Ac polarographic determination of the rate of ion transfer for a series of alkylammonium ions at the nitrobenzene/water interface

Abstract

The rate of ion transfer across the polarized nitrobenzene/water interface has been determined for twelve homologous alkylammonium ions by using phase-selective ac polarography. A new cell with a two-electrode configuration was used to minimize the interference arising from the non-ideal behaviour of the non-polarized nitrobenzene/water interface. Compensation of the iR drop by means of a positive feedback method has been proven to be useful for obtaining reliable kinetic parameters. The apparent standard rate constants, k s, for all alkylammonium ions were of the order of 0.1 cm s −1. k s increased slightly with increasing ionic radius from trimethylammonion ion to tetraethylammonium ion and then decreased with a further increase in the radius to tetrapropylammonium ion. This dependence of k s on the ionic radius suggests that, in the ion transfer of smaller alkylammonium ions, the desolvation-resolvation process is involved in the rate-determining step, whereas the effect of hydrodynamic friction prevails for larger alkylammonium ions.