Method for catalyzing air oxidation of n-butane by metal complex

Abstract

The invention discloses a method for catalyzing air oxidation of n-butane by a metal complex. According to the method, n-butane is taken as a raw material, an organic solvent and a cocatalyst are added, air is taken as an oxidizing agent, a metal complex with a structural formula as shown in a general formula (I) is taken as a catalyst, a catalytic reaction is carried out under the conditions that the reaction temperature is controlled to be 40-110 DEG C and the reaction pressure is controlled to be 0.1-6.0 MPa, and 2-butanone is prepared, and the dosage of the catalyst is 0.01%-1 mol% of that of the raw material; the method disclosed by the invention has the advantages of mild reaction conditions, good catalytic effect, relatively high conversion rate, simple process and the like; belongs to the technical field of homogeneous catalysis.

Description

Technical Field

[0001] The present invention relates to a method for catalytic air oxidation of n-butane by a metal complex. Specifically, it relates to a method for preparing a metal complex, and a homogeneous catalytic oxidation method for preparing 2-butanone from n-butane using the synthesized metal complex as a catalyst and air as an oxidant; it belongs to the field of homogeneous catalysis. Background Art

[0002] 2-Butanone (MEK) is an important organic synthesis intermediate, widely used in industrial production of various high-value products, such as inks, paints, lubricants, dewaxing agents, and can also be used in pharmaceutical production, dyes, detergents, and fragrances, etc. At the same time, 2-butanone is also an important organic synthesis intermediate, which can be used to produce butanedione, methyl ethyl ketone peroxide, and antioxidants, etc. It is also an important organic solvent with excellent solubility and a liquid fuel additive. Currently, the MEK market has grown to $3.26 billion and the production volume has reached 1.75 million tons.

[0003] At present, several effective processes for preparing 2-butanone have been developed in the academic or industrial fields. The more commonly used industrial methods are the n-butene method, the cumene method, the fermentation method, and the liquid-phase oxidation method of n-butane. Among them, the two-step oxidation method of n-butene includes two reaction steps: the hydration of n-butene to sec-butanol and the dehydrogenation of sec-butanol to methyl ethyl ketone. According to different catalysts, there are mainly three methods for the hydration of n-butene to sec-butanol: batch hydration with sulfuric acid, direct hydration with resin, and direct hydration with heteropolyacid; there are generally two methods for the dehydrogenation of sec-butanol to methyl ethyl ketone: gas dehydrogenation method and liquid dehydrogenation method. At present, due to the strong corrosiveness of the catalyst in the n-butene oxidation method, expensive titanium material equipment needs to be purchased, which leads to an increase in production costs, and the product separation process is also relatively complex. Therefore, the n-butene oxidation method cannot be industrially produced on a large scale at present. The cumene method involves the alkylation reaction of n-butene with benzene to form isobutylbenzene, then the oxidation of isobutylbenzene to form cumene hydroperoxide, and then decomposition under acidic conditions. After concentration treatment of the oxidation liquid, methyl ethyl ketone and phenol are obtained, and finally methyl ethyl ketone is obtained through separation. Although this method has mild reaction conditions and less corrosion to equipment, the reaction process flow is complex and the operating conditions are relatively strict, and it has not been widely applied at present. The biological fermentation method actually first ferments glucose to obtain 2,3-butanediol, and then obtains methyl ethyl ketone through sulfuric acid-catalyzed dehydration. Although this method has a simple process, rapid reaction, and relatively high reactant conversion rate and product yield, due to the strong corrosiveness of sulfuric acid, it will corrode equipment, and the "three wastes" caused by this method cause serious environmental pollution and it is difficult to put into production on a large scale. The liquid-phase oxidation method of n-butane is mainly a method for producing acetic acid, and methyl ethyl ketone is one of the by-products, accounting for about 16% of the acetic acid content. This process is a gas-liquid phase reaction, with cobalt acetate-sodium acetate as the catalyst, acetic acid as the solvent, the reaction pressure is 5.6 MPa, the reaction temperature is 160 °C - 225 °C, and the mass ratio of methyl ethyl ketone to acetic acid is 0.4:1.0. At present, 20% of methyl ethyl ketone in the United States is produced by this method, and due to the development of the acetic acid production process towards the low-pressure carbonylation of methanol, the prospect of preparing methyl ethyl ketone by the liquid-phase oxidation method of n-butane is relatively dim.

[0004] Therefore, it has important practical significance and application prospects to develop a biomimetic catalytic air oxidation process of n-butane to prepare 2-butanone with mild reaction conditions, green and high efficiency.

[0005] Chinese invention patent CN201210301836.6 discloses a method for preparing 2-butanone by oxidizing n-butane with oxygen at a relatively high temperature using metal phthalocyanine as a catalyst. Although this method overcomes the disadvantages of pollution and high production costs, the catalytic effect is not ideal. Oxidizing n-butane with oxygen as the oxygen source has certain production safety risks.

[0006] Chinese invention patent CN 1202410263903.2 discloses a method for the bionic catalysis of n-butane oxidation to prepare 2-butanone. This method uses n-butane as the raw material, air as the oxidant, a metal complex as the catalyst, adds a solvent and a co-catalyst, and controls the reaction temperature at 50-100 °C and the reaction pressure at 0.1-6.0 MPa to carry out the catalytic reaction to obtain 2-butanone with high selectivity. However, the preparation of the catalyst in this method is relatively cumbersome, the catalyst is difficult to recover, and the conversion rate of n-butane is not high. Summary of the Invention

[0007] In order to overcome the defects existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for the catalytic oxidation of n-butane with air by a metal complex.

[0008] To achieve the purpose of the present invention, the technical solution adopted is:

[0009] A method for the catalytic oxidation of n-butane with air by a metal complex, using n-butane as the raw material, adding an organic solvent and a co-catalyst, using air as the oxidant, using a metal complex shown by the structural formula as in general formula (I) as the catalyst, controlling the reaction temperature at 40-110 °C and the reaction pressure at 0.1-6.0 MPa to carry out the catalytic reaction to obtain 2-butanone, and the dosage of the catalyst is 0.01%-1 mol% of the raw material.

[0010]

[0011] In formula (I):

[0012] M is selected from one of the metal atoms Cu, Ag, Au, Fe, Co, Ni, Zn;

[0013] R1 are all selected from one of aldehyde group and amino group; R2 is selected from one of hydrogen, methyl and ethyl.

[0014] Further, in the above method for the catalytic oxidation of n-butane with air by a metal complex, the dosage of the co-catalyst is 0.5-25.0 mol% of the raw material.

[0015] Further, in the above method for the catalytic oxidation of n-butane with air by a metal complex, the co-catalyst is one of N-hydroxyphthalimide, phthalimide, N-bromophthalimide, 3-nitrophthalimide, hexahydrophthalimide, 4-bromophthalimide, N-hydroxysuccinimide.

[0016] Further, in the above method for the catalytic oxidation of n-butane with air by a metal complex, the organic solvent is one of ethanol, isopropanol, hexafluoroisopropanol, dichloromethane, N,N-dimethylformamide, tetrahydrofuran, ethyl acetate, methyl benzoate, acetonitrile, benzonitrile.

[0017] Furthermore, in the above-mentioned method of catalyzing the oxidation of n-butane by air using a metal complex, the catalytic reaction temperature is 40-110°C.

[0018] Furthermore, in the above-mentioned method of catalyzing the oxidation of n-butane by air using a metal complex, the catalytic reaction pressure is 0.1 to 6.0 MPa.

[0019] Furthermore, the above-mentioned method for catalyzing the air oxidation of n-butane using a metal complex is prepared by the following method: adding a pyrazole compound, a metal oxide, a solvent, and a catalyst to a reactor, reacting at 100-140° C. for 48-96 hours, filtering after completion of the reaction, washing the filter cake, and drying in a vacuum drying oven to obtain a metal complex having a structural formula represented by general formula (I);

[0020] The molar ratio of the formaldehyde, metal oxide and pyrazole compound is 2.5:1:2.5.

[0021] Furthermore, in the above-mentioned method of catalyzing the oxidation of n-butane by air using a metal complex, the metal oxide is one of silver oxide, gold oxide, iron oxide, cobalt oxide, nickel oxide, zinc oxide or cuprous oxide.

[0022] Furthermore, in the above-mentioned method of catalyzing the air oxidation of n-butane using a metal complex, the pyrazole compound is 1H-pyrazole-4-carboxaldehyde or 3,5-dimethyl-1H-pyrazole-4-carboxaldehyde or 4-aminopyrazole or 3,5-dimethyl-1H-pyrazole-4-amine.

[0023] Furthermore, in the above-mentioned method of catalyzing the oxidation of n-butane by air using a metal complex, the solvent is ethanol; and the catalyst is pyridine.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The technical solution provided by the present invention involves adding a catalyst to a solvent and a co-catalyst, allowing n-butane and air to undergo an oxidation reaction under the action of the catalyst to produce 2-butanone. The purpose of adding the co-catalyst is to facilitate the generation of free radicals in the system, which capture the secondary hydrogen of n-butane to generate 2-butyl radicals, thereby facilitating the activation of oxygen. The metal complex has a good activation effect on molecular oxygen at low temperatures, thereby accelerating the conversion of n-butane at low temperatures.

[0026] 2. The technical solution provided by the present invention has a high conversion rate of n-butane in various reaction systems, high selectivity, easy product separation, low catalyst usage, and the catalyst and co-catalyst can be reused by centrifugation or filtration.

[0027] 3. The technical solution provided by the present invention uses air as an oxidant, avoiding problems such as severe equipment corrosion, environmental pollution, and safety caused by peroxyacids, nitric acid, sulfuric acid, etc., and the conditions are mild.

[0028] 4. The catalyst of the technical solution provided by the present invention is simple to synthesize, recyclable, reusable, has a simple process, low production cost, is green and safe, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the infrared spectrum of the metal complex shown in general formula (II) used in Examples 1-7;

[0030] Figure 2 is the XRD spectrum of the metal complex shown in general formula (II) used in Examples 1-7;

[0031] Figure 3 is the gas chromatogram of the product provided in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The present invention will be further described below in conjunction with the embodiments, but the protection scope of the present invention is not limited to the scope shown in the embodiments.

[0033] Example 1

[0034] In a high-pressure reactor, 0.5 mg of the metal complex (M = Cu, R = hydrogen) shown in general formula (II) was added successively, 4 mmol of the co-catalyst N-hydroxyphthalimide was added, 20 mL of acetonitrile solution was added, 10 mmol of n-butane and 2 MPa of air were charged, and the mixture was stirred at 70 °C for 7 h. After gas chromatography detection, the gas chromatogram is referred to Figure 3 , the conversion rate of n-butane is 80%, and the selectivity of 2-butanone is 99%.

[0035] Example 2

[0036] In a high-pressure reactor, 100 mg of the metal complex (M = Cu, R = hydrogen) shown in general formula (II) was added successively, 1 mmol of the co-catalyst N-hydroxyphthalimide was added, 20 mL of acetonitrile solution was added, 15 mmol of n-butane and 2 MPa of air were charged, and the mixture was stirred at 70 °C for 7 h. After gas chromatography detection, the conversion rate of n-butane is 50%, and the selectivity of 2-butanone is 99%.

[0037] Example 3

[0038] In a high-pressure reactor, 2 mg of the metal complex shown by the general formula (II) (M = Cu, R = hydrogen) was successively added, 4 mmol of the cocatalyst N-hydroxyphthalimide was added, 20 mL of an acetonitrile solution was added, 30 mmol of n-butane and 2 MPa of air were charged, and the mixture was stirred at 60 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 60%, and the selectivity for 2-butanone was 96%.

[0039] Example 4

[0040] In a high-pressure reactor, 2 mg of the metal complex shown by the general formula (II) (M = Cu, R = hydrogen) was successively added, 20 mL of a benzonitrile solution was added, 4 mmol of the cocatalyst N-hydroxyphthalimide was added, 10 mmol of n-butane and 2.0 MPa of air were charged, and the mixture was stirred at 60 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 40%, and the selectivity for 2-butanone was 80%.

[0041] Example 5

[0042] In a high-pressure reactor, 2 mg of the metal complex shown by the general formula (II) (M = Cu, R = hydrogen) was successively added, 4 mmol of the cocatalyst N-hydroxyphthalimide was added, 20 mL of an acetonitrile solution was added, 10 mmol of n-butane and 0.5 MPa of air were charged, and the mixture was stirred at 60 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 40%, and the selectivity for 2-butanone was 90%.

[0043] Example 6

[0044] In a high-pressure reactor, 2 mg of the metal complex shown by the general formula (II) (M = Cu, R = hydrogen) was successively added, 4 mmol of the cocatalyst N-hydroxyphthalimide was added, 20 mL of an acetonitrile solution was added, 10 mmol of n-butane and 6.0 MPa of air were charged, and the mixture was stirred at 70 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 80%, and the selectivity for 2-butanone was 85%.

[0045] Example 7

[0046] In a high-pressure reactor, 2 mg of the metal complex shown by the general formula (II) (M = Cu, R = hydrogen) was successively added, 2 mmol of the cocatalyst N-hydroxyphthalimide was added, 20 mL of an acetonitrile solution was added, 10 mmol of n-butane and 4.0 MPa of air were charged, and the mixture was stirred at 60 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 50%, and the selectivity for 2-butanone was 88%.

[0047] The structural formula of the metal complex general formula (II) described in Examples 1 - 7 is as follows:

[0048]

[0049] Synthesis steps of the metal complex shown in General Formula (II): 240 mg of 1H-pyrazole-4-carbaldehyde (2.5 mmol), 143 mg of cuprous oxide (1 mmol), 30 mL of ethanol, and 1 mL of pyridine were successively added to a 50 mL Schlenk tube and reacted at 120 °C for 72 h. After the reaction, a pale yellow solid product was observed to precipitate at the bottom of the reaction tube. It was filtered, and the filter cake was washed with methanol (20 mL × 3) and dried in a vacuum drying oven for 12 h to obtain the metal complex shown in General Formula (II).

[0050] The infrared spectrum of this metal complex is referred to Figure 1 , Figure 1 The infrared spectrum shows that there is an obvious peak near 1050 cm -1 attributed to the bending vibration of C=0, and the peak at 795 cm -l is attributed to the bending vibration of C-H on the imidazole ring. There is an obvious peak at 550 m -1 belonging to the characteristic stretching frequency of C-N. These observations confirm the successful synthesis of this catalyst; the XRD spectrum is referred to Figure 2 , Figure 2 The XRD spectrum shows obvious diffraction peaks at 7°, 20°, and 27°, corresponding to the characteristic signal peaks of this complex.

[0051] Example 8

[0052] In a high-pressure reactor, 2 mg of the metal complex shown in General Formula (II) (M1 = Ag, R = hydrogen) was successively added, 2 mmol of the co-catalyst N-hydroxyphthalimide, 20 mL of acetonitrile solution, 10 mmol of n-butane and 2.0 MPa of air were charged, and it was stirred at 60 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 50%, and the selectivity for 2-butanone was 93%.

[0053] The structural formula of the metal complex in General Formula (II) described in Example 8 is as follows:

[0054]

[0055] Synthesis steps of the metal complex shown in General Formula (II): 240 mg of 1H-pyrazole-4-carbaldehyde (2.5 mmol), 232 mg of silver oxide (1 mmol), 30 mL of ethanol, and 1 mL of pyridine were successively added to a 50 mL Schlenk tube, and the reaction was carried out at 120 °C for 72 h. After the reaction was completed, a pale yellow solid product was observed to precipitate at the bottom of the reaction tube. The product was filtered, and the filter cake was washed with methanol (20 mL × 3) and dried in a vacuum drying oven for 12 h to obtain the metal complex shown in General Formula (II).

[0056] Example 9

[0057] In a high-pressure reactor, 2 mg of the metal complex shown in General Formula (II) (M1 = Au, R = hydrogen), 2 mmol of the cocatalyst N-hydroxyphthalimide, 20 mL of acetonitrile solution were successively added, 10 mmol of n-butane and 2.0 MPa of air were charged, and the mixture was stirred at 60 °C for 7 h. After gas chromatography detection, the conversion rate of n-butane was 55%, and the selectivity for 2-butanone was 95%.

[0058] The structural formula of the metal complex of General Formula (II) described in Example 9 is shown as follows:

[0059]

[0060] Synthesis steps of the metal complex shown in General Formula (II): 240 mg of 1H-pyrazole-4-carbaldehyde (2.5 mmol), 303 mg of AuCl3 (1 mmol), 30 mL of ethanol, and 1 mL of pyridine were successively added to a 50 mL Schlenk tube, and the reaction was carried out at 120 °C for 72 h. After the reaction was completed, a pale yellow solid product was observed to precipitate at the bottom of the reaction tube. The product was filtered, and the filter cake was washed with methanol (20 mL × 3) and dried in a vacuum drying oven for 12 h to obtain the metal complex shown in General Formula (II).

[0061] Example 10

[0062] In a high-pressure reactor, 2 mg of the metal complex shown in General Formula (II) (M1 = Fe, R = hydrogen), 2 mmol of the cocatalyst N-hydroxyphthalimide, 20 mL of acetonitrile solution were successively added, 10 mmol of n-butane and 2.0 MPa of air were charged, and the mixture was stirred at 60 °C for 7 h. After gas chromatography detection, the conversion rate of n-butane was 60%, and the selectivity for 2-butanone was 90%.

[0063] The structural formula of the metal complex of General Formula (II) described in Example 9 is shown as follows:

[0064]

[0065] Synthesis steps of the metal complex shown in general formula (I): 240 mg of 1H-pyrazole-4-carbaldehyde (2.5 mmol), 127 mg of FeCl2 (1 mmol), 30 mL of ethanol, and 1 mL of pyridine were successively added to a 50 mL Schlenk tube and reacted at 120 °C for 72 h. After the reaction, a pale yellow solid product was observed to precipitate at the bottom of the reaction tube. It was filtered, and the filter cake was washed with methanol (20 mL × 3) and dried in a vacuum drying oven for 12 h to obtain the metal complex shown in general formula (II).

[0066] Example 11

[0067] In a high-pressure reaction kettle, 2 mg of the metal complex shown in general formula (II) (M = Cu, R = methyl) was successively added, 4 mmol of the co-catalyst N-hydroxyphthalimide was added, 20 mL of acetonitrile solution was added, 15 mmol of n-butane and 2.0 MPa of air were charged, and the mixture was stirred and reacted at 70 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 80%, and the selectivity for 2-butanone was 95%.

[0068] Example 12

[0069] In a high-pressure reaction kettle, 2 mg of the metal complex shown in general formula (II) (M = Cu, R = methyl) was successively added, 2 mmol of the co-catalyst N-hydroxyphthalimide was added, 20 mL of acetonitrile solution was added, 10 mmol of n-butane and 2.0 MPa of air were charged, and the mixture was stirred and reacted at 60 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 45%, and the selectivity for 2-hexanone was 95%.

[0070] Example 13

[0071] In a high-pressure reaction kettle, 2 mg of the metal complex shown in general formula (II) (M = Cu, R = methyl) was successively added, 2 mmol of the co-catalyst phthalimide was added, 20 mL of acetonitrile solution was added, 10 mmol of n-butane and 2.0 MPa of air were charged, and the mixture was stirred and reacted at 60 °C for 7 h. By gas chromatography detection, the conversion rate of n-butane was 35%, and the selectivity for 2-butanone was 77%.

[0072] The structural formula of the metal complex general formula (II) described in Examples 11 - 13 is as follows:

[0073]

[0074] Synthesis steps of the metal complex shown in General Formula (II): Add 310 mg of 3,5-dimethyl-1H-pyrazole-4-carbaldehyde (2.5 mmol), 143 mg of cuprous oxide (1 mmol), 30 mL of ethanol, and 1 mL of pyridine into a 50 mL Schlenk tube in sequence. React at 120 °C for 72 h. After the reaction, observe that a pale yellow solid product precipitates at the bottom of the reaction tube. Filter, wash the filter cake with methanol (20 mL × 3), and dry it in a vacuum drying oven for 12 h to obtain the metal complex shown in General Formula (II).

[0075] Example 14

[0076] In a high-pressure reaction kettle, add 2 mg of the metal complex (M = Cu, R = hydrogen) shown in General Formula (III) in sequence, add 4 mmol of the co-catalyst N-bromophthalimide, 20 mL of acetonitrile solution, charge 10 mmol of n-butane and 2.0 MPa of air, and stir and react at a temperature of 60 °C for 7 h. After detection by gas chromatography, the conversion rate of n-butane is 20%, and the selectivity of 2-butanone is 95%.

[0077] Example 15

[0078] In a high-pressure reaction kettle, add 2 mg of the metal complex (M = Cu, R = hydrogen) shown in General Formula (I) in sequence, add 2 mmol of the co-catalyst N-hydroxyphthalimide, 20 mL of acetonitrile solution, charge 10 mmol of n-butane and 2.0 MPa of air, and stir and react at a temperature of 60 °C for 7 h. After detection by gas chromatography, the conversion rate of n-butane is 60%, and the selectivity of 2-butanone is 78%.

[0079] Example 16

[0080] In a high-pressure reaction kettle, add 2 mg of the metal complex (M = Cu, R = hydrogen) shown in General Formula (III) in sequence, add 4 mmol of the co-catalyst phthalimide, 20 mL of acetonitrile solution, charge 10 mmol of cyclopentane and 2.0 MPa of air, and stir and react at a temperature of 60 °C for 7 h. After detection by gas chromatography, the conversion rate of cyclopentane is 40%, and the selectivity of cyclopentanone is 90%.

[0081] The structural formula of the metal complex shown in General Formula (III) described in Examples 14 - 16 is as follows:

[0082]

[0083] Synthesis steps of the metal complex shown by general formula (Ⅲ): Add 208 mg of 4-aminopyrazole (2.5 mmol), 143 mg of cuprous oxide (1 mmol), 30 mL of ethanol, and 1 mL of pyridine into a 50 mL Schlenk tube in sequence, react at 120 °C for 72 h. After the reaction is completed, a pale yellow solid product is observed to precipitate at the bottom of the reaction tube. Filter, wash the filter cake with methanol (20 mL × 3), and dry it in a vacuum drying oven for 12 h to obtain the metal complex shown by general formula (Ⅲ).

[0084] Example 17

[0085] In a high-pressure reactor, add 2 mg of the metal complex shown by general formula (Ⅲ) (M = Cu, R = methyl) in sequence, add 4 mmol of the cocatalyst phthalimide, 20 mL of acetonitrile solution, charge 10 mmol of n-butane and 2.0 MPa of air, and stir and react at a temperature of 60 °C for 7 h. After detection by gas chromatography, the conversion rate of n-butane is 20%, and the selectivity of 2-butanone is 95%.

[0086] Example 18

[0087] In a high-pressure reactor, add 2 mg of the metal complex shown by general formula (Ⅲ) (M = Cu, R = methyl) in sequence, add 2 mmol of the cocatalyst N-hydroxyphthalimide, 20 mL of acetonitrile solution, charge 10 mmol of n-hexane and 2.0 MPa of air, and stir and react at a temperature of 60 °C for 7 h. After detection by gas chromatography, the conversion rate of n-hexane is 60%, and the selectivity of 2-hexanone is 75%.

[0088] Example 19

[0089] In a high-pressure reactor, add 2 mg of the metal complex shown by general formula (Ⅲ) (M = Cu, R = methyl) in sequence, add 4 mmol of the cocatalyst N-hydroxyphthalimide, 20 mL of acetonitrile solution, charge 10 mmol of cyclohexane and 2.0 MPa of air, and stir and react at a temperature of 70 °C for 7 h. After detection by gas chromatography, the conversion rate of cyclohexane is 70%, and the selectivity of cyclohexanone is 65%.

[0090] The structural formula of the metal complex general formula (Ⅲ) described in Examples 17 - 19 is as follows:

[0091]

[0092] Synthesis steps of the metal complex shown in general formula (Ⅲ): Add 310 mg of 3,5-dimethyl-1H-pyrazole-4-carbaldehyde (2.5 mmol), 143 mg of cuprous oxide (1 mmol), 30 mL of ethanol, and 1 mL of pyridine into a 50 mL Schlenk tube in sequence. React at 120 °C for 72 h. After the reaction is completed, a pale yellow solid product is observed to precipitate at the bottom of the reaction tube. Filter, wash the filter cake with methanol (20 mL × 3), and dry it in a vacuum drying oven for 12 h to obtain the metal complex shown in general formula (Ⅲ).

[0093] Comparative Example 1

[0094] In a high-pressure reactor, add 2 mg of the metal complex shown in general formula (Ⅲ) described in Example 14, 20 mL of acetonitrile solution, charge 10 mmol of n-butane and 2 MPa of air, and stir at a temperature of 60 °C for 7 h. After detection by gas chromatography, the conversion rate of n-butane is 16%, and the selectivity for 2-butanone is 65%.

[0095] Comparative Example 2

[0096] In a high-pressure reactor, add 2 mmol of the cocatalyst N-hydroxyphthalimide, 20 mL of acetonitrile solution, charge 10 mmol of n-butane and 2 MPa of air, and stir at a temperature of 60 °C for 7 h. After detection by gas chromatography, the conversion rate of n-butane is 20%, and the selectivity for 2-butanone is 80%.

Claims

1. A method for catalytic air oxidation of n-butane by a metal complex, characterized in that, Using n-butane as a raw material, adding an organic solvent and a co-catalyst, using air as an oxidant, and using a metal complex with a structural formula as shown in the general formula (I) as a catalyst, the catalytic reaction is carried out under the conditions of a reaction temperature of 40-110 °C and a reaction pressure of 0.1-6.0 MPa to obtain 2-butanone, and the catalyst dosage is 0.01%-1 mol% of the raw material; In formula (I): M is selected from one of the metal atoms Cu, Ag, Au, Fe, Co, Ni, Zn; R1 are all selected from one of aldehyde group and amino group; R2 is selected from one of hydrogen, methyl, and ethyl.

2. The method for catalytic air oxidation of n-butane by a metal complex according to claim 1, wherein, The dosage of the co-catalyst is 0.5-25.0 mol% of the raw material.

3. A method for catalytically oxidizing n-butane with air using a metal complex according to claim 1, characterized in that, The co-catalyst is one of N-hydroxyphthalimide, phthalimide, N-bromophthalimide, 3-nitrophthalimide, hexahydrophthalimide, 4-bromophthalimide, N-hydroxysuccinimide.

4. A method for catalytically oxidizing n-butane with air using a metal complex according to claim 1, characterized in that, The organic solvent is one of ethanol, isopropanol, hexafluoroisopropanol, dichloromethane, N,N-dimethylformamide, tetrahydrofuran, ethyl acetate, methyl benzoate, acetonitrile, benzonitrile.

5. A method for catalytically oxidizing n-butane with air using a metal complex according to claim 1, characterized in that, The catalytic reaction temperature is 40-110 °C.

6. A method for catalytic air oxidation of n-butane by a metal complex according to claim 1, characterized in that, The catalytic reaction pressure is 0.1-6.0 MPa.

7. A method for catalytic air oxidation of n-butane by a metal complex according to claim 1, characterized in that, The metal complex is prepared by the following method: adding a pyrazole compound, a metal oxide, a solvent, and a catalyst to a reactor, reacting at 100-140 °C for 48-96 h, after the reaction is completed, filtering, washing the filter cake, and drying in a vacuum drying oven to obtain a metal complex with a structural formula as shown in the general formula (I); The molar ratio of formaldehyde, metal oxide, and pyrazole compound is 2.5:1:2.

5.

8. A method for catalytic air oxidation of n-butane by a metal complex according to claim 7, characterized in that, The metal oxide is one of silver oxide, gold oxide, iron oxide, cobalt oxide, nickel oxide, zinc oxide, cuprous oxide.

9. A method for catalytic air oxidation of n-butane by a metal complex according to claim 7, characterized in that, The pyrazole compound is 1H-pyrazole-4-carbaldehyde or 3,5-dimethyl-1H-pyrazole-4-carbaldehyde or 4-aminopyrazole or 3,5-dimethyl-1H-pyrazol-4-amine.

10. A method for catalytic air oxidation of n-butane by a metal complex according to claim 7, characterized in that, The solvent is ethanol; the catalyst is pyridine.

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