Oxidation by manganese dioxide

Aniline Oxidation. Even though this is quite an old process, it still has limited use to produce hydroquinone on a commercial scale. In the first step, aniline is oxidized by manganese dioxide in aqueous sulfuric acid. The resulting benzoquinone, isolated by vapor stripping, is reduced in a second step by either an aqueous acidic suspension of iron metal or by catalytic hydrogenation. 

Arsenite can be oxidized by manganese dioxides in soils. The rate constants for the depletion of As(III) by bimessite and cryptomelane are much higher than those by pyrolusite due to the difference in the crystallinity and specific surfaces of the Mn oxides (Oscarson et al., 1983). The ability of the Mn dioxides to sorb As(III) and As(V) is related to the specific surface and the point-of-zero charge of the oxides. The one-to-one relationship between the amount of As(III) depleted and the amount of As(V) appearing in solution was reported by Oscarson and colleagues (1983). 

Alkyl groups can be oxidized, as for example the benzyl group in compound (148), to a benzoyl group by permanganate or (better) by selenium dioxide.42 Similarly, the benzyl alcohol in compound 149 is oxidized by manganese dioxide.87 The thiol 150, treated with ferricyanide, gives the disulfide 151.65 Oxidation of thiol 150 with nitric acid is thought to... 

Diaminoimidazoles (741) and 1,2-diaminobenzimidazoles (743) can be oxidized by manganese dioxide or lead tetraacetate to give a useful synthesis of 3-amino-l,2,4-triazines (742) and -benzotriazines (744) (76SC457, 76TL903, 77JOC542, 78JOC2693). 

The structure of the methyl ester m.p. 174° C. (XL) was proven (5) mainly by the fact that the corresponding dibasic acid (XLI R = H) and its dimethyl ester (XLI R = Me) are oxidized with periodate and that the dimethyl ester is oxidized by manganese dioxide to a trisubstituted a,/ -unsaturated ketone (XLII) which regenerates (XLII R = Me) with sodium borohydride. 

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. 

Conjugated—a,/)-unsaturated or aromatic—aldehydes are oxidized by manganese dioxide in the presence of one equivalent of sodium cyanide to give an acyl cyanide (Formula C in Figure 17.18) via an intermediate cyanohydrin (B in Figure 17.18), which is also either an allylic or a benzylic alcohol. Alcohols of this kind can be oxidized by a relatively weak oxi-... 

Research on the important, and difficult, problem of removing small quantities of carbon monoxide from the air has shown that this can be best effected, by catalytic oxidation at room temperature, by mixtures of oxides, which are far more effective than any of the oxides singly.2 While neither manganese dioxide, silver oxide, nor copper oxide will oxidize carbon monoxide rapidly at room temperature, mixtures of manganese dioxide and copper oxide (60/40) will do so silver oxide also much accelerates the oxidation by manganese dioxide. It is stated that 1 per cent, of potash is beneficial, but larger amounts retard the oxidation. Not all oxides accelerate thus cobalt oxide retards oxidation. Various mixtures of manganese dioxide and other oxides as promoters are sold as Hopcalite. ... 

The next important reaction is a Michael addition so the alcohol must first be oxidized to a ketone. As it is an allylic alcohol, it can be oxidized by manganese dioxide. The ring is further flattened as three atoms are now trigonal. But-3-enyl Grignard reagent is next added with Cu(I)... 

The preparation of the dihydropyrrolizine analogues [e.g. (30)] of the unsaturated pyrrolizidine alkaloids has also been studied comprehensively. Several procedures have been shown to be effective in one or more instances, e.g. oxidation by manganese dioxide in chloroform, dehydrogenation by... 

Pluviine is not oxidized by manganese dioxide. Since the double bond is not conjugated with the aromatic ring nor a,p to the nitrogen atom, it... 

The cis relationship between the phenyl and methoxyl groups in CLIX has been confirmed by recent synthetic studies of Uyeo and his co-workers (86). Dihydroisotazettinol (in which the 3-hydroxyl and the phenyl are trans) was oxidized by manganese dioxide to CLIXa. Treatment of CLIXa with lithium aluminum hydride and cyclization of the resultant triol with dilute sulfuric acid gave an ether (CLIXb), the methi-odide of which afforded the neutral compound CLIXc upon Emde reduction. The synthesis of CLIXc started with CLIXd, the condensation product of piperonyl cyanide and methyl acrylate. Dieckmann... 

Leuco compounds that have been isolated in substance are best oxidized by manganese dioxide or lead dioxide in hydrochloric acid, yielding dye salts... 

It has long been known280,281 that 1,1 -binaphthalene is formed when naphthalene is oxidized by manganese dioxide and sulfuric acid ... 

The remediation of chromium-contaminated sites requires knowledge of the processes that control migration and transformation of chromium. Chromium(VI) can be reduced to chromium(III) in the presence of ferrous iron, reduced sulfur compounds, or organic matter in soil. However, chromiu-m(III) also can be oxidized by manganese dioxide, a common mineral found in many soils (Bartlett 1991 Palmer and Wittbrodt 1991 Pandey etal. 2003). Usually, Part of any chromium(VI) added to a soil or sediment will be reduced very rapidly, especially under acid conditions. On the other hand, excess chromium(VI) may persist for years in soils or lagoons without reduction (Bolan et al. 2003). The addition of organic amendments such as manure enhanced the rate of reduction of chromium(VI) to chromium(III) in soils low in organic matter (Bolan et al. 2003). 

Partial hydrolysis of 0,0-diacetyl-0-methylgolceptine gave a monoacetyl derivative that was oxidized by manganese dioxide to an a, -unsaturated ketone. Reduction of this ketone with sodium borohydride gave 0-methylgolceptine and a C-2 epimer. The latter formed an isopropylidene derivative (70). 

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