Hydrogen peroxide decay rate

Figure 5. Hydrogen peroxide decay rate constants in surface-water samples from Sharpes Bay (in June and September), Jacks Lake, Ontario, Canada, from the East (Station 23), Central (Station 84), and West Basin (Station 357) of Lake Erie and the Chesapeake Bay, plotted as a function of bacteria...

The first detailed investigation of the reaction kinetics was reported in 1984 (68). The reaction of bis(pentachlorophenyl) oxalate [1173-75-7] (PCPO) and hydrogen peroxide cataly2ed by sodium saUcylate in chlorobenzene produced chemiluminescence from diphenylamine (DPA) as a simple time—intensity profile from which a chemiluminescence decay rate constant could be determined. These studies demonstrated a first-order dependence for both PCPO and hydrogen peroxide and a zero-order dependence on the fluorescer in accord with an earher study (9). Furthermore, the chemiluminescence quantum efficiencies Qc) are dependent on the ease of oxidation of the fluorescer, an unstable, short-hved intermediate (r = 0.5 /is) serves as the chemical activator, and such a short-hved species "is not consistent with attempts to identify a relatively stable dioxetane as the intermediate" (68). 

Based on the analytical figures of merit of the methods in Table 1, the best precision and selectivity are accomplished by using the decay rate rather than the formation rate or conventional CL-measured parameters such as the peak height or area under the CL curve. Table 2 gives the selectivity factor, expressed as decay-rate and peak-height tolerated concentration ratio, for the CL determination of hydrogen peroxide using SF-CLS. As can be seen, the selectivity factor was quite favorable in most instances. 

The majority of investigators found the reaction to be first order in hydrogen peroxide. Accordingly, the decay of H202 can be described formally by the rate law... 

The reaction pathway appears to involve the formation of superoxoiron(III) bleomycin prior to that of activated bleomycin , which appears to be a peroxoiron(III) complex, although the source of the second electron is uncertain. Activated bleomycin can be synthesized directly by reaction of hydrogen peroxide with iron(III)-bleomycin. In the absence of DNA, activated bleomycin decays to the Fem complex, with damage to the antibiotic. In the presence of DNA, degradation products appear with a rate of formation equal to the rate of loss of activated bleomycin. The polymeric products of DNA degradation have not been characterized, but they decompose to give free bases, released in the sequence T> C> A> G. 

Lepidocrocite (-y-FeOOH) has also been used as a catalyst for Fentonlike reactions [54]. First-order decomposition of hydrogen peroxide was observed in the presence of this catalyst. Peroxide decay at 20 g/L catalyst was found to be pseudo-first-order and pH-dependent, with rate constant values reported from 0.102 hr-1 at pH 3.3 to 0.326 hr-1 at pH 8.9. In this system benzoic acid degradation was fastest at the low pH value. Under these conditions, acid dissolution of the lepidocrocite was observed to produce... 

In a second serie of experiments the concentration of hydrogen peroxide in the droplets was varied in the range from 2 x 10 5 to 5 x 10 3 mol l l while the other experimental conditions were kept constant. The pH of the droplets was set to 4.0. Again the S(IV)aq decay showed a pseudo-first-order kinetic. The measured rate constants are plotted in a log-log diagram in Figure 5 in dependence of the respective H2O2-concentration. 

The oxidation of ascorbic acid in certain reactions has given evidence of an intermediate with the properties of a free radical which could be formed by one-electron oxidation. Thus, the rate-limiting step of ascorbic acid oxidation by Fe + and H2O2 was this one-electron oxidation (G12). Such a radical has now been identified in hydrogen peroxide-ascorbic acid solutions at pH 4.8 by electron paramagnetic resonance spectroscopy. The free radical, commonly referred to as monodehydroascorbic acid, decayed in about 15 minutes at this acid pH. It was also formed during the enzymatic oxidation of ascorbic acid by peroxidase (Yl). The existence of the monodehydroascorbic acid radical makes possible very... 

Hydrogen peroxide, cuprum perchloride, and perchloric acid were used as acceptors in aqueous solutions. The experimentally observed process of hydrated electron decay in solutions of these three substances obeyed the first-order reaction law. Kinetic characteristics of observed processes were calculated by the method of the least squares using 15-20 photo-oscillograms. Values of rate constants of corresponding pseudo-first order reactions are shown in Table I. There one can see also values of bimolecular rate constants calculated on the basis of above data. The rate constant does not vary occasionally within some limits but it changes monotonously with the variation of concentration. This may mean that some process of the decay of the intermediates was not taken into consideration. It was shown in earlier work (J), that we had satisfactory agreement with the experiment supposing that the process was the mono-molecular intermediates decay. 

Several pathways can account for the decomposition of hydrogen peroxide In natural waters. Some of these decay processes not only remove H2O2, but also result In the oxidation of chemicals, possibly Including various pollutants, that are present In natural waters. These processes Include direct oxidation (5), peroxidase-catalyzed oxidation (6), and free radical oxidation Initiated by photochemical or metal-catalyzed decomposition (7). Little Is known about the significance and rates of these various processes under environmental conditions, but they have all been shown to occur rapidly with certain organic substrates In the laboratory. 

Figure 3. Dependence of first-order rate constant for decay of hydrogen peroxide on concentration of Chiamydomonas sp.

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