Transformations cerium

The inhibition of thymidylate synthase is recognized as a viable tqiproach to the control of cancer and DNA viral infections. Mertes and coworkers proposed S-quinone derivatives of 2 deoxyuridine S -I iosphate as potential irreversible inhibitors of this enzyme and prepared the quinones (32a) by oxidative demethylation of the appropriate dimethoxyarenes using CAN. Interestingly, the quinones (32b) were also prepared from the corresponding dimethoxyarenes but using silveifU) oxide and nitric acid in aqueous dioxane to effect this transformation. Cerium(IV) ammonium nitrate could not be used, due to precipitation. 

Mosander discovered the new element in the following manner he transformed cerium (III) oxide into the carbonate, which he dissolved in nitric acid and evaporated to dryness. He pulverized the residue to a fine powder and treated it with cold dilute nitric acid, in which the more basic lanthanum oxide was dissolved, while cerium oxide remained undissolved. He then separated the lanthanum from... 

Earlier studies made Mosander suspect that cerium oxide obtained from cerite contains a foreign substance. He attempted to separate it by shaking cerium oxide hydrate with water, introducing chlorine gas to transform cerium oxydul into cerium oxide and the unknown substance into chlorure. Insoluble yellow cerium oxide was precipitated in the operation. From the filtrate he again precipitated the solute with potassium hydrate, shook the suspension and again introduced chlorine gas. Further cerium oxide was precipitated and the rest was dissolved. He repeated this operation several times, in this manner he succeeded to separate the total amount of cerium oxide and obtain a chlorure from which potassium hydrate precipitated a hydrate that did not turn yellow in air and when treated with chlorine, was completely soluble in water. Thus the separation was terminated, and the oxide which is not further oxidized by chlorine gas was termed lanthanum oxide, as generally known. 

Some metals oxidise at a rate which decreases, rather than increases (Type 2 in Fig. 1.89). Cerium behaves in this fashion at temperatures between 40°C and 130°C, and Loriers has suggested that the curve derives from the competition between the two oxides Ce20j and Ce02. It was proposed that the inner layer Ce2 0j was continuous and grew under diffusion control but transformed at a constant rate to an outer layer of Ce02. That is, if we writer and z as the thickness of the inner and outer layers respectively, then... 

Another well-known transformation of carbonyl derivatives is their conversion to pinacols (1,2-diols) via an initial one-electron reduction with highly active metals (such as sodium, magnesium, aluminum, samarium iodide, cerium(III)/ I2, yttrium, low-valent titanium reagents (McMurry coupling), etc.), amines, and electron-rich olefins and aromatics as one-electron donors (D).43 Ketyl formation is rapidly followed by dimerization44 (equation 22). 

Both iron(IIl) and cerium(IV) salts in methanol transformed ( )-9-pro-penylcarbazole into a comparable dimer (101) however, the Z isomer, in which steric factors restrict conjugation between the double bond and the... 

Bromide 280 (derived by bromination of silyl enol ether 270) undergoes both zinc- and cerium-mediated cleavage under mild and essentially neutral conditions, and was used to prepare the nucleoside-containing C-glycoside 282 (Scheme 73) [ 112,113], The aldehyde 281 used in this transformation was exceptionally sensitive to basic conditions which completely precluded use of a conventional enolate obtained by deprotonation of ketone 265 (Sect. 4.3.1). 

The promotion ability of cerium is attributed to its capability to form crystalline oxides with lattice defects, which may act as active sites [25]. In addition, the presence of cerium oxide in the catalyst improves its thermal stability and mechanical resistance [26]. Cerium is the most frequent additive used for preparation of the automobile converter catalyst that transforms carbon monoxide, hydrocarbons and nitrogen oxides [27,28]. 

A final inclusion here is quinone 100 that is available in 85% yield from cerium(IV) demethylation of diether 99 it has yet to be transformed into alkylidene derivatives168. 

Many metal chlorides when heated with an excess of nitric acid are converted into the nitrates. Thus, J. L. Smith found that the transformation occurs with potassium or sodium chloride in the presence of 7 to 8 parts of nitric acid J. S. Stas said that at 40°-50°, potassium, sodium, or lithium chloride require respectively 3, 4, and 5-5 parts of nitric acid. J. L. Smith said that ammonium chloride and nitric acid yield nitrous oxide. H. Wurtz found that auric, cadmium, cerium, lanthanum, didymium, ferric, and platinic chlorides are decomposed by nitric acid incompletely and with difficulty. S. Schlesinger said that the two copper chlorides, mercurous, zinc, and lead chlorides, are decomposed, but, added H. Wurtz, with difficulty and incompletely while mercuric ajid silver chlorides are not attacked. F. Rose found cobalt amminochlorides are readily converted into the nitrate. 

The same reason was given in the literature for the formation of a number of other bimetallic oxocomplexes such as Cd4Sn4(p4-O)(OCH2Bu,)10(OAc)10 [325] and [PbTi2(p4-0)(0Et)7(0Ac)]2 [320]. When the alkoxides of zirconium, hafnium, or cerium are used for this reaction, the formation of the oxocomplexes can be due to the elimination of an unsaturated hydrocarbon from the initial alkoxide [1565], leading to the formation of monometallic oxoalkox-ides as intermediates (the latter are formed already on desolvation of [M(OR)4(ROH)]2 and are always present as admixtures in the samples of des-olvated M(OR)4, where R is a primary or secondary radical [1612] (see also Section 12.12). In this case the possible sequence of transformations (taking place usually on reflux in toluene) can look as follows ... 

With this end in view, phenyldimcthylsilyl tri-n-butylstannane was added under the influence of zero-valent palladium compound with high regioselectivity and in excellent yield to the acetylene 386 to give the metallated olefin 387 (Scheme 56). The vinyl lithium carbanion 388 generated therefrom, was then converted by reaction with cerium(lll) chloride into an equilibrium mixture (1 1) of the cerium salts 389 and 390 respectively. However, the 1,2-addition of 389 to the caibonyl of 391, which in principle would have eventually led to ( )-pretazettine, did not occur due to steric reasons — instead, only deprotonation of 391 was observed. On the other hand, 390 did function as a suitable nucleophile to provide the olefinic product 392. Exposure of 392 to copper(II) triflate induced its transformation via the nine membered enol (Scheme 55) to the requisite C-silyl hydroindole 393. On treatment with tetrafluoroboric acid diethyl ether complex in dichloromethane, compound 393 suffered... 

Two tandem alkene metathesis-oxidation procedures using Grubb s second-generation ruthenium catalyst resulted in unique functional group transformations. Use of sodium periodate and cerium(III) chloride, in acetonitrile-water, furnished cis-diols. Oxidation with Oxone, in the presence of sodium hydrogencarbonate, yielded a-hydroxy ketones.296 Secondary alcohols are oxidized to ketones by a hydrogen... 

Thioamides of 3-oxoacids 118 are transformed into 1,2,4-dithiazolidines 29 by treatment with cerium ammonium nitrate (CAN) in MeOH or with CF3SC1 in CH2CI2 (Equation 16) <1996SC4165, 2001SC189>. The thermal conversion of 6/7-1,3,5-oxathiazine A-oxides 119 in refluxing benzene results in 1,2,4-oxathiazolines 20 with extrusion of R CHO. This reaction involves the heterodiene intermediate 120, which can be independently trapped by the reaction with EtOH (Scheme 32) <2003TL2517, 2004HAC175>. 

Fig. 7.4 High-resolution transmission electron microscopy (TEM) image of a rhodium on a modified cerium oxide (Ceo.gTbo.202 x) after reduction, showing how the metal is almost epitaxially attached to the support, (a) TEM image (b,c) digital diffraction patterns obtained by Fourier transformation from the images (d) structure model ...

Three thermal effects are observed in the heating curve of initial Mm the first one - at 595 °C, his nature is unknown, and two thermal effects at 780 °C and 810 °C. The effect at 780 °C is associated with a polymorphous transformation in pure Ce y -5 726 5 °C, and the second one is responsible for melting pure cerium at 815 °C. Evidently the presence of the thermal effects and the difference in their temperature ranges as compared with the literature data are related to the chemical composition of starting mishmetal. Chemical analysis has shown that the base of the mishmetal is Ce 82.9 wt. % and La - 16.7 wt. %. 

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