,2H),6.86(dd,J=6.0,2.8Hz,2H),4.01(s,3H),3.96(s,6H);

[0122] 13 C NMR (100MHz, CDCl3) δ167.8,166.6,157.8,156.7,150.2,110.0,107.3,107.2,55.6,55.2;

[0123] RMS(ESI+)calcd for C 18 H 18 N3O3 + (M+H) + 324.1343, found 324.1346.

[0124] The ligand (4,4',4”-trimethoxy-2,2':6',2”-terpyridine) (64.6 mg, 0.2 mmol) was dissolved in 5 mL of chloroform, and then added dropwise to 10 mL of acetonitrile solution of FeCl3 (32 mg, 0.2 mmol). The mixture was stirred at room temperature for 4 h, and then 5 mL of diethyl ether was added to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with diethyl ether until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 12 (55 mg, 57%) was obtained.

[0125] Preparation Example 12: Preparation of Iron Complex 13

[0126]

[0127] Preparation of ligand 4'-phenyl-2,2':6',2”-terpyridine:

[0128]

[0129] 2-Acetylpyridine (1.6 mL, 15 mmol), KOH (2.3 g, 4.0 mmol), and 70 mL of anhydrous ethanol were added to a 250 mL flask. Then, benzaldehyde (3.3 mL, 30 mmol) was added, and the mixture was stirred for 10 min, followed by the addition of 45 mL of concentrated ammonia. The mixture was stirred at room temperature for 5 h to obtain a suspension. The solid was filtered off and washed with ethanol until the filtrate was colorless. The crude product was recrystallized from ethanol to give a white solid (1.6 g, 34% yield). 1 H NMR (400MHz, CDCl3) δ8.75(s,2H),8.75–8.72(m,2H),8.68(d,J=7.6Hz,2H),7.94–7.84(m,4H),7.55–7.43(m,3H),7.38–7.32(m,2H); 13 C NMR(100MHz, CDCl3)δ156.2,155.8,150.2,149.1,138.4,136.8,128.9,128.8,127.3,123.7,121.3,118.8; HRMS(ESI+)calcd for C 21 H 16 N3 + (M+H) + 310.1339, found 310.1334.

[0130] The ligand 4'-phenyl-2,2':6',2”-terpyridine (1.0 g, 3.2 mmol) was dissolved in 20 mL of CHCl3, and then added dropwise to 20 mL of FeCl3 (0.52 g, 3.2 mmol) in acetonitrile. The mixture was stirred at room temperature for 4 h to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with acetonitrile until the filtrate was colorless. After vacuum drying, a yellow solid Fe(III) catalyst 13 (1.3 g, 87% yield) was obtained. Single crystals of Fe(III) catalyst 13 were obtained by volatilization of the acetonitrile saturated solution of the complex at room temperature (single crystal data are shown in Table 2, and the ellipsoidal diagram of the single crystal stereostructure is shown in Table 2). Figure 2 ).

[0131] Table 2

[0132]

[0133]

[0134] Preparation Example 13: Preparation of Iron Complex 14

[0135]

[0136] The ligand 4'-(4-methoxyphenyl)-2,2':6',2”-terpyridine (67.8 mg, 0.2 mmol) was dissolved in 5 mL of chloroform, and then added dropwise to 10 mL of acetonitrile solution of FeCl3 (32 mg, 0.2 mmol). The mixture was stirred at room temperature for 4 h, and then 5 mL of diethyl ether was added to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with diethyl ether until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 14 (60 mg, 60%) was obtained.

[0137] Preparation Example 17: Preparation of Iron Complex 15

[0138]

[0139] Preparation of ligand 4,4”-di(tert-butyl)-4'-(4-tert-butylphenyl)-2,2':6',2”-terpyridine:

[0140]

[0141] Add 4-tert-butylpyridine (5 g, 37 mmol), AgNO3 (0.5 g, 2.9 mmol), formic acid (9.1 g, 103 mmol), 50 mL CH2Cl2, and 10 mL H2O to a 250 mL flask. Slowly add a solution of (NH4)2S2O8 (12.6 g, 55 mmol), 40 mL H2O, and 30 mL concentrated H2SO4 at 0 °C. After allowing the mixture to cool to room temperature, heat under reflux for 4 h. After the reaction mixture cools to room temperature, separate the layers. Dry and concentrate the organic phase, then purify by rapid column chromatography (pure CHCl3, Rf = 0.3) to obtain a yellow liquid, 2-acetyl-4-tert-butylpyridine (1.5 g, 23% yield).

[0142] To a 250 mL flask, first add 0.81 g (5 mmol) of 2-acetyl-4-tert-butylpyridine, 0.28 g (5 mmol) of KOH, and 20 mL of anhydrous ethanol, followed by the addition of 2.0 g (11 mmol) of 4-tert-butylbenzaldehyde. After stirring for 10 min, add 19 mL of concentrated ammonia solution and stir overnight at room temperature to obtain a gray suspension. Filter the precipitate and wash with water and cold methanol. Recrystallize the crude product from ethanol to give a white solid (0.48 g, 20% yield).1 H NMR (400MHz, CDCl3) δ8.79(s,2H),8.76(s,2H),8.65(d,J=5.2Hz,2H),7.90(d,J= 8.4Hz,2H),7.53(d,J=8.4Hz,2H),7.41–7.35(m,2H),1.45(s,18H),1.38(s,9H); 13 C NMR (100MHz, CDCl3) δ161.3,155.9,155.5,152.3,150.3,148.7,135.3,127.0,125.9,121.2,118.8,118.6,35.1,34.7,31.3,30.5; HRMS(ESI+)calcdfor C 33 H 40 N3 + (M+H) + 478.3217, found 478.3224.

[0143] The ligand 4,4”-di(tert-butyl)-4'-(4-tert-butylphenyl)-2,2':6',2”-terpyridine (95.4 mg, 0.2 mmol) was dissolved in 5 mL of chloroform, and then added dropwise to 10 mL of FeCl3 (32 mg, 0.2 mmol) in acetonitrile. The mixture was stirred at room temperature for 4 h, and then 5 mL of diethyl ether was added to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with diethyl ether until the filtrate was colorless. After drying under vacuum, a yellow solid Fe(III) catalyst 15 (70 mg, 55%) was obtained. Example 15: Preparation of iron complex 16

[0144]

[0145] Preparation of ligand 2,2':6',2”:6”,2”':6”',2””-tetrapyridine (2,2':6’,2”:6”,2”':6”',2””-quinquepyridine)

[0146]

[0147] Under nitrogen protection, 6-bromobipyridine (0.9 g, 3.8 mmol), K₂CO₃ (0.53 g, 3.8 mmol), Pd(OAc)₂ (0.13 g, 0.58 mmol), NBu₄Br (0.61 g, 1.9 mmol), and 10 mL of DMF were added to a 100 mL Schlenk flask, and the mixture was heated to 120 °C. Then, 25 mL of isopropanol was added, and the mixture was heated at 120 °C for another 3 h. After the reaction mixture cooled to room temperature, 50 mL of H₂O and 50 mL of CH₂Cl₂ were added, followed by separation. The organic phase was washed three times with water, dried, concentrated under reduced pressure, and subjected to rapid column chromatography (PE / EA = 5:1, Rf = 0.3) to give a white solid (240 mg, 41% yield). 1 H NMR (400MHz, CDCl3) δ8.71 (d, J=4.8Hz, 2H), 8.65 (dd, J=7.6Hz, 4.4Hz, 4H), 8.48 (d, J=7.2Hz,2H),7.99(t,J=7.6Hz,2H),7.86(td,J=7.6,1.6Hz,2H),7.36–7.29(m,2H); 13 C NMR(100MHz, CDCl3)δ156.2,155.4,155.2,149.1,137.8,136.9,123.7,121.2,121.0,121.0; HRMS(ESI+)calcd for C 20 H 15 N4 + (M+H) + 311.1291, found 311.1287.

[0148] The ligand 2,2':6',2”:6”,2”':6”',2””-tetrapyridine (200 mg, 0.65 mmol) was dissolved in 5 mL of CHCl3, and then added dropwise to 5 mL of FeCl3 (104 mg, 0.65 mmol) in acetonitrile. The mixture was stirred overnight at room temperature to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with acetonitrile until the filtrate was colorless. After vacuum drying, a yellow solid Fe(III) catalyst 16 (209 mg, 62% yield) was obtained. Single crystals of Fe(III) catalyst 16 were obtained by volatilization of the complex in a methanol-saturated solution at room temperature (single crystal data are shown in Table 3, and the ellipsoidal diagram of the single crystal stereostructure is shown in Table 3). Figure 3 ).

[0149] Table 3

[0150]

[0151]

[0152] Preparation Example 16: Preparation of Iron Complex 17

[0153]

[0154] The ligand 2,6-di(1-pyrazolyl)pyridine (500 mg, 2.4 mmol) was dissolved in 10 mL of CHCl3, and then added dropwise to 10 mL of FeCl3 (380 mg, 2.4 mmol) in acetonitrile. The mixture was stirred at room temperature for 6 h to obtain a yellow suspension. The solid was filtered, and the filter cake was washed with acetonitrile until the filtrate was colorless. After vacuum drying, a brownish-red solid, Fe(III) catalyst 17 (430 mg, 49%), was obtained. Single crystals of Fe(III) catalyst 17 were obtained by volatilization of the acetonitrile saturated solution of the complex at room temperature (single crystal data are shown in Table 4, and the ellipsoidal diagram of the single crystal stereostructure is shown in Table 4). Figure 4 ).

[0155] Table 4

[0156]

[0157]

[0158] Preparation Example 17: Preparation of Iron Complex 18

[0159]

[0160] The ligand 2,2′:6′,2″-terpyridine (1.0 g, 4.3 mmol) and FeCl2·4H2O (0.42 g, 2.1 mmol) were dissolved in 60 mL of methanol. After stirring vigorously for 1 hour, NH4PF6 (2.0 g, 5.2 mmol) was added and stirring was continued vigorously for another 30 minutes. The solid was filtered, and the filter cake was washed with diethyl ether and dried under vacuum to obtain a dark purple solid Fe(III) catalyst 18 (1.6 g, 94% yield).

[0161] Example 1:

[0162] The following schemes are standard conditions.

[0163] Add 0.2 mL of Fe(terpy)Cl3 solution (8 mg Fe(terpy)Cl3 in 20 mL HFIP) and 50 μL of ammonium chloride solution (0.54 g dissolved in 10 mL water) to a weighing bottle (35 × 70 mm). Then add 10 mL of hexafluoroisopropanol (HFIP). Place the weighing bottle into the reactor. After assembling the reactor, replace the air in the reactor three times with 5 bar compressed air, then depressurize to 1 bar, and then fill with 5 bar CH4 and 20 bar CO. Stir for a specified time (8 hours) at room temperature under 400 nm LED irradiation. After turning off the light source, connect the reactor outlet valve to the GC-MS injection line to detect the gaseous byproduct CO2, and quantify using the external standard method. After detecting the gaseous products, slowly vent the reactor, disassemble the reactor, add an internal standard to the reaction solution, and take a portion of the reaction mixture for quantification. Acetic acid, hexafluoroisopropyl acetate, and methanol can be detected using GC-FID and... 1 H NMR (V 反应液 / 氘代二氯甲烷 =2 / 1) Quantitative detection, formic acid can be used 1 Quantitative detection using H NMR.

[0164] In Tables 6-11, the unit μmol of the product indicates the amount of product in the reaction solution after the reaction is complete.

[0165] The following TON values ​​are calculated using the following formula:

[0166] Total moles of (acetic acid + hexafluoroisopropyl acetate + methanol + formic acid) / moles of iron catalyst.

[0167] (1) Catalyst screening data are shown in Table 5. Other conditions are the same as those recorded in the standard conditions.

[0168] Table 5

[0169]

[0170] (2) The experimental data are shown in Table 6. Other conditions are the same as those recorded in the standard conditions.

[0171] Table 6

[0172]

[0173] (3) The additive screening data are shown in Table 7. Other conditions are the same as those recorded in the standard conditions.

[0174] Table 7

[0175]

[0176]

[0177] (4) The reaction temperature screening data are shown in Table 8. Other conditions are the same as those recorded in the standard conditions.

[0178] Table 8

[0179]

[0180] (5) Screening data for partial pressure of methane, air or oxygen are shown in Table 9. Other conditions are the same as those recorded in the standard conditions.

[0181] Table 9

[0182]

[0183]

[0184] Air means air.

[0185] (6) The screening data for catalyst loading and carbon monoxide partial pressure are shown in Table 10. Other conditions are the same as those recorded in the standard conditions.

[0186] Table 10

[0187]

[0188] (7) The screening data for iron catalysts are shown in Table 11. Other conditions are the same as those recorded in the standard conditions.

[0189] Table 11

[0190]

[0191]

[0192] Note a 0.05 μmol cat. 12, 48 h. b 0.05μmol cat.12,1bar CH4,48h.

[0193] Example 2: Flow Photoreaction

[0194] The reaction flow diagram is as follows Figure 5 As shown.

[0195] Weigh 8 mg of iron catalyst Fe(terpy)Cl3 and 108 mg of ammonium chloride into a 250 mL reagent bottle, then add 200 mL of HFIP. Sonicate the reaction mixture to dissolve all solids. First, attach a 50 mL reagent bottle containing pure solvent to the liquid pump of the flow reactor. Turn on the LED light and the chiller for cooling the LED light, setting the temperature to 25 degrees Celsius. Turn on the high-low temperature control unit for the reaction glass module, setting the temperature to 25 degrees Celsius. Next, set the back pressure valve to 15 bar. Turn on the liquid pump and pump the pure solvent HFIP into the flow microreactor at a rate of 1 mL / min. Open the main valves of the gas cylinders for methane, carbon monoxide, and air. Rotate the secondary pressure reducing valve to adjust the cylinder outlet pressure to 20 bar. Use the flow controller to control the flow rate of methane at 2 mL / min, carbon monoxide at 10 mL / min, and air at 1 mL / min. Once the system pressure stabilizes, stop the liquid pump, replace the pure solvent with the prepared reaction solution, and begin the reaction. After 30 minutes, take samples using centrifuge tubes, add internal standards, and acetic acid, hexafluoroisopropyl acetate, and methanol can be determined using GC-FID and... 1 Formic acid can be detected and quantified by ¹H NMR. 1 Quantitative detection using H NMR.

[0196] For the gaseous product CO2, a gas-liquid separator needs to be connected to the back pressure valve. After the reaction stabilizes, the gas outlet of the gas-liquid separator is directly passed into 100 mL of clear saturated Ba(OH)2 aqueous solution. After 30 minutes, the absorption is stopped, the solution obtained from the absorption is filtered, the filter cake is washed three times with ultrapure water, the solid is dried at 150 degrees and weighed, and the amount of CO2 generated in the reaction is calculated based on the mass of the obtained barium carbonate solid.

[0197] The data from the control experiment under flow conditions are shown in Table 12:

[0198] Table 12

[0199]

[0200]

Claims

1. A method for catalytically preparing acetic acid from methane, characterized in that, It includes the following steps: In the presence of a solvent, and under the influence of light, an iron catalyst, chloride ions, and an oxidant, methane and carbon monoxide undergo a methane oxidative carbonylation reaction to yield acetic acid. The iron catalyst is selected from one or more of Et4NFeCl4, ferric chloride, ferric bromide, ferric trifluoromethanesulfonate, ferrous trifluoromethanesulfonate, ferric trifluoroacetate, ferric sulfate, ferric nitrate, ferric phosphate, ferric tetrafluoroborate, ferric perchlorate, ferrous perchlorate, ferric oxalate, ferric acetylacetone, ferric p-benzenesulfonate, ferric ammonium ethylenediaminetetraacetate, ferric sodium ethylenediaminetetraacetate, ferric ethylenediaminetetraacetate, ferrous chloride, ferrous bromide, ferrous sulfate, ferrous oxalate, ferrous phosphate, ferrous tetrafluoroborate, ferrous perchlorate, ferrous acetate, ferrous carbonate, iron complexes as shown in Formula I, iron complexes as shown in Formula II, iron complexes as shown in Formula III, iron complex 6, iron complex 7, iron complex 16, and iron complex 18; in: Z can be F, Cl, Br, or I independently; X 1 Independently N, O, or S; R, R 1 and R 2 H and C independently 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl, -O-halogenated C 1-6 Alkyl, -COO-C 1-6 Alkyl, C 6-10 aryl, 5-10 heteroaryl, with one or more R a Replacement C 6-10 aryl or aryl with one or more R a The substituted 5-10 heteroaryl group, wherein the heteroatoms in the 5-10 heteroaryl group are independently selected from one, two or three of N, O and S, and the number of heteroatoms is independently one, two or three. R a Independently for C 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl or -O-halogenated C 1-6 alkyl.

2. The method for catalytically preparing acetic acid from methane as described in claim 1, characterized in that, It meets one or more of the following conditions: (1) The C 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl, -O-halogenated C 1-6 Alkyl and -COO-C 1-6 C in alkyl 1-6 Alkyl groups are independently C 1-4 Alkyl groups, such as methyl, ethyl, n-propyl, isobutyl, n-butyl, isobutyl, sec-butyl, or tert-butyl; (2) The C 6-10 aryl and one or more R a Replacement C 6-10 C in aryl 6-10 The aryl group can be phenyl or naphthyl, for example, phenyl; (3) Z is Cl; (4) R is independent of C 6-10 aryl or aryl with one or more R a Replacement C 6-10 Aryl group, for example, R is independently phenyl, (5)X 1 Independently N or O; (6)R 1 Independently H or C 1-6 Alkyl groups; such as H or isopropyl groups; (7)R 2 H and C independently 1-6 Alkyl, Halogenated C 1-6 Alkyl, -OC 1-6 Alkyl, -COO-C 1-6 Alkyl, C 6-10 aryl or aryl with one or more R a Replacement C 6-10 Aryl groups; for example, H, -COO-CH3, -CF3, tert-butyl, methoxy, phenyl, 3. The method for catalytically preparing acetic acid from methane as described in claim 1, characterized in that, The iron complex shown in Formula I is any of the following iron complexes: Alternatively, the iron complex shown in Formula II may be any of the following iron complexes: Alternatively, the iron complex shown in Formula III may be any of the following iron complexes:

4. The method for catalytically preparing acetic acid from methane according to any one of claims 1-3, characterized in that, It meets one or more of the following conditions: (1) The iron catalyst is Et4NFeCl4, ferric chloride, ferrous chloride, ferric trifluoromethanesulfonate, ferrous trifluoromethanesulfonate, ferric perchlorate, ferrous perchlorate, ferrous tetrafluoroborate, ferric ammonium ethylenediaminetetraacetate, ferric sodium ethylenediaminetetraacetate, ferric ethylenediaminetetraacetate, iron complex as shown in Formula I, iron complex as shown in Formula II, iron complex as shown in Formula III, iron complex 6, iron complex 7, iron complex 16, or iron complex 18; preferably, the iron catalyst is Et4NFeCl4, ferric chloride, ferrous chloride, ferric trifluoromethanesulfonate, ferrous trifluoromethanesulfonate, ferric perchlorate, ferrous perchlorate, ferrous tetrafluoroborate, iron complex as shown in Formula I, iron complex as shown in Formula II, iron complex as shown in Formula III, iron complex 6, iron complex 7, iron complex 16, or iron complex 18; more preferably, the iron catalyst is (2) The molar ratio of the iron catalyst to the volume of the solvent is (0.001-1) μmol: 1 mL, for example (0.001-0.5) μmol: 1 mL, or for example 0.01 μmol: 1 mL, 0.02 μmol: 1 mL, 0.05 μmol: 1 mL or 0.1 μmol: 1 mL; (3) The solvent is selected from one or more of water, hydrocarbon solvents, halogenated hydrocarbon solvents, alcohol solvents, nitrile solvents and acid solvents, for example, selected from one or more of water, alcohol solvents, nitrile solvents and acid solvents, or for example, alcohol solvents, acid solvents or a mixture of alcohol solvents and water; (4) The source of the chloride ions is selected from one or more of lithium chloride, ammonium chloride, magnesium chloride, calcium chloride, aluminum chloride, HCl, tetramethylammonium chloride, tetraethylammonium chloride and pyridine hydrochloride, such as lithium chloride, ammonium chloride, magnesium chloride, calcium chloride, aluminum chloride, HCl, tetramethylammonium chloride, tetraethylammonium chloride or pyridine hydrochloride. (5) The molar ratio of the chloride ions to the iron catalyst is (1-10000):1, for example (1-1000):1, for example (1-600):1, and for example 100:1, 125:1, 250:1, 300:1 or 500:1; (6) The oxidant is air, oxygen, hydrogen peroxide or persulfate, such as air, or compressed air; (7) The light is ultraviolet light and / or visible light with a wavelength of 300nm-780nm, for example, light with a wavelength of 360nm-420nm; (8) The temperature of the methane oxidative carbonylation reaction should be such that the solvent does not boil. For example, the temperature of the methane oxidative carbonylation reaction is -10℃ to 100℃, or 20℃ to 70℃, or 20℃, 25℃, 30℃, 40℃ or 60℃.

5. The method for catalytically preparing acetic acid from methane as described in claim 4, characterized in that, It meets one or more of the following conditions: (1) The alcohol solvent is hexafluoroisopropanol; (2) The nitrile solvent is acetonitrile; (3) The acid solvent is acetic acid; (4) The solvent is a mixture of alcohol and water, such as hexafluoroisopropanol and water; (5) The volume ratio of water to alcohol solvent is (0-1):1, for example (0-0.1):1, or (0-0.03):1, or even 0.002:1, 0.0025:1, 0.005:1 or 0.02:1; (6) When the solvent includes water, the water and the source of the chloride ions participate in the methane oxidative carbonylation reaction in the form of a chloride-containing solution.

6. The method for catalytically preparing acetic acid from methane according to any one of claims 1-3, characterized in that, The methane oxidative carbonylation reaction is carried out in a reaction vessel; Preferably, it satisfies one or more of the following conditions: (1) The pressure range of the carbon monoxide is 1-150 bar, for example 5-120 bar, or for example 10 bar, 20 bar, 50 bar or 100 bar; (2) The pressure range of the methane is 1-100 bar, for example 1-20 bar, or even 2 bar, 5 bar or 10 bar; (3) The oxidant is air or oxygen, and the pressure range of the oxidant is 0.01-10 bar, for example 0.01-6 bar, or for example 1 bar, 2 bar or 5 bar; (4) The oxidant is air or oxygen, and the oxidant is introduced by gas replacement method, and the number of gas replacements is 3-5 times.

7. The method for catalytically preparing acetic acid from methane according to any one of claims 1-3, characterized in that, The methane oxidative carbonylation reaction is carried out in a flow photoreactor; Preferably, it satisfies one or more of the following conditions: (1) The iron catalyst, chloride ions and the solvent participate in the reaction in the form of a mixed solution. The flow rate of the mixed solution is (0.1-5) mL / min, for example (0.5-3) mL / min, or even 1 mL / min; (2) The flow rate of the methane is (1-30) mL / min, for example (1-10) mL / min, or for example 2 mL / min; (3) The flow ratio of the carbon monoxide to the methane is (1-30):1, for example (5-15):1, or for example 5:1; (4) The flow rate ratio of the oxidant to the methane is (0.1-5):1, for example (0.1-1):1, or for example 0.5:

1.

8. The method for catalytically preparing acetic acid from methane as described in claim 1, characterized in that, The reaction system for the methane oxidative carbonylation reaction consists of the following components: light, iron catalyst, chloride ions, oxidant, solvent, methane, and carbon monoxide.

9. The use of an iron complex of formula I, formula II, formula III, formula 6, iron complex 7, iron complex 16 or iron complex 18 as described in any one of claims 1-3 as a catalyst in the oxidative carbonylation of methane.

10. An iron complex or its crystal form, said iron complex being any of the following compounds:

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