Method for continuously preparing phosphorous acid trialkyl ester

Abstract

The invention discloses a method for continuously preparing trialkyl phosphite, which comprises the following steps of: metering and conveying phosphorus trichloride and alkyl alcohol serving as raw materials into respective precoolers through pumps, precooling, carrying out continuous flow mixing reaction and vacuum continuous hydrogen chloride removal for N times after precooling, and rectifying and purifying to obtain a high-purity trialkyl phosphite product, the total time of the continuous flow mixing reaction is 0.001-10s, the total time of the vacuum continuous hydrogen chloride removal is 0.1-30s, the inner diameter of a pipeline of a continuous flow reactor used in the continuous flow mixing reaction is 0.01-10mm, a refrigerant is introduced outside the continuous flow reactor to control the temperature, and N is any integer of 1-4. The continuous flow reactor and the vacuum continuous degassing device are connected in series, so that the continuous preparation of the trialkyl phosphite is realized, the generation of an acidolysis byproduct dialkyl phosphite is effectively reduced through extremely short retention time control and efficient heat transfer, the reaction efficiency is high, an acid-binding agent is not needed in the reaction process, the system is simple, the cost is low, the yield is high, and the method is suitable for industrial production. The industrial production is easy to realize.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and in particular to a method for continuously preparing trialkyl phosphite. Background Art

[0002] Trialkyl phosphites are a class of widely used organic reagents. For example, trimethyl phosphite can be used to synthesize insecticides such as dichlorvos, phosphamidon, monocrotophos, and chlorpyrifos. It is also the main intermediate for the production of new organophosphorus flame retardants. It can also be used as a synthetic polymerization catalyst and coating additive, and there is a large market demand for it.

[0003] The preparation processes of trialkyl phosphite are: ① ester exchange method ( Pesticides, 1972, (01): 1-11 ), using phosphorus trichloride as raw material to generate triphenyl phosphite, and then undergoing ester exchange reaction with methanol in the presence of sodium methoxide, the crude product yield is 93%, and the phenol recovery rate is over 90%. This process route is long, the phenol wastewater treatment is troublesome, and the cost is relatively high. ② Ammonium carbamate method ( Pesticides, 1973, (03): 30-37 ), using phosphorus trichloride and methanol as raw materials, dichloroethane as solvent, and ammonium carbamate as acid binding agent, the yield is 85%. ③ Ammonia or tertiary amine method ( Pesticides, 1981(05):29-31; Shanxi Chemical Industry, 1999, 19(3):3) , using phosphorus trichloride and methanol as raw materials, ammonia or tertiary amine as acid binding agent, and reacting in an inert solvent. This is also the method currently adopted in industrial production. Usually, in order to suppress side reactions, the acid binding agent used needs to be greatly excessive, and additional acid binding agent and inert solvent recovery steps are required, which increases production costs.

[0004] Phosphorus trichloride reacts easily with methanol or ethanol, and the reaction generates hydrogen chloride. However, since the product trimethyl phosphite or triethyl phosphite is extremely unstable in acid, it is very easy to acidify and generate phosphorous acid diester under the condition that hydrogen chloride is generated in the reaction. Synthesis and Scale-up of Dimethyl Phosphite, Master's Thesis, Zhejiang University, 2003 ), the current methods all require the addition of alkali to neutralize the hydrogen chloride generated by the reaction in situ. The reaction process is highly exothermic. The higher the temperature, the easier it is for the acidolysis side reaction to proceed. Therefore, the kettle reaction needs to be added slowly, and the production efficiency and yield are not ideal. Therefore, there are reports on the use of microchannel reactors to prepare triethyl phosphite (CN119264181), but it still requires the addition of excess ammonia, and the use of acid binding agents is not eliminated at the source of the process, so the cost is still high. In addition, although there are cases of similar products being synthesized without the addition of acid binding agents, such as tripropyl phosphite ( Plastic Additives, 2006(02):29-30 ) is synthesized by reacting phosphorus trichloride with propanol, with a yield of only 61.8%. Regarding the stability of trialkyl phosphites, the shorter the alkyl carbon chain, the less stable the product is in acidic environments. Therefore, developing an efficient, high-yield, direct synthesis method without an acid binder remains a significant challenge for the industry. Summary of the Invention

[0005] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a method for continuously preparing trialkyl phosphite, which avoids the use of acid binding agents, thereby improving reaction efficiency and reducing costs.

[0006] The technical solution adopted by the present invention is as follows: a method for continuously preparing trialkyl phosphite, comprising the following steps: phosphorus trichloride and alkyl alcohol as raw materials are respectively metered and delivered into respective precoolers by pumps for precooling; after precooling, the raw materials undergo N times of continuous flow mixing reaction and vacuum continuous hydrogen chloride removal; and then are purified by distillation to obtain a high-purity trialkyl phosphite product; the total time of the continuous flow mixing reaction is 0.001-10 seconds, and the total time of the vacuum continuous hydrogen chloride removal is 0.1-30 seconds; the inner diameter of the pipeline of the continuous flow reactor used in the continuous flow mixing reaction is 0.01-10 mm; a refrigerant is passed through the outside of the continuous flow reactor for temperature control; and N is any integer from 1 to 4.

[0007] Furthermore, the alkyl group is a methyl group or an ethyl group.

[0008] Furthermore, when N is an integer of 2-4, the raw alkyl alcohol is divided into corresponding parts, pre-cooled and then participates in the corresponding continuous flow mixing reaction. 4. The method for continuously preparing trialkyl phosphite according to claim 1, characterized in that: Furthermore, the molar flow ratio of phosphorus trichloride to total alkyl alcohol is 1:3-4, the outlet temperature of the precooler is controlled at -70°C-0°C, and the reaction temperature of the continuous flow reactor is -60°C-20°C.

[0009] Furthermore, the continuous flow reactor includes a tubular reactor or a microchannel reactor.

[0010] Furthermore, the temperature in the vacuum degassing device is -60°C~20°C, and the pressure is -0.098MPa~-0.03MPa.

[0011] Compared with the prior art, the present invention has the following advantages: (1) The present invention utilizes a continuous flow reactor to continuously prepare trialkyl phosphite, which has the following advantages: ① No acid binding agent is required, which is low in cost; ② The micro-sized reactor has high heat exchange efficiency, which avoids acidolysis by-products caused by local excessive temperature; ③ The extremely short reaction residence time and degassing residence time allow for efficient removal of hydrogen chloride, effectively avoiding the generation of acidolysis by-products.

[0012] (2) The process of the present invention further controls the parameters such as the feed temperature of the raw materials, the reaction temperature and the pressure in steps, thereby further improving the reaction yield and the purity of the product, which is conducive to the realization of industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1The present invention is a schematic diagram of a single-stage process for continuously preparing trialkyl phosphite using a reaction device.

[0014] Figure 2 The present invention is a schematic diagram of a process in which the reaction apparatus for continuously preparing trialkyl phosphite is connected in series in multiple stages. DETAILED DESCRIPTION

[0015] The present invention will be further described below with reference to specific embodiments and the accompanying drawings, but the protection scope of the present invention is not limited thereto.

[0016] like Figure 1 The figure shows a continuous process for preparing trialkyl phosphite when N is 1. In the figure, the raw materials phosphorus trichloride and alkyl alcohol are respectively metered and delivered by pumps into respective precoolers for precooling. After precooling, they enter a continuous flow reactor for mixed reaction. The reaction liquid enters a vacuum continuous degassing device to remove hydrogen chloride gas to obtain a crude product. The crude product is purified by distillation to obtain a high-purity trialkyl phosphite product.

[0017] Example 1

[0018] Use Figure 1 In the apparatus and process shown, phosphorus trichloride and methanol are respectively transported into respective precoolers through metering pumps at a molar flow ratio of 1:3.02 and cooled to -70°C, and then enter the tubular reactor for rapid mixing and reaction. The outside of the tubular reactor is temperature-controlled by a refrigerant with a tube diameter of 10 mm. The reaction temperature is controlled at -60°C with a residence time of 1 s. The reaction liquid flows directly into a vacuum continuous degassing device. The temperature of the material in the device is -60°C, the residence time is 25 s, and the pressure is -0.098 MPa. The reaction liquid flows out of the vacuum continuous degassing device for sampling and testing. The product purity is 98%. The collected reaction liquid is distilled, and the product trimethyl phosphite yield is 90% and the purity is 99.9%.

[0019] Example 2

[0020] Use Figure 1 In the device and process shown, phosphorus trichloride and methanol are respectively transported into respective precoolers through metering pumps at a molar flow ratio of 1:4 and cooled to -20°C, and then enter the microchannel reactor for rapid mixing and reaction. The temperature of the outside of the microchannel reactor is controlled by a refrigerant, the channel size is 0.1 mm, the reaction temperature is controlled at 10°C, the residence time is 0.001s, and the reaction liquid flows directly into the vacuum continuous degassing device. The temperature of the material in the device is -10°C, the residence time is 0.5s, and the pressure is -0.06MPa. The reaction liquid flows out of the degassing device and is sampled and tested for product purity of 89%. After collecting the reaction liquid and distilling it, the yield of the product trimethyl phosphite is 88% and the purity is 99.9%.

[0021] Example 3

[0022] Use Figure 1 In the device and process shown, phosphorus trichloride and ethanol are respectively transported into respective precoolers through metering pumps at a molar flow ratio of 1:3.5 and cooled to 0°C, and then enter the microchannel reactor for rapid mixing and reaction. The temperature of the microchannel reactor is controlled by a refrigerant, the channel size is 0.5 mm, the reaction temperature is controlled at 20°C, the residence time is 0.01 s, and the reaction liquid flows directly into the vacuum continuous degassing device. The temperature of the material in the device is 0°C, the residence time is 10 s, and the pressure is -0.03 MPa. The reaction liquid flows out of the degassing device for sampling and testing, and the product purity is 98%. After collecting the reaction liquid and distilling it, the yield of the product triethyl phosphite is 95% and the purity is 99.9%.

[0023] like Figure 2 The figure shows a continuous process for preparing trialkyl phosphite when N is 3. In the figure, the raw materials phosphorus trichloride and alkyl alcohol are respectively metered and delivered by pumps into respective precoolers for precooling. The alkyl alcohol is divided into three parts. After precooling, the phosphorus trichloride and one part of the alkyl alcohol enter the first-stage continuous flow reactor for mixing reaction. The reaction liquid enters the first-stage vacuum continuous degassing device to remove hydrogen chloride gas. The reaction liquid then enters the second-stage continuous flow reactor for mixing reaction with the second part of alkyl alcohol. The reaction liquid enters the second-stage vacuum continuous degassing device to remove hydrogen chloride gas. The reaction liquid then enters the third-stage continuous flow reactor for mixing reaction with the third part of alkyl alcohol. The reaction liquid enters the third-stage vacuum continuous degassing device to remove hydrogen chloride gas to obtain a crude product. The crude product is purified by distillation to obtain a high-purity trialkyl phosphite product.

[0024] Example 4

[0025] Use Figure 2The device and process shown are three-stage series reaction devices. Phosphorus trichloride is fed once from the first-stage reaction device, and methanol is divided into three equal parts and enters the three-stage reactor in sequence. The first-stage continuous flow reactor is a microchannel reactor with a size of 0.01 mm. The molar flow ratio of the methanol feed is 1.1 eq of the total phosphorus trichloride. The precooler outlet temperature is -40 ° C, the reaction temperature is 0 ° C, the residence time is 6 s, and the temperature in the first-stage vacuum continuous degassing device is controlled at -40 ° C, the residence time is 1 s, and the pressure is -0.05 MPa; the second-stage continuous flow reactor is a tubular reactor with a tube diameter of 3 mm. The molar flow ratio of the methanol feed is 1.1 eq of the total phosphorus trichloride, and the methanol precooler outlet temperature is -30 ° C. The reaction temperature is -5°C, the residence time is 2s, the temperature in the second-stage vacuum continuous degassing device is controlled at -30°C, the residence time is 5s, and the pressure is -0.06MPa; the third-stage continuous flow reactor is a tubular reactor with a tube diameter of 3mm, the methanol feed molar flow ratio is 1.1eq of the total phosphorus trichloride, the methanol precooler outlet temperature is -20°C, the reaction temperature is -10°C, the residence time is 0.05s, the temperature in the third-stage vacuum continuous degassing device is controlled at -20°C, the residence time is 15s, and the pressure is -0.07MPa; the product purity of the reaction liquid sampled at the outlet of the third-stage reaction device is 98%, and the product yield after distillation of the collected reaction liquid is 97% and the purity is 99.9%.

[0026] Example 5

[0027] The residence time in the first-stage continuous flow reactor was 10 s, the residence time in the second-stage continuous flow reactor was 10 s, and the residence time in the third-stage continuous flow reactor was 10 s. Other conditions were the same as those in Example 4, and the final product yield was only 35%. The reaction residence time was too long, causing the product dimethyl phosphite to be acidolyzed to form by-products such as dimethyl phosphite and monomethyl phosphite.

[0028] Example 6

[0029] The residence time in the first stage vacuum continuous degasser was 1 min, the residence time in the second stage vacuum continuous degasser was 1 min, and the residence time in the third stage vacuum continuous degasser was 1 min. Other conditions were the same as in Example 4, and the final product yield was only 45%. Excessive residence time in the degasser prolonged the contact time between hydrogen chloride and trimethyl phosphite, resulting in acid hydrolysis of the product to form by-products such as dimethyl phosphite and monomethyl phosphite.

[0030] Example 7

[0031] The reaction temperature of the first, second, and third stage continuous flow reactors was 30°C, and the other conditions were the same as in Example 4. The final product yield was only 28%. Excessively high temperatures exacerbated the acidolysis of the dimethyl phosphite product to produce byproducts such as dimethyl phosphite and monomethyl phosphite.

[0032] Example 8

[0033] The temperature of the first, second, and third stage vacuum continuous degassing apparatuses was all 40°C, and all other conditions were the same as in Example 4. The final product yield was only 8%. Excessively high temperatures exacerbate the acidolysis of the dimethyl phosphite product, producing byproducts such as dimethyl phosphite and monomethyl phosphite.

[0034] Example 9

[0035] The diameter of the first-stage continuous flow reactor was 6 mm, the diameter of the second-stage continuous flow reactor was 12 mm, and the diameter of the third-stage continuous flow reactor was 12 mm. Other conditions were the same as those in Example 4. The final product yield was only 21%. The oversized diameters prevented timely heat removal from the reactors, resulting in excessively high reaction mass temperatures and aggravated the acidolysis of the product, dimethyl phosphite, to form byproducts such as dimethyl phosphite and monomethyl phosphite.

[0036] Comparative Example 1: In a reaction flask, first add 3.02eq methanol or ethanol, cool to a certain temperature, and slowly add phosphorus trichloride dropwise. During the addition process, control the reaction flask to a negative pressure state, and degas hydrogen chloride during the reaction. After the addition is completed, immediately take samples for analysis and testing. The experimental results at different temperatures are shown in the following table: Table 1 Summary of products from the reaction of adding phosphorus trichloride to alkyl alcohol as substrate

[0037] Comparative Example 2: In a reaction flask, add phosphorus trichloride first, cool to a certain temperature, and slowly add 3.02eq of methanol or ethanol dropwise. During the addition process, control the reaction flask to a negative pressure state, and remove hydrogen chloride gas during the reaction. After the addition is completed, immediately take samples for analysis and testing. The experimental results at different temperatures are shown in the following table: Table 2 Summary of products of the reaction of adding alkyl alcohol with phosphorus trichloride as substrate

[0038] Comparing Table 1 and Table 2 with Example 4, it can be found that the continuous batch addition of alcohol adopted in the present invention is more conducive to the formation of the main product.

[0039] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A method for continuously preparing trialkyl phosphite, characterized in that: The following steps are involved: The raw materials, phosphorus trichloride and alkyl alcohol, are respectively metered and delivered into respective precoolers by pumps for precooling. After precooling, the products undergo N times of continuous flow mixing reaction and vacuum continuous hydrogen chloride removal, and are then purified by distillation to obtain a high-purity trialkyl phosphite product. The total time of the continuous flow mixing reaction is 0.001 to 10 seconds, and the total time of the vacuum continuous hydrogen chloride removal is 0.1 to 30 seconds. The inner diameter of the pipe of the continuous flow reactor used in the continuous flow mixing reaction is 0.01 to 10 mm. A refrigerant is passed outside the continuous flow reactor for temperature control. N is any integer from 1 to 4.

2. A method for continuously preparing trialkyl phosphite according to claim 1, characterized in that: The alkyl group is methyl or ethyl.

3. A method for continuously preparing trialkyl phosphite according to claim 1, characterized in that: When N is an integer of 2-4, the raw alkyl alcohol is divided into corresponding parts, pre-cooled and then participates in the corresponding continuous flow mixing reaction.

4. A method for continuously preparing trialkyl phosphite according to claim 1, characterized in that: The molar flow ratio of phosphorus trichloride to total alkyl alcohol is 1:3~4, the outlet temperature of the precooler is controlled at -70℃~0℃, and the reaction temperature of the continuous flow reactor is -60℃~20℃.

5. A method for continuously preparing trialkyl phosphite according to claim 1, characterized in that: Continuous flow reactors include tubular reactors or microchannel reactors.

6. A method for continuously preparing trialkyl phosphite according to claim 1, characterized in that: The temperature inside the vacuum degassing device is -60℃~20℃, and the pressure is -0.098MPa~-0.03MPa.

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