Synthesis and Improving the Crystallinity of a Squaranine Covalent Organic Framework by Modifying the Preparation Method and Using it as a Green and Metal-Free Catalyst for the Synthesis of Enaminone

Abstract

Herein, a modified synthesis method was presented and the effect of using an aqueous acetic acid solution in the process of synthesizing SQCOF was investigated. Adding a catalytic amount of aqueous solution of acetic acid as a co-catalyst has contributed to improving the quality of crystallinity. Effective parameters in the synthesis of SQCOF, including the concentration and volume of the co-catalyst and reaction solvent, were optimized. Then, the prepared SQCOF was used as a metal-free catalyst with Brønsted acid groups in the condensation reaction between 1,3-dicarbonyl compounds and primary amines. SQCOF was used under solvent-free conditions for the synthesis of enaminones at ambient temperature by mild manual grinding with a mortar and pestle and showed excellent catalytic performance in the above reaction. High performance and efficiency (62 to 96%), high TOF (833 to 1283 h⁻¹), short reaction time, easy operation, minimizing the consumption of toxic organic solvents, absence of heavy metals in the framework and green conditions are the main advantages of this study. Also, SQCOF shows good chemical stability and recyclability (7 runs) and acts as an efficient catalyst in the synthesis of β-enaminones.

Graphical Abstract