A process for the synthesis of a flame-retardant diazo coupling adapted to water-insoluble macromolecular alkylphenols

Abstract

The present application relates to the technical field of organic synthesis fine chemical industry, and particularly relates to a kind of flame-retardant diazo coupling synthesis process, the process uses the complex solvent composed of tetrachloroethylene and methanol as organic reaction medium, under alkaline conditions, in the two-phase system formed by organic phase and aqueous phase, diazonium salt is coupled with water-insoluble macromolecular alkyl phenol.The present application uses the completely non-flammable characteristics of tetrachloroethylene, completely eliminates the safety hazards of flammable and explosive traditional methanol+strong base coupling system, greatly reduces the workshop explosion-proof grade requirement and safety production risk;Raw materials and products in organic phase are completely dissolved throughout the process, there is no suspended sludge, no wall sticking solid, coupling section does not need to carry out filtering and slag removal operation, significantly reduces the amount of hazardous waste, simplifies the process flow;The strong base two-phase interface reaction system can be adapted to all water-insoluble long-chain, large steric hindrance alkyl-substituted macromolecular phenol, and can be used for the synthesis of many kinds of benzotriazole ultraviolet absorber intermediates.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis and fine chemical technology, and in particular to a flame-retardant diazo coupling synthesis process suitable for water-insoluble macromolecular alkylphenols. Background Technology

[0002] The industrial synthesis of benzotriazole UV absorbers relies on two key reactions: diazotization of aromatic amines and coupling with large-molecule phenols. Small-molecule water-soluble phenolic substrates can be directly coupled using a weak base process in pure water; however, for long-chain alkyl-substituted, sterically hindered large-molecule phenols, which are extremely hydrophobic and completely insoluble in pure water systems, the industry must use methanol organic solvents to dissolve the substrates and combine them with liquid alkali to construct a strongly alkaline coupling environment.

[0003] Existing traditional processes suffer from three major drawbacks: First, extremely high safety risks. Methanol has a low flash point and high volatility, making it highly susceptible to flash explosions, temperature surges, and uncontrolled decomposition of diazonium salts in the presence of liquid alkali and diazonium salts. This necessitates high explosion-proof levels in the workshop, making management difficult and increasing safety investment costs. Second, severe product precipitation and large amounts of solid waste. Pure methanol systems have poor solubility for macromolecular coupling products, resulting in the precipitation of large quantities of products as solid powder and wall-adhering sludge during the reaction. Frequent shutdowns for filtration and sludge removal are required, generating large amounts of hazardous organic solid waste and hindering operational continuity. Third, narrow substrate applicability. Macromolecular phenols with different chain lengths and steric hindrances exhibit significantly different reaction behaviors in pure methanol systems, resulting in insufficient process versatility. Each substrate often requires individual adjustment of process parameters.

[0004] Therefore, those skilled in the art are dedicated to developing a flame-retardant diazo coupling synthesis process for water-insoluble macromolecular alkylphenols that can solve the problems of poor safety, excessive solid waste, and weak versatility. Summary of the Invention

[0005] To address the shortcomings of existing methanol-liquid-alkali strong-base coupling processes, such as flammability and explosiveness, easy precipitation of solids in the product, large amount of sludge, and narrow substrate applicability, this invention provides a novel diazo coupling process that features two-phase layering, complete organic phase dissolution of raw materials and products, no organic solid sludge, flame retardancy and explosion prevention, and compatibility with all water-insoluble macromolecular alkylphenols. This invention optimizes only the two core processes of diazotization and coupling, without altering existing mature post-processing procedures in the factory, making it highly industrially feasible. In view of the aforementioned deficiencies of the prior art, To achieve the above objectives, the present invention provides a flame-retardant diazo coupling synthesis process adapted to water-insoluble macromolecular alkylphenols. The process uses a compound solvent composed of tetrachloroethylene and methanol as the organic reaction medium, and performs a coupling reaction between the diazonium salt and the water-insoluble macromolecular alkylphenol in a two-phase system consisting of an organic phase and an aqueous phase under alkaline conditions.

[0006] Preferably, in the compound solvent, the mass ratio of tetrachloroethylene to methanol is 3:1 to 6:1.

[0007] Preferably, the alkaline conditions are achieved by adding liquid alkali, and the pH value of the system is controlled between 11.0 and 12.0.

[0008] Preferably, the coupling reaction is carried out at a temperature of 0°C to 12°C.

[0009] Preferably, the process further includes a diazotization stage, which is carried out in a pure water acidic system without the addition of organic solvents and alkaline materials.

[0010] Preferably, the diazotization process is operated as follows: 60 parts of the substituted aromatic amine are added to 250 parts of an acidic aqueous solution of 50% sulfuric acid, 250 parts of water are added dropwise, the reaction temperature is controlled at -5℃ to 5℃, 180 parts of a 20% sodium nitrite aqueous solution are added dropwise for diazotization, and 5 parts of urea are added after the reaction is completed. Remove residual nitrite from the system.

[0011] Preferably, the water-insoluble macromolecular alkylphenol is selected from one or more of dicumylphenol, di-tert-butylphenol, tert-octylphenol, di-tert-pentylphenol, or nonylphenol.

[0012] Preferably, the water-insoluble macromolecular alkylphenol raw material and the products generated by the coupling reaction are completely dissolved in the organic phase composed of tetrachloroethylene and methanol, and no solid is precipitated during the entire reaction process, so there is no need to perform filtration and slag removal operations in the coupling section.

[0013] Preferably, after the coupling reaction is completed, the system is allowed to stand and separate into layers, with the product concentrated in the lower organic phase, which is then separated from the upper alkaline aqueous phase by liquid-liquid separation.

[0014] The beneficial effects of this invention are: 1. Intrinsically safe: By utilizing the completely non-flammable properties of tetrachloroethylene, the flammable and explosive safety hazards of the traditional methanol + strong alkali coupling system are completely eliminated, and the explosion-proof requirements of the workshop and the safety production risks are greatly reduced.

[0015] 2. No organic solid residue and no filtration required: The raw materials and products in the organic phase are completely dissolved throughout the process, with no suspended sludge or solids adhering to the walls. The coupling section does not require filtration and slag removal, which significantly reduces the amount of hazardous waste generated and simplifies the process.

[0016] 3. Broad-spectrum and versatile: This strongly basic two-phase interfacial reaction system is compatible with all water-insoluble long-chain, sterically hindered alkyl-substituted macromolecular phenols and can be used for the synthesis of intermediates of various benzotriazole ultraviolet absorbers.

[0017] 4. Easy to implement in industrial applications: This invention only optimizes two front-end processes, diazotization and coupling, and is fully compatible with existing mature post-processing processes such as reduction, refining and crystallization in factories. It does not require major equipment modifications and has a high cost-performance ratio for industrial implementation. Detailed Implementation The flame-retardant diazo coupling synthesis process for water-insoluble macromolecular alkylphenols of the present invention only includes the diazo chemical process and the coupling process, and does not involve subsequent post-processing steps such as reduction, ring closure, purification, crystallization, and drying. The general process steps of the diazo chemical process and the coupling process are as follows: 1. Diazo chemical processing section The substituted aromatic amine feedstock is added to an acidic pure water system, and the reaction temperature is controlled between -5℃ and 5℃. Sodium nitrite aqueous solution is slowly added dropwise to complete the diazotization reaction. After the reaction, an appropriate amount of urea is added to quench any residual nitrite nitrogen, yielding a stable and clear diazonium salt aqueous solution. This process does not involve the addition of any organic solvents or alkaline materials, fundamentally avoiding the risk of diazonium salt decomposition in organic solvents or alkaline environments, thus ensuring the efficient generation and stable storage of diazonium salt.

[0018] 2. Coupling section—two-phase strongly alkaline reaction ① Preparation of compound flame-retardant solvent: Tetrachloroethylene and methanol are compounded at a mass ratio of 3:1 to 6:1 to form an organic reaction medium. Water-insoluble macromolecular alkylphenol raw material is added to the above compound solvent and stirred at room temperature until completely dissolved to obtain a transparent and homogeneous organic raw material liquid.

[0019] In this step, methanol can be slightly soluble across the organic and aqueous phases, providing hydroxide ions at the interface between the two phases. This activates the originally inert macromolecular alkylphenols into highly reactive phenoxy anions, thus ensuring the smooth progress of the strongly basic coupling reaction. Tetrachloroethylene plays a dual role: firstly, as a flame-retardant inert solvent with no flash point, it completely suppresses the inherent flammability and explosion risk of the methanol-strong alkali system, achieving intrinsic safety; secondly, it has extremely strong dissolving power for macromolecular alkylphenol raw materials and coupling products, firmly locking all organic materials in the organic phase and preventing the precipitation of organic solids.

[0020] ② Construction of the alkaline system: Liquid alkali was used as an alkalinity regulator and added to the system in batches to stably control the overall pH value of the system within the strongly alkaline range of 11.0 to 12.0. Liquid alkali is insoluble in tetrachloroethylene but miscible with methanol, and can efficiently transfer alkalinity at the interface between the two phases to maintain the alkaline environment required for the reaction.

[0021] ③ Low-temperature two-phase coupling: The reaction temperature is controlled between 0℃ and 12℃. The previously prepared diazonium salt aqueous solution is slowly added dropwise to the organic system. The diazo coupling reaction of the macromolecular phenol is stably completed at the liquid-liquid interface formed by the organic phase and the aqueous phase. During the reaction, the system maintains a clear two-phase separation state. The organic phase is clear and transparent, with no solid precipitation or sludge adhering to the wall. After the coupling reaction is completed, the system is allowed to stand and separate. The product is enriched in the lower organic phase and can be separated from the upper alkaline aqueous phase by a simple liquid-liquid separation operation without the need for filtration and sludge removal.

[0022] The present invention will be further described in detail below with reference to specific embodiments.

[0023] Examples 1-5 were all performed according to the aforementioned general process steps, except that the water-insoluble macromolecular alkylphenol was fixed as 2,4-dicumylphenol. Only the mass ratio of tetrachloroethylene to methanol was changed to investigate the effect of different ratios on the reaction conversion rate and system state. The specific operating parameters are as follows: Diazotization: 60g of pure water and 250g of 50% sulfuric acid were added to the reactor, followed by 60g of o-nitroaniline; the reactor temperature was lowered to control the temperature at -2℃ to 2℃, and 180g of 20% sodium nitrite aqueous solution was slowly added dropwise. Diazotization was completed by maintaining the temperature at low temperature; after the reaction was completed, 5g of urea was added, and the mixture was stirred to completely eliminate residual nitrite, resulting in a stable diazonium salt aqueous solution for later use.

[0024] Organic phase preparation: Mix tetrachloroethylene and methanol evenly according to the proportions shown in Table 1 to prepare a compound flame retardant solvent; add 120g of 2,4-dicumylphenol and stir thoroughly at room temperature until completely dissolved to obtain a transparent homogeneous organic raw material liquid.

[0025] Coupling reaction: Add 330g of 30% liquid alkali to the system and adjust the overall pH value of the system to stabilize at 11.5; control the temperature of the reactor at 4℃~7℃, and slowly add all the diazonium salt aqueous solution dropwise at a uniform rate. After the addition is completed, keep the system at a low temperature to complete the two-phase coupling reaction.

[0026] Reaction phenomena: In all examples, the system maintained a liquid-liquid two-phase separation state. The organic phase was clear, bright red, with no solid precipitation and no sludge adhering to the walls. After standing and separating, the lower layer was a brownish-red organic phase enriched with products, and the upper layer was a light yellow alkaline wastewater. The organic phase did not require filtration and could be directly separated and discharged. The conversion rate results of each example are shown in Table 1.

[0027] Table 1. Effect of different tetrachloroethylene / methanol ratios on reaction conversion rate

[0028] As shown in Table 1, when the mass ratio of tetrachloroethylene to methanol is in the range of 3:1 to 6:1, the conversion rate remains above 70%. The macromolecular substrate and product are completely dissolved in the organic phase, with no organic solid sludge generated. The system has no flash point and no risk of combustion or explosion. The process is stable and controllable, meeting the requirements for safe industrial production. Among them, the conversion rate reaches the highest (80%) when the tetrachloroethylene:methanol ratio is 5:1, which is the optimal ratio of this invention.

[0029] Examples 6-10: Substrate universality verification experiments To verify the process versatility of this invention for water-insoluble macromolecular alkylphenols with different structures, various substrates with different structures were used, employing the optimal tetrachloroethylene:methanol ratio of 5:1, while other operating conditions remained the same as in Examples 1-5. The experimental results are shown in Table 2.

[0030]

[0031] Table 2. Reaction conversion rates of different substrates under the process of this invention. As shown in Table 2, all tested substrates were able to stably complete the coupling reaction in the process system of this invention, with no solid precipitation in the organic phase and a smooth reaction without by-product agglomeration. Although the conversion rates fluctuated due to differences in molecular structure and steric hindrance among different substrates, all exhibited good reactivity, fully verifying the broad applicability of this process to various water-insoluble macromolecular alkylphenols. For cases with low conversion rates, improvements can be made by further optimizing parameters such as reaction temperature, pH value, or dropping rate, which falls within the scope of conventional process optimization techniques for those skilled in the art.

[0032] As can be seen from the above embodiments, the present invention has the following significant beneficial effects: 1. Intrinsically safe: By utilizing the completely non-flammable property of tetrachloroethylene, the flammable and explosive safety hazards of the traditional methanol + strong alkali coupling system are completely eliminated, and the explosion-proof requirements of the workshop and the safety production risks are greatly reduced.

[0033] 2. No organic solid residue and no filtration required: The raw materials and products in the organic phase are completely dissolved throughout the process, with no suspended sludge or solids adhering to the walls. The coupling section does not require filtration and slag removal, which significantly reduces the amount of hazardous waste generated and simplifies the process.

[0034] 3. Broad-spectrum and versatile: This strongly basic two-phase interfacial reaction system is compatible with all water-insoluble long-chain, sterically hindered alkyl-substituted macromolecular phenols and can be used for the synthesis of intermediates of various benzotriazole ultraviolet absorbers.

[0035] 4. Easy to implement in industrial applications: This invention only optimizes two front-end processes, diazotization and coupling, and is fully compatible with existing mature post-processing processes such as reduction, refining and crystallization in factories. It does not require major equipment modifications and has a high cost-performance ratio for industrial implementation.

[0036] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A flame-retardant diazo coupling synthesis process adapted to water-insoluble macromolecular alkylphenols, characterized in that: The process uses a compound solvent composed of tetrachloroethylene and methanol as the organic reaction medium. Under alkaline conditions, in a two-phase system consisting of an organic phase and an aqueous phase, the diazonium salt and the water-insoluble macromolecular alkylphenol undergo a coupling reaction.

2. The synthesis process as described in claim 1, characterized in that: In the compound solvent, the mass ratio of tetrachloroethylene to methanol is 3:1 to 6:

1.

3. The synthesis process as described in claim 1, characterized in that: The alkaline conditions are achieved by adding liquid alkali, and the pH value of the system is controlled between 11.0 and 12.

0.

4. The synthesis process as described in claim 1, characterized in that: The coupling reaction occurs at temperatures ranging from 0°C to 12°C.

5. The synthesis process as described in claim 1, characterized in that: The process also includes a diazotization stage, which is carried out in a pure water acidic system without the addition of organic solvents or alkaline materials.

6. The synthesis process as described in claim 5, characterized in that, The diazo chemical process is operated as follows: 60 parts of the substituted aromatic amine are added to 250 parts of an acidic aqueous solution of 50% sulfuric acid, along with 250 parts of water. The reaction temperature is controlled at -5℃ to 5℃. Then, 180 parts of a 20% sodium nitrite aqueous solution are added dropwise. After diazotization, 5 parts of urea are added to remove residual nitrite from the system.

7. The synthesis process as described in claim 1, characterized in that: The water-insoluble macromolecular alkylphenol is selected from any one of dicumylphenol, di-tert-butylphenol, tert-octylphenol, di-tert-pentylphenol, or nonylphenol.

8. The synthesis process as described in claim 1, characterized in that: The water-insoluble macromolecular alkylphenol raw material and the products generated by the coupling reaction are completely dissolved in the organic phase composed of tetrachloroethylene and methanol. No solids are precipitated during the entire reaction process, and no filtration and slag removal operation is required in the coupling section.

9. The synthesis process as described in claim 1, characterized in that: After the coupling reaction is completed, the system is allowed to stand and separate into layers. The product is enriched in the lower organic phase and separated from the upper alkaline aqueous phase by liquid-liquid separation.

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