Cation polyphosphate

Controlled-release fertilisers can be made by coating the granules with paraffin wax or urea formaldehyde. This limits the access of water and reduces the rate of solubilisation [34]. Slow-release fertilisers based on mixed cation polyphosphates have been patented [35]. 

Economy 1960-1980 Cations, polyphosphates, gluconates, vanadates molybdates, phosphono acids, polyacrilates, soluble oils, carboxilates, surface active chelates... 

Complex Ion Formation. Phosphates form water-soluble complex ions with metallic cations, a phenomenon commonly called sequestration. In contrast to many complexing agents, polyphosphates are nonspecific and form soluble, charged complexes with virtually all metallic cations. Alkali metals are weakly complexed, but alkaline-earth and transition metals form more strongly associated complexes (eg, eq. 16). Quaternary ammonium ions are complexed Htde if at all because of their low charge density. The amount of metal ion that can be sequestered by polyphosphates generally increases... 

Sequestration forms the basis for detergent and water-treatment appHcations of polyphosphates. Sequestration of hardness ions by sodium tripolyphosphate used in detergent formulations prevents the precipitation of surfactants by the hardness ions. Sodium polyphosphate glass (SHMP) may be added to water system to prevent the formation of calcium or magnesium scales by reducing the activity of the hardness ions. However, if the ratio of cation to polyphosphate is too high at a given pH, insoluble precipitates such as may result instead of the soluble polyphosphate complexes. The... 

Various polyphosphates are effective sequestering agents under appropriate conditions. The best known of these is sodium hexametaphosphate (10.14), the cyclic hexamer of sodium orthophosphate. Further examples are the cyclic trimer sodium trimetaphosphate (10.15), as well as the dimeric pyrophosphate (10.16), the trimeric tripolyphosphate (10.17) and other linear polyphosphates (10.18). All of these polyanions function by withdrawing the troublesome metal cation into an innocuous and water-soluble complex anion by a process of ion exchange as shown in Scheme 10.7 for sodium hexametaphosphate. Hence these compounds are sometimes referred to as ion-exchange agents. 

Coenzymes complement the catalytic action of the amino-acid functional groups. They are bound to apoenzymes (apoproteins) either covalently or non-covalently. It is interesting to note that non-covalently-bound coenzymes are polyanions at neutral pH as exemplified by the structures of glutathione (GSH) [17] and thiamine pyrophosphate [18]. Shinkai and Kunitake (1976b, 1977a) demonstrated the efficient binding of glutathione and coenzyme A (a polyphosphate) to cationic micelles and cationic polysoaps. Thus, the combina- ... 

This Group IIA (or Group 2) element (atomic symbol, Ca atomic number, 20 atomic weight, 40.078 electronic configuration = ls 2s 2p 3s 3p 4s ) loses both As electrons to form a divalent cation of 0.99A ionic radius. Ionic calcium combines readily with oxygen ligands (chiefly water, phosphates, polyphosphates, and carbox-ylates) to form stable metal ion complexes. Ca under-... 

Among condensed phosphate systems with polyvalent cations, the very complicated calcium salts have been much studied and a great number of compounds have been detected, often with several modifications (5, 27, 28, 34, 54, 79, 186, 137, 191, 198, 204, 211, 276, 805, 830). In this system special interest attaches to the occurrence of crystalline cross-linked phosphates (see Section V) and of calcium pentaphosphate, CayiPsOis (see Section IV,D,/). The end-product obtained by heating Ca(H2P04)2 in the free atmosphere is the high-molecular calcium polyphosphate, which crystallizes in several forms. The condensed strontium phosphates (246, 805) are similarly complicated and cannot readily be made the subject of a brief review. 

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). 

As in the hydrolysis of polyphosphates (Sections IV,B, and IV,E,1), hydrolysis of the trimetaphosphate anion is eatalytically accelerated by added cations. Their effect is attributed, as in the ease of the polyphosphates, to the formation of complex ions of the type CafPsOs)- or Ba(P309)- and Na PsOs)3 (130, I44, 146). 

Ions which do not have a rare gas configuration appear not to fit into this rule. They are much more firmly bound than the alkali and alkaline earth cations. A dependence on radius is not observed and for Hg(I) the binding is stronger with the diphosphate anion than with triphosphate 366). (See, also the binding of cations by highmolccular polyphosphates, Section IV,E,/,d.) For the analysis and determination of triphosphates, see Section VII,B. 

Polyphosphates seem to pass through a minimum of stability for a chain length of about n = 10 359). Decreasing the pH accelerates hydrolysis. Thus, for example, the following values of tVi are found for high-molecular anions at 60°C with varying pH. Added cations have a similar action to... 

H+ ions. Addition of 0.164 milli-equivalents of cations per millimole of NaP03 increases the rate constant K for the degradation of polyphosphates at pH 8 and 60°C by the following factors relative to the constant K0 in absence of added salts 361). 

Catalytic Action of Various Cations on the Rate of Hydrolysis of Polyphosphates... 

The composition of the precipitates formed by polyphates depends on the way in which they are produced. If a solution of the precipitating cation is added to a polyphosphate solution, or if the solid polyphosphate is treated with the salt solution, only part of the cation of the phosphate taken is, as a rule, replaced by the precipitating cation 92, 290, 291). Conversely, when precipitation occurs by adding polyphosphate to a concentrated solution of the salt precipitates are formed which contain only the cation of the salt 177, 324). 

Partial replacement of cations when using excess of alkali phosphate was at first interpreted by supposing that the cations were in part bound as a complex with the polyphosphates. This led to incorrect conclusions regarding the molecular size of polyphosphates, which persist even now in the designation of Graham s salt as hexametaphosphate. The correct interpretation of these very complicated relationships stems from the discovery that in dilute solutions of polyphosphates even salts of the alkali metal ions are only partially dissociated—up to a maximum of 30-40% 260, 280, 282, 288, 333). The degree of dissociation a for alkali polyphosphates depends on many factors. Thus, for example, the effective degree of... 

If the exchange constants for the cations are compared with their catalytic activity (Table XI) and the order of their degrees of dissociation in polyphosphate solutions (Table XII), a considerable measure of correlation will be recognized. It follows that the cations become more active catalytically as they become more strongly bonded to the polyphosphate anions. This also accords with the increase in their effectiveness as the dielectric constant of the solvent is decreased. 

In addition to the ability of polyphosphates to bond cations they also possess the important property of hindering the formation of large crystallites of CaCO i and of solid boiler scale, even when present at very small concentrations (239). This property, which is used in the threshold or in-noculation process, is based on the bonding or adsorption of polyphosphate chains on the surface of the crystal nucleus. These then hinder its further growth or aggregation. The effectiveness of detergents to which polyphosphates have been added must also be related to their adsorption on the... 

Since all condensed phosphates are ultimately degraded to monophosphate in hot solution, especially at low pH, the total phosphorus(V) content of a substance may readily be determined after hydrolysis either gravimetrically or titrimetrically (109). However, as soon as it is a question of estimating the content of separate components in mixtures of condensed phosphates insuperable difficulties are encountered if methods depending on precipitation, titration, or a combination of the two are used. Even a quantitative precipitation of monophosphate is impossible if polyphosphates with chain length of n = 3 or more arc present in the solution. The precipitating cation and the compound to be precipitated by it are partly kept in solution by the polyphosphate part of the polyphosphate is also carried down by the precipitate. Both of these effects depend in their extent in different ways on the nature and quantity of the substances present and the analysis gives a correct quantitative result only in isolated instances... 

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