Electrochemical determination of the lipophilicity scale of arenediazoniumions based on the ion transfer across the liquid vertical bar liquid interface

A lipophilicity scale of 14 monovalent arenediazonium ions has been establi shed on the basis of the standard Gibbs energy of ion transfer between the 1,2-dichloroethane (DCE) and water (W), Delta G(tr,i)(o.DCE-->W) The ion tr ansfer processes of all arenediazonium ions studied using cyclic voltammetr y at the planar DCE \ W interface are reversible, i.e. diffusion-controlled . Apparent values of Delta G(tr,i)(o'.DCE-->W) estimated from the mid-point potential in cyclic voltammograms range from 17.7 to -11.3 kJ mol(-1) at 2 0 degrees C. The comparison of Delta G(tr,i)(o'.DCE-->W) values obtained ex perimentally for arenediazonium ions with those for the corresponding amino substitutents obtained from a theoretical calculation of partition coeffic ients between W and 1-octanol evidences the importance of charge distributi on 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 b e determined electrochemically based on the assumption that the value of th e diffusion coefficient of an arenediazonium ion is the same as that of the corresponding ammonium ion. (C) 2000 Elsevier Science S.A. All rights rese rved.