1. Introduction

In practically all chemistry, biology, chemical engin eering, biotechnology, and other multidisciplinary s cientific and technological processes, solvents are u tilized to help transmit mass and heat as well as to make separations and purifications easier. In addition, solvents are extensively utilized for the purification of chemical compounds via extractions, separations, chromatography, or crystallizations.(Curzons et al., 1999; Henderson et al., 2011).Some of them have been used in organic synthesis for long time for instance benzene, petroleum ether (a low boiling mixture of aliphatic hydrocarbon), diethyl ether, dichloromethane, 1,2- dichloroethane, chloroform, n-hexane, diethyl ether, Di isopropyl ether, 1,2-dimethoxy ethane,1,4 dioxane and chloroform are categorized as toxic harmful substances(Sheldon,2019).To minimize the ecological impacts caused by solvents and to reduce the cost associated with waste disposal and environmental remediation, it is important to mindfully select solvents that conform to the principles of green chemistry.(Slater & Savelski, 2007) .Green chemistry is the use of a series of principles that will reduce the use or generation of hazardous substances during the design, production and application of chemical products. In 1998, Anastas and Warner explicitly explained the fifth principle of green chemistry- “safer solvents and auxiliaries”- “the use of auxiliary substance (e.g., solvents, separations, etc.) should be made unnecessary whenever possible and, innocuous when used. “The key aspects that specify green solvents are low toxicity, functionally safe to use (Incombustible, nonexplosive), naturally abundant and easily available, cost-efficient, and ready separation from the reaction mixture. In this chapter include Water, Supercritical fluids (supercritical carbon dioxide (CO2) and supercritical water), Ionic liquids (ILs), Deep eutectic solvent (DES), Bio solvent and other organic green solvents are discussed.