TWO STEP-ONE ELECTRON TRANSFER MECHANISM FOR THE REACTION OF TERNARY DIPICOLINATOCHROMIUM(III) COMPLEX INVOLVING 2-AMINOPYRIDINE WITH N-BROMOSUCCINIMIDE

The oxidation of a ternary complex, [Cr(III)(DPA)(L)(H2O2](+) (DPA = dipicolinic acid and L = 2-aminopyridine) in aqueous solution to chromium(VI) has been studied spectrophotometrically over the 20-40 degrees C range. The reaction is first order with respect to both [NBS] and [Cr], and increases with pH over the 5.92-6.93 range. The experimental rate law is consistent with a mechanism in which the hydroxy species, [Cr(III)(DPA)(L)(H2O)(OH)] is significantly more reactive than their conjugate acid. The effect of the surfactants, such as cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecylsulphate (SDS, an anionic surfactant), on the reaction rate has been studied. CTAB has no effect on the reaction rate while SDS inhibits one. The activation parameters have been calculated. It is assumed that a two step-one electron transfer takes place via an inner-sphere mechanism.