Oxidation, atmospheric

This IS the important state of vanadium in aqueous solution it is neither strongly oxidising or strongly reducing and acidic solutions are stable to atmospheric oxidation ... 

Ether so obtained is anhydrous, and almost entirely free from other impurities. On standing, however, it undergoes slight atmospheric oxidation, with the formation of traces of diethyl peroxide, (CaH jaOa. The formation of this peroxide can be largely checked, however, by storing the distilled ether over fresh sodium wire, preferably in the dark. 

Physical properties. All solid except m -cresol, CH3CJH4OH, which is a liquid. All colourless when pure, but frequently slightly coloured due to atmospheric oxidation. All have in varying degrees a characteristic odour of carbolic acid. Phenol, the cresols and resorcinol have a caustic action on the skin. 

Fehling s solution. Aqueous solutions of aliphatic aldehydes are almost invariably acidic owing to atmospheric oxidation, and therefore... 

Action of sodium hydroxide. Does not undergo the Cannizzaro reaction. It dissolves in dil. NaOH solution, giving a yellow solution from which the aldehyde is precipitated unchanged on acidification. If heated with cone. NaOH solution, salicylaldehyde slowly undergoes atmospheric oxidation to salicylic acid. 

Sodium hydroxide. Dissolve a few crystals of benzoquinone in 10% aqueous NaOH solution and shake gently. The solution turns rapidly brown and then almost black owing to atmospheric oxidation. 

Pure aniline has a b.p. of 184°. When freshly distilled it is a colourless liquid, but becomes discoloured on standing, particularly when exposed to light owing to atmospheric oxidation. The colour may usually be removed by distillation from a little zinc dust. 

Hydrochloric acid should not be used for acidifying the alkaline solution since the yellow colour, due to the ferric chloride formed, causes the Prussian blue to appear greenish. For the same reason, ferric chloride should not be added—as is frequently recommended a sufficient concentration of ferric ions is produced by atmospheric oxidation of the hot alkaline solution. The addition of a little dfiute potassium fluoride solution may be advantageous in assisting the formation of Prussian blue in a readily filterable form. 

Poljraer surfaces can be easily modified with microwave or radio-frequency-energized glow discharge techniques. The polymer surface cross-links or oxidizes, depending on the nature of the plasma atmosphere. Oxidizing (oxygen) and nonoxidizing (helium) plasmas can have a wide variety of effects on polymer surface wettability characteristics (92). 

Gas-phase oxidation of thiols has been discussed in some depth (33). This review mainly emphasi2es atmospheric processes, but a section on nitrogen oxides and thiols appears to be broadly appHcable. The atmospheric oxidation chemistry of thiols is quite different from that of alcohols. 

In addition to the acid—base components shown in Figure 9, various organic acids are often found. Many of these acids are by-products of the atmospheric oxidation of organic matter released into the atmosphere. Of special interest are formic, acetic, oxaUc, and benzoic acids, which have been found in rainwater in concentrations occasionally exceeding a few micromoles per Hter. 

MetaUic arsenic is stable in dry air, but when exposed to humid air the surface oxidizes, giving a superficial golden bronze tarnish that turns black upon further exposure. The amorphous form is more stable to atmospheric oxidation. Upon heating in air, both forms sublime and the vapor oxidizes to arsenic trioxide [1327-53-3] AS2O2. Although As O represents its crystalline makeup, the oxide is more commonly referred to as arsenic trioxide. A persistent garliclike odor is noted during oxidation. 

Oxidation. Atmospheric oxidation of 1,2-dichloroethane at room or reflux temperatures generates some hydrogen chloride and results in solvent discoloration. A 48-h accelerated oxidation test at reflux temperatures gives only 0.006% hydrogen chloride (22). Addition of 0.1—0.2 wt. % of an amine, eg, diisopropylamine, protects the 1,2-dichloroethane against oxidative breakdown. Photooxidation in the presence of chlorine produces monochloroacetic acid and 1,1,2-trichloroethane (23). 

The most important reactions of trichloroethylene are atmospheric oxidation and degradation by aluminum chloride. Atmospheric oxidation is cataly2ed by free radicals and accelerated with heat and with light, especially ultraviolet. The addition of oxygen leads to intermediates (1) and (2). 

Sulfur dyes are used for dyeing ceUulosic fibers. They are insoluble in water and are reduced to the water-soluble leuco form for appHcation to the substrate by using sodium sulfide solution. The sulfur dye proper is then formed within the fiber pores by atmospheric oxidation (5). Sulfur dyes constitute an important class of dye for producing cost-effective tertiary shades, especially black, on ceUulosic fibers. One of the most important dyes is Cl Sulfur Black 1 [1326-82-5] (Cl 53185), prepared by heating 2,4-dinitrophenol with sodium polysulfide. 

Diphenylhydrazine (hydrazobenzene) [122-66-7] M 184.2, m 34°, 44°, 175°/10mm, 222°/40mm, pKe i -1.7. Crystd from hot EtOH containing a little ammonium sulfide or H2SO3 (to prevent atmospheric oxidation), preferably under nitrogen. Dried in a vacuum desiccator. Also crystd from pet ether (b 60-100°) to constant absorption spectrum. HCl, from EtOH has m 163-164°(dec). Picrate, from C6H6, has m 123°(dec). 

SCOTT, G., Atmospheric Oxidation and Antioxidants, Elsevier, Amsterdam (1965)... 

SPONTANEOUS COMBUSTION Coiubustion that results when materials undergo atmospheric oxidation... 

LOCAT units can be used for tail-gas clean-up from chemical or physical solvent processes. They can also be used directly as a gas sweetening unit by separating the absorber/oxidizer into two vessels. The regenerated solution is pumped to a high-pres.sure absorber to contact the gas. A light slurry of rich solution comes off the bottom of the absorber and flows to an atmospheric oxidizer tank where it is regenerated. A dense slurry is pumped off the base of the oxidizer to the melter and sulfur separator. 

Fe(H20)6] (and, indeed, all other Fe" species in Table A) unstable wrt atmospheric oxidation. In practice the oxidation in acidic solutions is slow and, if the pH is increased, the potential for the Fe "/Fe" couple remains fairly constant until the solution becomes alkaline and hydrous Fe203 (considered here for convenience to be Fe(OH)3) is precipitated. But here the change is dramatic, as explained below. 

S. Al-Malaika, Atmospheric Oxidation and Antioxidants, voi. I, (G. Scott, ed.), Elsevier Science Publishers, Amsterdam, Chap. 5 (1993). 

Flux material used during welding, brazing or braze welding to clean the surfaces of the joint, prevent atmospheric oxidation and to reduce impurities. 

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