Manganese dioxide oxidation side reactions

In comparison with manganese dioxide, the DDQ reagent has several advantages for the oxidation of allylic alcohols. The quinone method is more reproducible only one equivalent of oxidant need be added and generally fewer side reactions are observed. On the other hand, the workup of DDQ reactions often requires chromatography and in the simpler cases lower isolated yields may be realized. 

Oxidation of side-chain. To a mixture of 1 g of the substance and 30 ml of water add sodium carbonate (about 1 g, or enou to make alkaline). Add solid potassium permanganate in small portions, shaking after each addition, so that in all about 4 g of permanganate is used. Reflux for 15 minutes, or until reaction is complete (e.g. as indicated by the disappearance of an oil up to 5 hours may be required). Cool and acidify with dilute sulphuric acid. Pass sulphur dioxide (or add sodium sulphite solution) until the manganese dioxide has dissolved. Filter, or remove the desired acid by ether extraction. If necessary, decolourize the product by warming with charcoal in excess of sodium carbonate solution, filtering and acidifying the filtrate. RecrystaUize from water or alcohol. 

This study focused on the deactivation of the Mn/Ce catalysts during reaction. The catalytic oxidation of phenol in aqueous solution to carbon dioxide, water and other side-products was selected as the test reaction. Catalysts were prepared from amorphous precursors using the citrate method and controlling the calcination temperature. Activity performance as a function of the time on stream was studied by simultaneously analyzing the conversion of phenol, the total organic carbon content of the catiyst, the cations eluted and the elemental composition of both cerium and manganese. Experimental conditions were widely varied. Fresh and used catalysts were also analyzed by BET surface area, X-Ray Diffraction and X-Ray Photoelectron Spectroscopy. 

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