Water has been around and is the most important liquid in biomaterials and global environments. Taking into consideration the current environmental issues, there are many potential advantages of replacing organic or unnatural solvents with water. In contrast to many other solvents, for example, water is physically and chemically specific. “Water is a contaminant or bad solvent” has been common sense in organic synthesis. Nevertheless, in the recent decades, chemists have begun investigating the possibility of using water as solvent for organic reactions. Actually water not only provides a medium for solution but often participates as a reactant in elementary chemical events on a molecular scale. This review will treat with the specific features of water including structure and properties from ambient to supercritical conditions, then focus on strategies of dissolving technique for organics in water and recent advantages in performing organic reactions with water.

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Stable nitroxyl radical 2, 2, 6, 6-tetramethylpiperidinyl-1-oxy (TEMPO) is an excellent and versatile catalyst for oxidation of alcohols. In combination with hypochlorite, primary and secondary alcohols are oxidized to the corresponding aldehydes and ketones, respectively. In the presence of transition metals, exemplified ruthenium and copper, TEMPO catalyzes aerobic oxidation of alcohols; The combinational use of Cu/TEMPO is only effective with primary alcohols, whereas the combination of RuCl₂ (PPh₃) ₃/TEMPO works as a catalyst for a broad range of alcohols. From the viewpoint of green chemistry, efficient recycling of TEMPO has been investigated by immobilizing TEMPO on polymer. The TEMPO-catalyzed oxidation of alcohols in ionic liquids has been attained by using functionalized TEMPO and both the solvent and the catalyst can be recovered and reused.

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