Solvation of ions—XX. The ferrocene—ferricinium couple and its role in the estimation of free energies of transfer of single ions
1973; Elsevier BV; Volume: 18; Issue: 12 Linguagem: Inglês
10.1016/0013-4686(73)87030-6
ISSN1873-3859
Autores Tópico(s)Analytical Chemistry and Sensors
ResumoThe ferrocene-ferricinium electrode (Pt/Foc, Fic+) was investigated in water, acetonitrile, ethanol, DMSO and DMF using single scan cyclic voltammetry and phase sensitive ac polarography. The oxidation-reduction is pseudo-reversible in all five solvents with an electrochemical rate constant of approximately 10−2 cm/s. In all solvents a slow irreversible chemical step involving the ferricinium cation follows electron transfer, so that slow cyclic voltammetry or polarography rather than potentiometry is preferred if ferrocene is to be used as a reference electrode in non-aqueous solvents. The Strehlow assumption, ΔGtr(Foc) = ΔGtr(Fic+ gives very different free energies of transfer of single ions from non-aqueous solvents to water when compared with the TATB assumption that ΔGtr(Ph4As+) = ΔGtr(Ph4B−). This discrepancy is likely to be because ferricinium is only a moderately large cation, so that ΔGtr(Fic+) is less positive than ΔGtr(Foc) for transfer to water. The discrepancy is not because of abnormal electrochemical behavior of the Pt/Foc, Fic+ electrode in water or other solvents. Values of E° vs nhe, H2O in a variety of solvents based on the TATB assumption are presented.
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