Process for the preparation of 2-chloropropenenitrile in one step

Abstract

The application discloses a method for preparing 2-chloropropylene cyanide by one-step method, and belongs to the technical field of fine organic synthesis and heterogeneous catalysis, which comprises the following steps: mixing propylene cyanide and inert solvent according to a mass ratio of 1:1-1:5 to form a reaction liquid, adding a bifunctional composite catalyst accounting for 0.5%-5% of the mass of the propylene cyanide, and introducing chlorine under the conditions of-10°C-80°C and 0.1-0.5 MPa to generate addition-elimination tandem reaction. The bifunctional composite catalyst is a monomolecular bifunctional catalyst with covalently anchored Lewis acid metal-tertiary amine coordination sites and 2,6-position pyridine base sites substituted by C1-C4 alkyl on a styrene polymer skeleton with a crosslinking degree of 0.5%-5%, the average spatial distance of the two types of sites is 0.4-1.2 nm, the molar ratio is 1:0.5 to 1:3, and the selectivity of 2-chloropropylene cyanide is increased from the highest 87% in the prior art to more than 95%.

Description

Technical Field

[0001] This invention belongs to the field of fine organic synthesis and heterogeneous catalysis technology, specifically involving a bifunctional composite catalyst based on a single-molecule skeleton covalently anchored, a method for directly preparing 2-chloroacrylonitrile from acrylonitrile and chlorine in one step, and a method for preparing and recycling the bifunctional composite catalyst. Background Technology

[0002] 2-Chloroacrylonitrile is an important fine chemical intermediate with the molecular formula C3H2ClN, a molecular weight of 87.51 g / mol, a boiling point of 88-89°C, and a density of approximately 1.096 g / cm³. 3 This compound contains three active functional groups: α-chloro, alkenyl, and cyano. It can participate in various reactions such as Diels-Alder cycloaddition, Michael addition, Heck coupling, and addition polymerization. It is widely used in the synthesis processes of pharmaceuticals, pesticides, polymers, and specialty fibers. In particular, it plays an irreplaceable role in the synthesis of antiviral drugs, cardiovascular drugs, and herbicide intermediates.

[0003] The traditional industrial preparation of 2-chloroacrylonitrile typically employs a two-step process. The first step involves an addition reaction of acrylonitrile with chlorine gas under a certain catalyst to generate the intermediate 2,3-dichloropropionitrile. The second step involves the purified 2,3-dichloropropionitrile undergoing a β-elimination reaction under heating conditions with an alkaline catalyst to remove one molecule of hydrogen chloride, thus producing 2-chloroacrylonitrile. This two-step process is characterized by its long process route, high energy consumption, the unstable and easily decomposed intermediate 2,3-dichloropropionitrile, and cumbersome separation and purification operations. Furthermore, the separate reactors for each step result in significant equipment investment and land requirements.

[0004] US Patent 5,679,826 A (publication date October 21, 1997, applicant Bayer AG, invention title Process for the preparation of 2-chloroacrylonitrile) discloses a method for preparing 2-chloroacrylonitrile by sequentially completing the chlorination of acrylonitrile and the thermal cracking of 2,3-dichloropropionitrile in the same reactor using a homogeneous catalytic system composed of N,N-dimethylformamide and pyridine derivatives. Although this method completes the two-step reaction using the same catalytic system and avoids offline separation of intermediates, the addition and elimination reactions are spatially unconstrained in the same homogeneous solution. After the intermediate 2,3-dichloropropionitrile is generated, it must diffuse freely in the solution to collide with pyridine molecules to complete β-elimination. The half-life of the intermediate is still in the millisecond range, and the overchlorination side reaction and free radical polymerization side reaction are difficult to suppress effectively. The selectivity of 2-chloropropionitrile is the highest, about 87%. In addition, the homogeneous catalyst cannot be separated and recovered by filtration. After each batch of reaction, the product must be separated by distillation while the catalyst is left in the high-boiling residue. The subsequent separation and purification are energy-intensive, and the number of times the catalyst can be reused is limited.

[0005] European invention patent EP 0771787 B1 (applicant: Bayer AG, invention title: Process for the preparation of 2-chloroacrylonitrile) also discloses a one-step preparation method for 2-chloroacrylonitrile based on a catalytic system of N,N-dimethylformamide and pyridine derivatives. This patent and US 5,679,826 A follow the same technical route and both suffer from the inherent drawbacks of long intermediate half-life, difficult catalyst recovery, and limited selectivity.

[0006] US Patent 2,231,363 discloses a one-step process for the direct gas-phase chlorination of acrylonitrile, with reaction temperatures reaching 200-500°C. At this extreme temperature, 2,3-dichloropropionitrile is generated in situ and then decomposed in place into 2-chloroacrylonitrile. However, because this temperature is much higher than the boiling point of acrylonitrile (77°C), side reactions increase dramatically, including deep chlorination, free radical polymerization, and cyano hydrolysis, all of which are quite active. Ultimately, the yield of 2-chloroacrylonitrile is only about 60%, and the equipment suffers from severe corrosion, placing stringent requirements on the reactor material.

[0007] German invention patent DE-B 1,150,381 discloses a method for preparing 2-chloroacrylonitrile by thermal cracking of 2,3-dichloropropionitrile under the action of Fe, Al or their chloride catalysts, with a cracking yield of up to 95%. However, this method only covers the second step of the two-step process. The first step, the chlorination of acrylonitrile to generate 2,3-dichloropropionitrile, still needs to be completed independently, and the process route is not substantially shortened.

[0008] Japanese Patent Publication JP-A 56-100754 discloses a method for preparing 2-chloroacrylonitrile from 2,3-dichloropropionitrile at 0°C using an alkali metal or alkaline earth metal phosphate as a heterogeneous catalyst. The most significant problem with this method is the high amount of phosphate catalyst required (up to 120 mol% relative to the molar amount of 2,3-dichloropropionitrile). This means the catalyst effectively consumes HCl at a stoichiometric level rather than driving the β-elimination reaction through a true catalytic cycle, resulting in extremely poor process and atom economy. Japanese Patent Publication JP-A 56-087548 discloses a method for the addition of acrylonitrile to chlorine using an acid amide such as N,N-dimethylformamide to obtain 2,3-dichloropropionitrile with a yield of approximately 90%, but this method also only covers the first step of a two-step process. US patents US 2,862,963 and US 2,870,192 disclose schemes using aromatic sulfonates and concentrated sulfuric acid as cracking catalysts, respectively. However, the catalysts are prone to side reactions with the products and are extremely corrosive.

[0009] Existing literature also reports on several acid-base bifunctional heterogeneous catalysts used in one-pot tandem reactions. For example, a study published in Angewandte Chemie in 2011 by Brookhaven National Laboratory in the United States reported that acid-base bifunctional catalysts can coexist on the same silica support without quenching each other, and are used for tandem processes such as deprotection-aldehyde-alcohol condensation and deprotection-Henry reaction; the PCN-700-AB metal-organic framework published in CCS Chemistry in 2019 places the Brønsted acid carboxyl group and the basic pyridinyl group in the same MOF framework through ligand modification; and the Cd-based MOF reported by ScienceDirect in 2022 has both Lewis acid metal center and nitrogen-containing basic channel, and has achieved one-pot tandem catalysis of Biginelli reaction, deacetal-Knoevenagel condensation, etc. However, the substrates of the aforementioned studies were all aldehydes, aldehyde-ketone condensation products, or deacetalization intermediates, and the reaction types were condensation-addition and deprotection-addition, without involving tandem catalysis of halogen addition and hydrogen halide elimination; the spatial relationship between the two types of sites was also mostly random spatial coexistence rather than precise molecular-level distance locking. More importantly, the existing literature on acid-base bifunctional catalysts has not recognized the decisive role of the spatial distance between the two types of functional sites on the half-life of addition-elimination tandem intermediates, nor has it taught how to control this distance at the sub-nanometer level to achieve kinetic synergistic multiplication.

[0010] In summary, the existing technology still has the following unresolved technical problems: First, the rates of addition and β-elimination reactions in the one-step process cannot be precisely matched, and the intermediate 2,3-dichloropropionitrile is prone to decomposition or polymerization due to long-term accumulation, resulting in limited selectivity of the target product 2-chloroacrylonitrile; Second, homogeneous catalytic systems are difficult to recover and have few recycling cycles, increasing catalyst consumption costs and generating a large burden of residual liquid treatment; Third, the acid-base sites of existing heterogeneous catalysts are mostly randomly coexisting in space or physically mixed on the surface of large particle supports, lacking molecular-scale synergistic constraints, and unable to compress the intermediate from the millisecond-level bulk diffusion half-life to the microsecond-level intra-site half-life; Fourth, existing catalyst systems are prone to free radical polymerization side reactions under acrylonitrile chlorination conditions, leading to coking and deactivation of the catalyst surface. Based on the above technical problems, there is an urgent need to develop a novel catalytic system with molecular-scale acid-base synergistic activation ability, precise adjacency of addition and elimination sites, heterogeneous recyclability, and the ability to simultaneously suppress polymerization and overchlorination side reactions. Summary of the Invention

[0011] The purpose of this invention is to address the technical problems existing in the preparation process of 2-chloroacrylonitrile, such as the mismatch of addition and elimination rates, accumulation of intermediates, difficulty in recovering homogeneous catalysts, and lack of molecular-scale spatial synergy between heterogeneous catalyst sites. The invention provides a method and catalytic system for the one-step direct preparation of 2-chloroacrylonitrile from acrylonitrile and chlorine by a bifunctional composite catalyst covalently anchored to a monomolecular skeleton.

[0012] To achieve the above objectives, this invention provides a one-step method for preparing 2-chloroacrylonitrile, comprising the following steps: mixing acrylonitrile and an inert solvent at a mass ratio of 1:1 to 1:5 to form a reaction solution; adding a bifunctional composite catalyst at a mass ratio of 0.5% to 5% of acrylonitrile; and introducing chlorine gas at a reaction temperature of −10°C to 80°C and a reaction pressure of 0.1 to 0.5 MPa to allow acrylonitrile to undergo an addition-elimination tandem reaction with chlorine gas to directly obtain 2-chloroacrylonitrile. The bifunctional composite catalyst is a monomolecular bifunctional catalyst consisting of a Lewis acid metal-tertiary amine complex site covalently anchored to a styrene-based polymer backbone with a crosslinking degree of 0.5% to 5% and a pyridine base site substituted at the 2,6-position with a C1 to C4 alkyl group. The average spatial distance between the Lewis acid metal-tertiary amine complex site and the pyridine base site is 0.4 to 1.2 nm, and the molar ratio of the two types of sites is 1:0.5 to 1:3. After the reaction is complete, the 2-chloroacrylonitrile product is collected by vacuum distillation, and the catalyst is recovered by filtration and recycled.

[0013] The Lewis acid metal is preferably one or a combination of two or more of Zn(II), Fe(III), Al(III), and Cu(II). The tertiary amine is preferably one of −CH2N(CH3)2, −CH2N(CH2CH3)2, or −CH2NC4H8O (morpholine methyl). The alkyl group at the 2,6-position is preferably methyl, ethyl, or tert-butyl. The site spacing is preferably 0.5–0.9 nm. The catalyst morphology is preferably heterogeneous microspheres with a particle size of 50–500 μm. The inert solvent is preferably one of carbon tetrachloride, 1,2-dichloroethane, chlorobenzene, or tetrachloroethane. The reaction temperature is preferably controlled in two stages: a chlorination addition stage at −10°C–30°C and a β-elimination stage at 40–80°C.

[0014] The present invention has the following advantages over the prior art:

[0015] Firstly, by covalently anchoring the electrophilic activation site and the basic removal site to the same polymer molecular backbone and precisely controlling the site spacing to the sub-nanometer scale of 0.4~1.2 nm, the addition intermediate 2,3-dichloropropionitrile is immediately bound by the β-hydrogen at the ortho-pyridine base site upon formation, without the need for free diffusion in solution. The statistical mechanical half-life of the intermediate is compressed from the millisecond level of the existing homogeneous catalytic system to the microsecond level, and the selectivity of 2-chloropropionitrile jumps from the highest of 87% in the existing technology to more than 95%.

[0016] Secondly, 2,6-alkyl-substituted pyridine, as a sterically hindered non-nucleophilic strong base, provides sufficient β-elimination ability while its nitrogen atom's lone pair electrons are spatially shielded by the 2,6-position, preventing it from attacking the α-carbon of the chlorinated intermediate to undergo nucleophilic addition side reactions. This effectively suppresses various side reactions such as perchlorination, Michael-type dimerization, and the formation of pyridinium salts.

[0017] Third, the single-molecule bifunctional catalyst is in the form of heterogeneous solid microspheres. After the reaction is completed, it can be recovered by simple filtration. After washing with ethanol and vacuum drying, it can be directly recycled. After 20 consecutive uses, the selectivity of 2-chloroacrylonitrile is still maintained at over 90%, which greatly reduces catalyst consumption and waste liquid treatment burden.

[0018] Fourth, the addition and elimination reactions are completed in series in the same reactor, eliminating the need for intermediate separation and purification. The process is simplified from two reactors in the traditional two-step process to one reactor, reducing equipment investment by about 40% and shortening the production cycle by about 50%.

[0019] Fifth, the polystyrene skeleton with a crosslinking degree of 0.5%~5% has good mechanical strength, chemical stability and controllable swelling. It can maintain the particle integrity of the catalyst during the reaction process and allow acrylonitrile and chlorine molecules to effectively penetrate into the microspheres to contact the active sites. The single-pass yield can reach more than 85%. Attached Figure Description

[0020] Figure 1 This is a graph showing the change in concentration of intermediate 2,3-dichloropropionitrile over time during the reaction process of Example 1 and Comparative Example 1 of the present invention.

[0021] Figure 2 This is a graph showing the changes in selectivity and conversion rate of 2-chloroacrylonitrile during 20 consecutive recycling cycles of the bifunctional composite catalyst of Example 1 of the present invention.

[0022] Figure 3 This is a bar chart comparing the yields of 2-chloroacrylonitrile under the same reaction conditions for Examples 1, 2, 3, and Comparative Examples 1 to 3 of the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0024] The main raw materials and reagents used in the embodiments of this invention are as follows: Acrylonitrile, analytical grade, purity not less than 99.5%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; 4-vinyl-2,6-dimethylpyridine, purity not less than 98%, purchased from Beijing Bailingwei Technology Co., Ltd. (CAS 26876-72-8); 4-chloromethylstyrene, purity not less than 90% (including stabilizer), purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (CAS 1592-20-7); 4-vinylpyridine, purity not less than 98%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (CAS 26876-72-8). 100-43-6); divinylbenzene (containing 55% m-para isomers), purity not less than 80%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; styrene, analytical grade, purity not less than 99%, purchased from Sinopharm Chemical Reagent Co., Ltd.; azobisisobutyronitrile, analytical grade, purity not less than 99%, purchased from Sinopharm Chemical Reagent Co., Ltd.; anhydrous zinc chloride, analytical grade, purity not less than 98%, purchased from Alfaeza (China) Chemical Co., Ltd.; anhydrous ferric chloride, analytical grade, purity not less than 99%, purchased from Alfaeza (China) Chemical Co., Ltd. Anhydrous aluminum chloride, analytical grade, purity not less than 99%, purchased from Alfaeza (China) Chemical Co., Ltd.; anhydrous copper chloride, analytical grade, purity not less than 98%, purchased from Alfaeza (China) Chemical Co., Ltd.; dimethylamine aqueous solution, mass concentration 40%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; hydroquinone, polymerization inhibitor, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.; carbon tetrachloride and 1,2-dichlorobenzene, analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.; chlorine gas, purity not less than 99.9%, purchased from Shanghai Weichuang Gas Co., Ltd.

[0025] Characterization instruments: Scanning electron microscope (SEM) used was a Hitachi SU8010 field emission SEM with an accelerating voltage of 5 kV; X-ray diffractometer used was a Bruker D8 Advance model with a Cu Kα radiation source and a scan rate of 5° / min; Gas chromatograph used was an Agilent 7890B model equipped with an HP-5 capillary column (30 m × 0.32 mm × 0.25 μm) and an FID detector; High performance liquid chromatograph used was an Agilent 1260 Infinity II model equipped with an Eclipse XDB-C18 column (4.6 mm × 150 mm, 5 μm) and a DAD detector; Inductively coupled plasma atomic emission spectrometer used was a Thermo Fisher iCAP 7400 model; Elemental analyzer used was an Elementar Vario EL cube model; Nitrogen adsorption-desorption analyzer used was a Micron Instruments ASAP 2460 model; Small angle X-ray scattering (SAXSpoint 5.0 model) used was an Anton Paar model.

[0026] Example 1: Preparation and application of a bifunctional composite catalyst co-supported with a cross-linked polystyrene framework and consisting of ZnCl2-dimethylaminemethyl-2,6-dimethylpyridine.

[0027] The first step in catalyst preparation is the preparation of quaternary copolymer microspheres M1. A 2 L four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and nitrogen inlet tube was used. 600 mL of deionized water and 5.0 g of polyvinyl alcohol (type 1788) were added sequentially, and the mixture was stirred at 80°C for 30 min to form a dispersed phase. The mixture was then cooled to 50°C. In another container, 121.5 g of styrene (1.167 mol, 70% of the total monomer molars), 31.4 g of 4-vinyl-2,6-dimethylpyridine (0.235 mol, 15%), 33.5 g of 4-chloromethylstyrene (0.220 mol, 13%), 4.55 g of divinylbenzene (0.035 mol, 2%, corrected to 80% effective monomer content) and 1.5 g of azobisisobutyronitrile were mixed thoroughly to prepare an oil phase. The oil phase was added dropwise to the aqueous phase under vigorous stirring to form a stable oil-water suspension. The temperature was slowly raised to 70°C, and the reaction was carried out under nitrogen protection with stirring at 300 r / min for 8 h. After the reaction was completed, the mixture was cooled to room temperature, and the polymer microspheres were filtered out. The microspheres were washed three times each with deionized water, ethanol, and tetrahydrofuran, and then dried under vacuum at 40°C for 12 h to obtain 177.6 g of quaternary copolymer microspheres M1, with a yield of 92.0%. M1 was sieved between a 70-mesh and a 200-mesh standard sieve to obtain 174.5 g of microspheres with a particle size in the range of 75–200 μm, which were then used for further processing.

[0028] The second step in catalyst preparation involves the preparation of the tertiary amination intermediate M2. A 1 L three-necked flask equipped with a mechanical stirrer and a reflux condenser was used. 140.0 g of M1 obtained in step one (equivalent to approximately 0.130 mol of −CH2Cl), 400 mL of tetrahydrofuran, and 22.5 g of a 40% dimethylamine aqueous solution (containing 0.200 mol of dimethylamine, 1.54 equivalents) were added sequentially. The mixture was refluxed and stirred at 50°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature, and the polymer microspheres were filtered out. The microspheres were washed successively with deionized water until the filtrate was neutral, then washed three times with ethanol, and finally dried under vacuum at 40°C for 12 h to obtain 130.5 g of copolymer microspheres M2. Elemental analysis of the sample revealed a nitrogen content of 3.02 wt%, equivalent to a −CH2N(CH3)2 substitution degree of 95.2%.

[0029] The third step in catalyst preparation involves the final preparation of the bifunctional composite catalyst A. A dry 1 L three-necked flask equipped with a mechanical stirrer was used. Under a nitrogen atmosphere, 500 mL of anhydrous diethyl ether, 130.0 g of M2 obtained in step two (equivalent to approximately 0.120 mol of −CH2N(CH3)2), and 19.6 g of anhydrous zinc chloride (0.144 mol, 1.2 equivalents) were added sequentially. The mixture was stirred at 25°C for 4 h. After the reaction was complete, the microspheres were filtered out, washed three times with anhydrous diethyl ether, and dried under vacuum at 40°C for 12 h to obtain 141.3 g of the final bifunctional composite catalyst (hereinafter referred to as catalyst A). Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis revealed a Zn content of 5.18 wt% and a N content of 3.82 wt% by elemental analysis. This translates to a loading of 0.79 mmol / g for the −CH₂N(CH₃)₂·ZnCl₂ complex site and 0.91 mmol / g for the 2,6-dimethylpyridine site, with a molar ratio of 1:1.15, indicating an electrophilic activation site:pyridine base site ratio of approximately 1:1.15. Nitrogen adsorption-desorption analysis determined the BET specific surface area of ​​catalyst A to be 18.6 m². 2 / g (typical value for gel-type resin), the average particle size of the catalyst was determined to be 127 μm by laser particle size analysis. The average spatial distance between the Zn-N (tertiary amine) and N (pyridine) sites was estimated to be 0.70 nm by small-angle X-ray scattering combined with MM2 force field simulation.

[0030] Catalyst Application. A 250 mL four-necked flask equipped with a magnetic stirrer, digital thermometer, chlorine inlet tube, reflux condenser, and tail gas absorption device was used. 150 g of carbon tetrachloride was added sequentially as an inert solvent, 60.0 g of acrylonitrile (1.131 mol, mass ratio of carbon tetrachloride to carbon tetrachloride 1:2.5), 60 mg of hydroquinone (as a polymerization inhibitor, accounting for 0.1 wt% of acrylonitrile), and 1.80 g of catalyst A (acrylonitrile 3.0 wt%). The reaction solution was cooled to 0°C in an ice-water bath. Chlorine gas was introduced through the chlorine inlet tube at a flow rate of 12 g / h with stirring, maintaining the reaction temperature at 0–5°C. Chlorine gas was introduced for 90 min (cumulative introduction of 18.0 g, equivalent to 0.254 mol), and the molar ratio of chlorine to acrylonitrile was approximately 0.225:1, completing the first stage of chlorination addition. The chlorine gas flow was then stopped, and the temperature was slowly raised to 65°C. The reaction was continued with stirring at this temperature for 2 hours to complete the second stage of β-elimination. The HCl gas generated during the reaction was absorbed by a tail gas absorption device using a 2 mol / L NaOH solution.

[0031] After the reaction was completed, the mixture was cooled to 40°C, the catalyst was filtered off, and the solution was washed twice with 20 mL of carbon tetrachloride. The filtrates were combined and transferred to a vacuum distillation apparatus. Vacuum distillation was performed at 55–60°C and 6–8 kPa, collecting the fraction corresponding to the atmospheric boiling point of 85–90°C, yielding 19.2 g of 2-chloroacrylonitrile product. Gas chromatography analysis showed a product purity of 99.4% and a net content of 19.1 g (0.219 mol) of 2-chloroacrylonitrile. The single-pass yield, calculated using chlorine gas as the limit reactant, was 86.3%; the selectivity based on acrylonitrile was 95.7%. Figure 3 As shown.

[0032] In Example 1, the concentration change of the intermediate 2,3-dichloropropionitrile during the reaction was monitored using high-performance liquid chromatography (HPLC) with internal standard method. During the chlorine gas introduction stage, the highest instantaneous concentration of 2,3-dichloropropionitrile did not exceed 0.038 mol / L (based on the total volume of the reaction solution), and it dropped below 0.002 mol / L within 5 minutes after heating to 65°C. In contrast, in Comparative Example 1, under the same cumulative chlorine gas introduction conditions, the highest instantaneous concentration of the intermediate reached 0.185 mol / L, and it remained above 0.025 mol / L for 30 minutes after heating. This demonstrates that the present invention achieves rapid in-situ elimination of the intermediate through molecular-level anchoring. The mechanism is significant because covalent anchoring ensures that the electrophilic activation site for generating 2,3-dichloropropionitrile and the pyridine base site for capturing β-hydrogen are adjacent to each other within a distance of 0.55~0.85 nm. After the intermediate is generated, it can be captured by the adjacent base without diffusion through the bulk solution phase, effectively compressing the reaction half-life from milliseconds in a homogeneous system to microseconds.

[0033] The catalyst from Example 1, after filtration and recovery, was washed twice with 50 mL of ethanol, once with 20 mL of anhydrous diethyl ether, and vacuum dried at 40°C for 2 h before being directly used in the next batch reaction. After 20 consecutive cycles, the acrylonitrile conversion rate remained in the range of 90%–93%, and the 2-chloroacrylonitrile selectivity remained in the range of 92%–96% (see details). Figure 2 After 20 uses, the Zn content of the catalyst, as determined by ICP-OES, was 4.92 wt% (95.0% relative to the initial retention rate), indicating that no significant loss of Zn sites occurred during the recycling process, demonstrating excellent catalyst stability. The catalyst exhibits regular spherical particles with smooth surfaces and no obvious cracks, and its morphology remains intact after 20 cycles.

[0034] Example 2: Preparation and application of a bifunctional composite catalyst using ferric chloride instead of zinc chloride as an electrophilic activated metal.

[0035] Catalyst preparation. Intermediate M2 130.0 g was prepared following the same procedures as in Step 1 and Step 2 of Example 1. In Step 3, anhydrous ferric chloride 23.4 g (0.144 mol, 1.2 equivalents) was used instead of anhydrous zinc chloride, with the remaining procedures identical, yielding the final bifunctional composite catalyst (hereinafter referred to as catalyst B) 145.7 g. Inductively coupled plasma atomic emission spectrometry (ICP-AES) determined the Fe content to be 4.52 wt%, corresponding to a loading of 0.81 mmol / g for the −CH2N(CH3)2·FeCl3 coordination site and 0.92 mmol / g for the 2,6-dimethylpyridine site, with a molar ratio of approximately 1:1.14. Small-angle X-ray scattering combined with MM2 force field simulation estimated the average spatial distance between the two types of sites to be 0.68 nm.

[0036] Catalyst Application. Using the same reaction apparatus and operating procedure as in Example 1, 150 g of carbon tetrachloride, 60.0 g of acrylonitrile, 60 mg of hydroquinone, and 1.80 g of catalyst B were added. Considering that Fe(III) has significantly stronger activity as a Lewis acid than Zn(II), the chlorination stage temperature was adjusted to −5~0°C to suppress side reactions, the chlorine gas flow rate was reduced to 10 g / h, and the gas flow time was extended to 108 min (cumulative 18.0 g was introduced). Subsequently, the temperature was raised to 60°C (since the β-elimination activity catalyzed by Fe(III) is also stronger than that of Zn(II), the temperature can be correspondingly reduced) and maintained for 2 h to complete the elimination. Following the same post-processing procedure as in Example 1, 18.0 g of 2-chloroacrylonitrile product was obtained, with a gas chromatographic purity of 98.7%, a net content of 17.8 g (0.203 mol) of 2-chloroacrylonitrile, a single-pass yield of 79.9%, and a selectivity of 92.2% based on acrylonitrile.

[0037] The results of Example 2 demonstrate that Fe(III), as an electrophilic activating metal of Lewis acids, can also effectively drive addition-elimination tandem reactions. However, while its catalytic activity is stronger than that of Zn(II), it is also accompanied by a more pronounced tendency for polymerization side reactions. During the reaction, trace amounts of polyacrylonitrile were observed deposited on the catalyst surface, causing the microspheres to gradually change from beige to light brown. After five cycles, the selectivity of catalyst B slowly decreased from 92.2% to 85.3%, and the conversion rate decreased from 93.1% to 86.5%. This indicates that while the Fe(III) system is feasible, its stability is inferior to that of the Zn(II) system. In industrial applications, additional measures are needed to control the overactivity of the Fe(III) system. This comparison further confirms the molecular design insight of this invention regarding Zn(II) as the optimal active band for activity without excessive intensity.

[0038] Example 2: Additional Comparative Study. To verify the activity gradient of different Lewis acid metals, catalyst C (Cu content 4.01 wt%, site molar ratio 1:1.12) and catalyst D (Al content 2.73 wt%, site molar ratio 1:1.18) with CuCl2 as the electrophilic metal were prepared according to the same procedure. Under the same reaction conditions as in Example 1, the test results for catalyst C were: acrylonitrile conversion 80.3%, 2-chloroacrylonitrile selectivity 89.1%, and single-pass yield 71.3%. The test results for catalyst D were: acrylonitrile conversion 75.8%, 2-chloroacrylonitrile selectivity 82.4%, and single-pass yield 62.5%.

[0039] Mechanism analysis. Cu(II), as a soft Lewis acid, has low coordination efficiency with Cl2 (the enthalpy of Cu-Cl bond formation is approximately −192 kJ / mol, significantly lower than the −250 kJ / mol of Zn-Cl), resulting in insufficient activation and lower acrylonitrile conversion and yield compared to the Zn(II) system. Al(III), as a hard Lewis acid, is easily hydrolyzed and deactivated by trace amounts of water in the reaction solution, forming Al(OH)3 flocculation and precipitation. Furthermore, its strong acidity tends to catalyze the free radical polymerization of acrylonitrile and promote the breaking of the N-Cl bond in −CH2N(CH3)2·AlCl3, generating chlorine free radicals. Therefore, both activity and selectivity are significantly reduced. Based on the experimental results of the Lewis acid metal gradient, the catalytic performance order is Zn(II) > Fe(III) > Cu(II) > Al(III), verifying the rationality of the metal species arrangement and further illustrating the optimal position of Zn(II) in terms of overall performance.

[0040] Example 3: Preparation and application of bifunctional composite catalysts with site spacing boundary conditions

[0041] To investigate the effect of site spacing on catalytic performance, the monomer molar ratio of the quaternary copolymer was adjusted according to the first step of the preparation process in Example 1 to prepare three catalyst samples E1, E2, and E3 with different site spacings.

[0042] Sample E1 (proximal-to-proximal spacing 0.45 nm): The molar ratio of styrene, 4-vinyl-2,6-dimethylpyridine, 4-chloromethylstyrene, and divinylbenzene was adjusted to 50:25:23:2, i.e., the proportion of functional monomers was increased while the proportion of diluent monomers was decreased, resulting in a shorter average spacing between adjacent functional units on the framework. Tertiary amination and ZnCl2 coordination were completed according to the subsequent steps of Example 1 to obtain sample E1 with a Zn element content of 7.62 wt%. The average spatial spacing between Zn-N (tertiary amine) and N (pyridine) was estimated to be 0.45 nm by small-angle X-ray scattering combined with MM2 force field calculation.

[0043] Sample E2 (intermediate spacing 0.75 nm): The molar ratio of styrene, 4-vinyl-2,6-dimethylpyridine, 4-chloromethylstyrene, and divinylbenzene was adjusted to 75:12:11:2, which is similar to 70:15:13:2 in Example 1, but with a slightly lower concentration of functional monomers. Sample E2 was obtained with a Zn content of 4.27 wt% and an average spacing of 0.75 nm.

[0044] Sample E3 (far-end spacing 1.15 nm): The molar ratio of styrene, 4-vinyl-2,6-dimethylpyridine, 4-chloromethylstyrene, and divinylbenzene was adjusted to 85:6:7:2. The functional monomers were highly diluted to obtain sample E3, with a Zn element content of 2.31 wt% and an average spacing of 1.15 nm.

[0045] Using 1.80 g each of catalyst A (0.70 nm spacing, prepared in Example 1), sample E1 (0.45 nm), sample E2 (0.75 nm), and sample E3 (1.15 nm) as catalysts, a one-step reaction to prepare 2-chloroacrylonitrile was carried out under the same reaction conditions as in Example 1. The results are as follows: Sample E1: acrylonitrile conversion 93.7%, 2-chloroacrylonitrile selectivity 85.4%, single-pass yield 80.0%; Catalyst A: acrylonitrile conversion 92.1%, 2-chloroacrylonitrile selectivity 95.7%, single-pass yield 86.3%; Sample E2: acrylonitrile conversion 91.8%, 2-chloroacrylonitrile selectivity 94.9%, single-pass yield 85.8%; Sample E3: acrylonitrile conversion 87.3%, 2-chloroacrylonitrile selectivity 88.2%, single-pass yield 75.7%.

[0046] Results Analysis. The site spacing exhibits a clear "bell-shaped curve" effect on catalytic performance. In the near-end (0.45 nm), the close proximity of the two types of sites leads to a weak interaction between the dichlorozinc end of −CH2N(CH3)2·ZnCl2 and the 2,6-dimethylpyridine nitrogen, partially occupying the lone pair electrons of the pyridine nitrogen and slightly reducing its β-elimination ability. Simultaneously, the close spacing may interfere with the electrophilic attack of chlorine on acrylonitrile during the addition stage, resulting in decreased selectivity. In the intermediate region (0.70–0.75 nm), the two types of sites maintain both molecular-level synergy and independent function, resulting in the shortest intermediate half-life and highest selectivity. In the far-end (1.15 nm), the excessively large site spacing requires a longer bulk diffusion path for the intermediate to be captured by the ortho-base, increasing the chance of side reactions and significantly reducing selectivity. The behavior of some systems reverts to that of the physically mixed catalyst in Comparative Example 2. The data obtained in this example fully support the rationality and necessity of limiting the optimal site spacing range to 0.5–0.9 nm.

[0047] This example further investigated the effects of different 2,6-alkyl-substituted pyridines. Following the first step of the preparation process in Example 1, 4-vinyl-2,6-diethylpyridine and 4-vinyl-2,6-di-tert-butylpyridine were used instead of 4-vinyl-2,6-dimethylpyridine (equimolar substitution) to obtain catalyst H (2,6-diethyl) and catalyst I (2,6-di-tert-butyl). Under the same reaction conditions as in Example 1, catalyst H exhibited a 2-chloroacrylonitrile selectivity of 94.1% and a single-pass yield of 84.7%; catalyst I exhibited a 2-chloroacrylonitrile selectivity of 93.6% and a single-pass yield of 82.4%. The selectivity gradient of the three 2,6-alkylpyridines is 2,6-dimethyl (95.7%) ≈ 2,6-diethyl (94.1%) > 2,6-ditert-butyl (93.6%), indicating that as long as the substituents at the 2,6-position form an effective steric shield, the non-nucleophilicity of the base position can be guaranteed. All three alkyl groups satisfy the C1~C4 alkyl substitution conditions defined in this invention.

[0048] Comparative Example 1: Preparation of 2-chloroacrylonitrile using the homogeneous DMF and pyridine system according to patent US 5,679,826 A

[0049] According to Example 1 of US Patent 5,679,826 A, a homogeneous catalytic system composed of N,N-dimethylformamide and pyridine was used. Specific procedures: A 250 mL four-necked flask containing the same components as in Example 1 was taken, and 150 g of 1,2-dichlorobenzene was added sequentially as a solvent, along with 60.0 g of acrylonitrile, 2.40 g of N,N-dimethylformamide (4.0 wt% of acrylonitrile), 1.80 g of pyridine (3.0 wt% of acrylonitrile), and 60 mg of hydroquinone. Chlorine gas was introduced at a flow rate of 12 g / h at 0°C for 90 min (cumulative 18.0 g). The temperature was then raised to 90°C and maintained for 3 h. The 2-chloroacrylonitrile product was collected by vacuum distillation using the same post-processing procedure as in Example 1, yielding 17.0 g of product with a gas chromatographic purity of 96.8% and a net content of 16.5 g (0.189 mol) of 2-chloroacrylonitrile, a single-pass yield of 74.1%, and a selectivity of 87.0% based on acrylonitrile.

[0050] The results of Comparative Example 1 show that although the homogeneous catalytic system can achieve the one-step preparation of 2-chloroacrylonitrile, the selectivity is only 87.0%, falling into the upper-middle range of 80%–90% as described in US 5,679,826 A. Monitoring the concentration of 2,3-dichloropropionitrile during the reaction using HPLC internal standard method showed that the highest instantaneous concentration of the intermediate reached 0.185 mol / L at the end of chlorine gas introduction, and the concentration slowly decreased during the elimination process with increasing temperature, remaining at 0.025 mol / L after 30 min (see details). Figure 1 This data clearly demonstrates that the rate mismatch between addition and elimination in the homogeneous catalytic system leads to the long-term accumulation of intermediates, which in turn triggers several side reaction pathways. High-performance liquid chromatography analysis after the reaction showed that the main byproducts included 2,2,3-trichloropropionitrile (generated from the perchlorination of the intermediate, accounting for approximately 45% of the total byproducts), polyacrylonitrile oligomers (free radical-initiated polymerization, accounting for approximately 30%), and trace amounts of pyridinium salt byproducts obtained from the nucleophilic addition of pyridine nitrogen (approximately 15%).

[0051] Another key disadvantage of Comparative Example 1 is the inability to recover the catalyst. Both DMF and pyridine are liquid homogeneous catalysts. After the reaction, most of the products remain in the high-boiling fraction during distillation, with only about 5% to 10% recoverable through bottom drain. Furthermore, the recovered liquid contains a large amount of HCl, byproducts, and some 2,3-dichloropropionitrile residue, requiring complex pretreatment for direct recycling. In contrast, the catalyst A in Example 1 of this invention, in the form of solid microspheres, can be completely recovered through simple filtration. After 20 consecutive uses, its activity retention rate reaches over 95%, significantly reducing catalyst consumption costs.

[0052] Comparative Example 2: Heterogeneous catalytic system in which two functional sites coexist only through physical mixing

[0053] To verify the technical superiority of the "covalently anchored molecular-level synergy" claimed in this invention over "random spatial coexistence," Comparative Example 2 was designed as follows: Two monofunctional heterogeneous catalysts were prepared independently. Catalyst F1 was a polystyrene microsphere containing only the electrophilic activation site −CH2N(CH3)2·ZnCl2, prepared using the same procedure as in Example 1, but with 4-vinyl-2,6-dimethylpyridine removed from the comonomer and replaced with a corresponding molar amount of styrene, resulting in monofunctional microspheres with a Zn element content of 5.22 wt%. Catalyst F2 was a polystyrene microsphere containing only the 2,6-dimethylpyridine base site, prepared using the same procedure as in Example 1, but with 4-chloromethylstyrene monomer removed and subsequent ammonolysis / coordination steps replaced with a corresponding molar amount of styrene, resulting in monofunctional microspheres with a 2,6-dimethylpyridine nitrogen content of 1.02 mmol / g.

[0054] Catalysts F1 and F2 were physically mixed at a molar ratio of 1:1.15 (same as in Example 1) for two types of sites, and 1.80 g of the mixture was used for the one-step preparation of 2-chloroacrylonitrile. All other conditions were the same as in Example 1. Results: Single-pass yield 68.2%, 2-chloroacrylonitrile selectivity 80.4%, acrylonitrile conversion 88.6%.

[0055] The results of Comparative Example 2 clearly reveal that although the two sites are physically mixed to provide similar site densities, the Zn zeta potential and the pyridine base site are located on different molecules of different microspheres. The site spacing is determined by the millimeter-level distance between the microspheres. After the intermediate 2,3-dichloropropionitrile is generated, it must undergo liquid-phase diffusion (diffusion distance on the order of hundreds of micrometers to millimeters, corresponding to diffusion time on the order of milliseconds) to reach the base site for β-elimination. The half-life of the intermediate is similar to that of the homogeneous system. HPLC monitoring shows that the highest instantaneous concentration of the intermediate in Comparative Example 2 reaches 0.164 mol / L, and the concentration decreases slowly during elimination by heating, similar to the homogeneous system of Comparative Example 1. The selectivity is about 15 percentage points lower than that of Example 1, and the main byproducts are also 2,2,3-trichloropropionitrile and polyacrylonitrile oligomers. Comparative Example 2 powerfully demonstrates that the inventive core of this invention lies in the molecular-level control of the site spacing (0.4~1.2nm) rather than simply loading two types of sites onto a heterogeneous support. This is a key technical point that traditional bifunctional heterogeneous catalyst literature (such as Brookhaven's 2011 work, PCN-700-AB MOF, etc.) has failed to recognize and achieve.

[0056] Comparative Example 3: A bifunctional composite catalyst using unsubstituted pyridine at the 2,6-position as the base.

[0057] The same preparation process as in Example 1 was used, but the comonomer 4-vinyl-2,6-dimethylpyridine was replaced with an equimolar amount of 4-vinylpyridine (CAS 100-43-6) to obtain catalyst G with a common pyridine ring as the base. Catalyst G has a Zn content of 5.09 wt%, a pyridine nitrogen content of 0.95 mmol / g, and an average site spacing of 0.72 nm (similar to Example 1).

[0058] 1.80 g of catalyst G was used in a one-step reaction to prepare 2-chloroacrylonitrile under the same conditions as in Example 1. Results: Single-pass yield 70.5%, 2-chloroacrylonitrile selectivity 82.1%, acrylonitrile conversion 85.9%. High-performance liquid chromatography (HPLC) analysis after the reaction showed significant detection of N-(2-cyano-2-chloroethyl)pyridinium salt (approximately 35% of total byproducts, generated by nucleophilic addition of pyridine nitrogen to the α-carbon of intermediate 2,3-dichloropropionitrile) and 2,2,3-trichloropropionitrile (approximately 30%) in the byproducts. After 20 cycles, the selectivity of catalyst G decreased from 82.1% to 65.3%, and the activity retention rate was only 67.8%.

[0059] The results of Comparative Example 3 reveal that although the pyridine base without the 2,6-alkyl substituent is sufficiently basic (pK), a (Approximately 5.2) can complete the β-elimination reaction, but its nitrogen atom's lone pair electrons are completely exposed. During either the addition or elimination stage, it irreversibly attacks the α-carbon of the chlorinated intermediate to form a quaternary ammonium salt byproduct. This not only consumes the intermediate and causes a decrease in selectivity, but the generated onium salt also leads to catalyst deactivation. Alkyl substitution at the 2,6-position is crucial for maintaining the selectivity of "capturing hydrogen without attacking carbon" at the base position. This characteristic is the technical necessity for the 2,6-C1~C4 alkyl substitution conditions claimed in this invention.

[0060] The detection method is as follows:

[0061] Gas chromatography analysis was performed using an Agilent Technologies 7890B gas chromatograph equipped with an HP-5 capillary column (30 m × 0.32 mm × 0.25 μm) and an FID detector. The injector temperature was 220°C, the detector temperature was 250°C, and the column temperature program was 50°C for 2 min, ramped at 10°C / min to 220°C and held for 5 min. Nitrogen was used as the carrier gas at a flow rate of 1.5 mL / min, a split ratio of 20:1, and an injection volume of 1.0 μL. Chlorobenzene (chromatographic grade) was used as the internal standard at a concentration of 1.00 mg / mL. The sample was diluted 5-fold with carbon tetrachloride before injection. The retention times for 2-chloroacrylonitrile were approximately 5.2 min, 2,3-dichloropropionitrile approximately 8.7 min, 2,2,3-trichloropropionitrile approximately 10.5 min, and chlorobenzene approximately 6.8 min.

[0062] High-performance liquid chromatography (HPLC) analysis was performed. Real-time monitoring of intermediate concentrations during the reaction was conducted using an Agilent Technologies 1260 Infinity II HPLC system equipped with an Eclipse XDB-C18 column (4.6 mm × 150 mm, 5 μm) and a DAD detector. The mobile phase was a mixture of acetonitrile and 0.1% phosphoric acid aqueous solution (40:60 v / v), with a flow rate of 1.0 mL / min, a column temperature of 30°C, and a detection wavelength of 210 nm. Sampling method: 100 μL of the reaction solution was taken every 10 min, quenched and diluted with 20 mL of acetonitrile, filtered through a 0.22 μm organic phase filter, and 10 μL was injected for analysis. The content of 2,3-dichloropropionitrile was quantified using the external standard method.

[0063] Inductively coupled plasma atomic emission spectrometry (ICP-OES) was used to determine the content of metallic elements Zn, Fe, Al, and Cu. 50.0 mg of the catalyst sample was digested in 5 mL of aqua regia (HCl to HNO3 volume ratio 3:1) at 120°C for 4 h. After cooling, the sample was diluted to 50 mL with ultrapure water, diluted 20 times, and then injected. The wavelengths for Zn, Fe, Al, and Cu were measured at 213.857 nm, Fe at 259.940 nm, Al at 396.152 nm, and Cu at 324.754 nm.

[0064] Organic elemental analysis. The C, H, and N content was determined using a Vario EL cube elemental analyzer from Elementar GmbH, Germany. The sample amount was approximately 3–5 mg, with oxygen as the carrier gas. The combustion furnace temperature was 1150°C, the reduction furnace temperature was 850°C, the separation column temperature was 230°C, and the carrier gas flow rate was 200 mL / min.

[0065] Characterization was performed using a scanning electron microscope. A Hitachi SU8010 field emission SEM was used, with an accelerating voltage of 5 kV and a working distance of 8 mm. Samples were attached to the stage with double-sided conductive adhesive and observed after gold sputtering for 90 seconds.

[0066] Nitrogen adsorption-desorption determination. An ASAP 2460 instrument from Micron Instruments (USA) was used. Samples were first degassed under vacuum at 120°C for 6 h, followed by adsorption-desorption determination in a liquid nitrogen bath at −196°C. Specific surface area was calculated using the BET method, and pore size distribution was calculated using the BJH method.

[0067] Small-angle X-ray scattering was performed using an Anton Paar SAXSpoint 5.0 small-angle X-ray scatterer with a CuKα radiation source at a wavelength of 1.5418 Å. The scattering vector q was measured in the range of 0.01–0.6 Å. -1The sample was loaded into a quartz capillary tube with an inner diameter of 1 mm, and data were collected at 25°C for 30 min. The average spatial spacing of the bifunctional sites was estimated by combining the results of the MM2 force field simulation.

[0068] The experimental data are summarized and analyzed as follows:

[0069] The key performance data of Examples 1, 2, and 3, as well as Comparative Examples 1, 2, and 3, were systematically summarized and analyzed. The data summary is shown in Table 1, and the details are as follows:

[0070] serial number Catalyst characteristics Conversion rate / % Selectivity / % One-way yield / % Highest concentration of intermediate (mol / L) Example 1 <![CDATA[Covalently anchored ZnCl2 + 2,6-dimethylpyridine, spacing 0.70 nm]]> 92.1 95.7 86.3 0.038 Example 2 <![CDATA[Covalently anchored FeCl3 + 2,6-dimethylpyridine, spacing 0.68 nm]]> 93.1 92.2 79.9 0.042 Example 3 Sample E2 <![CDATA[Covalently anchored ZnCl2 + 2,6-dimethylpyridine, spacing 0.75 nm]]> 91.8 94.9 85.8 0.040 Comparative Example 1 DMF+pyridine homogeneous catalytic system 85.2 87.0 74.1 0.185 Comparative Example 2 Physical mixing of catalysts F1 and F2 88.6 80.4 68.2 0.164 Comparative Example 3 <![CDATA[Covalent anchoring of ZnCl2 + ordinary pyridine]]> 85.9 82.1 70.5 0.112

[0071] Data analysis reveals the technical advantages of this invention. First, the highest instantaneous concentration of the intermediate in Example 1, 0.038 mol / L, is only 20.5% of that in Comparative Example 1 (homogeneous) and 23.2% of that in Comparative Example 2 (physical mixing), confirming the core mechanism of molecular-level synergistic significant shortening of the intermediate's half-life.

[0072] Secondly, the 2-chloroacrylonitrile selectivity of 95.7% in Example 1 was 8.7 percentage points higher than that of 87.0% in Comparative Example 1 (homogeneous) and 13.6 percentage points higher than that of 82.1% in Comparative Example 3 (non-sterically hindered pyridine), demonstrating the key role of steric hindrance design at the 2,6-position alkyl group in suppressing nucleophilic side reactions.

[0073] Third, compared with Comparative Example 2, both Example 1 and Comparative Example 2 are heterogeneous systems with similar Zn loadings. However, Example 1 showed a selectivity 15.3 percentage points higher and a single-pass yield 18.1 percentage points higher than Comparative Example 2, fully demonstrating the decisive influence of covalent anchoring on molecular-level spatial constraints relative to physical mixing on catalytic performance. This comparison effectively eliminates the technical equivalence question that "any heterogeneous morphology can obtain the same catalytic performance under the same Zn loading."

[0074] Fourth, regarding cycle stability, Example 1 maintained a 95.0% retention rate after 20 cycles, which was significantly better than Comparative Example 3's 67.8% (due to catalyst deactivation caused by the accumulation of pyridinium salt byproducts) and Comparative Example 2's 85.3% (due to the gradual breakage of physically mixed microspheres due to asynchronous swelling). This further demonstrates the synergistic effect of steric design and covalent anchoring on catalyst lifetime.

[0075] Fifth, the nonlinear synergistic effect is quantitatively demonstrated. If the single-pass yields of catalysts F1 (potential affinity only) and F2 (base site only) under the same reaction conditions are tested separately, they are 3.2% and 1.8% respectively, with a simple linear superposition of 5.0%; while the single-pass yield of catalyst A in Example 1 of this invention reaches 86.3%, and the nonlinear gain factor is as high as 17.3 times, far exceeding the reasonable expectation of any linear effect. This fully proves that the underlying structural design of this invention brings about a kinetic multiplication effect at the statistical mechanics level, rather than a simple addition of functional components.

[0076] The aforementioned series of quantitative data fully demonstrates, from a mechanistic perspective, the creative leap of this invention compared to existing technologies. There is a clear and traceable causal chain between its underlying structure (covalent anchoring + sub-nanometer spacing) and its end-performance (selectivity, single-pass yield, cycle stability).

[0077] The mechanism of the molecular-level synergistic catalytic effect achieved by the one-step preparation method of 2-chloroacrylonitrile provided by this invention can be systematically explained from the following three aspects.

[0078] Firstly, the molecular mechanism of electrophilic activation of chlorine molecules. Lewis acid metal Zn(II) coordinates with the lone pair electrons of the nitrogen atom in −CH2N(CH3)2 to form the −CH2N(CH3)2·ZnCl2 structure. The Zn(II) center retains an empty orbital that can act as a σ acceptor, interacting with the lone pair electrons of the terminal Cl atom in the Cl2 molecule to form the Zn⋯Cl−Cl pre-activated product. Quantum chemical calculations show that this pre-activation reduces the Cl−Cl bond dissociation energy from 242 kJ / mol to approximately 232 kJ / mol (a decrease of about 10 kJ / mol), while simultaneously polarizing the charge distribution on the two Cl atoms, increasing the positive charge of the distal Cl atom by about 0.18 e, thus lowering the energy barrier for its electrophilic attack on the β-carbon of acrylonitrile by about 12 kJ / mol. Acrylonitrile further enhances the electrophilic tendency of the β-carbon of the carbon-carbon double bond through the weak coordination of the nitrile nitrogen with Zn(II). Under the synergistic effect of both, the electrophilic attack of chlorine on the β-carbon generates a β-chlorocarbocation intermediate, which then... - The anti-Markovnikov addition reaction, initiated from the α-side, yields 2,3-dichloropropionitrile. This molecular mechanism explains why Zn(II) is a mild yet highly efficient electrophilic activating metal relative to Cu(II) and Al(III).

[0079] Secondly, the molecular mechanism of the β-elimination reaction. If 2,3-dichloropropionitrile is formed and remains free in the bulk phase, it needs to diffuse to encounter a base site for β-elimination. However, in the catalyst of this invention, the intermediate, once formed, is located only 0.5–0.9 nm away from the adjacent 2,6-dimethylpyridine nitrogen. Although the lone pair of electrons of the 2,6-dimethylpyridine nitrogen cannot undergo nucleophilic addition due to the spatial shielding of the 2,6-methyl group, its angle is sufficient to capture the hydrogen atom on the α-carbon of the intermediate. During the capture process, Cl−C… α Synchronous heterolytic cracking of bonds, generating Cl - The product flows away from the α-carbon towards the zinc end (the zinc-chlorine bond formation rate constant is much higher than the bulk solvation rate), completing the E2-type anti-coplanar β-elimination to give 2-chloroacrylonitrile and release HCl. The HCl is then fixed by excess 2,6-dimethylpyridine in a protonated form, avoiding the reverse addition of the product.

[0080] Third, the statistical mechanical effect at the molecular level. From a statistical mechanical perspective, the half-life τ of the homogeneous catalytic intermediate 2,3-dichloropropionitrile is controlled by diffusion-collision, and is approximately 10 mol / L in a 0.038 mol / L 1,2-dichlorobenzene solvent medium. -3 The timescale is on the order of milliseconds (s). In this invention, the intermediate in the catalyst is within the field of view of the base site at a distance of 0.7 nm at the instant of formation, and its half-life is controlled by the nearest-neighbor diene reaction, estimated to be approximately 10. -6 The half-life is reduced to the order of seconds (µs), shortening it by approximately three orders of magnitude. This reduction in intermediate half-life directly corresponds to a decrease in the chance of side reactions. Perchlorination requires a secondary collision between the intermediate and the second Cl2 molecule, with the rate proportional to the square of the intermediate concentration. Radical polymerization requires the intermediate to be initiated by a free radical, with the rate proportional to the product of the intermediate concentration and the free radical concentration. The significant reduction in intermediate concentration decreases the rates of these side reactions by two to three orders of magnitude, thereby achieving a jump in selectivity from 87% to over 95%.

[0081] In summary, a clear causal chain exists between the technical effects of this invention and its molecular-level structural design. Covalent anchoring and sub-nanometer spacing control are the causes; the synergistic molecular-level adjacency of addition activation and elimination is the effect; the order-of-magnitude compression of intermediate half-life and suppression of side reactions are the benefits; and the leaps in selectivity and cycling stability are the ultimate value. The entire causal chain is interconnected, irreversible, and irreplaceable. Any technical solution that deviates from covalent anchoring and sub-nanometer spacing (such as the homogeneous system of Comparative Example 1 or the physically mixed system of Comparative Example 2) cannot reproduce the ultimate performance of this invention.

[0082] The molecular-level synergistic mechanism revealed in this invention has universal significance. In any reaction system involving a two-step tandem reaction of electrophilic addition and base elimination, if the two functional sites can be covalently anchored to a sub-nanometer proximity, similar orders of magnitude compression of intermediate half-lives and selective transitions can theoretically be achieved. This invention verifies the effectiveness of this mechanism using an acrylonitrile-chlorine system as a specific example and provides a structural reference for the green preparation process of other haloolefins.

[0083] The mechanical properties, thermal stability, and chemical stability of the catalyst of this invention have been verified through repeated experiments. After the reaction, the catalyst undergoes filtration, washing, and vacuum drying processes without significant particle breakage. After 20 cycles, the particle integrity retention rate remains above 92%. During continuous operation at 80°C for 4 hours in the β-elimination phase, no significant pyrolysis of the catalyst framework occurs, the Zn loss rate is less than 5%, and the pyridine nitrogen retention rate is above 97%. It maintains good swelling stability in inert solvents such as carbon tetrachloride, 1,2-dichloroethane, chlorobenzene, and tetrachloroethane, with swelling degree variations ranging from 1.15 to 1.28 times. No framework dissolution or depolymerization was observed.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art can make equivalent substitutions, modifications, and improvements to the technical solutions of the present invention according to actual needs without departing from the technical principles and scope of protection of the present invention. All such equivalent substitutions, modifications, and improvements should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the appended claims.

Claims

1. A one-step method for preparing 2-chloroacrylonitrile, characterized in that, Includes the following steps: Acrylonitrile and an inert solvent are mixed at a mass ratio of 1:1 to 1:5 to form a reaction solution. A bifunctional composite catalyst, accounting for 0.5% to 5% of the mass of acrylonitrile, is added. Chlorine gas is introduced at a reaction temperature of −10°C to 80°C and a reaction pressure of 0.1 to 0.5 MPa to allow acrylonitrile to undergo an addition-elimination tandem reaction with chlorine gas to directly obtain 2-chloroacrylonitrile. The bifunctional composite catalyst is a monomolecular bifunctional catalyst consisting of a Lewis acid metal-tertiary amine complex site covalently anchored to a styrene polymer backbone with a crosslinking degree of 0.5% to 5% and a pyridine base site substituted with C1 to C4 alkyl groups at the 2,6-position. The average spatial distance between the Lewis acid metal-tertiary amine complex site and the pyridine base site is 0.4 to 1.2 nm, and the molar ratio of the two types of sites is 1:0.5 to 1:

3.

2. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The Lewis acid metal is one or a combination of two or more of Zn(II), Fe(III), Al(III), and Cu(II).

3. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The tertiary amine is one of −CH2N(CH3)2, −CH2N(CH2CH3)2, or −CH2NC4H8O.

4. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The pyridine with C1-C4 alkyl substitution at the 2,6-position is one of 2,6-dimethylpyridine, 2,6-diethylpyridine, or 2,6-ditert-butylpyridine.

5. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The average spatial distance between the Lewis acid metal-tertiary amine coordination site and the pyridine base site is 0.5~0.9 nm.

6. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The styrene-based polymer backbone is one of styrene-divinylbenzene crosslinked copolymer, styrene-4-vinylpyridine-divinylbenzene crosslinked copolymer, or styrene-methacrylate-divinylbenzene crosslinked copolymer.

7. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The bifunctional composite catalyst is in the form of heterogeneous microspheres with a particle size of 50~500 μm.

8. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The reaction temperature is controlled in two stages: the temperature of the chlorination addition stage is −10°C to 30°C, and the temperature of the β-elimination stage is 40 to 80°C.

9. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, The inert solvent is one of carbon tetrachloride, 1,2-dichloroethane, chlorobenzene, or tetrachloroethane; the mass ratio of acrylonitrile to the inert solvent is 1:1.5 to 1:

3.

10. The method for preparing 2-chloroacrylonitrile in one step according to claim 1, characterized in that, After the reaction is completed, the reaction solution is filtered to separate and recover the bifunctional composite catalyst. The catalyst is washed with ethanol and dried under vacuum at 40°C for 2 h before being recycled. After 20 consecutive uses, the selectivity of 2-chloroacrylonitrile remains above 90%. The filtrate after separation is distilled under reduced pressure at 50-70°C to collect the 2-chloroacrylonitrile product.

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