Reactions in Strongly Alkaline Solution

Alkaline reaction conditions occur in food, e. g., in the isolation of sucrose from sugar beet and in 

In this disaccharide, fructose is present mainly as the pyranose (Ila) and, to a small extent, as the furanose (lib). 

Lactulose utihzation in infant nutrition is under consideration since it acts as a bifidus factor and prevents obstipation. 

Oxidation of the enediol occurs in the presence of oxygen or other oxidizing agents, e. g., Cu +, resulting in carboxyhc acids. In such a reaction with glucose, the main products are D-arabinonic and 

The nonstoichiometric sugar oxidation process in the presence of alkali is used for both qualitative and quantitative determination of reducing sugars (Fehling s reaction with alkaline cupric tartrate Nylander s reaction with alkaline trivalent bismuth tartrate or using Benedict s solution, in which cupric ion complexes with citrate ion). Hydroxyaldehydes and hydroxyketones are formed by chain cleavage due to retroaldol reaction under nonoxidative conditions using dilute alkali at elevated temperatures or concentrated alkali even in the cold. 

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The kinetics of the xanthation of sucrose were studied in the same year by Cherkasskaya, Pakshver, and Kargin, who determined potentiometric-ally the concentrations of the dithiocarbonate derivative and also of inorganic sulfide and trithiocarbonate. The rate of formation of 0-(sodium thiol-thiocarbonyl)sucrose was found to pass through a maximum with increasing alkali concentration, presumably due to a shift of the equilibrium in favor of side reactions in strongly alkaline solution. This result appears to parallel the qualitative findings of Lieser and Hackl for polysaccharides. 

The mechanism of reaction in strongly alkaline solutions proposed by Li and White is... 

These compounds are stable, green, crystalline solids, less stable in solution and easily oxidized. Tetrahedral structures are assigned on the basis of magnetism (/ieff = 3.0-3.3 B.M. at 298°K) and electronic spectra, in which properties they closely resemble tetrahedral nickel(n) species such as NiX2(PR3)2 and [NiX(PR3)3] +. The Co1 product of the following reaction in strongly alkaline solution may be tetrahedral ... 

The formation of trisubstituted A-4 thiazoline-2-ones from the corresponding thiones analogs can be performed by oxidation with hydrogen peroxide under basic conditions. This reaction is strongly dependent on the pH of the medium. Higher yields are obtained in strongly alkaline solution (883). 

The alkah manganates(V) in strongly alkaline solution (45—50% at 0°C) are all blue. In water these manganate(V) compounds instantly disproportionate into manganate(VI) and Mn02. Lithium manganate(V), prepared by reaction of LiMnO and excess LiOH at 124°C, is an exception. This compound is relatively stable in 3% LiOH solution at 0°C and in absolute methyl alcohol. 

The reaction in equation 55 occurs when there is insufficient hydrogen peroxide reductant in the absorber solution. Monitoring of the hydrogen peroxide concentration is important because is unstable in strong alkaline solutions, decomposing to water and oxygen. A small excess of sodium hydroxide is... 

Potassium permanganate may also be used in strongly alkaline solutions. Here two consecutive partial reactions take place ... 

At low pH values, dimerization must involve the combination of two neutral carbon radicals since the same ( ) / meso ratio is obtained as from the photochemical reaction of the carbonyl compound in methanol [26], a process which also involves neutral radicals. The switch in isomer ratio to that characteristic of alkaline media occurs in the region of pH close to the value of pKj for the neutral radical. Dimerization then occurs in a fast reaction between the radical-anion and the neutral radical. In strongly alkaline solutions where the pH pK the major reactive species formed at the potential of the first reduction wave is the radical-anion. Reaction between two radical-anions is relatively slow due to coulorobic repulsion so that dimerization in strongly alkaline solution still occurs by reaction... 

As discussed above, Pt is the reference electrode material for H2 evolution since it is the most active elemental cathode. H2 is formed on Pt with a Tafel slope of 30-40 mV, the lowest ever observed for this reaction. Its cost makes this metal unsuitable for routine applications. In fact, cathode materials traditionally used in technology have long been iron or mild steel in acidic solution and Ni in (strongly) alkaline solution. Steel can also be used in moderately basic solution. 

There are two approaches to the analysis. In the first, the extractable ammonium-N is determined by a Kjeldahl distillation, and this is subtracted from the value for ammonium plus nitrate (and nitrite) determined by a further separate Kjeldahl distillation preceded by reduction with nascent hydrogen produced by the reaction of Devarda s alloy (45% Al, 50% Cu, 5% Zn) in strongly alkaline solution ... 

Several reactions of diquaternary salts of 4,4 -bipyridine have attracted attention. The behavior of 1,1 -dialkyl diquaternary salts in strong alkaline solution has long been of interest. They give intense blue-violet colorations on treatment with aqueous potassium hydroxide, and the deep color is discharged on shaking in air. The blue-violet color is largely due to radical cations such as 94. The mechanism of the reaction of paraquat dication (95) with alkali has been elucidated. There are several competing... 

The trail-blazing patent of Goto et al. ( ) for the oxidative dehydrogenation of aminoalcohols to the corresponding aminocarboxylic acid salts over Raney copper catalysts in strongly alkaline solutions was cast in terms of the general reaction... 

The electrochemical oxidation of aromatic aldehydes (1) must be studied in strongly alkaline media. Acidity functions for strongly alkaline aqueous solutions of alkali metal and quaternary ammonium hydroxides, corresponding to dissociation of proton (H ), are well established (2, 3). Substituted anilines and diphenylamines (4,5) and indoles (6) were used as acid-base indicators for establishment of such scales, but whether an acidity scale based on one type of indicator can be rigorously applied to acid-base equilibria involving structurally different acidic groups for reactions in strongly alkaline media remains questionable. For substituted anilines, behavior both parallel (7) and nonparallel (8) to the H scale based on indole derivatives has been reported. The limited solubility of anilines in aqueous solutions of alkali metal hydroxides, the reactions of the aniline derivative with more than one hydroxide ion, irreversible substitution reactions (9), and the possibility of hydroxide ion addition rather than... 

The mesomeric quinonemethides and 0-quinonemethides described above are somewhat more stable than the simple p-quinonemethides whose properties are already well known even from classical studies. The o-quinonemethides XX and XVII do not add on water even in solution in aqueous organic solvents their solution in dioxane/water is stable for months. They do not add on methanol or higher alcohols and react only slowly with phenols and organic acids. The addition of water is not catalyzed by mild alkalies the red color of the phenoxide ion (XVIII) prevails for weeks in soda solution. Addition of water occurs more rapidly in strongly alkaline solution. The addition of mineral acids and reduction by sodium borohydride are instantaneous. The addition of HC1 is rapid even at pH 4.0, the conditions used for determining the carbonyl content of lignin by the hydroxylamine hydrochloride reaction 13). 

That this reaction proceeds is related to the fact that Na+(aq) can exist at strongly alkaline pH the high solubility in water of Na OH is likewise related to the stability of Na+(aq). Sodium(I) forms no anionic species, even in strongly alkaline solution. 

In strongly alkaline solutions the hydroxyl radical is transformed into its basic form, the oxide monoanion radical [reaction (10)]. The... 

Kobussen et al. [281 285] have carried out a detailed study of the oxygen evolution reaction on La05Ba(lr)CoO3 principally in strongly alkaline solution. Following reaction order studies [282], impedance measurements [283, 286], and overpotential decay behavior studies [287], a modified Krasil -shchikov [288] mechanism was proposed for oxygen evolution on this oxide catalyst. The first three steps of this mechanism are similar to eqns. (52)-(55) written as equilibrium processes. An alternative to step reaction (54) was... 

The electrode reaction is over the greater part of the pH region a two-electron reduction to the alcohol, but in strongly alkaline solution an appreciable amount of pinacol is formed. The stereochemistry of the pinacol mixture has not yet been investigated. 

The reversible potential for the oxygen system in an air saturated solution varies from about +1.23v (hydrogen scale) at pH= 0 to about +0.40v in strong alkaline solutions. In neutral solution the potential is about +0.81v. It should not be necessary to consider reactions at more noble potentials than the above for most metals since (iQ)o is about 10 amp/cm or less on their surface. ... 

Equation (10) is a useful tool to establish outer-sphere mechanisms in cases in which neither the reduction potential nor the self-exchange rate for one of the reactants is known. Such a case has been presented for the reduction of Ag(III) with [Fe(CN)6] , Mn04 ", [WCCNlg] , and [MoCCNlg] " in strong alkaline solution (46). The reaction... 

In strongly alkaline solution, the reaction is of second order in hypobro-... 

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