A Review on Greener Approach for Synthesis of Hydrazone Schiff Bases

Various properties of hydrazone Schiff bases have been intensively investigated in several research fields due to their diverse pharmaceutical and biological activities. They are extensively used as chelating ligands in coordination chemistry, with wide applications in biology, medicine, analytical chemistry, catalysis, optics, and the synthesis of heterocyclic compounds. Hydrazone Schiff bases are mostly synthesized using hazardous chemicals and conventional volatile organic solvents. Because of their importance, this review primarily focuses on eco-friendly techniques and environmentally benign catalysts or solvents to increase yield, reduce reaction time, enhance selectivity, and facilitate the easy separation of products with high purity. Recently, a major challenge in organic synthesis has been to develop greener techniques that offer environmental and economic advantages over conventional processes. The study compares conventional methods with alternative methodologies for the synthesis of hydrazones, including microwave irradiation, the grinding method, the ultrasonic method, solvent-free reaction conditions, and the use of green solvents such as polyethylene glycol, as well as new-generation 'designer solvents' like ionic liquids and deep eutectic solvents.