Preparation method of bibenzyl compound

Abstract

The invention discloses a method for preparing bibenzyl compounds from benzyl alcohol compounds. According to the method, a bulk-phase or supported iron-based catalyst is used for catalyzing a dehydroxylation reduction coupling reaction of benzyl alcohol in a reducing atmosphere, and a bibenzyl carbon-carbon coupling product is obtained in one step. The catalyst involved in the method takes iron as a main body and one or more than two of VIII group or IB group metals as auxiliaries, and the content of the metals is 0.05%-1%. The invention provides the green and efficient method for preparing the bibenzyl compound, the substrate benzyl alcohol is cheap and easy to obtain, the reducing agent can be hydrogen, no solid waste is generated, the production cost is low, and the functional group tolerance is good. The method is suitable for large-scale preparation of the functional organic matter containing the 1, 2-diphenylethane mother nucleus.

Description

Technical Field

[0001] The invention relates to a method for preparing a bibenzyl compound by carbon-carbon coupling in one step using a benzyl alcohol compound obtained from biomass or other routes under the action of an iron-based catalyst. Background Art

[0002] The molecular skeleton of bibenzyl compounds contains 1,2-diphenylethane structure, and its molecular flexibility is higher than that of 1,2-diphenylethylene (stilbene compounds). As an important organic synthesis intermediate, bibenzyl compounds have potential application value in the fields of biomedicine, dyes, solvents, polymers, etc. At present, bibenzyl compounds still lack green and efficient synthesis technology, and their mainstream synthesis routes can be divided into three categories according to substrates: one is the Friedel-Crafts alkylation reaction of benzene and 1,2-dihaloethane, and the catalyst generally selects anhydrous AlCl3; the second is the reductive coupling of halogenated benzyl in the presence of active metals, and halogenated benzyl generally selects benzyl chloride or benzyl bromide, and the active metal is Na, Mg, Zn, Al, etc.; the third is to start from benzaldehyde, first obtain benzoin through benzoin condensation, and then hydrodeoxygenate to synthesize bibenzyl, and Ni catalyst can generally be selected. The above methods 1 and 2 will generate equivalent waste halides while producing bibenzyl, and the reagents involved are relatively active, which poses safety risks in large-scale production. Path 3 is a two-step method with low efficiency and high production cost.

[0003] The patents and literatures reported so far have introduced greener and more efficient bibenzyl synthesis routes, each with its own unique selection of substrates and reducing agents.

[0004] The literature (ACS Cataysis, 2021, 11, 7, 4338–4348) prepared a copper-modified titanium dioxide catalyst and used it in the UV-photocatalytic reduction coupling reaction of benzyl bromide to synthesize bibenzyl, achieving an apparent quantum yield of up to 15%. Isopropanol was used as a solvent and hydrogen donor in the article.

[0005] The literature (Chemistry-a European Journal, 2021, 27, 1292–1296) synthesized an 8-hydroxyquinoline molybdenum catalyst for the reductive coupling reaction of benzyl alcohol compounds. The yield of the target product bibenzyl can reach up to 60%. The authors believe that the electron-donating property of the 8-hydroxyquinoline ligand plays an important role in the reaction, and the reaction is carried out by homolytic cleavage of the CO bond of the alcohol to generate benzyl radicals. They used the relatively expensive triphenylphosphine as a reducing agent.

[0006] The literature (Synthesis, 2021, 53(17): 3094-3100) reported an in situ activation strategy to synthesize bibenzyl. The dimethyl oxalate added to the reaction system can partially react with benzyl alcohol, and the generated benzyl oxalate undergoes reductive coupling under the action of a homogeneous nickel catalyst to generate bibenzyl. The reducing agent used in the reaction is metallic manganese.

[0007] In summary, the currently reported bibenzyl synthesis routes still have disadvantages such as the generation of equivalent waste, limited reducing agents and harsh reaction conditions, and are not suitable for large-scale industrial production. Summary of the invention

[0008] The present invention provides a method for preparing a bibenzyl compound by carbon-carbon coupling in one step from a benzyl alcohol compound under the action of an iron-based catalyst. The catalyst can use hydrogen as a reducing agent, the reaction byproduct is water, the catalyst cost is low, and it is easy to separate and recover after the reaction.

[0009] The reaction uses an iron-based catalyst, one or more of the metals of group VIII or group IB as an auxiliary agent, the metal content is 0.05%-1%, the catalyst precursor is prepared by a coprecipitation method, and is directly mixed with the reaction materials after heat treatment and reduction carbonization, and a reducing atmosphere is introduced to catalyze the one-step reduction coupling of benzyl alcohol to prepare bibenzyl compounds.

[0010] The main active component of the catalyst is iron, and the auxiliary agent is one or a mixture of two or more of cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, iridium, platinum and gold in any ratio, and the mass content of the auxiliary agent is 0.05%-1%.

[0011] The preparation method of the catalyst is as follows:

[0012] 1) Dissolve a certain amount of iron salt in ultrapure water in advance, and control the concentration of iron ions at 0.5-5 mol / L. In this step, a carrier may be added to form a suspension or not.

[0013] The iron salt can be one of ferric chloride, ferric nitrate, ferric acetylacetonate and ferric acetate, and the type of anion of the iron salt is not limited to the above types.

[0014] The carrier is one or a mixture of two or more of aluminum oxide, silicon oxide, rare earth oxide (such as cerium oxide), titanium oxide and magnesium oxide in any ratio.

[0015] 2) Dissolve the precipitant in ultrapure water, heat to 50-100° C., control the precipitant / iron molar ratio between 1-5, and the precipitant concentration between 0.5-5 mol / L.

[0016] The precipitant can be one of ammonium carbonate, sodium hydroxide and potassium hydroxide.

[0017] 3) Mix the iron precursor solution and the precipitant, stir at 50-100° C. for 3-6 hours, and age for 3-6 hours. Separate the catalyst from the solution and wash it thoroughly with ultrapure water.

[0018] 4) Re-dispersing the catalyst in water, adding a metal solution at a metal / iron molar ratio of 0.05%-1%, stirring for 1-12 hours, and filtering or directly evaporating to dryness to obtain a catalyst precursor.

[0019] 5) Calcination of catalyst precursor: Place the catalyst in an atmosphere of He, Ar, N2, etc. at 300°C-600°C for 10-600 seconds or in a muffle furnace at 300°C-600°C for 1-6 hours.

[0020] The catalyst needs to be activated before use: place the catalyst in a hydrogen atmosphere, program the temperature to 250-400°C, reduce for 2-15 hours, switch the atmosphere to hydrogen + carburizing gas, and treat at 200-400°C for 1-40 hours.

[0021] The ratio of hydrogen and carbonized gas in the mixed atmosphere is hydrogen:carbonized gas=0.1-5.

[0022] The carbonized gas may be one or more of carbon monoxide, ethylene, carbon dioxide, methane, propane, and butadiene.

[0023] The catalytic reaction is carried out in a closed reactor or a fixed bed, the pressure of the reducing atmosphere at room temperature in the reactor is 0.2-1Mpa, and the reaction temperature is 160-250°C.

[0024] The reducing atmosphere may be pure hydrogen or a mixture of hydrogen and carbon monoxide, and the ratio thereof may be adjusted.

[0025] The reaction can be carried out in a solvent or without a solvent. The solvent used is one or more of alkyl aromatic hydrocarbons, alkanes, and heterocyclic hydrocarbons. The reaction substrate concentration is > 0.1 mol / L.

[0026] The reaction equation is:

[0027] R1 represents a substituent on the benzene ring, which can be -OH, -OMe, halogen, aromatic ring, etc. The number of substituents is 0-3, and the position of the substituents is arbitrary; or the benzene ring in the reaction equation can also be replaced by a pyridine ring, a furan ring or a thiophene ring;

[0028] R2 represents an α-substituent, which may be -H, an aromatic ring or an alkyl group.

[0029] The catalyst can be magnetically separated after the reaction, and the recovered catalyst can be reactivated for recycling. The present invention uses a bulk or supported iron-based catalyst to catalyze the dehydroxylation reduction coupling reaction of benzyl alcohol in a reducing atmosphere to obtain a bibenzyl carbon-carbon coupling product in one step. The catalyst involved in the method is mainly iron, and one or more of the metals of Group VIII or Group IB are used as auxiliary agents. The benzyl alcohol of the present invention is cheap and easy to obtain, the reducing agent can be hydrogen, no solid waste is generated, the production cost is low, and the functional group tolerance is good. The method is suitable for large-scale preparation of functional organic matter containing 1,2-diphenylethane parent core. DETAILED DESCRIPTION

[0030] Example 1: Preparation of iron precursor

[0031] Dissolve 4 g of ammonium carbonate in 60 ml of water, transfer to a 80°C water bath and stir to dissolve. Take another 20 mmol of ferric nitrate nonahydrate and dissolve in 20 g of water. After dissolution, pour it directly into the ammonium carbonate solution, continue stirring at 70°C for 3.5 h, and age at 70°C for 3.5 h. Centrifuge the mixture, discard the supernatant, and wash three times with ultrapure water.

[0032] Example 2: Preparation of supported metal catalyst

[0033] The iron precursor obtained in Example 1 was redispersed with 60 ml of water (iron precursor dispersion), and 10 g / L iridium trichloride hydrate solution was dropped into it. The resulting mixture was stirred for 12 hours. The catalyst suspension was stirred to dryness in a 100°C metal sand bath, and the resulting precipitate was Irx / FeOOH. Irx / FeOOH was calcined at 500°C in an Ar atmosphere for 1 min, and the resulting catalyst was Irx / Fe2O3 (x represents the molar fraction of the loaded metal Ir (relative to Fe), x=0.1%).

[0034] Same as above, other conditions remain unchanged, the input amount of iridium trichloride solution is changed, and the prepared catalyst is Irx / Fe2O3 (x represents the molar fraction of the loaded metal, which is x=0, 0.05%, 0.1%, 0.2%, 0.4%, 0.8%, 1%).

[0035] Same as above, other conditions remain unchanged, change the type of metal additives, add chloride salts of cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, iridium, platinum, and gold respectively, and you can get Mex / Fe2O3 (Me represents the type of different metal additives, x represents the molar fraction of the loaded metal, x = 0.1%)

[0036] Example 3: Catalyst preactivation

[0037] The catalysts obtained in Example 2 were placed in a hydrogen atmosphere, heated from room temperature to 400°C at 2°C / min, maintained for 10 h, cooled to room temperature, the atmosphere was switched to synthesis gas (hydrogen: carbon monoxide = 2:1, volume ratio), heated from room temperature to 260°C, maintained for 8.5 h, cooled to room temperature, and argon was introduced for protection. Comparative Example 1: Preparation of reduced iron catalyst

[0038] The iron precursor in Example 1 was placed in a hydrogen atmosphere, the temperature was raised from room temperature to 400° C. at 2° C. / min, maintained for 10 h, and then cooled to room temperature. The obtained catalyst was recorded as α-Fe.

[0039] Comparative Example 2: Preparation of Catalyst with Molybdenum as Promoter

[0040] 10 g / L ammonium molybdate solution (instead of 10 g / L iridium trichloride hydrate solution) was added to the iron precursor dispersion in Example 2 so that the molar fraction of molybdenum relative to iron was 0.1%, and other conditions remained unchanged (other processes and conditions were the same as in Example 2). The resulting catalyst was recorded as Mo / Fe2O3.

[0041] Comparative Example 3: Preparation of a catalyst with cerium as an additive

[0042] 10 g / L cerium nitrate solution (instead of 10 g / L iridium trichloride hydrate solution) was added to the iron precursor dispersion in Example 2 so that the molar fraction of cerium relative to iron was 0.1%. Other conditions remained unchanged (other processes and conditions were the same as in Example 2). The obtained catalyst was recorded as Ce / Fe2O3.

[0043] Comparative Example 4: Preparation of supported copper catalyst

[0044] Weigh 0.6 g of copper nitrate trihydrate and dissolve it in 5 g of deionized water, add 50 mL of 20 wt% ammonia water, add 1 g of fumed silica, adjust the pH to 11 with 10 wt% nitric acid, stir in a water bath at 80°C for 6 h to volatilize the ammonia, filter the catalyst, then dry it in an oven at 80°C, and calcine it in air at 400°C for 2 h. The calcined catalyst is reduced in a H2 atmosphere at 400°C for 1 h. The obtained catalyst is recorded as Cu / SiO2.

[0045] Example 4: Catalyst Performance Evaluation

[0046] A kettle reactor can be selected for the reaction: 10 mmol of benzyl alcohol compound is added to a 50 ml reactor, 10 ml of tetrahydrofuran, 2 mmol of dodecane as an internal standard, 120 mg of catalyst (the catalyst obtained in Example 3) is added, 1 MPa of hydrogen is charged, and the reaction is carried out at 220° C. for 8 hours. After the reactor is cooled to room temperature, the reaction liquid is separated by centrifugation. According to gas chromatography, the conversion rate of benzyl alcohol is 100%, and the yield of the target product bibenzyl is 20-71%.

[0047] Example 5: Effect of different Ir loadings on catalyst performance:

[0048] Table 1 Effect of different Ir loadings on catalyst performance (catalysts obtained in Example 3)

[0049]

[0050]

[0051] Note: The reaction process and conditions are the same as those in Example 4, except that the reaction temperature is 220°C, the hydrogen pressure is 1 MPa, the substrate is benzyl alcohol 2.5 mmol, the solvent is n-hexane 10 mL, the reaction time is 12 h, and the by-products include a small amount of alkylbenzene oligomers.

[0052] It can be seen from Table 1 that when the Ir loading is 0.1% (Ir:Fe=0.1:100, molar ratio), the yield of the target product bibenzyl reaches the maximum.

[0053] Example 6: Effect of different metal promoters on catalyst performance (reaction process and conditions see Example 4):

[0054] Table 2 Effects of different metal promoters on the performance of catalysts (respectively the catalysts obtained in Example 3):

[0055]

[0056] Note: The reaction process and conditions are the same as those in Example 4, except that the reaction temperature is 220°C, the hydrogen pressure is 1 MPa, the substrate is benzyl alcohol 2.5 mmol, the solvent is n-hexane 10 mL, the reaction time is 12 h, and the by-products include a small amount of alkylbenzene oligomers.

[0057] As can be seen from Table 2, compared with using metallic iridium as a reaction aid, using other metals does not significantly improve the reaction performance. Considering the price and reaction efficiency, metallic ruthenium, iridium, and rhodium can be selected as aids.

[0058] Example 7: Reaction performance of Ir0.1% / Fe2O3 on different substrates

[0059] Table 3 Reaction performance of the catalyst Ir0.1% / Fe2O3 obtained in Example 3 to different substrates

[0060]

[0061] Note: The reaction process and conditions are the same as those in Example 4, except that the reaction temperature is 220°C, the hydrogen pressure is 1 MPa, the substrate alcohol is 2.5 mmol, the solvent tetrahydrofuran is 10 mL, and the reaction time is 12 h.

[0062] Comparative Examples 5-8: Performance evaluation of the catalysts prepared in Comparative Examples 1-4

[0063] Table 4 Performance evaluation of comparative catalysts

[0064]

[0065]

[0066] Note: The reaction process and conditions are the same as those in Example 4, except that the reaction temperature is 220°C, the hydrogen pressure is 1 MPa, the substrate is benzyl alcohol 2.5 mmol, the solvent is n-hexane 10 mL, the reaction time is 12 h, and the by-products include a small amount of alkylbenzene oligomers.

[0067] As can be seen from Table 4, the efficiency of pure reduced iron catalyst is not high, and the doping of oxophilic metal additives such as molybdenum and cerium is not very helpful in improving the selectivity of the target product 1,2-diphenylethane. On non-iron-based catalysts, such as typical copper-based catalysts, hydrodeoxygenation of benzyl alcohol mainly occurs, and no coupling products are detected, which shows that iron plays a dominant role in the coupling reaction.

Claims

1. A method for preparing a bibenzyl compound, characterized in that: The bibenzyl compound is prepared by reductive deoxygenation coupling of benzyl alcohol, the reaction uses an iron-based catalyst, one or more metals of Group VIII or Group IB are used as promoters, and the molar content of the metal relative to iron is 0.05%-1%, preferably 0.05-0.2%, and more preferably 0.1-0.15%; The iron-containing catalyst precursor is prepared by a co-precipitation method. The iron-containing catalyst precursor is loaded with a metal and then subjected to heat treatment, and then reduced and carbonized to obtain a target catalyst.

2. The preparation method according to claim 1, characterized in that: The main active component of the catalyst is iron, and the auxiliary agent is one or a mixture of two or more of cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, iridium, platinum and gold in any ratio; It may contain a carrier or no carrier, and the mass content of iron relative to the carrier is 5-25wt%, preferably 10-15wt%; The carrier is one or a mixture of two or more of aluminum oxide, silicon oxide, rare earth oxide (such as cerium oxide), titanium oxide and magnesium oxide in any ratio.

3. The preparation method according to claim 1 or 2, characterized in that: The preparation method of the catalyst is as follows: 1) dissolving iron salt in water, and controlling the concentration of iron ions to 0.5-5 mol / L (preferably 1-2 mol / L). In this step, a carrier may be added to prepare a suspension or no carrier may be added; 2) dissolving the precipitant in water, heating to 50-100° C. (preferably 60-80° C.), controlling the precipitant / iron molar ratio between 1-5 (preferably 2-3), and the alkaline precipitant concentration between 0.5-5 mol / L (preferably 1-1.5 mol / L); 3) mixing the iron precursor solution with the precipitant, stirring at 50-100° C. (preferably 60-80° C.) for 3-6 hours, turning off the stirring and aging at the same temperature for 3-6 hours; separating the iron-containing catalyst precursor precipitate from the solution and washing with water; 4) Re-dispersing the iron catalyst precursor in water, adding a metal solution at a metal / iron molar ratio of 0.05%-1%, stirring for 1-15h (preferably 8-12h), filtering or directly evaporating to dryness to obtain a catalyst precursor; 5) Calcination of catalyst precursor: the catalyst precursor is placed in one or more atmospheres of He, Ar, N2, etc. at 300°C-600°C (preferably 350-400°C) for 10-600 seconds (preferably 500-600 seconds) or in a muffle furnace air atmosphere at 300°C-600°C (preferably 350-400°C) for 1-6 hours (preferably 4-5 hours); 6) The catalyst needs to be activated before use: place the catalyst in a hydrogen atmosphere, program the temperature to 250-400°C (preferably 300-400°C), reduce for 2-15h, switch the atmosphere to hydrogen + carbonization gas, and treat at 200-400°C (preferably 220-300°C) for 1-40h (preferably 8-12h); The volume ratio of hydrogen and carburized gas in the mixed atmosphere is hydrogen:carburized gas = 0.1-5 (preferably 1.5-2.5); The carbonized gas may be one or more of carbon monoxide, ethylene, carbon dioxide, methane, propane, and butadiene.

4. The preparation method according to claim 3, characterized in that: The iron salt may be one or more of ferric chloride, ferric nitrate, ferric acetylacetonate, and ferric acetate, and the type of anion of the iron salt is not limited to the above-mentioned types; The alkaline precipitant may be one or more of ammonium carbonate, sodium hydroxide and potassium hydroxide.

5. The preparation method according to claim 1, characterized in that: The catalytic reaction is carried out in a closed reactor or a fixed bed, the pressure of the reducing atmosphere at room temperature in the reactor is 0.2-1Mpa (preferably 0.5-1Mpa), and the reaction temperature is 160-250°C (preferably 180-220°C); the catalyst is directly mixed with the reaction materials and introduced into the reducing atmosphere, so as to catalyze the one-step reduction coupling of benzyl alcohol to prepare bibenzyl compounds; The reducing atmosphere can be pure hydrogen or a mixture of hydrogen and carbon monoxide, the ratio of which can be adjusted, wherein the volume content of carbon monoxide is 0-50% (preferably 0-10%).

6. The preparation method according to claim 1 or 5, characterized in that: The reaction can be carried out in a solvent or in the absence of a solvent. The solvent used is one or more of C7-C18 alkylbenzene, C5-C18 alkane, tetrahydrofuran, acetonitrile, dimethyl sulfoxide, tert-butyl methyl ether, pyridine, and chloroform. The reaction substrate concentration is >0.1 mol / L, preferably 0.5-1 mol / L.

7. The preparation method according to claim 1 or 5, characterized in that: The reaction equation is: R1 represents a substituent on the benzene ring, which can be one or more of -H, -OH, -OMe, halogen, C1-C8 alkyl aromatic ring, phenyl, pyridine, furan, thiophene, etc. The number of substituents is an integer of 0-3, and the position of the substituents is arbitrary; the benzene ring in the reaction equation can also be replaced by a pyridine ring, a furan ring or a thiophene ring; R2 represents an α-substituent, which may be one or more of -H, C6-C18 aromatic ring, phenyl, pyridine, furan, thiophene or C1-C8 alkyl.

8. The preparation method according to claim 1 or 5, characterized in that: The catalyst can be magnetically separated after the reaction, and the recovered catalyst can be reactivated for recycling.

9. The preparation method according to claim 1 or 5, characterized in that: The reaction time of the catalytic system in the closed reactor is 4-15h (preferably 10-12h); The space velocity in the fixed bed reactor is 100-1000 h-1 (preferably 800-1000 h-1).

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