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Kinetics of the cis-trans isomerization of azobenzene Ciccone, Stefania

Abstract

The catalytic effects of several acids and metal salts on the cis-trans isomerization of azobenzene in aqueous ethanol were examined kinetically. The effect of perchloric acid is apparently due to H⁺ ions: a catalytic mechanism involving the formation of the conjugate acid of azobenzene has been postulated to interpret these results. To account for the much higher catalytic activity found for hydrochloric acid, an additional path, involving catalysis by undissociated HCl molecules has been proposed. Acetic acid was found to be inactive. Of the metal salts examined only those of Cu⁺⁺ shoved pronounced catalytic activity, which is interpreted in terms of a catalytic mechanism involving coordination of cupric ions with the azo group. Simultaneous coordination of Cu⁺⁺ and H⁺ has been proposed to account for the high catalytic activity of cupric salts in the presence of acids.

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