Reaction conditions, manganese dioxide

N- Aminoaziridines have been converted to alkenes by reaction with a variety of oxidizing agents (70JA1784). Usually, the deamination reaction is stereospecific. The oxidation of l-amino-2,3-diphenylaziridines with manganese dioxide, however, was not stereospecific. The trans compound gives entirely frans-stilbene, whereas the cfs-aziridine forms a mixture of 85% trans- and 15% c -aikene. cw-Stilbene is not isomerized to trans under the reaction conditions, and the results are explained in terms of an azamine intermediate which can isomerize through a tautomeric equilibrium. 

The standard potential e of reaction (1) is 0.56 volt and of reaction (2) 0.60 volt. By suitably controlling the experimental conditions (e.g. by the addition of barium ions, which form the sparingly soluble barium manganate as a fine, granular precipitate), reaction (1) occurs almost exclusively. In moderately alkaline solutions permanganate is reduced quantitatively to manganese dioxide. The half-cell reaction is ... 

Mechanistically it is likely that the resonance-stabilised anion resulting from deprotonation at the 4-position of benzanthrone couples with non-ionised benzanthrone. Linkage across the 3- and 3 -positions under more strongly alkaline conditions may also involve loss of a proton, coupling and oxidation (Scheme 6.15). Chlorination of benzanthrone followed by an Ullmann reaction produces 3,3 -bibenzanthronyl (6.78), which readily undergoes 4,4,-coupling under mild conditions. 3,3 -Bibenzanthronyl is available from benzanthrone directly by treatment with manganese dioxide in sulphuric acid. 

The reaction of the iron-complex salts 602 and 779 with the arylamine 973 afforded the iron complexes 976 and 977, both in 96% yield. Subsequent O-acetylation provided the corresponding acetates 978 and 979 in almost quantitative yield. The iron-mediated arylamine cyclization of the O-acetyl derivative 978 using very active manganese dioxide provided the carbazole 971 in 72% yield. Under similar reaction conditions, the O-acetyl derivative 979 gave a mixture of the carbazoles 972 and 980 in 35% and 17% yield, respectively (650,651) (Scheme 5.136). 

According to reaction 15.47, for which the Nernst equation gives Eh = +0.401 V at pH 14.0, the oxidation of water is clearly favored by alkaline conditions (see Exercise 15.3). At the same time, however, many oxidation half-reactions also have lower Eh values in basic media. For example, Eh for the manganate/manganese dioxide couple... 

The alkaline dry cell is a modified version of the Leclanche cell in which the acidic NH4C1 electrolyte of the Leclanche cell is replaced by a basic electrolyte, either NaOH or KOH. As in the Leclanche cell, the electrode reactions involve oxidation of zinc and reduction of manganese dioxide, but the oxidation product is zinc oxide, as is appropriate to the basic conditions ... 

Catalytic reduction of thiopyrylium salts under forcing conditions yields tetrahy-drothiopyrans, but oxidation with manganese dioxide of the unsubstituted thiopyrylium cation (first obtained by Pettit [100]) affords thiophene-2-carbaldehyde in a reaction without analogy to pyrylium salts [101], Like a- and y-benzylic positions in pyrylium salts, methyl(ene) groups of alkyl substituents in thiopyrylium cations are usefully acidic and as such the corresponding anhydrobases may be trapped by various nucleophiles. 

The reaction conditions for FDAM labeling were optimized for cellulose to fit into the usual activation protocol prior to dissolution in DMAc/LiCl (9%). FDAM can be prepared in the GPC eluant DMAc from 9f/-fluorcn-2-yl-carboxaldehyde via its hydrazone by oxidation with excess manganese dioxide [78]. 

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