Quinolinium dichromate

Quinolinium dichromate (QDC) oxidations of primary and secondary alcohols both proceed via a cyclic chromate ester. Acrylonitrile polymerization was observed in the oxidation of several para- and meffl-substituted benzaldehydes to the corresponding benzoic acids by quinolinium chlorochromate (QCC). QCC oxidations of diphenacyl sulfide and of aromatic anils have been studied. 

The oxidation of diols by quinolinium dichromate (QDC) shows a first-order dependence on QDC and acid.5 The oxidation of phenols to quinones by quinolinium dichromate in aqueous acetic acid is acid catalysed rate-determining formation of a cationic intermediate is indicated by a p value of —3.79 and further analysis shows the rates to be influenced equally by both inductive and resonance effects of the substituents.6... 

A DIE of k 2o/k )2o = 3.2 has been found in the hydrolysis of a-benzoyloxystyrenes, 382, in concentrated perchloric acid solution450. The rate of hydrolysis was found to be linear with the acidity function, Ho- A small inverse deuterium KIE, A h /I d = 0.78, at the -carbon has been found in the oxidation of cinnamic and crotonic acids451 by quinolinium dichromate. The reaction involves electrophilic attack on the double bond and a carbonium-ion intermediate (p = —4.0). A small inverse D KIE (k /k ->) = 0.80, p = —4.0] has been also observed452 in the acid cleavage of substituted styrenes by quinolinium dichromate in DMF in the presence of acid452. 

Oxidation of aliphatic aldehydes by quinolinium dichromate in aqueous acetic acid shows first-order kinetics in substrate and oxidant, and second-order with respect to H+.319 Hydrated aldehyde and protonated oxidant are suggested to be the reactive species, with Zucker-Hammett plots supporting proton abstraction by water in the slow step. 

Oxidation of long-chain aliphatic aldehydes by quinolinium dichromate has been studied in aqueous acetic acid-sulfuric acid mixtures.321... 

Oxidation of several primary aliphatic alcohols with potassium dichromate, pyri-dinium dichromate, quinolinium dichromate (QDC), imidazolium dichromate, nico-tinium dichromate, isonicotinium dichromate, pyridinium fluorochromate (PFC), quinolinium fluorochromate, imidazolium fluorochromate, pyridinium chlorochromate (PCC), quinolinium chlorochromate (QCC), and pyridinium bromochromate (PBC), in aqueous acetic acid and in the presence of perchloric acid, showed similar kinetics. The values of the reaction constants did not differ significantly, indicating operation of a common mechanism.1... 

Quinolinium dichromate (17) shows the solubility profile common to most chromium based oxidants—sparingly soluble in chlorinated solvents, but more soluble in more polar solvents. It has been mainly used in dichloromethane at reflux, or in DMF at 30 C to oxidize primary alcohols. Secondary alcohols are also oxidized reasonably well. 

Quinolinium dichromate displays reverse selectivity to PDC in dichloromethane primary alcohols can be oxidized directly to acids, but in DMF the oxidation is selective for the preparation of aldehydes. 

Substituted benzaldehydes are oxidized by quinolinium dichromate in DMF containing HCl, with electron-releasing substituents accelerating the reaction p = —0.90). The first step, hydrogen abstraction, is rate-determining the deuterium solvent isotope effect is 5.14 at 333 K. 

The oxidation of serine and threonine by quinolinium dichromate (QDC), in acidic medium, is first order in each substrate, oxidant, and acid. The absence of a KIE indicates that there was no cleavage of the carbon-hydrogen bond in the rate-determining... 

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