Cerium derivatives

The production of cerium derivatives begins with ore beneficiation and production of a mineral concentrate. Attack on that concentrate to create a suitable mixed lanthanide precursor for later separation processes follows. Then, depending on the relative market demand for different products, there is either direct production of a cerium-rich material, or separation of the mixed lanthanide precursor into individual pure lanthanide compounds including compounds of pure cerium, or both. The starting mineral determines how the suitable mixed lanthanide precursor is formed. In contrast the separation... 

Production of Cerium Derivatives. Moderately pure (90—95%) cerium compounds can be made from rare-earth chloride through oxidation with, for example, hypochlorite to produce an iasoluble cerium hydrate. The other lanthanides remain ia solutioa. The hydrate, oa calciaatioa, coaverts to Ce02. 

Addition of 2,6-dimethoxypyrimidine-4-cerium chloride 371 to the chiral lactone 370 occurred without racemization of the chiral center, and the product 372 was subsequently used in a successful total synthesis of (—)-7-epicylindro-spermopsin <2002JA4950, 2005JOC1963>. The cerium reagent was prepared situ from 4-bromo-2,6-dimeth-oxypyrimidine by sequential addition of butyllithium and cerium trichloride. Addition of the same dimethoxypyrimidine-4-cerium derivative to a chiral lactam has also been reported <1999J(P1)1193>. 

The mononuclear unsolvated constitution has been structurally defined for the early (Ce) [61] and late ( Sc , Y, Yb) elements (Table 3) [62,63]. The geometry of the Sc and Y derivatives is described as approximately trigonal planar with the metal center 0.13 and 0.09 A, respectively, displaced from the 03-plane. In contrast, the cerium derivative exhibits a pyramidal structure (Fig. 7). As in the Ln[N(SiMe3)2]3 complexes, the cerium atom is disordered and... 

Production Processes for Cerium and Cerium Derivatives (Overview)... 

Cerium-oxalate, -carbonate and -hydroxide are considered to be the most important precursors for cerium-derivatives on a commercial scale. The cerium derivatives are yielded from these compounds by additional chemical and/or physical treatment. For example, cerium oxide may be formed easily by calcining cerium carbonate or/and cerium oxalate respectively. 

A fraction of Ce, La. Nd and Pr derived from bastnasite or monazite is a typical feedstock in the recovery process of cerium on a commercial scale. Separation of the rare-earth elements may be achieved by splitting the mixed rare-earth elements into a cerium/lanthanum and didymium (Nd/Pr) fraction first. The cerium/lanthanum fraction may be used as a further feedstock in a second extraction stage and will yield high pure cerium and lanthanum solution respectively. Cerium can then be precipitated as. for example, an oxalate or a carbonate which may be used as precursor for cerium derivatives. 

A major technological application of steadily growing importance for cerium is the vehicle emission control to remove pollutants from vehicle (auto-exhaust) emissions [14]. This market currently consumes a significant portion of the annually production of cerium derivatives. 

The ability of cerium oxide to act as an oxidizing agent underlies the potential use of various cerium derivatives as additives to aid combustion. In order to reduce the particle emissions in Dieser cerium containing compounds are used as additives in this application [15]. 

Addition of zinc(II) chloride to the lithium compound 4 gave the zinc derivative 6, which is stable even at 50 °C in tetrahydrofuran. The palladium-catalyzed coupling reaction of the zinc salt with vinyl iodides, vinyl triflates and aryl iodides produced vinyl and aryl derivatives 7 and 8 (Table 1, entries 11-16). Cerium derivatives of cyclopropenone acetals were prepared by addition of the lithium salt 4 to a suspension of anhydrous cerium(III) chloride in tetrahydrofuran at — 70 C. The resulting organocerium reagent coupled with oc-aminoaldehydes (Table 1, entry 17). ° ... 

As shown by the rearrangement of 10, the second double bond of the pericyclic system can also be incorporated in a ring. Cope substrates 13. 16, 19. and 22 are obtained with high diastereoselectivity by addition of the corresponding cerium derivatives to 58 r)- 1063 "ftig dichlorocerium reagents proved to be superior to the vinyllithium reagents, as the latter cause excessive enolization. 

Although the metal was not isolated, micro quantities of pure AcjOj, AcF3, AcC13, etc. were obtained and shown to be iso-morphouswith the corresponding lanthanum and cerium derivatives. 

The cerium derivative, Ce5Te3[TeSi(TMS)3], was structurally char-... 

The NMR experiments with cerium derivatives (RC5H4)4Ce2( Li SR )2 show that the thiolates do exchange bridging ligands in a solution [11]. This process in most cases results in some broadening of the resonance. 

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