A Comparative Kinetic and Mechanistic Study on the Oxidation Behaviour of Halogenated Fluorenes by Permanganate in Alkaline Medium

Abstract

The oxidation kinetics of fluorene (Fl) and its halogenated derivatives, namely, 2,7-dichlorofluorene (Fl-Cl), 2,7-dibromofluorene (Fl-Br) and 2,7-diiodofluorene (Fl-I), using potassium permanganate in alkaline medium has been studied spectrophotometrically at a constant ionic strength of 0.1 mol dm-3 and at 25 °C. A first order kinetics has been observed in these reactions with respect to [permanganate]. Fractional-first order dependences of the reactions on the [reductants] and [alkali] were revealed. No significant effect on the reaction rates by increasing ionic strength was recorded. Intervention of free radicals was observed in the reactions. The reactions mechanism describing the kinetic results has been proposed which involves formation of 1:1 intermediate complexes between fluorene derivatives and the active species of permanganate. The final reactions products were identified by GC/MS and FT-IR analyses in all cases as the corresponding ketones (9H-fluorenone derivatives). Under comparable experimental conditions, the order of the oxidation rate of fluorine derivatives was: Fl > Fl-I > Fl-Br > Fl-Cl. The reactions constants involved in the different steps of the reactions mechanism have been evaluated. With admiration to rate-limiting step of these reactions, the activation parameters were recorded and discussed.