Sulfonic acid-functionalized polypropylene fiber: highly efficient and recyclable heterogeneous Brønsted acid catalyst†
A sulfonic acid-functionalized polypropylene fiber, capable of acting as a supported catalyst in the accomplishment of the Biginelli reaction, is presented. Excellent results, in terms of chemical yields, catalyst dosage, work-up procedure and catalytic recyclability, are reported for the metal-free catalyzed one-pot synthesis of a number of substituted 3,4-dihydropyrimidin-2-(1H)-ones/-thiones (DHPMs). The catalyst can be prepared by a simple process from inexpensive and readily available polypropylene fiber, after completion of the catalytic reaction, the catalyst was simply recovered with common tweezers and recycled with excellent stability and activity even after 11 runs, which in turn is very attractive for economic interest and industrial safety. This is the first report about the application of the polypropylene fiber as a new support for heterogeneous catalysis in the practice of organic synthesis in an environmentally friendly manner.