Hydrogen peroxide second-order rate constants

Photolytic. A carbon dioxide yield of 46.5% was achieved when aniline adsorbed on silica gel was irradiated with light (X >290 nm) for 17 h (Freitag et al., 1985). Products identified from the gas-phase reaction of ozone with aniline in synthetic air at 23 °C were nitrobenzene, formic acid, hydrogen peroxide, and a nitrated salt having the formula [CeHsNHsl NOs" (Atnagel and Himmelreich, 1976). A second-order rate constant of 6.0 x 10 " cmVmolecule-sec at 26 °C was reported for the vapor-phase reaction of aniline and OH radicals in air at room temperature (Atkinson, 1985). 

The production of ethylene from methional (3-thiomethylpropanal) was induced by the oxidation of xanthine by dioxygen catalysed by xanthine oxidase The second-order rate constant for the reaction of hydroxyl radicals with methional was estimated by pulse radiolysis to amount to 8.2 x lO s while the superoxide anion reacted more slowly The short lag period of the ethylene production induced by the oxidation of xanthine could be overcome by the addition of small amounts of hydrogen peroxide. The reaction was inhibited by SOD or by catalase, and by scavengers of hydroxyl radicals, so that the Haber-Weiss reaction was implicated... 

Figure 4. Second-order rate constant k(2) for oxidation of sulfur(lV) by hydrogen peroxide defined according to d[S(VI)]/dt = k(2>[H202][S(IV)], as a function of solution pH. Solid curve is fit to data by Overton (29). Dashed lines (slope = -1 corresponding to H+ catalyzed oxidation of HS03 in pH range 3 to 6) are arbitrarily placed to encompass most of the data. Temperature 25°C except as indicated. For references see (29).

The bromide ion does not appear to react with one form of the enzyme-hydrogen peroxide complex. It is clear that at least two pH-dependent intermediates are present, which react with bromide to yield the oxidized bromine species. The second-order rate constant for the reaction between bromide and these peroxo-intermediates w is estimated to be 1.7 X 10 s" Bromide also acts as an inhibitor of the enzyme in a... 

The dramatic increases in reaction rates that occur in enzyme-catalyzed reactions can be seen for representative systems in the data given in Table 2.2.4 The hydrolysis of the representative amide benzamide by acid or base yields second-order rate constants that are over six orders of magnitude lower than that measured for ben-zoyl-L-tyrosinamide in the presence of the enzyme a-chymotrypsin. An even more dramatic rate enhancement is observed for the hydrolysis of urea The acid-catalyzed hydrolysis is nearly 13 orders of magnitude slower than hydrolysis with the enzyme urease. The disprotionation of hydrogen peroxide into water and molecular oxygen is enhanced by a factor of 1 million in the presence of catalase. 

CAT reacts with hydrogen peroxide with a rate constant of an order of 10 M" s in a broad range of pH [210]. Reactions 14 and 15 are very fast, the values of kj and kj being 1.7x10 M s and 2.6x10 M s, respectively, for rat liver CAT [207]. The turnover number (number of peroxide molecules decomposed per CAT molecule per second) is in the case of CAT and hydrogen peroxide 3.5x10 [211]. 

Common quenchers are oxygen, xenon, hydrogen peroxide, iodide, and amines. The constant fe is a second-order rate constant for a diffusion-controlled process. It is related to the translation diffusion coefficients of the fluorescence molecule and the quencher and hence is related to the radius of encounter. 

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. 

Hydrogen peroxide in aqueous solution decomposes by a first-order reaction to water and oxygen. The rate constant for this decomposition is 7.40 X 10 /s. What quantity of heat energy is initially liberated per second from 2.00 L of solution that is 1.50 M H2O2 See Appendix C for data. 

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