Acid metaphosphates

Apart from nitrate ions, the direct reduction of carbonate, phosphate, and silicate anions have all been reported. Some controversy surrounds the electroreduction of sulfate ions water may be implicated in this process. Inman and Wrench could only induce cathodic electroactivity of sulfate ions dissolved in a chloride melt by release of SO3, the conjugate acid, with a stronger Lux-Flood acid, metaphosphate, P03. While the alkali metal and alkaline earth sulfates, carbonates, and nitrates are clearly ionic, borate, phosphate, and silicate melts are highly polymerized. In such systems, the mobile cations move freely about the anion lattice network, which comprises a temperature- and compositional-dependent equilibrium between ion fragments of variable chain length. Inman and Franks observed kinetically limited electroreduction processes in a phosphate melt, as might be expected if only the smallest fragments of the dynamic polymer equilibrium are electroactive. 

NaH2(P03)3l Sodium dihydrogen polyphosphate (sodium acid metaphosphate)... 

When sodium acid metaphosphate was first discovered, one form of [Na2H(P03)3]n salt was extremely easy to crystallize as a pure compound. After some initial work was completed, I decided that the remainder of this system should be explored. Three more new salts were discovered, but the initial supply of the first discovered salt had become exhausted. 

Two of the new salts discovered in the sodium acid metaphosphate were fibrous with asbestiform crystals and both are respectable candidates for fiber applications. If the salt, [Na2H(P03)3] , was ever to be practical, a better way of crystallization was surely required. The salt [Na3H(P03)4]n was very easily made and had properties that should have been quality fibers. It had a very slow rate of solution and was similar to Maddrell s salt in many of its properties. The phase diagram for this system is presented in Figure 5.9. The diagram was particularly difficult to obtain because these salts were inclined to become unstable at temperatures approaching their melting temperatures. 

Seeding is very important when growing condensed phosphates, and yet seeding is very poorly understood. Currently it is impossible to know, before a crystal is tried experimentally, whether or not it will induce crystallization in a melt. The first crystals of the sodium acid metaphosphate system were obtained while passing an electrical current through a melt of an amorphous salt. It was never known for certain if this was responsible for the crystallization, or was merely chance and crystallization would have occurred spontaneously without the electric... 

Figure 5.9. The phase diagram for the sodium acid metaphosphate system area A contains Na2H2(P03>4 plus liquid area B contains Na2H(P03>3 plus liquid area C contains Na3H(P03>4 plus liquid area D contains [NaPOa] plus liquid.

The monofluorophosphates can be prepared by neutralization of monofluorophosphoric acid (1). Sodium monofluorophosphate [7631 -97-2] is prepared commercially (57) by fusion of sodium fluoride and sodium metaphosphate, and the potassium monofluorophosphate [14104-28-0] can be prepared similarly. Insoluble monofluorophosphates can be readily prepared from reaction of nitrate or chloride solutions with sodium monofluorophosphate. Some salts are prepared by metathetical reactions between silver monofluorophosphate [66904-72-1] and metal chlorides. 

Chemical Designations - Synonyms Sodium phosphate is generic term and includes the following (1) monosodium phosphate (MSP sodium phospWe, monobasic), (2) disodium phosphate (DSP sodium phosphate dibasic), (3) trisodium phosphate (TSP sodium phosphate, tribasic), (4) sodium acid pyrophosphate (ASPP SAPP disodium pyrophosphate (TSPP), (6) sodium metaphosphate (insoluble sodium metaphosphate), (7) sodium trimetaphosphate, and (9) sodium tripolyphosphate (STPP TPP) Chemical Formula (1) NaHjPO (2) Na HPO (3) NajPO (4) Na H P O, (5) Na P O, (6) (NaPOj) (7) (NaP03)3 (8) (NaP03) NaO (9) Na,P30,o. 

These compounds were formerly called meta-phosphoric acids and metaphosphates but the lURAC cyclo- nomenclature is preferred as being structurally more informative. The only... 

The earliest formulations, as reported by Rollins (1879), Gaylord (1889), Ames (1893), Hinkins Acree (1901) and Fleck (1902), were variously based on syrupy orthophosphoric acid or unstable mixtures of meta-phosphoric acid and sodium metaphosphate in solution. Some used solid pyrophosphoric acid. Many were grossly inferior cements which were hydrolytically unstable. 

J. P. Guthrie, Hydration and Dehydration of Phosphoric Acid Derivatives Free Energies of Formation of the Pentacoordinate Intermediates for Phosphate Ester Hydrolysis and of Monomeric Metaphosphate, J. Am. Chem. Soc. 1977, 99, 3391. 

The monomeric metaphosphate ion itself commands a fair amount of attention in discussions of metaphosphates. It is postulated as an intermediate of numerous hydrolysis reactions of phosphoric esters 52 S4,S5) and also of phosphorylation reactions S6> kinetic and mechanistic studies demonstrate the plausibility of such an assumption. In addition, the transient formation of ester derivatives of meta-phosphoric acid — in which the double-bonded oxygen can also be replaced by thio and imino — has also been observed they were detected mainly on the basis of the electrophilic nature of the phosphorus. 

As for the acetyl phosphate monoanion, a metaphosphate mechanism has also been proposed 78) for the carbamoyl phosphate monoanion 119. Once again, an intramolecular proton transfer to the carbonyl group is feasible. The dianion likewise decomposes in a unimolecular reaction but not with spontaneous formation of POf as does the acetyl phosphate dianion, but to HPOj and cyanic acid. Support for this mechanism comes from isotopic labeling proof of C—O bond cleavage and from the formation of carbamoyl azide in the presence of azide ions. 

Reactions of Phosphoric Acid and its Derivatives.—Theoretical studies on the conformational properties of cyclic and acyclic phosphate esters, including calculations of angle and torsional strain,66 and on the reactivity of monomeric metaphosphates,67 have appeared. 

These neutralization processes may be used for the preparation of various complex fluorides without actually isolating the acid or the base. Thus, for example, if equivalent quantities of metallic silver and gold are dissolved in bromine trifluoride and all volatile material is removed in vacuum, the salt AgAuFg remains. The usefulness of this method is increased by the apparent existence in bromine trifluoride solution of both acids and bases which are not sufficiently stable to be isolated. This is well illustrated by the reaction of potassium metaphosphate with bromine trifluoride, which gives a quantitative yield of KPFg ... 

Elemental composition P 38.73%, H 1.26%, O 60.01%. The compound may be identified by physical properties alone. It may be distinguished from ortho and pyrophosphates by its reaction with a neutral silver nitrate solution. Metaphosphate forms a white crystalline precipitate with AgNOs, while P04 produces a yellow precipitate and P20 yields a white gelatinous precipitate. Alternatively, metaphosphate solution acidified with acetic acid forms a white precipitate when treated with a solution of albumen. The other two phosphate ions do not respond to this test. A cold dilute aqueous solution may be analyzed for HPO3 by ion chromatography using a styrene divinylbenzene-based low-capacity anion-exchange resin. 

Anhydrous salt white crystalline powder slightly hygroscopic forms sodium acid pyrophosphate, Na2H2P20 on heating above 225°C and sodium metaphosphate (NaPOsln at about 350 to 400°C very soluble in water, aqueous solution acidic. 

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