Hydrolysis of cerium

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 temperature of the oil bath must be kept below 100°C to minimize the hydrolysis of cerium(lll) chloride heptahydrate to CeOCI. 

The other area where cerium cations may have an influence is in complex formation in the solution immediately adjacent to the surface, in the dissolution and precipitation phase via replacement of Al(OH)[ " species with Ce(OH) " species. For example, moderate levels of Ni have been observed on the surface of boehmite-like stractures developed after treatment in solutions containing NiCl and NaCl, and it was proposed that oxide formation involved Ni/Al complex formation in the solution adjacent to the developing oxide. Although hydrolysis of cerium ions in solution is well known, and mixed AFCe precipitates may form at the metal/solution interface, the low concentration of cerium observed on the surface of the alloys treated in CeCl solution suggests that substitution of Al(OH) species with Ce(OH) species does not occur under the conditions of pseudoboehmite growth. Certainly at room temperature Ce(OH)j forms at higher... 

Equation (3.8) can, however, be easily extended to include polymeric species. The same technique can then be utilised to derive any hydrolysis species stability constant from the average ligand number formulation. Where polymeric species form, the average ligand number is dependent upon the metal concentration utilised in each experiment as is shown in Figure 3.4. These data have been obtained for the hydrolysis of cerium(IV). When polymeric hydrolysis species are to be determined, it is necessary to perform a series of experiments at different total metal concentrations. In this case, it is necessary to assume the stoichiometry of the species likely to form, and typically, a computer program is then used to investigate which of the proposed species, and their associated... 

Danesi, P.R. (1966) Studies on the hydrolysis of metal ions. Part 58. The hydrolysis of cerium(IV) in 3 M (Na)NOj medium. Acta Chem. Scand., 21, 143-151. 

Cerium(IV) is a strong oxidising agent and, as such, it has a number of chemical applications as an oxidant. In studying the hydrolysis of cerium(IV), a number of studies have utilised oxidation-reduction reactions in determining the relevant stability constants. As a tetravalent cation with a relatively small ionic radius, the hydrolysis of cerium(IV) occurs at very low pH. Consequently, data have been provided that show that the metal ion is extensively hydrolysed even at a pH of around 0 (i.e. Imoll" H" ) (Baes and Mesmer, 1976). Cerium(IV) is used as an analogue for plutonium(IV) in nuclear fuel manufacturing studies. 

The data given in Table 8.55 are only for perchlorate media. There is also some data reportedin nitrate media. Wadhawan, Sankhla and Mehrotra (1973) reported a stability constant (log j) for CeOH of 0.99 in 1 moll HNOj. This value appears to be in reasonable agreement with that given by Everett and Skoog (1971) in perchloric acid at the same ionic strength and temperature. The datum of Wadhawan et al. is retained in the present review. Danesi (1966) studied the hydrolysis of cerium(IV) in a 3moll (H,Na)N03 medium and at 25 C. Only polymeric species were postulated, with evidence provided for the formation of Ce2(OH)3, Ce2(OH) and Ceg(OH)22. There is no confirmation of the formation of these species elsewhere in the literature, and these species have not been proven to form for other tetravalent cations. As such, they are not retained in this review. 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

The second group includes SAHs obtained by radical grafting of acrylonitrile (AN) on natural polymers, mostly starch, under the action of cerium initiators [43 -46, 50, 51], The proper crosslinked hydrophilic polymer is formed at the stage of alkali hydrolysis of grafted polyacrylonitrile (PAN), the final characteristics depending on many factors, in particular the sort of starch [46], the methods of its preparation [51], the component ratio, etc. The nature of starch is exhibited through... 

Results and Discussion. Of the 12 samples of starch graft copolymer synthesized, half were hydrolyzed to anionic polyelectrolytes. Synthesis data on these 6 samples are given in Table 2. These particular samples were chosen for hydrolysis because the samples can be intercompared to see the effect of synthesis variables on ultimate product properties. Samples 5, 8, and 11 have the same mole ratio of cerium ion to starch backbone, N, in their reaction mixture. Samples 7, 8, and 9 all have the same refctable mass per starch molecule,... 

Cerium(III) nitrate is used for the separation of cerium from other rare-earth elements. It also is used as a catalyst in hydrolysis of phosphoric acid esters. 

Separation based on valency change.—The easy oxidation of Ce3 to Ce4+ permits its isolation from other rare earths. The separation of cerium is usually performed by selective leaching with acids, or by complete dissolution [129, 130] followed by hydrolysis. The solvent extraction behaviour of Ce(N03)4 has been extensively studied. Among the various extractants, alcohols, ethers, organic and inorganic acids, ketones etc., TBP proved to be most advantageous in large scale operations [131,132]. 

Cerium(IV) ammonium nitrate (CAN) is effective for oxidative hydrolysis of phenyl esters substituted by hydroxyl, methoxyl, and dimethylamino groups in CH3CN-H20 at 0°. 

Bamann et al.119 also found that the hydrolysis of di- and tri-peptides is catalyzed by rare earth ions at pH 8.6. Cerium(IV) and Cem were particularly effective even at a temperature of 37 °C. The same reactions with La111 as a catalyst were much slower and only occurred at an appreciable rate at 70 °C. Many of these reactions merit further study. 

In the quantitative determination of cerium, use is made of the fact that cerous oxalate is insoluble in neutral and acid solution. Since a quantitative yield is not necessary in this preparation, some of the cerium is sacrificed to insure complete removal of any iron that may be present. In order to have a neutral solution for the hydrolysis of the iron, a slight excess of ceric oxide is used. 

C (190-196) and by the thermal decomposition of the trifluoride at 800°C in air (191, 197, 198). The lanthanum compound itself may also be prepared by hydrolysis of the trifluoride (199) and by the reaction of the oxide with molten sodium fluoride (200). On treatment with CFCI3 (201), it is converted back to the trifluoride. The cerium analog has been prepared from Ce02 by reaction with CeF3 at 2750°C (202) or with CeF3 and cerium metal at 900°C in a nickel tube (203). The infrared spectra of these solids have been reported (204). 

The cerium hydroxyl carbonate could be obtained through hydrothermal treatments, for example the hydrothermal treatment of cerium oxalate (Li et al., 1996). The most feasible way is to utilize the sealed reaction of Ce with urea CO(NH2)2 in aqueous solution. The hydrolysis of urea in water leads to (NH4)2C03 and provides the base to change the... 

Use Separation of cerium from other rare earths, catalyst for hydrolysis of phosphoric acid esters. 

Y butenolides 22 were obtained in good yields and as essentially single stereoisomers (Table 5.2). In these studies, the tat leucine derived SchifTbase ligand 18a gave rise to the best diastereo and enantioselectivities, and even with the less expensive valine derived Schiffbase ligand, the products were formed with 97% ee. Removal of the N aryl group was readily accomplished with cerium ammonium nitrate followed by acidic hydrolysis of the intermediate aza quinone. 

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