title: EPR studies on the kinetics of the α-hydroxyethyl radical generated by Fenton-like chemistry.
abstract: Flow systems, either stopped or continuous, have long been at the core of kinetic studies of chemical reactions. Such flow systems need to be coupled with appropriate spectroscopic or otherwise techniques for the detection of the chemical species studied. If paramagnetic species are formed or consumed during the investigated reaction, electron paramagnetic resonance (EPR) with its nanomolar sensitivity can be the spectroscopic method of choice. However, not much literature is available on the application of EPR to quantitatively study kinetics of chemical reactions in the liquid state. Herein, we report the characterisation of the commercially available mixing resonator ER 4117 MX from Bruker using the TEMPO-dithionite reaction as a standard. Furthermore, this setup was used to study the kinetics of the Fenton-like system of TiCl3/H2O2 and ethanol forming theα-hydroxyethyl radical. Potential contributions of reactions with O2, H2O2, Ti(3+/4+), and self-recombination in the decay of theα-hydroxyethyl radical were investigated and the bimolecular decay was shown to be the dominant decay pathway, with a decay rate constant of 6.6×10(8) M(-1) s(-1). This study shows the effectiveness and capabilities of EPR as a direct, sensitive and in-situ method in kinetic studies.
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, 53115 Bonn, Germany.
authors.forename: Erik
authors.initials: E
authors.lastname: Schubert
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, 53115 Bonn, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Hett
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, 53115 Bonn, Germany. Electronic address: schiemann@pc.uni-bonn.de.
authors.forename: Olav
authors.initials: O
authors.lastname: Schiemann
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, 53115 Bonn, Germany.
authors.forename: Yaser
authors.initials: Y
authors.lastname: NejatyJahromy
keywords: EPR spectroscopy; Fenton; Hydroxyethyl radical; Kinetics