Electrochemical determination of the lipophilicity scale of arenediazonium ions based on the ion transfer across the liquid ∣ liquid interface

A lipophilicity scale of 14 monovalent arenediazonium ions has been established on the basis of the standard Gibbs energy of ion transfer between the 1,2-dichloroethane (DCE) and water (W), ΔGtr,io,DCE→W The ion transfer processes of all arenediazonium ions studied using cyclic voltammetry at the planar DCE ∣ W interface are reversible, i.e. diffusion-controlled. Apparent values of ΔGtr,io′,DCE→W estimated from the mid-point potential in cyclic voltammograms range from 17.7 to −11.3 kJ mol−1 at 20°C. The comparison of ΔGtr,io′,DCE→W values obtained experimentally for arenediazonium ions with those for the corresponding amino substitutents obtained from a theoretical calculation of partition coefficients between W and 1-octanol evidences the importance of charge distribution over the aromatic moiety in determining the lipophilicity. The ammonium substituents of diazonium ions are 23 kJ mol−1 more hydrophilic than the diazonium ions. The precise concentration of arenediazonium ions in W can be determined electrochemically based on the assumption that the value of the diffusion coefficient of an arenediazonium ion is the same as that of the corresponding ammonium ion.