Hydrogen in alkaline

The reduction of indigo by electrolytic hydrogen in alkaline suspension, the fluid being warmed, has already been carried out by Fr. Goppelsroder3 and v. Wartha.4 Mullerus 5 easily reduced indigosulphonic acid. 

Exchange of hydrogen in alkaline solution was reported by Franke and M5nch and subsequently confirmed but attributed to exchange of phosphite formed by alkaline decomposition. A study by proton nmr methods reports simple first-order dependence on the concentrations of HjPOJ and OD. At 25°C and H = 2.0, the rate parameters are k = (6.0+0.7)10 l.mole . sec ( a = 18.9 0.5 kcal.mole ). Reaction of D2POJ and OH has k = (1.92 0.1)10 l.mole sec ( a = 18.7 kcal.mole ). It is suggested that there may be general base catalysis, from qualitative observations of the effect of phosphate. 

The usefulness of the Amadori rearrangement in chemical synthesis was demonstrated by Weygand who showed how n-arabinose, instead of the more expensive n-ribose, could be used in the preparation of riboflavin. Condensation of n-arabinose with 3,4-dimethylaniline in the presence of an acid catalyst gave the Amadori rearrangement product, 1-deoxy-l-(3,4-dimethylanilino)-D-er2/ liro-pentulose (not isolated), which could be catalytically hydrogenated in alkaline solution to produce the desired intermediate, l-deoxy-l-(3,4-dimethylanilino)-D-ribitol. Also, Amadori re-... 

The lactone (464) was reduced with lithium aluminium hydride to the (20/ )-18,20-diol. Regeneration of the A -3-keto-group afforded the keto-diol (465). Catalytic hydrogenation in alkaline medium selectively reduced the double bond at C(4) and gave the desired configuration of 5)5-H. Acetylation at C(18) was followed by oxidation, which provided the diketo-pregnane (466). Hydroxy-la tion of the -double-bond of (466) with osmium tetroxide gave the 3a,9a-... 

Hydrogen termination of the silicon surface appears to occur over the whole pH range from acidic to basic whenever the surface is not covered with an oxide film. The silicon surface is found to be covered with hydrogen in alkaline solution even under... 

Since most metallic sulphides are insoluble, many are precipitated when hydrogen sulphide is passed through solutions containing ions of the metals. Some are precipitated in acid, and others in alkaline... 

The amount of oxygen evolved is not related to the degree of bleaching (40). Oxidative decoloring is caused by hydrogen peroxide or by the HO ions present in alkaline solution. Hydrogen peroxide is also an effective solvent for melanin (41). 

Weak to moderate chemiluminescence has been reported from a large number of other Hquid-phase oxidation reactions (1,128,136). The Hst includes reactions of carbenes with oxygen (137), phenanthrene quinone with oxygen in alkaline ethanol (138), coumarin derivatives with hydrogen peroxide in acetic acid (139), nitriles with alkaline hydrogen peroxide (140), and reactions that produce electron-accepting radicals such as HO in the presence of carbonate ions (141). In the latter, exemplified by the reaction of h on(II) with H2O2 and KHCO, the carbonate radical anion is probably a key intermediate and may account for many observations of weak chemiluminescence in oxidation reactions. 

The reduction of the nitro group to yield aniline is the most commercially important reaction of nitrobenzene. Usually the reaction is carried out by the catalytic hydrogenation of nitrobenzene, either in the gas phase or in solution, or by using iron borings and dilute hydrochloric acid (the Bechamp process). Depending on the conditions, the reduction of nitrobenzene can lead to a variety of products. The series of reduction products is shown in Figure 1 (see Amines byreduction). Nitrosobenzene, /V-pbenylbydroxylamine, and aniline are primary reduction products. Azoxybenzene is formed by the condensation of nitrosobenzene and /V-pbenylbydroxylamine in alkaline solutions, and azoxybenzene can be reduced to form azobenzene and hydrazobenzene. The reduction products of nitrobenzene under various conditions ate given in Table 2. 

Hydrogen peroxide greatly accelerates the decomposition of ozone in alkaline solutions because of formation of HOg, which reacts rapidly with ozone to form the radical ion (25). When the concentration of H2O2 exceeds 10 Af, the decomposition of ozone is initiated faster by HOg than by... 

Rate studies show that base-cataly2ed reactions are second order and depend on the phenolate and methylene glycol concentrations. The most likely path involves a nucleophilic displacement by the phenoxide on the methylene glycol (1), with the hydroxyl as the leaving group. In alkaline media, the methylolated quinone intermediate is readily converted to the phenoxide by hydrogen-ion abstraction (21). 

The perhydroxyl ion, OOH , derived from the dissociation of hydrogen peroxide in alkaline solution, is generally considered the active agent in the bleaching of wood pulp using hydrogen peroxide. This ionization may be expressed by the following reversible reaction ... 

Steric and inductive effects determine the rate of formation of the pentacovalent siUcon reaction complex. In alkaline hydrolysis, replacement of a hydrogen by alkyl groups, which have lower electronegativity and greater steric requirements, leads to slower hydrolysis rates. Replacement of alkyl groups with bulkier alkyl substituents has the same effect. Reaction rates decrease according to ... 

Most mineral acids react vigorously with thorium metal. Aqueous HCl attacks thorium metal, but dissolution is not complete. From 12 to 25% of the metal typically remains undissolved. A small amount of fluoride or fluorosiUcate is often used to assist in complete dissolution. Nitric acid passivates the surface of thorium metal, but small amounts of fluoride or fluorosiUcate assists in complete dissolution. Dilute HF, HNO, or H2SO4, or concentrated HCIO4 and H PO, slowly dissolve thorium metal, accompanied by constant hydrogen gas evolution. Thorium metal does not dissolve in alkaline hydroxide solutions. 

Hydrogen peroxide bleaching is performed in alkaline solution where part of the hydrogen peroxide is converted to the perhydroxyl anion (eq. 14). 

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