Electrochemical oxidation characteristics of p-substituted phenols using a boron-doped diamond electrode.
Electrochemical oxidation of some p-substituted phenols (p-nitrophenol, p-hydroxybenzaldehyde, phenol, p-cresol, and p-methoxyphenol) with electron-donating and -withdrawing substituents was studied to reveal the relationship between the structure and the electrochemical reactivity of p-substituted phenols using a boron-doped diamond electrode by voltammetry and bulk electrolysis. Voltammetric study shows that the oxidation peak potentials of p-substituted phenols become more positive with an increase of Hammett's constants, that is, the direct electrochemical oxidation of p-substituted phenol with an electron-withdrawing group is more difficult than that of p-substituted phenol with an electron-donating group. However,the p-substituted phenols with electron-withdrawing groups are degraded faster than those with electron-donating groups in bulk electrolysis, which is opposite to the result obtained on the Pt electrode. These results indicate that the p-substituted phenols are mainly degraded by indirect electrochemical oxidation with hydroxyl radicals on a boron-doped diamond electrode. Under the attack of hydroxyl radicals, the release of p-substituted groups from the aromatic ring is the rate-limiting step. Since electron-withdrawing groups are easy to be released, the p-substituted phenols with these groups are degraded faster than those with electron-donating groups. Therefore, the degradation rates of the p-substituted phenols rise with an increase of Hammett's constants.
Zhu
Xiuping
X
College of Environmental Science and Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China.
Shi
Shaoyuan
S
Wei
Junjun
J
Lv
Fanxiu
F
Zhao
Huazhang
H
Kong
Jiangtao
J
He
Qi
Q
Ni
Jinren
J
D001895:Boron / Q000737:chemistry*; D018130:Diamond / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D004572:Electrolysis; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*
D010636:Phenols; D018130:Diamond; D001895:Boron