Significant effect of 5,10,15,20-meso-tetraarylporphyrinatoiron(III) chloride/triflate and acidic/neutral/basic imidazolium ionic liquids in catalytic oxidation of phenols

• Published in: Journal of molecular liquids 2018-06, Vol.260, p.292-303
• Main Authors: Ahmad, Sohail, Gautam, Renu, Singhal, Anchal, Chauhan, S.M.S.
• Format: Article
• Language: English
• Subjects: Catalysis; Ionic liquids; Phenols; Porphyrins
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2018.03.017

The influence of acidic, neutral and basic ionic liquids and their binary mixture with dichloromethane on the reactivity of iron(III)porphyrins was investigated during oxidation of phenols with hydrogen peroxide catalysed by 5,10,15,20-tetraarylporphyrinatoiron(III) chloride and 5,10,15,20-tetraarylporphyrinatoiron(III) triflate. The generation of different intermediates of iron(III) porphyrin in different ILs was studied through viscosity, density, UV–Vis and 1H NMR spectroscopy. The heterolytic cleavage efficiency of (TAP)FeIII-OOH and formation of quinone using iron(III)porphyrin (TAP)FeIIICl with Cl atom as an axial ligand, is influenced by the structure of imidazolium moiety and the counteranion following the order [(CH2)4SO3HMIm]CF3COO>[Hmim]CF3COO>[bmim]TFA»»negligible amount in [bmim]CF3SO3, [Hmim]CF3SO3, [bmim]BF4, [bmim]PF6 and [bmim]Cl. On the other hand, the heterolytic cleavage efficiency of (TAP)FeIII-OOH with iron(III)porphyrin (TAP)FeIIICF3SO3 with triflate as an axial ligand, was found in the following order [(CH2)4SO3HMIm]CF3SO3>[Hmim]CF3SO3>[(CH2)4SO3HMIm]CF3COO>[Hmim]CF3COO>[bmim] CF3COO>[bmim]PF6≈[bmim]BF4≈[bmim]CF3SO3, while epoxidation and polymerization were mainly observed in basic and neutral ILs. The reactive intermediates formed by the reaction of monooxygen donors with (TAP)FeIIICl varied with ILs, as (TAP)+∙FeIV=O intermediate was dominated in acidic ILs, while (TAP)FeIV=O was formed in neutral ILs and (TAP)FeIII-OO– was formed in basic ILs. [Display omitted] •Effect of axial ligand of iron(III)porphyrin on the oxidation of phenols•Effect of cation and anion of imidazolium ionic liquids on oxidation of phenols•Effect of density of reaction medium on the oxidation of phenols•Interaction studies between ironIIIporphyrin and ionic liquids using NMR technique•Study of formation of different reactive intermediates in different conditions