A Fe2O3-KCl / CaO catalyst, its preparation method and application

Abstract

This invention relates to the field of organic synthesis catalysis, and particularly to an Fe₂O₃-KCl / CaO catalyst, its preparation method, and its applications. The Fe₂O₃-KCl / CaO catalyst, prepared via a sol-gel method, achieves high dispersion and stable binding of Fe and K active components on a calcium oxide support. CaO serves as the support and provides abundant basic sites, while the K component further enhances basicity and modulates surface properties. The Fe component provides specific Lewis acidic centers, enabling the catalyst to simultaneously activate the carboxyl group and three phenolic hydroxyl groups of gallic acid. This efficiently catalyzes the tandem methyl esterification and methyl etherification reactions of gallic acid and dimethyl carbonate, thereby achieving highly selective synthesis of methyl 3,4,5-trimethoxybenzoate. This method is simple, atom-economical, and environmentally friendly, possessing high industrial application potential. It solves the problem of existing catalysts having single functions, making it difficult to achieve highly selective and efficient green synthesis of methyl 3,4,5-trimethoxybenzoate.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis catalysis technology, specifically to a method for preparing an Fe2O3-KCl / CaO catalyst, its preparation method, and its application. Background Technology

[0002] Methyl 3,4,5-trimethoxybenzoate, a crucial intermediate in drug synthesis, is widely used in the synthesis of various drugs. It is key to the successful synthesis of numerous drugs, including the antibacterial drug trimethoprim, the anti-anxiety drug trimetomidine, and the gastrointestinal drug trimebutine maleate. Therefore, a stable supply and efficient synthesis of methyl 3,4,5-trimethoxybenzoate are of paramount importance for ensuring the production of these drugs, meeting clinical needs, and advancing related drug development.

[0003] The traditional industrial synthesis route for methyl 3,4,5-trimethoxybenzoate typically employs a two-step process: using gallic acid as a raw material, it first undergoes methyl etherification with dimethyl sulfate in the presence of excess sodium hydroxide, followed by methyl esterification with methanol catalyzed by concentrated sulfuric acid to obtain the target product. This process utilizes large amounts of strong acids, strong bases, and highly toxic reagents, is cumbersome, and is accompanied by serious equipment corrosion, high-salt wastewater, and safety hazards. Therefore, exploring and developing green, environmentally friendly, and sustainable synthesis technologies for methyl 3,4,5-trimethoxybenzoate has become an inevitable choice for the chemical industry to achieve sustainable development.

[0004] In recent years, with the rise of green chemistry and increased emphasis on environmental protection, researchers have begun to explore new methods for synthesizing methyl 3,4,5-trimethoxybenzoate using dimethyl carbonate (DMC), a green methylating agent, as a raw material. Dimethyl carbonate, as an environmentally friendly reagent, possesses advantages such as low toxicity, no pollution, and high atom economy, and has broad application prospects in the field of pharmaceutical synthesis. In this new synthetic route, dimethyl carbonate acts as both a methylating and esterifying agent, reacting with gallic acid. The aim is to simultaneously achieve the methylation of the phenolic hydroxyl group and the esterification of the carboxyl group in a single reaction, thereby simplifying the synthetic steps, reducing waste generation, and improving the greenness of the synthetic process. However, to achieve this goal, the key lies in developing a bifunctional catalyst capable of simultaneously and selectively catalyzing the methylation of the carboxyl group and the methylation of the phenolic hydroxyl group.

[0005] Calcium oxide, as a widely available and inexpensive solid strong base, has been proven to have good catalytic activity in the methylation reaction of dimethyl carbonate (DMC) and phenol. However, calcium oxide alone is too alkaline. In this strongly alkaline environment, carboxyl groups are more prone to side reactions, such as saponification or decarboxylation, failing to effectively activate carboxyl groups for esterification and thus affecting the formation of the target product. Moreover, calcium oxide has a single function, only providing an alkaline environment, which cannot effectively activate carboxyl groups for esterification reactions, resulting in low esterification efficiency. In addition, calcium oxide has a low specific surface area, meaning that the number of active sites on its surface is limited, which is not conducive to the adsorption and reaction of reactant molecules on its surface. At the same time, during the reaction, active sites are prone to sintering, leading to a gradual decrease in catalyst activity, a shortened lifespan, and the need for frequent catalyst replacement, increasing production costs.

[0006] Therefore, the key to solving current technical challenges and promoting the green synthesis of methyl 3,4,5-trimethoxybenzoate lies in how to construct a composite active site catalyst with both controllable acidity and enhanced alkalinity by using calcium oxide as a basic support and alkaline source and loading it with multifunctional auxiliary agents. Summary of the Invention

[0007] To address the problem that existing catalysts have limited functionality and are difficult to synthesize methyl 3,4,5-trimethoxybenzoate with high selectivity and high efficiency in a green manner, this invention provides a Fe2O3-KCl / CaO catalyst, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention employs the following technical solution: This application provides a method for preparing a Fe2O3-KCl / CaO catalyst, comprising: The CaO precursor, iron component precursor and potassium chloride were dissolved in water to obtain the precursor sol; The precursor sol was heated once, stirred, and citric acid was added. Then it was heated a second time to evaporate and dried to obtain a dry gel precursor. The dry gel precursor was calcined to obtain the Fe2O3-KCl / CaO catalyst.

[0009] Optionally, in the Fe2O3-KCl / CaO catalyst, the molar ratio of iron, calcium and potassium is 1:(15-25):(2-4).

[0010] Optionally, the CaO precursor is selected from one or more of calcium acetate monohydrate, calcium oxalate, and calcium nitrate.

[0011] Optionally, the iron component precursor is selected from one or more of ferric nitrate, ferric chloride, and ferric citrate.

[0012] Optionally, the molar ratio of citric acid to all metal ions in the precursor sol is (1.2-1.5):1.

[0013] Optionally, the temperature for the first heating is 75℃-85℃, and the temperature for the second heating evaporation is 95℃-120℃.

[0014] Optionally, the calcination temperature is 700℃-900℃ and the time is 4-8h.

[0015] A Fe2O3-KCl / CaO catalyst prepared using the above-mentioned Fe2O3-KCl / CaO catalyst preparation method, wherein the Fe2O3-KCl / CaO catalyst uses calcium oxide as the core support and basic component, and the calcium oxide is supported with iron as an acidic center and potassium as a basic modulation center.

[0016] The above-mentioned Fe2O3-KCl / CaO catalyst is used in the synthesis of methyl 3,4,5-trimethoxybenzoate, including: Gallic acid, dimethyl carbonate, and Fe2O3-KCl / CaO catalyst were mixed and reacted at 170℃-200℃ and a back pressure of 1-4MPa for 5-12 hours to obtain methyl 3,4,5-trimethoxybenzoate.

[0017] Optionally, the molar ratio of gallic acid to dimethyl carbonate is (1:10)-(1:30), and the amount of Fe2O3-KCl / CaO catalyst added is 1%-10% of the mass of gallic acid.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a Fe2O3-KCl / CaO catalyst. This method utilizes a sol-gel method to achieve high dispersion and stable bonding of iron (Fe) and potassium (K) active components on a calcium oxide (CaO) support. This results in a Fe2O3-KCl / CaO catalyst possessing composite active sites that combine controllable acidity and enhanced basicity. CaO, as a support for the Fe and K active components, not only provides support for them but also offers abundant basic sites. These basic sites can adsorb and activate acidic groups in reactants during specific catalytic reactions, promoting the reaction process. The K active component, acting as a basicity modulation center, further enhances basicity and modulates surface properties. The Fe active component, as an acidic center, provides specific Lewis acidic centers that can interact with the phenolic hydroxyl groups in gallic acid, activating them and making them more readily involved in subsequent methyl esterification and methyl etherification reactions. This catalyst can simultaneously activate the carboxyl group and three phenolic hydroxyl groups of gallic acid, allowing all active groups in gallic acid to participate in the reaction. This enables highly efficient catalysis of the tandem methyl esterification and methyl etherification reactions of gallic acid and dimethyl carbonate, leading to the highly selective synthesis of methyl 3,4,5-trimethoxybenzoate. This reduces the difficulty and cost of subsequent separation and purification, improves product purity and quality, and meets the quality requirements of industrial production. This method is simple, atom-economical, and environmentally friendly, possessing significant potential for industrial application.

[0019] A Fe2O3-KCl / CaO catalyst prepared using the above-described method is disclosed. The catalyst uses calcium oxide as the core support and a basic component. The calcium oxide is supported with iron as an acidic center and potassium as a basicity-modulating center. Calcium oxide, as the core support and basic component, provides abundant strongly basic sites. In catalyzing reactions involving gallic acid, these basic sites can adsorb the carboxyl groups of gallic acid, making them more readily involved in subsequent chemical reactions, lowering the activation energy, and increasing the reaction rate. The iron supported on the calcium oxide, as an acidic center, can activate the three phenolic hydroxyl groups of gallic acid, altering their electron cloud distribution, enhancing their reactivity, and promoting the reaction between the phenolic hydroxyl groups and the reactants, thereby driving the entire catalytic reaction. Potassium, as a basicity modulating center, can further regulate the acidity and basicity of the catalyst surface. It can not only alter the distribution and intensity of basic sites on the calcium oxide surface but also affect the properties of ferric acid centers. Through this modulating effect, the acidity and basicity of the catalyst surface can be brought to a more suitable ratio, optimizing the adsorption and activation state of reactants on the catalyst surface, improving the selectivity and activity of the catalytic reaction, and enabling the simultaneous and efficient activation of the carboxyl and phenolic hydroxyl groups of gallic acid, resulting in the highly selective synthesis of the target product, methyl 3,4,5-trimethoxybenzoate. This catalyst can simultaneously activate the carboxyl and phenolic hydroxyl groups of gallic acid, allowing the two reaction steps to proceed smoothly and seamlessly, achieving one-step synthesis of the target product. It exhibits good stability and a long service life, reducing energy consumption and equipment investment in the green synthesis of methyl 3,4,5-trimethoxybenzoate, thereby comprehensively reducing the cost of green synthesis of methyl 3,4,5-trimethoxybenzoate and enhancing the company's competitiveness in the market.

[0020] In the synthesis of methyl 3,4,5-trimethoxybenzoate, the Fe2O3-KCl / CaO catalyst, through acid-base synergy and highly dispersed active components, facilitates the highly selective, efficient, and green synthesis of methyl 3,4,5-trimethoxybenzoate. It also boasts advantages such as simple process, low energy consumption, and environmental friendliness, making it an ideal choice for industrial production and potentially driving technological upgrades in related pharmaceutical and fine chemical fields. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of a method for preparing a Fe2O3-KCl / CaO catalyst according to the present invention. Detailed Implementation

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0024] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0025] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0026] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0029] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0030] The one-step catalytic synthesis of methyl 3,4,5-trimethoxybenzoate from gallic acid using dimethyl carbonate as a methylating agent requires a tandem reaction mechanism where the catalyst possesses both highly efficient acidic and basic sites to drive the methylation of the carboxyl group and the methylation of the phenolic hydroxyl group, respectively. However, catalysts with calcium oxide as a support and basic sites cannot provide the necessary acidic centers due to their single and excessively strong basicity, making it difficult for the tandem reaction to proceed synergistically. Directly introducing acidic sites requires solving a core challenge: how to precisely control the strength relationship between the acid and basic active sites to avoid mutual antagonism and prevent side reactions such as excessive decomposition of dimethyl carbonate caused by strong acid sites or decarboxylation caused by strong basic environments. Therefore, achieving highly efficient synergistic acid-base catalysis at the molecular scale is of great significance for promoting the green synthesis of methyl 3,4,5-trimethoxybenzoate.

[0031] To solve the above problems, see [link to relevant documentation]. Figure 1 This invention discloses a method for preparing a Fe2O3-KCl / CaO catalyst, comprising: S1: Dissolve the CaO precursor, iron component precursor, and potassium chloride in water to obtain a precursor sol. Specifically, dissolve the CaO precursor, iron component precursor, and potassium chloride in deionized water at a molar ratio of iron, calcium, and potassium of 0.25:(15-25):(2-4) in the Fe2O3-KCl / CaO catalyst, and stir at room temperature to form a stable precursor sol. Preferably, the molar ratio of iron, calcium, and potassium in the Fe2O3-KCl / CaO catalyst is 1:(15-25):(2-4). More preferably, the molar ratio of iron, calcium, and potassium in the Fe2O3-KCl / CaO catalyst is 1:20:3. Preferably, the CaO precursor is selected from one or more of calcium acetate monohydrate, calcium oxalate, and calcium nitrate; the iron component precursor is selected from one or more of ferric nitrate, ferric chloride, and ferric citrate.

[0032] S2: The precursor sol is heated once, stirred, and citric acid is added. It is then heated a second time to evaporate the mixture and dried to obtain a dry gel precursor, specifically: The precursor sol was heated to 75℃-85℃ and stirred for 0.5-2 hours. Citric acid was added as a complexing agent, and the mixture was stirred continuously. It was then heated a second time to 95℃-120℃ to evaporate and dry, yielding a fluffy dry gel precursor. The citric acid reacts with all metal ions (including Ca2+) in the precursor sol. 2+ Fe 3+ and K + The molar ratio of the sum of the moles of the two molecules is (1.2-1.5):1.

[0033] S3: The dry gel precursor was calcined to obtain the Fe2O3-KCl / CaO catalyst, specifically: The dry gel precursor was ground and then calcined at 700℃-900℃ for 4-8 hours in air to obtain the Fe2O3-KCl / CaO catalyst.

[0034] The present invention also provides a Fe2O3-KCl / CaO catalyst prepared by the above-described Fe2O3-KCl / CaO catalyst preparation method, wherein the Fe2O3-KCl / CaO catalyst uses calcium oxide as a core support and an alkaline component, and the calcium oxide is loaded with iron as an acidic center and potassium as an alkaline modulation center.

[0035] The above-mentioned Fe2O3-KCl / CaO catalyst is used in the synthesis of methyl 3,4,5-trimethoxybenzoate, including: Gallic acid, dimethyl carbonate, and Fe₂O₃-KCl / CaO catalyst are mixed and reacted at 170℃-200℃ and a back pressure of 1-4 MPa for 5-12 h to obtain methyl 3,4,5-trimethoxybenzoate. The molar ratio of gallic acid to dimethyl carbonate is (1:10)-(1:30), and the amount of Fe₂O₃-KCl / CaO catalyst added is 1%-10% of the mass of gallic acid. Preferably, the reaction of gallic acid and dimethyl carbonate as raw materials for the tandem methylation synthesis of methyl 3,4,5-trimethoxybenzoate is carried out in a high-pressure reactor equipped with a coil heat exchanger, a back pressure valve, and an exhaust port. The generated gas (carbon dioxide) is condensed and discharged through the back pressure valve.

[0036] Example 1 Weigh out 7.047 g (40.0 mmol Ca) of calcium acetate monohydrate (Ca(CH3COO)2·H2O, M=176.18 g / mol), 0.8080 g (2.0 mmol Fe) of ferric nitrate nonahydrate (Fe(NO3)3·9H2O, M=404.00 g / mol), and 0.4473 g (6.0 mmol K) of potassium chloride (KCl, M=74.55 g / mol), and dissolve them together in 100 mL of deionized water. Stir at room temperature until completely clear to obtain the precursor sol. The precursor sol was placed in an 80°C constant temperature water bath and stirred continuously for 1 hour. Then, 11.99 g (62.4 mmol) of citric acid (C6H8O7, M=210.14 g / mol) was added, and the temperature was raised to 100°C with continuous stirring to evaporate the water. After about 1 hour, the solution gradually transformed into a viscous, transparent, and homogeneous sol, eventually forming a non-flowing wet gel. The wet gel was transferred to a 115°C forced-air drying oven and statically dried for 16 hours to obtain a fluffy, porous, and fragile dry gel precursor. The dry gel was thoroughly ground into a fine powder in a mortar and placed in a crucible. The crucible was then placed in a muffle furnace and heated to 800°C at a rate of 5°C / min. The mixture was then calcined at this temperature for 6 hours and allowed to cool naturally to room temperature. The sintered body was then removed and ground again to obtain the target Fe2O3-KCl / CaO catalyst. The molar ratio of iron, calcium, and potassium in the Fe2O3-KCl / CaO catalyst was 1:20:3, and it was designated as Cat-A.

[0037] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Fe2O3-KCl / CaO catalyst Cat-A 170 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Fe2O3-KCl / CaO catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 99.0%, the selectivity was 96.8%, and the chromatographic yield was 95.8%.

[0038] Example 2 Weigh out 7.047 g (40.0 mmol Ca) of calcium acetate monohydrate (Ca(CH3COO)2·H2O, M=176.18 g / mol), 0.202 g (0.5 mmol Fe) of ferric nitrate nonahydrate (Fe(NO3)3·9H2O, M=404.00 g / mol), and 0.4473 g (6.0 mmol K) of potassium chloride (KCl, M=74.55 g / mol), and dissolve them together in 100 mL of deionized water. Stir at room temperature until completely clear to obtain the precursor sol. The precursor sol was placed in an 80°C constant temperature water bath and stirred continuously for 1 hour. Then, 11.99 g (62.4 mmol) of citric acid (C6H8O7, M=210.14 g / mol) was added, and the temperature was raised to 100°C with continuous stirring to evaporate the water. After about 1 hour, the solution gradually transformed into a viscous, transparent, and homogeneous sol, eventually forming a non-flowing wet gel. The wet gel was transferred to a 115°C forced-air drying oven and statically dried for 16 hours to obtain a fluffy, porous, and fragile dry gel precursor. The dry gel was thoroughly ground into a fine powder in a mortar and placed in a crucible. The crucible was then placed in a muffle furnace and heated to 800°C at a rate of 5°C / min. The mixture was then calcined at this temperature for 6 hours and allowed to cool naturally to room temperature. The sintered body was then removed and ground again to obtain the target Fe2O3-KCl / CaO catalyst. The molar ratio of iron, calcium, and potassium in the Fe2O3-KCl / CaO catalyst was 0.25:20:3, and it was designated as Cat-B.

[0039] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Fe2O3-KCl / CaO catalyst Cat-B 170 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Fe2O3-KCl / CaO catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 98.0%, the selectivity was 78.6%, and the chromatographic yield was 77.0%.

[0040] Example 3 Weigh out 7.047 g (40.0 mmol Ca) of calcium acetate monohydrate (Ca(CH3COO)2·H2O, M=176.18 g / mol), 0.8080 g (2.0 mmol Fe) of ferric nitrate nonahydrate (Fe(NO3)3·9H2O, M=404.00 g / mol), and 0.596 g (8.0 mmol K) of potassium chloride (KCl, M=74.55 g / mol), and dissolve them together in 100 mL of deionized water. Stir at room temperature until completely clear to obtain the precursor sol. The precursor sol was placed in an 80°C constant temperature water bath and stirred continuously for 1 hour. Then, 11.99 g (62.4 mmol) of citric acid (C6H8O7, M=210.14 g / mol) was added, and the temperature was raised to 100°C with continuous stirring to evaporate the water. After about 1 hour, the solution gradually transformed into a viscous, transparent, and homogeneous sol, eventually forming a non-flowing wet gel. The wet gel was transferred to a 115°C forced-air drying oven and statically dried for 16 hours to obtain a fluffy, porous, and fragile dry gel precursor. The dry gel was thoroughly ground into a fine powder in a mortar and placed in a crucible. The crucible was then placed in a muffle furnace and heated to 800°C at a rate of 5°C / min. The mixture was then calcined at this temperature for 6 hours and allowed to cool naturally to room temperature. The sintered body was then removed and ground again to obtain the target Fe2O3-KCl / CaO catalyst. The molar ratio of iron, calcium, and potassium in the Fe2O3-KCl / CaO catalyst was 1:20:4, denoted as Cat-C.

[0041] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Fe2O3-KCl / CaO catalyst Cat-C 170 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Fe2O3-KCl / CaO catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 99.0%, the selectivity was 89.5%, and the chromatographic yield was 88.6%.

[0042] Example 4 Weigh out 5.124 g (40.0 mmol Ca) of calcium oxalate (CaC2O4, M=128.10 g / mol), 0.8080 g (2.0 mmol Fe) of ferric nitrate nonahydrate (Fe(NO3)3·9H2O, M=404.00 g / mol), and 0.4473 g (6.0 mmol K) of potassium chloride (KCl, M=74.55 g / mol). Dissolve them together in 100 mL of deionized water and stir at room temperature until completely clear to obtain the precursor sol. Place the precursor sol in an 80℃ constant temperature water bath and stir continuously for 1 h. Then add 11.99 g (62.4 mmol) of citric acid (C6H8O7, M=210.14 g / mol) and heat to 100℃ while stirring continuously to evaporate the water. After about 1 h, the solution gradually transforms into a viscous, transparent, and homogeneous sol, eventually forming a non-flowing wet gel. The wet gel was transferred to a 115℃ forced-air drying oven and statically dried for 16 h to obtain a fluffy, porous, and brittle dry gel precursor. The dry gel was thoroughly ground into a fine powder in a mortar and placed in a crucible. The crucible was then placed in a muffle furnace and heated to 800℃ at a programmed rate of 5℃ / min. The mixture was then calcined at this temperature for 6 h and allowed to cool naturally to room temperature. The sintered body was then removed and ground again to obtain the target Fe2O3-KCl / CaO catalyst. The molar ratio of iron, calcium, and potassium in the Fe2O3-KCl / CaO catalyst was 1:20:3, denoted as Cat-D.

[0043] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Fe2O3-KCl / CaO catalyst Cat-D 170 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Fe2O3-KCl / CaO catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 92.8%, the selectivity was 91.7%, and the chromatographic yield was 89.7%.

[0044] Example 5 Weigh out 7.047 g (40.0 mmol Ca) of calcium acetate monohydrate (Ca(CH3COO)2·H2O, M=176.18 g / mol), 0.32439 g (2.0 mmol Fe) of ferric chloride (FeCl3, M=162.195 g / mol), and 0.4473 g (6.0 mmol K) of potassium chloride (KCl, M=74.55 g / mol). Dissolve them together in 100 mL of deionized water and stir at room temperature until completely clear to obtain the precursor sol. Place the precursor sol in an 80 °C constant temperature water bath and stir continuously for 1 h. Then add 11.99 g (62.4 mmol) of citric acid (C6H8O7, M=210.14 g / mol) and heat to 100 °C while stirring continuously to evaporate the water. After about 1 h, the solution gradually transforms into a viscous, transparent, and homogeneous sol, eventually forming a non-flowing wet gel. The wet gel was transferred to a 115℃ forced-air drying oven and statically dried for 16 h to obtain a fluffy, porous, and brittle dry gel precursor. The dry gel was thoroughly ground into a fine powder in a mortar and placed in a crucible. The crucible was then placed in a muffle furnace and heated to 800℃ at a programmed rate of 5℃ / min. The mixture was then calcined at this temperature for 6 h and allowed to cool naturally to room temperature. The sintered body was then removed and ground again to obtain the target Fe2O3-KCl / CaO catalyst. The molar ratio of iron, calcium, and potassium in the Fe2O3-KCl / CaO catalyst was 1:20:3, denoted as Cat-E.

[0045] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Fe2O3-KCl / CaO catalyst Cat-E 170 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Fe2O3-KCl / CaO catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 95.6%, the selectivity was 85.3%, and the chromatographic yield was 81.5%.

[0046] Example 6 Weigh out 9.446 g (40.0 mmol Ca) of calcium nitrate tetrahydrate (Ca(NO3)2·4H2O, M=236.15 g / mol), 1.616 g (4.0 mmol Fe) of ferric nitrate nonahydrate (Fe(NO3)3·9H2O, M=404.00 g / mol), and 0.596 g (8.0 mmol K) of potassium chloride (KCl, M=74.55 g / mol). Dissolve them together in 100 mL of deionized water and stir at room temperature until completely clear to obtain the precursor sol. Place the precursor sol in an 80 °C constant temperature water bath and stir continuously for 1 h. Then add 11.99 g (62.4 mmol) of citric acid (C6H8O7, M=210.14 g / mol) and heat to 100 °C while stirring continuously to evaporate the water. After about 1 h, a non-flowing wet gel is formed. The wet gel was transferred to a 115℃ forced-air drying oven and statically dried for 16 h to obtain a dry gel precursor. The dry gel was ground and placed in a muffle furnace, where the temperature was programmed to rise to 800℃ at a rate of 5℃ / min, and calcined at a constant temperature for 6 h. After natural cooling, it was ground to obtain the target Fe2O3-KCl / CaO catalyst, in which the molar ratio of iron, calcium and potassium was 1:15:2, denoted as Cat-F.

[0047] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and 170 mg of Cat-F catalyst were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then established, and the temperature was raised to 180 °C for 8 h. After the reaction, the mixture was filtered, and the filtrate was analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 98.2%, the selectivity was 82.5%, and the chromatographic yield was 81.0%.

[0048] Example 7 Weigh out 7.047 g (40.0 mmol Ca) of calcium acetate monohydrate (Ca(CH3COO)2·H2O, M=176.18 g / mol), 0.392 g (1.6 mmol Fe) of ferric citrate (FeC6H5O7, M=244.94 g / mol), and 0.477 g (6.4 mmol K) of potassium chloride (KCl, M=74.55 g / mol). Dissolve them together in 100 mL of deionized water and stir at room temperature until completely clear to obtain the precursor sol. Place the precursor sol in an 80 °C constant temperature water bath and stir continuously for 1 h. Then add 11.99 g (62.4 mmol) of citric acid (C6H8O7, M=210.14 g / mol) and heat to 100 °C. Continue stirring to evaporate the water. After about 1 h, a non-flowing wet gel is formed. The wet gel was transferred to a 115℃ forced-air drying oven and statically dried for 16 h to obtain a dry gel precursor. The dry gel was ground and placed in a muffle furnace, where the temperature was programmed to rise to 800℃ at a rate of 5℃ / min, and calcined at a constant temperature for 6 h. After natural cooling, it was ground to obtain the target Fe2O3-KCl / CaO catalyst, in which the molar ratio of iron, calcium and potassium was 1:25:4, denoted as Cat-G.

[0049] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Cat-G catalyst (170 mg) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then established, and the temperature was raised to 180 °C for 8 h. After the reaction, the mixture was filtered, and the filtrate was analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 98.5%, the selectivity was 86.6%, and the chromatographic yield was 85.3%.

[0050] Example 8 Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (200 mmol, 18 g, molar ratio n(DMC):n(gallic acid) = 10:1), and Fe2O3-KCl / CaO catalyst Cat-A1 70 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Fe2O3-KCl / CaO catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 75.4%, the selectivity was 96.5%, and the chromatographic yield was 72.8%.

[0051] Example 9 Catalyst Cat-A, prepared in Example 1, was used. Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (600 mmol, 54.05 g, molar ratio n(DMC):n(gallic acid) = 30:1), and 170 mg of Cat-A catalyst were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was then set, and the temperature was raised to 200 °C for 8 h. After the reaction, the temperature was lowered, the mixture was filtered, and the filtrate was analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 99.6%, the selectivity was 92.5%, and the chromatographic yield was 92.1%.

[0052] Example 10 Catalyst Cat-A, prepared in Example 1, was used. Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and 170 mg of Cat-A catalyst were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. The back pressure was set to 4 MPa, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gases were released, and the mixture was filtered. The filtrate was then analyzed by liquid chromatography. The results showed that the conversion rate of gallic acid was 99.5%, the selectivity was 95.0%, and the chromatographic yield was 94.5%.

[0053] Comparative Example 1 Pure calcium oxide catalyst, denoted as Cat-O, was prepared using only 7.047 g (40.0 mmol Ca) of calcium acetate monohydrate as a precursor, without the addition of an iron source or potassium chloride, and employing the same sol-gel and calcination process as in Example 1.

[0054] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Fe2O3-KCl / CaO catalyst Cat-O 170 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Cat-O catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. HPLC analysis after the reaction showed that the conversion rate of gallic acid was 85.2%, but the selectivity for the target product was less than 5%, with the main products being 3,4,5-trimethoxybenzoic acid and the decarboxylation product 1,2,3-trimethoxybenzene. This result clearly demonstrates that a single calcium oxide basic support is completely ineffective in driving the esterification reaction and also causes a decarboxylation side reaction.

[0055] Comparative Example 2 Analytical pure CaO powder, Fe2O3 powder and KCl powder were physically ground and mixed in a mortar for 30 min according to the final elemental molar ratio (1:20:3) of Example 1 to obtain the physically mixed catalyst Cat-H.

[0056] Gallic acid (20.0 mmol, 3.402 g), dimethyl carbonate (400 mmol, 36.03 g, molar ratio n(DMC):n(gallic acid) = 20:1), and Fe2O3-KCl / CaO catalyst Cat-H 170 mg (5% of the mass of gallic acid) were added sequentially to a 100 mL stainless steel high-pressure reactor. The reactor was sealed, and the system was purged with nitrogen three times. A back pressure of 3 MPa was set, and the temperature was raised to 180 °C for 8 h. After the reaction, the temperature was lowered to room temperature, residual gas was released, and the Cat-H catalyst was filtered out. The filtrate was then analyzed by liquid chromatography. The results showed that the yield of the target product was less than 10.0%, and the decarboxylation byproducts increased significantly. This indicates that simple physical mixing cannot achieve effective synergistic catalysis, demonstrating that the compact composite structure constructed by the sol-gel method is crucial for achieving acid-base synergistic catalysis.

[0057] Based on the above experimental results, the Fe2O3-KCl / CaO bifunctional catalyst provided by this invention constructs highly dispersed and stable composite active centers via the sol-gel method, thereby successfully driving a tandem reaction using dimethyl carbonate as a green methylation reagent, achieving a one-step, efficient conversion of gallic acid to methyl 3,4,5-trimethoxybenzoate. The entire process is highly operable, operates under mild conditions, boasts high atom economy, and produces no harmful wastewater discharge, demonstrating significant advantages in green chemistry. This catalyst is the core of this technical system and is expected to provide a feasible solution for the clean production of methyl 3,4,5-trimethoxybenzoate.

[0058] In summary, this invention provides a method for preparing a Fe2O3-KCl / CaO catalyst, its application, and its innovative solution. By employing a sol-gel method to ingeniously construct an iron-potassium composite active center on a calcium oxide support, it innovatively solves the core challenge of the incompatibility and synergistic effect of acid-catalyzed methyl esterification and base-catalyzed methyl etherification mechanisms within the same system. This catalyst exhibits excellent catalytic efficiency in the synthesis of methyl 3,4,5-trimethoxybenzoate using dimethyl carbonate as a methylating agent, providing a novel technological route with significant industrial potential for the green and efficient synthesis of methyl 3,4,5-trimethoxybenzoate.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A method for preparing a Fe2O3-KCl / CaO catalyst, characterized in that, include: The CaO precursor, iron component precursor and potassium chloride were dissolved in water to obtain the precursor sol; The precursor sol was heated once, stirred, and citric acid was added. Then it was heated a second time to evaporate and dried to obtain a dry gel precursor. The dry gel precursor was calcined to obtain the Fe2O3-KCl / CaO catalyst.

2. The method for preparing the Fe2O3-KCl / CaO catalyst according to claim 1, characterized in that, In the Fe2O3-KCl / CaO catalyst, the molar ratio of iron, calcium and potassium is 1:(15-25):(2-4).

3. The method for preparing the Fe2O3-KCl / CaO catalyst according to claim 1, characterized in that, The CaO precursor is selected from one or more of calcium acetate monohydrate, calcium oxalate, and calcium nitrate.

4. The method for preparing the Fe2O3-KCl / CaO catalyst according to claim 1, characterized in that, The iron component precursor is selected from one or more of ferric nitrate, ferric chloride, and ferric citrate.

5. The method for preparing the Fe2O3-KCl / CaO catalyst according to claim 1, characterized in that, The molar ratio of citric acid to all metal ions in the precursor sol is (1.2-1.5):

1.

6. The method for preparing the Fe2O3-KCl / CaO catalyst according to claim 1, characterized in that, The temperature for the first heating is 75℃-85℃, and the temperature for the second heating and evaporation is 95℃-120℃.

7. The method for preparing the Fe2O3-KCl / CaO catalyst according to claim 1, characterized in that, The roasting temperature is 700℃-900℃, and the time is 4-8 hours.

8. A Fe2O3-KCl / CaO catalyst prepared using the method for preparing the Fe2O3-KCl / CaO catalyst according to any one of claims 1-7, characterized in that, The Fe2O3-KCl / CaO catalyst uses calcium oxide as the core support and alkaline component, with iron as the acidic center and potassium as the alkaline modulation center loaded on the calcium oxide.

9. The application of the Fe2O3-KCl / CaO catalyst according to claim 8 in the synthesis of methyl 3,4,5-trimethoxybenzoate, characterized in that, include: Gallic acid, dimethyl carbonate, and Fe2O3-KCl / CaO catalyst were mixed and reacted at 170℃-200℃ and a back pressure of 1-4MPa for 5-12 hours to obtain methyl 3,4,5-trimethoxybenzoate.

10. The application of the Fe2O3-KCl / CaO catalyst according to claim 9 in the synthesis of methyl 3,4,5-trimethoxybenzoate, characterized in that, The molar ratio of gallic acid to dimethyl carbonate is (1:10)-(1:30), and the amount of Fe2O3-KCl / CaO catalyst added is 1%-10% of the mass of gallic acid.

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