Electroreduction of Organic Compounds, 35. Quantum Chemical Calculations of Reaction Pathways for the Cathodic Dehalogenation of Chlorodibenzofurans and Oligochlorobenzenes

Abstract

Quantum chemical (DFT) calculations on the course of the electroreductive carboxylation of chloroarenes were performed. An explanation for the extraordinary behaviour of 2- chlorodibenzofuran (2) as compared with the corresponding 1-chloro, 3-chloro and 4-chloro derivatives was sought for and was found in the particular reaction coordinate of 2 and in the SOMO spin density distributions of the four isomers. In the same way, the regioselectivity in the formation of dicarboxylic acids from hexachloro- and 1,2,4,5-tetrachlorobenzene was investigated by DFT-MO calculations and was shown to be due to orbital effects besides steric hindrance.

Electroreduction of Organic Compounds, 36 [1]. Electroreduction of Chlorinated Methyl Benzoates

“…We have observed a similar effect for the cathodic dehalogenation of 2-chlorodibenzofuran, which gives 2-chloro-1,4-dihydrodibenzofuran instead of the expected dibenzofuran [18]. This effect could be rationalized by quantum chemical calculations [1], which we have also performed for 1, 2 and 3 (see below). Expectedly, even further hydrogenation was observed at E red = −2.20 V, as shown in Scheme 2.…”

“…All other reduction waves belong to irreversible processes and are due to the transfer of two electrons (see Fig. 1) with concomitant elimination of a chloride anion via an ECEC mechanism [1,11] as exemplified for the methyl monochlorobenzoates in Eqs. 1 -4:…”