A phenol-free phosphite and a method for its preparation in a basic ionic liquid

Abstract

The application discloses a kind of phenol-free phosphite and its preparation method in basic ionic liquid, the method is with C3-C18 straight-chain or branched aliphatic alcohol as unit alcohol, with ethylene glycol, diethylene glycol, dipropylene glycol, tripropylene glycol or polyethylene glycol with molecular weight 200-800 as dihydric alcohol, with phosphorus trichloride or trialkyl phosphite as phosphorus-containing compound, in the basic ionic liquid prepared by imidazole salt or quaternary ammonium salt and potassium hydroxide, esterification or ester exchange reaction is carried out at 50-180 DEG C for 1-24 hours, and polymeric phenol-free phosphite is obtained after separation and purification.The molar ratio of monohydric alcohol and dihydric alcohol is 10:1-1:2, the molar ratio of phosphorus-containing compound and dihydric alcohol is 0.8:1-3:1, and the amount of basic ionic liquid is 1%-30% of the total mass of reaction system.The basic ionic liquid has the dual functions of catalyst and acid-binding agent, and can be recovered and recycled after phase separation.The method does not depend on any phenolic raw material, and completely avoids the problem of phenolic residue.The obtained product has low color, good thermal stability, strong hydrolysis resistance and low volatility, and can be used as high-efficiency antioxidant and thermal stabilizer in polyvinyl chloride, polyurethane and other engineering plastics.

Description

Technical Field

[0001] This invention relates to the field of phosphite preparation, specifically to a phenol-free phosphite and its preparation method in an alkaline ionic liquid. Background Technology

[0002] Phosphite compounds, as auxiliary antioxidants and heat stabilizers, play an indispensable role in the processing and use of polymer materials such as polyolefins, polyvinyl chloride (PVC), and polyurethane. Currently, my country's phosphite industry is rapidly developing towards environmental friendliness and high performance, but it still faces some significant technological challenges.

[0003] The production of traditional phosphite products (such as triphenyl phosphite (TNPP)) heavily relies on raw materials such as phenol, phenyl phenol, and bisphenol A, inevitably resulting in the residue of these harmful phenolic substances in the final product. These substances not only release odors during polymer processing but may also migrate and leach from the finished product, posing potential risks to the environment and human health. This significantly limits their application in sensitive areas such as food packaging, medical devices, and children's toys. Therefore, developing phosphites completely free of phenolic structures has become an urgent need in the industry.

[0004] To address the aforementioned issues, several synthetic routes for phenol-free phosphites have been proposed. For example, Chinese patent application CN102503975A discloses a phenol-free phosphite derivative and its preparation method, which obtains the product through condensation and transesterification reactions of bisphenol compounds, phosphorus derivatives, and higher fatty alcohols, with the phenol residue controllable to 0.5 wt% or less. However, the raw materials of this technical solution still cannot be separated from bisphenol compounds, and the introduction of benzene ring structures is not completely eliminated in essence. Another Chinese patent application CN103012483A discloses the use of triisopropyl phosphite and pentaerythritol as raw materials, reacting them under the action of an alkaline catalyst, followed by the addition of a fatty alcohol for transesterification, resulting in a product structure without benzene rings. Although this route avoids the use of phenolic raw materials, it brings new application problems: the molecular weight of the product is determined by the fixed ratio of raw materials, lacking effective controllability; at the same time, pentaerythritol derivatives generally have defects such as high freezing points and poor compatibility with non-polar resins such as polyolefins, which limits their universality in various substrates.

[0005] In terms of synthesis processes, when using phosphorus trichloride to synthesize phosphites via a direct (phenol-free) method, traditional techniques rely on organic amines such as triethylamine and pyridine as acid-binding agents to absorb the hydrogen chloride produced as a reaction byproduct. For example, Chinese patent application CN101538279A employs a similar amine-based acid-binding agent system. After the reaction, the generated amine salts must be removed by filtration. This additional separation step not only lengthens the production process but also generates a large amount of amine-containing waste. Although some studies indicate that organic solvents and catalysts can be recovered, in industrial practice, establishing an efficient recovery system often means a significant increase in process complexity and cost.

[0006] Ionic liquids, as green media with low vapor pressure, good thermal stability, and customizable structure and function, have attracted widespread attention in the field of catalytic synthesis in recent years. In esterification and transesterification reactions, ionic liquids have shown the potential to replace traditional catalysts. For example, acid-functionalized ionic liquids have been successfully applied to catalyze the transesterification of rapeseed oil to produce biodiesel; compared with sulfuric acid, ionic liquids are recyclable and have a shorter reaction time. Other studies have applied degradable ionic liquids to the synthesis of α-aminophosphates, achieving catalyst recycling in the aqueous phase. Furthermore, Chinese patent application CN119331014A discloses a method for preparing tris(2,4-di-tert-butylphenyl) phosphite using a tetramethylguanidinine ionic liquid as a catalyst, obtaining high-yield, high-purity products under mild conditions, and the catalyst is easily recoverable. However, the product prepared by this method still contains a phenolic ring (2,4-di-tert-butylphenol residues), essentially still belonging to the category of phenol-containing phosphites, failing to solve the application limitations caused by phenolic residues.

[0007] A review of existing technologies reveals that, in the synthesis of phenol-free phosphites, there is still a lack of a clean production method that can completely avoid the benzene ring structure, effectively control the molecular weight during the preparation of polymeric products, and simultaneously avoid the use of organic amine acid-binding agents and the difficulties in catalyst recovery. Specifically, the shortcomings of existing technologies can be summarized in three aspects:

[0008] Firstly, regarding the degree of avoidance of phenolic structures. For example, although patent application CN102503975A claims to be phenol-free, its raw materials involve bisphenol compounds; patent application CN103012483A avoids the introduction of benzene rings, but at the cost of sacrificing the product's molecular weight controllability and resin compatibility; while the ionic liquid catalysis scheme (CN119331014A) still falls within the scope of synthesizing phenol-containing phosphites. In other words, existing technologies have not yet achieved a balance between complete phenol-free production and adjustable performance.

[0009] Secondly, there are inherent problems with the acid-binding agent system. When using the direct phosphorus trichloride method for synthesis, although organic amines can effectively absorb hydrogen chloride as acid-binding agents, the amine salts generated after the reaction must be removed by filtration. This step increases equipment investment and operating cycle. More importantly, the treatment cost of amine salts as solid waste is high, which contradicts the development concept of green chemistry.

[0010] Thirdly, regarding the recycling of catalysts and reaction media. Although ionic liquids have demonstrated the advantage of recyclability in various catalytic reactions, in the field of phenol-free phosphite synthesis, existing research either uses traditional organic amine systems or, despite introducing ionic liquids, still produces phenol-containing products. An integrated technical solution that simultaneously satisfies the three conditions of "phenol-free product structure," "tunable polymerizable molecular weight," and "ionic liquid catalysis combined with solvent and recyclability" has not yet been reported.

[0011] Therefore, how to solve the problems of phenol residue, difficulty in separating acid-binding agents, cumbersome catalyst recovery, and difficulty in balancing product molecular weight with resin compatibility are still urgent issues to be addressed in the preparation of phenol-free phosphites. Summary of the Invention

[0012] To address the shortcomings of existing technologies, this invention provides a phenol-free phosphite and its preparation method in an alkaline ionic liquid. This method utilizes a specific alkaline ionic liquid as a multifunctional catalyst and reaction medium, achieving the clean production of phenol-free, low-odor, high-molecular-weight phosphite. The specific technical solution is as follows:

[0013] This invention provides a method for synthesizing phenol-free phosphites in an alkaline ionic liquid, comprising the following steps:

[0014] 1) Preparation of alkaline ionic liquid: Using 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium bromide, tetramethylammonium chloride, tetraethylammonium chloride or tetrapropylammonium chloride as cation sources, dissolve them in anhydrous ethanol, add potassium hydroxide dropwise in an amount equal to the amount of the cation source, stir the reaction at 500-800 r / min at 55℃-65℃ for 20-30 hours, filter to remove the solid precipitate, remove the ethanol by rotary evaporation, and then vacuum dry at 45℃-45℃ for 18-26 hours to obtain a clear and transparent alkaline ionic liquid;

[0015] 2) Formation of the reaction system: Under the protection of an inert atmosphere, the monohydric alcohol, dihydric alcohol and the alkaline ionic liquid obtained in step 1) are mixed and stirred evenly at a speed of 500-800 r / min to form a reaction system.

[0016] 3) Esterification or transesterification reaction: Add a phosphorus-containing compound to the reaction system of step 2), react at 50℃~180℃ for 1~24 hours, cool after the reaction is completed, and obtain the phenol-free phosphite by separation and purification.

[0017] In the aforementioned method for synthesizing phenol-free phosphites in an alkaline ionic liquid, in step 1), the alkaline ionic liquid is 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, or tetrapropylammonium hydroxide.

[0018] In the aforementioned method for synthesizing phenol-free phosphites in alkaline ionic liquids, in step 2), the monohydric alcohol is a straight-chain or branched fatty alcohol with 3 to 18 carbon atoms; the dihydric alcohol is selected from one or more of ethylene glycol, diethylene glycol, dipropylene glycol, tripropylene glycol, or polyethylene glycol with a molecular weight of 200 to 800; the molar ratio of the monohydric alcohol to the dihydric alcohol is 10:1 to 1:2.

[0019] In the aforementioned method for synthesizing phenol-free phosphites in alkaline ionic liquids, step 2) involves using alkaline ionic liquids in an amount of 1% to 30% of the total mass of the reaction system.

[0020] In the aforementioned method for synthesizing phenol-free phosphites in an alkaline ionic liquid, the amount of alkaline ionic liquid used is 5% to 15% of the total mass of the reaction system.

[0021] In the aforementioned method for synthesizing phenol-free phosphites in alkaline ionic liquids, step 3) involves phosphorus-containing compounds, which are phosphorus trichloride or trialkyl phosphites, including one or more of trimethyl phosphite, triethyl phosphite, or triisopropyl phosphite.

[0022] In the aforementioned method for synthesizing phenol-free phosphites in alkaline ionic liquids, in step 3), the amount of phosphorus-containing compound used is such that the molar ratio of the phosphorus-containing compound to the diol is 0.8:1 to 3:1.

[0023] In the aforementioned method for synthesizing phenol-free phosphite in alkaline ionic liquid, step 3) involves determining the reaction endpoint by observing the reflux condition: the reaction is terminated when reflux no longer occurs within 0.5 hours or more; after cooling, the alkaline ionic liquid and mechanical impurities are removed by filtration to obtain the product.

[0024] In the aforementioned method for synthesizing phenol-free phosphite in alkaline ionic liquid, step 3) involves the following separation and purification: after the reaction is completed, deionized water or a low-polarity solvent (e.g., ethyl acetate) is added to the reaction system for extraction to separate the organic phase containing the product. The organic phase is washed with water until neutral, and then dried, filtered, and distilled under reduced pressure to remove the solvent and unreacted raw materials, thereby obtaining the phenol-free phosphite.

[0025] In the aforementioned method for synthesizing phenol-free phosphites in alkaline ionic liquids, step 3) involves a mixed solution of the alkaline ionic liquid produced during the separation and purification process. This aqueous phase is then dehydrated and directly reused in the next batch of reactions.

[0026] The beneficial effects of this invention are:

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) In the traditional synthesis process of phosphites, phenol, bisphenol A, and phenolic compounds are both raw materials and unavoidable residues. Even some patented technologies that claim to be phenol-free still contain bisphenol compounds in their raw materials, and essentially do not break away from the phenolic ring structure. This invention does not rely on any phenolic starting materials at all, and solves the problem of phenolic residues from the source. The resulting product does not contain any migratable phenolic substances and can be directly used in food contact materials, medical devices, children's toys and other application fields with strict safety requirements.

[0029] 2) Conventional direct phosphorus trichloride process requires the use of organic amines such as triethylamine and pyridine to absorb the byproduct hydrogen chloride. After the reaction, the amine salts must be removed by filtration. This step not only increases equipment investment and operation time, but also generates difficult-to-handle solid waste. This invention uses an alkaline ionic liquid that simultaneously serves as an acid-binding agent, catalyst, and reaction solvent. The reaction system is homogeneous, and the ionic liquid can be recovered by simple phase separation after the reaction. After dehydration, it can be directly used for the next batch of reaction. No amine salt waste is generated in the whole process, completely eliminating the traditional organic amine acid-binding agent and the separation problems it brings.

[0030] 3) In view of the problems in the existing technology of phenol-free phosphite schemes using pentaerythritol as raw material, although the introduction of benzene ring is avoided, its molecular structure is fixed and lacks adjustment space. Moreover, the freezing point of pentaerythritol derivatives is generally high and the compatibility with non-polar resins is poor. The present invention adopts a compound system of monohydric alcohol and dihydric alcohol. By adjusting the ratio of the two and the chain length of the dihydric alcohol, the molecular weight distribution and flexibility of the product can be flexibly controlled, thereby adapting to the compatibility requirements of different substrates such as polyolefins, polyesters, polyurethanes, and engineering plastics. This achieves effective control of the molecular weight of the product and improves the compatibility with polymer materials.

[0031] 4) In existing technologies, whether organic amine acid-binding agents or traditional catalysts are used, multiple separation, washing, and filtration steps are often required. In this invention, the strong alkalinity of the alkaline ionic liquid effectively activates the alcohol hydroxyl groups, allowing esterification or transesterification reactions to proceed stably within a temperature range of 50–180°C under mild process conditions. After the reaction, the target product can be obtained through extraction, washing, and vacuum distillation. The separated aqueous phase is rich in ionic liquid and can be reused after removing only water. The entire process is greatly simplified, making continuous production easier to achieve.

[0032] 5) The polymeric phenol-free phosphite prepared by this invention has a high molecular weight and superior hydrolytic stability compared to traditional small-molecule phosphites. It also exhibits low volatility and is less prone to precipitation during processing. Furthermore, due to the absence of phenol rings in its structure, the product has a light color and will not adversely affect the initial color or long-term aging discoloration of polymeric products. These characteristics give it a significant competitive advantage in high-end fields such as automotive engineering plastics, high-performance films, and electronic packaging materials, providing enterprises with environmentally friendly additive solutions with independent intellectual property rights. Attached Figure Description

[0033] Figure 1 The infrared spectrum of the moderately alkaline ionic liquid prepared in Example 1 of this invention;

[0034] Figure 2 The NMR spectrum of the alkaline ionic liquid prepared in Example 1 of this invention is shown. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. All pharmaceuticals involved in the embodiments are commercially available, and those without a purity rating are industrial or reagent grade.

[0036] Example 1: Preparation of alkaline ionic liquids

[0037] 0.125 mol of 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium bromide, tetramethylammonium chloride, tetraethylammonium chloride, and tetrapropylammonium chloride were dissolved in 119.5 g of anhydrous ethanol (99.7%). 0.125 mol of potassium hydroxide (KOH) was added dropwise, and the mixture was stirred thoroughly (600 r / min) for 24 h. The solid KBr was removed by filtration, and the solutions were rotary evaporated at 60 °C until excess solvent was removed. The solutions were then vacuum dried at 50 °C for 24 h to obtain five clear and transparent alkaline ionic liquids. 1-Butyl-3-methylimidazolium hydroxide ([Bmim]OH), 1-Propyl-3-methylimidazolium hydroxide ([PMIm]OH) Tetramethylammonium hydroxide (TMAH) Tetraethylammonium hydroxide (TEAOH) and Tetrapropylammonium hydroxide (TPAOH), such as Figure 1 and Figure 2 As shown, for future reference.

[0038] Example 2

[0039] Nitrogen gas was introduced into a 250 mL three-necked flask equipped with a magnetic stirrer, thermometer, and reflux condenser for protection. Decanol (15.8 g, 0.1 mol), dipropylene glycol (6.7 g, 0.05 mol), and 1-butyl-3-methylimidazolium hydroxide ([BMIm]OH, 2.5 g, 10% of the total mass of the reaction system) were added sequentially. The mixture was stirred (600 rpm) and heated to 80 °C. Then, trimethyl phosphite (12.4 g, 0.1 mol) was slowly added dropwise through a constant-pressure dropping funnel, controlling the dropping rate to maintain the reaction temperature at 80 °C. After the addition was complete, the oil bath temperature was increased to 120 °C and the reaction was carried out for 6 hours. After the reaction was complete, the mixture was cooled to room temperature. 50 mL of deionized water was added, and the mixture was stirred and allowed to stand to separate into layers. The aqueous phase (containing [BMIm]OH, which can be recycled) was separated, and the organic phase was washed twice with deionized water until neutral. After drying the organic phase with anhydrous magnesium sulfate and filtering, it was subjected to vacuum distillation at 120°C under a vacuum of 0.095 MPa for 1 hour to remove residual low-boiling substances, yielding a colorless, transparent, viscous liquid, which is the phenol-free polymerized phosphite product.

[0040] Example 3

[0041] In the same apparatus as in Example 1, nitrogen protection was applied. Lauryl alcohol (18.6 g, 0.1 mol), polyethylene glycol PEG-400 (20.0 g, 0.05 mol), and tetraethylammonium hydroxide (TEAOH, 2.0 g, approximately 5% of the total mass of the reaction system) were added and mixed. Phosphorus trichloride (6.9 g, 0.05 mol) was slowly added dropwise while stirring (600 rpm), controlling the dropping rate to maintain the reaction temperature at 5°C. After the addition was complete, the temperature was slowly raised to 100°C, and the reaction was carried out for 8 hours. During this period, hydrogen chloride gas was released and absorbed with an alkaline solution. After the reaction was complete, the mixture was cooled to room temperature, and 50 mL of toluene and 30 mL of water were added for extraction. The aqueous phase was separated, and the organic phase was washed with water until neutral, dried, and filtered (under the same conditions as in Example 2). The filtrate was distilled under reduced pressure to remove toluene and unreacted alcohol, yielding a light yellow transparent liquid product, which is the phenol-free polymerized phosphite product.

[0042] Example 4

[0043] In the same apparatus as in Example 1, nitrogen protection was applied. Isotridecyl alcohol (21.4 g, 0.11 mol), trimethylpentanediol (7.3 g, 0.05 mol), and 1-propyl-3-methylimidazolium hydroxide ([PMIm]OH, 3.0 g, approximately 8% of the total mass of the reaction system) were added and mixed thoroughly. Triethyl phosphite (16.6 g, 0.1 mol) was added dropwise under stirring (600 rpm), and the mixture was heated to 150°C and reacted for 4 hours. After the reaction was complete, the mixture was cooled to room temperature, and ethyl acetate and water were added for extraction and separation. The organic layer was washed with water until neutral, dried, and filtered (under the same conditions as in Example 2). The solvent and low-boiling substances were removed by vacuum distillation to obtain a colorless, transparent liquid product, which is the phenol-free polymerized phosphite product.

[0044] Example 5

[0045] In the same apparatus as in Example 1, nitrogen protection was applied. Isodecyl alcohol (21.6 g, 0.14 mol), dipropylene glycol (7.3 g, 0.05 mol), and 1-butyl-3-methylimidazolium hydroxide ([BMIm]OH, 4.0 g, 6% of the total mass of the reaction system) were added and mixed thoroughly. Trimethyl phosphite (24.8 g, 0.20 mol) was added dropwise under stirring at 600 rpm, and the reaction was carried out at 130 °C for 6 h. The generated methanol was distilled off using a fractionating column. After the reaction was complete, the mixture was cooled, and water was added for extraction to separate the lower ionic liquid aqueous solution. The solution was dried and filtered. The upper organic phase was washed with water until neutral, dried over anhydrous magnesium sulfate, and then distilled under reduced pressure at 120 °C and 1 kPa for 1 h to obtain a colorless, transparent liquid product, which was the phenol-free polymerized phosphite product.

[0046] Example 6

[0047] In the same apparatus as in Example 1, nitrogen protection was used. Laureth alcohol (37.2 g, 0.20 mol), neopentyl glycol (10.4 g, 0.10 mol), and 1-propyl-3-methylimidazolium hydroxide ([PMIm]OH, 3.5 g, 4.5% of the total mass of the reaction system) were added and mixed. Triethyl phosphite (33.2 g, 0.20 mol) was added dropwise with stirring, and the mixture was heated to 150 °C for 5 h. The generated ethanol was distilled off using a fractionating column. After the reaction was complete, the mixture was allowed to cool and then extracted with petroleum ether and a small amount of water, separating the lower ionic liquid aqueous solution. The organic phase was washed with water, dried, filtered, and the solvent was removed under reduced pressure to obtain a light yellow, low-viscosity liquid, which was the phenol-free polymerized phosphite product.

[0048] Example 7

[0049] In the same apparatus as in Example 1, under nitrogen protection and ice bath cooling, octanol (26.0 g, 0.20 mol), polyethylene glycol PEG400 (40.0 g, 0.10 mol), and tetramethylammonium hydroxide (TMAH, 2.0 g, 4% of the total mass of the reaction system) were mixed. Phosphorus trichloride (13.8 g, 0.10 mol) was slowly added dropwise with stirring, and the temperature was controlled below 40 °C. After the addition was complete, the temperature was gradually increased to 100 °C, and the reaction was carried out for 8 hours, with nitrogen purging to remove the generated hydrogen chloride. After the reaction was completed, the mixture was allowed to cool and then extracted with toluene. The organic phase was washed with dilute alkali and water until neutral. The lower ionic liquid aqueous solution was separated. After drying, toluene and a small amount of water were removed by vacuum distillation to obtain a light yellow, transparent, viscous liquid, which is the phenol-free polymerized phosphite product. TMAH is strongly alkaline and can catalyze efficiently at low temperatures. Using PEG segments, the product has excellent compatibility with PVC plasticizers.

[0050] Example 8

[0051] In the same apparatus as in Example 1, under nitrogen protection, isotrigine alcohol (42.8 g, 0.22 mol), trimethylolpropane (13.4 g, 0.10 mol), and tetraethylammonium hydroxide (TEAOH, 5.0 g, 5% of the total mass of the reaction system) were mixed. Triisopropyl phosphite (41.6 g, 0.20 mol) was slowly added dropwise with stirring, and the reaction was carried out at 160°C for 10 hours. Isopropanol was then distilled off. Due to the large molecular weight of the product, the viscosity increased significantly in the later stages of the reaction. After the reaction was completed, the mixture was allowed to stand and cool to 60°C, diluted with ethyl acetate, and then washed repeatedly with warm water to separate the organic phase. After drying, the solvent was removed by vacuum distillation to obtain a light yellow viscous liquid, which was the phenol-free polymerized phosphite product.

[0052] Example 9

[0053] In the same apparatus, under nitrogen protection, stearyl alcohol (27.0 g, 0.10 mol), trimethylpentanediol (14.6 g, 0.10 mol), and tetrapropylammonium hydroxide (TEAOH, 4.5 g, 6% of the total mass of the reaction system) were mixed. Triphenyl phosphite (31.0 g, 0.10 mol) was slowly added dropwise with stirring, and the reaction was carried out under reduced pressure at 150 °C for 6 hours, with the generated phenol being continuously extracted from the system. Gas chromatography was used to monitor the phenol content until it was below 0.1%. After the reaction was completed, the mixture was allowed to cool and stand, warm water was added and stirred, and the mixture was allowed to stand and separate into layers. The lower layer was a basic ionic liquid aqueous solution (which was retained for recycling). The upper organic phase was washed with warm water, dried with anhydrous magnesium sulfate, washed with water, dried, and distilled under reduced pressure to obtain a white, soft, waxy solid, which is the phenol-free polymerized phosphite product. TPAOH has significant steric hindrance and organic compatibility, and can efficiently catalyze the transesterification reaction of long-chain fatty alcohols. This example demonstrates that even starting with phenol-containing raw materials, the present invention can obtain phosphite products with ultra-low phenol content through deep transesterification.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and not restrictive in all respects. Furthermore, it should be understood that although this specification describes embodiments, it does not encompass only one technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for synthesizing phenol-free phosphites in an alkaline ionic liquid, characterized in that: Includes the following steps: 1) Preparation of alkaline ionic liquid: Using 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium bromide, tetramethylammonium chloride, tetraethylammonium chloride or tetrapropylammonium chloride as cation sources, dissolve them in anhydrous ethanol, add potassium hydroxide dropwise in an amount equal to the amount of the cation source, stir the reaction at 55℃~65℃ and 500~800 r / min for 20~30 hours, filter to remove the solid precipitate, remove the ethanol by rotary evaporation, and then vacuum dry at 45℃~45℃ for 18~26℃ hours to obtain a clear and transparent alkaline ionic liquid; 2) Formation of the reaction system: Under the protection of an inert atmosphere, the monohydric alcohol, dihydric alcohol and the alkaline ionic liquid obtained in step 1) are mixed and stirred evenly at a speed of 500-800 r / min to form a reaction system. 3) Esterification or transesterification reaction: Add a phosphorus-containing compound to the reaction system of step 2), react at 50℃~180℃ for 1~24 hours, cool after the reaction is completed, and obtain the phenol-free phosphite by separation and purification.

2. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 1, characterized in that: In step 1), the alkaline ionic liquid is 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, or tetrapropylammonium hydroxide.

3. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 1, characterized in that: In step 2), The monohydric alcohol is a straight-chain or branched fatty alcohol with 3 to 18 carbon atoms. The diol is selected from one or more of ethylene glycol, diethylene glycol monohydrate, dipropylene glycol monohydrate, dipropylene glycol trihydrate, or polyethylene glycol with a molecular weight of 200 to 800. The molar ratio of the monohydric alcohol to the dihydric alcohol is 10:1 to 1:

2.

4. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 3, characterized in that: In step 2), the amount of alkaline ionic liquid used is 1% to 30% of the total mass of the reaction system.

5. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 4, characterized in that: The amount of alkaline ionic liquid used is 5% to 15% of the total mass of the reaction system.

6. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 1, characterized in that: In step 3), the phosphorus-containing compound is phosphorus trichloride or a trialkyl phosphite, wherein the trialkyl phosphite includes one or more of trimethyl phosphite, triethyl phosphite, or triisopropyl phosphite.

7. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 6, characterized in that: In step 3), the amount of phosphorus-containing compound used is such that the molar ratio of phosphorus-containing compound to diol is 0.8:1 to 3:

1.

8. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 1, characterized in that: In step 3), the reaction endpoint is determined by observing the reflux: when reflux no longer occurs within 0.5 hours, the reaction is terminated; after cooling, the alkaline ionic liquid and mechanical impurities are removed by filtration to obtain the product.

9. The method for synthesizing phenol-free phosphite in an alkaline ionic liquid according to claim 1, characterized in that: In step 3), the separation and purification are as follows: after the reaction is completed, deionized water or a low-polarity solvent is added to the reaction system for extraction to separate the organic phase containing the product. The organic phase is washed with water until neutral, and then dried, filtered and distilled under reduced pressure to remove the solvent and unreacted raw materials to obtain the phenol-free phosphite.

10. The method for synthesizing phenol-free phosphites in an alkaline ionic liquid according to claim 9, characterized in that: In step 3), the aqueous phase generated during the separation and purification process is a mixed solution rich in the alkaline ionic liquid. This aqueous phase is directly reused in the next batch of reaction after dehydration treatment.

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