In situ functionalized sulfonic copolymer toward recyclable heterogeneous catalyst for efficient Beckmann rearrangement of cyclohexanone oxime

Exploring environmentally friendly, efficient and recyclable heterogeneous catalysts for low-temperature liquid-phase organic reactions are important for the development of green and sustainable processes. In this work, we applied an in situ sulfonated polymeric solid acid H-PDVB-SO₃H for catalyzing liquid-phase Beckmann rearrangements for the first time, with post-sulfonated sample and other various counterparts as control catalysts. H-PDVB-SO₃H was prepared by copolymerization of divinylbenzene with sodium p-styrene sulfonate under solvothermal condition, followed by ion-exchanging to convert the polymer into proton form. It possessed a large surface area, plenty of mesopores and high sulfur content, and exhibited the high yield to ε-caprolactam (75%) with quite steady reusability in the heterogeneous Beckmann rearrangement of cyclohexanone oxime. The catalyst also showed good substrate compatibility with such a high reaction rate that the reaction time was as short as 1 h. No any co-catalysts or metals were used in the catalytic system, making the catalyst an environmentally friendly and efficient candidate for Beckmann rearrangements.