Hydrogen peroxide, catalytic effects

Chemical kinetics at tubular electrodes (systems of circular cross-section) have been considered recently in [77, 78]. Both for catalytic ErevCcat and for E vCirr (follow-up) mechanisms the theory of linear-sweep voltammetry and cyclic voltammetry was elaborated. The effects of the reaction rate constant, of the flow velocity, and of the potential scan rate on the shape of current curves are presented graphically. The deductions derived from both theories were tested on the reduction of Fe(III) in the presence of hydrogen peroxide (catalytic system) and on the oxidation of 1,4-phenylenediamine in alkaline medium (E vCin. mechanism). 

Hemocyanin from molluscan and crustacean sources is able to decompose hydrogen peroxide catalytically (Ghiretti, 1956 Felsenfeld and Printz, 1959). This catalase-like action is due to the presence of copper in the hemocyanin molecule. However, equivalent amounts of copper alone have no effect on the decomposition of HgOj. Among the copper complexes of the amino acid tested, only Cu-arginine is active. 

Concentration Effects. The reactivity of ethyl alcohol—water mixtures has been correlated with three distinct alcohol concentration ranges (35,36). For example, the chromium trioxide oxidation of ethyl alcohol (37), the catalytic decomposition of hydrogen peroxide (38), and the sensitivities of coUoidal particles to coagulation (39) are characteristic for ethyl alcohol concentrations of 25—30%, 40—60%, and above 60% alcohol, respectively. The effect of various catalysts also differs for different alcohol concentrations (35). 

Because osmium tetroxide is expensive, and its vapors are toxic, alternate methods have been explored for effecting vic-glycol formation. In the aliphatic series, olefins can be hydroxylated with hydrogen peroxide with the use of only a catalytic amount of osmium tetroxide. Anhydrous conditions are not necessary 30% hydrogen peroxide in acetone or acetone-ether is satisfactory. The intermediate osmate ester is presumably cleaved by peroxide to the glycol with regeneration of osmium tetroxide. When this reaction was tried on a A -steroid, the product isolated was the 20-ketone ... 

In this work, catalysts containing iron supported on activated carbon were prepared and investigated for their catalytic performance in the direct production of phenol fiom benzene with hydrogen peroxide and the effect of Sn addition to iron loaded on activated carbon catalyst were also studied. 

The performance of various solvents can be explained with the help of the role of these solvents in the reaction. These solvents help in keeping teth benzene and hydrogen peroxide in one phase. This helps in the easy transport of both the reactants to the active sites of the catalyst. The acetonitrile, and acetone adsorption data on these catalysts (Fig. 6), suggests that acetonitrile has a greater affinity to the catalytic surface than acetone. There by acetonitrile is more effective in transporting the reactants to the catalyst active sites. At the same time, they also help the products in desorbing and vacating the active sites. 

Gallot et al. (1998) studied the catalytic oxidation of 3-hexanol with hydrogen peroxide. The data on the effect of the solvent (CH3OH) on the partial conversion, y, of hydrogen peroxide are given in Table 4.1. The proposed model is ... 

Syn-hydroxylation of alkenes is also effected by a catalytic amount of osmium tetroxide in the presence of hydrogen peroxide. Originally developed by Milas, the reaction can be performed with aqueous hydrogen peroxide in solvents such as acetone or diethyl ether.58 Allyl alcohol is quantitatively hydroxylated in water (Eq. 3.12).59... 

Metal-ion catalysis of hydrogen peroxide decomposition can generate perhydroxyl and hydroxyl free radicals as in Scheme 10.26 [235]. The catalytic effects of Fe2+ and Fe3+ ions are found to be similar [235]. It is not necessary for the active catalyst to be dissolved [237], as rust particles can be a prime cause of local damage. The degradative free-radical reaction competes with the bleaching reaction, as illustrated in Scheme 10.27 [237]. Two adverse consequences arise from the presence of free radicals ... 

Other cationic surfactants such as TTAB, DTAB, DODAB, STAC, CEDAB, and DDDAB have been used in CL reactions with less frequency. Thus, tetradecyltrimethylammonium bromide [TTAB] has been used to increase the sensitivity of the method to determine Fe(II) and total Fe based on the catalytic action of Fe(II) in the oxidation of luminol with hydrogen peroxide in an alkaline medium [47], While other surfactants such as HTAB, hexadecylpiridinium bromide (HPB), Brij-35, and SDS do not enhance the CL intensity, TTAB shows a maximum enhancement at a concentration of 2.7 X 10 2 M (Fig. 11). At the same time it was found that the catalytic effect of Fe(II) is extremely efficient in the presence of citric acid. With regard to the mechanism of the reaction, it is thought that Fe(II) forms an anionic complex with citric acid, being later concentrated on the surface of the TTAB cationic micelle. The complex reacts with the hydrogen peroxide to form hydroxy radical or superoxide ion on the... 

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