Cerium addition initiated

An alternative process for opening bastnasite is used ia Chiaa high temperature roastiag with sulfuric acid followed by an aqueous leach produces a solution containing the Ln elements. Ln is then precipitated by addition of sodium chloride as a mixed sulfate. Controlled precipitation of hydroxide can remove impurities and the Ln content is eventually taken up ia HCl. The initial cerium-containing product, oace the heavy metals Sm and beyond have been removed, is a light lanthanide (La, Ce, Pr, and Nd) rare-earth chloride. 

Several reviews and research papers discussing the application and extension of this method have appeared.40 For example, Weber et al.41 reported an interesting result in which cerium acted as a counterion in the modified proline auxiliary (SAMEMP 40) for selective addition of organocerium reagents to hydrazones. The initial adduct was trapped with either methyl or benzyl chloro-formate to afford the stable /V-aminocarbonatc 41 (Scheme 2-24). From this example readers can see that this proline chiral auxiliary can be used not only for a-alkylation but also for nucleophilic addition, which is discussed in detail later. 

Commercial catalysts vary in the degree to which they are regenerable at reactor temperatures as shown on Figure 18. The initial SO2 removal for all five materials was adjusted to an equal basis by varying the amount of additive used 0.8% magnesia-based, 3% lanthanum-based, 10% of both cerium/alumina and... 

It is obvious that if the initiation step of a polymerization with the alcohol-cerium (IV) system takes place by addition of the alcohol radical to the monomer, assuming that cellulose acts similarly, one may expect grafting to occur (46). 

As it can be observed in Fig. 4, when only methane is added to the feed, catalyst A shows the best behaviour, followed by catalysts B and U. According to this, the addition of cerium to the zirconium hydroxide increases the activity of the zirconia-supported palladium catafysts. Comparing the performance of the cerium-containing catalysts, it is remarkable that catalyst B presents a poorer performance, than catalyst A (slightly lower initial conversion and foster deactivation). This result suggests that the interaction between Pd and Ce, revealed in the TPR experiments, does not enhance the activity of the active phase (Pd). In contrast, the interaction Ce-Zr in catalysts A increases the thermal stability, considered as the main foctor for preventing catalyst deactivation in these reactions [9]. 

Reaction of 1,2,3-triazine with nucleophiles usually leads to ring opening via attack at C-4. However, silyl enol ethers react with chloroformate/l,2,3-triazine salts to give 5-substituted 2,5-dihydro-l,2,3-triazines, which can be re-aromatised using cerium(lV) ammonium nitrate. In this case, initial addition of the electrophile takes place at N-2, leading to the specific activation of C-5. ... 

Finally, cerium(IV) ammonium nitrate can serve as the radical source by itself, generating NO3 radicals If by photolysis. The addition of such radicals to cyclo-alkynes 20 initiates an interesting tandem reaction [12]. Transannular hydrogen atom abstraction by the vinyl radical 21 affords the intermediate 22, which undergoes a 5-exo cyclization to the radical 23. In the last step, the ketone 24 is formed by elimination of NO2 in moderate yield thus, the overall sequence can be described as a self-terminating radical reaction (Scheme 7). 

Oxidative functionalization of alkenes. Activated by cerium(IV) ammonium nitrate in methanol Ph2Se2 initiates addition to an alkene. Some unsaturated alcohols undergo phenylselenocycloetherification, and in case that the activation is by a photoinduced electron transfer process the phenylseleno group of the products can be replaced. 

In the oxidation of organic species, terminal oxidation products are CO2, HCOOH (formic acid) and H2O. As Ce(lV) is typically the hmiting reagent, intermediate products are often identified to confirm reaction pathways. Since cerium(IV) is a one-electron oxidant and the organic substrates are two-electron donors, the chemistry of the oxidized substrate involves subsequent reactions of free radical species. The presence of free radicals is verified experimentally by the initiation of polymerization upon addition of methacrylic acid, or other easily polymerized organic species. In some cases the radicals are stable enough to have been studied by ESR (electron spin resonance) methods. There are a few examples of reactions which exhibit an inverse dependence on [Ce(III)], which can be interpreted in terms of hydrolytic dimers or reversible reactions of the type... 

Cerium oxide-based technology was then modified for European diesel passenger cars with the addition of a relatively small amount of zeolite as well as additional precious metal to meet European requirements for gaseous CO and HC reductions. The purpose of the zeolite was to adsorb gaseous HC (mostly vm-burned diesel fuel) during cold start conditions and subsequently release them to the catalyst once the latter was sufficiently active to initiate catalytic oxidation on the Pt (138). As the exhaust temperature and catalyst light-off is achieved, the HC desorbing from the zeolite is catalytically oxidized over the Pt. 

In a transition-metal-free approach to indolo[2,3-d]quinolizines, our group has shown that the four-component reaction between tryptamines, a,p-unsaturated aldehydes, p-dicarbonyl compounds, and ethanol in the presence of cerium(IV) ammonium nitrate as a Lewis acid catalyst gives direct access to indolo[2,3-a]quinolizines 93 (Scheme 3.29) [72], On the basis of previous work on related multicomponent reactions [73], this domino transformation was proposed to comprise the initial formation of a p-enaminone by reaction between the primary amine and dicarbonyl components, its Michael addition to the unsaturated aldehyde, a hemiaminalization reaction, and a final Pictet-Spengler reaction initiated by the formation of a vinylo-gous acyliminium species. This method could also be extended to the preparation of benzo[fl]quinolizines. 

The intermediacy of azido-radicals in the cerium (iv) oxidation of metallic azides to molecular nitrogen has been demonstrated by olefin trapping a-azido-jS-nitratoalkanes are formed (Scheme 153), with a regioselectivity consistent with initial addition of the azido-radical. 

Addition of iodide and the pseudohalide azide (NJ) had a similar effect as addition of chloride, whereas addition of nitrate, sulfate or perchlorate ions had no effect. The oscillation period after the initial state was found to be identical with that of the unperturbed system. When the amount of chloride added is less than the amount of cerium(IV) present initially, no observable inhibition is expected. This system is more sensitive to addition of chloride after the oscillating reaction has started than to initial addition of chloride ions smaller amounts of chloride ions are required to induce inhibition or to suppress the oscillations completely. Because of this inhibitory effect, the glass vessels used to prepare the solutions for a Belousov-Zhabotinsky experiment should be clean and free of chloride ions. Moreover, in the preparation of the ferroin indicator solution 1,10-phenanthroline must be used in its free base form and not in the form of the hydrochloride salt. If one wants to monitor the periodic changes in the chemical potential of the solution, one must use a reference electrode that does not leak chloride ions. Conventional calomel electrodes or silver/silver chloride electrodes are not suitable, but double-junction version of these electrodes are adequate. 

Jin and co-workers obtained 1.5-nm ultra-thin ceria nanorods from a cerium stearate precursor. The reaction was carried up at 270°C in 1-octadecene with the addition of 1-octadecanol. The authors ascribed the formation of nanorods to the oriented attachment of ultra-small ceria nanocrystals grown in the initial stage of the reaction. 

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