demorol
(Hive Bee)
04-05-03 11:52
No 424047
      Oxidation of some ethers with zinc dichromate
(Rated as: excellent)
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This article was listed under the references in Potential for gamma-Butyrolactone Synthesis from Tetrahydrofuran and 1,4-Butanediol (../rhodium/chemistry /gbl.synthesis.microgram.html), so I decided to post reaction details for oxidation of some ethers.

Chromium(VI) Based Oxidants; Zinc Dichromate Trihydrate: A Versatile and Mild Reagent for the Oxidation of Organic Compounds

Abstract: Zinc dichromate trihydrate is an easily prepared, stable, and cheap reagent for the efficient oxidation of organic compounds in aprotic organic solvents at room temperature.

Zinc Dichromate Trihydrate
To the cold solution of chromic acid (236g, 2 mol), prepared by the addition of chromium trioxide (200g, 2 mol) to a 3.4 M solution of sulfuric acid (590mL), zinc carbonate (125g, 1 mol) is added in portions within 15 min. A dark reddish solution is obtained. Evaporation of the solvent under vacuum affords an orange-red slurry, which is completely dried on the surface of a highly dried clay plate in the air. Yield: 268g (80%).

Oxidation of Dibenzyl Ether (9b); Typical procedure:
In a 50mL RB flask, equipped with a condenser, a solution of dibenzyl ether (8b; 396mg, 2 mmol) in CH2Cl2 (25mL) is prepared, the oxidant (2g, 6 mmol) is added, and the mixture is magnetically stirred for 24 min at room temp. The mixture is filtered, the filtrate is evaporated, and the resulting mixture is cromatographed on a silica gel column (30-270 mesh). Elution with benzene affords liquid benzyl benzoate (9b). Microdistillation of the liquid product at 317-322C at atmospheric pressure affords the purified ester. Yield: 360mg (85%). GLC analysis shows >96% purity.

Ethers (8a-c) in dichloromethane are reactive towards oxidation with this reagent and their coresponding esters (9a-c) are produced in good yields.







Reference: Synthesis, pp 285 (1986)

I'm dreaming of the white crystals.