Liquid-phase Beckmann Rearrangement Of Cyclohexanone Oxime To Caprolactam Over Solid Sulfonic Acid

Caprolactam is an important organic chemical raw material. It is widely used to automobile, spinning, medicine, electron and machinery trades. At present, the last step of commercial processes for caprolactam is Beckmann rearrangement of cyclohexanone oxime Catalyzed by fuming sulfuric acid or concentrated sulfuric acid. A large amount of ammonium sulfate as by-product was formed in this process. And brings equipment corrosion, high cost etc. Vapor-phase Beckmann rearrangement over solid acid catalysts can avoid ammonium sulfate, however, because of its high reaction temperature, catalysts can easily inactivate. In this work, we explored the liquid-phase Beckmann rearrangement of cyclohexanone oxime under mild condition by using solid sulfonic acid instead of liquid fuming sulfuric acid as catalysts. Different catalyzed systems of solid sulfonic acid were examined.First of all, the liquid-phase Beckmann rearrangement over D-72 sulfonic acid resin (4.2mmol/g of acidity) had been researched. The influences of solvent, reaction time, reaction temperature, amount of catalyst etc were examined. what is more, the optimized reaction conditions and the reuse of catalyst was investigated. Results indicate that under the condition of cyclohexanone oxime 1.0g, D-72 sulfonic acid resin 0.5g, 0.1g/ml of consentration of oxime (DMSO as solvent), at 130℃for 6h, cyclohexanone oxime conversion can reach 100% and selectivity of caprolactam reaches 86.24%. This catalyst can be easily separated, and conveniently recovered for recycled use. Cyclohexanone, dimer and trimer of caprolactam were the main by-products under this catalyzed system.Moreover, the liquid-phase rearrangement over Amberlyst-35 sulfonic acid resin (4.2mmol/g of acidity) had been explored. The optimized condition were 1.0g of cyclohexanone oxime, 0.5g of Amberlyst-35 sulfonic acid resin, 0.1g/ml of consentration of oxime (DMSO as solvent), at 130℃for 6h. It can be found that Amberlyst-35 sulfonic acid resin gave the results with 100% of conversion and 80.79% of selectivity to caprolactam. The catalyst can be easily separated, and reused in subsequent reactions.In addition, the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam over amidosulfonic acid was researched. Some influence factors such as amount of catalyst, reaction time, reaction temperature et al. were investigated. It should be noted that the reaction rate of this catalyzed system is fast, and the material of cyclohexanone oxime can translate completely in 2h. However, it only gave the result with 26.97% of selectivity to caprolactam and formed many kinds of by-products. The optimized condition were 1.0g of cyclohexanone oxime, 1.0g of amidosulfonic acid, 0.067g/ml of concentration of oxime (DMSO as solvent), at 130℃for 2h. It gave 100% of conversion of cyclohexanone oxime and 26.97% of selectivity to caprolactam.