Kinetics of the photochemical reactions of the croconate dianion in aqueous solution

Abstract

The kinetics of the photochemical reactions of the dianion of croconic acid (1,2-dihydroxycyclopentenetrione) have been studied in aqueous solution in the presence of electron acceptors. In neutral solutions the quantum yield for disappearance of croconate dianion was small (< 10 −3 ) but was substantially increased in basic solution and in the presence of electron acceptors. At pH 12 in the presence of 4-nitrobenzylbromide and biacetyl a quantum yield of 1 was obtained. The kinetics of the rate of disappearance of croconate dianion as a function of pH and concentration of acceptor showed that the excited dianion is oxidized by acceptors and reacts with hydroxyl ion. A mechanism is proposed that, by assuming reasonable values for the rate constants involved, is shown to be consistent with the results. Keywords: photolysis, kinetics, croconate dianion, electron transfer.