Silica-supported polyphosphoric acid (PPA-SiO2): An efficient and reusable heterogeneous catalyst for ecofriendly organic synthesis

This review discusses the advances in the use of silica-supported polyphosphoric acid (PPA-SiO2) as a green and reusable heterogeneous catalyst in the preparation of various organic compounds and pharmaceutical intermediates. PPA-SiO2 could be recovered and reused several times without significant loss of their efficiency. In this review, we attempt to give an overview of the applications of PPA-SiO2 as a catalyst in condensation, cyclization, and addition reactions for the preparation of various organic compounds.