Rice hull-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to the field of catalytic organic synthesis, and particularly discloses a rice hull-based catalyst as well as a preparation method and application thereof. The rice hull-based catalyst is used for catalyzing the cross-coupling reaction of terminal alkyne; the rice hull-based catalyst is characterized in that a Cu < 2 + > imprinting pre-coordination compound and mesoporous SiO2 are connected through-O-Si-bonds to form a net structure; the Cu < 2 + > imprinting pre-coordination compound is a multi-core Cu < 2 + > complex. The rice hull-based catalyst can accelerate the cross-coupling reaction of terminal alkyne and accelerate the reaction speed of generating a 1, 3-diyne compound, the conversion rate is high, and the use amount of a substrate is effectively reduced. The rice hull-based catalyst has high selectivity when catalyzing cross-coupling reaction of terminal alkyne of different substituent groups, and other oxidizing agents and other reaction aids do not need to be added. The rice hull-based catalyst adopted by the invention has excellent selectivity on cross coupling of different substrates, and compared with the prior art, the rice hull-based catalyst has a wider application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of catalytic organic synthesis, and in particular to a rice husk-based catalyst and a preparation method and application thereof. Background Art

[0002] The cross-coupling reaction of terminal alkynes is one of the important reactions in the field of organic synthesis and has a wide range of applications in the fields of drug synthesis and materials. The reaction was first reported by German chemist Carl A. Glaser in 1869, so it is also called the Glaser coupling reaction, and many improvements have been derived after years of research.

[0003] Most of the Glaser reactions use transition metals to catalyze the self-coupling reaction of terminal alkynes. The transition metals used are Cu, Au, Pd, etc. Compared with noble metal catalysts such as Au and Pd, copper catalysts are cheaper and will not pollute the environment due to the use of phosphine ligands or amine ligands. In addition, Jia et al. use a method of CuI / I catalysis, which catalyzes the homogeneous coupling reaction of terminal alkynes with good yield. However, the cuprous catalyzed Glaser reaction in CuI / I is extremely sensitive to substrates containing phosgene or oxygen, which may cause the generation of side reactions, affecting yield and selectivity. In addition, when using cuprous catalysts, it is usually necessary to use excessive oxidants and other auxiliary agents to improve the efficiency and selectivity of the reaction.

[0004] Although some heterogeneous catalysts currently developed for Glaser reactions achieve high selectivity for asymmetric products, due to their low conversion rates, in order to obtain the desired products, an excess of substrate, i.e., the amount of terminal alkyne compounds, needs to be added during the reaction. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a rice husk-based catalyst and a preparation method and application thereof. The catalytic action of the rice husk-based catalyst effectively promotes the cross-coupling reaction of terminal alkynes, and the overall reaction conversion rate is high, reducing the amount of substrate used.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A first aspect of the present invention provides a rice husk-based catalyst, wherein the rice husk-based catalyst is used to catalyze the cross-coupling reaction of terminal alkynes;

[0008] The rice husk-based catalyst is Cu 2+ The imprinted pre-coordinated compound is connected with the mesoporous SiO2 through -O-Si- bonds to form a network structure; the Cu 2+ In the imprinted pre-coordinated compound, each nitrogen atom binds two Cu 2+ ;

[0009] The rice husk-based catalyst is prepared according to the following method:

[0010] When Schiff base is mixed with copper ions, the nitrogen atom on the Schiff base coordinates with the copper ions to form Cu 2+ Imprinted pre-coordinated compound, Cu 2+ The imprinted pre-coordinated compound is mixed with mesoporous SiO2, Cu 2+ The ethoxy group on the imprinted pre-coordination compound undergoes alcoholysis reaction with the hydroxyl group on the surface of the mesoporous SiO2 to form an -O-Si- bond, thereby obtaining the rice husk-based catalyst; the mesoporous SiO2 is obtained by a hydrothermal synthesis method using rice husk ash as a silicon source.

[0011] The rice husk-based catalyst in the present invention can provide more catalytic active sites, thereby improving the catalytic effect, accelerating the cross-coupling reaction of terminal alkynes, effectively improving the conversion rate, and reducing the amount of terminal alkyne compounds. 2+ In the imprinted pre-coordination, each nitrogen atom binds two Cu 2+ , forming multi-core Cu 2+ The complex has a larger number of coordination sites, Cu 2+ Provide more adsorption active sites, and then Cu 2+ The imprinted pre-coordinated compound is loaded on the mesoporous SiO2, and the network structure formed increases the number of catalytic active sites. These active sites can more effectively adsorb and convert substrates, thereby improving the catalytic efficiency and reducing the amount of substrate used.

[0012] The nitrogen atom in the Schiff base of the present invention coordinates with the copper ion, and the electron supply capacity of nitrogen is affected by the electron effect of the nitrogen side group, which directly affects the stability of the copper ion coordination. Therefore, the nitrogen atom in the amine group on the Schiff base of the present invention has a strong electron supply property and can form a stable Cu 2+ By imprinting pre-coordinated compounds, multi-core Cu can be synthesized by introducing multi-chelated coordinated nitrogen atoms and adjusting the distance between coordinated atoms. 2+ The complexes can improve the catalytic effect of rice husk-based catalysts. 2+ The imprinted pre-coordinated compound was modified on the mesoporous SiO2, and the surface of the obtained rice husk-based catalyst became rough and formed a network structure, providing more Cu 2+ The adsorbed active sites can improve the catalytic effect of the catalyst, accelerate the cross-coupling reaction of terminal alkynes, effectively improve the conversion rate, and reduce the amount of terminal alkyne compounds.

[0013] In another preferred embodiment, the Schiff base is a salicylaldehyde Schiff base; 2+Derived from copper salt, the copper salt is any one of CuCl2, CuSO4, Cu(NO3)2; preferably, the copper salt is CuCl2, and the rice husk-based catalyst prepared therefrom has the best catalytic effect and the highest activity. The present invention selects salicylaldehyde Schiff bases because different types of Schiff bases may have different spatial structures and geometric shapes. For example, the molecular structure of some Schiff bases may have a large stereo effect, which limits the way or coordination number of its coordination with metal ions. A more planar or rigid Schiff base may have a higher coordination ability and a more stable complex. Therefore, the present invention selects salicylaldehyde Schiff bases to provide more adsorption active sites for copper ions, thereby improving the catalytic activity, and the Cu formed by it 2+ The imprinted pre-coordinated compounds have good stability.

[0014] In another preferred embodiment, the molar ratio of the Schiff base to the copper ion is 1 to 2:1; 2+ The molar mass ratio of the imprinted pre-coordinated compound to the mesoporous SiO2 is 10mmol:1.2g~1.3g.

[0015] The second aspect of the present invention provides a method for preparing the rice husk-based catalyst, comprising the following steps:

[0016] The salicylaldehyde Schiff base is mixed with a copper salt, wherein the molar ratio of the salicylaldehyde Schiff base to the copper ion in the copper salt is 1 to 2:1, and a coordination chelation reaction occurs in an ethanol environment at 35°C to 80°C to obtain the Cu 2+ Imprinting pre-coordinated compound; in the ethanol solution, the initial concentration of copper salt is 0.5 mol / L to 1 mol / L;

[0017] Hexadecyltrimethylammonium bromide, ammonia water and water are mixed to obtain a treatment liquid; a silicon source is mixed with the treatment liquid, the pH is adjusted to 10-11, and a hydrothermal reaction is carried out at 100° C. to 120° C. for 48 h to 72 h to obtain the mesoporous SiO2; the mass volume ratio of the silicon source, hexadecyltrimethylammonium bromide, water and ammonia water is 1 g: 0.4 g to 0.6 g: 15 to 25 mL: 12 to 15 mL;

[0018] Cu 2+ The imprinted pre-coordinated compound and mesoporous SiO2 are mixed in a mass volume ratio of 10 mmol:1.2-1.3 g, and reacted at 70-100° C. for 46-48 hours to obtain a rice husk-based catalyst.

[0019] In another preferred embodiment, the specific preparation process of the silicon source is as follows:

[0020] The rice husk powder is soaked in a hydrochloric acid solution, filtered, washed to neutrality, and heated at 700°C to 750°C for 30min to 45min to obtain rice husk ash;

[0021] The rice husk ash and the alkaline solution are mixed in a mass ratio of 1:4-6, extracted at 80°C-90°C for 4h-5h, filtered, and precipitated to obtain a silicon source.

[0022] In another preferred embodiment, the alkaline solution is a sodium hydroxide solution with a concentration of 2 mol / L to 3 mol / L;

[0023] The mass percentage of the ammonia water is 25% to 28%; the mass percentage of the hydrochloric acid solution is 2% to 3%.

[0024] The third aspect of the present invention provides an application of the rice husk-based catalyst in catalyzing the cross-coupling of terminal alkynes to synthesize 1,3-diyne compounds.

[0025] A fourth aspect of the present invention provides a method for preparing a 1,3-diyne compound, comprising the following steps:

[0026] Mixing a terminal alkyne compound, a solvent and a base, adding the rice husk-based catalyst, carrying out a catalytic oxidation reaction at 45° C. to 55° C. for 15 h to 20 h, centrifuging, collecting the filtrate, and purifying to obtain the 1,3-diyne compound;

[0027] The molar volume ratio of the rice husk-based catalyst IIP-Cu, the terminal alkyne compound, and the solvent is 0.2 mmol to 0.5 mmol: 1 mmol: 2 mL to 3 mL;

[0028] The molar amount of the base accounts for 10% to 35% of the terminal alkyne compound.

[0029] In another preferred embodiment, the solvent is obtained by mixing reagent A and water in a volume ratio of 1:1 to 7;

[0030] The reagent A is any one of methyl sulfoxide, N,N-dimethylformamide, methanol, tetrahydrofuran, ethanol, 1,4-dioxane, polyethylene glycol, and acetonitrile;

[0031] The base is any one of 1,8-diazabicycloundec-7-ene, potassium carbonate, triethylamine, triethylenediamine, and sodium hydroxide.

[0032] In another preferred embodiment, the specific process of the purification is as follows:

[0033] The filtrate is extracted with dichloromethane, dried with anhydrous Na2SO4, filtered, concentrated, and purified by column chromatography to obtain the 1,3-diyne compound;

[0034] The eluent used in the column chromatography is a mixed solution of ethyl acetate and petroleum ether in a volume ratio of 50 to 52:1.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The rice husk-based catalyst in the present invention is Cu 2+ Each nitrogen atom in the imprinted pre-coordinated compound binds two Cu 2+ , thus providing more Cu 2+ Active sites for adsorption of more Cu 2+ ; Then through the -O-Si- bond, Cu 2+ The imprinted pre-coordinated compound is loaded on the mesoporous SiO2, and the network structure formed can effectively increase the number of catalytic active sites, thereby more effectively adsorbing and converting reactants, improving catalytic efficiency, and effectively reducing the amount of substrate used.

[0037] (2) The present invention coordinates the copper ions with the nitrogen atoms in the amine groups on the Schiff base, introduces multiple chelated coordinated nitrogen atoms and adjusts the distance between the coordinated atoms to synthesize polynuclear Cu 2+ The complex can improve the catalytic effect of the rice husk-based catalyst; the divalent copper ions are then loaded on the surface of the mesoporous SiO2 to obtain a rice husk-based catalyst, which can accelerate the cross-coupling reaction of terminal alkynes and speed up the reaction rate of generating 1,3-diyne compounds. Moreover, the entire reaction process is mild and does not require the addition of other oxidants or other reaction aids. Only oxygen in the air is needed as an oxidant to achieve excellent selectivity and good catalytic effect, and the conversion rate is high, which effectively reduces the amount of substrate used.

[0038] (3) The present invention provides the use of a rice husk-based catalyst in catalyzing the cross-coupling of terminal alkynes with different substituents to synthesize 1,3-diyne compounds. The rice husk-based catalyst, terminal alkyne compounds with different substituents, a base and a solvent are reacted under an air atmosphere to obtain 1,3-diyne compounds in high yield. The application of the catalyst in the reaction of catalyzing the cross-coupling of terminal alkynes with different substituents to generate 1,3-diyne compounds has achieved excellent selectivity and yield. The present invention uses rice husk materials as carriers to prepare the catalyst, which has low preparation costs, mild reaction conditions, and high catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a characterization result diagram of the morphology of rice husk-based catalysts. In the figure, RH represents rice husk powder, RH@MCM-41 represents mesoporous SiO2, and IIP-Cu represents rice husk-based catalysts.

[0040] Figure 2The figure shows the elemental composition and chemical state of the rice husk-based catalyst analyzed using X-ray photoelectron spectroscopy technology; wherein a is the elemental composition analysis result diagram, b is the high-resolution N1s XPS spectrum diagram of IIP-Cu, and c is the high-resolution Cu 2p XPS spectrum diagram of IIP-Cu.

[0041] Figure 3 It is the X-ray energy dispersion spectrum mapping result diagram of rice husk based catalyst; wherein a is the X-ray energy dispersion spectrum mapping result diagram of C, b is the X-ray energy dispersion spectrum mapping result diagram of N, c is the X-ray energy dispersion spectrum mapping result diagram of O, d is the X-ray energy dispersion spectrum mapping result diagram of Si, and e is the X-ray energy dispersion spectrum mapping result diagram of Cu. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention. The following test methods and detection methods, unless otherwise specified, are conventional methods; the reagents and raw materials, unless otherwise specified, are commercially available.

[0043] Most of the traditional methods for preparing 1,3-conjugated diyne compounds still use transition metal catalysis. Although they have high yields, the use of noble metals greatly limits their subsequent applications, and the use of phosphine ligands or amine ligands will cause pollution to the environment. When monovalent copper salts are used instead of noble metals, a large amount of additives are required to improve the reaction efficiency and selectivity. Some heterogeneous catalysts currently developed for Glaser reactions, although they achieve high selectivity for asymmetric products, require a large excess of substrates and high temperature conditions to obtain the ideal product, which is contrary to the concept of green chemistry.

[0044] The present invention provides a rice husk-based catalyst and a preparation method and application thereof. A rice husk-based catalyst with high catalytic activity is prepared using rice husk as a carrier. When the catalyst is applied to the catalytic synthesis of 1,3-diyne compounds from terminal alkynes with different substituents, no other oxidants or other reaction aids need to be added. Only oxygen in the air is needed as an oxidant to achieve good selectivity and excellent catalytic effect. A rice husk-based catalyst is obtained by adding copper ions to an alcohol solution of salicylaldehyde Schiff base to form a pre-coordinated compound and then adding pretreated mesoporous SiO2 thereto. The catalyst is prepared using waste rice husk as a carrier, with low preparation cost and mild reaction conditions. The obtained rice husk-based catalyst has high catalytic activity.

[0045] A rice husk-based catalyst, its preparation method and application are described in detail below.

[0046] Example 1

[0047] A method for preparing a rice husk-based catalyst comprises the following steps:

[0048] S1. Mix 2.2137 g of 3-aminopropyltriethoxysilane, 1.4655 g of salicylaldehyde and 20 mL of ethanol, heat to 80° C. and reflux for 24 h. Monitor the reaction by thin layer chromatography. After the reaction is completed, a salicylaldehyde Schiff base alcohol solution is obtained.

[0049] S2, 0.6723g of CuCl2 was dissolved in 10mL of ethanol, and salicylaldehyde Schiff base alcohol solution was slowly added dropwise to react at 25°C to obtain Cu 2+ imprinted alcohol solution of the pre-coordinated compound; wherein the Cu in CuCl2 2+ The molar ratio of the salicylaldehyde Schiff base to the salicylaldehyde Schiff base alcohol solution is 1:2.

[0050] S3. Soak the rice husk powder in a 2.5% by mass hydrochloric acid solution for 0.5 h, filter, wash until neutral, dry, put into a muffle furnace and ash at 700°C for 30 min to obtain rice husk ash; then, alkalize and extract the rice husk ash with a 2 mol / L sodium hydroxide solution at 80°C for 5 h, filter, take the precipitate, and dry to obtain a silicon source; wherein the mass ratio of the ashing rice husk powder to the sodium hydroxide solution is 1:4.

[0051] S4. Dissolve hexadecyltrimethylammonium bromide in water and add 26% ammonia water by mass to obtain a treatment solution; add a silicon source to the treatment solution, adjust the pH to 10, and perform a hydrothermal reaction at 120°C for 72 hours to obtain mesoporous SiO2, which is recorded as RH@MCM-41; wherein the mass volume ratio of the silicon source, hexadecyltrimethylammonium bromide, water and ammonia water is 1g:0.58g:20mL:12.8mL.

[0052] S5, Cu 2+ The alcohol solution of the imprinted pre-coordinated compound was mixed with 1.2 g of RH@MCM-41, heated to 80 °C for 48 h, filtered, washed with anhydrous ethanol three times, and dried at 80 °C to obtain a rice husk-based catalyst, in which Cu 2+ Imprinting of pre-coordinated compounds in alcohol solution Cu 2+ The molar mass of the imprinted pre-coordinated compound was 10 mmol.

[0053] The morphology of the IIP-Cu prepared in Example 1 was characterized. Figure 1 As shown in the figure, the infrared spectra of rice husk and rice husk-based catalyst before and after pretreatment were compared and analyzed. The FT-IR spectrum of RH at 3403 cm -1 , 2855cm -1 and 1109cm -1The characteristic peaks at 1109cm-1 are attributed to the bending vibrations of OH bonds, CH bonds and Si-O-Si bonds. For RH@MCM-41, since no new functional groups are introduced, the characteristic peak positions do not change significantly compared with RH. However, compared with RH@MCM-41, IIP-Cu has a new Si-O-Si bending vibration at 1109cm-1. -1 A strong absorption peak appeared at 2925 cm, proving that Si-OH and Si-OEt were successfully cross-linked with the surface of RH@MCM-41. -1 and 2855cm -1 The characteristic peak of the CH bond at 1564cm is stronger than that at RH@MCM-41, which is caused by the introduction of -CH2 on the functional monomer of the modification group. -1 The new characteristic peak at 3403cm belongs to the typical bending vibration of C=N bond. And due to the introduction of -NH2 group, -1 and 1612cm -1 The absorption band at is greatly enhanced, indicating that the Schiff base functional groups are successfully introduced on the surface of the RH@MCM-41 composite material, thus indicating that IIP-Cu is successfully synthesized.

[0054] The elemental composition and chemical state of the IIP-Cu prepared in Example 1 were analyzed using X-ray photoelectron spectroscopy technology. Figure 2 As shown in Figure a, the presence of carbon, silicon, nitrogen, oxygen, chlorine and copper elements in the IIP-Cu material, compared with the RH@MCM-41 spectrum, the newly added elements can successfully indicate that the functional modification groups and copper elements have been successfully introduced into the RH@MCM-41 support material. The high-resolution N1s XPS spectrum of IIP-Cu is shown in Figure b, which can be decomposed into CN / C=N and HN bonds, respectively, at 399.58eV and 401.65eV, which is consistent with the previous FT-IR analysis results. In addition, the peak with a binding energy of 402.69eV can be attributed to the Cu-N bond, indicating that the coordination form of copper ions in the catalyst IIP-Cu mainly exists in the form of Cu-N bonds. The high-resolution Cu 2p XPS spectrum of IIP-Cu is shown in Figure c, and the peaks at 932.1eV and 952.0eV are attributed to Cu + , the peaks at 933.2eV and 953.0eV are attributed to Cu 2+ The high-resolution Cu 2p XPS spectrum of IIP-Cu shows that there are Cu + and Cu 2+ In addition, the existence of Cu-N bonds was still observed in the high-resolution Cu 2p XPS spectrum, which further explains the chemical state and coordination mode of copper ions in IIP-Cu.

[0055] In addition, the X-ray energy dispersive spectral mapping of the rice husk-based catalyst IIP-Cu showed that C, N, O, Si and Cu elements were uniformly distributed on the surface of the rice husk-based material, such as Figure 3 As shown. From the above description, it can be seen that copper ions are uniformly dispersed on the surface of the rice husk-based catalyst without agglomeration, which further indicates that we have successfully synthesized the rice husk-based catalyst IIP-Cu with rice husk as the carrier.

[0056] Example 2

[0057] Synthesis of 1,3-Diyne Compounds

[0058] 1. Selection of reaction solvent

[0059] IIP-Cu in Example 1, 1 mmol of phenylacetylene and 1 mmol of 4-ethynylanisole were mixed, and 2 mL of different solvents and 1,8-diazabicycloundec-7-ene were added to the reaction bottle in sequence, and the reaction was carried out at 50°C and 1 atm of air for 15 h. The reaction process was tracked by thin layer chromatography. After the reaction was completed, the system was centrifuged, and the separated reaction solution was extracted with dichloromethane, dried with anhydrous Na2SO4, filtered, concentrated, and purified by column chromatography to obtain the target product 1,3-conjugated diyne; wherein the eluent used in the column chromatography was a mixed solution of ethyl acetate and petroleum ether with a volume ratio of 50:1; the specific yield is shown in Table 1. wherein the amount of IIP-Cu added accounted for 2.5 mol% of the molar percentage of the terminal alkyne compound, and the amount of 1,8-diazabicycloundec-7-ene added accounted for 20 mol% of the molar percentage of the terminal alkyne compound, and the reaction equation was as follows:

[0060]

[0061] Table 1 Conversion rate of 1,3-conjugated diyne obtained in different solvents

[0062]

[0063]

[0064] Note: DBU refers to 1,8-diazabicycloundec-7-ene, the same below.

[0065] As shown in the experimental results of Table 1, when methanol and water in a volume ratio of 1:1 are selected as the solvent, the reaction conversion rate is the highest, so a mixed solution of methanol and water is used as the solvent of the reaction system, and further optimization and adjustment are performed.

[0066] 2. Selection of different proportions of reaction solvents

[0067] Using the preparation method in 1, different ratios of methanol and water were selected for reaction, and the conversion rates are shown in Table 2.

[0068] Table 2 Effect of different ratios of methanol to water on reaction conversion rate

[0069]

[0070] As shown in the experimental results in Table 2, when the ratio of methanol to water reaches 3:17, the reaction conversion rate is the highest. Under this reaction condition, the conversion rate increases first and then decreases with the increase of water content. The experimental results show that due to the intervention of the surface modification group of the carrier, the hydrophilicity of the catalyst material is greatly enhanced, enabling it to catalyze the reaction in a mixed solvent containing water. However, under pure water conditions, the conversion rate drops significantly. This is because under pure water conditions, the catalyst material cannot be well dispersed in the reaction system, and there are agglomeration and wall adhesion phenomena, which leads to a decrease in catalyst utilization. In addition, the reaction raw materials have poor solubility in water. Multiple factors lead to a sharp decline in the conversion rate when the water content exceeds 90%. Therefore, it was finally determined that the ratio of methanol to water was 3:17 as the reaction solvent.

[0071] 3. Selection of alkali type

[0072] The preparation method in 1 was adopted, and different bases were selected for reaction. The conversion rates are shown in Table 3.

[0073] Table 3 Effect of different bases on reaction conversion rate

[0074]

[0075] Note: “-” means the item is not included.

[0076] As shown in the experimental results of Table 3, the effect of base on the cross-coupling reaction of terminal alkynes was studied. As can be seen from the table, under the condition of not adding any base, there is still a yield of 15%, but the selected inorganic base in this reaction, the conversion rate does not exceed 20%, indicating that the presence of inorganic base does not bring positive benefits to the reaction, and the addition of NaOH even inhibits the reaction. This is because the inorganic base has a strong alkalinity, thereby destroying the copper ion structure dispersed on the surface of the catalyst material, resulting in a decrease in conversion rate. The selected organic base system has a yield of more than 20%, and the introduction of DBU makes the reaction yield reach 84%. Although DBU is a strong alkaline reagent, it is a weak nucleophilic reagent, which makes it easier to combine with protons and not easy to combine with carbon atoms. At the same time, DBU has a certain reducibility, which can reduce the divalent copper on the catalyst surface to a monovalent state, thereby accelerating the start of the terminal alkyne coupling reaction, greatly improving the reaction conversion rate, so DBU is selected as the base used in the reaction system.

[0077] 4. Selection of catalyst dosage

[0078] The preparation method in 1 was adopted, and different catalyst amounts were selected to carry out the reaction. The conversion rates are shown in Table 4.

[0079] Table 4 Effect of different catalyst dosage on reaction conversion rate

[0080]

[0081]

[0082] As shown in the experimental results in Table 4, the effect of the amount of catalyst on the reaction conversion rate was investigated. The experimental results show that when the catalyst content is low, it is difficult for the reaction to reach a high conversion rate within 15 hours. When the catalyst content reaches 2.5 mol%, the reaction can reach a high conversion rate after 15 hours. As the amount of catalyst added continues to increase, the conversion rate reaches the highest. Therefore, the amount of fixed catalyst used is 2.5 mol%.

[0083] 5. Gas selection

[0084] The preparation method in 1 was adopted, and the reaction was carried out in the presence of different gases. The conversion rates are shown in Table 5.

[0085] Table 5 Effect of different gases on reaction conversion rate

[0086]

[0087] As shown in the experimental results in Table 5, under the optimal reaction conditions obtained, the reaction system was filled with nitrogen, and the reaction did not occur at all. Due to the lack of oxidation by the oxidant oxygen, the formed copper acetylene intermediate was difficult to convert into the corresponding coupling product. This further shows that oxygen in the air participates in the reaction, and the copper acetylene intermediate is oxidized by oxygen to the corresponding target product, releasing the copper ions on the surface of IIP-Cu, allowing it to enter the next cycle, thereby verifying the catalytic mechanism of the reaction.

[0088] 6. Selection of different substrate dosages

[0089] The preparation method in 1 was used to carry out the reaction at different substrate dosages, and the conversion rates are shown in Table 6.

[0090] Table 6 Effect of different substrate amounts on reaction conversion rate

[0091]

[0092]

[0093] Since the addition ratio of two different substrates in the cross-coupling reaction of terminal alkynes will have a certain influence on the selectivity of the reaction, the addition ratio of two different substrates has been studied. The results are shown in Table 6. When the ratio is controlled at 1:1, the target product yield is 84%. When the reaction ratio is controlled at 1:1.1 and 1:1.2, it can be found that the yield of the corresponding product of the cross-coupling is not significantly improved compared to the ratio of 1:1. Excess p-methoxyphenylacetylene will gradually convert into the corresponding product of p-methoxyphenylacetylene self-coupling as the reaction time increases after the phenylacetylene is consumed, thereby causing waste. Although the reaction yield is the highest at a ratio of 1:1.2, considering that the yield improvement is limited and it is necessary to increase a relatively large amount of raw materials, the reaction ratio of 1:1 is selected as the feed ratio for the subsequent substrate exploration of the cross-coupling of terminal alkynes in combination with the concept of green chemistry, and subsequent research is carried out.

[0094] Taking the rice husk-based catalyst IIP-Cu prepared in Example 1 and the above optimized reaction conditions 1-6 as an example, the application effect thereof in the catalytic synthesis of 1,3-diyne compounds is explored.

[0095] Application Example 1

[0096] 40 mg of rice husk-based catalyst IIP-Cu, 1.0 mmol of substrate A / 1.1 mmol of substrate B, 0.2 mmol of D DBU and 2 ml of methanol / H2O (3:17) were added to the reaction bottle in sequence, and the reaction was carried out at 50°C and 1 atm of air for 15 h. The reaction process was tracked by thin layer chromatography. After the reaction was completed, the system was centrifuged, and the separated reaction solution was extracted, dried with anhydrous Na2SO4, filtered, concentrated, and separated by column chromatography to obtain the target product 1,3-conjugated diyne. The specific results are shown in Table 7. The reaction equation is as follows:

[0097]

[0098] Table 7 1,3-diyne compounds obtained by cross-coupling reaction of terminal alkyne compounds with different substituents

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105] From the results in Table 7, it can be seen that, based on the optimization of reaction conditions, the present invention expands the substrate range of terminal alkynes with different substituents. The research results show that the tested substrates including electron-withdrawing substituents F, Cl, Br, CF3; electron-rich substituents alkyl, propionyl, methoxy aryl acetylenes can all successfully undergo cross-coupling reactions to generate corresponding asymmetric aryl-containing 1,3-diyne products, such as products a to h, with a high yield of 81% to 86%.

[0106] Phenyl acetylene with -NH2 group can also be used under the same conditions to provide asymmetric 1,3-diyne target products, such as products i-l, with a yield of 80-86%. At the same time, aryl terminal alkynes containing electron-rich substituents can undergo cross-coupling reactions with 2-methyl-3-butyn-2-ol to obtain 1,3-diyne compounds with aryl and alkyl groups at both ends, such as product mq. Aromatic alkynes containing halogen substitutions, -Cl, such as products r and s, -Br, such as product t, -F, such as product u, and even strong electron-withdrawing groups, such as product v, can also react and prepare the desired asymmetric 1,3-diyne with good yields.

[0107] In addition, under standard conditions, 4-methoxyphenylacetylene can undergo cross-coupling reaction with 1-ethynyl-1-cyclohexene, such as product w, with a yield of 86%. More importantly, aliphatic alkyne compounds also have good reactivity, such as product x.

[0108] This proves that the prepared rice husk-based catalyst IIP-Cu has good reaction activity, reaction selectivity and versatility, can catalyze most cross-coupling reactions containing terminal alkynes, and can achieve good actual separation yields.

[0109] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A rice husk-based catalyst, characterized in that: The rice husk-based catalyst is used to catalyze the cross-coupling reaction of terminal alkynes; the rice husk-based catalyst is composed of Cu 2+ The imprinted pre-coordinated compound is connected with the mesoporous SiO2 through -O-Si- bonds to form a network structure; the Cu 2+ In the imprinted pre-coordinated compound, each nitrogen atom binds two Cu 2+ ; The rice husk-based catalyst is prepared according to the following method: When the Schiff base is mixed with copper ions, the nitrogen atom in the amine group of the Schiff base coordinates with the copper ions to form Cu 2+ Imprint the pre-coordinated compound and then add Cu 2+ The imprinted pre-coordinated compound is mixed with mesoporous SiO2, Cu 2+ The ethoxy group on the imprinted pre-coordinated compound undergoes alcoholysis reaction with the hydroxyl group on the surface of the mesoporous SiO2 to form an -O-Si- bond, thereby obtaining the rice husk-based catalyst; the mesoporous SiO2 is obtained by a hydrothermal synthesis method using rice husk ash as a silicon source.

2. The rice husk-based catalyst according to claim 1, characterized in that The Schiff base is a salicylaldehyde Schiff base; The Cu 2+ Derived from copper salt, the copper salt is any one of CuCl2, CuSO4, Cu(NO3)2.

3. The rice husk-based catalyst according to claim 2, characterized in that The molar ratio of the Schiff base to the copper ion is 1 to 2:1; 2+ The molar mass ratio of the imprinted pre-coordinated compound to the mesoporous SiO2 is 10mmol:1.2g-1.3g.

4. A method for preparing the rice husk-based catalyst according to claim 3, characterized in that: The following steps are involved: The salicylaldehyde Schiff base is mixed with a copper salt, wherein the molar ratio of the salicylaldehyde Schiff base to the copper ion in the copper salt is 1 to 2:1, and a coordination chelation reaction occurs in an ethanol environment at 35°C to 80°C to obtain Cu 2+ Imprinting pre-coordinated compound; the initial concentration of copper salt in ethanol is 0.5 mol / L to 1 mol / L; Mixing hexadecyltrimethylammonium bromide, ammonia water and water to obtain a treatment solution; mixing a silicon source with the treatment solution, adjusting the pH to 10-11, and hydrothermally reacting at 100-120°C for 48-72 hours to obtain the mesoporous SiO2; the mass volume ratio of the silicon source, hexadecyltrimethylammonium bromide, water and ammonia water is 1g: 0.4g-0.6g: 15-25mL: 12-15mL; Cu 2+ The imprinted pre-coordinated compound and mesoporous SiO2 are mixed in a molar mass ratio of 10 mmol:1.2 g-1.3 g, and reacted at 70° C.-100° C. for 46 h-48 h to obtain a rice husk-based catalyst.

5. The method for preparing a rice husk-based catalyst according to claim 4, characterized in that: The specific preparation process of the silicon source is as follows: The rice husk powder is soaked in a hydrochloric acid solution, filtered, washed to neutrality, and heated at 700°C to 750°C for 30min to 45min to obtain rice husk ash; The rice husk ash and the alkaline solution are mixed in a mass ratio of 1:4-6, extracted at 80°C-90°C for 4h-5h, filtered, and the precipitate is obtained to obtain a silicon source.

6. The method for preparing a rice husk-based catalyst according to claim 5, characterized in that: The alkaline solution is a sodium hydroxide solution with a concentration of 2 mol / L to 3 mol / L; The mass percentage of the ammonia water is 25% to 28%; the mass percentage of the hydrochloric acid solution is 2% to 3%.

7. Use of the rice husk-based catalyst according to claim 3 in catalyzing the cross-coupling of terminal alkynes to synthesize 1,3-diyne compounds.

8. A method for preparing a 1,3-diyne compound, characterized in that: The following steps are involved: The terminal alkyne compound, the solvent and the alkaline reagent are mixed, and the rice husk-based catalyst according to claim 3 is added, and the catalytic oxidation reaction is carried out at 45° C. to 55° C. for 15 h to 20 h, and the mixture is centrifuged, and the supernatant is taken and purified to obtain the 1,3-diyne compound; wherein the molar volume ratio of the terminal alkyne compound, the rice husk-based catalyst and the solvent is 1 mmol: 0.2 mmol to 0.5 mmol: 2 mL to 3 mL; The molar amount of the alkaline reagent accounts for 10% to 35% of the molar amount of the terminal alkyne compound.

9. The method for preparing a 1,3-diyne compound according to claim 8, characterized in that: The solvent is obtained by mixing reagent A and water in a volume ratio of 1:1 to 7; The reagent A is any one of methyl sulfoxide, N,N-dimethylformamide, methanol, tetrahydrofuran, ethanol, 1,4-dioxane, polyethylene glycol, and acetonitrile; The alkaline reagent is any one of 1,8-diazabicycloundec-7-ene, potassium carbonate, triethylamine, triethylenediamine, and sodium hydroxide.

10. The method for preparing a 1,3-diyne compound according to claim 8, characterized in that: The specific process of the purification is as follows: The filtrate is extracted with dichloromethane, dried over anhydrous Na2SO4, filtered, concentrated, and purified by column chromatography to obtain the 1,3-diyne compound; The eluent used in the column chromatography is a mixed solution of ethyl acetate and petroleum ether in a volume ratio of 50 to 52:1.

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