Synthesis method of high-purity hydroquinone dihydroxyethyl ether

Abstract

The invention relates to the technical field of synthesis of hydroquinone dihydroxyethyl ether, in particular to a synthesis method of high-purity hydroquinone dihydroxyethyl ether. Comprising the following steps: enabling hydroquinone and ethylene carbonate to react in the presence of a compound catalyst in the absence of a solvent and under the protection of inert gas; after the reaction is finished, cooling a reaction mixture, and adding a reducing agent for reduction treatment to obtain a reaction crude product; sequentially carrying out reduced pressure rectification and melt crystallization treatment on the reaction crude product to obtain refined hydroquinone dihydroxyethyl ether; by adopting a compound catalyst system consisting of a basic catalyst and an organic catalyst, the reaction selectivity and efficiency are remarkably improved, and the generation of monosubstituted byproducts is effectively inhibited; and by combining the reduction treatment at the later stage of the reaction and the purification process of vacuum distillation and melt crystallization, impurity introduction and oxidation side reaction are avoided, so that the hydroquinone dihydroxyethyl ether with high purity and low product chroma is efficiently obtained.

Description

Technical Field

[0001] This invention relates to the field of hydroquinone dihydroxyethyl ether synthesis technology, and more specifically, to a method for synthesizing high-purity hydroquinone dihydroxyethyl ether. Background Technology

[0002] Polyurethane crosslinking agents fall into two main categories: hydroxyl-based and amine-based compounds. Amine-based compounds cannot be used in combination with MDI (diphenylmethane diisocyanate), while hydroxyl-based compounds, when used as crosslinking agents for MDI, can yield polyurethane polymers with satisfactory performance. Hydroquinone dihydroxyethyl ether (HQEE) has a wide range of applications as a crosslinking agent in the synthesis of polyurethane polymers. It exhibits good compatibility with MDI and can improve various performance indicators of polyurethane materials, such as strength, heat resistance, and resilience.

[0003] There are three main synthetic routes for hydroquinone dihydroxyethyl ether (HQEE): 1. Chloroethanol method: Hydroquinone is first reacted with sodium hydroxide to form a sodium salt, which is then reacted with chloroethanol to prepare HQEE. This route has a low yield and long preparation time for HQEE. Chloroethanol is expensive, resulting in high raw material costs. It also generates chlorine-containing wastewater, which has a significant environmental burden. This route has essentially no industrialization value.

[0004] 2. Ethylene oxide (EO) method: HQEE is prepared by reacting ethylene oxide and hydroquinone in the presence of a catalyst. However, this route introduces ethylene oxide, increasing the risk of infection, has a relatively long reaction time, and involves complex subsequent processing.

[0005] 3. Ethylene carbonate (EC) method: Hydroquinone and ethylene carbonate react in the presence of a catalyst to prepare HQEE; however, the existing ethylene carbonate method usually uses a single alkaline catalyst, such as sodium hydroxide or potassium hydroxide. This system has poor catalytic selectivity, is prone to producing monosubstituted byproducts, and results in a darker product color. Summary of the Invention

[0006] This invention provides a method for synthesizing high-purity hydroquinone dihydroxyethyl ether. By employing a composite catalyst system composed of a basic catalyst and an organic catalyst, the method significantly improves reaction selectivity and efficiency, effectively suppressing the formation of monosubstituted byproducts. Furthermore, by conducting the reaction under solvent-free and inert gas protection conditions, combined with post-reaction reduction treatment and a combined purification process of vacuum distillation and melt crystallization, the method fundamentally avoids the introduction of impurities and oxidation side reactions, thereby efficiently obtaining high-purity hydroquinone dihydroxyethyl ether with low product color. This solves the problems mentioned in the background art, namely: Existing ethylene carbonate processes typically employ a single alkaline catalyst, such as sodium hydroxide or potassium hydroxide. This system suffers from poor catalytic selectivity, is prone to producing monosubstituted byproducts, and results in products with a darker color.

[0007] To achieve the above objective, the method for synthesizing high-purity hydroquinone dihydroxyethyl ether includes the following steps: S1. Under solvent-free and inert gas protection, hydroquinone and ethylene carbonate are reacted at 110-190°C in the presence of a compound catalyst, wherein the compound catalyst is composed of a basic catalyst and an organic catalyst, and the total amount of the compound catalyst is 2%-5% of the mass of hydroquinone; S2. After the reaction is complete, the reaction mixture is cooled to 60-90℃, and a reducing agent is added for reduction treatment to obtain the crude product. S3. The crude product of the reaction is subjected to vacuum distillation and melt crystallization in sequence to obtain purified hydroquinone dihydroxyethyl ether.

[0008] In the above technical solution, in the overall reaction system of S1, the target product is generated with high selectivity through the catalytic ring-opening addition reaction of hydroquinone and ethylene carbonate by strictly controlling the reaction in an inert atmosphere and solvent-free environment.

[0009] Solvent-free conditions avoid the problem of solvent molecules participating in side reactions or affecting catalyst efficiency, thereby simplifying the subsequent purification process and improving atom economy.

[0010] In S1, the inert gas is selected from nitrogen and argon. Inert gas protection is crucial because the phenolic hydroxyl groups of hydroquinone are easily oxidized by oxygen in the air to generate quinone colored substances, which leads to a darker color of the product.

[0011] The composite catalyst system consists of a synergistic effect of a basic catalyst and an organic catalyst: the basic catalyst is selected from one of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate. The primary function of the basic catalyst is to promote the deprotonation of the phenolic hydroxyl group of hydroquinone to generate a more nucleophilic phenoxy anion. This phenoxy anion then attacks the carbonyl carbon atom of ethylene carbonate, initiating the ring-opening of the ethylene oxide ring to generate the desired hydroxyethyl ether bond.

[0012] However, single basic catalysts exhibit poor selectivity, easily leading to the continued reaction of the first hydroxyethylated molecule, generating undesirable monosubstituted byproducts, i.e., a molecule of hydroquinone is only linked to one hydroxyethyl group. Therefore, this technical solution introduces an organic catalyst, selected from triphenylphosphine and dimethylimidazole, which can activate ethylene carbonate through different catalytic pathways, complementing the basic catalyst and significantly improving the reaction rate and selectivity of hydroquinone dihydroxyethyl ether, effectively suppressing the excessive formation of monosubstituted byproducts. The reaction temperature is further limited to 150℃-170℃, with a reaction time of 3-5 hours. This temperature range provides sufficient energy to overcome the reaction barrier, ensuring the ring-opening addition reaction proceeds at a considerable rate, while avoiding excessively high temperatures that could lead to material carbonization or the formation of other degradation byproducts.

[0013] It should be further explained that the mechanism of action of a single basic catalyst is relatively direct and crude. Its main function is to promote the deprotonation of the phenolic hydroxyl group of hydroquinone, generating a nucleophilic phenoxy anion. However, the nucleophilic attack of this phenoxy anion on ethylene carbonate lacks regioselectivity, and the reactive intermediate has high energy, resulting in a single reaction pathway and poor controllability. As a result, once a phenolic hydroxyl group is hydroxyethylated, the acidity of the remaining hydroxyl group in the resulting monosubstituted intermediate weakens, and the reactivity decreases. Meanwhile, the abundant alkaline catalyst in the system will continue to drive another more active phenoxy anion. This phenoxy anion, whether from unreacted hydroquinone or monosubstituted products, will attack ethylene carbonate. However, due to changes in steric hindrance and electronic effects, this attack is more likely to occur on different molecules, resulting in the accumulation of monosubstituted byproducts (i.e., one molecule of hydroquinone is only connected to one hydroxyethyl ether), rather than efficiently generating the target hydroquinone dihydroxyethyl ether. To overcome the inherent limitations of a single basic catalytic pathway, this technical solution introduces an organic catalyst (such as triphenylphosphine or dimethylimidazole). The addition of triphenylphosphine or dimethylimidazole does not simply enhance the basicity, but rather opens up a completely new reaction channel that runs parallel to and complements the basic catalyst.

[0014] Triphenylphosphine first reacts with ethylene carbonate via nucleophilic addition to form a highly reactive zwitterionic intermediate. This intermediate, as a pre-activated vinyl donor, undergoes a fundamental change in its reaction sites and electron distribution, making it more preferentially and selectively attacked by phenoxy anions, thereby greatly guiding the formation of hydroquinone dihydroxyethyl ether.

[0015] Dimethylimidazole, as a nitrogen-containing heterocyclic carbene precursor, initiates a chain reaction by directly opening ethylene carbonate to form a highly reactive alkoxide. Both of these novel pathways effectively intercept and guide the reaction process, complementing the basic catalytic pathway. This not only significantly accelerates the overall reaction rate but, more importantly, provides a more energy-efficient and selective reaction route, thermodynamically and kinetically promoting the efficient grafting of the two hydroxyethyl groups onto the hydroquinone molecule. This effectively suppresses the excessive formation of monosubstituted byproducts at the source, ultimately yielding the target product, hydroquinone dihydroxyethyl ether, with high selectivity.

[0016] In step S2, the temperature is lowered and a reducing agent is added. The addition of this reducing agent reduces trace amounts of colored oxide impurities (mainly quinone compounds) that may be generated during the reaction to colorless, original phenolic structures, thus significantly improving the product's color. After the reaction, the mixture is cooled to 60-90℃. Excessive temperature may cause the reducing agent to decompose and become ineffective or lead to unnecessary reactions in the product; excessively low temperature increases the viscosity of the mixture, hindering sufficient contact and uniform reaction between the reducing agent and the colored impurities. Therefore, this scheme uses a temperature range of 60-90℃. The added reducing agent is selected from sodium sulfite, sodium bisulfite, and sodium dithionite, possessing strong reducing properties. It can selectively reduce quinone groups to phenolic hydroxyl groups without affecting existing functional groups such as ether bonds and hydroxyl groups in the system.

[0017] In S3, the crude product obtained after the cooling reduction treatment in S2 is subjected to vacuum distillation and melt crystallization. Specifically, the vacuum distillation process involves distilling off unreacted ethylene carbonate under a vacuum of 0.09-0.095 MPa, separating the monosubstituted byproducts, and finally collecting the fraction at 200-220℃ to obtain crude hydroquinone dihydroxyethyl ether. The melt crystallization process involves heating the crude hydroquinone dihydroxyethyl ether obtained from vacuum distillation to complete melting, then cooling it to the crystallization temperature at a cooling rate of 0.5-1℃ / min, allowing it to crystallize for 1-2 hours, and then draining the mother liquor to obtain hydroquinone dihydroxyethyl ether crystals. The initial vacuum distillation utilizes the differences in volatility among the components in the mixture for separation. The high vacuum environment significantly lowers the boiling points of each component, avoiding the high temperatures required for atmospheric distillation, thus preventing the decomposition or polymerization of heat-sensitive products and impurities at high temperatures. The distillation process typically proceeds in order of increasing boiling point, sequentially separating and recovering unreacted excess ethylene carbonate, monosubstituted byproducts with intermediate boiling points, and other intermediate fractions, ultimately collecting the high-boiling target product, hydroquinone dihydroxyethyl ether.

[0018] The purity of the crude hydroquinone dihydroxyethyl ether obtained through distillation has been significantly improved, but it may still contain small amounts of impurities with very similar structures and properties, as well as some high-boiling-point colored impurities. The subsequent melt crystallization technique utilizes the differences in freezing point, crystal shape, and lattice capacity between the target product and these trace impurities for purification: the crude hydroquinone dihydroxyethyl ether is heated to complete melting, and then slowly cooled under controlled conditions, allowing the purest hydroquinone dihydroxyethyl ether molecules to preferentially and orderly precipitate to form crystals, while impurities, which are not easily incorporated into the crystal lattice, accumulate in the remaining mother liquor. After crystal growth is complete, the mother liquor containing most of the impurities is discharged, yielding highly pure hydroquinone dihydroxyethyl ether crystals, thus ensuring that the final product meets high standards in both chemical purity and color.

[0019] Based on this, in S1, the molar ratio of hydroquinone to ethylene carbonate is 1:3-1:3.15; this ratio is designed based on a moderate excess of the theoretical molar ratio of 1:2. The necessity of this ratio is that, firstly, ethylene carbonate undergoes thermodynamic losses due to volatilization and partial decomposition at reaction temperatures of 110-190℃. A moderate excess can compensate for these losses and ensure that there is always a sufficient amount of reagent participating in the reaction. Secondly, and more importantly, according to the principle of chemical equilibrium, the increased concentration of excess ethylene carbonate as a reaction substrate can continuously drive the reaction equilibrium towards the positive direction, providing a basis for the second-step hydroxyethylation reaction. This is because after the first phenolic hydroxyl group is etherified, the molecular electron cloud density is redistributed, and the nucleophilic reactivity of the remaining phenolic hydroxyl group is significantly reduced. Higher reaction driving force and more frequent molecular collision probability are required to overcome the energy barrier and complete the second-step substitution. At this time, the excess ethylene carbonate, by increasing its local concentration in the reaction system, greatly promotes the reaction rate and conversion degree with the low-activity monosubstituted intermediate, thereby forcing the reaction to tend to be complete and minimizing the possibility of the reaction stopping at the single ether stage.

[0020] In addition, in S1, stirring is required during the reaction process, with a stirring speed of 200-400 rpm. In the early stage of the reaction, it is usually a solid-liquid heterogeneous system (hydroquinone is a solid powder, and ethylene carbonate is a liquid). Although it may become homogeneous in the middle and later stages due to dissolution or melting, there are still viscosity changes. Sufficient mechanical stirring can effectively break the liquid film boundary layer on the surface of solid particles, greatly increase the dissolution and dispersion rate of solid reactant (hydroquinone) and its contact area with liquid ethylene carbonate, ensure the maximization of intermolecular collision frequency, and provide a uniform and sufficient kinetic driving force for the reaction. Secondly, the precisely controlled stirring shear force can maintain the temperature uniformity of the reaction system, remove the heat of reaction in time, and prevent side reactions such as violent decomposition of ethylene carbonate or coking of products caused by local overheating, thus ensuring the selectivity and safety of the reaction. Finally, this rotational speed range provides sufficiently strong fluid turbulence to overcome the potential increase in system viscosity and prevent reactants or intermediates from settling and agglomerating due to poor mixing, which could lead to incomplete reactions or the formation of byproducts. It also avoids excessive shearing, oxygen entrainment caused by liquid surface vortices, and unnecessary energy consumption that may be caused by excessively high rotational speeds. Thus, it provides a uniform and stable reaction environment for the entire reaction at the microscale, making it an indispensable engineering control method for obtaining high-purity, high-yield target products.

[0021] In addition, in S1, the mass ratio of the basic catalyst to the organic catalyst in the composite catalyst is 1:1 to 4:1. During the reaction, the phenolic hydroxyl group of the monoether intermediate is affected by the electron-donating effect of the introduced hydroxyethoxy group, which weakens its acidity and significantly reduces its reactivity. At this time, the catalytic efficiency of the basic catalyst is greatly reduced. As a nucleophilic catalyst, the organic catalyst can preferentially react with the carbonyl group of ethylene carbonate, activate its molecule, and significantly reduce the energy barrier of the second etherification reaction. Therefore, the 1:1 baseline ratio ensures that there is a sufficient amount of organic catalyst in the system to effectively activate ethylene carbonate, providing the necessary and stable catalytic ability to overcome the kinetic obstacles of the second step reaction and preventing the reaction from stalling at the single ether stage. The 4:1 upper limit avoids the overuse of organophosphorus (as it may promote side reactions and is costly), while ensuring the dominant role of the alkaline catalyst to maintain the necessary alkaline environment of the reaction system and to compensate for its slight deactivation due to hygroscopicity, reaction with carbon dioxide or trace amounts of water generated in the reaction. Ultimately, the two catalysts work synergistically at the optimal ratio to maximize their strengths and minimize their weaknesses, jointly driving the reaction to proceed efficiently and selectively toward the formation of the target diether product.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: By employing a composite catalyst system consisting of alkaline and organic catalysts, the reaction selectivity and efficiency were significantly improved, and the formation of monosubstituted byproducts was effectively suppressed. Furthermore, by conducting the reaction under solvent-free conditions and inert gas protection, combined with post-reaction reduction treatment and a combined purification process of vacuum distillation and melt crystallization, the introduction of impurities and oxidation side reactions were fundamentally avoided, thereby efficiently obtaining high-purity hydroquinone dihydroxyethyl ether with low product color. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the method steps in Embodiment 1 of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Current methods for synthesizing ethylene carbonate typically employ a single alkaline catalyst, such as sodium hydroxide or potassium hydroxide. This system suffers from poor catalytic selectivity, readily producing monosubstituted byproducts and resulting in products with a darker color. This invention provides a method for synthesizing high-purity hydroquinone dihydroxyethyl ether, such as… Figure 1 As shown, Example 1

[0026] Includes the following steps: S1. Under solvent-free and inert gas protection, hydroquinone and ethylene carbonate are reacted at 160°C in the presence of a compound catalyst for 4 hours. The molar ratio of hydroquinone to ethylene carbonate is 1:3.07. The compound catalyst consists of a basic catalyst and an organic catalyst, and the total amount of the compound catalyst is 3.5% of the mass of hydroquinone. In this step, nitrogen is preferably used as the inert gas in this embodiment. Sodium hydroxide is used as the alkaline catalyst and triphenylphosphine is used as the organic catalyst in the compound catalyst. The mass ratio of alkaline catalyst to organic catalyst is 2.5:1. During the reaction, stirring is required and the stirring speed is 300 rpm. S2. After the reaction is complete, the reaction mixture is cooled to 75°C, and a reducing agent is added for reduction treatment to obtain the crude product. In this step, the reducing agent is sodium sulfite in this embodiment; S3. The crude product of the reaction is subjected to vacuum distillation and melt crystallization in sequence to obtain purified hydroquinone dihydroxyethyl ether. In this step, the specific steps of vacuum distillation are as follows: under a vacuum of 0.093 MPa, unreacted ethylene carbonate is first distilled off, then monosubstituted byproducts are separated, and finally the fraction with a boiling range of 210°C under the same vacuum is used to obtain crude hydroquinone dihydroxyethyl ether. The specific steps of the melt crystallization process are as follows: the crude hydroquinone dihydroxyethyl ether obtained by vacuum distillation is heated to complete melting, and then cooled to the crystallization temperature at a cooling rate of 0.7℃ / min. After crystallization for 1.5 hours, the mother liquor is discharged to obtain hydroquinone dihydroxyethyl ether crystals. Example 2

[0027] Includes the following steps: S1. Under solvent-free and inert gas protection, hydroquinone and ethylene carbonate are reacted at 150°C in the presence of a compound catalyst for 3 hours. The molar ratio of hydroquinone to ethylene carbonate is 1:3. The compound catalyst is composed of a basic catalyst and an organic catalyst, and the total amount of the compound catalyst is 2% of the mass of hydroquinone. In this step, nitrogen is preferably used as the inert gas in this embodiment. Sodium hydroxide is used as the alkaline catalyst and triphenylphosphine is used as the organic catalyst in the compound catalyst. The mass ratio of alkaline catalyst to organic catalyst is 1:1. During the reaction, stirring is required and the stirring speed is 200 rpm. S2. After the reaction is complete, the reaction mixture is cooled to 60°C, and a reducing agent is added for reduction treatment to obtain the crude product. In this step, the reducing agent is sodium sulfite in this embodiment; S3. The crude product of the reaction is subjected to vacuum distillation and melt crystallization in sequence to obtain purified hydroquinone dihydroxyethyl ether. In this step, the specific steps of vacuum distillation are as follows: under a vacuum of 0.09 MPa, unreacted ethylene carbonate is first distilled off, then monosubstituted byproducts are separated, and finally the fraction with a boiling range of 200°C under the same vacuum is used to obtain crude hydroquinone dihydroxyethyl ether. The specific steps of the melt crystallization process are as follows: the crude hydroquinone dihydroxyethyl ether obtained by vacuum distillation is heated to complete melting, and then cooled to the crystallization temperature at a cooling rate of 0.5℃ / min. After crystallization for 1 hour, the mother liquor is discharged to obtain hydroquinone dihydroxyethyl ether crystals. Example 3

[0028] Includes the following steps: S1. Under solvent-free and inert gas protection, hydroquinone and ethylene carbonate are reacted at 170°C in the presence of a compound catalyst for 5 hours. The molar ratio of hydroquinone to ethylene carbonate is 1:3.15. The compound catalyst is composed of a basic catalyst and an organic catalyst, and the total amount of the compound catalyst is 5% of the mass of hydroquinone. In this step, nitrogen is preferably used as the inert gas in this embodiment. Sodium hydroxide is used as the alkaline catalyst and triphenylphosphine is used as the organic catalyst in the compound catalyst. The mass ratio of alkaline catalyst to organic catalyst is 4:1. During the reaction, stirring is required and the stirring speed is 400 rpm. S2. After the reaction is complete, the reaction mixture is cooled to 90°C, and a reducing agent is added for reduction treatment to obtain the crude product. In this step, the reducing agent is sodium sulfite in this embodiment; S3. The crude product of the reaction is subjected to vacuum distillation and melt crystallization in sequence to obtain purified hydroquinone dihydroxyethyl ether. In this step, the specific steps of vacuum distillation are as follows: under a vacuum of 0.095 MPa, unreacted ethylene carbonate is first distilled off, then monosubstituted byproducts are separated, and finally the fraction with a boiling range of 220°C under the same vacuum is used to obtain crude hydroquinone dihydroxyethyl ether. The specific steps of the melt crystallization process are as follows: the crude hydroquinone dihydroxyethyl ether obtained by vacuum distillation is heated to complete melting, and then cooled to the crystallization temperature at a cooling rate of 1℃ / min. After crystallization for 2 hours, the mother liquor is discharged to obtain hydroquinone dihydroxyethyl ether crystals. Example 4

[0029] In this embodiment, the difference from Example 1 is that, in S1, argon is used as the inert gas; potassium hydroxide is preferably used as the alkaline catalyst, and dimethylimidazole is used as the organic catalyst; sodium bisulfite is used as the reducing agent in S2; and the remaining step parameters are the same as in Example 1. Example 5

[0030] In this embodiment, the difference from Example 1 is that, in S1, sodium carbonate is preferably used as the alkaline catalyst; in S2, sodium dithionite is used as the reducing agent; and the remaining step parameters are the same as in Example 1. Example 6

[0031] In this embodiment, the difference from Example 1 is that, in S1, potassium carbonate is preferably used as the alkaline catalyst; the remaining step parameters are the same as in Example 1.

[0032] Experimental Example 1: Performance comparison experiment of hydroquinone dihydroxyethyl ether preparation examples: Experimental subjects: Examples 1 to 6.

[0033] Table 1: Comparison of Synthetic Performance in Examples 1 to 6

[0034] Conclusion: According to the experimental data in Table 1, Example 1 exhibits the best overall performance, with a hydroquinone conversion rate of over 99.5%, a catalyst system selectivity for the target product of up to 95.5%, a distillation yield of 92.0%, a final purity of 99.95%, and a product color of less than 20 APHA, indicating that it has the highest reaction efficiency, product purity, and color. In comparison, although Example 2 has relatively lower performance across the board, its reaction conditions are likely milder and less expensive, making it suitable for conventional industrial scenarios where absolute purity requirements are not high but cost control is stringent. Examples 3 and 4 maintain extremely high levels of conversion and purity, and the product color (<25 APHA) is well controlled, making them suitable for high-end applications where product color is strictly regulated. Example 5 has a high conversion rate but slightly lower selectivity and a slightly inferior product color (<30 APHA), which may reflect the balance between reaction rate and specificity of its catalyst system, making it suitable for intermediate production where slight color is acceptable and subsequent refining processes are required. Example 6 has the closest performance to Example 1, especially in terms of catalyst system selectivity for the target product and product color, making it an ideal alternative to Example 1, suitable for continuous or large-scale production that also pursues high quality.

[0035] Comparative Example 1: Includes the following steps: S1. Under solvent-free and inert gas protection, hydroquinone and ethylene carbonate are reacted at 100°C in the presence of a compound catalyst for 2 hours. The molar ratio of hydroquinone to ethylene carbonate is 1:2.5. The compound catalyst is composed of a basic catalyst and an organic catalyst, and the total amount of the compound catalyst is 1% of the mass of hydroquinone. In this step, nitrogen is preferably used as the inert gas in this embodiment. Sodium hydroxide is used as the alkaline catalyst and triphenylphosphine is used as the organic catalyst in the compound catalyst. The mass ratio of alkaline catalyst to organic catalyst is 0.5:1. During the reaction, stirring is required and the stirring speed is 100 rpm. S2. After the reaction is complete, the reaction mixture is cooled to 50°C, and a reducing agent is added for reduction treatment to obtain the crude product. In this step, the reducing agent is sodium sulfite in this embodiment; S3. The crude product of the reaction is subjected to vacuum distillation and melt crystallization in sequence to obtain purified hydroquinone dihydroxyethyl ether. In this step, the specific steps of vacuum distillation are as follows: under a vacuum of 0.09 MPa, unreacted ethylene carbonate is first distilled off, then monosubstituted byproducts are separated, and finally the fraction with a boiling range of 200°C under the same vacuum is used to obtain crude hydroquinone dihydroxyethyl ether. The specific steps of the melt crystallization process are as follows: the crude hydroquinone dihydroxyethyl ether obtained by vacuum distillation is heated to complete melting, and then cooled to the crystallization temperature at a cooling rate of 2℃ / min. After crystallization for 3 hours, the mother liquor is discharged to obtain hydroquinone dihydroxyethyl ether crystals.

[0036] Comparative Example 2: Includes the following steps: S1. Under solvent-free and inert gas protection, hydroquinone and ethylene carbonate are reacted at 200°C in the presence of a compound catalyst for 6 hours. The molar ratio of hydroquinone to ethylene carbonate is 1:3.5. The compound catalyst is composed of a basic catalyst and an organic catalyst, and the total amount of the compound catalyst is 6% of the mass of hydroquinone. In this step, nitrogen is preferably used as the inert gas in this embodiment. Sodium hydroxide is used as the alkaline catalyst and triphenylphosphine is used as the organic catalyst in the compound catalyst. The mass ratio of alkaline catalyst to organic catalyst is 5:1. During the reaction, stirring is required and the stirring speed is 500 rpm. S2. After the reaction is complete, the reaction mixture is cooled to 100°C, and a reducing agent is added for reduction treatment to obtain the crude product. In this step, the reducing agent is sodium sulfite in this embodiment; S3. The crude product of the reaction is subjected to vacuum distillation and melt crystallization in sequence to obtain purified hydroquinone dihydroxyethyl ether. In this step, the specific steps of vacuum distillation are as follows: under a vacuum of 0.095 MPa, unreacted ethylene carbonate is first distilled off, then monosubstituted byproducts are separated, and finally the fraction with a boiling range of 220°C under the same vacuum is used to obtain crude hydroquinone dihydroxyethyl ether. The specific steps of the melt crystallization process are as follows: the crude hydroquinone dihydroxyethyl ether obtained by vacuum distillation is heated to complete melting, and then cooled to the crystallization temperature at a cooling rate of 2℃ / min. After crystallization for 3 hours, the mother liquor is discharged to obtain hydroquinone dihydroxyethyl ether crystals.

[0037] Experimental Example 2: Performance comparison experiment of hydroquinone dihydroxyethyl ether preparation examples: Experimental subjects: Example 1, Comparative Example 1 and Comparative Example 2.

[0038] Table 2: Effect of reaction parameters exceeding the preferred range on synthesis performance

[0039] Conclusion: According to the experimental data in Table 2, Example 1 showed the best performance in all core indicators, including hydroquinone conversion rate, catalyst system selectivity for the target product, distillation yield, final purity, and product color. Its efficient catalyst system and mature process conditions ensured ultra-high purity and excellent appearance at high yield, making it an excellent solution for the industrial production of high-quality hydroquinone dihydroxyethyl ether. Comparative Example 1 had a significantly low conversion rate, resulting in a large amount of unreacted raw materials. Although its catalyst system had acceptable selectivity for the target product, the low hydroquinone conversion rate (85.0%) and severe product color (>100 APHA) indicated incomplete reaction or the introduction of unknown impurities. While Comparative Example 2 achieved a high hydroquinone conversion rate of 98.5%, its extremely low catalyst system selectivity for the target product (65.0%) indicated a fundamental defect in the catalyst system or reaction conditions, generating a large number of byproducts, leading to a sharp decrease in final yield, reduced purity, and extremely poor color.

[0040] Comparative Example 3: In this comparative example, during the reaction in S1, the compound catalyst was omitted, and only sodium hydroxide as a single catalyst was used for the reaction. The remaining steps and parameters were the same as in Example 1.

[0041] Comparative Example 4: In this comparative example, during the reaction in S1, the compound catalyst was omitted, and only potassium hydroxide as a single catalyst was used for the reaction. The remaining steps and parameters were the same as in Example 1.

[0042] Comparative Example 5: In this comparative example, during the reaction in S1, the compound catalyst was removed, and only sodium carbonate as a single catalyst was used for the reaction. The remaining steps and parameters were the same as in Example 1.

[0043] Comparative Example 6: In this comparative example, during the reaction in S1, the compound catalyst was removed, and only potassium carbonate as a single catalyst was used for the reaction. The remaining steps and parameters were the same as in Example 1.

[0044] Comparative Example 7: In this comparative example, during the reaction in S1, the compound catalyst was removed, and only a single organic catalyst, triphenylphosphine, was used for the reaction. The remaining steps and parameters were the same as in Example 1.

[0045] Comparative Example 8: In this comparative example, during the reaction in S1, the compound catalyst was removed, and only a single organic catalyst, dimethylimidazole, was used for the reaction. The remaining steps and parameters were the same as in Example 1.

[0046] Experimental Example 3: Performance comparison experiment of hydroquinone dihydroxyethyl ether preparation examples: Experimental subjects: Example 1, Comparative Examples 3 to 8.

[0047] Table 3: Performance Comparison of Compound Catalysts and Single Catalyst Systems

[0048] Conclusion: According to the experimental data in Table 3, in the process of synthesizing hydroquinone dihydroxyethyl ether, Example 1, which uses a compound catalyst, achieved the best overall performance. Its hydroquinone conversion rate, catalyst system selectivity for the target product, distillation yield, final purity and product color are all superior. In contrast, although comparative examples 3 and 4, which used single strong base catalysts, had high conversion rates (>99.0%), the catalyst system had poor selectivity for the target product and poor product color. Comparative examples 5 and 6, which used weak base catalysts, had obvious defects of insufficient conversion rates. In contrast, comparative examples 7 and 8, which used single organic catalysts, had severely low conversion rates, resulting in a decrease in yield.

[0049] Comparative Example 9: In this comparative example, during the reaction in S1, the solvent-free protection in the reaction conditions was removed, and dimethylacetamide was added as the reaction solvent during the reaction. The remaining step parameters were the same as in Example 1.

[0050] Comparative Example 10: In this comparative example, the vacuum distillation process is omitted in step S3, and melt crystallization is used directly. The parameters of the remaining steps are the same as in Example 1.

[0051] Comparative Example 11: In this comparative example, the melting and crystallization process in step S3 is omitted, and vacuum distillation is used directly. The parameters of the remaining steps are the same as in Example 1.

[0052] Comparative Example 12: In this comparative example, the hydroquinone dihydroxyethyl ether was synthesized using the chloroethanol method in the prior art. The reaction route is as follows: hydroquinone first reacts with sodium hydroxide to generate sodium salt, and then reacts with chloroethanol to prepare hydroquinone dihydroxyethyl ether.

[0053] Comparative Example 13: In this comparative example, the ethylene oxide (EO) method of the prior art was used to synthesize hydroquinone dihydroxyethyl ether.

[0054] Experiment Example 4: Performance comparison experiment of hydroquinone dihydroxyethyl ether preparation examples: Experimental subjects: Example 1, Comparative Examples 9 to 13.

[0055] Table 4: Effects of process steps on synthesis performance

[0056] Conclusion: Based on the experimental data in Table 4, Example 1 is once again verified to have the best overall performance. Under the premise of near-complete conversion of hydroquinone (>99.5%), it achieves a catalyst system selectivity of up to 95.5% for the target product, a distillation yield of 92.0%, and finally obtains an ultra-high purity of 99.95% and an excellent product color of <20 APHA.

[0057] In comparison, any process modification resulted in a significant decrease in product purity: Comparative Example 9, due to the addition of dimethylacetamide solvent, experienced a reduction in the selectivity of the catalyst system for the target product (93.0%) and the distillation yield (89.5%), ultimately leading to a deterioration in purity to 97.85%; Comparative Examples 10 and 11, due to defects in their purification processes, were unable to effectively remove impurities, resulting in purities of 97.50% and 97.70%, respectively, and the product color of Comparative Example 11 (≈40) deteriorated significantly; while Comparative Examples 12 and 13, both traditional methods, suffered from inherent defects. The former showed a reduction in the selectivity of the catalyst system for the target product (75.0%) and the distillation yield (65.0%), and the latter, although achieving a higher purity of 99.20%, had a lower selectivity of the catalyst system for the target product (88.0%) and a lower product color (≈50) than Example 1, and neither could simultaneously achieve high purity, high yield, and high quality.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing high-purity hydroquinone dihydroxyethyl ether, characterized in that, Includes the following steps: S1. Under solvent-free and inert gas protection, hydroquinone and ethylene carbonate are reacted at 110-190°C in the presence of a compound catalyst, wherein the compound catalyst is composed of a basic catalyst and an organic catalyst, and the total amount of the compound catalyst is 2%-5% of the mass of hydroquinone; S2. After the reaction is complete, the reaction mixture is cooled to 60-90℃, and a reducing agent is added for reduction treatment to obtain the crude product. S3. The crude product of the reaction is subjected to vacuum distillation and melt crystallization in sequence to obtain purified hydroquinone dihydroxyethyl ether.

2. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S1, the molar ratio of hydroquinone to ethylene carbonate is 1:3 to 1:3.

15.

3. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S1, the reaction temperature is 150℃-170℃, and the reaction time is 3-5 hours.

4. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S1, the alkaline catalyst is selected from one of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate; The organic catalyst is selected from triphenylphosphine and dimethylimidazole.

5. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S1, the inert gas is selected from nitrogen and argon.

6. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S1, stirring is required during the reaction process, with a stirring speed of 200-400 rpm.

7. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S1, the mass ratio of alkaline catalyst to organic catalyst in the composite catalyst is 1:1 to 4:

1.

8. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S2, the reducing agent is selected from one of sodium sulfite, sodium bisulfite, and sodium dithionite.

9. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: In S3, the specific steps of the vacuum distillation are as follows: under a vacuum of 0.09-0.095 MPa, unreacted ethylene carbonate is first distilled off, then monosubstituted byproducts are separated, and finally, the fraction with a boiling range of 200-220℃ under the same vacuum is used to obtain crude hydroquinone dihydroxyethyl ether.

10. The method for synthesizing high-purity hydroquinone dihydroxyethyl ether according to claim 1, characterized in that: The specific steps of the melt crystallization process described in S3 are as follows: the crude hydroquinone dihydroxyethyl ether obtained by vacuum distillation is heated to complete melting, and then cooled to the crystallization temperature at a cooling rate of 0.5-1℃ / min. After crystallization for 1-2 hours, the mother liquor is discharged to obtain hydroquinone dihydroxyethyl ether crystals.

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