Continuous solvent-free benzoxazine preparation method

Abstract

The invention discloses a continuous solvent-free benzoxazine preparation method, and belongs to the technical field of chemical synthesis. The continuous solvent-free benzoxazine preparation method comprises the following steps: feeding a formaldehyde solution, a phenolic compound and an amine compound through a sample injection pump, mixing by using a micromixer, introducing into a microreactor for reaction, cooling by using a cooler, discharging liquid through a back pressure valve, and extracting and separating to obtain a benzoxazine product. The invention provides the method for continuously preparing benzoxazine through the micro-channel reactor without external field assistance and an organic solvent, the technical problems that the existing continuous preparation technology needs a large amount of solvent to participate in the reaction, the environmental pollution is serious, the product quality is poor and the like are solved, and the device can realize continuous production and is beneficial to industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, and in particular to a method for continuously preparing benzoxazine without solvent. Background Art

[0002] Benzoxazine is a class of heterocyclic compounds containing a benzene ring and an oxazine ring (a six-membered heterocyclic ring containing one oxygen atom and one nitrogen atom). Benzoxazine monomers can undergo polymerization through thermal initiation to form a thermosetting polymer material, namely polybenzoxazine resin. As a phenolic resin, polybenzoxazine resin has excellent heat resistance, low volume shrinkage during curing, low hygroscopicity, good mechanical and electrical properties, and molecular structure diversity. It can be widely used in aerospace, electronics, automotive industry, building materials, and high-performance composite materials.

[0003] Traditional benzoxazine synthesis often adopts intermittent operation, and the synthesis methods mainly include solution method, solvent-free method and suspension method. The solution method is to dissolve the reaction raw materials in a suitable solvent, mostly organic solvents, such as dioxane, toluene, chloroform, dimethylformamide (DMF), etc., and react at a certain temperature for a period of time to obtain benzoxazine monomer. The solvent method has good mixing effect and uniform reaction, but the reaction rate is slow, the reaction time is long, and the solvent is easy to remain and affect the later application. In addition, the use and volatilization of a large amount of organic solvents are not in line with the concept of environmental protection. The solvent-free method is to directly mix and heat the reaction materials until at least one reactant melts to make the system a liquid mixture, and react at a certain temperature to avoid the use of solvents. However, the reaction temperature of the solvent-free method is high, the heat transfer is uneven, and it is easy to cause local overheating and promote side reactions, reduce product quality, and is not suitable for systems with high melting points and large melt viscosities. The suspension method uses water as the dispersion medium. Under the action of the suspending agent, the benzoxazine monomer is obtained through unit operations such as stirring, cooling, filtering, and washing. Although it also avoids the use and pollution of organic solvents and reduces production costs, the product yield is low and the purity is not high.

[0004] Most of the existing benzoxazine synthesis methods are prepared by intermittent operation, and there are still problems such as long reaction time (generally more than 5h), complex operation, low production efficiency, batch difference, unstable product quality, large equipment volume, and difficulty in industrial amplification. In recent years, the application of continuous and miniaturized technology in the field of synthesis can effectively overcome the shortcomings of traditional intermittent reactor processes, greatly improve the heat and mass transfer effects of reactors, and improve production efficiency and product quality. However, the current benzoxazine continuous synthesis methods mostly use solution methods, which require the use of a large amount of organic solvents, cause great environmental pollution, and are not conducive to environmental protection and the concept of "green chemistry". The traditional intermittent solvent-free method has the shortcomings of low product yield and purity due to poor mass and heat transfer effects, and still needs further improvement. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing benzoxazine continuously without solvent, so as to solve the above-mentioned problems in the background technology. The present invention provides a method for preparing benzoxazine continuously through a microchannel reactor without external field assistance and organic solvent, which solves the technical problems that the existing continuous preparation technology requires a large amount of solvent to participate in the reaction, causes great environmental pollution, and has poor product quality.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing benzoxazine in a continuous solvent-free manner, comprising the following steps:

[0008] The formaldehyde solution, phenolic compounds and amine compounds are fed through a sampling pump, mixed with a micro mixer, introduced into a micro reactor for reaction, cooled with a cooler, and then discharged through a back pressure valve, extracted and separated to obtain a benzoxazine product;

[0009] The device used in the method for continuous solvent-free preparation of benzoxazine comprises an injection pump, a micro mixer, a micro reactor, a cooler, and a back pressure valve; the liquid outlet of the injection pump is connected to the liquid inlet of the micro reactor through the micro mixer, the liquid outlet of the micro reactor is connected to the liquid inlet of the cooler, the liquid outlet of the cooler is connected to the liquid inlet of the back pressure valve, and the back pressure valve is provided with a liquid outlet.

[0010] Preferably, the micro mixer is three-way or four-way.

[0011] Preferably, the flow rate of the formaldehyde solution, phenolic compounds and amine compounds in the injection pump is 0.5-100 mL / min.

[0012] Preferably, the molar ratio of formaldehyde to phenolic compounds and amine compounds in the formaldehyde solution is 1.8-2.2:1:1-1.2.

[0013] Preferably, the formaldehyde solution is a formaldehyde aqueous solution with a concentration of 37-40 wt%.

[0014] Preferably, the phenolic compound is a compound containing a phenol structure with a melting point below 100°C.

[0015] Preferably, the phenolic compound is one of phenol, methylphenol, dimethylphenol, cardanol, eugenol, galactol, coumarin, thymol, vanillin and echinol.

[0016] Preferably, the amine compound is a primary amine compound having a melting point below 100°C.

[0017] Preferably, the amine compound is one of C1-C18 aliphatic primary amine, aniline, methyl-substituted aniline, aminopropyltriethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

[0018] Preferably, the reaction temperature in the microreactor is 80-170° C., the residence time is 0.5-60 min, and the pressure is from normal pressure to 10 MPa.

[0019] Preferably, the entire reaction system is carried out in a thermostatic box, and the temperature of the system is controlled by the thermostatic box to ensure liquid transportation of all materials.

[0020] Preferably, the microreactor is a stainless steel tube with two ends open in a spiral shape, which is hollow or contains stainless steel fillers, and the inner diameter of the tube is 1-20 mm.

[0021] Preferably, the stainless steel filler is one of a θ ring, a spring, and a triangular spiral ring.

[0022] The beneficial technical effects of the present invention are as follows:

[0023] The present invention provides a method for continuously preparing benzoxazine through a microchannel reactor without external field assistance and organic solvent, which solves the technical problems of the existing continuous preparation technology that requires a large amount of solvent to participate in the reaction, causes great environmental pollution, and has poor product quality.

[0024] The method provided by the present invention does not require the use of organic solvents, is more environmentally friendly, and effectively overcomes the problems of long reaction time, complex operation, low production efficiency, poor product quality and low purity in traditional methods. The device can be produced continuously, which is conducive to industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 The process flow chart of the continuous solvent-free preparation of benzoxazine in Examples 1-4 of the present invention is shown in Figure 1. In which, 1, 2, and 3 are sample injection pumps, 4 is a micro mixer, 5 is a micro reactor, 6 is a cooler, 7 is a back pressure valve, and 8 is a thermostat.

[0027] Figure 2 This is the 1H NMR spectrum of the benzoxazine prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0029] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0030] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0031] The words “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0032] Unless otherwise specified, the "normal pressure" in the present invention is 0.1013 MPa.

[0033] The "room temperature" in the present invention is 10-30°C unless otherwise specified.

[0034] The formaldehyde aqueous solution used in the following examples and comparative examples of the present invention is a commercially available formaldehyde aqueous solution with a concentration of 37-40 wt %.

[0035] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0036] Figure 1 The process flow chart of the continuous solvent-free preparation of benzoxazine in Examples 1-4 of the present invention is shown in Figure 1. In which, 1, 2, and 3 are sample injection pumps, 4 is a micro mixer, 5 is a micro reactor, 6 is a cooler, 7 is a back pressure valve, and 8 is a thermostat.

[0037] Figure 1The device in the embodiment is composed of injection pumps 1, 2, 3, micro mixer 4, micro reactor 5, cooler 6, back pressure valve 7, and thermostat 8; the liquid outlets of injection pumps 1, 2, 3 are connected through micro mixer 4 and connected with the liquid inlet of micro reactor 5, the liquid outlet of micro reactor 5 is connected with the liquid inlet of cooler 6, the liquid outlet of cooler 6 is connected with the liquid inlet of back pressure valve 7 for controlling pressure, and the back pressure valve 7 is provided with a liquid outlet. The whole reaction device is placed in thermostat 8 for temperature control. In the following embodiments, if there is no special explanation, the whole device is operated at room temperature.

[0038] Example 1

[0039] A method for continuously preparing benzoxazine without solvent, comprising the following steps:

[0040] A mixed solution of p-cresol and formaldehyde aqueous solution (volume ratio 1:1.57) enters from the inlet of injection pump 1 (flow rate 7.3mL / min), and n-butylamine enters from the inlet of injection pump 2 (flow rate 2.7mL / min), and then enters micro mixer 4 through a tee (the molar ratio of cresol, n-butylamine and formaldehyde is 1:1.02:2.2), and then enters microreactor 5 for reaction; the reaction temperature is 130°C, the residence time is 10min, and the reaction system pressure is 1MPa; the microreactor 5 is a stainless steel hollow tube with openings at both ends in a spiral shape, the tube inner diameter is 3.2mm, and the tube length is 15m;

[0041] After the reaction is completed, the reaction liquid is cooled through the cooling tube 6 and flows out through the back pressure valve 7; the crude product is extracted with dichloromethane, washed three times with 1M sodium hydroxide solution, and then washed three times with deionized water, the solvent is removed by rotary evaporation, and vacuum dried at 60°C for 12 hours to obtain benzoxazine.

[0042] Figure 2 This is the 1H NMR spectrum of the benzoxazine prepared in Example 1 of the present invention.

[0043] 1 H NMR(400MHz,Chloroform-d)δ6.90(d,1H),6.75(s,1H),6.66(d,1H),4.82(s,2H),3 .94(s,2H),2.77-2.68(m,2H),2.24(s,3H),1.54(p,2H),1.34(h,2H),0.92(t,3H).

[0044] Example 2

[0045] A method for continuously preparing benzoxazine without solvent, comprising the following steps:

[0046] Phenol and formaldehyde aqueous solutions were heated to 70°C to prepare a mixed solution (volume ratio of 1:1.68) and introduced from the inlet of injection pump 1 (flow rate 69 mL / min), and aniline was introduced from the inlet of injection pump 2 (flow rate 31 mL / min), and then entered into micro mixer 4 through a tee (the molar ratio of phenol, aniline and formaldehyde was 1:1.1:2.0), and then introduced into micro reactor 5 for reaction; the reaction temperature was 140°C, the residence time was 5 min, and the reaction system pressure was 3 MPa; the micro reactor 5 was a stainless steel hollow tube with two ends open in a spiral shape, the inner diameter of the tube was 4 mm, and the length of the tube was 10 m;

[0047] After the reaction is completed, the reaction liquid is cooled through the cooling tube 6, flows out through the back pressure valve 7, and the temperature of the thermostat 8 is controlled at 70° C. The crude product is extracted with dichloromethane, washed three times with 1M sodium hydroxide solution, and then washed three times with deionized water, the solvent is removed by rotary evaporation, and vacuum dried at 60° C. for 12 hours to obtain benzoxazine.

[0048] 1 H NMR (600MHz, DMSO-d6) δ7.23(t,2H),7.13(d,2H),7.10(s,1H),7.08(t,1H),6.85(t,2H),6.72(d,1H),5.44(s,2H),4.65(s,2H).

[0049] Example 3

[0050] A method for continuously preparing benzoxazine without solvent, comprising the following steps:

[0051] Phenol (heated to 50°C), formaldehyde aqueous solution, and aminopropyltriethoxysilane are introduced from the inlets of injection pumps 1, 2, and 3, respectively, with inlet flow rates of 15.9 mL / min, 28.3 mL / min, and 51.8 mL / min, respectively, and enter the micro-mixer 4 through a four-way junction (the molar ratio of phenol, aminopropyltriethoxysilane, and formaldehyde is 1:1.2:2.1), and then introduced into the micro-reactor 5 for reaction; the reaction temperature is 100°C, the residence time is 30 min, and the reaction system pressure is 2 MPa; the micro-reactor 5 is a stainless steel tube with two ends open and spirally containing 2×2 mm θ ring fillers, the inner diameter of the tube is 10 mm, and the length of the tube is 9.2 m;

[0052] After the reaction is completed, the reaction liquid is cooled through the cooling tube 6, flows out through the back pressure valve 7, and the temperature of the thermostat 8 is controlled at 50° C. The crude product is extracted with dichloromethane, washed three times with 1M sodium hydroxide solution, and then washed three times with deionized water, the solvent is removed by rotary evaporation, and vacuum dried at 60° C. for 12 hours to obtain benzoxazine.

[0053] 1H NMR(400MHz,Chloroform-d)δ7.10(t,1H),6.94(d,1H),6.85(t,1H),6.76(d, 1H),3.98(s,12H),3.81(q,4H),1.67(dt,2H),1.22(t,6H),0.70-0.59(m,2H).

[0054] Example 4

[0055] A method for continuously preparing benzoxazine without solvent, comprising the following steps:

[0056] Cardanol (heated to 60°C), octadecylamine (heated to 60°C), and formaldehyde aqueous solution were introduced from the inlets of injection pumps 1, 2, and 3, respectively, with inlet flow rates of 3.3 mL / min, 3.6 mL / min, and 1.5 mL / min, respectively, and entered into micro-mixer 4 through a four-way junction (the molar ratio of cardanol, octadecylamine, and formaldehyde was 1:1.08:1.9), and then introduced into micro-reactor 5 for reaction; the reaction temperature was 100°C, the residence time was 55 min, and the reaction system pressure was 1.5 MPa; micro-reactor 5 was a stainless steel tube with openings at both ends in a spiral shape and containing 1.5×1.5 mm triangular spiral ring filler, the inner diameter of the tube was 12 mm, and the length of the tube was 1 m;

[0057] After the reaction is completed, the reaction liquid is cooled through the cooling tube 6, flows out through the back pressure valve 7, and the temperature of the thermostat 8 is controlled at 60° C. The crude product is extracted with dichloromethane, washed three times with 1M sodium hydroxide solution, and then washed three times with deionized water, the solvent is removed by rotary evaporation, and vacuum dried at 60° C. for 12 hours to obtain benzoxazine.

[0058] 1 H NMR(400MHz,Chloroform-d)δ6.90(d,1H),6.71(d,1H),6.62(s,1H),5.43(m,2 H),5.31(m,2H),4.80(s,2H),3.92(s,2H),2.8-1.2(m,42H),0.9-0.96(m,6H).

[0059] Comparative Example 1

[0060] A method for preparing benzoxazine in an intermittent solvent-free manner, comprising the following steps:

[0061] 36.57 g of n-butylamine (0.51 mol), 89.27 g of formaldehyde aqueous solution (1.1 mol) and 54.07 g of p-cresol (0.5 mol) were added to a 500 mL flask, stirred and refluxed at 80° C. for 5 h. The crude product was extracted with dichloromethane, washed three times with 1 M sodium hydroxide solution, and then washed three times with deionized water, the solvent was removed by rotary evaporation, and vacuum dried at 60° C. for 12 h to obtain benzoxazine.

[0062] Effect verification

[0063] The ring closure rate of the benzoxazine obtained in each embodiment and comparative example was calculated as follows: Taking Example 1 as an example, the H proton of the benzyl group (Ph-CH3) was selected as the standard, and its chemical shift was δ = 2.24 ppm. The H proton chemical shift of the methylene peak (O-CH2-N) of the oxazine ring was δ = 4.83 ppm. When the ring was completely closed, the theoretical ratio of the peak areas of the two was 3:2. According to the measured product 1 The percentage of the peak area ratio of δ=2.24 ppm to δ=4.83 ppm on the HNMR spectrum to the theoretical ratio is defined as the ring closure rate of benzoxazine. The ring closure rate and yield of the product are shown in Table 1.

[0064] Table 1

[0065] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Yield (%) 90.1 94.5 93.7 95.6 88 Closed loop rate (%) 89 92 91 94 84

[0066] As shown in Table 1, the benzoxazine synthesized by the process of Examples 1-4 has a higher product yield and structure closure rate than that of Comparative Example 1, which significantly improves the quality of the synthesized product.

[0067] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for continuous solvent-free preparation of benzoxazine, characterized in that: The following steps are involved: Formaldehyde solution, phenolic compounds and amine compounds are fed through a sampling pump, mixed with a micro mixer, introduced into a micro reactor for reaction, cooled by a cooler, and then discharged through a back pressure valve for extraction and separation to obtain a benzoxazine product.

2. The method according to claim 1, characterized in that The molar ratio of formaldehyde to phenolic compounds and amine compounds in the formaldehyde solution is 1.8-2.2:1:1-1.

2.

3. The method according to claim 1, characterized in that The formaldehyde solution is a formaldehyde aqueous solution with a concentration of 37-40wt%.

4. The method according to claim 1, characterized in that: The phenolic compound is a compound containing a phenol structure and having a melting point below 100°C.

5. The method according to claim 4, characterized in that The phenolic compound is one of phenol, methylphenol, dimethylphenol, cardanol, eugenol, galactol, coumarin, thymol, vanillin and echinol.

6. The method according to claim 1, characterized in that The amine compound is a primary amine compound with a melting point lower than 100°C.

7. The method according to claim 6, characterized in that The amine compound is one of C1-C18 aliphatic primary amine, aniline, methyl-substituted aniline, aminopropyltriethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

8. The method according to claim 1, characterized in that The reaction temperature in the microreactor is 80-170° C., the residence time is 0.5-60 min, and the pressure is from normal pressure to 10 MPa.

9. The method according to claim 1, characterized in that: The entire reaction system is carried out in a constant temperature box, and the temperature of the system is controlled by the constant temperature box to ensure liquid transportation of all materials.

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