Aqueous solution disproportionation reactions

It has come to the authors attention that data cited by Maxwell (II) indicate that Reaction 5 does not occur in aqueous solution. Disproportionation reactions... 

Table 6 presents a summary of the oxidation—reduction characteristics of actinide ions (12—14,17,20). The disproportionation reactions of UO2, Pu , PUO2, and AmO are very compHcated and have been studied extensively. In the case of plutonium, the situation is especially complex four oxidation states of plutonium [(111), (IV), (V), and (VI) ] can exist together ia aqueous solution ia equiUbrium with each other at appreciable concentrations. 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

Both monocalcium phosphate and dicalcium phosphate dissolve incongmently in water, disproportionating to more basic calcium phosphate and phosphoric acid. The extent of these reactions varies with the temperature and the amount of water. If water is added gradually to anhydrous monocalcium phosphate, equiUbrium conditions first correspond to a mixture of the anhydrous salt and its monohydrate. After conversion to the monohydrate, further reaction affords dicalcium phosphate plus free phosphoric acid. Dicalcium phosphate decomposes in aqueous solution to the more basic hydroxyapatite and phosphoric acid via intermediate octacalcium phosphate. The compHcated stepwise conversion of the acidic mono- and dicalcium phosphates to hydroxyapatite is summarized in equations 6—9. The kinetics are quite complex. 

Dichloramine. The least stable chloramine, dichloramine [3400-09-7] has not been prepared in pure form. However, it has sufficient stabiUty in dilute organic or aqueous solutions for deterrnination of some physical and chemical properties. It has a pungent odor and can impart an odor or off-taste to water at concentrations above 0.8 ppm. Dichloramine can be produced by reaction of HOCl with a slight excess of NH in the pH range 4—7 or by disproportionation of NH2CI at pH 3.5—4.0 ... 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

Anhydrous NaC102 crystallizes from aqueous solutions above 37.4° but below this temperature the trihydrate is obtained. The commercial product contains about 80% NaC102. The anhydrous salt forms colourless deliquescent crystals which decompose when heated to 175-200° the reaction is predominantly a disproportionation to C103 and Cl but about 5% of molecular O2 is also released (based on the C102 consumed). Neutral and alkaline aqueous solutions of NaC102 are stable at room temperature (despite their thermodynamic instability towards disproportionation as evidenced by the reduction potentials on p. 854). This is a kinetic activation-energy effect and, when the solutions are heated near to boiling, slow disproportionation occurs ... 

More recently Hand et al. (ref. 9) have studied the decomposition reaction of N-chloro-a-amino acid anions in neutral aqueous solution, where the main reaction products are carbon dioxide, chloride ion and imines (which hydrolyze rapidly to amine and carbonyl products). They found that the reaction rate constant of decarboxylation was independent of pH, so they ruled out a proton assisted decarboxylation mechanism, and the one proposed consists of a concerted decarboxylation. For N-bromoamino acids decomposition in the pH interval 9-11 a similar concerted mechanism was proposed by Antelo et al. (ref. 10), where the formation of a nitrenium ion (ref. 11) can be ruled out because it is not consistent with the experimental results. Antelo et al. have also established that when the decomposition reaction takes place at pH < 9, the disproportionation reaction of the N-Br-amino acid becomes important, and the decomposition goes through the N,N-dibromoamino acid. This reaction is also important for N-chloroamino compounds but at more acidic pH values, because the disproportionation reaction... 

Cobalt(II) complexes of three water-soluble porphyrins are catalysts for the controlled potential electrolytic reduction of H O to Hi in aqueous acid solution. The porphyrin complexes were either directly adsorbed on glassy carbon, or were deposited as films using a variety of methods. Reduction to [Co(Por) was followed by a nucleophilic reaction with water to give the hydride intermediate. Hydrogen production then occurs either by attack of H on Co(Por)H, or by a disproportionation reaction requiring two Co(Por)H units. Although the overall I easibility of this process was demonstrated, practical problems including the rate of electron transfer still need to be overcome. " " ... 

In order to elucidate the causes of the increased stability of the hydrolyzed cluster ions compared with the unhydrolyzed ions, further studies were made of the behaviour of [Te2X8]3 (where X = Cl,Br, or I) in solutions of hydrogen halides [43,52,80,87]. The studies were performed mainly in relation to the most stable and most readily synthesized [Tc2C18]3- ion (Fig. la) kinetic methods with optical recording were employed. The identity of the reaction products was in most cases confirmed by their isolation in the solid phase. The studies showed that the stability of the [Tc2X8]3 ions (where X = Cl, Br, or I) in aqueous solutions is determined by the sum of competing processes acid hydrolysis complex formation with subsequent disproportionation and dissociation of the M-M bonds, and oxidative addition of atmospheric oxygen to the Tc-Tc multiple bond. 

While this decomposition reaction is slow at room temperature, the disproportionation process can be accelerated by heat, certain catalysts (e.g., metal ions), and light. Traces of alkali metal ions are normally present in aqueous solutions stored in glass bottles, so plastic or wax-coated glass containers reduce the concentration of metal ion catalysts. Brown-colored containers limit the wavelengths of light that can be absorbed by the solution, restricting the initiation of the disproportionation reaction. 

The fact that 4-hydroxycyclohexene can be formed both by a reaction in which two radicals disappear16 and in a reaction which does not consume radicals complicates the calculation of the yield of radicals in the /-radiolysis (continuous radiolysis) of N2O-saturated aqueous solution of 1,4-cyclohexadiene. Von Sonntag and coworkers14 wrote that the yield of radical 4 is 0.31 pmolJ-1. From their data it must be concluded that 4-hydroxycyclohexene (yield of 0.25 pmolJ-1) is formed solely by reaction 15, neglecting its formation by disproportionation (reaction 16). However, they found a yield of... 

Write the net ionic equation and the half-reactions for the disproportionation of mercury(I) ions in aqueous solution to give liquid mercury and aqueous mercury(II) ions. Assume that mercury(I)... 

Reaction of silver(I) with macrocyclic tetraaza ligands has been found to be a facile process for forming silver(II) complexes.450,451 Metallic silver was a by-product in each of these reactions. In dry acetonitrile, however, no disproportionation occurred and with (57) a white silver(I) complex precipitated. The necessity for water to be present for disproportionation was shown by the fact that if this complex was then added to water or aqueous methanol solutions, disproportionation then readily occurred.451... 

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