p-Toluenesulfonic acid CAS 104-15-4

Theoretically, sulfur trioxide is the most effective sulfonating agent because it is directly added without removing the water produced by the reaction. Under suitable conditions, the product is almost exclusively p-toluenesulfonic acid. At present, the preparation of p-toluenesulfonic acid by sulfonation of toluene with sulfur trioxide is very common in foreign countries. According to reports, when toluene is sulfonated with gaseous sulfur trioxide in the liquid phase at 45~55°C, the product contains 20% xylene sulfonic acid, the isomer contains 85% p-toluenesulfonic acid, 9% o-toluenesulfonic acid and 6% m-toluenesulfonic acid. Experiments show that the dehydrating agent PZO. In the presence of sodium sulfide, m-toluenesulfonic acid cannot be obtained, and if sulfonation is carried out in the presence of sodium sulfide, the amount of vanadium produced is greatly reduced.

Some people use air-containing sulfur trioxide gas to sulfonate excess toluene, and the resulting p-toluenesulfonic acid only contains no more than 0.49% of other isomers and no more than 1.5% of sulfuric acid and sulfuric acid. .1% or less of xylyl alum. The advantage of sulfonating toluene with sulfur trioxide is that the reaction temperature is low, the speed is fast, and the stoichiometric feeding is used to obtain almost pure p-toluenesulfonic acid.

Sulfonation of toluene with sulfuric acid is the technique with the most and the longest history, and the sulfonation reaction is carried out as follows: CH3C Yin. Ten HZSO., head CH:C’H.S03H+H20 The research shows that the sulfonation reaction rate is proportional to the toluene concentration and inversely proportional to the square of the water content of sulfuric acid. Therefore, it is necessary to use less water-containing sulfuric acid and high-purity toluene, but the sulfonation reaction is a reversible reaction. Every time 1 mol of sulfuric acid is consumed, 1 mol of water is generated, and the concentration of water gradually increases with the progress of the reaction. of waste acid. In industrial production, partial pressure distillation is generally used to remove the water generated by the sulfonation reaction, so that the sulfonation reaction is completed.

Sulfonated toluene can generate both p-toluenesulfonic acid, o-toluenesulfonic acid, and m-toluenesulfonic acid. When using concentrated sulfuric acid, increasing the reaction temperature helps the conversion of the ortho-isomer to the para-isomer, but has no effect on the concentration of the meta-isomer. The lower acid concentration is conducive to the conversion of the para-isomer to the ratio of isomers. Practice has proved that the ratio of sulfuric acid to toluene does not have much effect 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 content of the para-isomer increases To 84%, the content of 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%, m-toluenesulfonic acid is 59.6 ± 2.5%. During the sulfonation process, more Side reactions such as sulfonation, oxidation, generation of vanadium and coordination, dealkylation, rearrangement and desulfonation.

A typical sulfonation method is to first add 50-60% sulfuric acid to the sulfonation reactor, then heat it to 120-180 °C, and directly pass the vaporized excess toluene into the sulfuric acid, and the escaping unreacted toluene vapor reacts with it. The steam of the generated water enters the water separator after being condensed, and after drying the unreacted toluene in the upper layer, it continues to vaporize into the sulfuric acid of the reactor, and the sulfonation reaction is terminated after the sulfuric acid is completely converted into toluenesulfonic acid.

The second sulfonation method is to first add an excess of 50-100% toluene in the sulfonation reactor, then heat to 100-115°C, and then gradually add 90-95% sulfuric acid to the refluxing toluene. The steam mixture escaping from the reactor is condensed and then stratified statically, the bottom water layer is discharged, and the upper toluene layer is returned to the sulfonation reactor until the water in the sulfuric acid and the theoretically generated water from the sulfonation reaction are the sum of Stop reflux after 70-75% of the steam is evaporated. The reflux operation generally takes 5~15h, and the product contains about 75~85% of p-toluenesulfonic acid, 10~20% of o-toluenesulfonic acid, 2~5% of m-toluenesulfonic acid, and less than 1% of unreacted sulfuric acid. and trace amounts of by-products.

The third sulfonation method is at atmospheric pressure. Toluene is directly sulfonated with sulfuric acid until the sulfonation reaction reaches equilibrium due to the reduction of sulfuric acid concentration, and then heated to 150-180 °C under vacuum conditions. After the unreacted toluene and the generated water are vaporized, the concentration of sulfuric acid increases again. In this way, the sulfonation and dehydration operations are carried out in a cycle, and most of the sulfuric acid is finally converted into toluenesulfonic acid. The feature of this process is that liquid toluene is added to sulfuric acid with a temperature higher than 120 °C and kept in a vacuum state, the vaporized toluene is directly contacted with sulfuric acid, and the sulfonation reaction occurs rapidly, and the toluene vapor escapes the sulfuric acid liquid level. Before, most of the toluene has been sulfonated, and the water generated by the reaction escapes with the toluene vapor, while the concentration of sulfuric acid can remain unchanged, and the unreacted toluene is condensed and recycled.

Sulfonic acid is a liquid sulfonating agent. When sulfonating toluene with it, hydrogen gas is released. Since water is not generated during sulfonation, it is not necessary to use higher temperature and partial pressure to remove water. The disadvantage is that The price of sulfonic acid is more expensive, and the released hydrogen is highly corrosive. The optimal temperature for sulfonating toluene with oxysulfonic acid is 35-45 °C, and equimolar chlorosulfonic acid should be slowly added within 2 to 3 hours, and then the product is heated to 60 °C, and there is hydrogen sulfide at this time. release. Among the isomers, there is no m-toluenesulfonic acid, containing 14-16% of the ortho-position and 84-86% of the p-toluenesulfonic acid, and the yield is about 90-95%.