Synthesis method of N-(2-cyanoethyl)-caprolactam

Abstract

The invention belongs to the field of organic synthesis, and relates to a synthesis method of N-(2-cyanoethyl)-caprolactam. According to the method, a double-base co-catalysis system is adopted, and epsilon-caprolactam and acrylonitrile are subjected to an addition coupling reaction to synthesize N-(2-cyanoethyl)-caprolactam. The method has the characteristics of easily available raw materials, high catalyst activity, simple operation, mild reaction conditions, high chemical selectivity and the like. The N-(2-cyanoethyl)-caprolactam prepared by the invention can be used for preparing organic strong base 1, 8-diazabicyclo [5, 4, 0] undecene (DBU) with important application value through hydrogenation and dehydration condensation.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and specifically relates to a method for synthesizing N-(2-cyanoethyl)-caprolactam. Background Art

[0002] N-(2-cyanoethyl)-caprolactam is a precursor for the synthesis of 1,8-diazabicyclo[5,4,0]undecene (DBU), an organic strong base with high application value. DBU plays an important role in CO2 capture and conversion, oil extraction and separation, photocuring system, microelectronics industry, high-end surface paint, medicine, polyurethane, organic synthesis and other fields. In the polyurethane industry, DBU is a low-odor gelling agent with strong catalytic activity, which is used in integral skin foam, microporous elastomer, rigid foam, etc. DBU can be combined with organic acid to prepare delayed catalysts for use in antibiotic synthesis. In organic synthesis, DBU is widely used in reactions such as elimination, isomerization, addition, esterification, etherification, amidation, diazotization, etc. The current domestic DBU market size is ~2,200 tons / year, and the price fluctuates between 70,000 and 100,000 yuan / ton. The consumption scale of DBU alone is 200 million yuan.

[0003]

[0004] Formula 1: Route for preparing DBU by caprolactam-acrylonitrile hydrogenation cyclization method

[0005] The synthesis methods of DBU reported in the literature mainly include aziridine-lactam method, lactam-acrylonitrile Hofmann reaction method, lactone-olefin diamine method, etc. Compared with the caprolactam-acrylonitrile hydrogenation cyclization method, the first three methods have higher raw material prices, harsh reaction conditions, lower total yields and fewer research reports. The synthesis route is shown in Formula 1 [Feng Xiaoqing, Shen Li, Wang Ruirui, Wang Yanchen, Song Guoqiang, Chemical Industry Progress, 2013, 32, 174-179]. However, the conventional process for preparing N-(2-cyanoethyl)-caprolactam by addition coupling in the first step mostly uses NaOH or KOH, which has many problems: 1) the reaction temperature is too high and difficult to control; 2) a large amount of polymer is easily produced, resulting in insufficient purity of N-(2-cyanoethyl)-caprolactam, which affects the subsequent reaction; 3) the reaction process requires water washing, extraction, etc., and the post-treatment steps are cumbersome [(a) Lin Jun, Cheng Xiaohong, Liu Fuchu, Synthetic Chemistry, 1994, 2, 37-41; (b); (b) MK Munshi, SMGade, MV Mane, D. Mishra, S. Pal, K. Vanka*, VHRane, AA Kelkar, J. Mol. Catal. A-Chem. 2014, 391, 144-149; (c) X.-D. Sun, Y.-J. Du, C.-Q. Li, C.-Z. Qi, Kinetics and Catalysis, 2010, 51, 653-656; (d) B. Nand, G. Khanna, A. Chaudhary, A. Lumb, JM Khurana, Curr. Org. Chem. 2015, 19, 790-812.]. Therefore, it is of great significance to find a more efficient catalyst system, simplify the reaction steps, and directly and efficiently synthesize N-(2-cyanoethyl)-caprolactam. Summary of the invention

[0006] The purpose of the present invention is to provide a method for synthesizing N-(2-cyanoethyl)-caprolactam, which synthesizes N-(2-cyanoethyl)-caprolactam through an addition coupling reaction of ε-caprolactam and acrylonitrile through a double-base co-catalytic system. The present invention has the characteristics of easy availability of raw materials, simple operation, mild reaction conditions, high catalyst activity, high chemical selectivity, etc.

[0007] The specific steps are as follows: add caprolactam I and a reaction solvent to a reactor with stirring, then add two alkali catalysts, and cool to 0-10°C. Then add acrylonitrile II dropwise, and control the reaction temperature to -10-100°C. After the addition, move the reactor to room temperature and continue stirring the reaction for 2-6 hours. After the reaction is completed, add glacial acetic acid to adjust the system pH to 6-7, remove the solvent under reduced pressure, and finally distill under reduced pressure to obtain the target product N-(2-cyanoethyl)-caprolactam, which is directly used in the next step of hydrogenation reaction.

[0008] The molar ratio of acrylonitrile II to ε-caprolactam I is 1 to 10:1;

[0009] The mass ratio of ε-caprolactam I to the base additive A is 100 to 1000:1;

[0010] The mass ratio of ε-caprolactam I to the base additive B is 100 to 1000:1;

[0011] The base additive A is t BuOK, KOH, NaOH, Na2CO3, NaHCO3, K2CO3, Cs2CO3, t BuONa, t At least one or more of BuOLi, LiHMDS, MeONa or K3PO4 or K3PO4, the base additive B is i At least one or more of Pr2NEt, NEt3, Cy2NMe, and DBU.

[0012] The reaction solvent is at least one or more of toluene, benzene, xylene, o-xylene, m-xylene, p-xylene, methanol, ethanol, isopropanol, dichloromethane, dichloroethane, carbon tetrachloride, ethyl acetate, ether, tetrahydrofuran, dimethyl sulfoxide or N,N-dimethylformamide, and N-methylpyrrolidone;

[0013] The catalytic reaction conditions are preferably: temperature of 0 to 30° C., reaction medium of toluene, xylene and m-xylene, pressure of normal pressure, and time of 2 to 6 hours.

[0014] Reaction equation of the present invention is:

[0015]

[0016] The invention adopts a double-base co-catalysis system to synthesize N-(2-cyanoethyl)-caprolactam through the addition coupling reaction of ε-caprolactam and acrylonitrile.

[0017] The N-(2-cyanoethyl)-caprolactam prepared by the invention can be subjected to hydrogenation and dehydration condensation to prepare the organic strong base 1,8-diazabicyclo[5,4,0]undecene (DBU) with important application value.

[0018] The invention has the characteristics of easy-to-obtain raw materials, simple operation, mild reaction conditions, high catalyst activity, high chemical selectivity and the like.

[0019] The present invention has the following advantages:

[0020] 1. Mild reaction conditions and simple operation.

[0021] 2. High catalyst activity

[0022] 3. The polymer has few impurities and high chemical selectivity. DETAILED DESCRIPTION

[0023] The following examples will further illustrate the present invention, but are not intended to limit the present invention. The nuclear magnetic resonance is measured by a Bruker nuclear magnetic resonance instrument, and the obtained yield is the separation yield of the reduced pressure distillation.

[0024] Example 1

[0025] t BuOLi and DBU act as co-catalysts to generate N-(2-cyanoethyl)-caprolactam III.

[0026] At room temperature, ε-caprolactam (0.4 mol, 45.26 g) and 30 mL of toluene were added to the reaction flask, followed by 113.2 mg of t BuOLi and 113.2mg DBU, cool to 0-10℃. Then add acrylonitrile (0.48mol, 25.47g) dropwise, and control the reaction temperature to 10-30℃. After the addition, move the reactor to room temperature, continue stirring the reaction for 3 hours, and monitor the reaction progress by GC. After the reaction is completed, add glacial acetic acid to adjust the pH to 6-7, remove the solvent under reduced pressure, and finally obtain the target product N-(2-cyanoethyl)-caprolactam III by vacuum distillation, 59.68g of colorless oil, 89.8% yield, GC shows that the product purity is >99%, which can be directly used for the next hydrogenation reaction. NMR hydrogen and carbon spectrum data of N-(2-cyanoethyl)-caprolactam III: 1 H NMR (400MHz, CDCl3) δ3.63(t,J=6.4Hz,2H),3.54-3.44(m,2H),2.63(t,J=6.4Hz,2H),2.57-2.51(m,2H),1.76-1.65(m,6H); 13 C NMR (101MHz, CDCl3) δ176.36,118.55,51.52,45.80,37.18,29.85,28.79,23.27,17.00.

[0027] Example 2

[0028] The process and conditions were the same as in Example 1, except that only 226.3 mg t BuOLi as catalyst (replacing 113.2 mg tBuOLi and 113.2 mg DBU), and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 57.61 g of colorless oil, with a yield of 86.6%. GC showed that the purity of the product was 95%.

[0029] Example 3

[0030] The process and conditions were the same as in Example 1, except that only 226.3 mg of DBU was added as catalyst (instead of 113.2 mg t BuOLi and 113.2 mg DBU), and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 50.35 g of colorless oil, 75.7% yield, and GC showed that the purity of the product was 90%.

[0031] Example 4

[0032] The process and conditions are the same as those in Example 1, except that the base catalyst DBU in Example 1 is replaced by an equal mass of i Pr2NEt, and the rest are the same as in Example 1. The reaction yielded N-(2-cyanoethyl)-caprolactam III, 47.61 g of colorless oil, 71.6% yield, and GC showed that the product purity was 90%.

[0033] Example 5

[0034] The process and conditions are the same as those of Example 1, except that the base catalyst in Example 1 is t BuOLi was replaced with KOH of equal mass, and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 58.73 g of colorless oil, with a yield of 88.3%. GC showed that the purity of the product was 97%.

[0035] Example 6

[0036] The process and conditions were the same as in Example 1, except that the reaction temperature in Example 1 was adjusted to 70°C, and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 57.83 g of a colorless oil, with a yield of 87.0%, and the purity of the product was 96% as shown by GC.

[0037] Example 7

[0038] The process and conditions were the same as those in Example 1, except that the reaction solvent toluene in Example 1 was replaced with an equal volume of m-xylene, and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 60.31 g of a colorless oil, with a yield of 90.7%, and GC showed that the product purity was >99%.

[0039] Example 8

[0040] The process and conditions were the same as those in Example 1, except that the reaction solvent toluene in Example 1 was replaced with an equal volume of dichloroethane, and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 55.47 g of a colorless oil, with a yield of 75.2%, and the purity of the product was 95% as shown by GC.

[0041] Example 9

[0042] The process and conditions were the same as those in Example 1, except that the reaction solvent toluene in Example 1 was replaced with an equal volume of tetrahydrofuran, and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 56.87 g of a colorless oil, with a yield of 85.5%, and GC showed that the product purity was 97%.

[0043] Example 10

[0044] The process and conditions were the same as those in Example 1, except that the amount of toluene used as the reaction solvent in Example 1 was increased to 100 mL, and the rest was the same as in Example 1. The reaction gave N-(2-cyanoethyl)-caprolactam III, 61.34 g of a colorless oil, with a yield of 92.3%, and GC showed that the product purity was >99%.

[0045] The above-mentioned implementation cases only express the implementation methods of the present invention, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for synthesizing N-(2-cyanoethyl)-caprolactam, characterized in that: Under the action of a dual-base catalyst system, ε-caprolactam I and acrylonitrile II are reacted by addition coupling reaction to synthesize N-(2-cyanoethyl)-caprolactam III; the reaction equation is as follows: The double base catalyst is base additive A and base additive B.

2. The synthesis method according to claim 1, characterized in that: The specific steps of the method are as follows: adding caprolactam I and a reaction solvent into a reactor with stirring, then adding two alkali catalysts (alkali additive A and alkali additive B), cooling to 0-10°C; then adding acrylonitrile II dropwise, controlling the reaction temperature at -10-100°C (preferably 0-30°C, more preferably 0-15°C); after the dropwise addition, moving the reactor to room temperature, continuing to stir and react for 2-6 hours; after the reaction is finished, adding glacial acetic acid to adjust the pH of the system to 6-7, removing the solvent under reduced pressure, and finally distilling under reduced pressure to obtain the target product N-(2-cyanoethyl)-caprolactam.

3. The synthesis method according to claim 2, characterized in that: The molar ratio of acrylonitrile II to ε-caprolactam I is 1 to 10:1, preferably 1 to 5:1, more preferably 1 to 3:1; The mass ratio of ε-caprolactam I to the base additive A is 100 to 1000:1, preferably 200 to 1000:1, and more preferably 500 to 1000:1; The mass ratio of ε-caprolactam I to the base additive B is 100 to 1000:1, preferably 200 to 1000:1, and more preferably 500 to 1000:

1.

4. A method for synthesizing N-(2-cyanoethyl)-caprolactam according to claim 1, 2 or 3, characterized in that: The base additive A is t BuOK, KOH, NaOH, Na2CO3, NaHCO3, K2CO3, Cs2CO3, t BuONa, t At least one or more of BuOLi, LiHMDS, MeONa or K3PO4 or K3PO4, the base additive B is i At least one or more of Pr2NEt, NEt3, Cy2NMe, and DBU.

5. The synthesis method according to claim 1 or 2, characterized in that: The reaction solvent is at least one or two or more of toluene, benzene, xylene, o-xylene, m-xylene, p-xylene, methanol, ethanol, isopropanol, dichloromethane, dichloroethane, carbon tetrachloride, ethyl acetate, ether, tetrahydrofuran, dimethyl sulfoxide or N,N-dimethylformamide, and N-methylpyrrolidone; the reaction medium is preferably at least one or two or three of toluene, xylene and m-xylene.

6. A method for synthesizing N-(2-cyanoethyl)-caprolactam according to claim 1 or 2, characterized in that: The catalytic reaction conditions are: the pressure is normal pressure.

7. The synthesis method according to claim 2, characterized in that: N-(2-cyanoethyl)-caprolactam can be hydrogenated and dehydrated to obtain the organic strong base 1,8-diazabicyclo[5,4,0]undecene (DBU) with important application value.

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