Cerium hydrogen peroxide reaction with

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. 

Hydrogen peroxide. The diluted solution, which may contain nitric or hydrochloric acid in any concentration between 0.5 and 3M or sulphuric add in the concentration range 0.25 to 1.5M, is titrated directly with standard cerium(IV) sulphate solution, using ferroin or /V-phenylanthranilic acid as indicator. The reaction is ... 

The effect on the induced reaction of the acidity cannot be satisfactorily considered with the kinetic data available. It was mentioned that the rate of reaction between hydrogen peroxide and peroxydisulphate is at maximum at about pH 5. In contrast, the value of Fj obtained cerimetrically goes through a flat maximum in the pH range from 1-2. This maximum should be regarded as an apparent one because the hydrolysis of cerium(IV) is considerable at pH s higher... 

Worked Example 8.1 In solution, the cerium(IV) ion reacts with aqueous hydrogen peroxide with a 1 1 stoichiometry. The reaction has a rate constant of 1.09 x 106 dm3 mol s. How fast is the reaction that occurs between CeIV and H202, if [CeIV] = 1CT4 mol dm-3 and [H202] = 1CT3 mol dm-3 ... 

Chromates, vanadates, and cerium salts give colour reactions with the reagent and should therefore be absent. Iron salts give a yellow colour with hydrogen peroxide, but this is eliminated by the addition of syrupy phosphoric acid. Fluorides bleach the colour (stable [TiF6]2 ions are formed), and large amounts of nitrates, chlorides, bromides, and acetates as well as coloured ions... 

Catalysis of the decomposition by several metal ions has been reported . The order in peroxomonosulphate was found to be one, except for reaction with cobalt(II) and cerium(IV) (both second-order in the sulphate) and manga-nese(II) (half-order). Formation of a complex with cerium(IV) and peroxomonosulphate has been both asserted and denied . Catalysis by copper(II) is not significant unless manganese is also added, at least in the presence of some hydrogen peroxide ... 

In the acid-catalysed process, dominant for pH less than 2, the products isolated may be oxygen (below 0.5 Af acid), peroxomonosulphuric acid, a mixture of the two, or may contain detectable amounts of hydrogen peroxide or ozone. The formation of hydrogen peroxide (at 98 °C in 2 M HjSO ) has been examined and shown to be catalysed by a number of metal ions. Under all conditions examined the oxygen liberated arises entirely from the peroxide . Exchange between S-labelled sulphate and peroxodisulphate proceeds very slowly, if at all, in this region . Further, it appears probable that this particular decomposition path does not involve intermediates which react at appreciable rate with cerium-(III) It has been suggested that the initial, overall, reaction is... 

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... 

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... 

An analytical application of cerimetry that is stiU in use is the determination of hydrogen peroxide by titration with a 0.1 M cerium(IV) sulfate solution to the pale blue end point of a ferroin indicator (Hurdis and Romeyn, 1954). The reaction is ... 

The fast reaction between cerium(IV) sulfate and hydrogen peroxide is useful to determine the concentration of hydrogen peroxide in solution by cerimetric titrations (see section 3). However, the decomposition of hydrogen peroxide by cerium(IV) in perchloric acid solution is slow at pH values above 0.7 (Baer and Stein, 1953 Ardon and Stein, 1956), at which colloid polymeric cerium(IV) complexes are formed. These are able to interact with hydrogen peroxide to afford colored complexes that are only slowly decomposed. At very low pH values, the polymeric complexes are not formed and decomposition of hydrogen peroxide is fast. 

As a result of reactions 9.9 to 9.15, a layer of cerium oxy-hydroxide with extremely low solubility is formed on top of the surface starting at the cathodic areas and extending all over the surface by a nucleation and grain growth mechanism [152]. The general equation of the process with hydrogen peroxide will then be written as [153] ... 

Hiatt et a/.34a-d studied the decomposition of solutions of tert-butyl hydroperoxide in chlorobenzene at 25°C in the presence of catalytic amounts of cobalt, iron, cerium, vanadium, and lead complexes. The time required for complete decomposition of the hydroperoxide varied from a few minutes for cobalt carboxylates to several days for lead naphthenate. The products consisted of approximately 86% tert-butyl alcohol, 12% di-fe/T-butyl peroxide, and 93% oxygen, and were independent of the catalysts. A radical-induced chain decomposition of the usual type,135 initiated by a redox decomposition of the hydroperoxide, was postulated to explain these results. When reactions were carried out in alkane solvents (RH), shorter kinetic chain lengths and lower yields of oxygen and di-te/T-butyl peroxide were observed due to competing hydrogen transfer of rm-butoxy radicals with the solvent. 

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