New Experimental and Mechanistic Investigation on the KSCN-H₂O₂-NaOH-Cu(II)-Catalyzed Oscillating System (Orbàn-Epstein Reaction): Inhibitory Effects by Diphenols

Abstract

The KSCN-H 2 O 2 -NaOH-Cu(II)-catalyzed system is one of the few reactions in which chemical oscillations can be observed in batch conditions. In the present paper, this oscillating reaction was revisited in a wide range of initial concentrations of all components in batch. A mixture with a long lasting oscillation time (1 h 34 min) and a great number of oscillations (24) was found and used to investigate the effect of temperature. An Arrhenius-type temperature dependence was observed from which an apparent "average activation energy" E av = 76 ± 5 kJ for the overall oscillatory reaction was observed. A mechanistic study based on a modified model analyzed by the stoichiometric network analysis approach gave a satisfactory agreement between calculated and experimental oscillating behaviors and temperature dependence. The addition of the three diphenols (catechol, resorcinol, and hydroquinone) causes perturbations similar to those observed in the Briggs-Rauscher oscillating system, i.e., an inhibition of the Correspondence to:Željko

Mechanism of the oscillating chemiluminescence reaction in the luminol‐H2O2‐KSCN‐CuSO4‐NaOH system

“…Simulation was carried out using the rate constants as listed in Refs. 4,16,23, and 24 by a Runge‐Kutta method. Although we could only reproduce an oscillating behavior with a set of given rate constants in Ref.…”

“…In Refs. 16,23, and 24, the reaction rates of M3, M8, M9, M19, and M20 did not include [OH − ] and [SCN − ]. We listed the reaction rate and the rate constants in Table 2.…”

“…Luo et al 4 proposed the reaction mechanism and estimated the rate constants of the reactions for the H 2 O 2 -KSCN-Cu(II) system. Wiśniewski et al 16 23,24 also carried out a detailed calculation for the Orbàn-Epstein reaction system. We would like to report for the first time direct and simultaneous measurement of the potential of Cu 2+ using a copper(II) ion electrode and counter electrode Ag/AgCl as well as the oxidation-reduction potential (ORP) using an ORP electrode (Pt electrode and counter electrode Ag/AgCl).…”

“…Jędrusiak et al 20 calculated the concentration of HO 2 Cu(OH) 2 − , − OS(O)CN, and HO 2 ·. Recently, Cervellati et al 23,24 also carried out a detailed calculation for the Orbàn‐Epstein reaction system.…”

Oscillating chemiluminescence reaction in the L‐012–H2O2–KSCN–CuSO4–NaOH system

“…Recently, Cervellati et al. also carried out a detailed calculation for the Orbàn–Epstein reaction system 9,10 . In our previous study, we calculated the concentration of OH·, HO 2 ·, ·OS(O)CN, and SO 3 · − which are thought to be the important chemical intermediates and proposed that the strong chemiluminescence was due to the reaction of luminol with the ·OS(O)CN radical and the ORP (oxidation reduction potential) reflected [HO 2 ·]/[ HO 2 − ] 11 …”