Veli-Matti Vuorenpalo

Mechanism of decomposition of peracetic acid by manganese ions and diethylenetriaminepentaacetic acid (DTPA)

Abstract The decomposition mechanism of peracetic acid by free Mn2+ ions and by Mn2+-diethylenetriaminepentaacetic acid complexes was studied by UV/Vis, electrospray ionization-time of flight-mass spectrometry (ESI-TOF-MS), electron spin resonance (ESR), and Raman spectroscopy. The experimental results demonstrate that a number of different oxidation states of manganese are involved in the decomposition reaction. Furthermore, the kinetics observed show oscillatory features that are characteristic of autocatalytic processes. Radical pathways were found to play a negligible role in the reaction. Based on the experimental observations, an overall reaction scheme for the decomposition process is proposed.

Stabilization of peracetic acid with aspartic acid diethoxy succinate (AES)

Abstract Stabilization of peracetic acid (PAA) by aspartic acid diethoxy succinate (AES) was studied by electron spin resonance, UV/Vis spectroscopy, electrospray ionization time-of-flight mass spectrometry and oxygen evolution measurements. The results indicate that Mn(II)-AES complexes may exist in both monomeric and dimeric forms. Dimerization is proposed to proceed via formation of an oxygen bridge between two Mn(II)-AES complexes. The equilibrium between these two forms depends strongly on pH, the monomeric form being favored under acidic conditions, while conditions close to neutral pH favor the dimeric form. In the presence of PAA, the dimer form was oxidized and finally yielded MnO2. Oxygen evolution measurements were carried out to demonstrate the efficiency of AES in stabilizing PAA solutions containing small amounts of Mn(II) impurities under acidic conditions.

Stabilization of H2O2 in the presence of Fe(II) and Mn(II) impurities under alkaline conditions

Abstract Stabilization of aqueous H2O2 solutions containing small amounts of transition metal impurities [e.g., Mn(II) and Fe(II)] was studied in terms of UV/Vis and electron spin resonance spectroscopy and oxygen concentration measurements at pH ∼11. The results show that aspartic acid diethoxy succinate (AES) could stabilize H2O2 solutions when Mn(II) and Fe(II) were present. Diethylenetriamine pentaacetic acid (DTPA) showed similar behavior, but was not able to stabilize the solutions as efficiently as AES. In the long-term regime, Na-poly-alpha-hydroxy-acrylate was almost as effective a stabilizing agent as AES. Na-acrylate-3-allyloxide-2-hydroxy propane Na-sulfonate copolymer (Aqualic) could decrease H2O2 decomposition by one order of magnitude, but it was the least efficient stabilizing agent among the substances studied. Furthermore, generation of superoxide radical was not suppressed in the presence of Aqualic.