Background and Overview
P-Toluenesulfonic acid (tsoh) was first prepared by Jaworsky in 1865 by sulfonating toluene with sulfuric acid. In 1869, Engelllardt and others discovered that ortho and meta isomers also existed in sulfonated mixtures. Since the sulfonating agent and sulfonation parameters of toluene can directly affect the distribution of isomers and the amount of by-products produced, and the properties of the isomers are very similar, toluenesulfonic acid is prone to desulfonation reactions. Therefore, it is difficult to separate and purify industrially. At present, p-toluenesulfonic acid, as an important fine chemical product, has been widely used in the synthesis of medicines, pesticides, stabilizers for polymerization reactions, and catalysts for organic synthesis. However, the domestically produced p-toluenesulfonic acid content is low, the free sulfuric acid is high, and the production process is It is backward and far from meeting the needs of all aspects, so it must actively develop and produce to meet the needs of the market.
Sulfonation of toluene
In industry, p-toluenesulfonic acid (tsoh) is prepared by sulfonating toluene. The sulfonating agents that can be used are sulfuric acid (including Concentrated sulfuric acid and fuming sulfuric acid), sulfur trioxide and chlorosulfonic acid. From the perspective of sulfonation speed, the higher the concentration of the sulfonating agent, the better (such as using pure sulfur trioxide or "written oleum"), but Too high a concentration will cause side reactions such as polysulfonation, oxidation, and formation of maple, and can also affect the position of the sulfonate group entering the benzene ring. Therefore, appropriate sulfonation conditions must be selected based on the type and concentration of the sulfonating agent.
Sulfuric acid sulfonation method
Using sulfuric acid to sulfonate toluene is the most commonly used process and has the longest history. The sulfonation reaction is carried out according to the following formula: CH3C Yin. Ten HZSO., CH:C'H.S03H+H20. Research shows that the sulfonation reaction speed is directly proportional to the toluene concentration and inversely proportional to the square of the sulfuric acid water content. Therefore, it is necessary to use sulfuric acid with less water content and toluene with high purity. However, the sulfonation reaction is a reversible reaction. Every lmol of sulfuric acid consumed produces lmol of water. The concentration of water gradually increases as the reaction proceeds, and finally reaches equilibrium, producing a large amount of water. of waste acid. In industrial production, partial pressure distillation is generally used to remove the water generated by the sulfonation reaction to complete the sulfonation reaction.
Sulfonated toluene can generate not only p-toluenesulfonic acid, but also o-toluenesulfonic acid and m-toluenesulfonic acid. When using concentrated sulfuric acid, increasing the reaction temperature helps convert the ortho-isomer into the para-isomer, but has no effect on the concentration of the meta-isomer. A lower acid concentration is beneficial to the conversion of the para-isomer into the ortho-isomer. The ratio of isomers. Practice has proven that the ratio of sulfuric acid to toluene does not have much impact on the distribution of isomers in the product.
The ratio of para- and ortho-toluenesulfonic acid is related to the sulfonation temperature. For example, at 0°C, the sulfonation mixture contains 53.5% of the para-isomer, while at 100°C, the para-isomer The content increased to 84%, while the content of the meta-isomer did not change. The equilibrium composition at 140°C is: p-toluenesulfonic acid is 37.2±2.2%, o-toluenesulfonic acid is 3.2±0.6%, and m-toluenesulfonic acid is 59.6±2.5%. During the sulfonation process, many other factors may occur. Side reactions such as sulfonation, oxidation, generation of alum and complex, dealkylation, rearrangement and desulfonation.
The typical sulfonation method is to first add 50 to 60% sulfuric acid to the sulfonation reactor, and then heat it to 120 to 180°C. The vaporized excess toluene is directly passed into the sulfuric acid, and the unreacted toluene that escapes is The steam and the water generated by the reaction are condensed and then enter the water separator. After drying the unreacted toluene in the upper layer, it continues to vaporize into the sulfuric acid in the reactor. The sulfonation reaction is terminated after all the sulfuric acid is converted into toluenesulfonic acid.
The second sulfonation method is to first add an excess of 50 to 100% toluene to the sulfonation reactor, then heat it to 100 to 115°C, and then gradually add 90 to 95% sulfuric acid to the refluxing toluene. . The steam mixture escaping from the reactor is condensed and then stratified, the bottom water layer is released, and the upper toluene layer is returned to the sulfonation reactor until the sum of the theoretical amounts of water generated by the water in the sulfuric acid and the sulfonation reaction is Stop refluxing after 70 to 75% of it is evaporated. The reflux operation generally takes 5 to 15 hours. The product contains about 75 to 85% p-toluenesulfonic acid, 10 to 20% o-toluenesulfonic acid, 2 to 5% m-toluenesulfonic acid, and less than 1% unreacted sulfuric acid. and trace amounts of by-products.
The third sulfonation method is under normal pressure. Directly sulfonate toluene with sulfuric acid until the sulfonation reaction reaches equilibrium due to the decrease in sulfuric acid concentration, and then heat to 150 to 180°C under vacuum conditions. After the unreacted toluene and generated water vaporize, the concentration of sulfuric acid increases again. , this cycle performs sulfonation and dehydration operations, and finally converts most of the sulfuric acid into toluenesulfonic acid. The characteristic of this process is that liquid toluene is added to sulfuric acid whose temperature is higher than 120°C and maintained in a vacuum state. The vaporized toluene directly contacts the sulfuric acid, and a sulfonation reaction occurs rapidly. When the toluene vapor escapes from the sulfuric acid liquid surface, Previously, most of the toluene had been sulfonated, and the water generated by the reaction escaped together with the toluene vapor, while the concentration of sulfuric acid could be maintained unchanged, and the unreacted toluene was condensed and recycled.
Sulfur trioxide sulfonation method
Theoretically, sulfur trioxide is the most effective sulfonating agent because it is only a direct addition without removing the water generated by the reaction. Under suitable conditions, the product is almost entirely p-toluenesulfonic acid. At present, the preparation of p-toluenesulfonic acid by sulfonating toluene with sulfur trioxide has been carried out abroad.�Universal. According to reports, when toluene is sulfonated with gaseous sulfur trioxide in the liquid phase at 45~55°C, the product contains 20% xylyl sulfonate, 85% p-toluenesulfonic acid, and 9% p-toluenesulfonic acid in the isomer. o-toluenesulfonic acid and 6% m-toluenesulfonic acid. Experiments have proven that the dehydrating agent PZO. In the presence of sodium sulfide, m-toluenesulfonic acid cannot be obtained. If sulfonation is carried out in the presence of sodium sulfide, the amount of alum produced will be greatly reduced.
Some people use air-containing sulfur trioxide gas to sulfonate excess toluene, and the generated p-toluenesulfonic acid only contains no more than 0.49% of other isomers, no more than 1.5% of sulfuric acid and sulfuric acid. .1% or less xylyl vitriol. The advantages of using sulfur trioxide to sulfonate toluene are low reaction temperature and fast reaction speed. According to stoichiometric feeding, almost pure p-toluenesulfonic acid is obtained.
Chlorosulfonic acid sulfonation method
Sulfonic acid is a liquid sulfonating agent. When it is used to sulfonate toluene, hydrogen gas is released. Since water is not generated during sulfonation, there is no need to use higher temperatures and partial pressure methods to remove water. The disadvantage is that the sulfonic acid is relatively expensive and the hydrogen released is highly corrosive. The optimal temperature for sulfonating toluene with oxysulfonic acid is 35-45°C, and an equal molar amount of chlorosulfonic acid should be slowly added within 2 to 3 hours, and then the product is heated to 60°C. At this time, hydrogen is present. release. Among the isomers, there is no m-toluenesulfonic acid, containing 14~16% of ortho-position and 84-86% of para-position toluenesulfonic acid, and the yield is about 90-95%.
Application of p-toluenesulfonic acid
Catalyst
It is as effective as sulfuric acid, but more effective than sulfuric acid in a wide range of reactions, including esterification, acetal formation, dehydration, alkylation, dealkylation, Beckmann rearrangement, polymerization and depolymerization. . Because it does not cause side reactions such as oxidation or carbon formation, the product obtained has high purity and light color.
Organic synthesis
P-Toluenesulfonic acid is commonly used to produce p-toluenesulfonamide, saccharin, chloramine T, p-toluenesulfonphthalein chloride and p-alumodiphthalamide, etc. The largest use of p-toluenesulfonic acid is in the production of p-cresol.
Stabilizer
In industry, p-toluenesulfonic acid and zinc oxide are commonly used to prepare zinc p-toluenesulfonate. In the copolymerization process of acrylonitrile and methyl acrylate or acrylonitrile and vinylidene chloride, zinc p-toluenesulfonate can be used as a stabilizer, and its dosage can reach 0.2%. P-toluenesulfonic acid can also be used in phenolic, epoxy and amino plastics, furniture varnishes, dyes, adhesives, synthetic anti-diabetic medicines and anti-stress additives for electroplating tanks. With the use of dimethylformamide as a solvent, With the introduction of one-step cyanoacrylate and cyanoacrylate devices, the demand for high-quality p-toluenesulfonic acid as a stabilizer is growing rapidly.
References
E.G. Hancock, Toluene and xylene and its industrial derivatives, 195~203, Chemical Industry Press
Kikr-othmer, EneyelodiaofChemiealTeehnol-ogy, andEdition.Vol.2(), 273~278 P.H. Groggins, Chemical Engineering Organic Synthesis Unit Process, 16. ~211, Fuel Chemical Engineering Press
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