Cerium complexes hydrolysis

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 hydrolysis of J-diketonate-modified cerium(IV) isopropoxide leads to the formation of colloidal solutions or gels. The complexation ratio (x = acac/Ce) appears to be the key parameter to tailor the size of cerium oxide particles. Precipitation is observed when x < 0.1, whereas sols are obtained when 0.1 < X < 1. The mean hydrodynamic diameter of these particles decreases from 450 to 15 A when x goes from 0.1 to 1. Only solute molecular clusters are formed when the complexing ratio becomes larger than 1 (1 < x < 2). 

Purex process, 941 Cerium(III) complexes cerium(IV) system water cleavage, 495 peptides hydrolysis, 425 Cerium(IV) complexes peptides hydrolysis, 425 Cerium-144 recovery, 959... 

Hydrolysis studies of the tetravalent cations are limited to Ce and the light (Pa, Th, U, and Pu) actinides (tables 8B and 9). Only in strong acid media do the tetravalent ions exist free of hydrolysis. Similarly, only at very low concentrations are mononuclear hydroxides of significance. For Ce(I V), stability constants have been determined for bi-, ter-, tetra-, and dodeca-cerium units and for species with molecular weights as large as 40,000 (Hardwick and Robertson 1951, Danes 1967, Louwrier and Steemers 1976). X-ray measurements of thorium and uranium solutions show polynuelear complexes built from... 

A DFT study of the hydrolysis mechanism of bis-p-nitrophenyl phosphate (BNPP) catalysed by a mononuclear zinc complex of 1,5,9-triazacyclododecane (45) was reported. The lanthanum tetraazamacrocycle (46 M=La) and its cerium counterpart (46 M = Ce) " were both highly effective catalysts for the hydrolysis at pH 5.7-7.6 of BNPP, the former enhancing the rate by a factor of 10 -fold. 

It is interesting, that phenyl cerium iodide obtained from Phi and Ce in the presence of Lil, unlike "common" PhCel, reacts with 1,2,2-trifluorostyrene and gives a mixture of cis-and trans-isomQTS of PhC(F)=C(F)CH(Ph)(H2)30H after hydrolysis [67]. In this case high reactive complexes of ate-iypQ containing lowvalent cerium are proposed to be formed ... 

The effects of added M + ions, M = Mn, Ni, Cu, or Zn, on rates of aquation and of racemization of [Cr(ox)3] are attributed to their effects on the hydration shell around the complex ion rather than to simple ion-pairing. The markedly different effects of different alkali-metal cations on base hydrolysis of the [Co(NH3)5Br] + cation" and on the cerium(rv) oxidation of methylmandelic acid " may have a similar explanation. Non-electrostatic factors are also important in salt effects on the formate plus chromate and iodide plus bromate reactions." Observed salt effects on rates of hydrolysis of a variety of anions such as [BFi]-, [SiFe] , and [S20 ] ... 

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