Preparation process for synthesizing carbonic ester compound through ester exchange

Abstract

The invention discloses a preparation process for synthesizing carbonic ester compounds through ester exchange, which comprises the following steps: dimethyl carbonate and diethylene glycol monobutyl ether are taken as raw materials, n-heptane and chloroform are taken as a composite solvent, potassium hydroxide is added, then ester exchange reaction is carried out, and the carbonic ester compounds are prepared, and the volume ratio of the n-heptane to the chloroform is 3: 1-4: 1; the composite solvent formed by the n-heptane and the chloroform can form a ternary azeotropic system with the reaction byproduct methanol, so that the distillation temperature of the methanol is reduced, a liquid separation device is facilitated to collect the methanol, and the reaction equilibrium is remarkably pushed to move rightwards; the n-heptane and chloroform composite solvent can reduce the loss of dimethyl carbonate and diethylene glycol monobutyl ether, potassium hydroxide can reduce the reaction temperature and improve the reaction rate, potassium hydroxide and the composite solvent system can synergistically improve the conversion rate of the raw materials, the yield of the carbonic ester compound is significantly improved, and the method is suitable for industrial production. The preparation method is simple and convenient to operate and is expected to realize industrial production.

Description

Technical Field

[0001] This invention relates to the field of transesterification technology, and more specifically to a process for preparing carbonate compounds through transesterification. Background Technology

[0002] In the field of green chemistry and functional materials, carbonate compounds are widely used in high-value-added niche products such as solvents, plasticizers, and electrolytes due to their excellent chemical stability, good solubility, and environmentally friendly properties. Traditional carbonate preparation is dominated by the phosgene process. This process, however, poses serious safety risks due to the highly toxic phosgene and corrosive byproducts, leading to equipment corrosion and environmental pollution. This directly contradicts the current green chemistry development philosophy. Therefore, developing low-toxicity, efficient, and sustainable carbonate synthesis routes has become a key technological challenge.

[0003] Transesterification, as a typical green organic synthesis technology, has advantages such as mild reaction conditions and easy separation of byproducts, and has gradually replaced the phosgene process as the mainstream process for carbonate synthesis. However, the transesterification reaction of dimethyl carbonate and diethylene glycol monobutyl ether is a reversible reaction. Limited by chemical equilibrium thermodynamics, after the reaction reaches equilibrium, the conversion rate of raw materials and the yield of the target carbonate will encounter significant bottlenecks, making it difficult to meet the efficiency and cost requirements of industrial production. Therefore, developing a technology that can break the original chemical equilibrium and drive the reaction towards the product direction is key to overcoming the efficiency bottleneck of transesterification reactions. In the synthesis of carbonate compounds from dimethyl carbonate and diethylene glycol monobutyl ether via transesterification, methanol is continuously generated as a byproduct during the transesterification process. When methanol is removed by distillation, a large amount of dimethyl carbonate and diethylene glycol monobutyl ether are also lost. This not only wastes raw materials but also severely restricts the shift of the reaction equilibrium towards the product direction, limiting the improvement of yield. Furthermore, the reaction system typically requires high temperatures and long reaction times, and the yield of the target product is low.

[0004] Therefore, there is an urgent need to develop a process for preparing carbonate compounds using dimethyl carbonate and diethylene glycol monobutyl ether as raw materials, in order to improve the conversion rate of raw materials and the yield of carbonate compounds. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a process for preparing carbonate compounds by transesterification, comprising: using dimethyl carbonate and diethylene glycol monobutyl ether as raw materials, and n-heptane and chloroform as a composite solvent, and adding potassium hydroxide to prepare the carbonate compounds via transesterification reaction, wherein the volume ratio of n-heptane to chloroform is 3:1-4:1; the composite solvent enables the continuous and efficient removal of methanol from the reaction system without the loss of large amounts of dimethyl carbonate and diethylene glycol monobutyl ether raw materials, thereby ensuring the effective concentration of the reactants in the reaction region, and by continuously reducing the methanol concentration, driving the chemical equilibrium to the right; at the same time, the selection of potassium hydroxide as a catalyst can reduce the reaction temperature and increase the reaction rate, and the potassium hydroxide and the composite solvent system can synergistically improve the raw material conversion rate and significantly improve the yield of carbonate compounds.

[0006] To achieve the above technical effects, the following technical solution is adopted: A method for preparing carbonate compounds by transesterification, using dimethyl carbonate and diethylene glycol monobutyl ether as raw materials, alkane solvent and chloroform as composite solvent, and potassium hydroxide added, is used to prepare the carbonates via transesterification reaction. The volume ratio of the alkane solvent to chloroform is 3:1-4:1. The reaction equation is as follows;

[0007] Furthermore, the alkane solvent is n-heptane; Furthermore, the amount of potassium hydroxide added is 0.5wt%-1wt% of the total weight of dimethyl carbonate and diethylene glycol monobutyl ether, and the potassium hydroxide is added in 3-4 portions during the reaction process; Furthermore, the molar ratio of dimethyl carbonate to diethylene glycol monobutyl ether is 1:2-1:3; Furthermore, the transesterification reaction temperature is 70 ℃-90 ℃; Furthermore, the transesterification reaction temperature is 75 °C; Furthermore, the transesterification reaction time is 2-4 h; Furthermore, the transesterification reaction time is 3 hours; Furthermore, the preparation method specifically includes the following steps: adding an alkane solvent and a chloroform azeotropic solvent to a reaction vessel, then adding dimethyl carbonate and diethylene glycol monobutyl ether; heating and stirring the reaction, and when the temperature reaches the reaction temperature, adding 1 / 3 of the total amount of potassium hydroxide catalyst, followed by adding 1 / 3 of the total amount of potassium hydroxide every half hour; the reaction vessel is connected to a liquid separation device, which continuously removes methanol generated during the reaction, and the separation device is connected to a condenser; after the reaction is completed, the product is obtained by cooling, washing, drying, and vacuum distillation to obtain monoester and diester products.

[0008] The present invention also provides carbonate compounds prepared by the above-described method for transesterification synthesis of carbonate compounds.

[0009] The beneficial effects of this invention are as follows: This invention utilizes n-heptane and chloroform as a composite solvent, with a liquid separation device connected to one end of the reaction vessel. This liquid separation device continuously removes methanol generated during the reaction. The significant polarity difference between n-heptane and chloroform and the reaction byproduct methanol allows the composite solvent to form a ternary azeotropic system with methanol, lowering the methanol distillation temperature and facilitating methanol collection by the liquid separation device. This shifts the reaction equilibrium to the right. Furthermore, the n-heptane and chloroform composite solvent reduces the loss of dimethyl carbonate and diethylene glycol monobutyl ether, allowing them to continue participating in the transesterification reaction within the system. Simultaneously, the potassium hydroxide catalyst lowers the reaction temperature and increases the reaction rate, synergistically improving the raw material conversion rate and significantly increasing the yield of carbonate compounds. The preparation method is simple and has the potential for industrial-scale production. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0011] Figure 1 This is a schematic diagram of the reaction apparatus in an embodiment of the present invention; Figure 2 The monoester product prepared in the embodiments of the present invention 1 H NMR spectrum; Figure 3 The monoester product prepared in the embodiments of the present invention 13 C NMR spectrum; Figure 4 The diester product prepared in the embodiments of the present invention 1 H NMR spectrum; Figure 5 The diester product prepared in the embodiments of the present invention 13 C10 NMR spectrum. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0013] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0014] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0015] This invention provides a technical solution: a method for preparing carbonate compounds by transesterification, using dimethyl carbonate and diethylene glycol monobutyl ether as raw materials, alkane solvent and chloroform as composite solvent, and potassium hydroxide added before transesterification reaction, wherein the volume ratio of alkane solvent to chloroform is 3:1-4:1; Furthermore, the alkane solvent is n-heptane; Furthermore, the amount of potassium hydroxide added is 0.5wt%-1wt% of the total weight of dimethyl carbonate and diethylene glycol monobutyl ether, and the potassium hydroxide is added in 3-4 portions during the reaction process; Furthermore, the molar ratio of dimethyl carbonate to diethylene glycol monobutyl ether is 1:2-1:3; Furthermore, the transesterification reaction temperature is 70 ℃-90 ℃; Furthermore, the transesterification reaction temperature is 75 °C; Furthermore, the transesterification reaction time is 2-4 h; Furthermore, the transesterification reaction time is 3 hours; Furthermore, the preparation method specifically includes the following steps: adding an alkane solvent and a chloroform azeotropic solvent to a reaction vessel, then adding dimethyl carbonate and diethylene glycol monobutyl ether; heating and stirring the reaction, and when the temperature reaches the reaction temperature, adding 1 / 3 of the total amount of potassium hydroxide catalyst, followed by adding 1 / 3 of the total amount of potassium hydroxide every half hour; the reaction vessel is connected to a liquid separation device, which continuously removes methanol generated during the reaction, and the separation device is connected to a condenser; after the reaction is completed, the product is obtained by cooling, washing, drying, and vacuum distillation to obtain monoester and diester products.

[0016] On the other hand, the present invention also provides carbonate compounds prepared by the above-described method for transesterification synthesis of carbonate compounds.

[0017] The embodiments of the present invention will be described in detail below. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation schemes and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0018] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0019] Example 1: like Figure 1 As shown, 120 mL of n-heptane and 40 mL of chloroform were added to a 500 mL dry two-necked flask. Then, 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether were added to the organic solvent. A magnetic stir bar was added. One end of the two-necked flask was connected to a liquid separator, which continuously removed methanol generated during the reaction, shifting the reaction equilibrium to the right. A condenser was connected to the separator, and the other end was plugged. The two-necked flask was heated and stirred in an oil bath until the temperature reached 75 °C. 0.3 g of potassium hydroxide was added as a catalyst. After reacting at 75 °C for half an hour, another 0.3 g of potassium hydroxide was added. After reacting for one hour, another 0.3 g of potassium hydroxide was added. The system reacted at 75 °C for a total of 3 hours. After the reaction was completed, the reaction mixture was cooled, washed four times with deionized water, and dried overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to distill was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and the amounts of the monoester, diester products, and the raw material dimethyl carbonate were calculated. The yields were then calculated using the following formulas:

[0020]

[0021] In the formula: C1 is the yield of the monoester product, C2 is the yield of the diester product, C3 is the total ester yield, n1 is the amount of the monoester product, n2 is the amount of the diester product, and n3 is the amount of the reactant dimethyl carbonate.

[0022] The yields of the monoester products prepared in Example 1 were calculated to be 52.0%, the yields of the diester products were 47.2%, and the total ester yield was 99.2%.

[0023] Figure 2-3 The monoester product prepared in Example 1 13 C NMR spectrum and 1 H NMR spectrum Figure 4-5 The diester product prepared in Example 1 13 C NMR spectrum and 1 H NMR spectrum; from Figure 2-5 The products obtained by this invention are di(diethylene glycol monobutyl ether) ester and diethylene glycol monobutyl ether ester.

[0024] Example 2 Add 128 mL of n-heptane and 32 mL of chloroform to a 500 mL dry two-necked flask. Then add 15 g of dimethyl carbonate and 80 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the liquid separator. Seal the other end of the liquid separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 70 °C, add 0.2 g of potassium hydroxide as a catalyst. After reacting at 70 °C for half an hour, add another 0.2 g of potassium hydroxide. After reacting for one hour, add another 0.2 g of potassium hydroxide. The system reacts at 70 °C for a total of 2 hours. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 47.8%, the yield of the diester product was 44.5%, and the total ester yield was 92.3%.

[0025] Example 3 Add 120 mL of n-heptane and 40 mL of chloroform to a 500 mL dry two-necked flask. Then add 20 g of dimethyl carbonate and 90 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the separator. Seal the other end of the separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 75 °C, add 0.2 g of potassium hydroxide as a catalyst. After reacting at 75 °C for half an hour, add another 0.2 g of potassium hydroxide. After reacting for one hour, add another 0.2 g of potassium hydroxide. The system reacts at 75 °C for a total of 2.5 h. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 52.8%, the yield of the diester product was 44.0%, and the total ester yield was 96.8%.

[0026] Comparative Example 1 Add 120 mL of n-heptane and 40 mL of chloroform to a 500 mL dry two-necked flask. Then add 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the separator. Seal the other end of the separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 75 °C, add 0.3 g of sodium hydroxide as a catalyst. After reacting at 75 °C for half an hour, add another 0.3 g of sodium hydroxide. After reacting for one hour, add another 0.3 g of sodium hydroxide. The system reacts at 75 °C for a total of 3 hours. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 43.0%, the yield of the diester product was 29.4%, and the total ester yield was 72.4%.

[0027] Comparative Example 2 Add 120 mL of n-heptane and 40 mL of chloroform to a 500 mL dry two-necked flask. Then add 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the separator. Seal the other end of the separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 90 °C, add 0.3 g of potassium carbonate as a catalyst. After reacting at 90 °C for half an hour, add another 0.3 g of potassium carbonate. After reacting for one hour, add another 0.3 g of potassium carbonate. The system reacts at 90 °C for a total of 4 hours. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 36.5%, the yield of the diester product was 27.7%, and the total ester yield was 64.2%.

[0028] Comparative Example 3 Add 120 mL of n-heptane and 40 mL of chloroform to a 500 mL dry two-necked flask. Then add 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the separator. Seal the other end of the separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 75 °C, add 0.3 g of sodium methoxide as a catalyst. After reacting at 75 °C for half an hour, add another 0.3 g of sodium methoxide. After reacting for one hour, add another 0.3 g of sodium methoxide. The system reacts at 75 °C for a total of 3 hours. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 39.2%, the yield of the diester product was 31.5%, and the total ester yield was 70.7%.

[0029] Comparative Example 4 160 mL of n-heptane was added to a 500 mL dry two-necked flask. Then, 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether were added to the organic solvent. A magnetic stir bar was added. One end of the flask was connected to a liquid separator, which continuously removed methanol generated during the reaction, shifting the reaction equilibrium to the right. A condenser was connected to the separator. The other end was plugged. The flask was heated and stirred in an oil bath until the temperature reached 75 °C. 0.3 g of potassium hydroxide was added as a catalyst. After reacting at 75 °C for half an hour, another 0.3 g of potassium hydroxide was added. After reacting for one hour, another 0.3 g of potassium hydroxide was added. The system reacted at 75 °C for a total of 3 hours. After the reaction was complete, the reaction mixture was allowed to cool, washed four times with deionized water, and dried overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 35.7%, the yield of the diester product was 27.7%, and the total ester yield was 63.4%.

[0030] Comparative Example 5 160 mL of chloroform was added to a 500 mL dry two-necked flask. Then, 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether were added to the organic solvent. A magnetic stir bar was added. One end of the flask was connected to a liquid separator, which continuously removed methanol generated during the reaction, shifting the reaction equilibrium to the right. A condenser was connected to the separator. The other end was plugged. The flask was heated and stirred in an oil bath until the temperature reached 75 °C. 0.3 g of potassium hydroxide was added as a catalyst. After reacting at 75 °C for half an hour, another 0.3 g of potassium hydroxide was added. After reacting for one hour, another 0.3 g of potassium hydroxide was added. The system reacted at 75 °C for a total of 3 hours. After the reaction was complete, the reaction mixture was allowed to cool, washed four times with deionized water, and dried overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 22.6%, the yield of the diester product was 14.7%, and the total ester yield was 37.3%.

[0031] Comparative Example 6 Add 120 mL of n-hexane and 40 mL of chloroform to a 500 mL dry two-necked flask. Then add 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the separator. Seal the other end of the separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 75 °C, add 0.3 g of potassium hydroxide as a catalyst. After reacting at 75 °C for half an hour, add another 0.3 g of potassium hydroxide. After reacting for one hour, add another 0.3 g of potassium hydroxide. The system reacts at 75 °C for a total of 3 hours. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 43.0%, the yield of the diester product was 29.3%, and the total ester yield was 72.3%.

[0032] Comparative Example 7 Add 120 mL of toluene and 40 mL of chloroform to a 500 mL dry two-necked flask. Then add 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the separator. Seal the other end of the separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 75 °C, add 0.3 g of potassium hydroxide as a catalyst. After reacting at 75 °C for half an hour, add another 0.3 g of potassium hydroxide. After reacting for one hour, add another 0.3 g of potassium hydroxide. The system reacts at 75 °C for a total of 3 hours. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 34.1%, the yield of the diester product was 19.5%, and the total ester yield was 53.6%.

[0033] Comparative Example 8 Add 120 mL of benzene and 40 mL of chloroform to a 500 mL dry two-necked flask. Then add 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether to the organic solvent. Add a magnetic stir bar. Connect one end of the two-necked flask to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. Connect a condenser to the separator. Seal the other end of the separator. Heat and stir the two-necked flask in an oil bath. When the temperature reaches 75 °C, add 0.3 g of potassium hydroxide as a catalyst. After reacting at 75 °C for half an hour, add another 0.3 g of potassium hydroxide. After reacting for one hour, add another 0.3 g of potassium hydroxide. The system reacts at 75 °C for a total of 3 hours. After the reaction is complete, allow the reaction mixture to cool, wash four times with deionized water, and dry overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 30.6%, the yield of the diester product was 25.0%, and the total ester yield was 55.6%.

[0034] Comparative Example 9 This embodiment provides a process for the preparation of carbonate compounds by transesterification, comprising the following steps: 120 mL of n-heptane and 40 mL of benzene are added to a 500 mL dry two-necked flask. Then, 17 g of dimethyl carbonate and 73 g of diethylene glycol monobutyl ether are added to the organic solvent. A magnetic stir bar is added. One end of the two-necked flask is connected to a liquid separator, which continuously removes methanol generated during the reaction, shifting the reaction equilibrium to the right. A condenser is connected to the separator, and the other end is plugged. An oil bath is turned on to heat and stir the two-necked flask. When the temperature reaches 75°C, 0.3 g of potassium hydroxide is added as a catalyst. After reacting at 75°C for half an hour, another 0.3 g of potassium hydroxide is added. After reacting for one hour, another 0.3 g of potassium hydroxide is added. The system reacts at 75°C for a total of 3 hours. After the reaction is complete, the reaction mixture is cooled, washed four times with deionized water, and dried overnight with anhydrous magnesium sulfate. The desiccant was then removed by filtration, and low-boiling-point solvents and raw materials were removed by rotary evaporation. Finally, the mixture was distilled under reduced pressure using an oil pump. Different fractions were obtained depending on the temperature. The first fraction to be distilled was the excess unreacted raw material, followed by the monoester product, and finally the diester product. The monoester and diester products were weighed separately, and their yields were calculated. The yield of the monoester product was 35.7%, the yield of the diester product was 31.7%, and the total ester yield was 67.4%.

[0035] As can be seen from the above examples and comparative examples, Examples 1-3 of the present invention use n-heptane and chloroform as a composite solvent and potassium hydroxide as a catalyst, which can synergistically improve the yield of esterification products, with a total ester yield greater than 90%. Among them, the total ester yield of Example 1 can reach 99.2%, which is significantly greater than the total ester yield of Comparative Examples 1-9. Furthermore, the use of the above solvent and catalyst can reduce the reaction temperature and reaction time. The composite solvent formed by n-heptane and chloroform in the present invention can reduce the loss of dimethyl carbonate and diethylene glycol monobutyl ether. The n-heptane and chloroform composite solvent can form a ternary azeotropic system with methanol, which reduces the distillation temperature of the by-product methanol, which is beneficial for the collection of methanol by liquid separation device and significantly pushes the reaction equilibrium to the right. At the same time, the selection of potassium hydroxide as a catalyst can reduce the reaction temperature and increase the reaction rate. Together with the composite solvent system, it can synergistically improve the conversion rate of raw materials and significantly improve the yield of carbonate compounds.

[0036] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A method for preparing carbonate compounds by transesterification, characterized in that, It is prepared by transesterification reaction using dimethyl carbonate and diethylene glycol monobutyl ether as raw materials, alkane solvent and chloroform as composite solvent, and potassium hydroxide is added. The volume ratio of alkane solvent to chloroform is 3:1-4:

1.

2. The method for preparing carbonate compounds by transesterification as described in claim 1, characterized in that, The alkane solvent is n-heptane.

3. The method for preparing carbonate compounds by transesterification as described in claim 1, characterized in that, The amount of potassium hydroxide added is 0.5wt%-1wt% of the total weight of dimethyl carbonate and diethylene glycol monobutyl ether, and the potassium hydroxide is added in 3-4 portions during the reaction.

4. The method for preparing carbonate compounds by transesterification as described in claim 1, characterized in that, The molar ratio of dimethyl carbonate to diethylene glycol monobutyl ether is 1:2 to 1:

3.

5. The method for preparing carbonate compounds by transesterification as described in claim 1, characterized in that, The transesterification reaction temperature is 70 ℃-90 ℃.

6. The method for preparing carbonate compounds by transesterification as described in claim 5, characterized in that, The transesterification reaction temperature is 75 °C.

7. The method for preparing carbonate compounds by transesterification as described in claim 1, characterized in that, The transesterification reaction time is 2-4 h.

8. The method for preparing carbonate compounds by transesterification as described in claim 1, characterized in that, The transesterification reaction time was 3 hours.

9. The method for preparing carbonate compounds by transesterification as described in claims 1-8, characterized in that, The preparation method specifically includes the following steps: adding an alkane solvent and a chloroform composite solvent to a reaction vessel, then adding dimethyl carbonate and diethylene glycol monobutyl ether, heating and stirring the reaction, and when the temperature reaches the reaction temperature, adding 1 / 3 of the total amount of potassium hydroxide, followed by adding 1 / 3 of the total amount of potassium hydroxide every half hour; the reaction vessel is connected to a liquid separation device, which continuously removes methanol generated during the reaction, and the separation device is connected to a condenser; after the reaction is completed, the monoester and diester products are obtained through cooling, washing, drying, and vacuum distillation.

10. Carbonate compounds prepared by the transesterification synthesis method for carbonate compounds as described in claims 1-9.

Images