A process for the preparation of diphenyl carbonate

Abstract

The application belongs to the technical field of organic synthesis and relates to a method for preparing diphenyl carbonate. The method uses a deep eutectic solvent (DES) as a catalyst to catalyze the one-pot reaction of CO2, carbon tetrachloride and phenol in the presence of an organic solvent, and the reaction conditions are as follows: the initial pressure of CO2 is 1-6 MPa, the temperature is 100-160 DEG C, and the time is 6-12 h. After the reaction, the layers are separated by standing, the lower layer DES can be directly recycled, the upper layer product phase is subjected to rectification to remove the organic solvent to obtain diphenyl carbonate, and the organic solvent can be recycled. The application solves the problems of difficult recovery of the catalyst, many by-products and low yield in the traditional method, has the advantages of high product purity, recyclable catalyst and solvent and simple operation, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing diphenyl carbonate by catalyzing the one-pot reaction of CO2, carbon tetrachloride and phenol in the presence of an organic solvent using DES as a catalyst. Background Technology

[0002] Diphenyl carbonate (DPC), an important organic carbonate, is one of the core raw materials for the synthesis of polycarbonate (PC). Polycarbonate, due to its excellent mechanical properties, light transmittance, and heat resistance, is widely used in many fields such as electronics, automobile manufacturing, building materials, and medical devices. In addition, diphenyl carbonate can also be used to synthesize various organic compounds, such as pharmaceutical intermediates and pesticide adjuvants, and also has certain applications as a plasticizer and solvent.

[0003] Currently, the main methods for preparing diphenyl carbonate include the phosgene method and the transesterification method. The phosgene method is a traditional method, using phosgene and phenol as raw materials. Although the process is relatively mature, phosgene is highly toxic, and the reaction produces a large amount of corrosive byproducts, requiring sophisticated equipment, and has been gradually phased out. The transesterification method mainly involves the transesterification of dimethyl carbonate (DMC) with phenol. This method uses low-toxicity raw materials and the products are easily separated, but the reactions are mostly reversible with low equilibrium conversion rates. Continuous product separation is necessary to increase the yield, increasing the complexity and cost of the process. Furthermore, the reaction typically requires high temperatures and pressures, resulting in significant energy consumption.

[0004] In the transesterification process for preparing diphenyl carbonate, the choice of catalyst system is crucial. Existing catalysts mainly include homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts mainly include organotin compounds and titanate compounds. Organotin catalysts have high catalytic activity and relatively mild reaction conditions, enabling high conversion rates in a short time. However, they are difficult to recover and reuse, resulting in catalyst residues in the product, affecting product quality, and increasing production costs and environmental burden. Titanate catalysts have poor stability, are easily hydrolyzed and deactivated during the reaction, and are sensitive to the acidity or alkalinity of the reaction system, limiting their applicability. For example, Chinese patent CN115260033A uses tetraphenyl titanate as a catalyst and employs molecular sieves to adsorb the methanol generated in the reaction. The reaction temperature is high, and the molecular sieves need to be calcined at 300-800℃ for 1-6 hours after use to achieve recycling, resulting in high energy consumption. Heterogeneous catalysts mainly include metal oxides and supported catalysts. Metal oxide catalysts, such as zinc oxide and lead oxide, have certain catalytic activity and stability and are easy to separate and recover. However, the activity of these catalysts is relatively low, and the reaction energy consumption and time costs are high. Supported catalysts typically support active components such as metal ions and metal oxides on supports like molecular sieves and activated carbon, improving the dispersion of active components and enhancing catalytic activity and stability. However, their preparation processes are relatively complex and costly, and the loss of active components during the reaction can affect the catalyst's lifespan. For example, Chinese patent CN114931975B uses Lewis acids and trifluoromethanesulfonates of metal salts to form a catalytic system, achieving lower reaction temperatures and pressures, but the catalyst cannot be recycled, increasing reaction costs. This invention utilizes the synergistic effect of DES and organic solvents. The strong polarity and hydrogen bonding network of DES dissolve phenol and activate CO2, while non-polar organic solvents regulate and suppress side reactions. Product separation is achieved through extraction, with a stable yield of over 62.1%, purity ≥98.5%, and selectivity ≥85.5%. Furthermore, the catalyst can be directly recycled, significantly superior to existing technologies.

[0005] Based on this, this invention proposes a method for preparing diphenyl carbonate using DES as a catalyst in the presence of an organic solvent via a one-pot reaction of CO2, carbon tetrachloride, and phenol. The reaction conditions are mild, with an initial CO2 pressure of 1-6 MPa and a reaction temperature of 100-160°C. This method requires less equipment and consumes less energy. Furthermore, the synergistic effect of DES and the organic solvent allows for efficient separation of the catalyst and product after the reaction by allowing the mixture to settle and separate. The DES phase can be directly recycled, and the organic solvent can also be recycled after distillation, significantly reducing production costs. This method achieves high-yield and high-purity synthesis of diphenyl carbonate, is simple to operate, and has good prospects for industrial application. Summary of the Invention

[0006] The purpose of this invention is to provide an efficient and highly selective method for synthesizing diphenyl carbonate.

[0007] Based on the above, this invention relates to a method for preparing diphenyl carbonate, characterized by using DES as a catalyst in the presence of an organic solvent to catalyze a one-pot reaction of CO2, carbon tetrachloride, and phenol to prepare diphenyl carbonate. The initial CO2 pressure is 1-6 MPa, the molar ratio of carbon tetrachloride to phenol is 2:1-4:1, the molar ratio of DES to phenol is 3:1-6:1, the reaction temperature is 100-160℃, and the reaction time is 6-12 h. After the reaction, the mixture is allowed to stand and separate into layers, yielding a lower DES phase and an upper product phase containing the organic solvent. The separated and recovered lower DES can be directly recycled. The upper product phase containing the organic solvent is purified by distillation to remove the organic solvent, yielding diphenyl carbonate with a yield ≥62.1%, purity ≥98.5%, and selectivity ≥85.5%. The organic solvent obtained from distillation can be recycled. The recovered DES, after being reused 10 times under the same experimental conditions, consistently yields diphenyl carbonate with a yield ≥60.0% and a selectivity ≥83.5%. The DES is composed of a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is selected from one of choline chloride (ChCl), tetrabutylammonium chloride (TBAC), and 1-butyl-3-methylimidazolium chloride ([Bmim]Cl); the hydrogen bond donor is selected from one of triethanolamine (TEA), ethylene glycol (EG), and diethylamine (DEA); the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1 to 1:3; and the organic solvent is selected from one of cyclohexane, o-xylene, and dichloromethane.

[0008] This invention solves this technical problem through the following technical solution:

[0009] The specific technical solution is illustrated using a eutectic solvent prepared by choline chloride and ethylene glycol in a molar ratio of 1:2. This eutectic solvent is named [ChCl][EG]2, and the naming method for other eutectic solvents follows the same principle.

[0010] Choline chloride and ethylene glycol were added to a 100 mL three-necked flask at a molar ratio of 1:2. The flask was placed on a thermostatic magnetic stirrer and heated to 70 °C under nitrogen protection. The mixture was stirred at 500 rpm for 2 hours until a homogeneous and transparent liquid was formed. The mixture was then cooled to room temperature to obtain [ChCl][EG]2, which was stored in a dry and sealed container for later use.

[0011] 0.3 mol carbon tetrachloride, 0.1 mol phenol, 0.45 mol [ChCl][EG]2, and 50 mL cyclohexane were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced into the reactor until the initial reaction pressure reached 3.5 MPa. The reaction was carried out at 130 °C for 9 hours. After the reaction, the mixture was allowed to stand and separate into two phases, yielding a lower DES phase and an upper product phase containing cyclohexane. The separated and recovered lower DES phase could be directly recovered and recycled, with a single-cycle recovery rate of 95.5%. The upper product phase was purified by distillation to remove cyclohexane, yielding diphenyl carbonate with a product yield of 65.6%, a selectivity of 87.5%, and a purity of 99.2%.

[0012] Compared with traditional methods, the present invention is characterized by:

[0013] 1. In this patent, DES serves as both a reaction medium and a catalyst, activating CO2, carbon tetrachloride, and phenol through hydrogen bonding networks and ionic interactions, thus avoiding the separation difficulties of traditional catalysts and achieving the green and efficient synthesis of diphenyl carbonate.

[0014] 2. The phase separation characteristics of DES and organic solvents realize an integrated "reaction-separation" system. At the same time, the non-polar organic solvent regulates the system to suppress side reactions, improve product selectivity, and realize the efficient recovery and recycling of DES catalyst and organic solvent.

[0015] 3. Overcoming the problems of traditional catalysts being difficult to recover and requiring harsh conditions, the reaction conditions are relatively mild and the operation is simple. The production cost is significantly reduced through catalyst and solvent recycling, making it suitable for industrialization. Detailed Implementation

[0016] The method of the present invention will be further described below with reference to embodiments, but this is not intended to limit the present invention.

[0017] Example 1: Choline chloride and ethylene glycol were added to a 100 mL three-necked flask at a molar ratio of 1:2. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [ChCl][EG]2. 0.3 mol carbon tetrachloride, 0.1 mol phenol, 0.45 mol [ChCl][EG]2, and 50 mL cyclohexane were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced until the initial reaction pressure in the reactor reached 3.5 MPa. The reaction was carried out at 130 °C for 9 hours. After the reaction, the mixture was allowed to stand and separate into two phases, yielding a lower DES phase and an upper product phase containing cyclohexane. The separated and recovered lower DES phase could be directly recycled, with a single-cycle recovery rate of 95.5%. The upper product phase was purified by distillation to remove cyclohexane, yielding diphenyl carbonate with a product yield of 65.6%, selectivity of 87.5%, and purity of 99.2%. The cyclohexane could be recycled.

[0018] Comparative Example 1: In a 100mL reactor equipped with a stirrer, heater, and condenser, under nitrogen protection, 20g of 4A molecular sieve was packed between the reactor and the condenser. 18.8g of phenol and 0.84g of tetraphenyl titanate were added to the reactor. After heating to 180℃, 9g of dimethyl carbonate was added dropwise over 3 hours, followed by a 7-hour reaction. The conversion rate of phenol was 42.77%, the selectivity for methyl phenyl carbonate was 27.94%, and the selectivity for diphenyl carbonate was 72.06%. The reacted molecular sieve was calcined at 450℃ for 5 hours and then reused.

[0019] Comparative Example 2: A catalytic system was constructed using Lewis acid ZnCl2 and trifluoromethanesulfonate Cu(OTf)2. 6 mmol of phenol, 3 mmol of ZnCl2, 0.125 mmol of Cu(OTf)2, and 15 mmol of carbon tetrachloride were added to a 25 mL reactor. The air inside the reactor was replaced with high-purity CO2, and the pressure inside the reactor was increased to 0.2 MPa. The reactor was heated and stirred to 100°C for 2 hours. After the reaction, it was cooled to room temperature, and the reaction liquid was collected, centrifuged, and a small amount of liquid was used for quantitative analysis of the product using GC. The yield of diphenyl carbonate was 58.7%, and the selectivity for diphenyl carbonate was 86.8%. The catalytic system was lost with the reaction liquid and could not be recycled.

[0020] Example 2: Choline chloride and triethanolamine were added to a 100 mL three-necked flask at a molar ratio of 1:1. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [ChCl][TEA]. 0.2 mol carbon tetrachloride, 0.1 mol phenol, 0.3 mol [ChCl][TEA], and 50 mL cyclohexane were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced to the initial reaction pressure of 1 MPa, and the reaction was carried out at 100 °C for 6 hours. After the reaction, the mixture was allowed to stand and separate into two phases, yielding a lower DES phase and an upper product phase containing cyclohexane. The separated and recovered lower DES phase could be directly recycled, with a single-cycle recovery rate of 95.2%. The upper product phase was purified by distillation to remove cyclohexane, yielding diphenyl carbonate with a product yield of 62.1%, selectivity of 85.5%, and purity of 98.5%. The cyclohexane could be recycled.

[0021] Example 3: Tetrabutylammonium chloride and ethylene glycol were added to a 100 mL three-necked flask at a molar ratio of 1:3. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [TBAC][EG]3. 0.4 mol carbon tetrachloride, 0.1 mol phenol, 0.6 mol [TBAC][EG]3, and 50 mL o-xylene were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced to the initial reaction pressure of 6 MPa, and the reaction was carried out at 160 °C for 12 hours. After the reaction, the mixture was allowed to stand and separate into layers, yielding a lower DES phase and an upper product phase containing o-xylene. The separated and recovered lower DES phase can be directly recycled, with a single-cycle recovery rate of 94.8%. The upper product phase was subjected to distillation to remove o-xylene, yielding diphenyl carbonate with a product yield of 62.1%, selectivity of 86.2%, and purity of 98.8%. The o-xylene can be recycled.

[0022] Example 4: 1-Butyl-3-methylimidazolium chloride and diethylamine were added to a 100 mL three-necked flask at a molar ratio of 1:2. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [[Bmim]Cl][DEA]2. 0.3 mol carbon tetrachloride, 0.1 mol phenol, 0.45 mol [[Bmim]Cl][DEA]2, and 50 mL dichloromethane were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced to the reactor until the initial reaction pressure reached 3.5 MPa. The reaction was carried out at 130 °C for 9 hours. After the reaction, the mixture was allowed to stand and separate into two phases, yielding a lower DES phase and an upper product phase containing dichloromethane. The separated and recovered lower DES phase could be directly recycled, with a single-cycle recovery rate of 95.0%. The upper product phase was purified by distillation to remove dichloromethane, yielding diphenyl carbonate with a product yield of 65.2%, selectivity of 87.3%, and purity of 99.0%. The dichloromethane could be recycled.

[0023] Example 5: Choline chloride and diethylamine were added to a 100 mL three-necked flask at a molar ratio of 1:1. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [ChCl][DEA]. 0.3 mol carbon tetrachloride, 0.1 mol phenol, 0.3 mol [ChCl][DEA], and 50 mL o-xylene were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced to the initial reaction pressure of 6 MPa, and the reaction was carried out at 100 °C for 12 hours. After the reaction, the mixture was allowed to stand and separate into layers, yielding a lower DES phase and an upper product phase containing o-xylene. The separated and recovered lower DES phase could be directly recycled, with a single-cycle recovery rate of 94.9%. The upper product phase was subjected to distillation to remove o-xylene, yielding diphenyl carbonate with a product yield of 63.0%, selectivity of 86.2%, and purity of 98.7%. The o-xylene could be recycled.

[0024] Example 6: Tetrabutylammonium chloride and triethanolamine were added to a 100 mL three-necked flask at a molar ratio of 1:3. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [TBAC][TEA]3. 0.2 mol carbon tetrachloride, 0.1 mol phenol, 0.6 mol [TBAC][TEA]3, and 50 mL dichloromethane were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced to the initial reaction pressure of 1 MPa, and the reaction was carried out at 160 °C for 6 hours. After the reaction, the mixture was allowed to stand and separate into two phases, yielding a lower DES phase and an upper product phase containing dichloromethane. The separated and recovered lower DES phase can be directly recycled, with a single-cycle recovery rate of 95.1%. The upper product phase was purified by distillation to remove dichloromethane, yielding diphenyl carbonate with a product yield of 63.5%, selectivity of 85.8%, and purity of 98.6%. The dichloromethane can be recycled.

[0025] Example 7: 1-Butyl-3-methylimidazolium chloride and ethylene glycol were added to a 100 mL three-necked flask at a molar ratio of 1:1. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [[Bmim]Cl][EG]. 0.4 mol carbon tetrachloride, 0.1 mol phenol, 0.45 mol [[Bmim]Cl][EG], and 50 mL cyclohexane were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced to the reactor until the initial reaction pressure was 3.5 MPa. The reaction was carried out at 100 °C for 12 hours. After the reaction, the mixture was allowed to stand and separate into layers, yielding a lower DES phase and an upper product phase containing cyclohexane. The separated and recovered lower DES phase could be directly recycled, with a single-cycle recovery rate of 95.3%. The upper product phase was purified by distillation to remove cyclohexane, yielding diphenyl carbonate with a product yield of 64.0%, selectivity of 86.5%, and purity of 98.9%. The cyclohexane could be recycled.

[0026] Example 8: Tetrabutylammonium chloride and diethylamine were added to a 100 mL three-necked flask at a molar ratio of 1:2. The mixture was heated to 70 °C and stirred for 2 hours under nitrogen protection to prepare [TBAC][DEA]2. 0.3 mol carbon tetrachloride, 0.1 mol phenol, 0.6 mol [TBAC][DEA]2, and 50 mL o-xylene were added to a 250 mL reactor and stirred until homogeneous. CO2 was introduced to the initial reaction pressure of 6 MPa, and the reaction was carried out at 130 °C for 6 hours. After the reaction, the mixture was allowed to stand and separate into layers, yielding a lower DES phase and an upper product phase containing o-xylene. The separated and recovered lower DES phase could be directly recycled, with a single-cycle recovery rate of 94.7%. The upper product phase was subjected to distillation to remove o-xylene, yielding diphenyl carbonate with a product yield of 64.8%, selectivity of 87.0%, and purity of 99.1%. The o-xylene could be recycled.

[0027] Example 9: The DES recovered in Example 1 was added to a 250 mL reactor along with 0.3 mol carbon tetrachloride, 0.1 mol phenol, 0.45 mol [ChCl][EG]2, and 50 mL cyclohexane. The mixture was stirred until homogeneous, and CO2 was introduced until the initial reaction pressure in the reactor reached 3.5 MPa. The reaction was carried out at 130 °C for 9 hours. After the reaction, the mixture was allowed to stand and separate into layers, yielding a lower DES phase and an upper product phase containing cyclohexane. The upper product phase was purified by distillation to remove cyclohexane, yielding diphenyl carbonate with a yield of 65.2%, a selectivity of 87.3%, and a purity of 99.2%. The cyclohexane was recyclable, and the separated and recovered lower DES could be directly recycled. Under the same experimental conditions, the product was reused 10 times. The yield of diphenyl carbonate obtained after each of the 10 reuses was ≥60.6%, and the selectivity was ≥83.8%.

[0028] Example 10: The DES recovered in Example 2 was added to a 250 mL reactor along with 0.2 mol carbon tetrachloride, 0.1 mol phenol, 0.3 mol [ChCl][TEA], and 50 mL cyclohexane. The mixture was stirred until homogeneous, and CO2 was introduced until the initial reaction pressure in the reactor was 1 MPa. The reaction was carried out at 100 °C for 6 hours. After the reaction, the mixture was allowed to stand and separate into layers, yielding a lower DES phase and an upper product phase containing cyclohexane. The upper product phase was purified by distillation to remove cyclohexane, yielding diphenyl carbonate with a yield of 61.8%, a selectivity of 85.1%, and a purity of 98.5%. The cyclohexane was recyclable, and the separated and recovered lower DES could be directly recycled. The product was reused 10 times under the same experimental conditions. The yield of diphenyl carbonate obtained after each of the 10 reuses was ≥60.0%, and the selectivity was ≥83.5%.

[0029] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A process for the preparation of diphenyl carbonate, characterized in that, The method comprises the following steps: The method comprises the following steps: The reaction conditions are as follows: the initial pressure of CO2 is 1-6 MPa, the molar ratio of carbon tetrachloride to phenol is 2:1-4:1, the molar ratio of DES to phenol is 3:1-6:1, the reaction temperature is 100-160 DEG C, and the reaction time is 6-12 h; The DES is composed of a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is selected from one of choline chloride, tetrabutylammonium chloride and 1-butyl-3-methylimidazolium chloride; the hydrogen bond donor is selected from one of triethanolamine, ethylene glycol and diethylamine; and the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1-1:3; The organic solvent is selected from one of cyclohexane, o-xylene and dichloromethane.