Salts of Polyvalent Cations

Little is known about the effects of other cations on bile salts (1). Calcium ions precipitate free bile salts readily. Calcium and magnesium also precipitate dihydroxy glycine conjugates, but not trihydroxy glycine conjugates or taurine conjugates. Since certain types of gallstones are primarily the calcium salts of abnormal bile acids [see (9) for summary of mechanism], it is important to establish the solubilities of bile salts of polyvalent cations alone and in mixtures with other ions. 

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Alkali Meta.IPhospha.tes, A significant proportion of the phosphoric acid consumed in the manufacture of industrial, food, and pharmaceutical phosphates in the United States is used for the production of sodium salts. Alkali metal orthophosphates generally exhibit congment solubility and are therefore usually manufactured by either crystallisation from solution or drying of the entire reaction mass. Alkaline-earth and other phosphate salts of polyvalent cations typically exhibit incongment solubility and are prepared either by precipitation from solution having a metal oxide/P20 ratio considerably lower than that of the product, or by drying a solution or slurry with the proper metal oxide/P20 ratio. 

For ionized or bulky head groups, the temperature at which the expanded to condensed film transition occurs will be lower than that for the corresponding unionized material. Slightly ionized salts of polyvalent cations, on the other hand, will have higher transition temperatures. 

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. 

Many orthophosphate salts, in particular those of polyvalent cations, exhibit incongment solubihty where disporportionation occurs in solution to yield a more basic orthophosphate salt and phosphoric acid. This hydrolytic disproportionation of orthophosphates should not be confused with the... 

The stability of the GdNaY zeolites in solutions containing cations (Na, K, Ca, Mg ) that typically occur in gastric and intestinal fluid was also studied. Using 0.025 M salt solutions (relatively high concentrations compared to the GI conditions), in the case of Na and K, no release of gadolinium was detected. However, in the presence of polyvalent cations (Ca " " and Mg " "), leaching of 2-5 % Gd(III) took place. 

A comparative study of the products of dehydration of the dihydrogen monophosphates of polyvalent cations showed that the stable end-products for cations with ionic radii between 0.57 and 1.03 A. (Cu++, Mg++, Ni++, Co++, Fe++, Mn++, Zn"1-1", Cd++, A1+++) are tetrametaphosphates. When the cations are either larger or smaller the end-products of dehydration are crystalline high-molecular polyphosphates (Li+, Be++, K+, Rb+, Cs+, Ag+, Zn++, Cd++, Hg++, Ca++, Sr++, Ba++ Pb++, Cr+++, Fe+++, Bi+++). In the case of the alkali salts only sodium trimetaphosphate occurs as a condensed phosphate with a cyclic anion (304, 305). Up to the present, an alkali tctrametaphosphate has not been observed as the dehydration product of a dihydrogen monophosphate. Consequently, alkali tetrametaphosphates arc obtainable only indirectly. Reference is made later (Section IV,C,4) to the fact that the tetraphosphates of barium, lead, and bismuth are formed as crystalline phases from melts of the corresponding composition. There are also reports of various forms of several condensed phosphates of tervalent iron and aluminum (31, 242, 369). 

The fact that most triphosphates of polyvalent cations which are difficultly soluble in water are soluble in excess of triphosphate, and that such polyvalent cations (e.g. Ca++) are either not precipitated or not quantitatively precipitated by the usual reagents from solutions of their salts containing triphosphate, has become of great commercial importance in water softening (90). The term sequestration is used in this connection. Numerous publications have appeared which are not mentioned in detail here, and which attempt to determine this property quantitatively. In general, the effect is attributed to the formation of relatively stable ion pairs or complexes, the stability of which is defined by the formation constants K or K. ... 

Monophosphorylation pastes made from starch monophosphates also have greater clarity, viscosity and stability than unmodified starches,64 but are sensitive to salts, especially polyvalent cations.65 Variability in residual ash can lead to variability in the viscosity of monophosphorylated starches. Monophosphate substitution also lowers the gelatinization temperature at 0.07 DS, a value much greater than is found in food starches, the gelatinization temperature is below room temperature. Native potato starch contains 0.07 to 0.09% bound phosphorus and wheat starch contains 0.055% phosphoms, primarily as phosphoglycerides in the latter case. The FDA allows up to 0.4% phosphate as phosphoms.58 Monophosphates were used commercially in the US until about 1970. 

Incompatibilities of anionic emulsifying wax are essentially those of sodium alkyl sulfates and include cationic compounds (quaternary ammonium compounds, acriflavine, ephedrine hydrochloride, antihistamines, and other nitrogenous compounds), salts of polyvalent metals (aluminum, zinc, tin, and lead), and thioglycollates. Anionic emulsifying wax is compatible with most acids above pH 2.5. It is also compatible with alkalis and hard water. 

A variety of organic compounds are oxidized by salts of polyvalent metals. We have already discussed one-electron oxidations by some Lewis acids and noted that the mechanisms of these oxidations are unknown. In contrast, oxidations by some other metal salts have been studied quite thoroughly and much is known about the mechanisms. Of particular interest to us are cobalt(III), man-aganese(III), lead(IV), and cerium(IV) salts, and the most commonly used are the acetates. Another contrast with the Lewis acids is that cation radicals formed in oxidations by salts of polyvalent metals usually have short lifetimes since they are involved in further... 

In the presence of polyvalent cations, the electric potential can be affected by the formation of bridges between cations and the adsorbents or by the formation of organic phosphate salts that precipitate on the reacting surfaces. For instance, with calcium ions the adsorption of myo-inositol hexakisphosphate increases above pH 5,... 

Thus, alginic acids form water-soluble salts with monovalent cations but are precipitated in the presence of polyvalent cations, such as Ca ", Sr ", and Ba , among others. pH of the medium has also an important role in the solubility of... 

With an ionic system, such displacement results from an increase in salinity of the aqueous pha.se, a reduction of the oil EACN either by using a shorter alkane or by adding polar or aromatic components, the addition of some lipophilic alcohol starting with n-pcntanol up to a few vol less with hexanol or higher alcohols. Finally the surfactant may be mixed with a less hydrophilic surfactant of the sante family (e.g.. with a longer tail). If dte system contains nonionic surfactants an increase in temperature would decrea.se the hydrophilic interaction quite rapidly while the electrolyte effect would be alnntsl negUgihIc. with the exception of polyvalent cation salts. 

For ions with univalent cations and polyatomic anions Cp is very roughly (3 1 )pbR, where v is the number of ions per formula unit of the salt and b is the number of bonds in the anion. Much fewer data are available for the Cp of molten salts with multivalent cations, practically limited to those with divalent cations and lanthanides, shown in Table 3.12. CorrelatiOTi expressions similar to Eq. (3.30) were presented in [202] for molten salts with polyvalent cations. 

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