The electro-oxidation of water and alcohols at BDD in hexafluoroisopropanol

Boron doped (BDD) diamond electrodes have a wide potential window and thus allow the formation of radicals and the investigation of their reactions. Hexafluoroisopropanol is able to extend greatly the life-time of radical cations. Here, we investigated the oxidation of a series of the hydroxyl containing species at a BDD electrode in that solvent: water and the simplest primary, secondary, and tertiary alcohols, i.e. methanol, i-propanol, and t-butanol. The ease of their oxidation does not follow the hydrogen basicity but rather the bond dissociation energy. The radicals formed from water, methanol, and i-propanol are very short-lived and we can detect electrochemically only the second reaction product, i.e. the hydrogen ions. In contrast, t-butanol is oxidised to an intermediate, which is transformed much more slowly within some seconds to another species. This species can be further oxidised more easily than the first intermediate or the initial reactant. There is some evidence, that the reactant molecules play a dual role: on the one hand they undergo oxidative hydrogen abstraction. On the other hand, they stabilise the produced hydrogen ions.