Preparation Of Immobilized Salicyl Hydroxamic Acid-transition Metal Complex And Its Catalytic Oxidation Performance

Hydroximic acid, also called hydroxamic acid or oximine acid, is a kind of importantmetal complexing agent and can form stable complexes with metal ions. The hydroxamic acidtransition metal complexes are known to be highly efficient oxidation catalysts which havebeen successfully used to homogeneously catalyze the transfer of an oxygen atom from agreat variety of oxidizing agents into hydrocarbon compounds to form oxygenic compoundswith high added value. And it possesses these features, such as easy synthesis, adjustablestructure, low price, strong antioxidant ability, and so on. However, the free hydroxamic acidtransition metal complex has some shortcomings, including the difficult separation, unablereusability, poor stability, and so forth. To overcome these drawbacks, this aiticle designedand prepared the supported salicylhydroxamic acid (SHA) and salicylhydroxamic acidtransition metal complexes. The chelating adsorption properties of the supportedsalicylhydroxamic acid for metal ions were studied, and the catalytic performances of thesupported salicylhydroxamic acid-transition metal complexes in the catalytic oxidationprocess of ethyl benzene were investigated in detail. This study is of significant meanings in thetreatment of wastewater containing heavy metals and the green catalytic oxidation of hydrocarboncompounds.Firstly SHA was covalently bound onto chloromethylated crosslinked polystyrenespheres (CMCPS) through the Friedel-Crafts alkylation reaction between CMCPS and SHAusing SnCl4as the Lewis acid catalyst, resulting in the functionalized spheres SHA/CPS. Thechelating adsorption behaviors of SHA/CPS for heavy metal ions including the adsorptionkinetics and thermodynamics were explored. The effects of various factors on its adsorptionbehaviors were investigated. SHA/CPS possesses very strong chelating ability for heavymetal ions. In particular, the saturated adsorption amount towards Cu2+ions could reach ashigh as34.2mg/g at45℃, pH=5.5. SHA/CPS also shows selective metal coordination with the chelating capacity decreasing in the order of Cu2+> Zn2+>> Pb2+. The adsorptionisotherms conform well to the Langmuir model, and the adsorption process is found to beentropy-driven and endothermic. Besides, SHA/CPS possesses the excellent reusability.Thentransition metal ions (Co(II), Cu(II), Fe(III), or Mn(II)) were then introduced to the resultingSHA-functionalized microspheres (SHA/CPS) through SHA-metal ion chelation. Theobtained microspheres M-SHA/CPS were explored as heterogenous catalysts for the aerobicoxidation of ethylbenzene (EB). Catalytic performances of M-SHA/CPS for the aerobicoxidation of EB in the absence of solvent were investigated and compared in detail. Theresults showed that M-SHA/CPS could effectively activate dioxygen and obviously catalyzethe oxidation of EB. The electronic structure of central metal ion had a strong effect on thecatalytic properties of M-SHA/CPS, and the yield of EBHP obtained using Fe-SHA/CPS ascatalyst was up to14%at100℃. The catalytic activity was affected by the Fe-SHA/CPSconcentration, additive concentration, and temperature. In addition, Fe-SHA/CPS had a goodreusability, and still showed good catalytic activity after seven catalytic cycles.5-Chloromethyl-Salicylhydroxamic Acid (CMSHA) was first prepared using1,4-bichloromethoxy-butane (BCMB) as the chloromethylation reagent. The grafted particlesPHEMA/SiO2was obtained by virtue of the surface-initiated graft-polymerization of2-hydroethyl methacrylate (HEMA) on silica gel particles under the redox initiating system.Subsequently, the nucleophilic substitution reaction between the hydroxyl group of thegrafted PHEMA and the chloromethyl group of CMSHA was carried out, resulting in thesalicylhydroxamic acid-functionalized composite particles SHA-PHEMA/SiO2. Finally, thecoordination reactions between the particles SHA-PHEMA/SiO2and metal ions (Co(II),Cu(II), Fe(III), Fe (II) were conducted, and the solid catalysts MSHA-PHEMA/SiO2wereobtained. The catalytic activity of them for the oxidation of EB by dioxygen was examined indetail, and the catalytic mechanism was explored. The effects of various of factors on thecatalytic performances of M-SHA-PHEMA/SiO2were also studied. The experimental resultsshow that the supported catalysts M-SHA-PHEMA/SiO2can effectively activate dioxygen,and obviously catalyze the oxidation of EB. The catalytic activities of M-SHA-PHEMA/SiO2 differ among the different metals, according to the following series: Cu(II)>> Co(II)>Fe(II)> Fe(III). Under the reaction conditions of110℃and the ordinary pressure of oxygen,the catalyst Cu(II)-SHA-PHEMA/SiO2gave wonderful results with35%yield and92%selectivity to the main product hypnone, and the other products, EBHP and aphenylethanolwere very few. In addition, the catalytic activity was affected by theCu(II)-SHA-PHEMA/SiO2concentration, additive concentration, and temperature.