Ceric perchlorate, oxidation

Oxidation of ketones by ceric perchlorate is catalysed by iridium(III) chloride, particularly in acidic media.320... 

Cerium(IV) is a powerful oxidant having numerous analytical and preparative applications. The kinetics of oxidation of a variety of substrates have been reported. Interpretation of studies of the kinetics of ceric oxidations is complicated by uncertainty regarding Ce(IV) speciation in aqueous solutions. In perchloric acid, Ce(IV) is at its most powerful, characterized by E° = 1.70 V (in 1 M acid, Morss 1985). As this potential is above the oxidation potential of water, its existence in aqueous solutions represents a metastable condition. The speciation of Ce(IV) in perchloric acid is dominated by hydrolytic species, even in moderately strong acid. The various ceric species in HCIO include Ce (aquo ion), CelOH) ", Ce(OH), various Ce(IV)-0-Ce(IV) dimers, and an apparent hydrolytic polymer. The latter two polynuclear species are not observed in ceric perchlorate solutions carefully prepared by electrolysis, leading one to suspect that they are one and the same thing, and perhaps are formed irreversibly in aqueous solutions. 

Aqueous ceric solutions are widely used as oxidants in quantitative analysis they can be prepared by the oxidation of Ce ( cerous ) solutions with strong oxidizing agents such as peroxodisulfate, S20g ", or bismuthate, BiOg". Complexation and hydrolysis combine to render (Ce" +/Ce +) markedly dependent on anion and acid concentration. In relatively strong perchloric acid the aquo ion is present but in other acids coordination of the anion is likely. Also, if the pH is increased, hydrolysis to... 

Sterically hindered, mesityl-substituted, stable enols 72 have been examined with regard to one-electron oxidation. Using two equivalents of a one-electron oxidant such as triarylaminium salts, iron(III)phenanthroline, thianthrenium perchlorate or ceric ammonium nitrate in acetonitrile-benzofurans 73 are obtained in good yields within a few seconds [111]. 

Two oxidants essentially dominate these oxidations lead tetraacetate in organic solvents and periodic acid in aqueous media. On occasion, other oxidation reagents cause the cleavage of vicinal diols ceric ammonium nitrate [424], sodium bismuthate [482, 483], chromium trioxide [482, 555], potassium dichromate with perchloric acid [949], manganese dioxide [817], and trivalent [779, 789] or pentavalent [798] iodine compounds. 

To eliminate the problem caused by oxidation of the phlegmatizing agents, it is common practice to distill hydrazoic acid from the azide solution or slurry using perchloric acid. The hydrazoic acid (boiling point 35.7°C)is distilled into a known volume of standard ceric ammonium nitrate. The excess ceric ammonium nitrate is titrated with either standard ferrous ammonium sulfate or sodium... 

Ceric ammonium nitrate (CAN), fl, 120-121, before references]. In an acid medium (acetic, formic, perchloric, nitric acid), the reagent oxidizes a single aromatic methyl group in high yield to an aldehyde group but oxidizes a second methyl group only under much more drastic conditions.3... 

As a result, rates of ceric oxidation in sulfuric acid solutions are normally slower than the corresponding rates in nitric or perchloric acids. 

Complete elimination of sulfate from the medium promotes the formation of a moderately strong precursor complex and permits resolution of the constants describing the kinetic results. Amjad et al. (1977) investigated the ceric oxidation of glycolic, lactic, a-hydroxyisobutyric and phenylglycohc (mandelic) acids in perchloric/nitric acid solutions. The reactions occur at stopped-flow lifetimes and proceed through moderately strong precursor complexes. The presumed reaction for the formation of the principal reactive intermediate is... 

The rate of ceric oxidation of substituted benzilic (2,2-diphenyi-2-hydroxyacetic) acid in sulfuric add, aqueous perchloric/acetic add and acetonitrile is the subject of two reports from Hanna and Sarac (1977a, b). The reaction proceeds like the other a-hydroxycarboxylic acids by oxidative decarboxylation, producing substituted benzo-phenones and COj. The primary interest in the first of these two reports (Hanna and Sarac 1977a) is in the organic chemical aspects of the reactions. However, it is observed that the relative rates vary with the media in the order H2SO4 > HC104/acetic acid > acetonitrile. Although little mechanistic information exists, it is apparent that the oxidation proceeds via an inner-sphere, electron transfer process. 

The oxidation of ascorbic acid by Ce(IV) is the subject of a report by Rajanna et al. (1979). The initial oxidation product is dehydroascorbic acid. Contrary to most of the studies discussed in this review, the substrate is the limiting reagent in this study, which was conducted in sulfuric, perchloric and nitric acid solutions. In sulfuric acid the rate-determining step appears to require a bimolecular reaction, while in perchloric and nitric acids oxidation via an intramolecular process is indicated. In sulfuric acid, Ce(S04)2 is presumed to be the active ceric species. A Michaelis-Menten plot of 1 versus 1 /[Ce(lV)] is linear with finite positive intercept, from which the constants quoted in table 6 are determined. 

Many rate studies involving cerium(iv) have been made in sulphate media (see ref. 9, Introduction) where there may be competition between the sulphate and any ligand for positions in the primary co-ordination sphere of the ceric ion in any inner-sphere mechanism. Recently, however, investigations have been made in perchlorate solutions where the effect is greatly diminished due to the weak co-ordinating power of the perchlorate anion. The oxidation of H2O2 has been reported, stopped-flow traces indicating... 

---