A process for the selective hydroaminomethylation of olefins to produce linear amines

Abstract

The application belongs to the technical field of fine chemical industry, and particularly relates to a method for preparing linear amine through selective hydrogen aminomethylation of olefin. The method uses olefin, amine, carbon monoxide or carbon dioxide and water as reaction raw materials, uses nitrogen heterocyclic carbene metal compound as a catalyst, uses pure water, ether, alcohol or benzene analogues as a solvent, and reacts at 80-200 DEG C for 4-48 hours to obtain corresponding linear (L) amine and branched (B) amine products. Compared with the prior art, the method can use cheap and easily available olefin and amine as starting raw materials, uses water as a hydrogen source, avoids using toxic and less stable phosphine ligands and high-pressure hydrogen, has a high reaction selectivity L / B value of 92 / 8, an amine yield of 96%, is simple to operate, and only needs simple post-treatment to obtain high-purity different amine products, and is suitable for industrial amplification and application.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a method for preparing linear amines by selective hydrogen amine methylation of olefins. Background Technology

[0002] Amines and their derivatives have broad application prospects in energy, materials, medicine, environment, and daily chemical industries, resulting in high demand and prices, making them a key focus of the fine chemical industry and chemical research in recent years. Industrially, amine preparation methods mainly include alkylation of ammonia / amines with alcohols and haloalkanes, reductive amination of aldehydes, and reduction of nitriles. However, these methods are essentially multi-step synthesis methods because alcohols, aldehydes, acids, nitriles, and alkyl halides are mainly prepared from oils or olefins through multiple steps such as hydrolysis, oxidation, hydrogenation, halogenation, and nitrification. Some of these steps require harsh reaction conditions, high temperatures and pressures, and high energy consumption; others are complex and pollute the environment. Therefore, a one-step synthesis of amines from olefins is of great significance. Hydrogen-amine methylation is an important method for converting olefins, hydrogen or water, carbon monoxide or carbon dioxide, and amines into amine compounds using transition metal catalysts. It achieves carbon chain growth and high-value olefins while possessing excellent atom economy, making it a major method for amine preparation. The difficulty in olefin hydrogen-amine methylation lies in the selective control of the reaction. Regardless of the catalytic system used, in addition to generating linear amines (L) and branched amines (B), alkenes are also prone to isomerization or further hydrogenation to generate corresponding alkanes. In particular, how to control the selectivity (L / B) of the olefin hydrogen amine methylation reaction is a bottleneck problem in this research field.

[0003] To date, numerous research groups both domestically and internationally have conducted a series of studies on the hydrogen amine methylation of olefins catalyzed by homogeneous catalysts, which have improved the selectivity (L / B) of olefin hydrogen amine methylation to some extent. However, the selectivity of this reaction remains low, and the requirement of high-pressure hydrogen gas, while improving the L / B selectivity, also promotes the formation of side reactions in olefin hydrogenation, leading to a decrease in the yield of amine products and increasing the difficulty and operating cost of subsequent separation and purification. Furthermore, in the reported olefin hydrogen amine methylation reactions using supported catalysts, the L / B ratio is typically low, increasing the difficulty and cost of separation and purification. In summary, compared to homogeneous catalysts, the reaction efficiency of existing heterogeneous catalytic systems remains relatively low. Therefore, how to combine the advantages of homogeneous and heterogeneous catalysis to design and develop a novel catalytic system to further improve the L / B value of olefin hydrogen amine methylation has become a focus of attention in academia and industry. Summary of the Invention

[0004] The purpose of this invention is to provide a safe, efficient, and highly selective method for preparing linear amines by selective hydrogen amine methylation of olefins.

[0005] The present invention provides a method for preparing linear amines by selective hydrogen amine methylation of olefins, using water as a hydrogen source and a nitrogen-containing heterocyclic carbene metal compound as a catalyst to catalyze the selective hydrogen amine methylation of olefins, thereby achieving the preparation of linear amines; the specific steps are as follows:

[0006] The reaction is carried out using olefins, carbon monoxide or carbon dioxide, water and amines as raw materials, pure water, ethers, alcohols, benzene analogs as solvents, and nitrogen heterocyclic carbene metal compounds as catalysts. The molar ratio of catalyst to amine is 1 / 10,000 to 1 / 1000, and the reaction is carried out at 80 to 200°C for 4 to 48 hours.

[0007] The linear amine product was obtained by column chromatography; the selectivity of the linear amine was determined by... 1 The solution after the reaction was analyzed by 1H NMR, with mesitylene as an internal standard.

[0008] The chemical reaction process of the method of the present invention is as follows:

[0009]

[0010] In this olefin, R1 is selected from ortho-, meta-, para-substituted or unsubstituted C6-C. 10 Aryl, C5-C8 straight-chain alkyl, C5-C6 cycloalkyl; in amine compounds, Ar is selected from ortho-, meta-, para-substituted or unsubstituted C6-C6 compounds. 10 Aryl, ortho-, meta-, para-substituted or unsubstituted C4-C 16 Heteroaryl; R2 is selected from C1-C4 straight-chain alkyl and C5-C6 cycloalkyl;

[0011] Wherein, “substituted” means that one or more hydrogen atoms in a group are replaced by a substituent selected from the group consisting of: halogen, C3-C6 alkyl, C4 ester, C5 carbonyl, C5 alkyl ether, C4 hydroxy, and C1-C2 alkoxy.

[0012] The chemical structural formula of the nitrogen heterocyclic carbene metal compound is as follows:

[0013] M(NHC) n (L) 4-n X

[0014] In the formula,

[0015] M is selected from group VIIIB transition metals: Ru, Rh, Ir, Pd, Ni, or a combination of several of them;

[0016] L is selected from cyclooctadiene, carbonyl, pyridine, triphenylphosphine, hydride, chloride, bromide, iodide, tetrafluoroborate, hexafluorophosphate, tetrahydrofuran, and BH4. - BH4CN -- BH4(Et)3 --AlH4 - ;

[0017] X is selected from chloride ion, bromide ion, iodide ion, tetrafluoroborate ion, hexafluorophosphate ion, or hexafluoroantimonate ion;

[0018] n can be 1, 2, or 3;

[0019] NHC is the nitrogen-containing heterocyclic carbene ligand represented by general formula I:

[0020]

[0021] In the formula,

[0022] R 1 R 2 Selected from: hydrogen, substituted or unsubstituted C1-C respectively 10 Alkyl, substituted or unsubstituted C3-C 10 Cycloalkyl, substituted or unsubstituted C6-C 24 Aryl, substituted or unsubstituted C7-C 25 Arylalkyl, substituted or unsubstituted C4-C 20 heteroaryl, of which R 1 and R 2 Same or different;

[0023] Ar is selected from: hydrogen, substituted or unsubstituted C6-C. 24 Aryl, substituted or unsubstituted C4-C 20 Mixed aromatics;

[0024] Wherein, “substituted” means that one or more hydrogen atoms in a group are replaced by a substituent selected from the group consisting of: halogen, C1-C4 alkyl, C1-C4 haloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, C1-C6 alkoxy, amino, C1-C4 carboxyl, and C1-C4 ester.

[0025] In this invention, the catalyst is a compound having the following structural formula:

[0026]

[0027] In this invention, the molar ratio of the amine to the olefin is 1 to 20, and the molar ratio of the solvent to the amine is 20 to 50. Preferably, the molar ratio of the solvent to the amine is 20 to 35.

[0028] In this invention, the preferred molar ratio of the nitrogen heterocyclic carbene metal compound to the amine is one ten-thousandth to one hundredth.

[0029] In this invention, the CO pressure is preferably 1 to 100 bar, and more preferably 20 to 50 bar.

[0030] In this invention, the preferred reaction temperature is 120 to 150°C.

[0031] The yield of the linear amine after the reaction in this invention was obtained by column chromatography, and the selectivity of the linear amine was utilized. 1 The measurements were performed using HNMR.

[0032] This invention uses inexpensive and readily available olefins and amines as raw materials, and pure water as a hydrogen source, to achieve carbon chain growth and olefin enrichment, yielding linear amines with high efficiency and selectivity. Studies have shown a clear correlation between the electronegativity of the nitrogen-heterocyclic carbene ligand and the catalyst activity. Specifically, the nitrogen-heterocyclic carbene ligand in the nitrogen-heterocyclic carbene metal coordination polymer exhibits strong σ-electron-donating ability, and the catalytic activity significantly improves with further enhancement of the ligand's electron-donating ability. Conversion can be completed at a catalytic concentration as low as 1%, with a reaction selectivity L / B value of 92 / 8 and an amine yield of 96%.

[0033] This invention uses inexpensive and readily available olefins and amines as starting materials, avoiding the use of high-pressure hydrogen and the relatively complicated and unstable synthesis of phosphine-containing ligands. The operation is simple, and high-purity linear amines can be obtained without complicated post-processing filtration, making it suitable for large-scale industrial applications.

[0034] The advantages of the method of the present invention are:

[0035] (1) The reaction has good linear selectivity and can obtain linear amines in high yield;

[0036] (2) The reaction does not require the use of bidentate phosphine ligands or bases or acids as additives, which avoids complicated post-processing.

[0037] (3) The reaction uses pure water as the hydrogen source, which avoids the use of high-pressure hydrogen gas. Attached Figure Description

[0038] Figure 1 The image shows the 1H NMR spectrum of the product obtained from the selective hydrogen methylation of 1-octene by the nitrogen heterocyclic carbene metal compound 2c catalyzed by Example 5.

[0039] Figure 2 The image shows the carbon NMR spectrum of the product obtained from the selective hydrogen methylation of 1-octene by the nitrogen heterocyclic carbene metal compound 2c catalyzed by Example 5. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the various embodiments of this invention will be described in detail below. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this invention to facilitate a better understanding of this application. However, the technical solutions claimed in the claims of this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0041] I. Preparation of Nitrogen Heterocyclic Carbene Metal Compounds

[0042] Example 1, Preparation of nitrogen-heterocyclic carbene iridium compound 1a:

[0043] The reaction formula is:

[0044]

[0045] Under nitrogen atmosphere, 0.5 mmol of cyclooctadiene iridium chloride dimer was added to a Schlenk tube, followed by three purgings. 10 mL each of dichloromethane and tetrahydrofuran were added, and the solution was stirred until clear. Potassium tert-butoxide (1 mmol) was added, and the mixture was stirred at room temperature for 1 hour. Dimethylimidazolium iodide (1 mmol) was then added, and stirring continued at room temperature for 4 hours. The solvent was removed by rotary evaporation, and the mixture was then separated by column chromatography and dried under vacuum to obtain the corresponding cyclooctadiene-coordinated nitrogen-containing heterocyclic carbene iridium compound 1a. Yield: 0.40 g, 76%. 1 HNMR (400MHz, DMSO-d6, 298K) δ = 7.25 (s, 2H, ArCH), 4.48 (s, 2H, COD-H), 3.75 (s, 6H, CH3), 3.08 ( s,2H,COD-H),2.03-2.15(m,4H,COD-H),1.60-1.75(m,2H,COD-H),1.28-1.42(m,2H,COD-H)ppm.

[0046] Example 2, Preparation of nitrogen-heterocyclic carbene iridium compound 1b:

[0047] The reaction formula is:

[0048]

[0049] Under nitrogen atmosphere, 0.5 mmol of cyclooctadiene iridium chloride dimer was added to a Schlenk tube, followed by three purgings. 10 mL each of dichloromethane and tetrahydrofuran were added, and the solution was stirred until clear. Potassium tert-butoxide (1 mmol) was added, and the mixture was stirred at room temperature for 1 hour. N-phenyl-N-methylimidazolium iodide (1 mmol) was then added, and stirring continued at room temperature for 4 hours. The reaction mixture was evaporated to dryness and then separated by column chromatography. After vacuum drying, the corresponding cyclooctadiene-coordinated nitrogen-containing heterocyclic carbene iridium compound 1b was obtained. Yield: 0.47 g, 80%.

[0050] Example 3, Preparation of nitrogen-heterocyclic carbene iridium compound 2b:

[0051] The reaction formula is:

[0052]

[0053] Under nitrogen atmosphere, 0.3 mmol of cyclooctadiene iridium chloride dimer was added to a Schlenk tube, followed by three purgings. 10 mL of ethanol was added, and sodium hydride (1.2 mmol) was added while stirring. The mixture was stirred at room temperature for 1 hour. Then, 2 mmol of N-phenyl-N-methylimidazolium iodide was added, and the mixture was stirred overnight at room temperature. The reaction solution was evaporated to dryness and then separated by column chromatography. After vacuum drying, the corresponding cyclooctadiene-coordinated nitrogen-containing heterocyclic carbene iridium compound 2b was obtained. Yield: 0.31 g, 72%.

[0054] 1 H NMR (400MHz, DMSO-d6, 298K) δ = 7.54-7.63 (m, 6H, ArCH), 7.37 (d, 2H, J = 2.0Hz, ArCH), 7.22-7.30 (m, 6H, ArCH), 4.53 (t, 2H, J = 6.2Hz, C OD-H),3.44-3.52(m,2H,COD-H),2.97(s,3H,CH3),2.20-2.31(m,2H,COD-H),2.07-2.18(m,2H,COD-H),1.63-2.53(m,2H,COD-H)ppm.

[0055] Example 4, Preparation of nitrogen-heterocyclic carbene iridium compound 2c:

[0056] The reaction formula is:

[0057]

[0058] Under nitrogen atmosphere, 0.3 mmol of cyclooctadiene iridium chloride dimer was added to a Schlenk tube, the tube was purged three times, 10 mL of ethanol was added, and sodium hydride (1.2 mmol) was added while stirring. The mixture was stirred at room temperature for 1 hour. Then, 2 mmol of N-aryl-N-methylimidazolium tetrafluoroborate was added, and the mixture was stirred overnight at room temperature. The reaction solution was evaporated to dryness and then separated by column chromatography. After vacuum drying, the corresponding cyclooctadiene-coordinated nitrogen-containing heterocyclic carbene-iridium compound was obtained. 0.3 mmol of the cyclooctadiene-coordinated product was dissolved in 10 mL of dichloromethane, and carbon monoxide was continuously bubbled through the solution at room temperature for 4 hours. After the reaction was complete, the solvent was concentrated to 2 mL, and sufficient diethyl ether was added to precipitate the product. The product was filtered, dried under vacuum, and the corresponding dicarbonyl-coordinated nitrogen-containing heterocyclic carbene-iridium compound 2c was obtained. Yield: 0.28 g, 66%.

[0059] 1 H NMR (400MHz, DMSO-d6, 298K) δ = 7.47 (d, 2H, J = 1.7Hz, ArCH), 7.40 (d, 2H, J = 1.3Hz, ArCH), 7. 15(d,4H,J=8.7Hz,ArCH),6.95-7.01(m,4H,ArCH),3.84(s,6H,OCH3),3.26(s,6H,CH3)ppm.

[0060] II. Synthesis of linear amines by selective hydrogen amine methylation of olefins.

[0061] Example 5: Linear amines were prepared using different nitrogen-containing heterocyclic carbene iridium compounds, and their relationship with the selective hydrogen amine methylation of olefins was investigated.

[0062]

[0063] A nitrogen-containing heterocyclic carbene iridium compound (0.005 mmol), N-methylaniline (0.5 mmol), H₂O (3 mL), and 1-octene (10 mmol) were added sequentially to a reaction vessel. The system was purged with carbon monoxide three times and pressurized to 50 atm. The reaction vessel was then placed in an oil bath and heated to 150°C for 48 hours. After the reaction, the reaction vessel was cooled to 0°C in an ice bath. Trimethoxybenzene was added as an internal standard, and the reaction solution was diluted with dichloromethane. The selectivity of the linear amine was determined by... 1 The solution after the reaction was analyzed by ¹H NMR, and high-purity linear amine compounds were subsequently obtained by column chromatography. The results are shown in Table 1: Table 1: Linear amines prepared from different nitrogen-heterocyclic carbene iridium compounds 1a-b, 2b-c, and their relationship with selective hydrogen methylation of 1-octene.

[0064] Cat. 1a 1b 2b 2c Yield (%) 87 91 93 96 L / B 78 / 22 82 / 18 88 / 12 92 / 8 .

[0065] Example 6: Linear amines were prepared using different solvents, and their relationship with selective hydroamine methylation of olefins was investigated.

[0066]

[0067] A nitrogen-containing heterocyclic carbene rhodium compound 2c (0.005 mmol), N-methylaniline (0.5 mmol), H₂O (3 mL), and 1-octene (10 mmol) were added sequentially to a reaction vessel. The system was purged with carbon monoxide three times and pressurized to 50 atm. The reaction vessel was then placed in an oil bath and heated to 150°C for 48 hours. After the reaction, the reaction vessel was cooled to 0°C in an ice bath. Trimethoxybenzene was added as an internal standard, and the reaction solution was diluted with dichloromethane. The selectivity of the linear amine was determined by... 1 The solution after the reaction was analyzed by ¹H NMR, and then high-purity linear amine compounds were obtained by column chromatography. The results are shown in Table 2.

[0068] Table 2 shows the results of linear amines prepared with different solvents and their relationship with the selective hydrogen methylation of 1-octene.

[0069] Solvent (3 mL) Tetrahydrofuran Toluene aniline water Yield (%) 12 33 26 96 L / B 92 / 8 88 / 12 85 / 15 92 / 8 .

[0070] Example 7: Linear amines were prepared using CO at different pressures, and the relationship with selective hydroamine methylation of olefins was investigated.

[0071]

[0072] A nitrogen-containing heterocyclic carbene iridium compound 2c (0.005 mmol), N-methylaniline (0.5 mmol), H₂O (3 mL), and 1-octene (10 mmol) were added sequentially to a reaction vessel. The system was purged with carbon monoxide three times and pressurized. The reaction vessel was then placed in an oil bath and heated to 150 °C for 48 hours. After the reaction, the reaction vessel was cooled to 0 °C in an ice bath. Trimethoxybenzene was added as an internal standard, and the reaction solution was diluted with dichloromethane. The selectivity of the linear amine was determined by... 1 The solution after the reaction was analyzed by ¹H NMR, and then high-purity linear amine compounds were obtained by column chromatography. The results are shown in Table 3.

[0073] Table 3 shows the preparation of linear amines under different CO pressures and their relationship with the selective hydrogen methylation of allylbenzene.

[0074] Pressure (CO, bar) 20 30 40 50 Yield (%) 32 51 63 96 L / B 92 / 8 92 / 8 92 / 8 92 / 8 .

[0075] Example 8: Linear amines were prepared using different temperatures, and their relationship with selective hydroamine methylation of olefins was investigated.

[0076]

[0077] A nitrogen-containing heterocyclic carbene iridium compound 2c (0.005 mmol), N-methylaniline (0.5 mmol), H₂O (3 mL), and 1-octene (10 mmol) were added sequentially to a reaction vessel. The system was purged with carbon monoxide three times and pressurized to 50 atm. The reaction vessel was then placed in an oil bath and heated for 48 hours. After the reaction, the reaction vessel was cooled to 0°C in an ice bath. Trimethoxybenzene was added as an internal standard, and the reaction solution was diluted with dichloromethane. The selectivity of the linear amine was determined by... 1 The solution after the reaction was analyzed by ¹H NMR, and then high-purity linear amine compounds were obtained by column chromatography. The results are shown in Table 4.

[0078] Table 4 shows the results of linear amines prepared at different temperatures and their relationship with the selective hydrogen methylation of 1-octene.

[0079] Temperature (°C) 120 130 140 150 Yield (%) 63 76 84 96 L / B 92 / 8 92 / 8 92 / 8 92 / 8 .

[0080] In Examples 5-8, using nitrogen-heterocyclic carbene iridium compounds 1a, 1b, and 2b yielded results similar to those obtained using nitrogen-heterocyclic carbene iridium compound 2c. These results will not be repeated here.

Claims

1. A method for preparing linear amines by selective hydrogenamine methylation of olefins, characterized in that, Using water as a hydrogen source and a nitrogen-containing heterocyclic carbene metal compound as a catalyst, the selective hydrogen amine methylation of olefins was catalyzed to achieve the preparation of linear amines; the specific steps are as follows: Using olefins, carbon monoxide, water, and amines as raw materials, pure water, tetrahydrofuran, toluene, or anisole as solvents, and nitrogen heterocyclic carbene metal compounds as catalysts, the molar ratio of catalyst to amine is 1 / 10,000 to 1 / 1000, and the reaction is carried out at 80 to 200 °C for 4 to 48 hours. The chemical reaction process is as follows: ； wherein R1in the olefin is selected from substituted or unsubstituted C6-C 10 aryl, C5-C8straight chain alkyl, C5-C6cycloalkyl; Ar in the amine compound is selected from substituted or unsubstituted C6-C 10 aryl, substituted or unsubstituted C4-C 16 heteroaryl; R2is selected from C1-C4straight chain alkyl, C5-C6cycloalkyl; The term "substituted" refers to the substitution of one or more hydrogen atoms in a group by a substituent selected from the group consisting of: halogen, C3-C6 alkyl, C4 ester, C5 carbonyl, C4 hydroxyl, and C1-C2 alkoxy. The catalyst is one of the compounds having the following structural formula: 。 2. The method for preparing linear amines according to claim 1, characterized in that, The molar ratio of the amine to the olefin is 1 to 20, and the molar ratio of the solvent to the amine is 20 to 50.

3. The method for preparing linear amines according to claim 1, characterized in that, In the reaction of this invention, the pressure of carbon monoxide is 1 to 100 bar.

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