Oxidation by Ce

Investigated is the influence of the purity degree and concentration of sulfuric acid used for samples dissolution, on the analysis precision. Chosen are optimum conditions of sample preparation for the analysis excluding loss of Ce(IV) due to its interaction with organic impurities-reducers present in sulfuric acid. The photometric technique for Ce(IV) 0.002 - 0.1 % determination in alkaline and rare-earth borates is worked out. The technique based on o-tolidine oxidation by Ce(IV). The relative standard deviation is 0.02-0.1. 

Oxidation by Ce(IV) sulphate of antimony(III) chloride in follows a kinetic law ... 

It is essential to characterize the reactant species in solution. One of the problems, for example, in interpreting the rate law for oxidation by Ce(IV) or Co(III) arises from the difficulties in characterizing these species in aqueous solution, particularly the extent of formation of hydroxy or polymeric species. We used the catalyzed decomposition of HjOj by an Fe(III) macrocycle as an example of the initial rate approach (Sec. 1.2.1). With certain conditions, the iron complex dimerizes and this would have to be allowed for, since it transpires that the dimer is catalytically inactive. In a different approach, the problems of limited solubility, dimerization and aging of iron(III) and (Il)-hemin in aqueous solution can be avoided by intercalating the porphyrin in a micelle. Kinetic study is then eased. 

Cerium(IV) oxidations of organic substrates are often catalysed by transition metal ions. The oxidation of formaldehyde to formic acid by cerium(IV) has been shown to be catalysed by iridium(III). The observed kinetics can be explained in terms of an outer-sphere association of the oxidant, substrate, and catalyst in a pre-equilibrium, followed by electron transfer, to generate Ce "(S)Ir", where S is the hydrated form of formaldehyde H2C(OH)2- This is followed by electron transfer from S to Ir(IV) and loss of H+ to generate the H2C(0H)0 radical, which is then oxidized by Ce(IV) in a fast step to the products. Ir(III) catalyses the A -bromobenzamide oxidation of mandelic acid and A -bromosuccinimide oxidation of cycloheptanol in acidic solutions. ... 

In perchloric acid, hexoses and pentoses are oxidized by Ce(IV) via formation of two complex intermediates. The first is partly oxidized following Michaelis-Menten kinetics and partly dissociated to the second, which is oxidized more slowly than the former.180 The first step in the oxidation of aldoses by Tl(III) in the same medium involves the C-l-C-2 cleavage of the aldehydo form of the sugar. Thus, D-glucose gives D-arabinose and formic acid. With an excess of oxidant the final product is carbon dioxide.181 In the presence of a catalytic amount of sulfuric acid in acetic acid, Tl(III) oxidizes maltose and lactose to the corresponding disaccharide aldonic acids. The reaction showed activation enthalpies and enthropies characteristic of second-order reactions.182... 

The complexes evolve N2O essentially quantitatively on oxidation by Ce-(804)2. Because of their instability and concurrent oxidation of X to X2, this reaction is best performed by adding [Ru(NH3)5(N20)]l2 to a frozen, degassed solution of Ce(S04)2 and allowing dissolution of [Ru(NH3)s(N20)]l2 to take place on warming to room temperature. The I2 liberated is easily trapped before analysis of the evolved gas. 

Other preparative methods make use of cyclobutadiene intermediates which react with acetylene compounds. The first method was reported by Criegee and his coworker 6) who prepared tetramethylcyclobutadiene from the 1,2-diiodo derivative (4). In the second method, the cyclobutadiene irontricarbonyl complex is oxidized by Ce,v to produce free cyclobutadiene (5) 7). This reaction is widely used for the synthesis of cyclobutadiene. 

Tris (2,2 -bipyridyl)ruthenium(II) has been used as the basis of CL detection of a wide range of compounds after oxidation to the ruthenium(III) complex. The analyte interacts with the ruthenium(III) complex reducing it to the ruthenium(II) complex in an excited state, which then emits CL as it returns to the ground state. In the present study, a flow injection procedure for SPAX determination with CL detection was proposed in which ruthenium(II) was oxidized by Ce(IV) solution. The CL emission intensity depended on the concentration of the analyte in the CL system. This work describes a relatively sensitive and rapid chemiluminescence method for SPAX determination based on tris(2,2 -bipyridyl)ruthenium(II) without sample pretreatment process. 

In no case was the formation of perovskite-like materials evidenced by means of XRD. Also, reactivity tests did not give any improvement with respect to the single metal fluorides the activity substantially turned out to be an average of that one of the single metal oxides. In the case of the CeF4/AgF mixture, we identified the Agp2 phase that is formed after AgF oxidation by Ce and... 

Stable. Easy to reduce. Prepared from lower oxidation states by oxidation by Ce ", Mn04 , Ag , CI2 or Br03 . 

Ruthenium(IV) [Ru(bipy)2py(OH2)] + can be oxidized by Ce or by controlled potentieil electrolysis to [Ru(0)(bipy)2pyp (hiu-o at 792cm ) which oxidizes PPhj to OPPhj (Scheme 33) 1136,1201-1204 i8q labeling shows that O transfer from Ru=0 to PPhj occurs via first order kinetics with rate constant A = 1.75 x 10 [Ru(0)(bipy)2py] has been used electrocatalytically... 

The blue dimer c/s,c/s[(bpy)2(H20)Ru(III)0Ru(III)(0H2)bpy)2] (Fig. 7) was among the first molecular species to show catalyzed water oxidation by Ce(lV) through a reaction mechanism which has been elucidated in detail by spectroscopic, electrochemical, and chemical mixing experiments [18] (Scheme 1). The key point... 

DFT and spectroscopic results indicate that, following the attack of water at the Ru(V)=0 sites, one has the formation of a first intermediate described as a terminal peroxide coordinated to Ru(lll) which undergoes further oxidation by Ce(IV) to give a 7 coordinated Ru(lV) complex where acts as a chelating ligand. Oxygen can be evolved both from [Ru(lV)00] and [Ru(V)00] structures following water attack. 

The primary motivation for these studies is the analysis of the reactivity patterns of organic compounds, when Ce(IV) is used as an oxidant. These patterns are determined for the most part by product analysis of selected series of organic compounds. The results obtained in two studies that bear more directly on the chemical behavior of Ce(IV) as an oxidant for hydrocarbons have been interpreted to indicate different mechanistic behavior of Ce(IV). In a product study of the oxidation of isodurene (1,2,3,5-tetramethyl benzene) by ceric ammonium nitrate compared to anodic oxidation, Eberson and Oberrauch (1979) concluded that the oxidation by Ce(IV) occurs via a H atom transfer from the alkylaromatic compound to Ce(IV). Badocchi et al. (1980) measured the variation of second-order rate constants for the oxidation of a series of alkylaromatic compounds with added Ce(III). These results along with those from the determination of kinetic deuterium isotope effect were dted to support a mechanism involving radical cations. The Ce(IV)/Ce(III) functions as an electron acceptor/donor in such a mechanism. 

Finally, there are two reports describing the oxidation of phenols. The first is from Pelizzetti et al. (1976) in which 4,4 -biphenyl diol is oxidized by Ce(IV) in perchlorate medium at reduced temperature. The product of oxidation, which proceeds at stopped-flow lifetimes, is the corresponding 4,4 -biphenoquinone. The oxidation reaction was studied under second-order conditions and indicates no acid concentration dependence with very rapid rates. The activation parameters are AH = 38 ( 13) kJmol and AS = —13 ( + 42) Imol consistent with an intramolecular rate-determining step. 

The simplest of the aldehydes is formaldehyde, whose oxidation by Ce(IV) in 2.0 M perchlorate media has been studied by Husain (1977). It is presumed that formaldehyde exists as a ketohydrate in acid solution (the hydration constant is lO M ). Michaelis-Menten kinetics describe the results, indicating the formation of a precursor complex. A detailed mechanism permits a calculation of the equilibrium quotients for formation of the Ce(IV)-formohydrate complex and the ionization of a... 

The rate of ceric oxidation of malonic add and its diethyl ester in acetic acid/sul-furic acid solutions has recently been reported by Vaidya et al. (1987). They find no evidence for precursor complex formation in either system. The reactive Ce(IV) species appear to be Ce(S04)2 ( 2) and CefSO ) " k 2). The second-order rate parameter for the oxidation of malonic add is 40 times greater than that for the ester. Oxidation of the ester is proposed to occur through the enol form yielding a malonyl radical analogous to that identified by Amjad and McAuley. Foersterling et al. (1987) find that the second-order rate constant for malonic acid oxidation by Ce(lV) in sulfuric acid is in excellent agreement with the value of Vaidya et al. They observe that Ce(III) does inhibit the reaction in sulfuric add, which they attribute to a reversible Ce(IV) malonic acid rate-controlling step. 

The use of Ce(IV) to probe the kinetics of outer-sphere electron transfer reactions has centered on compounds of the title metal ions whose primary coordination spheres (in the reduced state at least) are substitution inert on the time scale of electron transfer reactions. For example, Cyfert et al. (1980) investigated the effects of the variation of ionic strength on the rate of Fe(phen) oxidation by Ce(IV) in 0.125 M H2SO4 with different supporting electrolytes (table 9). Variation in the concentrations of NaCl or NaClO in the range of O.l-l.O M changed the rate constants from 1.08 to 0.81 X 10 s and 1.03 to 0.56 x 10 M s, respectively (25°C). The varia-... 

The study by Linn and Gould (1987) reported that Ce(IV) did not react with biphosphitopentaamineCo(III), whereas the hypophosphito complex reacts to yield decreasing amounts of Co(II) as the initial Ce(IV) concentration is increased. The proposed mechanism invokes competing reaction paths, internal electron transfer to the Co(III) center, and further oxidation by Ce(IV). 

The thioether is oxidized by Ce(IV) to its cation radical, which binds 0 or reacts with water. Both routes ultimately yield sulfoxide. The... 

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