FLASH PHOTOLYTIC GENERATION AND STUDY OF KETENE AND CARBOXYLIC-ACID ENOL INTERMEDIATES FORMED BY THE PHOTOLYSIS OF DIAZONAPHTHOQUINONES IN AQUEOUS-SOLUTION

Flash photolysis of each of five diazonaphthoquinones (1-diazo-2(1H)-o xonaphthalene-4-sulfonate, 2-diazo-1(2H)-oxonaphthalene-4-sulfonate, 2 -diazo-1(2H)-oxonaphthalene-5-sulfonate, phenyl 2-diazo-1(2H)-oxonapht halen-4-sulfonate, and phenyl 2-diazo-1(2H)-oxonaphthalene-5-sulfonate ) in aqueous solution was found to produce two short-lived intermediat es preceding the ultimate indenecarboxylic acid reaction products. Dec ay of the first of these intermediates is catalyzed weakly by hydroxid e ion but not by dilute perchloric acid nor by acetic acid buffers, an d its uncatalyzed reaction shows only weak solvent isotope effects; th is serves to identify this intermediate as the ketene formed by photo- Wolff rearrangement of the diazonaphthoquinone. Decay of the second in termediate is catalyzed by perchloric acid in dilute acid solutions, w ith saturation of this catalysis occurring in more concentrated acid, and it shows general acid catalysis in acetic acid buffers. The perchl oric acid catalyzed reaction gives an appreciable solvent isotope effe ct in the normal direction (k(H)/k(D) > 1), which increases in magnitu de as this catalysis becomes saturated. This serves to identify this i ntermediate as the indenecarboxylic acid enol formed by hydration of t he first intermediate. The form of acid catalysis by perchloric acid a nd the change in isotope effect indicates that this enol ketonizes thr ough its enolate ion, with a shift of initial state from enol to enola te as the acidity of the medium is decreased; analysis of the kinetic data shows the enols to be rather strong acids, with pK(a) = 0.4-1.3.