Method for selective photocatalytic oxidation of aryl alkane compound into aryl ketone or benzyl alcohol
By using the optical catalytic system of B-HTS-400 and lithium bromide, the challenge of O2 in the aroma compounds of aromatherapy compounds is solved, and the selective photocatalytic oxidation of the aromatane hydrocarbon compound is achieved , Low cost and the advantages of simplified operations.
Patent Information
- Application Number
- CN202411511985.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-28
- Publication Date
- 2025-01-28
AI Technical Summary
In the context of sustainable catalytic oxidation, there are huge challenges in the use of O2 as an oxidant to directly participate in benzyl oxidation systems of aromatic compounds, and effective catalytic systems are needed to achieve oxidation.
By-doped porous tubular nitride (B-HTS-400) is used as a photocatalyst, combined with lithium bromide as a synergistic catalyst, and using methanol or its mixed solvents as reactive solvents. Kidone or alcohol.
Under mild conditions, a variety of ketone -type compounds are selected at an 81.7%yield, and the alcoholic compounds are selected at a 63.1%yield, which reduces the cost, simplifies the operation steps, avoids precious metals and high energy and high energy. Use.
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Figure CN119371296A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of material chemistry, and in particular to a method for selective photocatalytic oxidation of an aryl alkane compound into an aryl ketone or benzyl alcohol. Background Art
[0002] Aromatic ketone compounds are not only important components of natural products, bioactive reagents and organic molecular building blocks, but also important skeletons and intermediates for the synthesis of active drugs. The benzyl group of aromatic compounds can be derivatized to obtain active compounds with various functions. The application of benzyl alcohol derivatives involves many fields such as natural active molecules, medicines, food additives and industrial chemicals. As early as the beginning of the 20th century, benzyl alcohol began to play an important role in drug synthesis.
[0003] Benzyl C(sp 3 )-H direct oxidation is one of the simple methods for synthesizing high value-added products. Alkyl aromatics are not only cheap and easy to obtain, rich in variety and usually used as common industrial raw materials, but also can be directly oxidized to synthesize aromatic ketones under relatively environmentally friendly and mild reaction conditions, which has attracted widespread attention from scholars. Scientists have developed the use of transition metal catalysis, photoelectric combined catalysis and other benzyl oxidation methods. The direct oxidation of the benzylic CH bond of aromatic compounds can be achieved by using high-valent metal oxidants such as potassium permanganate (KMnO4), chromium trioxide (CrO3), and other peroxidants such as tert-butyl peroxide (TBHP), potassium peroxydisulfate (Oxone), 3-chloroperoxybenzoic acid (m-CPBA), hydrogen peroxide (H2O2), and high-valent iodine. However, in the context of sustainable catalytic oxidation, green chemistry is the long-term goal pursued by scientific researchers. Among them, O2 has always been loved by chemists as a green and clean oxidant. At the same time, oxygen is a convenient, economical and environmentally friendly renewable green oxidant, which is very consistent with the sustainable development concept of green chemistry. However, there are still great challenges in the direct benzylic oxidation of aromatic compounds using O2 as an oxidant, and an effective catalytic system is required to achieve oxidation in this process. Summary of the invention
[0004] The present invention aims to provide a method for selectively photocatalytically oxidizing an aryl alkane compound into an aryl ketone or benzyl alcohol, so as to provide a more economical and simplified method for selectively photocatalytically oxidizing an aryl alkane compound into an aryl ketone or benzyl alcohol.
[0005] In this scheme, a method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol is used, using 2,3-dihydroindene shown in formula 1a as a substrate, light, porous tubular carbon nitride (B-HTs-400) as a photocatalyst, a synergistic catalyst, and any one or two of an organic solvent and water as a reaction solvent to synthesize the aryl ketone shown in formula 1b. The synthesis route is as follows:
[0006]
[0007] The working principle and beneficial effects of this scheme: Compared with the prior art, the present invention has developed a method for applying B-doped porous tubular carbon nitride to the selective photocatalytic oxidation of aromatic alkane compounds to aromatic ketones or benzyl alcohols, which effectively avoids the use of precious metals, electricity, and thermal energy, greatly reduces costs, improves atom economy, simplifies the operating steps, and selectively obtains aromatic ketone compounds with a yield of 81.7% under mild conditions, which provides a novel idea for the selective synthesis of aromatic ketone compounds.
[0008] Furthermore, the reaction solvent is methanol.
[0009] Furthermore, a reducing agent is included, and the reducing agent is a borane complex. The benzyl alcohol shown in the synthetic formula 1c is synthesized by the following synthetic route:
[0010]
[0011] Compared with the prior art, the present invention develops a method for applying B-doped porous tubular carbon nitride to the selective photocatalytic oxidation of aromatic alkane compounds to benzyl alcohol, which effectively avoids the use of precious metals, electricity, and thermal energy, greatly reduces the cost, simplifies the operation steps, and selectively obtains benzyl alcohol compounds with a yield of 63.1% under mild conditions, which provides a novel idea for the selective synthesis of benzyl alcohol compounds.
[0012] Furthermore, the reaction solvent is methanol and hexafluoroisopropanol in a mass ratio of 1:4.
[0013] Furthermore, the reaction solvent is isopropanol (HPLC) and hexafluoroisopropanol, with a mass ratio of 1:3.
[0014] Furthermore, the synergistic catalyst is lithium bromide.
[0015] Furthermore, the amount of lithium bromide used is 0 to 3 eq.
[0016] Furthermore, the amount of the porous tubular carbon nitride B-HTs-400 is 0 to 50 mg.
[0017] Furthermore, the reaction time is 0 to 24 hours.
[0018] Furthermore, the reaction atmosphere and dark reaction are air, oxygen or argon.
[0019] Furthermore, the B-doped porous tubular carbon nitride was applied to the selective photocatalytic oxidation of aromatic alkanes to aromatic ketones or benzyl alcohols. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 It is a screening bar chart of synergistic catalysts;
[0021] Figure 2 It is the LiBr dosage screening bar chart;
[0022] Figure 3 It is the B-HTs-400 dosage screening bar chart;
[0023] Figure 4 is a screening histogram of reaction time;
[0024] Figure 5 It is a screening bar chart of different solvents;
[0025] Figure 6 It is a bar chart of different reaction atmospheres and dark reaction screening;
[0026] Figure 7 It is a screening bar chart of the ratio of methanol and hexafluoroisopropanol mixed solvents;
[0027] Figure 8 It is a bar chart of different reaction atmospheres and dark reaction screening;
[0028] Fig. 9 It is a borane complex screening bar chart;
[0029] Fig.10 It is a bar chart for screening the dosage of borane ammonia complex;
[0030] Fig.11 is a bromination reagent screening bar chart;
[0031] Fig.12 It is the LiBr dosage screening bar chart;
[0032] Fig.13 It is the B-HTs-400 dosage screening bar chart;
[0033] Fig.14 is a screening histogram of reaction time;
[0034] Fig.15 It is a screening bar chart of mixed solvents of organic solvents and hexafluoroisopropanol;
[0035] Fig.16 It is a screening bar graph of the mixed solvent ratio of isopropanol (HPLC) and hexafluoroisopropanol;
[0036] Fig.17The free radical capture (EPR) spectra of B-HTs-400 are (a) holes, (b) superoxide radicals, (c) singlet oxygen, (d) sulfate radicals in oxygen atmosphere, (e) sulfate radicals in argon atmosphere, (f) comparison of sulfate radicals in oxygen and argon atmospheres;
[0037] Fig.18 is the isotope-labeled GC-MS graph of the B-HTs-400 catalytic reaction;
[0038] Fig.19 This is the cyclic voltammetry spectrum of B-HTs-400.
[0039] Fig. 20 This is the preparation process of B-HTs-400. DETAILED DESCRIPTION
[0040] The following is a further detailed description through specific implementation methods:
[0041] Example 1.1
[0042] 20 mg of B-HTs-400 was placed in a 20 mL reaction tube, 1 mL of methanol solution was added, and 2,3-dihydroindene (1a, 35.5 mg, 0.3 mmol) was added to the solution using a pipette. The reaction tube was placed in a photoreactor, the speed was set appropriately, and the temperature of the condensation circulation pump was set to 20-25 ° C. The reaction was carried out in air for 12 h as the initial reaction conditions. On this basis, the synergistic catalyst was first screened ( Figure 1 ), the results show that inorganic bases and organic bases are not as effective as bromination reagents as CH activation reagents. The reason may be that the system is based on free radical reactions with photocatalysis and material activation as the main body. Therefore, reagents that can produce free radicals under light conditions will be more in line with the reaction process. In addition, the photocatalytic oxidation yield of lithium bromide can reach 75.29%, so we choose lithium bromide as the best CH activation reagent.
[0043] Example 1.2
[0044] Based on the use of lithium bromide in Example 1.1, different amounts of lithium bromide (0, 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0, 1.5 eq.) were screened ( Figure 2), the results show that the yield can reach 34.53% without the synergistic effect of CH bond activation reagent, indicating that B-HTs-400 can oxidize the more active CH under light conditions, but its oxidation yield is not ideal. Therefore, the synergistic effect of bromination reagent is required. The yield will increase with the increase of lithium bromide. It may be that the increase in the concentration of bromide ions increases the probability of bromine becoming bromine free radicals under light. When the lithium bromide is 1eq., the yield can reach 78.49%. Therefore, we determined the amount of lithium bromide to be 1eq.
[0045] Example 1.3
[0046] Based on the amount of lithium bromide used in Example 1.2, different amounts of B-HTs-400 (0, 5, 15, 20, 25, 30 mg) were screened ( Figure 3 ), the results show that in the photocatalytic oxidation of benzyl CH bonds, no product is generated without the participation of B-HTs-400. With the addition of the catalyst, the product yield increases sharply. Therefore, the role of B-HTs-400 in photocatalytic oxidation is very important. However, with the further increase in the amount of catalyst, the yield first increases and then decreases. When the amount is 15 mg, the yield is the highest. The reason for this phenomenon may be related to the adsorption and activation ability of the material. The adsorption and activation ability of a small amount of catalyst is limited, so the yield is low. In addition, the excess catalyst makes the adsorbed substrate and activated oxygen too dispersed, resulting in a reduced probability of mutual combination. Therefore, we chose the optimal catalyst dosage of 15 mg.
[0047] Example 1.4
[0048] Based on the dosage of B-HTs-400 in Example 1.3, different reaction times (2, 4, 6, 8, 10, 12, 13, 14, 15 h) were screened. Figure 4 ), the results show that with the increase of reaction time, the yield first increases and then stabilizes. When the reaction time is 12h, the yield is 81.79%. The decrease in yield due to the extension of time may be due to operational errors or the formation of trace amounts of new by-products. Taking all factors into consideration, the optimal reaction time is 12h.
[0049] Example 1.5
[0050] Based on the reaction time in Example 1.4, different solvents (organic solvents, water and mixed solvents) were screened ( Figure 5), the experimental results show that we screened the commonly used polar aprotic solvents (, polar protic solvents and non-polar solvents. From the experimental data analysis, among the polar aprotic solvents, DMSO hardly reacted, and DMF had a yield of only 17.88%. It may be that the viscosity of the two is large and the dispersion of the catalyst is poor, which makes the reaction difficult. In addition, acetonitrile, tetrahydrofuran and 1,4-dioxane, which are also polar aprotic solvents with low viscosity, can obtain moderate yields; what is puzzling is that in polar protic solvents, the yields of methanol and ethanol are relatively good, while the yields of isopropanol, water and methanol-water solution are seriously reduced. In non-polar solvents, it is speculated that it may be the result of the combined influence of the properties of substrates, bromides and catalysts; similarly, the yields in non-polar solvents are high and low; considering all factors, the best reaction solvent is methanol.
[0051] Example 1.6
[0052] Based on the reaction solvent in Example 1.5, the reaction atmosphere (air, O2, Ar) and dark reaction were screened ( Figure 6 ). Light is essential, while the participation of oxygen greatly promotes the reaction. Almost no product is detected under argon conditions, which indicates that the oxygen of aromatic ketones comes from oxygen.
[0053] Example 2.1
[0054] 15 mg B-HTs-400, tetrabutylammonium bromide (0.06 eq.), borane amine complex (2 eq.) were placed in a 20 mL reaction tube, 1 mL of methanol solution was added, and 2,3-dihydroindene (1a, 35.5 mg, 0.3 mmol) was added to the solution using a pipette. The reaction tube was placed in a photoreactor, the speed was set appropriately, and the temperature of the condensation circulation pump was set to 20-25 ° C. The reaction was carried out in air for 12 hours as the initial reaction conditions. On this basis, different mixing ratios of methanol and hexafluoroisopropanol were first screened ( Figure 7 ), the results show that a single reaction solvent cannot produce ideal results. To our delight, the product 1c increased slightly after the addition of borane ammonia complex. Hexafluoroisopropanol can effectively prevent the oxidation of hydroxyl groups in this reaction system, so we chose methanol:hexafluoroisopropanol = 1:4.
[0055] Example 2.2
[0056] Based on the mixing ratio of methanol and hexafluoroisopropanol in Example 2.1, different reaction atmospheres (air, O2, Ar) and dark reactions were screened ( Figure 8 ), the results show that oxygen and light are important factors in this system, which also indirectly proves the one-pot two-step reaction process. Therefore, the reaction atmosphere is oxygen.
[0057] Example 2.3
[0058] Based on the reaction atmosphere in Example 2.2, different borane complexes were screened ( Fig. 9 ), the results show that the yield of the target product of borane ammine complex reaches 34.33% and product 1b is almost not generated. The target yields of borane ammine complex and borane tert-butylamine complex are relatively similar, but the chemical selectivity of borane tert-butylamine complex is relatively low, only 83.18%, so borane ammine complex is selected as the reducing agent.
[0059] Example 2.4
[0060] Based on the reducing agent in Example 2.3, the amount of borane (0, 0.5, 1, 1.5, 2, 2.5, 3 eq.) was screened. Fig.10 ), experimental data show that with the increase of borane ammonia complex, the yield of product 2c first increases and then decreases, and the generation of product 1b also shows a downward trend; when the amount of borane ammonia complex is less than 2eq., carbonyl compounds are still generated. It may be that the borane ammonia complex is continuously decomposed during the reaction, so that the amount of hydrogen transfer during the reduction of carbon groups decreases, which leads to a decrease in the target product and an increase in the cumulative amount of 2b. When the amount of borane ammonia complex is greater than or equal to 2eq., carbonyl compounds are almost undetectable. Therefore, we speculate that the gain and loss of hydrogen in the reduction process of borane complex may be equal, and the excess borane ammonia complex may strengthen the oxidation prevention step and weaken the oxidation step in the oxidation-reduction-oxidation prevention process, which leads to a decrease in the yield of 1c. Therefore, we choose the amount of borane ammonia complex to be 2eq.
[0061] Example 2.5
[0062] Based on the amount of borane used in Example 2.4, the bromination reagents (potassium bromide, lithium bromide, tetrabutylammonium bromide) were screened ( Fig.11 ). Experimental data show that the reaction proceeds strictly according to the steps of oxidation-reduction-antioxidation. The source of bromine directly affects the progress of the oxidation step. Therefore, the yields of different bromides vary greatly. We choose lithium bromide as the source of bromine radicals.
[0063] Example 2.6
[0064] Based on the bromination reagent in Example 2.5, the amount of lithium bromide (0, 0.5, 1, 1.5, 2, 2.5, 3 eq.) was screened ( Fig.12 ). The results show that excess bromine source cannot promote the formation of the target product, so we choose the amount of lithium bromide to be 1 eq.
[0065] Example 2.7
[0066] Based on the amount of lithium bromide in Example 2.6, different amounts of B-HTs-400 (5, 10, 15, 20, 25, 30 mg) were screened ( Fig.13 ), the results show that when the amount of catalyst is 15mg, the yield can reach 43.86% and the chemical selectivity is 98.97%. Excessive use of catalyst does not make the reaction proceed in the forward direction, which may be due to the adsorption problem of the catalyst, resulting in a decrease in yield. Therefore, we determined the amount of catalyst to be 15mg.
[0067] Example 2.8
[0068] Based on the different dosages of B-HTs-400 in Example 2.7, different reaction times (12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24 h) were screened. Fig.13 ), the results show that the target product is slightly increased with the extension of time, which may be due to the continuous occurrence of oxidation-reduction-antioxidation steps. However, after the time exceeds 18, not only the yield of 1c begins to slowly decline, but also the yield of 2b has a rebound trend. We speculate that the long-term reaction may cause the borane ammonia complex to continue to decompose, resulting in the weakening of the reduction-antioxidation step. In addition, the activated oxygen of the catalyst allows the generated hydroxyl compound to be directly oxidized to a carbonyl group. Therefore, we choose the optimal reaction time as 18h.
[0069] Example 2.9
[0070] Based on the different reaction times in Example 2.8, different organic mixed solvents were screened ( Fig.15 ), the results showed that replacing methanol with isopropanol (HPLC) could improve the yield of the target product. Therefore, we determined that the reaction solvent was a mixed solvent of isopropanol (HPLC): hexafluoroisopropanol.
[0071] Example 2.10
[0072] Based on the mixed solvent of isopropanol (HPLC): hexafluoroisopropanol in Example 2.9, different solvent ratios were screened ( Fig.16 ), the results showed that the target yield showed an upward trend with the increase of the ratio of hexafluoroisopropanol solvent. When IPA:HFIP=1:3, the yield of 2c could reach 63.1% and the chemical selectivity was greater than 99%.
[0073] Embodiment 11
[0074] Fig.17This is the free radical capture diagram of B-HTs-400. To confirm the existence of holes, superoxide radicals, and singlet oxygen, we conducted EPR tests, and the data showed the existence of the above-mentioned active oxidizing species.
[0075] Example 12
[0076] Fig.18 In order to analyze the oxygen source of the oxidation products catalyzed by B-HTs-400, oxygen isotope labeling experiments were carried out. The data showed that the oxygen source of aromatic ketones and benzyl alcohols was oxygen.
[0077] Example 13
[0078] Fig.19 The cyclic voltammogram of B-HTs-400 shows clearly that there is no redox peak in the absence of catalytic materials, nitrogen atmosphere and air conditions. It is worth noting that a relatively obvious reduction peak appears when oxygen is introduced during the test. Therefore, we speculate that B-HTs-400 has a certain reducing property to oxygen, which further proves that superoxide radicals may originate from the reduction of oxygen. In addition, when we introduced light, we found that not only there was a reduction peak in air and oxygen atmosphere, but also the value of its reduction potential increased. This shows that light may cause the catalyst to generate photogenerated electrons and holes, greatly improving the photocatalytic performance of B-HTs-400.
[0079] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.
Claims
1. A method for selective photocatalytic oxidation of aryl alkane compounds to aryl ketones or benzyl alcohols, characterized in that: The 2,3-dihydroindene shown in formula 1a is used as a substrate, light is applied, porous tubular carbon nitride (B-HTs-400) is used as a photocatalyst, a synergistic catalyst, and any one or two of an organic solvent and water are used as reaction solvents to synthesize the aromatic ketone shown in formula 1b. The synthesis route is as follows:
2. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 1, characterized in that: The organic solvent is methanol.
3. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 1, characterized in that: It also includes a reducing agent, wherein the reducing agent is a borane complex, and the benzyl alcohol shown in formula 1c is synthesized 4. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 3, characterized in that: The reaction solvent is methanol and hexafluoroisopropanol, and the mass ratio is 1:
4.
5. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 3, characterized in that: The reaction solvent is isopropanol (HPLC) and hexafluoroisopropanol, with a mass ratio of 1:
3.
6. A method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to any one of claims 2, 4 and 5, characterized in that: The synergistic catalyst is lithium bromide.
7. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 6, characterized in that: The amount of lithium bromide used is 0 to 3 eq.
8. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 7, characterized in that: The amount of the porous tubular carbon nitride B-HTs-400 is 0 to 50 mg.
9. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 7, characterized in that: The reaction time is 0 to 24 hours.
10. The method for selective photocatalytic oxidation of an aryl alkane compound to an aryl ketone or benzyl alcohol according to claim 7, characterized in that: The reaction atmosphere and dark reaction are air, oxygen or argon.