Abstract
WHEN dilute solutions of methylene blue in 0.1 N sulphuric acid are subjected to flash photolysis with orange-red light in the presence of ferrous sulphate (∼ 0.1 M), the kinetic curves obtained by monitoring at various wave-lengths can all be interpreted in terms of the following reaction scheme: By direct measurement, the rate constant (k d) for the dismutation of the semiquinone radical (B −) was found to be of the order 1.5 × 109 l. mole−1 sec.−1. By observing the degree to which the formation of leuco methylene blue (B 2−) was suppressed by the addition of ferric iron, the value of k 1/k d and hence k 1 (∼ 2.4 × 105 l. mole−1 sec.−1) was obtained. The latter is so much smaller than k d that the quantity of ferric iron produced by the photochemical reaction has no appreciable effect on the dismutation of the semiquinone radical.
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References
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Parker, C. A. ; Bridge, N. K., and Porter, G., Nature [182, 130 (1958)].
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PARKER, C. Photo-reduction of Methylene Blue and Thionine by Ferrous Sulphate using Flash Irradiation. Nature 182, 245–246 (1958). https://doi.org/10.1038/182245b0
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DOI: https://doi.org/10.1038/182245b0
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