title: Influence of halogen substituents on the catalytic oxidation of 2,4,6-halogenated phenols by Fe(III)-tetrakis(p-hydroxyphenyl) porphyrins and potassium monopersulfate.
abstract: The influence of halogen substituents on the catalytic oxidation of 2,4,6-trihalogenated phenols (TrXPs) by iron(III)-porphyrin/KHSO₅ catalytic systems was investigated. Iron(III)-5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (FeTHP) and its supported variants were employed, where the supported catalysts were synthesized by introducing FeTHP into hydroquinone-derived humic acids via formaldehyde poly-condensation. F (TrFP), Cl (TrCP), Br (TrBP) and I (TrIP) were examined as halogen substituents for TrXPs. Although the supported catalysts significantly enhanced the degradation and dehalogenation of TrFP and TrCP, the oxidation of TrBP and TrIP was not enhanced, compared to the FeTHP catalytic system. These results indicate that the degree of oxidation of TrXPs is strongly dependent on the types of halogen substituent. The order of dehalogenation levels for halogen substituents in TrXPs was F > Cl > Br > I, consistent with their order of electronegativity. The electronegativity of a halogen substituent affects the nucleophilicity of the carbon to which it is attached. The levels of oxidation products in the reaction mixtures were analyzed by GC/MS after extraction with n-hexane. The most abundant dimer product from TrFP via 2,6-difluoroquinone is consistent with a scenario where TrXP, with a more electronegative halogen substituent, is readily oxidized, while less electronegative halogen substituents are oxidized less readily by iron(III)-porphyrin/KHSO₅ catalytic systems.
authors.affiliation: Laboratory of Chemical Resources, Division of Sustainable Resources Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan. m-fukush@eng.hokudai.ac.jp
authors.forename: Masami
authors.initials: M
authors.lastname: Fukushima
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Mizutani
authors.forename: Shouhei
authors.initials: S
authors.lastname: Maeno
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Zhu
authors.forename: Hideki
authors.initials: H
authors.lastname: Kuramitz
authors.forename: Seiya
authors.initials: S
authors.lastname: Nagao
mesh_terms: D002384:Catalysis; D005290:Ferric Compounds / Q000737:chemistry*; D054879:Halogenation; D006219:Halogens / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D017680:Potassium Compounds / Q000737:chemistry*; D012996:Solutions; D013431:Sulfates / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D006219:Halogens; D010636:Phenols; D017680:Potassium Compounds; D012996:Solutions; D013431:Sulfates; D006418:Heme; C009007:potassium persulfate