Reactions of Cerium iv

Ionic strength and specific ion effects have been investigated in the oxidation of mandelic acid by cerium(iv) sulphate. Unlike the reaction in HCIO4 where there is spectrophotometric and kinetic evidence for complex formation, under these conditions there is a first-order rate dependence of both oxidant and reductant. The replacement of H+ by Li+, Na+, or K+ produces only a minor change in rate and has no effect on the activation parameters. Rate laws which are essentially similar have been established in the reactions with cyclohexane-1,4-diol cyclopentanone, and methyl isopropyl ketone. The enol form of the substrate is favoured as the active reagent in the latter two reactions. 

Khanna, K. Behari, and B. Krishna, Proc, Nat. Acad. Sci., India Sect. A, 1976, 

Saxena, K. M. Richards, and B. Krishna, Z. phys. Chem. (Leipzig), 1978, 

Oscillating chemical reactions continue to be investigated in sulphate media. Addition of a-monobromo-ketone, one of the products of the BrO 3-Ce v-cyclohexanone and Br03 -Ce -cyclopentanone systems has been shown to decrease and, in some instances, suppress the initial induction period. The inhibitory effects of Cl ions have also been described. In the gallic acid-bromate reaction catalysed by [Fe(phen)3]+/ + the enol is the reactive form of the organic substrate. The mechanism proposed is essentially that of 

Holecek, K. Handlir, and J. Klikorka, Coll. Czech. Chem. Comm., 1979, 44, 1060. 

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In the reaction of cerium(IV) salts in acid solution with reducing agents, the simple change... 

Reactions of cerium(IV) ions To study these reactions use a 01m solution of cerium(IV) sulphate, Ce(S04)2.4H20 or cerium(IV) ammonium sulphate Ce(S04)2.2(NH4)2S04.2H20. These solutions should contain a few per cent of free sulphuric acid. Both solutions are orange-yellow. On standing a fine... 

The synthesis and preliminary X-ray structure of the first organometallic Ce(IV) complex Ce(CsH8)2 was reported in 1976 [115] and reproduced in 1985 [116] by the reaction of cerium(IV) isopropoxide with triethylaluminum in the presence of cyclooctatetraene, as shown in Figure 8.35. The accurate sandwich molecule structure of cerocene has been eon-firmed by an X-ray structural study on the methyl substituted cerocene [Ce(MeCOT)2] [117], Subsequently, two more substituted cerocene analogs have been synthesized via a more efficient method, for example, controlled oxidation of cerium(III) precursors and one of these complexes has been structurally characterized [118],... 

Post-irradiation reduction of cerium(IV) occurs when concentrated sodium nitrate solutions in air-saturated 0.4M sulfuric acid containing 10 4M cerium(IV) are irradiated with a kilocurie G0Co source. A kinetic study of the reaction of cerium(IV) with nitrous acid established that the postirradiation reaction is reduction of cerium(IV) by nitrous acid. A computer program SLOPULSE was used to determine G(HNO>) by kinetic analyses of both the post-irradiation reduction of cerium(IV) and reduction of cerium(IV) by nitrous acid during irradiation. The importance of nitrous acid as an intermediate is evidenced by the high values for G(HN02)- For example, about 70% of the reduction of cerium(IV) in 5.0M sodium nitrate solutions is caused by nitrous acid with G(CeIU) = 6.04 and G(HNG2) = 2.22. 

Since G(Celn)fast in the presence of 10 3M isopropyl alcohol can be attributed to 2Gh2o2 + Goh, nitrate ion must inhibit reaction of cerium-(IV) with H atom. This is consistent with the proposal of Bakh (3) that H atom reduces nitrate ion according to Reaction f. However, N02 must not reduce cerium (IV) but forms nitrous acid by combination as proposed by Bakh (3), according to Reaction b. It is the effect of isopropyl alcohol on G(Cem)fast and G(HN02) which forces us to propose the sequence of Reactions a and b as the mechanism for reduction of cerium (IV) by nitrous acid. 

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... 

Greco, Cesca and Bertolini have reported that Ce(CgHQ)2 is an air-sensitive, brownish-red crystalline material that is synthesized in the reaction of cerium(IV) isopropoxide with triethylaluminum in cyclooc-tatetraene (COT). 3 ... 

A bimetallic mono-[8]annulene complex containing cerium(lll) and aluminuro(III) has been synthesized.67 [8]Annulenecerium(III)-di-u isopropoxydiethylaluminum was synthesized by the reaction of cerium(IV) isopropoxide with triethylaluminum in the presence of cyclooctatetraene and toluene as the solvent. 

The reaction of cerium(iv) complexes with phosphine has been investigated. Halide complexes are reduced at least ten times faster than sulphate or perchlorate analogues. There is no direct reaction between the oxidant and phosphine, and the reaction... 

The oxidation of co-ordinated thiol at carbon rather than at sulphur has been reported in the reaction of cerium(iv) [and neptunium(vi)] with (mercaptoacetato-05 )bisethylenediaminechromium(m). 

Y.K. (1982) Silver(I) catalysed oxidation of water with cerium(IV) in aqueous perchloric acid solutions and the reaction of cerium(IV) with silver(I) in the presence of bipyridyl. J. Chem. Soc, Dalton Trans., 549 -553. 

At this stage reference may be made to potential mediators, i.e. substances which undergo reversible oxidation-reduction and reach equilibrium rapidly. If we have a mixture of two ions, say M2+ and M +, which reaches equilibrium slowly with an inert electrode, and a very small quantity of cerium(IV) salt is added, then the reaction ... 

Method A Standardisation with arsenic (III) oxide. Discussion. The most trustworthy method for standardising cerium(IV) sulphate solutions is with pure arsenic(III) oxide. The reaction between cerium(IV) sulphate solution and arsenic(III) oxide is very slow at the ambient temperature it is necessary to add a trace of osmium tetroxide as catalyst. The arsenic(III) oxide is dissolved in sodium hydroxide solution, the solution acidified with dilute sulphuric acid, and after adding 2 drops of an osmic acid solution prepared by dissolving 0.1 g osmium tetroxide in 40mL of 0.05M sulphuric acid, and the indicator (1-2 drops ferroin or 0.5 mL /V-phenylanthranilic acid), it is titrated with the cerium(IV) sulphate solution to the first sharp colour change orange-red to very pale blue or yellowish-green to purple respectively. 

The course of the reaction has not been elucidated. Probably redox reactions involving cerium(IV) and arsenic(III) are catalyzed by iodide ions and organic iodine compounds with methylene blue acting as a redox indicator. 

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... 

The use of cerium(IV) ammonium nitrate (CAN) as a catalyst for an aza-Diels-Alder reaction was reported in two different publications. In one report Perumal and co-workers react a variety of anilines 86 and aldehydes 87 with enamine 88 in the presence of 5 mol% CAN to form a series of tetrahydroquinolines 89. The reactions were performed at room temperature with very short reaction times and in good yields. In addition, the resulting tetrahydroquinolines could be oxidized to the corresponding substituted quinolines using 2.5 eq of CAN in high yields <06TL3589>. 

As compounds exhibiting enhancing effects on CL reactions, a variety of phenols, e.g., firefly luciferin and 6-hydroxybenzothiazole derivatives [12,13], 4-iodophe-nol [14], 4-(4-hydroxyphenyl)thiazole [15], 2-(4,-hydroxy-3 -methoxy-benzyli-dene)-4-cyclopentene-l,3-dione (KIH-201) [16], and 2-(4-hydroxyphenyl)-4,5-diphenylimidazole (HDI) and 2-(4-hydroxyphenyl)-4,5-di(2-pyridyl)imidazole (HPI)[17] (Fig. 6A), and phenylboronic acid derivatives, e.g., 4-phenylylboronic acid [18], 4-iodophenylboronic acid [19], and4-[4,5-di(2-pyridyl)-l //-imidazol-2-yl]phenylboronic acid (DPPA) [20] (Fig. 6B), in the luminol/hydrogen peroxide/peroxidase system are well known. Rhodamine B and quinine are used as sensitizers in the CL-emitting reaction between cerium (IV) and thiol compounds. This CL reaction was successfully applied to the sensitive determination of various thiol drugs [21-32],... 

Write a balanced half-reaction for the reduction of cerium(IV) ions to cerium(III) ions. 

Clement and Paris [17] have devised a pair of methods for the determination of cobalt in steels, especially materials encountered in the nuclear industry. In the first technique, suitable for the analysis of solutions containing 8 to 160 mM cobalt(II), iron(III) is used to oxidize cobalt(II) in a picolinic acid medium, after which the resulting iron(II) is titrated po-tentiometrically with a standard solution of cerium(IV). An alternative procedure, for concentrations of cobalt(II) below 8 mM, involves a constant-current coulometric titration with electrogenerated cerium (IV) to measure the iron(II) that arises from the original reaction between cobalt(II) and iron(III). 

Stoichiometries. From preliminary observations on the reactions between cerium(IV) and each of Cr(C204)3 3, aV-Cr(0H2)2(C204)2 , and Cr(0H2)4C204+ it was evident that carbon dioxide is evolved, as identified by precipitation of barium... 

Measurement of Reaction Rates by Titrimetry. The rates of cerium(IV) consumption by each of Cr(C204)3 3, m-Cr(OH2)2(C204)2 and Cr(0H2)4C204+ were also measured by a direct titrimetric method. Solutions were prepared and mixed as for the spectrophotometric procedure. At appropriate times aliquots of the reactant solutions were quenched with known volumes of standard ferrous sulfate, and the excess ferrous ion was titrated potentiometrically with standard potassium dichromate,... 

The possible influence of oxygen was checked by using the titrimetric method to study the consumption of cerium(IV) by m-Cr(OH2)2(0204)2 in the absence of oxygen. Component solutions were introduced into a closed container, flushed with nitrogen, and without exposure to the atmosphere, mixed, and allowed to react. The usual method for quenching was used. Comparison of the results for a series of solutions studied in this way with the results for similar solutions studied by the ordinary procedure indicated that the exclusion of oxygen has no measurable effect on the rate of the reaction. 

Additional Studies on m-Cr (0H2)2(C204)2 Reaction. The kinetics of the rw-Cr(OH2)2(0204)2 reaction with cerium(IV) have been investigated in further detail. 

It is apparent that Cr(C2C>4)3 3, m-Cr(OH2)2(0204)2 , and Cr(0H2)4C2044 react smoothly with cerium(IV) in acidic-sulfate media, 1 mole of oxalate being oxidized for each 2 moles of cerium(IV) consumed. The observations made are consistent with the view that the three reactions proceed, at least initially, according to the stoichiometries represented by the respective Reactions 3,1, and 2. The initial absorbances of reactant solutions (values obtained by extrapolation of measured absorbances to zero time) agree well with the values calculated, on the basis of Beer s law, from the absorptivity coefficients of the components. Further, as the reactions in 1.83Af sulfuric acid proceed, the absorbances of the solutions move toward the values expected for the assumed products at rates which demonstrate the reactions are first order in cerium(IV) and complex—see, for example, Figure 2. We thus find no indication that reaction intermediates contribute measurably to the absorbances of reactant solutions, or that reaction conditions cause the rapid equilibration of any of the oxalato complexes with other species... 

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