Water as an Oxygen Source for Oxidation Reactions

The use of water as oxygen source for the catalytic oxidation of organic substrates is a clean alternative to the commonly used methods that utilize oxidizing agents based on contaminant metals such as chromium or manganese. In this chapter, a detailed description of the thermodynamic requirements of this type of reaction is given, with particular emphasis on the so-called organic-substrate-assisted water splitting (OSA-WS) reaction that generates hydrogen gas as the only byproduct of the reaction. Important considerations regarding the metal catalyst needed to perform these reactions are discussed, followed by specific examples described in the literature. Among them, are examples of epoxidation of alkenes, oxidation of sulfides to sulfoxides, and oxidation of alcohols to the corresponding carboxylic acids. In some cases, the energy input to perform the reaction comes from visible light by using photosensitizers or semiconductors as light-harvesting agents. Finally, two examples of photoelectrochemical cells (PECs) are described, where light-induced oxidation and reduction half reactions take place in separate compartments. This design provides an easy-to-process reaction where the oxidized organic compound and hydrogen gas byproduct are generated in independent compartments, and at the same time avoids undesired side reactions that may occur as a result of the mixture.