One of the most important transformations in a radical cation is the cleavage of a bond with formation of a cation and a radical. This process is much easier than that in the neutral molecule substrate, due to the strong electron withdrawing effect of the positive charge in the radical cation.[i]
The processes developed upon the bond fragmentation reaction are of particular interest; most of these reactions are involved in biological processes such us DNA repairing, stress oxidative and reactions with technological applications.
In relation to this, the dynamic and reactivity of highly unstable intermediates such as sulfide radical cations is desirable for the understanding of Electron Transfer (ET) and bond breaking reactions. The chemistry of sulfide radical cations has been explored with special emphasis on the competition between fragmentation and oxidation pathways. Three general studies may be outlined as follows: Photoinduced Electron Transfer (PET), chemical and biomimetic ET and enzymatic oxidations. Different alkyl phenyl sulfides were studied and the product distribution depends markedly on the nature of alkyl moiety, those which stabilize a carbocation give fast C-S bond fragmentation of the radical cation intermediate. These sulfides were used to evaluate the reaction pathways followed by peroxidase enzymes and their biomimetic model in sulfoxidation reactions.[ii] However, there is still no study on the effect of substitution on the PhS moiety of the molecule; substitution on the phenyl ring would change not only the oxidation potential of the sulfide but also the strength of the C-S bond.
In the present communication we will report the results from our study on the generation and reactivity of sulfide radical cations in solution. PET by different sensitizers will be employed for ionization of the substrate; and the effect of electron withdrawing and electron donation groups (R) on the fragmentation rate constant will be evaluated. Tools such as preparative photolysis, transient absorption spectroscopy and electrochemical methods will be used in order to gain insights into the reaction mechanism, and to evaluate the different channels these radical cations would follow.
