8340
R. Sokolová et al. / Electrochimica Acta 55 (2010) 8336–8340
the overall reduction mechanism of ioxynil. The half of the ioxynil
molecules provides the necessary protons for a two electron reduc-
tion of ioxynil as shown in Scheme 3. The two electron exhaustive
electrolysis in the presence of tetraoxalate yields exclusively 3-
iodo-4-hydroxybenzonitrile. No butylated ioxynil was found.
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4. Conclusions
The redox activity of halogenated hydroxybenzonitrile com-
pounds has been investigated in aprotic media. The polarographi-
cally and coulometrically observed one electron consumption per
one molecule of ioxynil is explained by the autoprotonation step
in its reduction mechanism. In effect, the process is a two electron
reduction involving only one half of the starting material. If the
source of the protons is other than the starting molecule, all ioxynil
is being converted to the dehalogenated product. The controlled
potential coulometry in the presence of the strong proton donor
confirms that two electrons are involved in the reduction process.
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Acknowledgements
This work was supported by the Grant Agency of the Czech
Republic (203/09/1607 and 203/08/1157) and Ministry of Educa-
tion (LC510 and COST OC140).
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