DUGi

Robust iron coordination complexes with N-based neutral ligands as efficient fenton-like catalysts at neutral pH

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@2072@@295536

The homogeneous Fenton-like oxidation of organic substrates in water with hydrogen peroxide, catalyzed by six different metal coordination complexes with N-based neutral ligands, was studied at ambient conditions and initial pH 7, employing hydrogen peroxide as the terminal oxidant. At low catalyst concentration, the catalytic oxidative depletion of toluene achieved by selected catalysts was much more efficient than that obtained by the Fenton reagent at pH 3. The influence of pH, the water matrix and the catalyst/hydrogen peroxide concentration were investigated for the oxidation of toluene employing [FeCl2(bpmcn)] (1, bpmcn = N,N′-bis(2-pyridylmethyl)-N, N′-dimethyl-trans-1,2-diaminocyclohexane), the most efficient catalyst of the series. Moreover, the evolution of catalysts [FeCl2(bpmcn)] (1) and [Fe(OTf)2(Pytacn)] (3, Pytacn = 1-(2-pyridylmethyl)-4,7-dimethyl- 1,4,7-triazacyclononane, OTf = trifluoromethanesulfonate anion) during the course of the reaction was also studied by electrospray ionization mass spectrometry (ESI-MS). The oxidation products derived from toluene oxidation were also analyzed. A plausible mechanism of toluene degradation using [FeCl2(bpmcn)] (1) and [Fe(OTf)2(Pytacn)] (3) as catalysts was proposed, which involves the coexistence of a metal-based path, analogous to that operating in organic media where substrate oxidation is executed by an iron(V)-oxo-hydroxo species, in parallel to a Fenton-type process where hydroxyl radicals are formed

M.C. thanks the European Research Council for a Starting Grant Fellowship (ERC-2009-StG-239910), MINECO of Spain (CTQ2012-37420-C02-01/BQU, Consolider-Ingenio CSD2010-00065) and the Catalan DIUE of the Generalitat de Catalunya (2009SGR637, and ICREA Academia Award). A.C. thanks the European Commission for a Career Integration Grant (FP7-PEOPLE-2011-CIG-303522). Ministerio de Ciencia e Innovacion (Spain) is acknowledged for financial support with the project SIRENA (CTQ2011-24114), for a Juan de la Cierva contract to R.G.-O. (JCI-2010-07104) and for a Ramon y Cajal contract to A. C. (RYC-2011-08683). Mr. Z. Codola is acknowledged for his help with the experimental setup for the determination of the overpressure generated into the reactors

American Chemical Society (ACS)