TetrametaPhosphate, sodium

Sodium tetrametaphosphate [13396-41-3] M 429.9, pKj 2.60, pKj 6.4, pKj 8.22, pK 11.4 (tetrametaphosphoric acid, H4P4O12). Crystd twice from water at room temperature by adding EtOH (300g of Na4P40i2,H20, 2L of water, and IL of EtOH), washed first with 20% EtOH then with 50% EtOH and air dried [Quimby J Phys Chem 58 603 1954]. 

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 infrared and ltaman spectra of sodium tetrametaphosphate differ little from those of the trimetaphosphates (57, 139). The Raman spectra of crystalline tetrametaphosphates vary with the nature of the cation (275) and, from the infrared spectra, different symmetries are assigned to the anions of different salts. 

Measurements of the electrical conductivity and solubility of difficultly soluble salts in sodium tetrametaphosphate solutions 62, 151, 196, 197) and potentiometric titrations lead to the assumption of the existence of complexes of the type of Na+(P40i2)3 Ba"1-1", Sr, Ca++, Mg++, Mn++, Ni++, Cu++(PiO]2) - La(P40i2) Cu(P40i2)26- and Ni(P40i2)26. No comparable dissociation constants for these have so far been given, though in any case they will be smaller than for the corresponding ion pairs of the trimetaphosphate anion 145). 

In strongly alkaline solution hydrolysis of sodium tetraphosphate takes place so much more slowly than that of the tetrametaphosphate that tetraphosphate accumulates in the solution in a practically pure state... 

Decomposition Half-Lives for Sodium Trimeta- and Tetrametaphosphate Anions in Aqueous Solution at 60°C as a Function of pH... 

Pure or very nearly pure sodium tetraphosphate is obtained in the bimolecular reaction involving alkaline cleavage of the cyclic anion of sodium tetrametaphosphate in aqueous solution at temperatures up to 40°C (233, 312, 355, 356). The tetraphosphate Na6P40i3-aq... 

K2P20 Potassium dimetaphosphate. Na2P209, Sodium trimetapnosphate. Pb2P4012, Lead tetrametaphosphate. (NH4)6PsP15, Ammonium pentametaphosphate. Na4P4019, Sodium hexametaphosphate. 

Sodium telluropentathionate 2-hydrate, 4 88, 89 Sodium tetrametaphosphate 4-hydrate, Na4P40i2-4H20, purification of, for preparation of sodium tetraphosphate, 6 98 Sodium tetraphosphate, Na P Oi3, for preparation of hexaguani-donium tetraphosphate 1-hydrate, 5 99... 

Three hundred grams of crude sodium tetrametaphosphate 4-hydrate (ca. 0.63 mol) is dissolved in 2 1. of water at room temperature and the solution filtered if necessary. The solution is stirred vigorously, and a total of 11. of 95% ethanol is added, the first part of the alcohol in a steady stream until precipitation begins and the remainder more slowly over a period of at least 30 minutes. The crystals are removed by filtering and are washed successively with 300 ml. of 35% ethanol and 300 ml. of 50% ethanol. Ethanol on the crystals is allowed to evaporate, and the crystals are dissolved in 1 1. of water, t The compound is reprecipitated as before by adding 500 ml. of 95% ethanol. J Two such precipitations eliminate phosphate impurities which give multiple end points in acid-base titrations.1 The yield of the air-dried product is 195 to... 

A 10 to 15% aqueous solution is prepared from the purified sodium tetrametaphosphate. The solution is cooled to room temperature, and sufficient cold concentrated sodium hydroxide solution to give a final concentration of 8.5 to 10% tetrametaphosphate and a mol ratio of hydroxide to tetrametaphosphate of 3 1 is added. The temperature is not permitted to rise above 40° during this addition. The resulting solution is stored at constant temperature, and aliquots are titrated periodically for excess sodium hydroxide to pH 10. When 1.90 to 1.95 mols of sodium hydroxide has been consumed, f giving a 9.8 to 11.5% solution of sodium tetraphosphate, an equal volume of 95% ethanol is added and the system allowed to stand until two clear liquid layers are formed. The upper layer is discarded, and the sirupy lower layer, containing about 46% sodium tetraphosphate, is reserved for procedure C.f... 

The most important cyclic phosphate is tetrametaphosphate, which can be prepared by heating copper nitrate with slightly more than an equimolar amount of phosphoric acid (75%) slowly to 400°. The sodium salt can be obtained by treating a solution of the copper salt with Na2S. Slow addition of P4O10 to ice water gives 75% of the P as tetrametaphosphate. 

Hexasodlum tetraphosphate is formed by careful hydrolysis of sodium tetrametaphosphate (see p. 553) (method of Thilo and Ratz) ... 

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