Sudies on Ionic Intermediates by Flash Photolysis

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Reactivity of dithiolanylium ions generated by flash photolysisi of 2-methoxy-2-aryl-1,3-dithiolane carrying various ring substituents were examined in aqueous solution. The isolated perchlorate salts of some of these carbocations were also studied for comparison. The substuent effect analyzes according to the Yukawa-Tsuno equation show that the transition state for the hydration of the carbocation is claser to the initial state rather than the product. Photolysis of 2-ethoxy-1,3-dithiolane in the presence of 9-cyanoanthracene (9CA) as an electron acceptor in methanol gave products of ring opening, that may result form the radical cation of the dithiolane.Laser photolysis (YAG, 266 nm) of various 9-alkoxy-9(p-methoxyphenyl)xanthene in aqueous solution whowed formation and decay of the 9-arylxanthenylium ion. The rate of the decay of the cation is dependent on the alkoxyl group, shwing that the decay occurs form the ion pair of the xanthenylium ion and the alkoxide anion.Photolysis of 9-benzylxanfhene in the presence of 9CA resulted in a complex mixture of pfoducts, but its photolysis in aqueous K_2S_2O_8 solution gave xanthone via xanthenol. The laser photolysis of 9-benzylxanthene showed a transient formation of xanthenylium ion. These results show that the raction mechanism involves an electron transfer form the xanthene to SO_<4->・and cleavage to five benxyl radical and xanthenylium ion which is hydrated to xanthenol. The xanthenol formed can rapidly be oxidezed to xanthenone.