Manganese dioxide oxidation solvent

Irradiation of the a -unsaturated ketone derived by manganese dioxide oxidation of methyl gibberellate, affords, in the solid state, a dimer in which addition of the unsaturated ketone across the terminal methylene group has occurred. Photolysis in solution leads to addition of the solvent to the unsaturated ketone. Some interest has centred on the partial synthesis of gibberellin Ajg (105), whose total synthesis was reported earlier. Details of the conversion of gibberellin A g into some 5-lactones related to gibberellin A15, and on the partial synthesis of gibberellin Ajg nor-ketone from 7-hydroxykaurenolide, reported... 

Polar solvents inhibit the reaction, presumably by interfering with the adsorption process as noted in the mechanism proposed for manganese dioxide oxidations. Oxidation of 1-heptanol to heptanal with Fetizon s reagent was quantitative when the solvent was 35% hexanes. When benzene was used as a solvent, the yield of heptanal dropped to 90% and was < 1% in ethyl acetate, methyl ethyl ketone, or acetonitrile. 69 Since the oxidation is a heterogeneous reaction, requiring adsorption of the alcohol substrate, as the surface area of the reagent increases (increased by precipitation on Celite), the rate of oxidation increases. An optimum ratio is reached beyond which increasing the silver carbonate/Celite ratio slows the oxidation. 69... 

It is sometimes required to oxidize the C-1 methyl group of a substituted isoquinoline to an aldehyde function. Such a transformation is usually carried out using selenium dioxide, in which case anhydrous conditions using dioxane as solvent often give superior yields. An alternate route, however, involves initial formation of the isoquinoline A-oxide followed by acetylation as indicated below. The final step is a manganese dioxide oxidation of a benzylic alcohol. ... 

Pyridinium chlorochromate has also been used (Chakraborty and Bordoloi, 1999) under microwave irradiation for the oxidation of alcohols to the corresponding carbonyl functions with an efficient and mild methodology. Microwave irradiation of alcohols with silica supported active manganese dioxide in solvent-free condition provides rapid and selective oxidation of alcohols to the corresponding carbonyl compounds (Varma et al., 1997). 

A solution of 30% aqueous hydrogen peroxide in trifluoroacetic acid is useful for destructive oxidation of the aromatic ring in preference to the side chains as is usual with most oxidants. During work-up operations, the excess peroxide must be catalytically decomposed with manganese dioxide before removal of solvent to prevent explosions. 

Solvents Water (purified water or water-for-injection grade) toluene, methanol, ethanol, ether, acetate, dimethyl sulfoxide, tetrahydrofuran, hexane, cyclohexane, dichloromethane, acetonitrile, acetone Oxidizing Agents Hydrogen peroxide, chromic acid, potassium permanganate, manganese dioxide, ozone... 

Manganese dioxide very soon became a widely used standard oxidant for the transformation of allylic and benzylic alcohols into aldehydes and ketones.4 It offers very mild conditions and is extremely selective for allylic and benzylic alcohols when it is not employed at a high temperature. On the other hand, the work-up of oxidations with M11O2 is very simple, involving just filtration of suspended solid and elimination of solvent. 

The selective oxidation of benzylic and allylic alcohols with active manganese dioxide in the presence of saturated alcohols is normally carried out by stirring or shaking a solution of the alcohol in an organic solvent in the presence of 5-20 equivalents of suspended active M11O2. 

Some commercial samples of precipitated manganese dioxide may be active enough for use directly in an oxidation process. To assess the activity of a sample of manganese dioxide, dissolve 0.25 g of pure cinnamyl alcohol in 50 ml of dry light petroleum (b.p. 40-60 °C) and shake the solution at room temperature for 2 hours with 2g of the sample of manganese dioxide (previously dried over phosphoric oxide). Filter, remove the solvent by evaporation and treat the residue with an excess of 2,4-dinitrophenylhydrazine sulphate in methanolt (Section 9.6.13, p. 1257). Collect the cinnamaldehyde 2,4-dinitrophenyl-hydrazone and crystallise it from ethyl acetate. An active dioxide should give a yield of the derivative, m.p. 255 °C (decomp.), in excess of 0.35 g (60%). 

Chlorine is the most abundant of the halogens, especially in sea water, a ton of which contains in grams chlorine 15,000, bromine 97, iodine 0-17 (ratio 106 6,000 1). Its preparation depends on the discharge of its ion, either directly (i.e., electrolytically) or by oxidation. The older methods of oxidation (by manganese dioxide or by air in presence of certain catalysts) have now been replaced for technical purposes by the electrolysis of sodium chloride, which is primarily for the production of caustic soda, the chlorine being a by-product the chloroparaffins which are now so much used as solvents were developed to utilize this chlorine. 

The same approach was applied again to the synthesis of lamellarin G trimethyl ether as shown in series b. The first three steps proceeded as expected, however the oxidation of compound 47b with manganese dioxide gave lamellarin G trimethyl ether in a disappointing yield (20%). The by-product was found to be the quinone derivative 50 formed by the preferred oxidation of the electron-rich phenolic ring. For this reason the oxidation was carried out with bromobenzene, palladium acetate and triphenylphosphine using DMF as the solvent and potassium carbonate as the base. Lamellarin G trimethyl ether was formed in 80% yield. 

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