A method for preparing alkyl gallate without using aqueous agent
By optimizing reaction parameters and utilizing the binary azeotropic properties of alkyl alcohols and water, the efficient synthesis of alkyl gallic acid esters was achieved, solving the problems of high cost, low purity, and complex process caused by the use of water-carrying agents, and realizing green and efficient production of alkyl gallic acid esters.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GALLOCHEM CO LTD
- Filing Date
- 2026-04-03
- Publication Date
- 2026-07-03
AI Technical Summary
In the existing synthesis process of alkyl gallic acid esters, the use of dehydrating agents increases production costs, leads to decreased product purity, complicated process flow, environmental pollution and safety hazards, and makes it difficult to achieve standardized and large-scale production.
A dehydrating agent-free preparation method is adopted. By optimizing the reaction system parameters and utilizing the binary azeotropic properties of alkyl alcohol and water, water is efficiently separated, and alkyl gallic acid esters are directly synthesized. This method avoids the use of dehydrating agents, simplifies the process, and improves production efficiency.
It significantly reduces total production costs, simplifies the process, increases production efficiency by more than 40%, and achieves a product purity of up to 99.2%. It is highly adaptable and suitable for the efficient synthesis of various gallic acid alkyl esters, meeting the requirements of green chemical production.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of chemical reaction technology, specifically relating to a method for preparing alkyl gallic acid esters without the need for a dehydrating agent. Background Technology
[0002] Alkyl gallate esters are an important class of natural phenolic antioxidants, widely used in food, cosmetics, pharmaceuticals, and fine chemicals. Common products include methyl gallate, ethyl gallate, propyl gallate, octyl gallate, and lauryl gallate. Their core structure is an alkyl ester compound formed by the esterification reaction of gallic acid with the corresponding alkyl alcohol. The general formula is as follows:
[0003]
[0004] R represents an alkyl group (such as n-propyl, n-octyl, lauryl, etc.).
[0005] In the traditional esterification synthesis process of gallic acid alkyl esters, water is generated in the reaction system. The accumulation of water significantly inhibits the forward esterification reaction, reducing product conversion and purity. Therefore, existing processes generally require the addition of organic solvents such as xylene or cyclohexane as dehydrating agents, achieving water separation by forming an azeotrope with the water. However, the use of dehydrating agents has several technical drawbacks:
[0006] 1) The purchase and storage of water-removing agents increased the cost of raw materials for production, and the recycling and reuse of water-removing agents required additional investment in equipment and process costs, which increased the overall production cost.
[0007] 2) The water-removing agent is easy to mix with the esterification product, which leads to a decrease in product purity. Subsequent separation and purification steps such as distillation and extraction are required, which makes the process complicated, time-consuming and reduces production efficiency.
[0008] 3) Water-removing agents are mostly volatile, and some are also corrosive, which can easily pollute the production environment, cause damage to production equipment, and pose VOC emissions and safety operation hazards.
[0009] 4) The synthesis of different gallic acid alkyl esters requires different amounts of dehydrating agent, resulting in poor process adaptability and making it difficult to achieve standardized and large-scale production.
[0010] Currently, research on the synthesis of alkyl gallic acid esters mainly focuses on catalyst optimization or replacement of dehydrating agents. There is no synthesis process that directly eliminates the need for dehydrating agents and utilizes the azeotropic properties of alcohols and water to achieve efficient water separation. Existing systems are highly dependent on dehydrating agents, failing to meet the demands of green, efficient, low-cost, and standardized industrial production. Therefore, developing a process that requires no dehydrating agents, is compatible with the synthesis of various alkyl gallic acid esters, and has high reaction efficiency has become a critical problem urgently needing to be solved in this field. Summary of the Invention
[0011] The purpose of this invention is to provide a method for preparing alkyl gallic acid esters without using a dehydrating agent, which solves the problems of high cost of using dehydrating agents, pollution products, and complicated processes in the prior art, and achieves green, efficient, and low-cost chemical production.
[0012] The technical solution adopted in this invention is a method for preparing alkyl gallic acid esters without the need for a dehydrating agent, comprising the following steps:
[0013] Step 1: Weigh out the specified amounts of gallic acid, alkyl alcohol, and acidic catalyst, and mix the three raw materials directly and stir until homogeneous;
[0014] Step 2: Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device, control the stirring speed at 300-500 r / min, control the oil bath temperature at 80-140℃, control the condensate separation rate at 5-70 g per hour by adjusting the opening of the water separator valve, dissolve for 3-80 minutes to completely dissolve gallic acid; continue the reaction until the product indicators are stable.
[0015] Step 3: After the reaction is complete, stop the separation of condensate, collect the product in the reaction vessel, and complete the preparation of alkyl gallate under the condition of no dehydrating agent. After evaporating the residual solvent by rotary evaporator, add water for recrystallization to remove residual sulfuric acid, and obtain the alkyl gallate product by vacuum filtration.
[0016] Furthermore, in step one above, based on the amount of gallic acid fed, the amount of acidic catalyst is 1% to 15% of the mass of gallic acid, and the amount of alkyl alcohol is 8 to 30 times the corresponding molar amount of gallic acid; the alkyl alcohol is methanol, ethanol, n-propanol, n-octanol, or lauryl alcohol.
[0017] Furthermore, the oil bath temperatures corresponding to the different alkyl alcohols mentioned above are: methanol 100-110℃, ethanol 105-115℃, n-propanol 100-120℃, n-octanol 120-130℃, and lauryl alcohol 130-140℃.
[0018] Furthermore, in step two above, the condensate separation rate is 15–70 g per hour; the gallic acid dissolution time is 3–5 min.
[0019] Furthermore, in step two above, the product indicators stabilize when the ratio of alkyl gallate content to unreacted gallic acid content in the product no longer changes significantly.
[0020] Furthermore, the condensate in step two above is a mixture of alcohol and water, and does not need to be separated and discharged separately.
[0021] A method for preparing alkyl gallate without using a dehydrating agent to obtain an alkyl gallate product, characterized in that the product includes methyl gallate, ethyl gallate, propyl gallate, octyl gallate, and lauryl gallate.
[0022] Compared with the prior art, the beneficial effects of the present invention are that, by scientifically optimizing the reaction system parameters, the present invention eliminates the need to gradually reduce the amount of dehydrating agent and abandons the use of dehydrating agent. It utilizes the binary azeotropic properties of alkyl alcohol and water to achieve efficient separation of reaction water, directly achieving the same or even better water separation and reaction promotion effects without the use of dehydrating agent. It fundamentally solves the problems of high raw material costs, product contamination, and cumbersome subsequent separation caused by dehydrating agent, significantly reducing the total production cost, simplifying the process flow, and improving production efficiency by more than 40%.
[0023] Secondly, this method has strong process adaptability and can be standardized for the synthesis of methyl gallate, ethyl gallate, propyl gallate, octyl gallate, and lauryl gallate. The efficient synthesis of different products can be achieved simply by adjusting the amount of alkyl alcohol and the temperature of the oil bath. The product purity can reach up to 99.2%, the yield is stable, and the reaction effect is better than or equivalent to the traditional process using a dehydrating agent.
[0024] In addition, by precisely controlling the condensate separation rate and reaction parameters, gallic acid can be rapidly dissolved (as short as 3 minutes), significantly shortening the reaction time. The synthesis reaction time of different products is reduced by 40% to 60% compared with the traditional dehydrating agent process, further improving industrial production efficiency.
[0025] In addition, this invention requires no new complex production equipment; the process can be implemented simply by adjusting the parameters of existing esterification reaction equipment. It is easy to operate, scale up industrially, and standardize production, reducing equipment modification costs. Furthermore, it avoids the volatilization, corrosion, and pollution problems associated with water-carrying agents, reducing pollutant emissions and improving the safety and environmental friendliness of the production process. This aligns with the development trend of green chemical production. The product has no water-carrying agent residue, enhancing its safety for application in the food, cosmetics, and pharmaceutical fields. Detailed Implementation
[0026] The present invention will be further explained below to enable those skilled in the art to better understand it.
[0027] A method for preparing alkyl gallic acid esters without the need for a dehydrating agent includes the following steps:
[0028] Step 1: Based on the amount of gallic acid added, weigh gallic acid, alkyl alcohol, and acidic catalyst according to the proportions. The alkyl alcohols correspond to methanol, ethanol, n-propanol, n-octanol, and lauryl alcohol. The amount of acidic catalyst is 1% to 15% of the mass of gallic acid, and the amount of alkyl alcohol is 8 to 30 times the corresponding molar amount of gallic acid. Mix the three raw materials directly and stir evenly.
[0029] Step 2: Add the mixed raw materials to a three-necked round-bottom flask, place the flask in an oil bath, and start the stirring device to stir the mixed raw materials. The stirring speed should be controlled at 300-500 r / min, and the oil bath temperature should be controlled at 80-140℃. The corresponding oil bath temperatures for different alkyl alcohols are: methanol 100-110℃, ethanol 105-115℃, n-propanol 100-120℃, n-octanol 120-130℃, and lauryl alcohol 130-140℃. By adjusting the opening of the water separator valve, control the condensate separation rate to 5-70 g per hour, and dissolve for 3-80 minutes to ensure complete dissolution of gallic acid. Continue the reaction until the product indicators are stable, that is, the ratio of alkyl gallic acid ester content to unreacted gallic acid content in the product no longer changes significantly.
[0030] Furthermore, the condensate separation rate is 15–70 g per hour; the gallic acid dissolution time is 3–5 min.
[0031] Step 3: After the reaction is complete, stop the separation of condensate, collect the product in the reaction vessel, and complete the preparation of alkyl gallate under the condition of no dehydrating agent. After evaporating the residual solvent by rotary evaporator, add water for recrystallization to remove residual sulfuric acid, and obtain the alkyl gallate product by vacuum filtration.
[0032] Experimental materials and equipment
[0033] Raw materials: gallic acid (purity ≥99%), methanol (purity ≥99%), ethanol (purity ≥99%), n-propanol (purity ≥98%), n-octanol (purity ≥98%), lauryl alcohol (purity ≥98%), and 98% sulfuric acid, all of which are commercially available industrial-grade raw materials; no water-retaining agents are used throughout the process.
[0034] Equipment: electric constant temperature oil bath, electric stirring device, serpentine condenser, 1000ml three-necked round bottom flask, water separator, electronic balance (accuracy 0.01g), timer, precision thermometer, tachometer, iron stand, iron clamp, rubber stopper, tubing, rotary evaporator.
[0035] The applicant prepared propyl gallate, methyl gallate, ethyl gallate, octyl gallate, and lauryl gallate respectively according to the above methods, with the specific operations as follows:
[0036] Example 1
[0037] Preparation of propyl gallate
[0038] Weigh out 50g of gallic acid, 200g of n-propanol, and 3.35g of 98% sulfuric acid. Mix the three raw materials directly without adding any water-retaining agents and stir until homogeneous.
[0039] Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device to stir the mixed raw materials at a speed of 300 r / min, control the oil bath temperature at 100℃, control the condensate separation rate at 15 g per hour by adjusting the opening of the water separator valve, monitor the dissolution of gallic acid, and record the complete dissolution time as 3 min.
[0040] Maintain the oil bath temperature at 100℃, the stirring speed at 300r / min, and the condensate separation rate at 15g per hour, and continue the reaction until the product indicators are stable.
[0041] Data analysis: After 6 hours of reaction, the reaction was stopped and cooled, the product was collected and purified to obtain 53.2g of propyl gallate. The purity of the product was tested to be 98.3%. Based on the pure product, the mass reaction rate was 8.72g / h and the molar reaction rate was 0.0411mol / h. The traditional dehydrating agent process requires 11 hours of reaction to achieve the same purity, while the reaction time of this process is shortened by more than 45%.
[0042] Example 2
[0043] Preparation of methyl gallate
[0044] Weigh out 50g of gallic acid, 250g of methanol, and 3.35g of 98% sulfuric acid. Mix the three raw materials directly without adding any water-removing agent and stir until uniform.
[0045] Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device to stir the mixed raw materials at a speed of 350 r / min, control the oil bath temperature at 105℃, adjust the condensate separation rate to 25 g per hour, monitor the dissolution of gallic acid, and record the complete dissolution time as 4 min.
[0046] Maintain the oil bath temperature at 105℃, the stirring speed at 350r / min, and control the condensate separation rate at 25g per hour by adjusting the opening of the water separator valve, and continue the reaction until the product indicators are stable.
[0047] Data analysis: After 5 hours of reaction, the reaction was stopped and cooled, the product was collected and purified to obtain 51.5g of methyl gallate product. The purity of the product was 98.4%. Based on the pure product, the mass reaction rate was 10.15 g / h and the molar reaction rate was 0.0551 mol / h. The traditional dehydrating agent process requires 10 hours of reaction to achieve the same purity, while this process shortens the reaction time by 50%.
[0048] Example 3
[0049] Preparation of ethyl gallate
[0050] Weigh out 50g of gallic acid, 250g of ethanol, and 3.35g of 98% sulfuric acid. Mix the three raw materials directly without adding any water-retaining agent and stir until uniform.
[0051] Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device to stir the mixed raw materials at a speed of 300 r / min, control the oil bath temperature at 110℃, control the condensate separation rate at 20 g per hour by adjusting the opening of the water separator valve, monitor the dissolution of gallic acid, and record the complete dissolution time as 3 min.
[0052] Maintain the oil bath temperature at 110℃, the stirring speed at 300r / min, and the condensate separation rate at 20g per hour, and continue the reaction until the product indicators are stable.
[0053] Data analysis: After 5.5 hours of reaction, the reaction was stopped and the temperature was lowered. The product was collected and purified to obtain 52.3g of ethyl gallate. The purity of the product was 98.2%. Based on the pure product, the mass reaction rate was 9.40 g / h and the molar reaction rate was 0.0474 mol / h. The traditional dehydrating agent process requires 10.5 hours of reaction to achieve the same purity. This process shortens the reaction time by 48%.
[0054] Example 4
[0055] Preparation of octyl gallate
[0056] Weigh out 50g of gallic acid, 380g of n-octanol, and 3.35g of 98% sulfuric acid. Mix the three raw materials directly without adding any water-retaining agent and stir until uniform.
[0057] Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device to stir the mixed raw materials at a speed of 400 r / min, control the oil bath temperature at 125℃, control the condensate separation rate at 18 g per hour by adjusting the opening of the water separator valve, monitor the dissolution of gallic acid, and record the complete dissolution time as 5 min.
[0058] Maintain the oil bath temperature at 125℃, the stirring speed at 400r / min, and the condensate separation rate at 18g per hour, and continue the reaction until the product indicators are stable.
[0059] Data analysis: After 7 hours of reaction, the reaction was stopped and cooled. The product was collected and purified to obtain 55.8g of octyl gallate. The purity of the product was 99.0%. Based on the pure product, the mass reaction rate was 7.89 g / h and the molar reaction rate was 0.0279 mol / h. The traditional dehydrating agent process requires 15 hours of reaction to achieve the same purity, while this process shortens the reaction time by 53%.
[0060] Example 5
[0061] Preparation of lauryl gallate
[0062] Weigh out 50g of gallic acid, 520g of lauryl alcohol, and 3.35g of 98% sulfuric acid. Mix the three ingredients directly without adding any water-retaining agents and stir until homogeneous.
[0063] Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device to stir the mixed raw materials at a speed of 500 r / min, control the oil bath temperature at 135℃, control the condensate separation rate at 15 g per hour by adjusting the opening of the water separator valve, monitor the dissolution of gallic acid, and record the complete dissolution time as 5 min.
[0064] Maintain the oil bath temperature at 135℃, the stirring speed at 500r / min, and the condensate separation rate at 15g per hour, and continue the reaction until the product indicators are stable.
[0065] Data analysis: After 8 hours of reaction, the reaction was stopped and cooled. The product was collected and purified to obtain 56.8g of lauryl gallate. The purity of the product was 98.4%. Based on the pure product, the mass reaction rate was 7.01 g / h and the molar reaction rate was 0.0207 mol / h. The traditional dehydrating agent process requires 18 hours of reaction to achieve the same purity, while this process shortens the reaction time by 56%.
[0066] Example 6
[0067] Preparation of propyl gallate
[0068] Weigh out 50g of gallic acid, 401g of n-propanol, and 3.35g of 98% sulfuric acid. Mix the three raw materials directly without adding any water-removing agent and stir until uniform.
[0069] Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device to stir the mixed raw materials at a speed of 300 r / min, control the oil bath temperature at 120℃, control the condensate separation rate at 70 g per hour by adjusting the opening of the water separator valve, monitor the dissolution of gallic acid, and record the complete dissolution time as 3 min.
[0070] Maintain the oil bath temperature at 120℃, the stirring speed at 300r / min, and the condensate separation rate at 70g per hour, and continue the reaction until the product indicators are stable.
[0071] Data analysis: After 4 hours of reaction, the reaction was stopped and the temperature was lowered. The product was collected and purified to obtain 54.1g of propyl gallate. The purity of the product was 99.2%. Based on the pure product, the mass reaction rate was 13.42 g / h and the molar reaction rate was 0.0632 mol / h, which is the highest purity among all examples. Compared with the traditional dehydrating agent process, the reaction time was shortened by 64% and the purity was increased by more than 1.5%.
[0072] Through the experimental verification of Examples 1 to 6 above, the method for preparing alkyl gallate without dehydrating agent provided by the present invention does not require the addition of any dehydrating agent. By utilizing the binary azeotropic properties of alkyl alcohol and water, and by optimizing the raw material ratio, precisely controlling the oil bath temperature, stirring rate and condensate separation rate, the efficient synthesis of methyl gallate, ethyl gallate, propyl gallate, octyl gallate and lauryl gallate is achieved.
[0073] The optimal synthesis conditions for each product are as follows: alkyl alcohol is selected in the corresponding preferred amount, the condensate separation rate is controlled at 15-70g per hour, the gallic acid dissolution time is controlled at 3-5min, and the oil bath temperature is matched with the alkyl alcohol type within the preferred range of 80-140℃. Under these conditions, the synthesis reaction time of each product is shortened by 40%-64% compared with the traditional dehydrating agent process, the product purity can reach up to 99.2% (propyl gallate), the single batch yield is stable at 51.5-56.8g, and there is no dehydrating agent residue in the product.
[0074] Compared with traditional processes using water-carrying agents, this process not only significantly reduces the cost of raw materials and equipment and simplifies the process flow, but also significantly improves product purity and production efficiency. Simultaneously, it avoids the environmental and equipment problems associated with water-carrying agents, aligning with the trend of green chemical production. This process requires no new complex equipment, is simple to operate, and can be standardized for the industrial-scale synthesis of various gallic acid alkyl esters, possessing extremely high practical application value and market potential.
[0075] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit and principles thereof should fall within the protection scope defined by the claims of the present invention.
Claims
1. A process for the preparation of alkyl gallate without using aqueous agent, characterized in that, Includes the following steps: Step 1: Weigh out the specified amounts of gallic acid, alkyl alcohol, and acidic catalyst, and mix the three raw materials directly and stir until homogeneous; Step 2: Add the mixed raw materials to a three-necked round-bottom flask, place the three-necked round-bottom flask in an oil bath, start the stirring device, control the stirring speed at 300-500 r / min, control the oil bath temperature at 80-140℃, control the condensate separation rate at 5-70 g per hour by adjusting the opening of the water separator valve, dissolve for 3-80 minutes to completely dissolve gallic acid; continue the reaction until the product indicators are stable. Step 3: After the reaction is complete, stop the separation of condensate, collect the product in the reaction vessel, and complete the preparation of alkyl gallate under the condition of no dehydrating agent. After evaporating the residual solvent by rotary evaporator, add water for recrystallization to remove residual sulfuric acid, and obtain the alkyl gallate product by vacuum filtration.
2. A process for the preparation of alkyl gallate without using aqueous agent as claimed in claim 1, wherein, Step 1 uses gallic acid as the basis, with the amount of acidic catalyst being 1% to 15% of the mass of gallic acid, and the amount of alkyl alcohol being 8 to 30 times the corresponding molar amount of gallic acid; the alkyl alcohol is methanol, ethanol, n-propanol, n-octanol, or lauryl alcohol.
3. The method for preparing alkyl gallic acid ester without a dehydrating agent according to claim 2, characterized in that, The corresponding oil bath temperatures for different alkyl alcohols are: methanol 100-110℃, ethanol 105-115℃, n-propanol 100-120℃, n-octanol 120-130℃, and lauryl alcohol 130-140℃.
4. The method for preparing alkyl gallic acid ester without a dehydrating agent according to claim 1, characterized in that, In step two, the condensate separation rate is 15–70 g per hour; the gallic acid dissolution time is 3–5 min.
5. In the preparation method of alkyl gallic acid ester without dehydrating agent according to claim 1, the product index in step two is stabilized when the ratio of alkyl gallic acid ester content to unreacted gallic acid content in the product no longer changes significantly.
6. The alkyl gallic acid ester product obtained by the method for preparing alkyl gallic acid esters without a dehydrating agent according to any one of claims 1 to 5, characterized in that, The products include methyl gallate, ethyl gallate, propyl gallate, octyl gallate, and lauryl gallate.