SCHEDULED MAINTENANCE
The dehydrogenation of ethanol in dilute aqueous solution photosensitised by benzophenones
Abstract
The photochemical properties of a series of water-soluble benzophenones have been evaluated in dilute aqueous solution. The compounds possess lowest-energy singlet and triplet excited states demonstrating considerable n,π* character. As such, irradiation of the compounds in aqueous solution containing ethanol (2% v/v) results in pinacol formation via a triplet-state hydrogen-abstraction process. In the presence of a colloidal Pt catalyst, the intermediate ketyl and 1-hydroxyethyl radicals can be used to reduce water to H2. The rate of H2 formation and its total yield depend upon the nature of the substituent used to solubilise the benzophenone. The rate at which the ketyl radical transfers an electron to the Pt particles can be rationalised in terms of thermodynamic and electrostatic factors.
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