Hydrogen peroxide constants

Hydrogen peroxide in aqueous solution is a weak dibasic aeid the dissociation constant for H2O2 — -1- HO2 is 2.4 x 10 ... 

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). 

Ca.ro s Acid. Caro s acid is named after Heinrich Caro (1834—1910), who first described its preparation and oxidi2ing properties ia 1898. Hereia Caro s acid is used to designate the equiUbrium mixtures that result from mixing hydrogen peroxide and sulfuric acid. These Hquids mix iastantly, generating a considerable amount of heat. The equiUbrium constant for this reaction is 0.1 (62). 

Fig. 2. Steps in advanced oxidation process (AOPs) involving o2one, hydrogen peroxide, and uv light of 254 nm. ( D) represents the doublet state ( ) represents quantum yield, and the other numbers associated with the reaction arrows are rate constants in units of (Af-s). Dashed arrows indicate...

Hydrogen peroxide, when pure, is an almost colourless (very pale blue) liquid, less volatile than water and somewhat more dense and viscous. Its more important physical properties are in Table 14.11 (cf. H2O, p. 623). The compound is miscible with water in all proportions and forms a hydrate H2O2.H2O, mp —52°. Addition of water increases the already high dielectric constant of H2O2 (70.7) to a maximum value of 121 at 35% H2O2, i.e. substantially higher than the value of water itself (78.4 at 25°). 

Hydrogen peroxide is a somewhat stronger acid than water, and in dilute aqueous solutions has p a(25°) = 11.65 0.02, i.e. comparable with the third dissociation constant of H3PO4 (p. 519) ... 

In a solution at a constant H+ concentration, iodide ions react with hydrogen peroxide to produce iodine. 

Heterogeneous rate constants, 12, 113 Hofmeister sequence, 153 Hybridization, 183, 185 Hydrodynamic boundary layer, 10 Hydrodynamic modulation, 113 Hydrodynamic voltammetry, 90 Hydrodynamic voltammogram, 88 Hydrogen evolution, 117 Hydrogen overvoltage, 110, 117 Hydrogen peroxide, 123, 176... 

HO-oxidation of an individual NMHCj produces H02 radicals with a yield aj, and oxidation of the NMHC oxidation product produces H02 in stoichiometric amount The lumped coefficients or yields a and p need not be integers, and represent the effectiveness of a particular NMHCj in producing RO2. and H02 radicals (lumped together as HO2) that will then oxidize NO. to N02 in processes such as R6 and R13, producing one net ozone molecule each. Alternatively, when the NO. concentration is low, peroxyl radicals may form PAN (as in R22) or hydrogen peroxide (as in R33) which are other oxidant species. In this formulation, transport is expressed by an overall dilution rate of the polluted air mass into unpolluted air with a rate constant (units = reciprocal time dilution lifetime=1// ). This rate constant includes scavenging processes such as precipitation removal as well as mixing with clean air. 

Uncertainties in Photochemical Models. The ability of photochemical models to accurately predict HO concentrations is undoubtedly more reliable in clean vs. polluted air, since the number of processes that affect [HO ] and [H02 ] is much greater in the presence of NMHC. Logan et al (58) have obtained simplified equations for [HO ] and [HO2 ] for conditions where NMHC chemistry can be ignored. The equation for HO concentration is given in Equation E6. The first term in the numerator refers to the fraction of excited oxygen atoms formed in R1 that react to form HO J refers to the photodissociation of hydrogen peroxide to form 2 HO molecules other rate constants refer to numbered reactions above. 

Hydroxylactonization of (—)-29 with hydrogen peroxide and formic acid gave the tricyclic compound 90, [a] +47.9° (ethanol). Reduction of 90 with lithium aluminum hydride, followed by acetylation, provided the triacetate 91, which was converted into the pentaacetates 92 and 93 by aceto-lysis. 0-Deacetylation of 92 and 93 gave 7 and 94, respectively The physical constants of all enantiomeric carba-sugars are listed in Table 1. 

The hexamine cobalt (II) complex is used as a coordinative catalyst, which can coordinate NO to form a nitrosyl ammine cobalt complex, and O2 to form a u -peroxo binuclear bridge complex with an oxidability equal to hydrogen peroxide, thus catalyze oxidation of NO by O2 in ammoniac aqueous solution. Experimental results under typical coal combusted flue gas treatment conditions on a laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

It is worth mentioning that an attempt was made by Tsao and Willmarth to determine the acid dissociation constant of HO2. The reaction between hydrogen peroxide and peroxydisulphate was used for the generation of the HO2 radical. However, these experiments, like others where the HO2 radical is studied under steady-state conditions, could yield only a value of acidity constant multiplied by a coefficient consisting of a ratio of kinetic parameters. Unfortunately, in this case there are no independent data for the kinetic coefficient, and the value of cannot be evaluated. Considering the kinetic analogue of the titration curve it can be stated only that ionization of HO2 becomes important in the pH range from 4.5-6.5. The value of acidity constant of HO2 obtained by Czapski and Dorfman is (3.5 + 2.0)x 10 mole.l. . ... 

The GSH reductase inhibitor l,3-bis(2-chloroethyl)-l-nitrosourea (BCNU) also promotes corneal swelling in the isolated cornea. The addition of GSH prevents the action of BCNU as the cornea needs a constant supply of NADPH for maintaining adequate concentrations of reduced glutathione for the detoxification of hydrogen peroxide. It has been shown that hydrogen peroxide and BCNU primarily affect the permeability of the endothelial cells rather than the active processes transporting sodium and chloride ions across the membrane (Riley, 1985). 

GSHPx, CAT and SOD, which normally protect cells from free-radical damage have not been detected in aqueous humour. It has therefore been su ested that damage by free radicals and hydrogen peroxide to the anterior segment is prevented by a non-enzymatic extracellular oxidoreduction system involving a constant supply of reduced glutathione to the aqueous fluid from the ciliary epithelium, cornea and lens (Riley, 1983). 

It is well established that aerobes constantly produce small amounts of oxygen-derived species, such as the superoxide radical (02 ), hydrogen peroxide (H2O2) and hypochlorous acid (HOCl), the latter being generated by... 

The electrochemical rate constants for hydrogen peroxide reduction have been found to be dependent on the amount of Prussian blue deposited, confirming that H202 penetrates the films, and the inner layers of the polycrystal take part in the catalysis. For 4-6 nmol cm 2 of Prussian blue the electrochemical rate constant exceeds 0.01cm s-1 [12], which corresponds to the bi-molecular rate constant of kcat = 3 X 103 L mol 1s 1 [114], The rate constant of hydrogen peroxide reduction by ferrocyanide catalyzed by enzyme peroxidase was 2 X 104 L mol 1 s 1 [116]. Thus, the activity of the natural enzyme peroxidase is of a similar order of magnitude as the catalytic activity of our Prussian blue-based electrocatalyst. Due to the high catalytic activity and selectivity, which are comparable with biocatalysis, we were able to denote the specially deposited Prussian blue as an artificial peroxidase [114, 117]. 

Dilling, W.L., Gonsior, S.J., Boggs, G.U., Mendoza, C.G. (1988) Organic photochemistry. 20. A method for estimating gas-phase rate constants for reactions of hydroxyl radicals with organic compounds from their relative rates of reaction with hydrogen peroxide under photolysis in 1,1,2-trichlorotrifluoroethane solution. Environ. Sci. Technol. 22, 1447-1453. 

Rate Constants (in M 1s 1) and Equilibrium Constants and Activation Parameters for Iron(III)-TAML Catalyzed Disproportionation of Hydrogen Peroxide (Eq. (17)) at 25°C and 0.1 M Phosphate... 

Figure 10 shows the instrumental setup used to implement the APP-CLS approach. It consists of (a) a CSTR that is a thermostated 10-mL glass reaction vessel accommodated in a commercially available spectrofluorimeter (a Hitachi F2000 model in this case) (b) a four-channel peristaltic pump with three channels used to dispense the reagent solutions and the fourth to keep the volume of the reaction mixture in the CSTR constant the three reagent solutions are as follows (1) 0.15 M hydrogen peroxide (2) 0.15 M sodium thiocyanate, 0.15 M sodium hydroxide, and 1.95 x 10 3 M luminol and (3) 6.0 x 10 4 M copper(II) sulfate ... 

Due to these reactions, hydrogen peroxide is an intermediate product of radiolysis of aerated water. Rate constants of free radical reactions with dioxygen and hydrogen peroxide are collected in Table 3.19. For the characteristics of solvated electron and information about its reactions, see monographs [219-223],... 

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