Reactivities of acridine compounds in hydride transfer reactions

Reactivities of acridine derivatives (10‐benzylacridinium ion, 1a ⁺, 10‐methylacridinium ion, 1b ⁺, and 10‐methyl‐9‐phenylacridinium ion, 1c ⁺) have been compared quantitatively for hydride transfer reactions with 1,3‐dimethyl‐2‐substituted phenylbenzimidazoline compounds, 2Ha–h . Reactions were monitored spectrophotometrically in a solvent consisting of four parts of 2‐propanol to one part of water by volume at 25 ± 0.1 °C. Reduction potentials have been estimated for acridine derivatives by assuming that the equilibrium constants for the reductions of 1a ⁺ –c ⁺ by 2Hb would be the same in aqueous solution and accepting ?361 mV as the reduction potential of the 1‐benzyl‐3‐carbamoylpyridinium ion. The resulting reduction potentials, E, are ?47 mV for 1a ⁺, ?79 mV for 1b ⁺, and ?86 mV for 1c ⁺. Each of acridine derivatives gives a linear Brønsted plot for hydride transfer reactions. The experimental slopes were compared with those obtained by Marcus theory. This comparison shows that the kinetic data are consistent with a one‐step mechanism involving no high‐energy intermediates. Copyright © 2007 John Wiley & Sons, Ltd.