engleski

Measurement of the reaction rate of alkoxyl radical with Fe(II) ion

The reaction rate of alkoxyl radical (tert-butoxyl) with Fe2+ has been measured using laser flash photolysis method. Tert-butoxyl radicals (t-BuOˇ) were generated by homolytic photodecomposition of di-tert-butylperoxide (1) using ruby laser (347 nm, duration of the flash 30 ns). The oxidation of Fe2+ with t-BuOˇ radicals (3) was studied under pseudo-first order conditions (Eqs. 1, 2, 3). On the basis of competitive kinetics the quantum yield of oxidation, F(Fe3+), follows from the scheme 1, where k0 refers to the overall rate of disappearance of the t-BuOˇ radicals in the system. The quantum yield F(Fe3+) was determined by measuring the absorbance of Fe3+ ion as [FeCl]2+ complex at 360 nm 2 micro s after the flash. The rate constant k3 was obtained from the relative rate constant kr (kr=k0/k3) and the value of k0. The rate constant k0 was determined under the same experimental conditions as in the measurement of the quantum yield F(Fe3+), with the exception that diphenylmethanol was used instead of Fe2+. The reaction of t-BuOˇ radical with diphenylmethanol (4) gives ketyl radicals with the known rate constant (Eq. 4). The quantum yield F(PH2 OH) was determined by measuring the maximum of absorbance at 535 nm. With the measured value of k0 = 6,2x106 s-1, the rate constant k3 = 3,4x108 dm3 mol-1 s-1.

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