Preparation method of o-vanillin-based epoxy monomer containing Schiff base

Abstract

The invention relates to a preparation method of an o-vanillin-based epoxy monomer containing a Schiff base bond. Biomass materials L-phenylalanine and o-vanillin are adopted as raw materials to prepare a Schiff base intermediate product, the Schiff base intermediate product and epichlorohydrin are mixed and reacted at high temperature under the action of a catalyst, a NaOH solution is added for further ring-closure reaction, and finally the reaction solution is extracted and subjected to rotary evaporation to prepare the o-vanillin-based epoxy monomer containing the Schiff base bond. The method conforms to the concept of green and environmental protection, the use of harmful chemical raw materials is reduced, the degradability of the epoxy resin can be improved, and the prepared epoxy resin is high in yield and has relatively high reaction activity and flame retardance.

Description

Technical Field

[0001] The invention relates to the field of bio-based epoxy resins, and in particular to a method for preparing a bio-based epoxy resin monomer containing a Schiff base bond. Background Art

[0002] Traditional bisphenol A epoxy resin accounts for about 79% to 80% of the epoxy resin industry because of its easy availability of raw materials, lowest cost and most common uses. One of its raw materials, bisphenol A, mainly comes from petroleum, which not only causes resource depletion problems, but also poses a great threat to the environment. At the same time, bisphenol A, as an endocrine disruptor, can cause endocrine disorders and cause great harm to the human body. With the increasing attention to sustainability and environmental responsibility, the recycling or reuse of epoxy resins after their effective service life has become a very important and necessary topic. However, due to the introduction of anhydride, amine and carboxylic acid curing agents, the strong three-dimensional network structure formed by the cross-linking curing reaction of epoxy resin has an insoluble nature and cannot be processed again after molding. Therefore, waste, aging and damaged epoxy resins are difficult to recycle and reuse, resulting in resource waste and solid waste pollution. Based on the above engineering background and limitations, the concept of degradable bio-based epoxy resin provides a way to study a new type of epoxy resin with sustainable utilization and excellent performance.

[0003] Current bio-based epoxy resins are thermosetting resins synthesized from renewable biomass raw materials such as vegetable oils, furan, lignin, rosin, vanillin, glycerol and itaconic acid. At the same time, by introducing a certain number of degradable covalent bonds such as acetal bonds, disulfide bonds and Schiff base bonds into the covalent cross-linked network, epoxy resins that can be degraded into small molecular monomers or oligomers under mild conditions can be prepared. This type of renewable biomass is the most likely material to replace bisphenol A, providing a feasible solution to the consumption of petroleum fuels and the growing environmental threats. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a method for preparing a bio-based epoxy monomer containing a Schiff base bond, and studies the preparation process of a Schiff base intermediate product using o-vanillin and L-phenylalanine as raw materials to obtain a bio-based epoxy containing a Schiff base bond. The raw materials are economical and environmentally friendly, the preparation process is simple and convenient, the yield is high, and it is safe and low-pollution.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme: a method for preparing an o-vanillin epoxy monomer containing a Schiff base bond, comprising the following steps:

[0006] S1: Take analytically pure L-phenylalanine and dissolve it in a solvent. Stir it in an oil bath at 60-100°C until it is completely dissolved to obtain Solution 1.

[0007] S2: Take analytically pure o-vanillin and dissolve it in a solvent. Add it to solution 1 under stirring, wherein the molar ratio of L-phenylalanine to o-vanillin is 1:(1-2.5). After mixing evenly, heat and stir in a 60-100°C oil bath for 5h-10h. After the solution drops to 25°C-40°C, filter and wash, and vacuum dry the product in an oven at 60°C-100°C for 16h-24h to obtain product 1.

[0008] S3: Mix product 1 and epichlorohydrin, add a catalyst, and react in an oil bath at 60°C-100°C for h-6h; after the solution is cooled to 25°C-40°C, add 50ml-100ml of sodium hydroxide solution, and react for 3h-6h to obtain solution 2; wherein the molar ratio of product 1 to epichlorohydrin is 1:(10-50), the molar ratio of product 1 to catalyst is 1:(0.025-0.1), and the sodium hydroxide solution is 20%-40%.

[0009] S4: Mix solution 2 with an extractant, combine the organic phases after extraction, add 100ml-200ml of a saturated sodium chloride solution, and remove excess water with a desiccant. Finally, perform rotary evaporation at 40°C-80°C in a rotary evaporator to obtain product 2, i.e., an o-vanillin epoxy monomer containing a Schiff base bond.

[0010] Furthermore, the chemical structures of the L-phenylalanine and o-vanillin are:

[0011]

[0012] Furthermore, the solvent in steps S1 and S2 is methanol, ethanol or isopropanol.

[0013] Furthermore, the catalyst in step S3 is any one or more of tetrabutylammonium bromide, triethylbenzylammonium chloride, and dodecyltrimethylammonium chloride.

[0014] Furthermore, in step S4, the extractant is dichloromethane, ethyl acetate or n-butanol.

[0015] Furthermore, in step S4, the desiccant is anhydrous magnesium sulfate, anhydrous calcium chloride or anhydrous sodium sulfate.

[0016] Compared with the prior art, the present invention has at least the following advantages:

[0017] (1) The o-vanillin used in the present invention is widely present in many plants, has a wide source and is low in cost, thus reducing the use of toxic chemical raw materials. The prepared bio-based epoxy resin is a renewable energy source, and the preparation process is simple, efficient, and has a high conversion rate.

[0018] (2) The o-vanillin-based epoxy resin prepared by the present invention introduces a reversible dynamic chemical bond, namely, a Schiff base, which enables the bio-based epoxy monomer to have higher reactivity during the curing process, thereby saving energy consumption and reducing carbon emissions during the preparation process.

[0019] (3) The o-vanillin-based epoxy resin prepared by the present invention has a degradable property due to the introduction of Schiff base chemical bonds, and has a higher residual carbon rate, and thus has better flame retardant properties.

[0020] It is very important to further elaborate on the principle of the method of the present invention and the synergy between the various steps in combination with the technical solution of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the reaction route of the epoxy monomer prepared by the present invention.

[0022] Figure 2a and Figure 2b These are the infrared spectra of product 1 and product 2, respectively.

[0023] Figure 3 This is the hydrogen NMR spectrum of product 1.

[0024] Figure 4 This is the hydrogen NMR spectrum of product 2. DETAILED DESCRIPTION

[0025] In order to further clearly and completely describe the implementation scheme of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and examples. These examples are purely illustrative and are only used to specifically describe the present invention rather than to limit the present invention.

[0026] Embodiment 1 A method for preparing an o-vanillin epoxy monomer containing a Schiff base bond comprises the following steps:

[0027] (1) Take 3.30 g (0.02 mol) of L-phenylalanine and add it to 75 ml of anhydrous ethanol. Heat it at 60°C until it is completely dissolved to obtain solution 1. Dissolve 3.04 g (0.02 mol) of o-vanillin in 75 ml of anhydrous ethanol and slowly pour it into solution 1. The resulting reaction system is reacted at 60°C for 5 hours, then cooled to 25°C, filtered and washed. The obtained product is vacuum dried for 16 hours to obtain product 1. The infrared spectrum of product 1 is shown in FIG. Figure 2aAs shown in the figure, 3110cm-1 and 1649cm-1 belong to the vibration peaks of the amino group (-NH2) of L-phenylalanine and the aldehyde group (-CHO) of o-vanillin. However, the characteristic peaks of -NH2 and -CHO in the spectrum of product 1 disappeared, and the vibration absorption peak of Schiff base (-C=N-) appeared at 1632cm-1, indicating that product 1 was successfully synthesized from o-vanillin and L-phenylalanine. The H NMR spectrum is shown in the figure Figure 3 As shown, it can be seen that the single peak at 9.96 ppm in the figure belongs to the hydrogen atom H1 of the hydroxyl group. The peaks of 6.31-7.19 ppm are attributed to the hydrogen atoms H3 and H7-H9 of the benzene ring. The peak of 7.49 ppm can be attributed to the hydrogen atom H2 of the Schiff base bond, and no signal peak related to the aldehyde (~9.5 ppm) was observed, indicating the formation of an imine bond (-C=N-).

[0028] (2) 2.99 g (0.01 mol) of product 1, 0.575 g (0.0025 mol) of triethylbenzyl ammonium chloride catalyst and 46.26 g (0.5 mol) of epichlorohydrin were mixed and reacted at 60° C. for 6 h. After the reaction was completed, the solution was cooled to 25° C., 50 ml of 20% sodium hydroxide solution was added, and the reaction was continued for 3 h.

[0029] (3) After extraction with ethyl acetate, the organic phases were combined, washed with excess saturated sodium chloride solution, and dried with anhydrous sodium sulfate. After filtering out the desiccant, the excess epichlorohydrin and ethyl acetate were removed by rotary evaporation at 60°C, and then dried in an oven at 70°C for 24 hours to finally obtain product 2. Its infrared spectrum is as follows Figure 2b As shown in the figure, the characteristic peaks at 1263cm-1, 845cm-1 and 724cm-1 prove the formation of epoxy groups, which belong to the stretching vibration, bending vibration and deformation vibration of epoxy groups respectively. At the same time, due to the reaction between the hydroxyl group of product 1 and the epoxy group of epichlorohydrin, the intensity of the hydroxyl peak in the spectrum of product 2 disappears. The H NMR spectrum is shown in the figure Figure 4 As shown, it can be seen that the characteristic peaks at 2.56-2.94 ppm in the figure are attributed to the hydrogen atoms H3 and H5 on the epoxy group.

[0030] Embodiment 2 A method for preparing an o-vanillin epoxy monomer containing a Schiff base bond comprises the following steps:

[0031] (1) 9.90 g (0.06 mol) of L-phenylalanine was added to 250 ml of anhydrous ethanol and heated at 70°C until completely dissolved to obtain solution 1. 11.4 g (0.075 mol) of o-vanillin was dissolved in 250 ml of anhydrous ethanol and slowly poured into solution 1. The obtained reaction system was reacted at 70°C for 6 h, then cooled to 35°C, filtered and washed, and the obtained product was vacuum dried for 20 h to obtain product 1.

[0032] (2) 14.95 g (0.05 mol) of product 1, 1.15 g (0.005 mol) of triethylbenzyl ammonium chloride catalyst and 138.78 g (1.5 mol) of epichlorohydrin were mixed and reacted at 80° C. for 6 h. After the reaction was completed, the solution was cooled to 25° C., 100 ml of 20% sodium hydroxide solution was added, and the reaction was continued for 3 h.

[0033] (3) After adding dichloromethane for extraction, the organic phases were combined, washed with excess saturated sodium chloride solution, and dried with anhydrous sodium sulfate. After filtering out the desiccant, the excess epichlorohydrin and dichloromethane were removed by rotary evaporation at 70°C, and then dried in an oven at 70°C for 24 hours to finally obtain product 2.

[0034] Embodiment 3 A method for preparing an o-vanillin epoxy monomer containing a Schiff base bond comprises the following steps:

[0035] (1) 4.95 g (0.03 mol) of L-phenylalanine was added to 100 ml of anhydrous ethanol and heated at 90°C until completely dissolved to obtain solution 1. 9.12 g (0.06 mol) of o-vanillin was dissolved in 100 ml of anhydrous ethanol and then slowly poured into solution 1. The obtained reaction system was reacted at 80°C for 10 h, then cooled to 40°C, filtered and washed, and the obtained product was vacuum dried for 24 h to obtain product 1.

[0036] (2) 2.99 g (0.01 mol) of product 1, 0.115 g (0.0005 mol) of triethylbenzyl ammonium chloride catalyst and 27.756 g (0.3 mol) of epichlorohydrin were mixed and reacted at 80° C. for 6 h. After the reaction was completed, the solution was cooled to 25° C., 100 ml of 40% sodium hydroxide solution was added, and the reaction was continued for 3 h.

[0037] (3) After adding dichloromethane for extraction, the organic phases were combined, washed with excess saturated sodium chloride solution, and dried with anhydrous sodium sulfate. After filtering out the desiccant, the excess epichlorohydrin and dichloromethane were removed by rotary evaporation at 70°C, and then dried in an oven at 70°C for 24 hours to finally obtain product 2.

[0038] Embodiment 4 A method for preparing an o-vanillin epoxy monomer containing a Schiff base bond comprises the following steps:

[0039] (1) 16.50 g (0.1 mol) of L-phenylalanine was added to 150 ml of anhydrous ethanol and heated at 100° C. until completely dissolved to obtain solution 1. 38.00 g (0.25 mol) of o-vanillin was dissolved in 150 ml of anhydrous ethanol and then slowly poured into solution 1. The obtained reaction system was reacted at 90° C. for 8 h, then cooled to 40° C., filtered and washed, and the obtained product was vacuum dried for 24 h to obtain product 1.

[0040] (2) 17.94 g (0.06 mol) of product 1, 0.69 g (0.003 mol) of tetrabutylammonium bromide catalyst and 55.512 g (0.6 mol) of epichlorohydrin were mixed and reacted at 90° C. for 6 h. After the reaction was completed, the solution was cooled to 35° C., 100 ml of 40% sodium hydroxide solution was added, and the reaction was continued for 6 h.

[0041] (3) After adding dichloromethane for extraction, the organic phases were combined, washed with excess saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. After filtering out the desiccant, the excess epichlorohydrin and dichloromethane were removed by rotary evaporation at 80°C, and then dried in an oven at 80°C for 24 hours to finally obtain product 2.

[0042] In summary, the present invention uses biomass materials L-phenylalanine and o-vanillin to prepare Schiff base intermediates, and then prepares vanillin-based epoxy monomers under the action of epichlorohydrin catalyst, providing a method for preparing a bio-based epoxy resin containing Schiff base. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with a preferred embodiment, it is not used to limit the present invention. Any technician in this field can make some changes or modifications to equivalent embodiments of equivalent changes without departing from the scope of the technical solution of the present invention using the technical content disclosed above. However, any brief introduction modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an o-vanillin epoxy monomer containing a Schiff base bond, characterized in that it comprises the following steps: S1: Take analytically pure L-phenylalanine and dissolve it in a solvent, and stir it in a 60-100°C oil bath until it is completely dissolved to obtain solution 1; S2: Take analytically pure o-vanillin and dissolve it in a solvent. Add it to solution 1 under stirring, wherein the molar ratio of L-phenylalanine to o-vanillin is 1:(1-2.5). After mixing evenly, heat and stir in a 60-100°C oil bath for 5h-10h. After the solution drops to 25°C-40°C, filter and wash, and vacuum dry the product in an oven at 60°C-100°C for 16h-24h to obtain product 1; S3: Mix product 1 and epichlorohydrin, add a catalyst, and react in an oil bath at 60°C-100°C for h-6h; after the solution is cooled to 25°C-40°C, add 50ml-100ml of sodium hydroxide solution, and react for 3h-6h to obtain solution 2; wherein the molar ratio of product 1 to epichlorohydrin is 1:(10-50), the molar ratio of product 1 to catalyst is 1:(0.025-0.1), and the sodium hydroxide solution is 20%-40%; S4: Mix solution 2 with an extractant, combine the organic phases after extraction, add 100ml-200ml of a saturated sodium chloride solution, and remove excess water with a desiccant. Finally, perform rotary evaporation at 40°C-80°C in a rotary evaporator to obtain product 2, i.e., an o-vanillin epoxy monomer containing a Schiff base bond.

2. The method for preparing the o-vanillin epoxy monomer containing a Schiff base bond according to claim 1, characterized in that: The chemical structures of the L-phenylalanine and o-vanillin are:

3. The method for preparing the o-vanillin epoxy monomer containing a Schiff base bond according to claim 1, characterized in that: The solvent in steps S1 and S2 is methanol, ethanol or isopropanol.

4. The method for preparing the o-vanillin epoxy monomer containing a Schiff base bond according to claim 1, characterized in that: The catalyst in step S3 is any one or more of tetrabutylammonium bromide, triethylbenzylammonium chloride, and dodecyltrimethylammonium chloride.

5. The method for preparing the o-vanillin epoxy monomer containing a Schiff base bond according to claim 1, characterized in that: In step S4, the extractant is dichloromethane, ethyl acetate or n-butanol.

6. The method for preparing the o-vanillin epoxy monomer containing a Schiff base bond according to claim 1, characterized in that: In step S4, the desiccant is anhydrous magnesium sulfate, anhydrous calcium chloride or anhydrous sodium sulfate.

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