Imidazolium dichromate

Steric effects dominate in the oxidation of dialkyl, alkyl phenyl and benzal methyl phenyl sulfides to their sulfoxides by quinolinium fluorochromate (QFC) in aqueous acetic acid. QFC oxidation of phenoxyacetic acids has been smdied. Imidazolium dichromate oxidations of a-hydroxy acids have been smdied. ... 

The oxidative potency of dichromates and chlorochromates decreases under less acidic conditions. This is so, for example, when a less acidic ammonium salt is included as counter-ion of a dichromate or chlorochromate anion. Thus, a number of ammonium dichromates and chlorochromates possessing a milder oxidative potency has been described with the specific purpose of allowing very selective oxidations of unsaturated alcohols in the presence of saturated ones. These selective dichromates and chlorochromates include bis(benzyltriethylammonium)dichromate,135 tetramethylethy-lenediammonium dichromate (TMEDADC),136 imidazolium dichromate (IDC),137 N, A -dimeth y I a m i n o py r id i n i u m chlorochromate (DMAPCC),138 l-(benzoylamino)-3-methylimidazolium chlorochromate (BAMICC)139 and butyltriphenylphosphonium chlorochromate (BTPPCC).140... 

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... 

Imidazolium dichromate is a selective oxidant for allylic and benzylic hydroxy groups. (Allylic alcohols are oxidized faster than benzylic alcohols.) The selectivity over saturate alcohols is similar to that of 4-(dimethylamino)pyridinium chlorochromate. DMF is recommended as the solvent for oxidations, since it appears that the choice of solvent is critical to obtaining high yields. This reagent has also been observed to cause some ( )/(Z)-isomerization during the oxidation of allylic alcohols. 

EtsN-HCl-CrOs, CICH2CH2CI, 2h, rt, 60-90% yield. This reagent was reported to work better than PCC (pyridinium chlorochromate ). Trimeth-ylsilyl chlorochromate, 2,6-dicarboxypyridinium chlorochromate, bistet-rabutylammonium dichromate, imidazolium dichromate, and CrOs/silica gel are also effective. 

The oxidation of monosubstituted aldonitrones to aldehyde and nitrosobenzene in MeCN/H20 mixture is first order in imidazolium dichromate (IDC) and nitrones, and a fractional order in acid. Added MnS04, 2,2 -bipyridyl (bpy), 1,10-phenanthroline and electron-withdrawing substituents decreased the rate which increased with the added oxalic acid and electron-releasing substituents. The rate data obeyed the Hammett relation. A mechanism involving the reaction of protonated nitrone with IDC in the rate-determining step is proposed." A similar oxidation in aqueous dimethyl-formamide (DMF) is of first-order dependence on IDC and aldonitrones, and H+ ions catalysed the rate. The rate decreased moderately with decrease in the dielectric constant. A mechanism of the reaction is proposed." ... 

The rate of oxidation of chalcones in ACOH-H2O has first order in imidazolium dichromate (INDC) and H+ ion and fractional order in the chalcones decreased with decreasing dielectric constant." The oxidation of phenoxyacetic acids in ACOH-H2O-HCIO4 is first order in nicotinium dichromate (NDC) and substrates, and second order in H+ ion. The electron-releasing substituents and increased percentage of AcOH increased the rate, which was decreased by electron-attracting substituents. The rate correlated with the Hammett relation, and Mn + ions exhibited noticeable catalytic effect." ... 

The oxalic acid-catalysed oxidation of Af,a-diphenylnitrones by imidazolium dichromate (IDC) is first order in the nitrone, IDC, and oxalic acid. A positive fractional order was obtained with respect to acidity. A mechanism involving the protonated nitrone as a reactive species has been proposed. Oxidation of substituted phenols with isonico-tinium dichromate in the presence of oxalic acid is first order in the reductant and oxidant but showed a fractional order in oxalic acid the Hammett plot is downward concave. Activation parameters have been determined and a mechanism has been proposed. The oxidation of some secondary alcohols," aliphatic aldehydes, and three lower oxyacids of... 

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