Treatment method of amidation reaction leftovers

Abstract

The invention relates to a treatment method of amidation reaction leftovers. The amidation reaction leftovers contain N, N-dioxalyl alanine ethyl ester, the treatment method comprises the step of carrying out transesterification on the leftovers and diethyl oxalate in a solvent to generate N-ethoxy oxalyl-L-alanine ethyl ester, and the solvent is an alcohol solvent. According to the method disclosed by the invention, the leftovers containing the N, N-dioxalyl alanine ethyl ester and the diethyl oxalate are subjected to transesterification in the alcohol solvent, so that the impurity N, N-dioxalyl alanine ethyl ester in the leftovers can be converted into the target product N-ethoxy oxalyl-L-alanine ethyl ester; further, the yield loss of the target product N-ethoxy oxalyl-L-alanine ethyl ester is inhibited, the yield of the target product is improved, and meanwhile, the cost is reduced. The treatment method can be used in a process for producing vitamin B6.

Description

Technical Field

[0001] The present invention specifically relates to a method for treating the waste materials of amidation reaction. Background Art

[0002] In the process of producing vitamin B6 by the oxazole route, using alanine as a raw material, reacting with oxalic acid and ethanolamine in an amidation reaction to form ethyl N-ethoxyoxalyl-L-alaninate, it is inevitable to generate waste materials containing impurities such as ethyl N,N-dioxalylalaninate

[0003] As a result, the yield of the target product ethyl N-ethoxyoxalyl-L-alaninate is lost by about 5%, and the mass of ethyl N,N-dioxalylalaninate accounts for about 75%-80% of the total amount of impurity waste materials.

[0004] In the prior art, there are the following several ways to treat this waste material: 1. Treat it as hazardous waste; 2. Patent CN118164869A purifies the waste material containing ethyl N,N-dioxalylalaninate by crystallization and pulping methods, hydrolyzes it under alkaline conditions and then neutralizes it to obtain alanine and oxalic acid (the reaction formula is as follows), and recycles the two back to the main reaction.

[0005]

[0006] However, treating it as hazardous waste will directly lead to the loss of the yield of the target product, increase the production cost, and also bring environmental pressure. Crystallization and pulping treatment of the waste material will increase the labor cost, and hydrolysis under alkaline conditions will generate a large amount of waste salts, increasing the environmental protection cost and having high energy consumption for water removal in the reaction. Summary of the Invention

[0007] The purpose of the present invention is to provide an improved method for treating the waste materials of amidation reaction. This treatment method can simply convert the impurity ethyl N,N-dioxalylalaninate in the waste materials into the target product ethyl N-ethoxyoxalyl-L-alaninate through a simple process, thereby increasing the yield of the target product and reducing the cost at the same time.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is:

[0009] A method for treating waste materials, the waste materials contain ethyl N,N-dioxalylalaninate, and the treatment method includes a step of performing a transesterification reaction between the waste materials and diethyl oxalate in a solvent to generate ethyl N-ethoxyoxalyl-L-alaninate, and the solvent is an alcohol solvent.

[0010] In the present invention, the waste materials refer to the residual solution in the bottom of the distillation column after the target product is rectified and purified, and the waste materials are usually relatively viscous.

[0011] In the prior art, in the process of producing vitamin B6 by the oxazole route, using alanine as a raw material, in the process of amidation reaction with oxalic acid and ethanolamine to form ethyl N-ethoxyoxalyl-L-alaninate, after the reaction system is purified by vacuum distillation to obtain ethyl N-ethoxyoxalyl-L-alaninate, the residual solution in the distillation equipment, i.e., the foots, will inevitably contain the impurity ethyl N,N-dioxalylalaninate. The existence of the foots results in a loss of about 5% in the yield of the target product ethyl N-ethoxyoxalyl-L-alaninate. Usually, the foots are directly treated as hazardous waste, or the ethyl N,N-dioxalylalaninate in the foots is purified by crystallization and slurrying, and then hydrolyzed and neutralized to obtain alanine and oxalic acid, and both can be used as raw materials for this step of the reaction. However, the above methods will produce waste salts and have high environmental protection costs. The inventors of the present application have found through a large number of studies that by subjecting the foots containing ethyl N,N-dioxalylalaninate to a transesterification reaction with diethyl oxalate in an alcohol solvent, the impurity ethyl N,N-dioxalylalaninate in the foots can be converted into the target product ethyl N-ethoxyoxalyl-L-alaninate, thereby inhibiting the loss of the yield of the target product ethyl N-ethoxyoxalyl-L-alaninate. The alcohol solvent can effectively dissolve ethyl N,N-dioxalylalaninate and diethyl oxalate, providing necessary conditions for the reaction to proceed. And when an alcohol solvent such as an ethanol system is applied in production, it does not introduce additional solvent impurities into the reaction system, reducing the post-treatment cost. While using other solvents such as chloroform, the conversion rate of this reaction is significantly reduced, which is not conducive to the recovery and conversion of impurities in the foots, and at the same time increases the post-treatment difficulty.

[0012] In some embodiments, the solvent is selected from one or more combinations of methanol, ethanol, propanol, and butanol.

[0013] In some embodiments, the solvent is ethanol.

[0014] In some embodiments, the mass of the solvent is 1-10 times, preferably 3-5 times, the mass of the foots. When the amount of the solvent is too small, the incomplete dissolution of diethyl oxalate and ethyl N,N-dioxalylalaninate is not conducive to the reaction; when the amount of the solvent is too large, the concentrations of the reactants diethyl oxalate and ethyl N,N-dioxalylalaninate decrease, which is not conducive to the improvement of the yield.

[0015] In some embodiments, in the foots, the mass percentage of ethyl N,N-dioxalylalaninate is 75%-80%.

[0016] In some embodiments, the foots further include at least one of ethyl N-ethoxyoxalyl-L-alaninate, diethyl oxalate, and ethyl L-alaninate.

[0017] Preferably, in the foots, the mass percentage of ethyl N-ethoxyoxalyl-L-alaninate is 0-25%.

[0018] Preferably, in the waste material, the mass percentage of diethyl oxalate is 0-5%.

[0019] Preferably, in the waste material, the mass percentage of L-alanine ethyl ester is 0-5%.

[0020] In some embodiments, the molar ratio of diethyl oxalate to diethyl N,N-dioxalylalaninate is 1-10:1, preferably 3-7:1, more preferably 5-7:1.

[0021] In some embodiments, the transesterification reaction is carried out in the presence of a catalyst, and the catalyst is selected from acid catalysts or base catalysts. More preferably an acid catalyst. Under the same conditions, the yield of the base catalyst is 3%-5% lower than that of the acid catalyst.

[0022] In some embodiments, the acid catalysts are selected from one or a combination of p-toluenesulfonic acid, sulfuric acid, phosphoric acid, and acidic resins.

[0023] In some embodiments, the base catalysts are selected from one or a combination of potassium methoxide, potassium ethoxide, sodium methoxide, and sodium ethoxide.

[0024] In some embodiments, the acidic resin is LXC-101 from Xi'an BlueSail New Materials Co., Ltd.

[0025] In some embodiments, the mass of the catalyst is 0.6%-5% of the mass of the waste material, preferably 1%-3%.

[0026] In some embodiments, the transesterification reaction is carried out under atmospheric pressure.

[0027] Preferably, the temperature of the transesterification reaction is 70-170°C, more preferably 70-80°C. When the reaction temperature is too low, the reaction rate is slow and the reaction time is long; when the reaction temperature is too high, it may cause the decomposition of diethyl oxalate and cannot increase the reaction yield anymore.

[0028] Preferably, the time of the transesterification reaction is 2-15 h, more preferably 10-15 h.

[0029] In some embodiments, the transesterification reaction is carried out under pressure.

[0030] Preferably, the pressure of the transesterification reaction is 1-2 MPa.

[0031] Preferably, the temperature of the transesterification reaction is 100-170°C, more preferably 100-150°C. When the reaction temperature is too low, the reaction rate is slow and the reaction time is long; when the reaction temperature is too high, diethyl oxalate may decompose and the reaction yield cannot be further increased.

[0032] Preferably, the time of the transesterification reaction is 2-15h, more preferably 2-5h.

[0033] In some embodiments, the treatment method further includes a step of recovering the solvent and diethyl oxalate after the transesterification reaction and rectifying N-ethoxyoxalyl-L-alanine ethyl ester.

[0034] Further, the solvent and diethyl oxalate can be recovered separately by rectification.

[0035] Further, the pressure for rectifying and recovering the alcohol solvent is normal pressure or slightly negative pressure, and the slightly negative pressure is preferably 30-50 KPa.

[0036] Further, the pressure for rectifying and recovering diethyl oxalate is an absolute pressure of 0.1-10 KPa, preferably an absolute pressure of 0.5-2 KPa.

[0037] Further, the pressure for rectifying N-ethoxyoxalyl-L-alanine ethyl ester is an absolute pressure of 10-1000 Pa, preferably an absolute pressure of 50-100 Pa.

[0038] The present invention also provides a synthesis process of vitamin B6, including a step of reacting alanine, oxalic acid, and ethanol as raw materials to generate N-ethoxyoxalyl-L-alanine ethyl ester, and the foot material containing N,N-dioxalylalanine ethyl ester is generated in this step: the synthesis process further includes a step of treating the foot material by using the aforementioned treatment method of the foot material.

[0039] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0040] In the present invention, the foot material containing N,N-dioxalylalanine ethyl ester is subjected to a transesterification reaction with diethyl oxalate in an alcohol solvent, and the impurity N,N-dioxalylalanine ethyl ester in the foot material can be converted into the target product N-ethoxyoxalyl-L-alanine ethyl ester, thereby inhibiting the yield loss of the target product N-ethoxyoxalyl-L-alanine ethyl ester, increasing the yield of the target product, and reducing the cost at the same time. Specific Embodiments

[0041] The present invention adopts a simple, effective and industrially applicable process to generate the product ethyl N-ethoxyoxalyl-L-alaninate from the impurity N,N-dioxalylalanine ethyl ester in the waste materials, thereby increasing the yield of the product and reducing the cost. Specifically, the present invention first conducts a transesterification reaction and then rectifies and recovers ethyl N-ethoxyoxalyl-L-alaninate. The specific method is as follows: First, dissolve N,N-dioxalylalanine ethyl ester and diethyl oxalate in an alcohol solvent, and in the presence of an acid or base catalyst, conduct a transesterification reaction to generate ethyl N-ethoxyoxalyl-L-alaninate; then recover the solvent and diethyl oxalate, and then conduct vacuum rectification to obtain the product ethyl N-ethoxyoxalyl-L-alaninate.

[0042] When the solvent is ethanol, the reaction formula is as follows:

[0043]

[0044] In the present invention, the impurity N,N-dioxalylalanine ethyl ester in the waste materials and diethyl oxalate are dissolved in an alcohol solvent and conduct a transesterification reaction in the presence of a catalyst to generate ethyl N-ethoxyoxalyl-L-alaninate. The process is simple, effective and suitable for industrial production.

[0045] The following further illustrates the above solution with specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited by the scope of the following embodiments; the implementation conditions adopted in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0046] Unless otherwise specified in the following embodiments, all raw materials are obtained through commercial purchase or prepared by conventional methods in the art.

[0047] Preparation Example 1

[0048] This preparation example provides a source of conventional waste materials containing the impurity N,N-dioxalylalanine ethyl ester:

[0049] L-alanine, oxalic acid, diethyl oxalate and ethanol were added to a reaction kettle and reacted at 90 - 140 °C for 50 h. After that, the reaction system was subjected to rectification for dehydration. The rectification pressure was atmospheric pressure and the bottom temperature of the column was 90 - 100 °C. After the reaction was completed, diethyl oxalate was recovered at an absolute pressure of 1 - 1.5 Kpa and a temperature of 150 - 160 °C. Finally, product rectification was carried out at an absolute pressure of 50 - 100 Pa and a temperature of 160 - 170 °C. The viscous solution remaining in the device after rectification was the residue containing impurity N,N-dioxalylalanine ethyl ester. Among them, the mass percentage of N,N-dioxalylalanine ethyl ester was 75% - 80%. In addition to N,N-dioxalylalanine ethyl ester, it mainly contained 0 - 25% of N-ethoxyoxalyl-L-alanine ethyl ester, 0 - 5% of diethyl oxalate, and 0 - 5% of L-alanine ethyl ester. More specifically, for example, the mass percentage of N,N-dioxalylalanine ethyl ester in the residue was 75%, N-ethoxyoxalyl-L-alanine ethyl ester was 24%, diethyl oxalate was 0.8%, and L-alanine ethyl ester was 0.2%.

[0050] Example 1

[0051] This example provides a method for treating the residue, and the specific steps are as follows:

[0052] 100 g of the residue in Preparation Example 1 (i.e., 75 g of N,N-dioxalylalanine ethyl ester, 0.26 mol), 1.3 mol of diethyl oxalate, 300 g of ethanol, and 1 g of p-toluenesulfonic acid were taken and placed in a 1000 ml autoclave. After purging with nitrogen three times, it was heated to 150 °C, and the pressure in the autoclave was about 1.0 MPa (gauge pressure) for heat preservation reaction for 2 h. Sampling and testing showed that the conversion rate of N,N-dioxalylalanine ethyl ester was 99.1%.

[0053] After the above materials were cooled, they were extruded. Ethanol was distilled off at atmospheric pressure, diethyl oxalate was recovered at 1 - 1.5 KPa (absolute pressure), and the fraction at 108 - 110 °C was collected by rectification at 50 - 100 Pa (absolute pressure) to obtain the product of N-ethoxyoxalyl-L-alanine ethyl ester, and its yield was 97.7%.

[0054] Examples 2 - 16

[0055] Basically the same as Example 1, the difference was only that: the reaction conditions (autoclave reaction temperature, autoclave reaction time, catalyst type, catalyst dosage, reaction solvent type, molar ratio of diethyl oxalate to N,N-dioxalylalanine ethyl ester) were changed. Specifically, see Table 1 below. The reaction conversion rate and the reaction yield after rectification are shown in Table 1 below.

[0056] Table 1

[0057]

[0058]

[0059] Example 19

[0060] This example provides a method for treating foot materials. A common reaction flask is used, and the reaction is carried out under normal pressure. The specific steps are as follows:

[0061] Take 100 g of the foot materials in Preparation Example 1 (i.e., 75 g of N,N - diethyl oxalylalaninate, 0.26 mol), 1.3 mol of diethyl oxalate, 300 g of ethanol, and 1 g of p - toluenesulfonic acid in a 1000 ml reaction flask. Heat to 76 °C and reflux for 10 h. Take a sample for detection, and the conversion rate of N,N - diethyl oxalylalaninate is 99.5%.

[0062] Distill off ethanol from the above materials under normal pressure, recover diethyl oxalate under 1 - 1.5 KPa (absolute pressure), and rectify and collect the fraction at 108 - 110 °C under 50 - 100 Pa (absolute pressure) to obtain the product of ethyl N - ethoxyoxalyl - L - alaninate, and its yield is 96.8%.

[0063] Examples 20 - 26

[0064] Basically the same as Example 17, the difference is only that: the reaction conditions are changed (types of catalysts, catalyst dosages, types of reaction solvents, molar ratio of diethyl oxalate to N,N - diethyl oxalylalaninate, reaction temperature, reaction time, etc.). Specifically, see Table 2 below. The reaction conversion rates and the reaction yields after rectification are shown in Table 2 below.

[0065] Table 2

[0066]

[0067] Comparative Examples 1 - 5

[0068] Basically the same as Example 1, the difference is only that: the reaction conditions are changed (types of reaction solvents, reaction temperature in the autoclave, catalyst dosages, etc.). Specifically, see Table 3 below. The reaction conversion rates and the reaction yields after rectification are shown in Table 3 below.

[0069] Table 3

[0070]

[0071]

[0072] It can be seen that in this application, the waste material containing ethyl N,N-dioxalylalaninate is subjected to a transesterification reaction with diethyl oxalate, and a specific alcohol solvent is selected as the reaction solvent. At the same time, by controlling the appropriate reaction temperature and catalyst dosage, the impurity ethyl N,N-dioxalylalaninate in the waste material can be converted into the target product ethyl N-ethoxyoxalyl-L-alaninate in a high yield, thereby inhibiting the yield loss of the target product ethyl N-ethoxyoxalyl-L-alaninate in the process of synthesizing vitamin B6.

[0073] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. However, the protection scope of the present invention cannot be limited thereby. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for treating waste material, wherein the waste material contains N,N-diazolylalanine ethyl ester, characterized in that: The treatment method comprises the steps of subjecting the waste material to an ester exchange reaction with diethyl oxalate in a solvent to generate N-ethoxyoxalyl-L-alanine ethyl ester, wherein the solvent is an alcohol solvent.

2. The method for processing scraps according to claim 1, characterized in that: The solvent is selected from one or more combinations of methanol, ethanol, propanol and butanol.

3. The method for processing scraps according to claim 1, characterized in that: The mass of the solvent is 1-10 times the mass of the heap material.

4. The method for processing scraps according to claim 1, characterized in that: In the scraps, the mass percentage of N,N-diazolylalanine ethyl ester is 75%-80%; the scraps also include at least one of N-ethoxyoxalyl-L-alanine ethyl ester, diethyl oxalate and L-alanine ethyl ester.

5. The method for processing scraps according to claim 1, characterized in that: The molar ratio of the diethyl oxalate to the N,N-diazolylalanine ethyl ester is 1-10:

1.

6. The method for processing scraps according to claim 1, characterized in that: The transesterification reaction is carried out in the presence of a catalyst, and the catalyst is selected from an acid catalyst or a base catalyst; preferably, the acid catalyst is selected from a combination of one or more of p-toluenesulfonic acid, sulfuric acid, phosphoric acid, and an acidic resin, and the base catalyst is selected from a combination of one or more of potassium methoxide, potassium ethoxide, sodium methoxide, and sodium ethoxide.

7. The method for processing scraps according to claim 5, characterized in that: The mass of the catalyst is 0.6%-5% of the mass of the heap material.

8. The method for processing scraps according to claim 1, characterized in that: The transesterification reaction is carried out under normal pressure; preferably, the temperature of the transesterification reaction is 70-170° C.; and / or, the time of the transesterification reaction is 2-15 h.

9. The method for processing scraps according to claim 1, characterized in that: The transesterification reaction is carried out under pressure; preferably, the pressure of the transesterification reaction is 1-2 MPa; the temperature of the transesterification reaction is 100-170° C.; and / or the time of the transesterification reaction is 2-15 h.

10. The method for processing scraps according to claim 1, characterized in that: The treatment method further comprises the steps of recovering the solvent and diethyl oxalate and distilling the N-ethoxyoxalyl-L-alanine ethyl ester after the transesterification reaction is completed.

11. A process for synthesizing vitamin B6, comprising the step of reacting alanine, oxalic acid and ethanol as raw materials to produce N-ethoxyoxalyl-L-alanine ethyl ester, wherein the step produces a waste material containing N,N-dioxalylalanine ethyl ester, characterized in that: The synthesis process further comprises the step of treating the waste material by using the waste material treatment method according to any one of claims 1 to 10.

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