Collect. Czech. Chem. Commun. 1983, 48, 3552-3558

Electrochemical dehalogenation of open-chain vicinal dihalides at mercury cathodes: The effect of leaving group identity on E1/2 values and on steric course

Jiří Závada, Josef Krupička, Oldřich Kocián and Magdalena Pánková

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6


The title problem has been investigated polarographically in the homologous series of erythro and threo-5,6-dihalodecanes (X = Br, Y = I; X == Cl, Y = I; X = F, Y = I; X = Br, Y = Br; X = Cl, Y = Br; X = F, Y = Br; X = Cl, Y = Cl; X = F, Y = Cl). Each dihalide from the series gave a single two-electron wave. A very pronounced dependence of half-wave potential on halogen group identity was found in the series, the E1/2 values ranging from -0.3 V (X = Br, Y = I) to -2.8 V (X = F, Y = Cl). Controlled-potential electrolyses of the dihalides were accomplished at mercury pool electrode affording always cis- and/or trans-5-decene as the sole product, in almost quantitative (>90%) yields. Stereochemistry of the dehalogenation was deduced from the olefin-isomer distribution data determined by VPC. Very marked differences were found in the series, the elimination stereochemistry ranging between a clean anti and a prevalent syn, in dependence on the identity and configuration of the halogen groups.