Pyridinium chlorochromate oxidation mechanism

The pyridinium chlorochromate (PCC) oxidations of pentaamine cobalt(III)-bound and unbound mandelic and lactic acids have been studied and found to proceed at similar rates.Free-energy relationships in the oxidation of aromatic anils by PCC have been studied. Solvent effects in the oxidation of methionine by PCC and pyridinium bromochromate (PBC) have been investigated the reaction leads to the formation of the corresponding sulfoxide and mechanisms have been proposed. The major product of the acid-catalysed oxidation of a range of diols by PBC is the hydroxyaldehyde. The reaction is first order with respect to the diol and exhibits a substantial primary kinetic isotope effect. Proposed acid-dependent and acid-independent mechanisms involve the rapid formation of a chromate ester in a pre-equilibrium step, followed by rate-determining hydride ion transfer via a cyclic intermediate. PBC oxidation of thio acids has been studied. ... 

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... 

Pyridinium chlorochromate as oxidant in organic synthesis 82S245. Pyridinium compounds, kinetics and mechanism of nucleophilic sub-... 

The reaction of alkyl- and halo-substituted phenols with Cr02Cl2 results mainly in the formation of quinones and diphenoquinones. Phenoxyl radicals are involved as intermediates. The mechanism of oxidation of a-hydroxycar-boxylic acids by pyridinium chlorochromate involves a rate-limiting hydride transfer. In the reaction of HOCD2CO2H, a kinetic isotope effect (W d) = 5.80 has been determined. Spectroscopic evidence for Cr(IV) and Cr(V) species has been obtained in the oxidation of alkylaromatics by chromyl acetate in acetic anhydride.Stopped-flow and esr studies show two stages (equations 22, 23) in the reactions of RCH2Ph, with both rates being decreased on deuteration at... 

The kinetics of oxidative deoximation (in AcOH) ofiV-methyl-2,6-diphenyl piperidin-4-one oximes by acid dichromate and of 3,5-dimethyl-2,6-diaryl piperidin-4-one oximes by pyridinium chlorochromate have been detennined and are found to be consistent with polar mechanisms, first order in each reactant and subject to acid catalysis. 

Suitable mechanisms have been proposed following determination of the kinetic and activation parameters for oxidation of 2-naphthol and cyclic ketones by nicotinium dichromate some a-amino acids by tripropylammonium fluorochromate " distyryl ketone by quinaldinium fluorochromate methanol by benzyltriethylammonium chlorochromate catalysed by 1,10-phenanthroline substituted benzyl alcohols by tetraethylammonium bromochromate L-cysteine by pyridinium bromochromate lactic acid and 3,5-dimethyl-2,6-diaryl piperidin-4-one oximes by pyridinium chlorochromate allyl alcohol by IDC benzophenoxime by bispyridine silver(I) dichromate and alkyl phenyl sulfides by cetyltrimethylammonium dichromate. A non-linear Hammett plot obtained for the oxidation of substituted benzyl alcohols by IDC has been attributed to the operation of substituent effect on two steps of the proposed mechanism. " Kinetic and activation parameters for oxidation of o-toluidine and of A-methyl-2,6-diphenyl piperidin-4-one oxime and its 3-alkyl derivatives by sodium dichromate have been determined and suitable mechanisms have been suggested. Micellar catalysis in the 1,10-phenanthroline-promoted chromic acid oxidation of propanol... 

---