Cerium reactions with chromium

Cerium(IV) was also used as an oxidizing agent in a study of the oxidation of the inert chelates formed with chromium(III) and oxalate ion. From kinetic measurements in aqueous sulfuric acid media, it was concluded that the oxidation of tris(oxalato)chromium(III) ion, cis-bis(oxalato)-chromate(III) ion, and the monooxalatochromium(III) ion follow initial second-order kinetics, and 1 mole of oxalate is oxidized to carbon dioxide for every 2 moles of cerium(IV) reduced to cerium(III). A detailed study of the oxidation of the bisoxalato chelate indicated that cerium(III) inhibits the reaction (197). 

Reaction of chromium carbene complex 170 (Scheme 17.23) with isonitriles led to aminonaphthalene derivatives (e.g., 172) [70]. This transformation was a key step for the total synthesis of the calphostin natural products. The crude aminophenol was treated with cerium(IV) to afford the o-quinone derivative. The photochemical... 

Solvent for Electrolytic Reactions. Dimethyl sulfoxide has been widely used as a solvent for polarographic studies and a more negative cathode potential can be used in it than in water. In DMSO, cations can be successfully reduced to metals that react with water. Thus, the following metals have been electrodeposited from their salts in DMSO cerium, actinides, iron, nickel, cobalt, and manganese as amorphous deposits zinc, cadmium, tin, and bismuth as crystalline deposits and chromium, silver, lead, copper, and titanium (96—103). Generally, no metal less noble than zinc can be deposited from DMSO. 

In the reactions of each of the oxalato complexes with cerium(IV) it is clear that no dichromate is formed until all the oxalate has been consumed. This observation is reasonable, for while the cerium(IV)-Cr(OH2)6+3 reaction is moderately rapid and while dichromate ion reacts sluggishly with even free oxalic acid, chromium(IV), a probable intermediate in the cerium(IV)-chromium(III) reaction, might be expected to behave very much like cerium(IV) toward the oxalato complexes. 

The kinetics of chromium(l 11 )-catalyscd oxidation of fonnic acid by Ce(TV) in aqueous H2SO4 can be rationalized in terms of initial formation of an outer-sphere complex involving oxidant, catalyst, and substrate (S), Ce(TV)(S)Cr(III), followed by an inner-sphere complex Ce(III)(S)Cr(IV). It is proposed that electron transfer occurs within this complex from substrate to Cr(TV) (with elimination of H+) followed by fast reaction to give CO2 (again with elimination of H+).54 In contrast, there was no kinetic evidence for the accumulation of a corresponding inner-sphere intermediate in the osmium(VIII)-catalysed Ce(TV) oxidation of DMSO to dimethyl sulfone here, the observed rate law was rationalized in terms of rate-determining bimolecular electron transfer from DMSO to Os(VHI) in an outer-sphere step.55 The kinetics of oxidation of 2-hydroxy-l-naphthalidene anil by cerium(IV) in aqueous sulfuric acid have been... 

Colour systems suitable for use in the spectrophotometric method may also be formed in redox reactions. Some examples of such reactions are the oxidation of Mn(II) to Mn04" or Cr(III) to Cr04, oxidation of dimethylnaphthidine with vanadium(V) or chromium(VI), oxidation of o-tolidine with cerium(lV) or with chlorine. Examples of oxidation reactions are also the iodide methods, in which iodide ions are oxidized with bromine to give iodate ions which, in turn, react with the excess of iodide anions to form free iodine (see Chapter 25). A colour effect of reduction also occurs, for example, in determinations of Se and Te in the form of coloured sols produced in the reduction of Se(lV) or Te(IV) to their elementary forms. 

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