Oxides solubility effects

The present survey will be confined to corrosion arising as a result of oxidation of the metal to ions, since little information on corrosion involving only metal-solubility effects is available. 

A few years later,3 it was shown that o-iodoxybenzoic acid (36)—itself a precursor in the preparation of Dess-Martin periodinane—is able to oxidize very effectively alcohols in DMSO solution. o-Iodoxybenzoic acid—normally referred to as IBX—exists mainly as a cyclic form 37, which crystallizes as a polymer with very low solubility in most solvents with the exception of DMSO. Although, IBX (36) was already known in 1893,4 this ultracentenial reagent found very little use till very recently, when awareness about its solubility in DMSO was raised. 

As discussed in Chapters 4 and 5, CBPC formation is governed by the oxide solubility. The solubility, in turn, is related to the Gibbs free energy, which is a function of temperature and pressure. As a result, the CBS formulation depends on the downhole temperature and pressure. The effect of the temperature on the solubility has already been discussed in Section 6.4. The pressure effect can be assessed in a similar manner, but as we shall see, it is negligibly small and can be ignored for all practical purposes. 

If we assume in Eq. 15.6 that the volume change AV does not depend on the temperature and pressure, we can write AVf = AVq, and the last two terms on the right-hand side reduce to (Pf — Pq)AVq. Calculations from this equation, based on the ionic radii of the right-hand side and the molecular radii of the left-hand side (see Ref. [4] for these data) of Eq. 15.3, indicate that AVq is very small even at a high pressure difference (Pf — Pq) Therefore, the pressure effects on the oxide solubility can be ignored, and the only variable one needs to consider while formulating the CBS slurry is the downhole temperature. 

In contrast to earlier reports, Palomo and coworicers found that chromium(VI) oxide will effect the oxidation of alcohols in one day at room temperature. They also found that the addition of semicatalydc amounts (0.3 equiv.) of crown ethers (either 18-crown-6 or 12-crown-4) led to significant rate enhancements. The crown ethers are thought to generate a soluble oxidizing agent, similar to the alkyl ammonium salts used for solid-liquid phase transfer with chromium(VI) oxide in dichloromethane (vide irfra). 

Embery, G. and Dugrad, P. H. The isolation of DMSO soluble components from human epidermis preparations A possible mechanism of action of dimethylsulf-oxide in effecting percutaneous migration phenomena. Journal of Investigative Dermatology 57 308-311, 1971. 

Potassium permanganate is very effective in oxidizing soluble manganese. In theory, it requires 1 mg/L of KMnO to oxidize of 0.52 mg of soluble manganese. 

As the induction of hepatic microsomal oxidative activity by a lipid-soluble drug (e.g. phenobarbitone) or xenobiotic could decrease the duration of action of therapeutic agents that are mainly eliminated by microsomal oxidation, the effect of induction would be considered a form of biochemical antagonism. Drug-induced inhibition of microsomal oxidative activity, without adjustment of dosage of a concomitantly administered therapeutic agent that undergoes extensive hepatic metabolism, could lead to toxicity. Cimetidine, ketoconazole and chloramphenicol inhibit hepatic microsomal enzyme activity. 

This species, completely characterized also by X-ray diffraction studies as its tetrahexylammonium salt (Figure 1)5 was responsible for the epoxidation of a series of structurally diversified olefins with typical selectivities of ca. 95% and chemical yields in the range 85-95%. These catalysts have found industrial applications in the epoxidation of alkenes and in the oxidative cleavage of alkenes to carboxylic acids. The favourable characteristics of these catalysts are thermal stability, ease of synthesis, stability to oxidation, solubility- in both water and organic solvents, effectiveness as phase transfer catalysts. 

Parameters describing the effect of particle sizes on the oxide- solubility changes in saturated solutions in the molten equimolar KCl-NaCl mixture at 700 °C... 

The substitution of the melt-anion in a molten alkali-metal halide, i.e. proceeding from chloride melts to bromides and iodides, results in the appreciable reduction in the contribution of the ionized constituent (Me2+ concentration) in the total oxide solubilities in the said melts. The data allow us to trace the effect of the constituent halide ion on the solubilities of metal-oxides in the corresponding melt. It should be noted that the substitution of chloride ions with bromide ones results in an appreciable reduction in the solubilities of all the metal-oxides studied, i.e. the values of pPMeo N become lower by 1-2 orders. At the same time, the oxide dissociation in the saturated solution of the oxide reduces. Thus, a considerable reduction in metal-oxide solubilities in bromide melts as compared with chloride ones can be explained in a similar way. Equilibrium (2.4.13) which takes place at the dissolution of a metal-oxide in an ionic halide melt is superimposed upon the interactions of the metal cation with the anions of the melt-solvent, which are denoted hereafter as X (equation (3.6.3)). 

From the above-mentioned studies [374, 375] it can be concluded that, up to now, systematic solubility investigations in molten potassium halides have not been performed. This also concerns other alkali-metal halide melts, although these results would be very useful for the estimation of the effect of melt acidity and anion composition on metal-oxide solubilities at 800 °C. 

We have also investigated the solubilities of MgO and CaO in molten potassium halides at 800 °C [197] to elucidate the effect of anion composition of the halide melt on metal-oxide solubility. The MgO was found to be practically insoluble in chloride and bromide melts, and the iodide-melt could not be investigated owing to intense iodine evolution from strongly acidic solutions. In contrast, CaO solubility products were determined successfully in all the potassium halide melts at 800 °C, by the potentiometric titration method. The corresponding potentiometric titration curves are shown in Fig. 3.7.16. 

In order to estimate the effect of the cation composition of melts based on alkali-metal halides upon the metal-oxide solubilities, we investigated the... 

The data on the solubility of CaO and ZnO in the chloride melts allow us to trace the effect of the acidic properties of the melt-constituent cation on the metal-oxide solubilities the ratio of the solubilities in K+, Na+ and Li+-based melts is 1 1.5 15. However, these are the total solubilities, and the data are distorted by the contribution of an appreciable concentration of non-dissociated oxide, which is not sensitive to changes in the melt-acidity. It should be emphasized that since we do not know the ratios of the ionized fraction to the non-dissociated one in all the melts studied, we cannot estimate quantitatively the oxoacidic properties of all the melts in question. This neglect of the metal-oxide s dissociation is because the said work was published in 1923, whereas the Lux definition was formulated only in 1939. Therefore, the authors of Ref. [327] did not take into account the dissociation of the oxides in the molten salts, which from our point of view, reduced the significance of this investigation. 

As with the dependences discussed above, the correlation of the metal-oxide solubility with the electronegativity by Allred and Rochow consists of two plots characterized by close slopes. The observed shift of the correlation dependences for s - and 3d-elements can be connected with the systematic difference of the calculated effective charge of the metal cations belonging to the mentioned groups. 

V.L. Cherginets, T.G. Deineka, O.V. Demirskaya and T.P. Rebrova, Potentiometric Investigation of Oxide Solubilities in Molten KCl-NaCl Eutectic. Effect of Surface Area of Solid Particles on the Solubilities, J. Electroanal. Chem. 593 (2002) 171-178. 

Microemulsions play a special role in the incorporation of food additives in finished products [150]. Aromas and some food dyes are typically oil-soluble compounds. It has been shown experimentally that microemulsions formed with Tween 20 are able to solubilise quite large quantities of flavours. Up to 3 moles of flavour could be solubilised per mole of Tween 20. Incorporation of vitamins in foods, e.g. vitamin E, and p-carotene turned out to be also effective. In this case, the solubilisation of vitamin E in nonionic micelles protects it from oxidation decomposition. Finally, the solubilisation of ascorbic acid in sardine oil microemulsion droplets prevents lipid oxidation. The effect is enhanced on adding tocopherol into the oil phase. 

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