The use of manganese dioxide

The oxidation of organic compounds by manganese dioxide has recently been reviewed. It is of limited application for the introduction of double bonds, but the advantages of mildness and simple workup make it attractive for some laboratory-scale transformations. Manganese dioxide is similar to chloranil in that it will oxidize A -3-ketones to A -dienones in refluxing benzene. Unfortunately, this reaction does not normally go to completion, and the separation of product from starting material is difficult. However, Sondheimer found that A -3-alcohols are converted into A -3-ketones, and in this instance separation is easier, but conversions are only 30%. (cf. Harrison s report that manganese dioxide in DMF or pyridine at room temperature very slowly converts A -3-alcohols to A -3-ketones.) 

The most satisfactory use of manganese dioxide for double bond introduction employs enol ethers as substrates  

Other analogs give yields of approximately 25%. been employed.  

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Andreozzi, R., et al.. The use of manganese dioxide as a heterogeneous catalyst for oxalic acid ozonation in aqueous solution, Appl. Catal. A, 138, 75, 1996. 

The limitations of manganese dioxide in a two electrode capacitor were overcome by using activated carbon at the negative electrode. Such an asymmetric system was previously proposed13, without sufficient explanation for the performance observed. In the present study, a deep study of the mechanism of charge storage for both electrodes allowed the system to be optimized. 

Two polarographic methods have been developed for the determination of cohalt(II) at concentrations ranging from approximately 1 to 80 mM in an aqueous sample. For the first method [15], which is suitable for samples containing large amounts of nickel]11), the cobalt(II) is oxidized to Co(NH3)6 in an ammoniacal medium with the aid of sodium perborate, after which the cobalt(III) species is determined. A second procedure [16] entails the use of lead dioxide in an acetic acid-acetate buffer containing oxalate to convert cobalt(II) to the 0(0204)3 ion, which can be subjected to polarographic reduction. This latter approach is well suited to the determination of cobalt in the presence of copper(II), iron(III), nickel(II), tin(IV), and zinc(II), whereas the chief interferences are cerium, chromium, manganese, and vanadium. 

Palladium acetate has also been used to catalyze oxidative cyclizations to produce the related dihydroindole in dimethylacetamide (DMA) in moderate yields <1997BMEL749> (Equation 68). Similar cyclizations have been reported to occur in the presence of manganese dioxide and nitrobenzoic acid <1997TL7207>. 

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%). 

The other patent by E. Schering2 describes the use of a cement diaphragm to separate anode from cathode. Several advantages are evident over the older process in which chlorine or carbon dioxide is used to decompose the manganate which results from the fusion of manganese dioxide with chlorate. These can be shown by comparing the equations representing the reactions —... 

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