A method for recycling use of o-nitrophenetole as a solvent for sulfonation reaction in preparation of toluic acid

Abstract

This invention discloses a method for recovering and reusing o-nitrobenzene, a solvent used in the sulfonation reaction for the preparation of Tobucic acid. After the sulfonation reaction is completed, the sulfonation reaction mixture is dissolved in water and separated under controlled low-temperature conditions below 5°C, and allowed to stand for sufficient separation and layering. The recovered o-nitrobenzene has a water content of less than 2 g / L, requiring no secondary treatment, and can be directly reused in the sulfonation reaction of 2-naphthol without affecting the yield and quality of the Tobucic acid product.

Description

Technical Field

[0001] This invention belongs to the field of chemical intermediate production technology, and relates to a technical method for the recovery and use of solvents in the sulfonation reaction during the preparation of Tubner acid. Background Technology

[0002] Currently, the preparation process of Tobler's acid involves dispersing and dissolving 2-naphthol in an inert organic solvent, then sulfonating it with chlorosulfonic acid to obtain 2-naphthol-1-sulfonic acid. This is followed by alkali neutralization, concentration, amination, acidification, and filtration to obtain Tobler's acid. Inert organic solvents that can be used in the sulfonation reaction include o-nitrobenzene, dichloroethane, o-dichlorobenzene, and tetrachloroethylene, with o-nitrobenzene being the most commonly used in China. In the sulfonation process, the amount of o-nitrobenzene used is large, more than three times the amount of 2-naphthol, and it must be recycled and reused. Excessive water content in the solvent increases the consumption of the sulfonating agent chlorosulfonic acid; therefore, the water content of o-nitrobenzene is typically controlled to be less than 4 g / L. In the existing process, the sulfonation reaction mixture is first neutralized with alkaline water, then allowed to separate into layers, with the lower layer being the raw material and the upper layer being o-nitrobenzene. Because the liquid emulsifies after neutralization, the separated o-nitrobenzene contains a large amount of the raw material solution, resulting in a high water content, requiring secondary treatment before reuse. Traditional secondary treatment methods for o-nitrobenzene include washing and distillation. Washing offers good process safety, but the recovered o-nitrobenzene has a high water content (up to 8 g / L) and consumes a large amount of chlorosulfonic acid. Distillation recovers high-quality o-nitrobenzene with a water content below 0.5 g / L. However, evaporation equipment is complex and energy-intensive, not only generating secondary pollution from distillation residues but also posing a fire and explosion hazard during the distillation of nitro compounds. Summary of the Invention

[0003] The purpose of this invention is to solve the problem in the above-mentioned traditional process that the sulfonation reaction mixture is first neutralized and then separated, resulting in a high water content of the recovered o-nitrobenzene solvent, which must be treated twice before it can be reused.

[0004] To achieve the above objectives, the technical solution adopted in this invention is: a method for recovering and using o-nitrobenzene, a solvent in the sulfonation reaction during the preparation of Tobler's acid, characterized in that: after the sulfonation reaction is completed, the reaction mixture is dissolved and separated under low-temperature conditions using water, ice, or water containing ice, and allowed to stand for separation. Once the material and o-nitrobenzene have fully separated into layers, the o-nitrobenzene is recovered. The obtained o-nitrobenzene is used directly for the sulfonation reaction of 2-naphthol without secondary treatment. The low-temperature conditions refer to maintaining the temperature of the material layer and the o-nitrobenzene layer at -5 to +5°C throughout the separation process. The total amount of water, ice, or water containing ice used to dissolve and separate the reaction mixture is 1-2 times the amount of 2-naphthol added. This invention uses a water content of less than 2 g / L in o-nitrobenzene as an indicator of sufficient separation between the material and o-nitrobenzene.

[0005] The technical solution adopted in this invention is based on:

[0006] 1.2-Naphthol-1-sulfonic acid in a strongly acidic aqueous solution does not readily emulsify with o-nitroethylbenzene, facilitating layer separation. The o-nitroethylbenzene carries less entrained material and has a low water content. Although 2-naphthol-1-sulfonic acid can slowly hydrolyze to 2-naphthol in a strongly acidic aqueous solution at room temperature, experiments have shown that below 5°C, especially below 0°C, the increase in 2-naphthol in a strongly acidic sulfonated solution diluted only with water without neutralization is negligible after 10 days of storage. The layer separation process can be completed within 2-3 hours and will not affect the yield and quality (2-naphthylamine content) of the product, Tobler acid.

[0007] 2. Chlorosulfonic acid is a strong sulfonating agent and therefore a purifying agent for o-nitrobenzene. Impurities in o-nitrobenzene are dissolved and removed by water along with the sulfonated material after sulfonation, preventing accumulation and interference with the sulfonation reaction. Therefore, o-nitrobenzene can be reused repeatedly without secondary distillation.

[0008] 3. The optimal water content of o-nitrobenzene recovered using the technical solution of this invention is below 1.5 g / L, slightly higher than the 0.5 g / L of the distillation method. However, considering energy consumption, equipment investment and operation, the method of this invention has significant technical advantages and economic benefits.

[0009] The present invention is described in more detail as follows: After the sulfonation reaction of 2-naphthol is completed, instead of neutralization with alkali, the reaction mixture is dissolved and separated with water. The mixture is kept at a low temperature and allowed to stand for separation to allow the sulfonated material to fully separate from o-nitrobenzene. When the water content of o-nitrobenzene is below 2 g / L, the lower layer is separated. The recovered o-nitrobenzene is used directly for the sulfonation reaction of 2-naphthol without further treatment. The water in the reaction mixture is water in a chemical sense; the water can be liquid, solid (ice), or a mixture of both. The temperature of the liquid water is 0°C. The water in the reaction mixture includes industrial water, especially condensate containing o-nitrobenzene produced in the concentration process of Tolvastatin production. During the separation process, the temperature of the material layer and the o-nitrobenzene layer is maintained at -5 to +5°C, preferably below 0°C. The amount of water used in the reaction mixture is 1-2 times the amount of 2-naphthol added.

[0010] The separated 2-naphthol-1-sulfonic acid aqueous solution still contains a small amount of o-nitrobenzene (approximately 1 / 10 of the o-nitrobenzene feed amount). To prevent hydrolysis, it should be immediately neutralized with alkali to obtain a 2-naphthol-1-sulfonate solution. After neutralization, a small amount of severely emulsified, highly hydrous o-nitrobenzene is separated. The neutralized solution is then evaporated and concentrated, and the condensate containing o-nitrobenzene is collected. This condensate is combined with the highly hydrous o-nitrobenzene separated by neutralization, cooled and frozen into a 1:1 ice-water mixture, which is used to dissolve and separate the next batch of 2-naphthol sulfonated reaction mixture.

[0011] This invention primarily addresses the problem that after each sulfonation reaction, all the sulfonation solvent, o-nitrobenzene, must undergo secondary washing or distillation before it can be reused. The main focus is on investigating the impact of the method of this invention on the yield and purity of the product, Tolvanovic acid. The key lies in controlling the low-temperature state during the separation of the sulfonation solution from o-nitrobenzene to avoid the decomposition of 2-naphthol-1-sulfonic acid in the sulfonation solution, which would affect the purity and yield of Tolvanovic acid. Furthermore, controlling the low residual amount of the sulfonation solution in o-nitrobenzene (expressed as water content) reduces the consumption of chlorosulfonic acid and improves the single-pass yield of Tolvanovic acid.

[0012] The method for recovering o-nitrobenzene, a solvent used in the sulfonation reaction during the preparation of Tobler's acid, disclosed in this invention, has the following advantages compared to existing technologies:

[0013] (1) The method of the present invention is extremely simple and solves the problem that the existing process of separating o-nitroethylbenzene in one step has high water content and requires secondary treatment.

[0014] (2) The method of the present invention separates and recovers o-nitrobenzene at low temperature and can be directly used for sulfonation, eliminating the pre-cooling process of the traditional process and simplifying the process.

[0015] (3) Compared with the washing method, the method of the present invention recovers o-nitrobenzene with a low water content.

[0016] (4) Compared with the distillation method for recovering o-nitrobenzene, the method of the present invention has simpler equipment, lower energy consumption, is safer, and does not cause secondary pollution from distillation residue.

[0017] (5) Most of the unsulfonated 2-naphthol dissolves in the recovered o-nitroethylbenzene and is directly returned to the sulfonation reaction, which improves the utilization rate of the material. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments. These embodiments are merely typical descriptions of the present invention and are not intended to limit the invention.

[0019] Example 1

[0020] 75g of 2-naphthol was dispersed in 220mL of o-nitrobenzene, and 65g of chlorosulfonic acid was added dropwise at 0-5℃. After the reaction was completed, hydrogen chloride was removed under reduced pressure. The reaction mixture was poured into an ice-water bath containing 40g of 0℃ water and 40g of crushed ice, and stirred until no crushed ice floated. The mixture was kept at 0℃ in an ice-water bath and allowed to stand for 1 hour to separate the layers. The upper layer of o-nitrobenzene contained 1.3g / L of water. The lower layer of 2-naphthol-1-sulfonic acid solution was removed, yielding 199mL of the upper o-nitrobenzene, which was used for the next batch of sulfonation reactions. The lower layer of 2-naphthol-1-sulfonic acid solution was neutralized with 10% sodium hydroxide solution and allowed to stand, after which 14mL of severely emulsified, high-water-content o-nitrobenzene was separated. The neutralized solution was further heated and concentrated to obtain a concentrated solution. 95mL of condensate and 5.8mL of o-nitrobenzene were collected. The concentrated condensate was combined with the high-water-content o-nitrobenzene separated by neutralization and frozen into a 1:1 mixture of ice and water for later use. The concentrated liquid was ammoniated, acidified, filtered, and dried to obtain 105g of Tolvae acid with a purity of 98.9% and containing 0.19% 2-naphthylamine.

[0021] Example 2

[0022] 75g of 2-naphthol was dispersed in 199mL of o-nitrobenzene recovered from the previous batch, and then 21mL of o-nitrobenzene was added. 65g of chlorosulfonic acid was added dropwise at 0-5℃ to react. After the reaction was complete, hydrogen chloride was removed under reduced pressure. The reaction mixture was poured into a frozen ice-water mixture containing o-nitrobenzene from the previous batch and stirred until the ice completely melted. The mixture was allowed to stand at 2℃ for 1 hour to separate into layers. The upper layer of o-nitrobenzene contained 1.2g / L of water. The lower layer of 2-naphthol-1-sulfonic acid solution was removed, and 214mL of the upper layer of o-nitrobenzene, containing 1.2g / L of water, was recovered for use in the next batch of sulfonation reactions. The lower layer of 2-naphthol-1-sulfonic acid solution was immediately neutralized with 10% sodium hydroxide solution. After standing, 15mL of severely emulsified, high-water-content o-nitrobenzene separated from the neutralized solution. The neutralized solution was further heated and concentrated to obtain a concentrated solution. 92mL of condensate and 5.5mL of o-nitrobenzene were collected. The condensate was combined with the high-water-content o-nitrobenzene separated by neutralization and frozen into a 1:1 mixture of ice and water for later use. The concentrated liquid was ammoniated, acidified, filtered, and dried to obtain 104.5g of Tobleric acid with a purity of 99.1% and containing 0.21% 2-naphthylamine.

Claims

1. A method for recovering and utilizing o-nitrobenzene, a solvent used in the sulfonation reaction during the preparation of Tobler's acid, characterized in that: After the sulfonation reaction of 2-naphthol is completed, under low temperature conditions, that is, the temperature of the material layer and the o-nitroethylbenzene layer is maintained at -5℃ to +5℃ throughout the separation process, the reaction mixture is dissolved and separated with water, ice or water containing ice, which is 1 to 2 times the amount of 2-naphthol. The mixture is allowed to stand and separate into layers until the sulfonated material and o-nitroethylbenzene are fully separated. The o-nitroethylbenzene is then recovered. The obtained o-nitroethylbenzene does not require secondary processing and can be directly used for the sulfonation reaction of 2-naphthol.

2. The method for recovering and using o-nitrobenzene, the solvent in the sulfonation reaction during the preparation of Tobler's acid as described in claim 1, is characterized in that: The water content in o-nitrobenzene is less than 2 g / L, which is used as an indicator of the complete separation of the material from o-nitrobenzene.