Oxidation of chlorophenols on Pt electrode in alkaline solution
studied by cyclic voltammetry, galvanostatic electrolysis, and gas chromatographymass
spectrometry*
Z. Ezerskis and Z. Jusys
Institute of Chemistry, A. Gostauto 9, 2600 Vilnius,
Lithuania
Abstract: Potentiodynamic investigations on a platinum electrode
show that oxidation of phenol, monochlorophenols, dichlorophenols, 2,3,6-,
2,4,5-, 2,4,6-trichlorophenols, and pentachlorophenol in 1 M NaOH solution,
containing 1 mM of phenols, proceeds in the potential region of Pt oxide
formation. The oxidation rate of phenols decreases with the increase
in the number of chlorine atoms in the benzene ring in the row: phenol
> monochlorophenols > dichlorophenols > trichlorophenols >
pentachlorophenol. The electrochemical stability of phenols, as studied
using a cyclic voltammetry, depends on their chlorination degree and
isomerism.
Galvanostatic oxidation of 1 M NaOH solutions containing 1 mM of phenol,
monochlorophenols, dichlorophenols, 2,3,6-, 2,4,5-, 2,4,6-trichlorophenols,
and pentachlorophenol were carried out on a platinum electrode using
30 mA cm2 current density. The electrolysis of the solutions was
performed in the course of 10 h, and concentration of phenols in the
anolytes was monitored during oxidation. The concentration of phenolic
compounds diminishes from 1 mM to 1050 mM during 45 h of
electrooxidation and does not change during further galvanostatic oxidation.
A decrease in concentration of phenols during galvanostatic electrolysis
weakly depends on the isomerism and a chlorination degree of the compounds.
A rapid decrease in concentration of studied phenols during the first
45 h of electrolysis and a nonselective oxidation of different
chlorophenols suggest that the oxidation proceeds via electrochemically
generated oxidants. Further decrease in concentration of phenols is
rather small due to deactivation of the electrode as a result of polymerization
of corresponding phenols and diffusion limitations.
* An issue of reviews and research papers based on
presentations made at the IUPAC/ICSU Workshop on
Electrochemistry and Interfacial Chemistry in Environmental Clean-up
and Green Chemical Processes, Coimbra, Portugal, 6-7 April, 2001.
** Corresponding author.
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