On the earlier unknown regularities of oxidation of ferrocene and its derivatives by hydrogen peroxide in water and organic solvents

Abstract

The oxidation of ferrocene and its derivatives (Fc) by hydrogen peroxide in an acidic medium was studied by electron spectroscopy in the visible region. The studied reaction of different Fc includes steps of their oxidation to the ferrocenium cation Fc+ formed in a pair with radical HO· and also the earlier unknown reactions of this cation with hydrogen peroxide and with hydroxyl radical. The first reaction proceeds as a redox process leading to the reduction of the ferrocenium cation to neutral ferrocene, and the second reaction follows the mechanism of radical substitution with the consecutive formation of the hydroxy derivatives of ferrocene Fc(OH)x and the corresponding ferrocenium cations with different contents of OH substituents. The necessary conditions for the second reaction to occur is an excessive concentration of hydrogen peroxide over the Fc concentration. The external manifestation of this process is a continuous shift of the absorption band of the ferrocenium cation to the long-wavelength range of the electronic spectrum, which can attain several tens of nanometers, and its broadening. The contribution of these reactions to the overall process of ferrocene oxidation can be made minimum and reduced to the ferrocenium cation formation only by decreasing the ratio of the initial concentrations C0(H2O2)/C0(Fc).