Oxidising action

By their oxidising action heating with copper and concen trated sulphuric acid yields brown fumes of nitrogen dioxide. 

These reactions illustrate the oxidising action of iodine. 

The following oxidation of camphor to camphor-quinone illustrates the oxidising action of selenium dioxide, and readily gives a crystalline product. 

Nitrobenzene is an extremely versatile solvent, and may frequently be employed for the crystallisation of compounds which do not dissolve appreciably in the common organic solvents. The vapour is somewhat poisonous, so that recrystaUisations must be carried out in the fume cupboard. After the crystals have been collected, they should be washed with a volatile solvent, such as benzene, alcohol or ether, to remove the excess of nitrobenzene (compare Section 11,32). The only disadvantage of nitrobenzene as a solvent is that it has a pronounced oxidising action at the boihng point. 

Nitrations are usually carried out at comparatively low temperatures at higher temperatures there may be loss of material because of the oxidising action of the nitric acid. For substances which do not nitrate readily with a mixture of concentrated nitric and sulphuric acids ( mixed acid ), the intensity of the reaction may be increased inler alia by the use of fuming sulphuric acid (containing up to 60 per cent, of sulphur trioxide) or by fuming nitric acid. Thus nitrobenzene is converted by a mixture of fuming nitric acid and concentrated sulphuric acid into about 90 per cent, of wi-dinitrobenzene and small amounts of the o- and p-isomers the latter are eliminated in the process of recrystallisation ... 

Periodic acid has a selective oxidising action upon compounds having two hydroxyl groups or a hydroxyl and an amino group attached to adjacent carbon atoms and is characterised by the cleavage of the carbon - carbon bond (Malaprade reaction) ... 

The facts in favour of the first are that cpiinonc, like a ])cioxicle, has a strong oxidising action, that on reduction it yields, not a glycol, but a dihydroxybenzene moreover, with I CI- instead of a tetra-chloro-deiivative, a dichloroben/cnc is foi ined. In favour of the ketone structure is the formation of a mono- ami di-o ime f(loldschiniclt). 

Most acids are corrosive to aluminium-base materials. The oxidising action of nitric acid at concentrations above about 80%, however, causes passivation of aluminium. Very dilute and very concentrated sulphuric acid dissolves aluminium only slowly. Figures 4.4 and 4.5 give corrosion data at various concentrations for these two acids. The corrosion rates of aluminium in other inorganic acids in dilute solution are shown in Fig. 4.6. Boric acid also exerts little attack on aluminium, while a mixture of chromic and phosphoric acids can be used for the quantitative removal of corrosion products from aluminium without attacking the metal. 

Sensitive substances which, as such, can be distilled in a vacuum, occasionally decompose when subjected abruptly while hot to large changes of pressure. In such cases the pressure is allowed to rise only after the contents of the flask have cooled. To proceed in this way is quite generally appropriate because thereby the very common oxidising action of hot air is also avoided. 

Experiment 1.—Dilute a few drops of formaldehyde or acetaldehyde with a few c.c. of water, add a small amount of ammoniacal silver solution, and divide the mixture between two test tubes. Into one test tube run a few drops of sodium hydroxide solution an immediate separation of metallic silver takes place. From the other solution after standing for some time in the cold, or more quickly on warming, the silver separates. Thus the oxidising action of ammoniacal silver solution is very considerably increased by sodium hydroxide (Tollens). Also test the reducing action of the aldehydes on Fehling s solution. 

Chlorine and bromine exert a more vigorous oxidising action than iodine, and although some tetrathionate may be formed, this is accompanied by much sulphate, the latter being the main product 6... 

In the finely divided state, arsenious oxide can be oxidised with oxygen under pressure in the presence of nitric acid, which acts as oxygen carrier.5 The oxidising action of the nitric acid usually ceases when reduction to nitric oxide has occurred, but nitric acid is regenerated by oxygen under pressure, thus ... 

The bromine atom of chromium pentaphenyl bromide is also replaced by the hydroxyl group when the compound is shaken in chloroform solution with an aqueous suspension of silver oxide. The other products present in the crude bromide remain dissolved in the chloroform, but since silver oxide seems to exert an oxidising action a mixture of bases results, and not pure chromium pentaphenyl hydroxide as might be anticipated. 

The oxidising action of hydrogen peroxide in the presence of ferrous sulphate, was first used by Fenton and applied by him in the conversion of the poly-hydric alcohols to the corresponding aldehydes. 

Hydrogen peroxide has the chemical formula H202 and consists of two linked oxygen atoms each with a hydrogen atom attached. It has a powerful oxidising action and is used as a bleaching agent. See also urea. 

Drainage water from coal mines is frequently charged with ferrous sulphate consequent upon the oxidation of pyrites in the coal, and upon evaporation yields the impure salt. The salt is readily obtained in a pure state by dissolving electrolytic iron in dilute sulphuric acid and allowing to crystallise, preferably in an inert atmosphere. Commercially ferrous sulphate is obtained by exposing heaps of pyrites to the oxidising action of the air. Ferrous sulphate and free sulphuric acid drain off into tanks, the acid being neutralised with scrap iron —... 

Tungsten dioxide thus acts as a powerful reducer, and will convert mercuric and cui>ric salts to the mercurous and cuprous condition, and precipitate the metal from ammoniacal silver solutions. The amorphous variety is soluble in hydrochloric and sulphuric acids, yielding red solutions which on standing undergo partial oxidation with loss of colour the ciystalline dioxide is unacted upon, even by the hot concentrated acids.Nitric acid has a slow oxidising action. Concentrated alkali solutions dissolve the amorphous oxide, with formation of the tungstate and liberation of hydrogen, but have no action on the crystalline variety. ... 

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