Electrofugalities of Acceptor-Substituted Tritylium Ions

Ionization rate constants of differently substituted trityl halides and carboxylates have been determined by conductimetry at 25 degrees C in aqueous acetonitrile and in acetone. Common ion return was suppressed by the addition of piperidine, which traps the generated tritylium ions. The obtained rate constants were subjected to Winstein-Grunwald and Hammett analyses. The solvolysis rate constants of trityl chlorides and bromides were employed to derive electrofugality parameters (E-f) of tritylium ions according to the linear free energy relationship log k(ion) = s(f)(E-f + N-f) (N. Streidl, B. Denegri, O. Kronja, H. Mayr, Acc. Chem. Res. 2010, 43, 1537-1549). A facile scheme for estimation of ionization rates of trityl derivatives is presented.