Porous Organic Polymer with Free Carboxylic Acids (Carboxy-POP) for Heterogeneous Catalytic One-Pot Synthesis of Xanthenes and Acridines

Porous organic polymers (POPs) - the emergent hydrothermally stable, amorphous and porous materials - have proven to be invaluable for catalytic applications. Through a rational bottom-up design, we have developed a Carboxy-POP, a POP that is adorned by Bronsted acid (COOH) functionalities, for heterogeneous catalysis. The Carboxy-POP has been comprehensively characterized by FT-IR, solid-state 13C NMR, SEM, TEM, etc. It exhibits a moderate porosity with a BET surface area of 381 m2 g-1 and acid concentration of 1.67 mmol/g. Its functional utility as an efficient heterogeneous catalyst for one-pot synthesis of a variety of xanthenes and acridines in excellent isolated yields (up to 98 %) is demonstrated. In contrast to the conventional methods, the advantages of the reported metal-free catalytic protocol include ease of operation, excellent isolated yields of the products, facile workup, and shorter reaction times. It is shown that the heterogeneous catalyst can be repetitively used with the catalytic activity almost intact even after 16 reaction cycles. A porous organic polymer (POP) endowed with free carboxylic acid functionalities, that is, Carboxy-POP, has been developed by Friedel-Crafts polyalkylation. Its application as a heterogeneous recyclable catalyst for the synthesis of acridines and xanthenes is demonstrated.image

Automated summary

A porous organic polymer (POP) with carboxylic acid functionalities, known as Carboxy-POP, has been developed for efficient heterogeneous catalytic reactions. The catalyst exhibits high catalytic activity, easy operation, high yields, short reaction times, and good recyclability.