Collect. Czech. Chem. Commun. 2004, 69, 242-260

Synthesis and Electrochemical Reduction of Methyl 3-Halo-1-benzothiophene-2-carboxylates

Michal Rejňáka,b, Jiří Klímab, Jiří Svobodaa and Jiří Ludvíkb,*

a Department of Organic Chemistry, Institute of Chemical Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic
b J. Heyrovský Institute of Physical Chemistry and Electrochemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8, Czech Republic


A preparative method of synthesis of the new methyl 3-iodo-1-benzothiophene-2-carboxylate was elaborated. Electrochemical behavior of methyl 3-chloro-, bromo- and iodo-1-benzothiophene-2-carboxylates 1-3, and of their reduction and dimer products 4, 5 in anhydrous dimethylformamide has been investigated at mercury and platinum electrodes using polarography, cyclic voltammetry and voltammetry on a rotating platinum disk electrode. The reduction in divided cells follows the ECE mechanism (electron - chemical step - electron), where the primary radical anion is split into a halide anion and neutral heterocyclic radical, which is immediately reduced by the second electron and protonated. The only reduction product is the methyl 1-benzothiophene-2-carboxylate (5); whereas the EDim mechanism (electron - dimer formation) leading to the dimeric species 4 was not observed under the above conditions. Reduction of 1-3 on platinum causes formation of a blocking film on the electrode. Sonication during electrolysis successfully reactivates the electrode.

Keywords: Halobenzothiophenes; Biaryls; Voltammetry; Electroreduction mechanism; Mercury and platinum electrodes; Adsorption; Sonication; Electrochemistry.

References: 38 live references.