Cerium oxidizing reagent

Aravamudan and Venkappayya75 oxidized dimethyl sulphoxide in acetate buffer of pH 4 to 4.5 and with a reaction time of only 1 min. They then added potassium iodide and acid and titrated with thiosulphate the iodine liberated by unused reagent. They reported that cerium(IV) and Cr(VI) were much less effective oxidizing reagents for the sulphoxide. A very similar procedure was used by Rangaswama and Mahadevappa76 to determine dimethyl sulphoxide and numerous other compounds with chloramine B. 

The compound cerium oxide (either Ce Oj or CeO ) is used to coat the inside of ovens because it was discovered that food cannot stick to oven walls that are coated with cerium oxide. Cerium compounds are used as electrodes in high-intensity lamps and film projectors used by the motion picture industry. Cerium is also used in the manufacturing and polishing of high-refraction lenses for cameras and telescopes and in the manufacture of incandescent lantern mantles. It additionally acts as a chemical reagent, a misch metal, and a chemical catalyst. Cerium halides are an important component of the textile and photographic industries, as an additive to other metals, and in automobile catalytic converters. Cerium is also used as an alloy to make special steel for jet engines, solid-state instruments, and rocket propellants. 

Ceric ammonium nitrate is used as a volumetric oxidizing reagent in many oxidation-reduction titrations. Cerium(IV) ion is a strong oxidant simdar to permanganate ion. It is the most widely-used primary standard among all Ce(IV) compounds. Other apphcations of this compound are in organic oxidation reactions and as a catalyst in polymerization of olefins. 

A review has focused on differentiation between polar and SET mechanisms through kinetic analysis.82 hi two separate reviews, the effects of solute-solvent interactions on electron-transfer reactions have been described.83,84 A review of the behaviour of radical cations in liquid hydrocarbons has given particular emphasis to those with high mobility.85 A paper presents selected studies in the formation of radicals by oxidation with manganese- or cerium-based reagents and then- application to C—C bond formation by SET processes.86... 

Method. A diagram of the cerium oxidation monitor is shown in Fig. 4.5 5 and appropriate flow-rates of the components are given. The reagent solution consists of 10 4 N cerium(IV) sulfate in 2 TV sulfuric acid. No catalyst is required for the reaction. PTFE... 

Oxidizing reagents such as tetravalent cerium or potassium permanganate solutions may be standardized by oxalic acid, sodium oxalate, or potassium iodide. The reactions of Ce4+ and permanganate ions with oxalic acid in acid medium are given below ... 

The C-Si bond of an SMA can also be cleaved by oxidizing reagents like cerium ammonium nitrate (CAN). Starting from (V-bis(trimethylsilyl)methylazetidinones, treatment with CAN probably leads to the oxidation product of the two C-Si bonds, i.e., the corresponding disilylketal that is hydrolyzed into the formamide to give the N-H azetidinones (yields >80%). This constitutes an alternate and more efficient way to sequential fluoride-induced desilylation. Peterson olefination, ozonolysis, and formamide decomposition when deprotection of bis(trimethylsilyl)methylated azetidinones into NH-azetidinones is required.228,230... 

The oxidative cleavage of Al-Boc groups with ammonium cerium(IV) nitrate (CAN) in acetonitrile has been reported,0 1 but the fact that, again, acidic or Lewis acidic rather than oxidative reaction conditions noight affect the reaction (CAN is, at least in aqueous solution, strongly acidic) should be kept in nnind. Boc-protected amino acids have been reported to be stable against other oxidative reagents. 

A sulfuric acid solution of cerium(IV) is nearly as potent an oxidizing reagent as is permanganate and can be substituted for the latter in most of the applications described with potassium permanganate. Cerium(IV) does not oxidize chloride ion at a detectable rate as does permanganate, and the reagent is indefinitely stable. On the other hand, the color of cerium(IV) is not sufficiently intense to serve as an indicator. In addition, the reagent cannot be used in neutral or basic solutions. 

Solutions of permanganate ion and cerium(IV) ion are strong oxidizing reagents whose applications closely parallel one another. Half-reactions for the two are... 

Cerium(III) may be detected at an excitation wavelength of 247 nm and an emission wavelength of 350 nm. To stabilize the cerium(IV) reagent, it is prepared in sulfuric acid of the concentration c = 0.5 mol/L. The addition of sodium bismutate serves to oxidize possible cerium(III) traces in the reagent to keep the residual fluorescence as low as possible. 

For the reaction of the column effluent with the cerium(IV) reagent, instead of a simple injection loop, Fields et al. used a solid-bed reactor with a volume of 2.8 mL. This relatively large volume is necessary to allow the required reaction time of at least two minutes for the oxidation of nitrite ions with cerium(IV). While the reaction of nitrite ions with cerium(IV) is comparatively slow, the maximum fluorescence yield with iodide is obtained in less than ten seconds. On the other hand, the reaction kinetics with thiosulfate appears to be completely different. As seen in the respective diagram in Fig. 6-21, this reaction is characterized by a fast rise of the fluorescence yield within a short time, which increases as the reaction product from Eq. (191), tetrathionate, also reacts slowly with cerium(IV). 

Another new cerium(IV) reagent, ceric triethylammonium nitrate (CTEAN), has been prepared for use in the mild high-yield oxidation of benzyUc alcohols and a-hydroxy ketones to the corresponding carbonyl compounds (Firouzabadi and Iranpoor, 1983). This CAN analog is stable, soluble in methylene chloride, acetonitrile, acetone, alcohols and water it gives high yields in simple, nonacidic solvents and produces minimal secondary products from carbon-carbon bond cleavage. 

Hydrophobic cerium(lV) reagents 308 7.1. Oxidations by bromate ions 344... 

Aromatic nitration or nitration in the benzylic position are often side reactions of oxidation reactions with ammonium hexanitratocerate(IV). In fact these unwanted reactions are one of the main drives to develop cerium(IV) reagents other than ammonium hexanitratocerate(IV). However, in some cases ammonium hexanitratocerate(IV) can be turned into a useful nitration reagent. A major parameter that governs the chemoselectivity of CAN is the solvent. 

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