Crown ethers chromium oxide

In contrast to earlier reports, Palomo and coworicers found that chromium(VI) oxide will effect the oxidation of alcohols in one day at room temperature. They also found that the addition of semicatalydc amounts (0.3 equiv.) of crown ethers (either 18-crown-6 or 12-crown-4) led to significant rate enhancements. The crown ethers are thought to generate a soluble oxidizing agent, similar to the alkyl ammonium salts used for solid-liquid phase transfer with chromium(VI) oxide in dichloromethane (vide irfra). 

ESR and visible spectroscopic evidence has been found for chromium(V) intermediates during the oxidation of [Cr(L)(OH] (L = hydroxyethylenediaminetriacetate or edta) and [Cr(LL)2(OH)2] (LL = ox, mal) with H202. Oxidation of [Cr(Hedta)(OH2)] with IO4 to Cr04 has also been studied/ The photochemical or thermal formation of chromium(V) complexes with crown ethers is reported from reactions of Cr207 in nonaqueous solvents in the presence of crowns. " ... 

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