Green Synthesis of 2,4-Diarylsubstituted Thiazoles Using Cellulose-Supported Sulfanilic Acid as an Environmentally Benign Heterogeneous Catalyst

In this work, a new efficient, environmental friendly and sustainable synthesis process of 2,4-diarylsubstituted thiazole, using cellulose supported sulfanilic acid (CSSA) as a reusable heterogeneous solid acid catalyst has been developed. The immobilization of sulfanilic acid on cellulose yielded the first biodegradable, low cost, metal-free catalytic system with good catalytic activity and easy recovery. The cyclocondensation of substituted alpha-haloketones and substituted thiobenzamides in the one pot under moderate conditions led to the synthesis of desirable thiazole compounds in high yields in short reaction times. The established process has the advantages of operational simplicity, good product selectivity, broad substrate scope, rapid work-up and little hazardous waste. The heterogeneous catalyst was easily separated by filtration and reused for several catalytic cycles without any loss of activity, thus proving its stability and reusability. The method was successful for some electron donor and electron acceptor substituents of the aromatic rings. Cellulose-supported sulfanilic acid showed enhanced reaction efficiency, catalyst recoverability and environmental sustainability in comparison with homogeneous acid catalysts. The catalytic efficiency of sulfanilic acid and porous, renewable cellulose support is enhanced by the accessibility of substrates and effective transfer of protons during cyclization via Brønsted acidic sites. This green synthetic methodology follows the principles of sustainable chemistry using a renewable catalyst support, no hazardous reagents, lower energy consumption, and recyclability of the catalyst. This method is green, inexpensive and practicable for the rapid synthesis of physiologically relevant 2,4-diaryl substituted thiazoles and has great potential in the medical, pharmaceutical and industrial heterocyclic chemistry.