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Abstract
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Organic electrosynthesis is a strong tool to produce a variety of functional compounds via electrochemically generated species as a key intermediate. [1]. Unique selectivity because of in situ formation of an active species at the interface, inversion in polarity by transfer of electron and variability in product formation by control of potential are some of advantage of electrosynthesis. Our previous studies show that the electrochemically generated p-quinone imine is a reactive intermediate and as a Michael acceptor, participates in different types of reactions [2,3]. In this work electrochemical oxidation of 5-aminosalicylic acid (mesalazine drug) has been studied in the presence of 2-methyl indole (3) as nucleophile (Scheme 1). Some electrochemical techniques such as: cyclic voltammetry using diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled-potential coulometry were used. Our results indicate the participation of electrochemically generated p-quinones in Michael-type addition reaction with 2-methyl indole (3) to form new indole derivatives. Diagnostic criteria of cyclic voltammetry, the consumption of 4e- electrons per molecule of mesalazine, and the spectroscopic data of the isolated products, indicated that the reaction mechanism of electrooxidation of 1 in the presence of 3 is ECE mechanism. Nature stability of p-quinone imine in comparison with o-quinones in one hand and stability of final products arising from intramolecular hydrogen bonding, on the other hand, are responsible for remaining the final products in quinone form.
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