Manganese, dioxide

Oxidation of the 3-hydroxy-A systenli with manganese dioxide in refluxing benzene affords a moderate yield of the corresponding 4,6-dien-3-one. These vigorous conditions also suffice to cleave the corticoid side chain (17a,21-dihydroxy-20-ketones) to give 17-keto steroids.  

17 -Hydroxyandrosta-4,6-dien-3-one. A suspension of 42 g of crude androsta-4,6-diene-3j ,17j -diol in 2000 ml of chloroform is treated with 250 g of activated, manganese dioxide. The mixture is then shaken vigorously for 15 min in a stoppered flask. The mixture is filtered and the manganese dioxide washed well with chloroform in order to elute material which initially remains adsorbed on the solid phase. The filtrate is concentrated to a pale yellow, crystalline residue. Recrystallization from acetonitrile gives 38 g (90%) of 17/ -hydroxyandrosta-4,6-dien-3-one as plates mp 211-214°. 

The performance of Leclanche and related batteries (Chapter 11 depends critically on the source or method of manufacture of the manganese dioxide because the activity and properties of the oxide vary with crystallite size, density 

Such cells do not permit continuous operation and have a very low space-time yield. This has led to the study of cells where the MnO is formed as a slurry in the anolyte in which case the manganese dioxide may be formed in a flow system e.g. a fllterpiess. Usually such systems use a lower temperature and a higher pH although successful in the laboratory and at the pilot-plant level flow-through parallel-plate or rotating-electrode designs have not seen widespread, full-scale use. 

Because of its inexpensive nature and widespread use as a cathode in batteries, Mn02 has been extensively studied from the viewpoint of its physicochemical properties and its cathodic behavior. It has also attracted 

Within 15 min of contact with MnOj dust (80% 1 fim) suspended in 0.1 ml normal saline the bronchial epithelial cells discharge their mucus, and their supranuclear cytoplasm shrinks and in some cases appears to be shed (Lloyd Davies and Harding 1949). 

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This reaction is also used on a large scale, to obtain iodine from seaweed. The ash from burnt seaweed ( kelp ) is extracted with water, concentrated, and the salts other than iodides (sulphates and chlorides) crystallise out. The more soluble iodides remain and the liquor is mixed with sulphuric acid and manganese dioxide added the evolved iodine distils off and is condensed. 

Oxidation to acids. Varm together in a small conical flask on a water-bath for lo minutes a mixture of 0 5 ml. of benzaldehyde or salicylaldehyde, 15 ml. of saturated KMn04 solution, and 0-5 g. of NajCOj. Then acidify with cone. HCl, and add 25% sodium sulphite solution until the precipitated manganese dioxide has redissolved. On cooling, benzoic or salicylic acid crystallises out. 

Suspend in a round-bottomed flask 1 g. of the substance in 75-80 ml. of boihng water to which about 0 -5 g. of sodium carbonate crystals have been added, and introduce slowly 4 g. of finely-powdered potassium permanganate. Heat under reflux until the purple colour of the permanganate has disappeared (1-4 hours). Allow the mixture to cool and carefully acidify with dilute sulphuric acid. Heat the mixture under reflux for a further 30 minutes and then cool. Remove any excess of manganese dioxide by the addition of a little sodium bisulphite. Filter the precipitated acid and recrystallise it from a suitable solvent (e.g., benzene, alcohol, dilute alcohol or water). If the acid does not separate from the solution, extract it with ether, benzene or carbon tetrachloride. 

Aromatic aldehydes react with the dimedone reagent (Section 111,70,2). All aromatic aldehydes (i) reduce ammoniacal silver nitrate solution and (ii) restore the colour of SchifiF s reagent many react with sodium bisulphite solution. They do not, in general, reduce Fehling s solution or Benedict s solution. Unlike aliphatic aldehydes, they usually undergo the Cannizzaro reaction (see Section IV,123) under the influence of sodium hydroxide solution. For full experimental details of the above tests, see under Ali-phalic Aldehydes, Section 111,70. They are easily oxidised by dilute alkaline permanganate solution at the ordinary temperature after removal of the manganese dioxide by sulphur dioxide or by sodium bisulphite, the acid can be obtained by acidification of the solution. 

The addition of a Whatman filter tablet or of a little diatomaceous earth (Super Cel. etc.) assists in the filtration of the finely divided manganese dioxide. 

In the laboratory it can be prepared by the electrolysis of water or by heating potassium chlorate with manganese dioxide as a catalyst. 

Chlorates Ammonium salts, acids, metal powders, sulfur, flnely divided organic or combustible materials, cyanides, metal sulfldes, manganese dioxide, sulfur dioxide, organic acids... 

Manganese dioxide Aluminum, hydrogen sulfide, oxidants, potassium azide, hydrogen peroxide, peroxosulfuric acid, sodium peroxide... 

Fig. 4.18 Plot of log (.x/(mg g" )) against log (p°/p) for the adsorption of nitrogen at 77 K on the samples of manganese dioxide referred to in Fig. 4.16. Outgassing temperature (A) room (B) 393 K (C)443 K (D) 493 K. For the points denoted by V in Curve A, a sample was outgassed at 493 K and charged with nonane before the final outgassing at room temperature. (Courtesy Lee and Newnham.)...

ANHBIOHCS - BETA-LACTAMS - PENICILLINS AND OTTiERS] (Vol 3) EMD. See Electrolytic manganese dioxide. 

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