Abstract
Abstract— A kinetic method for the identification of primary reactions in sensitized photooxidations is described. It is based on the calculation of Fractions of primary reactions of triplet sensitizer (3S) and singlet oxygen (1O2) as a function of substrate concentration (A) and on the comparison of experimental and theoretical curves. The theoretical curve that coincides with the experimental one indicates the mechanism of the chemical change observed. Only the quenching rate constants of 3S and 1O2 are needed for this calculation. The method enables one to distinguish the free radical and 1O2 mechanism. Applications of the method with 3‐indole acetic acid, 1‐histidine and N‐3 using phenosafranine as the sensitizing dye (aqueous solutions, pH 7.C7.2) are described. The chemical change followed in these experiments is the bleaching of p‐nitrosodimethylaniline (RNO) which gives precise and reproducible results. The bleaching of RNO is induced by the presence of some substrates which produce reactive intermediates with an oxidizing character. The kinetic method can be applied to any chemical change observed in different systems of sensitized photooxidations. The quantum yield of 3S and 1O2 formation need not be known.
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