Manganese dioxide, from reduction

It is made from manganese dioxide ores through a reductive roasting process (31—33). 

Chemistry. The alkaline cell derives its power from the reduction of the manganese dioxide cathode and the oxidation of the zinc anode. The reactions... 

An alternative access to murrayanine (9) was developed starting from the mukonine precursor 609. The reduction of the ester group of 609 using diisobutylaluminum hydride (DIBAL) afforded the benzylic alcohol 611. In a one-pot reaction, using very active manganese dioxide, 611 was transformed to murrayanine (9) (574) (Scheme 5.36). 

Manganese(II) oxide is obtained commercially from manganeseflV) oxide (manganese dioxide) by the reduction with hydrogen, carbon monoxide or methane at elevated temperatures (>800°C) ... 

Numerous modifications have been tried without improving the yield. The loss is probably due to a partial reduction of the quinone sulfonate by the sulfur dioxide liberated, but this was not prevented by adding manganese dioxide to the reaction mixture, and no pure product could be obtained from the mother liquor. 

Reduction is defined as the gain of electrons. The conversion of Ag1+ —> Ag° involves a gain of an electron by file silver ion and thus silver is reduced. Likewise, file permanganate ion Mn( )4 has MnfVII] but MnC>2 manganese dioxide has Mn[IV]. Thus file gain of three electrons by manganese causes a reduction in oxidation level of from +7 to +4. 

Oxidation of toluene-o-sulphonamide to saccharin. In a 600-ml beaker, mounted on an electric hot plate and provided with a mechanical stirrer, place 12 g (0.07 mol) of toluene-o-sulphonamide, 200 ml of water and 3g of pure sodium hydroxide. Stir the mixture and warm to 34-40 °C until nearly all has passed into solution (about 30 minutes). Introduce 19g (0.32 mol) of finely powdered potassium permanganate in small portions at intervals of 10-15 minutes into the well-stirred liquid. At first the permanganate is rapidly reduced, but towards the end of the reaction complete reduction of the permanganate is not attained. The addition occupies 4 hours. Continue the stirring for a further 2-3 hours, and then allow the mixture to stand overnight. Filter off the precipitated manganese dioxide at the pump and decolourise the filtrate by the addition of a little sodium metabisulphite solution. Exactly neutralise the solution with dilute hydrochloric acid (use methyl orange or methyl red as external indicator). Filter off any o-sulphonamidobenzoic acid (and/or toluene-o-sulphonamide) which separates at this point. Treat the filtrate with concentrated hydrochloric acid until the precipitation of the saccharin is complete. Cool, filter at the pump and wash with a little cold water. Recrystallise from hot water. The yield of pure saccharin, m.p. 228 °C, is 7.5 g (58%). 

A convenient method for the specific introduction of 2H or 3h (or both) into a molecule is by ketone reduction with labeled metal hydride. Beale and MacMillan (10) have utilized this method for the preparation of GAs labeled at the 1, 2 or 3 positions from GA3 or GA7 (Figure 12). One point of interest is the lithium borohydride reduction of the enone formed by manganese dioxide oxidation of GA3 or GA7. When the reaction is carried out in anhydrous tetrahydrofuran it proceeds in two steps. Initially the lithium enolate is formed which incorporates a proton at carbon-2 from the acid used in the work-up, forming the 3 ketone. This ketone is reduced to the 3 -alcohol by the borohydride which is decomposed more slowly than is the lithium enolate. Thus it is possible to introduce two different labels in a single reaction. 

Protopine has been isolated from Bocconia frutescens,110 Fumaria judaica,111 F. schleicheri,112 and Papaver bracteatum,146 cryptopine from F. schleicheri,112 and allocryptopine from B. frutescens110 and Zanthoxylum nitidum.141 The protopine ring-system has been prepared from tetrahydrobenzindenoazepines (75) by photo-oxidation to the amides (76) followed by reduction with lithium aluminium hydride and re-oxidation with manganese dioxide.148-150 The tetrahydrobenzindenoazepines have been prepared from A-chloroacetyl-/ -phenylethylamines (73) by cyclization to the lactam (74) followed by reaction with a benzyl bromide and phosphorus oxychloride. -Protopine (77 R R2 — CH2)148 and fagarine II (77 R1 = R2 = Me)149 have been synthesized in this way. 

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