Salts, oxygen reducing

Thiophene-1-oxide and 1 -substituted thiophenium salts present reduced aromaticity.144 A variety of aromaticity criteria were used in order to assess which of the 1,1-dioxide isomers of thiophene, thiazole, isothiazole, and thiadiazole was the most delocalized (Scheme 46).145 The relative aromaticity of those molecules is determined by the proximity of the nitrogen atoms to the sulfur, which actually accounts for its ability to participate in a push-pull system with the oxygen atoms of the sulfone moiety. The relative aromaticity decreases in the series isothiazole-1,1-dioxide (97) > thiazole-1,1 -dioxide (98) > thiophene-1-dioxide (99) then, one has the series 1,2,5 -thiadiazole-1,1 -dioxide (100) > 1, 2,4-thiadiaz-ole-1,1-dioxide (101) > 1,2,3-thiadiazole-1,1 -dioxide (102) > 1,3,4-thiadiazole-l,1-dioxide (103) in the order of decreasing aromaticity. As 1,2,5-thiadiazole-1,1-dioxide (100) was not synthesized, the approximations used extrapolations of data obtained for its 3,4-dimethyl-substituted analogue 104 (Scheme 46). 

As a general rule the presence of dissolved salts, chemically neutral towards oxygen, reduces the solubility of the gas. Thus, in the case of sea-water, the value for )9 falls with rising chlorine content, as indicated m the following table 3... 

Cobaltic Sulphate, Co2(S04)3.18H20, is obtained by electrolysis of cobaltous sulphate in a platinum dish, which serves as anode, the cathode consisting of a platinum wire immersed in a porous cell containing dilute sulphuric acid. The salt is deposited as blue silky needles round the anode. It is soluble in water, yielding an unstable blue solution which evolves oxygen, the salt being reduced to cobaltous sulphate. Upon exposure to air the crystals gradually decompose. In contact with hydrochloric acid, chlorine is evolved.3... 

The reaction is undoubtedly assisted by the Lewis acid character of aluminum salts which reduce the effective negative charge on oxygen. The remaining steps in the reduction are still more complex but also involve lithium and aluminum salts. For example, further reaction of the bis-alkoxide dianion could involve expulsion of as an... 

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. 

High purity acetaldehyde is desirable for oxidation. The aldehyde is diluted with solvent to moderate oxidation and to permit safer operation. In the hquid take-off process, acetaldehyde is maintained at 30—40 wt % and when a vapor product is taken, no more than 6 wt % aldehyde is in the reactor solvent. A considerable recycle stream is returned to the oxidation reactor to increase selectivity. Recycle air, chiefly nitrogen, is added to the air introducted to the reactor at 4000—4500 times the reactor volume per hour. The customary catalyst is a mixture of three parts copper acetate to one part cobalt acetate by weight. Either salt alone is less effective than the mixture. Copper acetate may be as high as 2 wt % in the reaction solvent, but cobalt acetate ought not rise above 0.5 wt %. The reaction is carried out at 45—60°C under 100—300 kPa (15—44 psi). The reaction solvent is far above the boiling point of acetaldehyde, but the reaction is so fast that Httle escapes unoxidized. This temperature helps oxygen absorption, reduces acetaldehyde losses, and inhibits anhydride hydrolysis. 

Another group of compounds called oxygen scavengers retard oxidation by reducing the available molecular oxygen. Products in this group are water soluble and include erythorbic acid [89-65-6] C HgO, and its salt sodium erythorbate [6381-77-7] C HgO Na, ascorbyl pahnitate [137-66-6] 22 38 7 ascorbic acid [50-81-7] C HgO, glucose oxidase [9001-37-0] and sulfites (23). 

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 ... 

Alkyl hydroperoxides can be Hquids or soHds. Those having low molecular weight are soluble in water and are explosive in the pure state. As the molecular weight increases, ie, as the active oxygen content is reduced, water solubiUty and the violence of decomposition decrease. Alkyl hydroperoxides are stronger acids than the corresponding alcohols and have acidities similar to those of phenols, Alkyl hydroperoxides can be purified through their alkali metal salts (28). 

---