Catalysed Reduction of Water by Ketyl Radicals

Ultraviolet irradiation of a wide variety of ketones in aqueous solution containing a low concentration of an alcohol results in the formation of the two corresponding ketyl radicals, which are strong reducing agents. In the presence of colloidal platinum particles, these radicals will reduce water to hydrogen gas with high overall quantum efficiency. This is a general reaction, able to operate in sunlight, for which the mechanism is discussed in detail. The importance of the colloidal catalyst is stressed and, by changing the catalyst, different reaction products are obtainable.