Cerium oxide-Hydrogen peroxide

Cerium(IV) oxide-Hydrogen peroxide, Ce02-H2 02. Cerium(IV) oxide is supplied by Alfa. 

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. 

Returning to the explanation of induced reactions, we can say the following. Friend s proposal , according to which the error in the H2O2 determination is caused by reaction (83) catalyzed by manganese(II) or cerium(III) formed in the primary reaction between hydrogen peroxide and permanganate or cerium(IV) cannot be accepted. The reaction between the ions mentioned and peroxydisulphate at room temperature is very slow, and, furthermore, the increase in acidity —in contrast to its effect on the induced reaction —promotes the oxidation. There is... 

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. 

Separations by selective precipitation depend primarily upon basicity differences. These differences can only operate when equilibrium between the solid phase and the solution is complete. Cerium is seperated commercially based on its reduced basic property in the tetravalent state. By adjusting the pH of a mixed rare-earth solution the cerium may be selectively precipitated out as a cerium(IV). In mixed rare-earth solutions the rare-earths arc present in the trivalent state. To precipitate the cerium. cerium(lll) must be converted into cerium(lV) by an oxidizing agent, e.g. hydrogen-peroxide. The more soluble trivalent rare-earths arc dissolved causing concentration of the less soluble ccrium(IV),... 

Until very recently the evidence for the existence of the HO2 radical in a condensed phase was based lai gely on kinetic measurements. However, recently it has been reported that the NMR spectrum of the HO2 radical may be observed in ice irradiated at very low temperatures (8, 11) and at room temperature in an aqueous solution (iO), where hydrogen peroxide is being oxidized by cerium (IV). 

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. 

---