Oxidation of Alcohols with Bis(trimethylsilyl)chromate
1307
Experimental
Products were characterized by GLC and by direct comparison with authentic samples. Yields are
based on GLC analysis. Montmorillonite K-10 was dried and simultaneously activated in a
microwave oven for 3 min at 780 W prior to use.
Preparation of bis(trimethylsilyl)chromate supported on montmorillonite K-10
To a solution of 6.4 ml hexamethylsiloxane (0.03 mol) in 20 ml of CH2Cl2, chromic anhydride
(0.03 mol) was added. The reaction mixture was stirred at 50ꢀC for 5 h. The CrO3 dissolved, and the
dark red mixture became homogeneous. Montmorillonite K-10 (13 g, pre-dried for 12 h at 120ꢀC
and activated in a microwave oven for 3 min) was added, and the resulting mixture was stirred for
further 5 h. The solvent and other volatile components were distilled off under reduced pressure to
afford 19 g of the supported chromium oxidant. The calculated 1.59 mmol of this typical batch of the
reagent were regarded as the effective chromium concentration.
Oxidation of cyclohexanol, general procedure
Montmorillonite K-10 (0.75 g, equivalent to 1.2 mmol of chromium(VI) oxidant) was placed in a
round bottom ¯ask and covered with 5 ml of CH2Cl2. Cyclohexanol (1.04 mmol) was added, and
after stirring the reaction mixture at room temperature for 10 min it was ®ltered and washed with
10 ml of CH2Cl2. Evaporation of the solvent afforded 99 mg of cyclohexanone (97.6%). GC analysis
showed the presence of negligible amounts of impurities.
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