Ti(IV)/trialkanolamine catalytic polymeric membranes: Preparation, characterization, and use in oxygen transfer reactions

New heterogeneous oxidation catalysts have been obtained by entrapping Ti(IV)/trialkanolamine complexes within polymeric membranes. The catalytic membranes were prepared by a nonsolvent-induced phase-inversion technique. Three polymers, polyvinylidene fluoride (PVDF), a modified polyetherketone (PEEK-WC), and polyacrylonitrile (PAN), with different functional groups and chemical-physical properties, were used to tune the reactivity of the catalytic polymeric membranes in the stereoselective oxidation to sulfoxide and chemoselective oxidation of secondary amines to nitrones by alkyl hidroperoxides. The chemical-physical analysis of the new catalytic membranes was carried out by SEM, EDX, IR, CAM, and XPS techniques. In particular, the XPS spectra showed a very interesting orientation effect of PVDF membranes on the entrapped Ti(IV)/trialkanolamine complex. PVDF-based catalytic membranes gave the best results, affording products in shorter reaction times, higher yields, and better selectivity compared with the corresponding homogeneous systems. The membranes can be recycled up to five runs with no loss of activity.