A method for preparing N,N-dimethylbenzylamine

Abstract

The present invention relates to the technical field of organic synthesis, and more specifically, the present invention relates to a method for preparing N, N-dimethylbenzylamine, including benzaldehyde and dimethylamine reacted in a jet loop reactor under the action of a catalyst. The raw material benzaldehyde used in the preparation method of the present application is non-toxic, easily available on the market and relatively low in price, halogen-free, and can avoid the shortcomings of equipment corrosion and catalyst poisoning. And the reaction yield is high, in line with the concept of green chemistry. In addition, compared with the existing N, N-dimethylbenzylamine preparation method, the wastewater treatment amount is large, the reaction yield is not high enough, the energy consumption is large, and the like, the synthesis process reaction device has high heat and mass transfer efficiency, large production capacity, small pollution, stable and safe reaction process, reaction catalyst recycling, and the product can obtain a product with a content of more than 99% by dehydration and rectification, and the product yield is high, reaching 97%.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and more specifically, to a method for preparing N,N-dimethylbenzylamine. Background Art

[0002] In the polyurethane industry, N,N-dimethylbenzylamine is a catalyst for polyester polyurethane block soft foam, polyurethane rigid foam and adhesive coatings. It is mainly used for rigid foam, which can make polyurethane foam have good initial fluidity and uniform pores, and the foam has good adhesion to the substrate. In addition, in terms of epoxy resin, N,N-dimethylbenzylamine can promote the curing of epoxy resin; and it is mainly used as an accelerator for acid anhydride, with a dosage of 1%; it is widely used as an accelerator for epoxy resin electronic potting materials, encapsulation materials, epoxy floor coatings, ship paints, etc. In the field of organic synthesis, N,N-dimethylbenzylamine is mainly used for organic drug synthesis (such as for the synthesis of quaternary ammonium salts and drug chlorhexidine, etc.), dehydrohalogenation catalyst, acid neutralizer, preservative and electron microscope section embedding accelerator, etc. N,N-dimethylbenzylamine is also used to synthesize quaternary ammonium salts and produce cationic surface active bactericides.

[0003] The existing conventional methods for preparing N,N-dimethylbenzylamine mainly include:

[0004] (1) Prepare N,N-dimethylbenzylamine by reacting benzylamine with methyl chloride. Methyl chloride is passed into benzylamine, heated, and the product is separated by distillation, with a yield of 61%. The disadvantages of this method are: methyl chloride is a toxic gas, which is very dangerous during production, by-products are produced in the reaction, separation and purification are difficult, and the yield is not high. The chemical reaction formula is as follows:

[0005]

[0006] (2) benzyl chloride and 20-40wt% dimethylamine aqueous solution are introduced into a glass module of a microchannel reactor by a feed pump in a certain molar ratio, mixed and heated for reaction; the obtained oil-water mixture is collected, cooled and allowed to stand for separation, and the upper oil layer is the reaction product N,N-dimethylbenzylamine. The reaction temperature is 50-90°C, the reaction time is 20-40S, the dimethylamine content in the dimethylamine aqueous solution is 25-35wt%, and the yield of N,N-dimethylbenzylamine is 85-90%.

[0007] The disadvantages of this method are that the product uses a microchannel reactor, which is difficult to mass produce, and the product quality and yield are poor, and there is still room for improvement. The chemical reaction formula is as follows:

[0008] Summary of the invention

[0009] In view of some problems existing in the prior art, the first aspect of the present invention provides a method for preparing N,N-dimethylbenzylamine, comprising reacting benzaldehyde and dimethylamine in a jet loop reactor under the action of a catalyst.

[0010] The present application conducts the reaction in a jet loop reactor, and has the following characteristics: ① good mass transfer performance; ② high heat transfer efficiency; ③ large operational flexibility and working volume; ④ large input power per unit volume; ⑤ simple structure, no agitators, and easy continuity of the reaction process; ⑥ good sealing performance; ⑦ easy for engineering scale-up.

[0011] In the present application, dimethylamine refers to anhydrous dimethylamine unless otherwise specified.

[0012] In one embodiment, the method for preparing N,N-dimethylbenzylamine comprises the following steps:

[0013] (1) introducing the catalyst and dimethylamine into a jet loop reactor and controlling the temperature to be 80-110° C.;

[0014] (2) Introduce hydrogen, control the pressure to 0.5-2 MPa, and pump in benzaldehyde for reaction.

[0015] (3) Dehydration and reduced pressure distillation to obtain the product.

[0016] In one embodiment, the temperature in step (1) is controlled to be 80-100°C.

[0017] In one embodiment, the pressure in step (2) is controlled to be 1-1.5 MPa.

[0018] The applicant found in the experiment that when the temperature is increased and the pressure is increased to increase the reaction rate, the yield of the product is affected, and it is unexpectedly found that the control temperature is 80-100 ° C and the control pressure is 1-1.5MPa. Not only the reaction rate is improved, but also the yield and purity are improved. The applicant believes that the possible reason is that the selectivity of the catalyst is high and the by-product impurities are low. Under the specific temperature and pressure conditions of this application, the difficulty of subsequent separation and purification work is reduced. When the temperature exceeds 80-100 ° C in this application, under the combination of the pressure of this application, the reaction rate is too fast, and the reaction system will not be controlled and the temperature will fly, resulting in uncontrollable dangers in industrial production.

[0019] Preferably, the molar ratio of benzaldehyde to dimethylamine is 1:(1.1-1.5), which may be 1:1, 1:1.3, 1:1.5, etc.

[0020] The applicant unexpectedly found that although the jet loop reactor in the present application enhances the mass transfer effect compared with the traditional stirred reactor, more dimethylamine still needs to be added, and the present application needs to control the molar ratio of benzaldehyde and dimethylamine to 1: (1.1-1.5), which improves the yield of the product to a certain extent. Increasing or slightly reducing the molar ratio will reduce the yield. The applicant believes that the possible reason is that the high-speed mobile phase contact bonding of benzaldehyde and dimethylamine is good, and the generated intermediate aminal can efficiently react with the catalyst, the molar ratio is unbalanced, and the reaction product and the by-product water will reduce the concentration of the raw material and reduce the effective collision between the raw material molecules.

[0021] In one embodiment, the catalyst is selected from one or more of palladium-carbon, platinum-carbon, palladium-aluminum composite catalyst, palladium-barium sulfate catalyst, platinum-aluminum composite catalyst, and palladium-nickel composite catalyst.

[0022] Preferably, the amount of the catalyst used is 0.01-5 wt % of the total weight of benzaldehyde and dimethylamine.

[0023] In one embodiment, step (1) comprises: introducing the catalyst and dimethylamine into a jet loop reactor, controlling the temperature to 80-110° C., keeping the materials circulating in the jet loop reactor, and the circulating jet flow rate to 100-400 m 3 / h.

[0024] The applicant unexpectedly found that the circulating injection flow rate in this application is controlled at 100-400m 3 / h, the product yield can reach about 97%, which may be due to controlling a certain circulating injection flow rate. At this time, the phases can be fully and closely contacted during vigorous stirring, reducing by-products, and under the coordinated effect of the reaction temperature and pressure in this application, the reaction process tends to proceed smoothly.

[0025] In one embodiment, in step (2), the time for pumping benzaldehyde is controlled to be 2-6 hours.

[0026] Preferably, the benzaldehyde is pumped in at a rate of 1570-1580 Kg / h.

[0027] The applicant unexpectedly found that in the preparation method of N, N-dimethylbenzylamine, the reaction temperature is controlled at 80-100 ° C, the pressure is 1-1.5 MPa, the molar ratio of benzaldehyde to dimethylamine is 1: (1.1-1.5), and the circulating injection flow rate is 100-400m 3 / h, and the rate of pumping benzaldehyde is 1570-1580Kg / h. The overall technical solution makes the reaction of synthesizing N,N-dimethylbenzylamine in the jet loop reactor stable, and the yield of the obtained product is stable between batches, which greatly improves the quality of the product.

[0028] In one embodiment, step (3) comprises: when the system pressure is stable and the hydrogen consumption stops, sampling and testing, when the benzaldehyde content is less than 0.3wt%, releasing the pressure and discharging the material, filtering and recovering the catalyst, dehydrating the material, and distilling under reduced pressure to obtain the finished product N,N-dimethylbenzylamine.

[0029] In the preparation method of N,N-dimethylbenzylamine of the present application, anhydrous dimethylamine reacts with benzaldehyde, and one benzaldehyde molecule combines with two dimethylamine molecules to generate an intermediate aminal. Under the action of a catalyst, the aminal is hydrogenated, and then one water and dimethylamine are removed to generate N,N-dimethylbenzylamine.

[0030] In one embodiment, the method for preparing N,N-dimethylbenzylamine comprises the following steps:

[0031] like Figure 1 , the catalyst in the catalyst tank 7 is introduced into the jet loop reactor, and then dimethylamine is fed, heated by the thermal oil pump 9, and the material is circulated in the jet loop reactor under the action of the reaction circulation pump 5; hydrogen is introduced to increase the system pressure, and then benzaldehyde is fed through the benzaldehyde feed pump 2, so that the reaction is carried out in the closed jet loop formed by the loop reactor body 3 and the jet mixer 4 through the pipeline. After the reaction is completed, the material is discharged after heat exchange and cooling through the reaction heat exchanger 6 and the thermal oil cooler 8.

[0032] Preferably, the reaction heat exchanger includes a tube side and a shell side, the tube side carries materials, the shell side carries heat transfer oil as a heat transfer medium, and the temperature of the heat transfer oil in the shell side can be controlled by the heat transfer oil and circulating water. According to the needs of heating and cooling the reaction, the temperature of the heat transfer medium is controlled to indirectly control the temperature of the reactor.

[0033] Preferably, the jet mixer is a high-pressure circulation pump structure with a Venturi jet tube.

[0034] Preferably, before preparing N,N-dimethylbenzylamine, the jet loop reactor is firstly replaced several times with nitrogen. The number of replacements can be conventionally selected by those skilled in the art.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The raw material benzaldehyde used in the preparation method of the present application is non-toxic, easily available on the market and relatively cheap, does not contain halogen, and can avoid equipment corrosion and catalyst poisoning and other shortcomings. And the reaction yield is high, which is in line with the concept of green chemistry. In addition, compared with the existing preparation method of N, N-dimethylbenzylamine, which has problems such as large wastewater treatment volume, insufficient reaction yield, and high energy consumption, the synthesis process reaction device has high heat and mass transfer efficiency, large production capacity, low pollution, stable and safe reaction process, and the reaction catalyst is recycled. The product can obtain a product with a content of more than 99% after dehydration and rectification, and the product yield is high, reaching 97%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A flow chart of the method for preparing N,N-dimethylbenzylamine for this application;

[0038] Among them, 1-benzaldehyde tank; 2-benzaldehyde feed pump; 3-loop reactor body; 4-jet mixer; 5-reaction circulation pump; 6-reaction heat exchanger; 7-catalyst tank; 8-thermal oil cooler; 9-thermal oil pump. DETAILED DESCRIPTION

[0039] The present invention is described below by specific implementation methods, but is not limited to the specific embodiments given below.

[0040] Example 1

[0041] A method for preparing N,N-dimethylbenzylamine is as follows:

[0042] The jet loop reactor was replaced three times with nitrogen; the palladium carbon catalyst (accounting for 3 wt% of the total amount of benzaldehyde and dimethylamine) was recovered to the jet loop reactor, and 2000 kg of dimethylamine was fed; the temperature was controlled at 100° C., and the material was kept circulating in the jet loop reactor (the circulating jet flow rate was 300 m 3 / h); hydrogen is introduced to increase the system pressure to 1.5Mpa; benzaldehyde is continuously pumped into the reactor, the molar ratio of benzaldehyde to dimethylamine is 1:1.5, the feed amount of benzaldehyde is 3150Kg, and the addition is completed in about 2h. When the system pressure is stable and the hydrogen consumption stops, sampling is performed for detection. When the benzaldehyde content is less than 0.3wt%, the pressure is released for filtration and the catalyst is recovered; the filtrate is dehydrated and distilled under reduced pressure to obtain the finished N,N-dimethylbenzylamine. The yield of the obtained N,N-dimethylbenzylamine finished product is 96.36wt%.

[0043] The experiment was repeated twice, and the measured yields of N,N-dimethylbenzylamine were 96.43 wt % and 96.84 wt %, respectively.

[0044] Example 2

[0045] The method for preparing N,N-dimethylbenzylamine is the same as that in Example 1, except that the ratio of benzaldehyde to dimethylamine is 1:1.3.

[0046] The yield of the obtained N,N-dimethylbenzylamine finished product is 94.49wt%.

[0047] Example 3

[0048] The method for preparing N,N-dimethylbenzylamine is the same as that in Example 1, except that the ratio of benzaldehyde to dimethylamine is 1:1.

[0049] The yield of the obtained N,N-dimethylbenzylamine finished product is 89.56wt%.

[0050] Example 4

[0051] The method for preparing N,N-dimethylbenzylamine is the same as that in Example 1, except that the temperature is controlled at 80°C.

[0052] The yield of the obtained N,N-dimethylbenzylamine finished product is 95.77wt%.

[0053] Example 5

[0054] The method for preparing N,N-dimethylbenzylamine is the same as that in Example 1, except that the system pressure is increased to 2.5 MPa.

[0055] The yield of the obtained N,N-dimethylbenzylamine finished product is 95.16wt%.

Claims

1. A method for preparing N,N-dimethylbenzylamine, characterized in that: The preparation method comprises: The jet loop reactor was replaced three times with nitrogen; the palladium carbon catalyst was recovered to the jet loop reactor, and 2000 kg of dimethylamine was fed; the temperature was controlled at 100 °C to keep the material circulating in the jet loop reactor; the circulating jet flow rate was 300 m 3 / h; hydrogen was introduced to increase the system pressure to 1.5Mpa; benzaldehyde was continuously pumped into the reactor, the molar ratio of benzaldehyde to dimethylamine was 1:1.5, the feed amount of benzaldehyde was 3150Kg, and the addition was completed in about 2h; when the system pressure was stable and the hydrogen consumption stopped, sampling was performed for detection, and when the benzaldehyde content was <0.3wt%, the pressure was released for filtration, and the catalyst was recovered; the filtrate was dehydrated and distilled under reduced pressure to obtain the finished N,N-dimethylbenzylamine; The palladium-carbon catalyst accounts for 3 wt% of the total amount of benzaldehyde and dimethylamine; The jet mixer is a high-pressure circulation pump structure with a Venturi jet tube.

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