silica-supported orthophosphoric acid (opa/sio2): preparation, characterization, and evaluation as green reusable catalyst for pinacolic rearrangement

In this paper, we report an easy-to-prepare, cost-effective, efficient, and reusable silica-supported orthophosphoric acid (opa) catalyst for pinacolic rearrangement. the surface properties of this catalyst were successfully characterized with the help of 31p nmr, tga, dsc, ft-ir, titration, and microscopy. opa, hydrogen bonded on the surface, is actually the active species and the reaction seems to occur in the liquid phase embedded in the silica support. as a consequence, the extracting solvent should be chosen with cautious to guarantee the recyclability of the catalyst. as example, pinacol rearrangement reactions were successfully realized with this catalyst and opa/sio2 proved to be as efficient as homogeneous orthophosphoric acid to promote the reaction of pinacol derivatives. when using dichloromethane as extracting solvent, opa/sio2 can be reuse up to ten times without a significant loss of activity. after ten runs, no physical damage of the catalyst has been observed by microscopy proving its suitability for such application.