Sulfamic acid functionalized PVC: a remarkably efficient heterogeneous reusable catalyst for the acid-catalyzed reactions

Sulfamic acid functionalized polyvinyl chloride catalysts (PVC-N-SO3H, N = EDA, DTA, TTA, TPA, PHA) were prepared as efficient heterogeneous solid acid catalysts via two-step treatment processes. The prepared catalysts were characterized by X-ray diffraction analysis (XRD), TG thermograms/derivative thermogravimetric (TG/DTG), transmission electron microscope (TEM), elemental mappings and energy-dispersive spectroscopy analyses (STEM-EDS), and FTIR measurements (FTIR) as well as acid-base back-titration. The acetalization of aldehydes (ketones) and alcohols to acetal (ketal) was selected to evaluate the acid catalytic performance of PVC-N-SO3H. The results showed that PVC-EDA-SO3H exhibit excellent activity and reusability due to its highly exposed sulfonic acid sites, high surface acid density (2.28 mmol g-1) for the conversion of aldehydes (ketones) to acetal (ketal). This new solid acid has obvious advantages in reusability and catalytic activity over traditional homogeneous concentrated sulfuric acid and heterogeneous sulfonated resin catalysts. Furthermore, PVC-EDA-SO3H exhibited an excellent catalytic performance in the synthesis of 12 acetals (ketals) as well as a good compatibility in the hydroxyalkylation of phenol with formaldehyde to bisphenol F (BPF) and the esterification reaction of oleic acid and methanol to biodiesel. More importantly, it could also be recovered easily and used repeatedly at least nine times without an obvious decrease in the activity.