Oxygen-free

Although sulphur dioxide, as a gas, is a reducing agent in the sense that it unites with oxygen, free or combined (for example in dioxides or peroxides) most of its reducing reactions in aqueous solution are better regarded as reactions of sulphurous acid (in acid solution), or the sulphite ion (in alkaline solution). 

In water pollution studies, the oxygen content can be measured by making the water alkaline and shaking a measured volume with an oxygen-free solution containing Mn- (aq). The solution is acidified with sulphuric acid, potassium iodide added and the liberated iodine titrated with sodium thiosulphate. 

Oxygen-free nitrogen in cylinders is available commercially but is, of course, more expensive than the normal commercial compressed gas. 

If preferred, the apparatiaa depicted in Fig. II, 7, 13 may be used. This enables an oxygen-free nitrogen atmosphere to be maintained in the apparatus and leads to the best yield of phenyl-lithium. 

Add 40 ml. of ethyl alcohol to 21 -5 g. of 70 per cent, ethylenediamine solution (0 -25 mol) dissolve 36 -5 g. of adipic acid (0 -25 mol) in 50 ml. of a 6 1 mixture of ethyl alcohol and water. Mix the two solutions, stir and cool. Filter off the resulting salt and recrystalliae it from 60 ml. of a 6 1 ethyl alcohol - water mixture, and dry the salt in the air. Heat the salt in an atmosphere of oxygen-free nitrogen or of carbon dioxide in an oil bath until it melts (ca. 160°) the product will sohdify after a short time. Reduce the pressure to 15 mm. of mercury or less and raise the temperature of the oil bath until the product remelts (about 290°) and continue the heating for 4r-5 hours. Upon coohng, a nylon type polymer is obtained. 

Barium is a metallic element, soft, and when pure is silvery white like lead it belongs to the alkaline earth group, resembling calcium chemically. The metal oxidizes very easily and should be kept under petroleum or other suitable oxygen-free liquids to exclude air. It is decomposed by water or alcohol. 

Compound 36 when treated by sulfur under nitrogen, leads to the thiazoline-2-thione (37) (Scheme 16) (43). Oxidation by O- or air of 36 (43) or 38 (45, 46) leads to the corresponding thiazoiine (39 or 40). Consequently, condensation reactions using catalysts like 36 must be run in strictly oxygen-free atmosphere (47-50). The isolation of traces of 3-benzyl-4-methyl-A-4-thiazoline-2-one (42) as a product of the oxidation of... 

Copper and Copper Alloys. The coppers are divided into oxygen-bearing and oxygen-free coppers. Numerous copper alloys are of commercial importance, including those alloys with zinc (brasses), with tin (phosphor bronzes), and with aluminum (aluminum bronzes) all are weldable. 

Water reacts violently with aH halogen fluorides. The hydrolysis process can be moderate by cooling or dilution. In addition to HF, the products may include oxygen, free halogens (except for fluorine), and oxyhalogen acids. 

Reduction. Hafnium oxide can be reduced using calcium metal to yield a fine, pyrophoric metal powder (see Calciumand calciumalloys). This powder contains considerable oxygen contamination because of oxygen s high solubility in hot hafnium, and caimot be consoHdated into ductile metal. To obtain low oxygen ductile hafnium, the feed must be an oxygen-free halide compound such as hafnium tetrachloride or potassium hexafluorohafnate [16871-86-6]. 

The majority of thermal polymerizations are carried out as a batch process, which requires a heat-up and a cool down stage. Typical conditions are 250—300°C for 0.5—4 h in an oxygen-free atmosphere (typically nitrogen) at approximately 1.4 MPa (200 psi). A continuous thermal polymerization has been reported which utilizes a tubular flow reactor having three temperature zones and recycle capabiHty (62). The advantages of this process are reduced residence time, increased production, and improved molecular weight control. Molecular weight may be controlled with temperature, residence time, feed composition, and polymerizate recycle. 

Values are minimum for the primary metal and maximum for impurity concentrations. Oxygen-free electrolytic copper containing 0.0001 wt % Bi and Cd and 0.00005 wt % Mn. 

Once purification of the niobium has been effected, the niobium can be reduced to the metallic form. The double fluoride salt with potassium, K2NbFy, can be reduced using sodium metal. The reaction is carried out in a cylindrical iron vessel filled with alternating layers of K NbF and oxygen-free sodium ... 

Titanium disulfide can also be made by pyrolysis of titanium trisulfide at 550°C. A continuous process based on the reaction between titanium tetrachloride vapor and dry, oxygen-free hydrogen sulfide has been developed at pilot scale (173). The preheated reactants ate fed iato a tubular reactor at approximately 500°C. The product particles comprise orthogonally intersecting hexagonal plates or plate segments and have a relatively high surface area (>4 /g), quite different from the flat platelets produced from the reaction between titanium metal and sulfur vapor. The powder, reported to be stable to... 

Obtaining pure ductile zirconium by reduction of the oxide is particularly difficult because of the tendency of hot zirconium to dissolve considerable amounts of oxygen, making the metal britde at room temperature. Therefore, it is common practice to reduce oxygen-free zirconium tetrachloride. 

Ghromium(II) Compounds. The Cr(II) salts of nonoxidizing mineral acids are prepared by the dissolution of pure electrolytic chromium metal ia a deoxygenated solution of the acid. It is also possible to prepare the simple hydrated salts by reduction of oxygen-free, aqueous Cr(III) solutions using Zn or Zn amalgam, or electrolyticaHy (2,7,12). These methods yield a solution of the blue Cr(H2 0)g cation. The isolated salts are hydrates that are isomorphous with and compounds. Examples are chromous sulfate heptahydrate [7789-05-17, CrSO 7H20, chromous chloride hexahydrate... 

The rod resulting from the dip-forming process is substantially oxygen-free because the oxygen content in the molten bath must be controlled at less than 20 ppm. 

Figure 12 contrasts the decrease in conductivity of ETP copper with that of oxygen-free copper as impurity contents are increased. The importance of oxygen in modifying the effect of impurities on conductivity is clearly illustrated. Phosphoms, which is often used as a deoxidizer, has a pronounced effect in lowering electrical conductivity in oxygen-free copper, but Httie effect in the presence of excess oxygen. 

Fig. 12. Decrease in copper conductivity in the presence of the indicated impurities (a) tough-pitch copper and (b) oxygen-free copper.

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