Hydrogen peroxide with cerium oxide

The e.s.r. spectra of oxovanadium ions in redox systems have been reported. The interaction of free-radicals generated using the reactions of cerium(iv) or ferrous ions with hydrogen peroxide with oxovanadium(v), produces a complex which decays in a first-order manner (k = 6-2 s at 22 °C) with the formation of vanadium(iv). The oxidation of phenetidines by bromate is catalysed by vanadium(v) and kinetic parameters involved in the interactions of various substrates with vanadium(v) have been correlated with electron configurations. The redox behaviour of oxo-3,5-disulphocatecholatovanadium(v) has been studied and the acidity dependence in the reaction with phenylethyl alcohol reported. In the... 

In the patent literature, extensive work was reported on developing slurries for SiC CMP with very few details and no explanation of the polish mechanisms. For example, Urushidani et al. [14] explored the use of Ce02, Cr203, and Fe203 as abrasives for polishing 6H-SiC but the RRs were not reported. Desai et al. [15] used several oxidizers such as hydrogen peroxide, ammonium cerium (IV) nitrate, oxone, periodates, iodates. 

Other examples are the use of osmium(VIII) oxide (osmium tetroxide) as catalyst in the titration of solutions of arsenic(III) oxide with cerium(IV) sulphate solution, and the use of molybdate(VI) ions to catalyse the formation of iodine by the reaction of iodide ions with hydrogen peroxide. Certain reactions of various organic compounds are catalysed by several naturally occurring proteins known as enzymes. 

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

Catalytic systems are by far the most studied methods for oxidizing alkyl side chains. Cobalt(II) acetate and cerium(III) acetate in the presence of a bromide ion activator in acetic acid with hydrogen peroxide are used for the transformation of toluenes to benzaldehydes, carboxylic acids and benzyl bromides (Figure 3.65). 

Redox chemistry with hydrogen peroxide is pH dependent for example, cerium(IV) is reduced to cerium(III) in acid, whereas cerium(III) is oxidized to cerium(IV) in alkali. The reductive step may be used to solubilize cerium in extraction from ores. 

Oxidation of iron(II) ions to iron (III) oxidation occurs slowly upon exposure to air. Rapid oxidation is effected by concentrated nitric acid, hydrogen peroxide, concentrated hydrochloric acid with potassium chlorate, aqua regia, potassium permanganate, potassium dichronate, and cerium(IV) sulphate in acid solution. 

In a second reaction, the activated hydrogen (taken up from the catalyst) is oxidized with molecular oxygen. According to Macrae, this second step proceeds through hydrogen peroxide (as an intermediate), the existence of which was demonstrated by the formation of cerium peroxide when the reaction was carried out in the presence of cerium (III) hydroxide. The hydrogen peroxide produced is rapidly decomposed by the catalyst. 

Oxidation of phenols. Barton et al. carried out some studies on the oxidation of phenols with hydrogen peroxide and samples of old cerium(IV) oxide. It was later found that the oxidations reported require activation if freshly prepared pure dioxide is used. It is dissolved in hot H2SO4, precipitated at pH 12 with sodium hydroxide, and then heated at ca. 900° for 24 hr. This material in combination with 30% H2O2 oxidizes phenols such as (1) to hydroperoxy-cyclohexadienones (2) in good yield. Other reported reactions are the oxidation of (4) to the oxide (5) and of (6) to juglone (7). This oxidation system probably... 

Oxidation of phenols. Barton et aO carried out some studies on the oxida-lion of phenols with hydrogen peroxide and samples of old cerium(IV) oxide. II was later found that the oxidations reported require activation if freshly pi e pared pure dioxide is used. It is dissolved in hot H2SO4, precipitated at pH... 

The oxides, (R.E.)203, are readily soluble in acids unless they have been ignited at high temperatures, in which case they dissolve more slowly. However, cerium(IAr) oxide dissolves in acids exceedingly slowly. It may be converted to the anhydrous sulfate by heating with concentrated sulfuric acid or may be reduced to cerium (III), and thus rendered soluble, by means of hydrogen peroxide or alkali metal iodide in acidic solution. 

The hydrous rare earth oxides are now washed into a 12-gal. crock, 8 gal. of water is added with stirring, the precipitate is allowed to settle, and then it is washed repeatedly by siphoning off wash waters until they are only shghtly basic. The hydrous oxides are then dissolved in concentrated nitric acid (with the aid of 3 per cent hydrogen peroxide if the quantity of cerium is significant). 

Formation of carbonyl compound derivatives Hasan Mehdi et al. [29] reported the use of imidazolium ILs as solvents for organic transformations with tetravalent cerium salts. Urea-hydrogen peroxide in the presence of catalytic amoimt of magnesium bromide efficiently oxidizes primary and secondary benzylic alcohols into the corresponding aromatic aldehydes and ketones [30]. Margarida M. Antrmes et al. [31] reported IL 1-butyl-3-methylimidazolium chloride ([bmim]Cl) as solvent, in the transformation of o-glucose into 5-(hydroxymethyl)-2-furaldehyde at 120 °C. 

Hydrogen peroxide decomposition catalysts can be added to ionomer membranes in small amounts to slow down the decomposition of the ionomer during fuel cell operation. Additions of cerium and manganese, in both oxide and ionic forms, have been shown to increase the oxidative stability of membranes by orders of magnitude, and fuel cells prepared with such membranes have shown substantial increases in hfetime under aggressive hot and dry operation [60-62]. Unfortunately, these metal ions and oxides can consume ion exchange capacity and negatively impact fuel cell performance. 

Recent attempts to apply cerium(III) chloride (hydrate) and lanthanum(III) acetate to the Lewis acid-catalyzed oxidation of phenols with hydrogen peroxide proved futile in fact, they provided the worst results of over 20 metal salts studied (Ito et al., 1983). Ruthenium trichloride was even better than boron triiluoride, presumably activating the peroxide molecule rather than serving as a one-electron oxidant. 

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