One-step method for synthesizing unsaturated carboxylic acid metal salt ZDA / ZDMA

Abstract

The invention discloses an efficient and green one-step synthesis method of unsaturated carboxylic acid metal salt ZDA / ZDMA capable of realizing large-scale production, and belongs to the technical field of synthesis of rubber additives. According to the method, a specific mixed solvent system is innovatively adopted, and high-selectivity and high-conversion-rate solid-liquid heterogeneous reaction of acrylic acid or methacrylic acid and zinc oxide is promoted under mild conditions. The polarity, dispersity and interfacial properties of a reaction medium are synergistically regulated and controlled through the solvent ratio and additives, in-situ precipitation and efficient separation of a product are achieved, mother liquor can be recycled, and the production cost and three-waste emission are greatly reduced. The preparation method breaks through the limitation of a traditional aqueous phase method and a direct synthesis method in the aspects of environmental protection, equipment dependence and product stability, provides an industrial path which is simple in process, mild in condition, high in yield and good in reproducibility, and is particularly suitable for preparation of auxiliaries of high-performance rubber composite materials.

Description

Technical Field

[0001] This invention relates to the field of rubber additive synthesis technology, specifically to an efficient and green synthesis method for unsaturated zinc carboxylate salts (ZDA / ZDMA) and their application in rubber composites. Background Technology

[0002] Unsaturated carboxylic acid metal salts are an important class of multifunctional additives in the rubber industry. Their applications in rubber modification and reinforcement have been reported, and Japan industrialized such products in the early 1980s. Among them, zinc, magnesium, and aluminum salts of methacrylic acid and acrylic acid show significant advantages. These additives exhibit good compatibility with various types of rubber and possess excellent high-temperature stability and solvent resistance. As reactive multifunctional additives, unsaturated carboxylic acid metal salts such as zinc methacrylate (ZDMA) contain double bonds and metal ionic bonds in their structure, exhibiting excellent compatibility with polar rubber matrices. Under the action of an organic peroxide initiation system, their active double bonds can undergo in-situ self-polymerization to form a polyzinc methacrylate phase with high cohesive strength. This self-polymer exhibits partial compatibility or incompatibility with the rubber matrix, achieving in-situ reinforcement of rubber nanocomposites through nanoscale dispersion and continuous network structures.

[0003] During vulcanization, the unsaturated carboxylic acid metal salt can undergo a grafting reaction with rubber molecules and initiate self-polymerization under the action of an initiator; the ionic bonds formed by metal cations and carboxylic acid anions within the molecule significantly improve the crosslinking density of vulcanized rubber by constructing an ionic crosslinking network, simultaneously optimizing stress relaxation characteristics and thermal stability, thereby synergistically improving the processing performance of rubber and the application performance of products.

[0004] The industrial synthesis of zinc acrylate compounds mainly includes four technical routes: direct synthesis, aqueous saponification, aqueous pH-controlled synthesis, and copolymerization functionalization.

[0005] CN112592267A reports a direct synthesis method that generates the target product by reacting methacrylic acid (MAA) with zinc oxide (ZnO) in the presence of an initiator (distilled water / hydrogen peroxide). The core steps involve heating MAA to 40-80 °C and then slowly adding ZnO (molar ratio 2:1); adding the initiator (3%–15% by weight of MAA) in portions while the MAA is in an agglomerated state; reacting at 60-120 °C for 40-80 minutes; followed by vacuum dehydration (moisture content ≤0.5%) and pulverization. Its advantages include the absence of saponification / metathesis side reactions and the absence of saline wastewater; however, it also suffers from drawbacks such as the corrosive effect of liquid MAA on equipment (requiring an enamel / titanium alloy reactor) and the need for dual-paddle counter-stirring to suppress agglomeration and localized overheating.

[0006] CN104725663A reports an aqueous saponification method in which MAA is saponified with NaOH / KOH to generate sodium / potassium salts, which are then metathesis-decomposed with zinc salts. This method mainly involves adding MAA dropwise to a hot NaOH aqueous solution for saponification, cooling to precipitate sodium salts, followed by metathesis-decomposition with ZnCl2, and then filtration and dehydration to obtain the target product. This method is mature, uses simple equipment, and is low-cost; however, it also has some limitations: the discharge of saline wastewater (NaCl / KCl) increases treatment costs by 30%, and fluctuations in product moisture content (5%–20%) reduce rubber crosslinking efficiency. This method is gradually being phased out due to environmental concerns.

[0007] Patents CN105399619A / CN105399619B report a pH-controlled reaction of MAA (monomethyl methacrylate) with ZnO in an aqueous phase to produce zinc monomethacrylate (Zn(MMA)₂·H₂O). This method uses a suitable reactor, adds 800g of water or circulating mother liquor, heats to 40°C and stirs continuously, then adds 2.5% (by weight) of zinc oxide (from water or circulating mother liquor). Methacrylic acid, in an equimolar amount to zinc oxide, is accurately weighed and placed in a dropping funnel. A pH meter probe is placed inside the reactor, and methacrylic acid is added dropwise over approximately one hour, maintaining the temperature at 40°C and closely monitoring the pH to ensure it does not fall below 5.9. After the addition is complete, stirring continues for 11 hours. Once the material thickens, it is filtered, and the filtrate is used as a circulating mother liquor for future use. The filter cake is spread evenly in an oven and dried at 80°C to obtain the final product. This synthesis method and process are highly efficient, with a comprehensive product yield exceeding 95%, effectively alleviating the shortage of zinc monomethacrylate production in my country. However, this process requires precise control of reaction temperature and pH value, the operation procedure is complicated, and the reaction cycle is long. These factors restrict production efficiency to some extent.

[0008] The CN106349420B copolymer functionalization method involves first reacting MAA with ZnO to generate monomers, followed by copolymerization with trialkylsilyl acrylate to form a multifunctional polymer. The products are mainly used in marine antifouling coatings and anticorrosive adhesives. However, it also has drawbacks, such as a 40% increase in cost due to the two-step synthesis process.

[0009] In summary, the direct synthesis method requires corrosion-resistant reactors (such as those made of enamel / titanium) due to the highly corrosive nature of methacrylic acid (MAA), and necessitates special stirring to control agglomeration and localized overheating. The aqueous saponification method, due to the discharge of saline wastewater (NaCl / KCl), increases treatment costs by 30%, and the fluctuation in product water content (5%-20%) significantly affects rubber crosslinking efficiency; therefore, it has been gradually phased out due to environmental pressures. The pH-controlled aqueous method requires strict pH maintenance (≥5.9) and continuous reaction for 12 hours (including 11 hours of stirring), resulting in high energy consumption and low operational tolerance. The copolymerization functionalization method is limited by a 40% cost increase due to two-step synthesis and monomer compatibility issues, hindering large-scale application; these problems urgently need to be overcome. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention aims to overcome these limitations by providing a one-step synthesis process based on a specific mixed solvent system for the efficient and selective preparation of unsaturated carboxylic acid metal salts ZDA / ZDMA. This method achieves an optimal balance between reaction rate, product purity, and process economy under mild conditions through the synergistic design of solvent composition and additives.

[0011] In a mixed solvent consisting of a good solvent and a poor solvent, acrylic acid or methacrylic acid reacts directly with zinc oxide to form the corresponding zinc salt precipitate. In this mixed solvent system, the poor solvent promotes product precipitation, while the other organic good solvent provides appropriate polarity to facilitate reactant dissolution and mass transfer. The synergistic effect of the two creates a unique reaction-precipitation microenvironment, effectively preventing product agglomeration and monomer self-polymerization, and significantly improving reaction yield and product filterability.

[0012] Adding a catalytic amount of sulfuric acid as an additive to the reaction not only slightly activates the zinc oxide surface and promotes the acid-base reaction, but also adjusts the system's slightly acidic pH, inhibiting the free radical homopolymerization side reaction of acrylic monomers during the reaction process, thereby improving reaction selectivity and stabilizing the product yield at over 95%. This one-step method enables the efficient, simple, and rapid industrial synthesis of the aforementioned target product. This method offers advantages such as mild reaction conditions, simple operation, and ease of large-scale production.

[0013] To achieve the above objectives, the present invention adopts the following technical solution.

[0014] The structure of the unsaturated carboxylic acid metal salt ZDA / ZDMA is shown in the following formula:

[0015] The R functional group includes methyl and other alkyl substituents; The one-step synthesis of unsaturated carboxylic acid metal salts ZDA / ZDMA involves the following reaction process:

[0016] The specific preparation method includes the following steps: 1) Add zinc oxide and reaction solvent to the reaction vessel, and add a certain amount of additives. Start stirring to distribute the materials evenly in the reaction system. Then slowly add 2-3 equivalents of (meth)acrylic acid. Place the system under 30 ℃ and seal it for 24 hours. 2) After monitoring the reaction until it is complete, cool it to room temperature and then perform solid-liquid separation. The crude product is dried, crushed and sieved to obtain the unsaturated zinc carboxylate metal salt ZDA / ZDMA. At the same time, the mother liquor can be recovered and reused.

[0017] In a preferred embodiment, the acrylic acid is selected from one of the following: acrylic acid or methacrylic acid; the amount of acrylic acid used is 2-3 times the equivalent of zinc oxide.

[0018] In a preferred embodiment, the zinc oxide is selected from the following: the particle size range of the zinc oxide is 0.01 μm-10 μm, micron-sized ZnO (0.5-10 μm), submicron-sized ZnO (100-500 nm), nano-sized ZnO (10-100 nm), or industrial-grade zinc oxide.

[0019] In a preferred embodiment, the reaction solvent is selected from one or more of the following: ethyl acetate, tetrahydrofuran, tert-butyl acetate, acetone, ethanol, dichloromethane, acetonitrile, benzene, toluene, chlorobenzene, N,N-dimethylformamide, dimethyl sulfoxide, n-hexane, cyclohexane, industrial grade PE, and water; the reaction solvent concentration is 0.5-2 M, calculated as zinc oxide.

[0020] In a preferred embodiment, the additive is selected from one of the following: hydrochloric acid, sulfuric acid, hydroquinone, tert-butylcatechol, 2,6-di-tert-butyl-p-cresol, tetrabutylammonium bromide, polyethylene glycol 8000, sodium dodecylbenzenesulfonate; the amount of the reaction additive, calculated as zinc oxide, is 0.1-3%.

[0021] In a preferred embodiment, the heating conditions are as follows: the temperature is 20-60 °C, and the reaction time is 8 h to 24 h.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Green and efficient process: The closed organic solvent system is adopted, and there is no wastewater discharge; the mother liquor can be recycled and the solvent consumption is low, which is in line with the principle of green chemical industry.

[0023] (2) Mild and controllable conditions: The reaction is carried out at room temperature, without the need for complex temperature control and precise pH adjustment. The operation is simple and the safety is high.

[0024] (3) Excellent product quality: The obtained product is a white powder with good flowability, high purity, extremely low water content (<0.5%), and good dispersibility in rubber.

[0025] (4) Strong adaptability of raw materials: Zinc oxide with different particle sizes from nano-scale to industrial grade can be used, which reduces the cost of raw materials and pretreatment requirements.

[0026] (5) Easy to scale up: The process is simple and the equipment requirements are ordinary (no special anti-corrosion materials are required), which is suitable for large-scale continuous or intermittent production. Attached Figure Description

[0027] Figure 1 This is the 1H NMR spectrum of the zinc acrylate product of this invention.

[0028] Figure 2 This is the carbon NMR spectrum of the zinc acrylate product of this invention.

[0029] Figure 3 This is the 1H NMR spectrum of the zinc methacrylate product of this invention.

[0030] Figure 4 This is the carbon NMR spectrum of the zinc methacrylate product of this invention.

[0031] Figure 5 This is a DSC test result of the zinc methacrylate product of this invention.

[0032] Figure 6 This is a SEM image of the zinc methacrylate product of this invention. Detailed Implementation Plan

[0033] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0034] Existing processes for preparing zinc acrylate compounds suffer from limitations such as high pollution emissions, low energy consumption and efficiency, complex reaction control, complex material agglomeration, and the risk of localized acid corrosion. These limitations result in significant bottlenecks in the environmental friendliness, equipment dependence, dispersion controllability, and product stability of existing zinc acrylate compound synthesis processes. This invention uses acrylic acid compounds and zinc oxide (ZnO) as raw materials, and reacts them in a one-step process with an organic solvent (a straight-chain alkane or a mixed solvent with toluene) to generate the target product. After drying and pulverizing, the target compound can be obtained, and the mother liquor can be recycled.

[0035] The technical solution of the present invention will be further described below.

[0036] This invention provides a one-step method for synthesizing unsaturated carboxylic acid metal salts ZDA / ZDMA, comprising the following steps: Using acrylic compounds of Formula 1 and zinc oxide as raw materials, and with a certain amount of additives, a one-step reaction is carried out in an organic solvent (chain alkanes or a mixed solvent with toluene) to generate the target (meth)acrylate zinc product. The mother liquor can be recycled. After monitoring the reaction to completion, the reaction system is cooled to room temperature, and then subjected to solid-liquid separation. The crude product is dried, pulverized, and sieved to obtain the unsaturated zinc carboxylate metal salt ZDA / ZDMA; at the same time, the mother liquor can be recovered and reused. The synthetic route is as follows:

[0037] To improve the yield of zinc acrylate and further ensure the market competitiveness of zinc acrylate compounds, the molar ratio of acrylic acid to zinc oxide is 1:0.505. With the excessive addition of acrylic acid, solid products of varying morphologies gradually appear in the reaction system, and the final product is relatively viscous.

[0038] To reduce the impact of reaction conditions on product properties, it is necessary to monitor and record reaction conditions such as temperature, pH, and reaction time during the synthesis process to ensure the quality and stability of the product.

[0039] To further reduce the environmental impact of the reaction, byproducts and waste that may be generated during the synthesis process need to be properly handled, and solvents need to be recycled.

[0040] It should be noted that the ratio of acrylic acid raw material to solvent is 600 kg: 1800-2400 L. The temperature range is 20-60 degrees Celsius. The reaction solvent used in this invention is one or more of ethyl acetate, tetrahydrofuran, tert-butyl acetate, acetone, ethanol, dichloromethane, acetonitrile, benzene, toluene, chlorobenzene, N,N-dimethylformamide, dimethyl sulfoxide, n-hexane, cyclohexane, industrial-grade PE, and water. Optimal conditions use straight-chain alkanes as poor solvents to disperse the products generated during the reaction, ensuring the quality and stability of the products and preventing the formation of resin-like polymerized zinc acrylate species.

[0041] The technical effects of the present invention will be described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Example 35

[0042] The product prepared in this embodiment has the following structure: In a reaction vessel, 341 kg of zinc oxide and 2400 L of a mixed solvent of toluene and ethyl acetate (2:1 ratio) were added. Stirring was started to evenly distribute the materials in the reaction system. Then, 600 kg of acrylic acid raw material was slowly added over 10-12 hours. The system was sealed and reacted at 25 °C for 12 hours. After monitoring the reaction until complete, the system was cooled to room temperature. Solid-liquid separation was performed. The crude product was dried, pulverized, and sieved to obtain the unsaturated zinc carboxylate metal salt ZDA. The mother liquor could be recovered and reused. The product yield was 97%, and the product was a white powder with a melting point of 240-244 °C. o C. 1 HNMR (400 MHz, (CD3)2SO) δ 6.06 (d, J = 6.3 Hz, 2H), 5.62 (t, J = 6.2 Hz, 1H). 13 C NMR (100 MHz, (CD3)2SO) δ 172.1, 134.1, 127.7. Example 36

[0043] The product prepared in this embodiment has the following structure: In a reaction vessel, 285 kg of zinc oxide and 1800 L of petroleum ether solvent were added. Stirring was started to evenly distribute the materials in the reaction system. Then, 600 kg of methacrylic acid was slowly added over 10-12 hours. The system was then sealed and reacted for another 12 hours under a 30°C insulated environment. After monitoring the reaction until complete, the system was cooled to room temperature. Solid-liquid separation was performed. The crude product was dried, pulverized, and sieved through an 80-mesh sieve to obtain the unsaturated zinc carboxylate metal salt ZDMA. The mother liquor could be recovered and reused. The product yield was 99%, and the product was a white powder with a melting point of 229-232°C. o C. 1 H NMR (400MHz, (CD3)2SO) δ 5.83 (s, 1H), 5.33 (s, 1H), 1.83 (s, 3H). 13 C NMR (100 MHz, (CD3)2SO) δ 173.6, 140.7, 122.3, 20.0. Referring to the above preparation method, the specific details of the examples regarding additives, temperature, and solvents are summarized below:

[0044]

[0045]

[0046] Replacing the industrial zinc oxide in Example 33 with other zinc oxides, such as micron-sized ZnO (0.5-10 μm), submicron-sized ZnO (100-500 nm), and nano-sized ZnO (10-100 nm), showed that their reactivity was similar and they achieved the same reaction effect, all yielding the target product in yields exceeding 90%. Replacing the solvents in Examples 27-32 with other solvents, such as benzene, chlorobenzene, N,N-dimethylformamide, dimethyl sulfoxide, cyclohexane, and industrial-grade PE, also yielded similar experimental results, all achieving yields exceeding 85% for the target product.

[0047] .

Claims

1. An unsaturated carboxylic acid metal salt ZDA or ZDMA, having the general structure as follows: ， R functional groups include but are not limited to methyl and other alkyl substituents.

2. A process for the one-step preparation of unsaturated carboxylic acid metal salts ZDA / ZDMA according to claim 1, characterized in that, In aprotic mixed solvent system, acrylic acid or methacrylic acid is reacted with zinc oxide, and the reaction equation is as follows: ， It is characterized by comprising the following steps: 1) In a reaction vessel, zinc oxide and a reaction solvent are added, stirring is started to uniformly distribute the materials in the reaction system, an additive is added, then 2-3 equivalents of (meth) acrylic acid are slowly added, and the system is sealed and reacted at 30 ℃ for 24 hours under insulation; 2) After monitoring the reaction to completion, the reaction system is cooled to room temperature, and then solid-liquid separation is performed, the crude product is dried and crushed and sieved to obtain the unsaturated carboxylic acid zinc metal salt ZDA / ZDMA; meanwhile, the mother liquor can be recycled and reused.

3. The process for the preparation of unsaturated carboxylate metal salt ZDA / ZDMA in one step synthesis as claimed in claim 2 wherein, The acrylic acid is selected from the following: acrylic acid, methacrylic acid; the amount of acrylic acid used is 2-3 equivalents of zinc oxide.

4. A process for the preparation of unsaturated carboxylate metal salt ZDA / ZDMA by one step synthesis as claimed in claim 2, wherein, the said process is characterized by, (a) reacting the unsaturated carboxylic acid with the metal salt in the presence of a solvent to form the unsaturated carboxylate metal salt ZDA / ZDMA. The particle size of the zinc oxide is in the range of 0.01 μm-10 μm, micron-grade ZnO (0.5-10 μm), sub-micron ZnO (100-500 nm), nano-ZnO (10-100 nm), and industrial-grade zinc oxide.

5. The process for the preparation of unsaturated carboxylate metal salt ZDA / ZDMA in one step as claimed in claim 2 wherein, The reaction solvent is selected from one of the following: ethyl acetate, tetrahydrofuran, tert-butyl acetate, acetone, ethanol, dichloromethane, acetonitrile, benzene, toluene, chlorobenzene, N,N - one or several of dimethylformamide, dimethyl sulfoxide, n-hexane, cyclohexane, technical grade PE and water; the reaction solvent is in a reaction concentration of 0.1-2 M based on the zinc oxide. ​ 6. The production method according to claim 2 or 3, characterized by, During the reaction, the polarity of the solvent and the additive are adjusted to inhibit the homopolymerization side reaction of the acrylic monomer, and the selectivity of the target product is improved; the additive is selected from the following: hydrochloric acid, sulfuric acid, hydroquinone, tert-butyl catechol, 2,6-di-tert-butyl-p-cresol, tetrabutylammonium bromide, polyethylene glycol 8000, and sodium dodecylbenzenesulfonate; the amount of the additive is 0.1-3% based on the amount of zinc oxide. 7.The method for preparing the unsaturated carboxylic acid metal salt ZDA / ZDMA by one-step synthesis according to claim 2, wherein the heating condition is at a temperature of 20-60 ℃, and the reaction time is 8 h~24 h.

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