The Measurement of the Gibbs Energy of Transfer Between Oil and Water Using a Nano‐Carbon Paste Electrode |
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| Authors: | Patrick Gan Denise Lowinsohn John S Foord Richard G Compton |
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| Affiliation: | 1. Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK;2. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QZ, UK, Fax: +44 (0) 1865 275410;3. Tel: +44 (0) 1865 275957;4. Department of Chemistry, Instituto de Ciências Exatas, Universidade Federal de Juiz de Fora, 36036‐330, Juiz de Fora, MG, Brazil |
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| Abstract: | The use of nano‐carbon paste electrodes for the measurement of Gibbs energies of transfer between oil and aqueous phases is reported. In this method the oil of interest is used as the binder for the nano‐carbon paste electrodes and the molecule of interest is dissolved in the organic or aqueous phase. Voltammetry is performed over a period of time and used to monitor the transfer of the molecule between the two phases. The method is illustrated for the transfer of ferrocenemethanol between water and oil using the ferrocenemethanol / ferroceniummethanol (FcCH2OH/FcCH2OH+) redox couple. Three pairs of voltammetric peaks were observed in a 0.1 M KCl solution when the nano‐carbon paste electrode was modified by dissolution of FcCH2OH in the binder oil: P1 E=0.23 V, 0.17 V vs. Ag/AgCl (1 M KCl)], P2 E=0.36 V, 0.32 V vs. Ag/AgCl (1 M KCl)] and P3 E=0.55 V, 0.46 V vs. Ag/AgCl (1 M KCl)]. These are assigned to the FcCH2OH species existing in the aqueous solution FcCH2OH(aq)/FcCH2OH+(aq)], originating in the oil (o) FcCH2OH(o)/FcCH2OH+(aq)] and to oxidation of adsorbed (ads) material on the nano‐carbon FcCH2OH(ads)] respectively. When supporting electrolyte containing the anions Cl?, NO3? or SCN? was used, an expulsion of the oxidised ferrocene occurred and the difference in midpoint potentials (Emid) between the peaks P1 and P2 observed in these experiments allowed the calculation of the Gibbs energy (ΔG°) of transfer of ferrocenemethanol from water to oil. The average ΔG° value thus obtained was (?12.7±0.2) kJ mol?1. For more hydrophobic anions (X?=PF6?, AsF6?), the electron transfer is coupled to the transfer of the anion into the oil and the ΔG° for the transfer of the ion pair of FcCH2OH+ and X? ions from water to oil was found to be ?1.3 and ?3.9 kJ mol?1 for PF6? and AsF6? respectively. |
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| Keywords: | Nano‐carbon paste electrode Paraffin oil Gibbs energy of transfer Ferrocenemethanol |
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