Ammonium chlorochromate

Symmetrical and unsymmetrical benzoins have been rapidly oxidized to benzils in high yields using solid reagent systems, copper(II) sulfate-alumina [105] or Oxone-wet alumina [105, 106] under the influence of microwaves (Scheme 6.32). Conventionally, the oxidative transformation of a-hydroxy ketones to 1,2-diketones is accomplished by reagents such as nitric acid, Fehling s solution, thallium(III) nitrate (TTN), ytterbium(III) nitrate, ammonium chlorochromate-alumina and dayfen. In addition to the extended reaction time, most of these processes suffer from drawbacks such as the use of corrosive acids and toxic metals that generate undesirable waste products. 

Other ammonium chlorochromates, occasionally used in the oxidation of alcohols, include pyrazinium-A-oxide (PzOCC),378 naphtyridinium (NapCC),394 pyrazinium (PzCC),394 tripyridinium hydrochloride (TPCC),378a triethylammonium,378b imidazolium and l-methylimidazolium,194e and ben-zyltrimethylammonium (BTMACC)387j chlorochromates. 

Keywords alcohol, ammonium chlorochromate, montmorillonite K-10, ketone... 

Preparation of Ammonium Chlorochromate/Montmorillonite K-10. To a solution of chromium trioxide (40 g, 0.4 mol) in water (100 mL) was added ammonium chloride (21.4 g, 0.4 mol) within 15 min at 40 °C. The mixture was cooled until a yellow-orange solid formed. Reheating to 40 °C gave a solution. Montmorillonite K-10 (200 g) was then added with stirring at 40 °C. After evaporation in a rotary evaporator, the orange solid was dried in vacuo for 2 h at 70 °C. It can be kept for several months in air at room temperature without losing its activity. 

Ammonium chlorochromate supported on montmorillonite K-10 (2.6 mmol) was mixed with the neat oxime (1.6 mmol) in a small beaker. The beaker was placed inside a microwave oven operating at full power (900 W). After completion of die reaction (monitored by TLC), the product was extracted with CH2C12. The filtrate was evaporated to dryness, and the residue was passed through a small bed of silica gel to afford die corresponding carbonyl compounds after removal of the solvent. 

Ammonium Fluochromate, Cr02(ONH4)F, the compound, NH4Cr04.2Cr(0F)2, ammonium chlorochromate, Cr02(0NH4)Cl, and chromoiodate, Cr63.NH4IO3.H2O, have been described, as also have chromates and dichromates of certain substituted ammonias. 

Montmorillonite K-10, FejNOsjs, MW, 80-90% yield.Bis(trimethylsilyl) chromate "" and ammonium chlorochromate/Montmorillonite K-IO " as the oxidant gives similar results. 

Nonaqueous procedures for oxidation of mandelic esters and the cleavage of p-nitro-phenylhydrazones and semicarbazones involves treatment with ammonium chlorochromate adsorbed on alumina. ... 

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