Water – the greenest solvent overall

The widespread use of solvents has long been an integral part of the fine chemical and pharmaceutical industries. However, as the conflicts between sustainable development and environmental protection becomes more prominent, the chemistry community has been increasingly aware of the importance of proactively choosing environmentally friendly solvents, as evidenced by the introduction of the 12 principles of green chemistry by Paul Anastas and John Warner over two decades ago, specifically the fifth principle “safer solvents and auxiliaries”. It has since become the guideline for practicing green development both in academia and industry. This report presented and summarized the advantages and disadvantages of various green solvents, including water (and supercritical or subcritical water), supercritical CO 2 , ionic liquids, 2-methyltetrahedronfuran (and other organic green solvents), and switchable solvents. The combination of solvent strategies and separation technologies was also briefly discussed. Collectively, there is no perfect solvent for all the chemical applications. Taking all aspects into consideration, water as a solvent is the greenest.