Reaction of Benzene with Cu(II)- and Fe(III)-Exchanged Hectorites

Abstract

Abstract--The reaction of benzene with exchangeable Cu(II) and Fe(III) in hectorite clay films was studied by electron paramagnetic resonance (EPR). The reaction when carried out in a sealed tube between 60* and 100*C produced a variety of organic radical products. The nature of these products depended on the concentration of water in the reaction medium and the reaction time. The free radicals were accompanied by a reduction in the oxidation state of the metal ions; this process had a zero-order dependence on the metal ion concentration. The activation energies determined from the zero-order rate constants are 67 _+ 11 kJ/mole (Cu(II)) and 46 _+ 6 kJ/mole (Fe(III)). The free radicals initially formed under anhydrous conditions appeared to populate sites in the interlayer region; the activation energies determined for this first order process are 57 • 9 kJ/mole (Cu(II)) and 42 • 3 kJ/mole (Fe(III)). These activation energies are within experimental error of those determined from the metal ion kinetics. The EPR signal due to organic radicals showed little temperature dependence; thus, exchange processes involving organic free radicals were probably not important in determining EPR lineshapes.

Formation of Environmentally Persistent Free Radicals on Microplastics under Light Irradiation

“…These results indicated that the generation of EPFRs was mainly determined by the chemical structures of MPs. This was consistent with previous studies in which EPFRs were mainly produced by the precursors of polycyclic/substituted aromatic compounds or polymers with a polyconjugated structure (namely, benzene rings). , On the one hand, benzene rings are prone to delocalize the unpaired electrons, inducing the formation of relatively stable free radicals . On the other hand, the steric and polarity effects of the electrophilic aromatic substitution inhibit the free radicals approaching the particular reaction sites. , As a consequence, EPR signals were observed in the irradiated PS and PF rather than PE and PVC.…”

“…45,53 On the one hand, benzene rings are prone to delocalize the unpaired electrons, inducing the formation of relatively stable free radicals. 58 On the other hand, the steric and polarity effects of the electrophilic aromatic substitution inhibit the free radicals approaching the particular reaction sites. 59,60 As a consequence, EPR signals were observed in the irradiated PS and PF rather than PE and PVC.…”

Transformation of Polycyclic Aromatic Hydrocarbons and Formation of Environmentally Persistent Free Radicals on Modified Montmorillonite: The Role of Surface Metal Ions and Polycyclic Aromatic Hydrocarbon Molecular Properties

“…This complex induces the electron transfer from PAHs to surface cations to cause oxidation, which ultimately leads to the formation of intermediate radicals or/and final products, such as PAH− quinones. 32,42,43 Significantly, our results demonstrate that properties of metal ions and PAHs affect the binding strength of CT complex, which influences the electron-transfer reaction and the formation of EPFRs. For example, electron-deficient cations [e.g., Fe(III) and Cu(II)] and electron-rich PAHs have relatively strong cation−π interactions, which result in an initial single electron transfer (SET) step to cause transformation of PAH readily.…”

Formation and Stabilization of Environmentally Persistent Free Radicals Induced by the Interaction of Anthracene with Fe(III)-Modified Clays

“…Previous studies suggest that the PAHs-based radical cations with g-factor of ∼2.0028 are readily formed through the direct electron-transfer from aromatic compounds to transition-metal ions on clay surface. 36,37 Thus, the g1 EPR signal can be ascribed to the formation of anthracene-type radical cations. The oxygencentered radicals, such as semiquinone radical anions, possess a g-factor >2.0040.…”