Manganese dioxide preparation methods

Preparation of 2-Cyc/opropy/methy/amino-5-Ch/orobenzophenone To a solution of 315 g (1.09 mols) of 2-cyclopropylmethylamino-5-chloroDenzhydrol in 4 liters of benzene is added 453.6 g (5.22 mols) of manganese dioxide, freshly prepared according to the method of Attenburrow et al, J.C.S. 1952, 1104. The mixture is then refluxed for VA hours, filtered, and the filtrate evaporated under vacuum. The reddish residue is recrystallized from 510 ml of 90% acetone-10% water, giving 181 g of pure 2-cyclopropylmethylamino-5-chloro-benzophenone, MP 79° to 80°C (58% yield). Upon concentration of the mother liquor a second crop of 2-cyclopropylmethylamino-5-chlorobenzophenone weighing 34.1 g and melting at 76.5°-78°C are obtained. 

Manganese dioxide has been nsed to carry out a range of chemical oxidations, and is the reagent of choice for the oxidation of allylic alcohols (Hndlicky 1990). There are several methods for its preparation that may acconnt for differences in its activity. Although it has seldom been exploited for the oxidation of contaminants, two widely different applications have been described ... 

Quinone may be prepared by the oxidation of aniline with dichromate or manganese dioxide and sulfuric acid.1 This is a more feasible commercial method than the one given. However, the oxidation of hydroquinone is more rapid and convenient and, hence is more desirable for use in the laboratory. Various materials have been oxidized by chemical means to give quinone they are quinic acid,2 hydroquinone,3 benzidine,4 -phenylene-diamine,5 sulfanilic acid,6 / -phenolsulfonic acid,7 arbutin,8 aniline black,9 and the leaves of various plants.10 Quinone is also formed by several other methods by the fermentation of fresh grass 11 by the action of iodine on the lead salt of hydroquin-... 

In the laboratory oxygen may be prepared by several chemical methods that involve thermal decomposition of solid oxides or 0x0 salts. The most convenient method of preparing oxygen is to heat potassium chlorate in the presence of manganese dioxide catalyst ... 

A general method of potential synthetic usefulness is the preparation of aromatic azapentalenes by oxidation of partially saturated systems. This has been used with success in a few cases (e.g., Sections III,A,3,d,108,109 III,B,3,c,293-295 III,A,284), but it has not been extensively explored. Recently, several workers have reported some possibly significant failures while attempting the dehydrogenation of nonaromatic systems. Various 2,3-dihydroimidazo[l,2-h]pyrazoles resisted oxidation to the corresponding aromatic system with manganese dioxide, chloranil, or dicyanodichloroquinone (DDQ),355 and a... 

The earliest methods for preparing cyclic a-diazo ketones involved the oxidation of the monohydrazones prepared from a-diketones, generally using mercuric oxide.7,8 Recent modifications of this procedure include the use of calcium hypochlorite in aqueous sodium hydroxide or activated manganese dioxide as oxidants.1 The latter reagent, especially, hoc ms preferable to mercuric oxide. The base-catalyzed decomposition of tile monotosylhydrazoneH of a-diketones has been... 

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. 

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. 

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