Autocatalytic Reaction Pathway on Manganese Dioxide Colloidal Particles in the Permanganate Oxidation of Glycine

Abstract

The progress of the reaction of permanganate ion with the amino acid glycine in near-neutral aqueous solutions was monitored with a UV-vis spectrophotometer at two different wavelengths in order to observe the decay of the oxidant (MnO 4 -, at 526 nm) and the formation of one of the reaction products (colloidal MnO 2 , at 418 nm). The use of a phosphate buffer resulted in the stabilization of MnO 2 as a soluble colloid during the kinetic runs. The experimental data are consistent with the hypothesis that of the two conjugated buffer ions H 2 PO 4 -/HPO 4 2-the acidic one (H 2 PO 4 -) is the predominant species responsible for that stabilization, suggesting that the formation of hydrogen bonds between the MnO 2 oxygen atoms and the hydrogen atoms from phosphate ions might be involved in the process. An increase of the phosphate concentration resulted in a notable decrease of both the molar absorption coefficient and the size of the MnO 2 colloidal particles. The reaction showed an autocatalytic behavior, but the kinetic plots deviated from the differential rate law usually employed for the study of autocatalytic reactions. The experimental data suggest that these deviations might be caused by the competitive adsorption of both phosphate ions and glycine on the surface of the MnO 2 colloidal particles, with the adsorption of the two species being too slow for the quasi-equilibrium approximation to hold, and resulting in an inhibition of the autocatalytic reaction pathway by phosphate ions.

Kinetics study on the oxidation of chlorophenols by permanganate

“…(6)- (11)) [15,[23][24][25]: (11)), and therefore their effect on the degradation of these CPs is negligible [26,27]. But the in situ formed MnO 2 could oxidize phenols and even autocatalyze permanganate oxidation and therefore enhance the removal efficiency of phenolic chemicals in weakly acidic conditions [28,29]. Moreover, the redox potential (E 0 ) of permanganate is 1.70 V under acidic conditions higher than that under alkaline conditions (E 0 = 0.59 V) [30].…”

Kinetics and Mechanism of Oxidation of l‐Histidine by Permanganate Ions in Sulfuric Acid Medium

“…On the other hand, permanganate is a unique oxidizing agent in neutral, alkaline, and acidic media. In acidic media, the permanganate ion (MnO) can exist in several different forms: HMnO 4 , H 2 MnO, and Mn 2 O 7 , depending on the nature of the reductant; the oxidant has been assigned with innersphere and outer‐sphere mechanism pathways in their redox reactions . In general, the reduction of the permanganate ion in acid medium goes to either Mn IV or Mn II , where the reduction potential of the Mn VII /Mn IV couple is 1.695 V and of the Mn VII /Mn II couple is 1.51 V .…”

Manganese Dioxide Nanostructures as a Novel Electrochemical Mediator for Thiol Sensors

“…Lately, manganese dioxide has been used as a catalyst in oxidation of sulfur-containing organic compounds, in particular, for applications in ecology [9,16]. While other metal oxide catalysts are easily poisoned by sulfur, manganese dioxide exhibits good stability [17].…”