Potassium trimetaphosphate

Potassium trimetaphosphate can be prepared directly by heating KH2PO4 with urea acting as a dehydrating agent at temperatures near 200 

In a more basic melt it is known that urea is capable of converting some M2O of a system to M2CO3, provided reaction temperatures are low enough that M2CO3 does not react with more condensed phosphate. An example is 

This reaction is not complete in experiments performed by the author, but since K2O is definitely a chain breaker or a ring opener, it can be seen why potassium trimetaphosphate can be formed thermally, at lower temperatures, where it would not normally be expected to form. Formation of K2CO3 removes K2O from the reaction zone. This reaction is similar to a well-known reaction of NH4CI with basic phosphates to make MCI and a more condensed phosphate. This lower-temperature chemistry is worthy of more study and should yield many surprising ways to make compounds that are not phase diagram entities, as they are prepared from melts. 

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The formation of potassium trimetaphosphate by condensation reactions at ordinary temperatures, and acid sodium trimetaphosphate, are dealt with in Sections VI,B,8 and V,A, respectively. 

Kurrol s potassium polyphosphate through a whole series of intermediate polyphosphates. The fact that potassium trimetaphosphate is formed by direct heating of K4(P40i2) to temperatures above 200°C is an indication of the occurrence of radical-like fragments as intermediate products 119). 

The sodium polyphosphate systems produce glasses very easily while it is difficult to make potassium glasses. The milky glassy masses of potassium metaphosphate compositions obtained by quenching the potassium melts are rich in potassium trimetaphosphate, though the phase diagram for the system contains none. Potassium cyclic triphosphate can be made thermally by dehydrating monopotassium orthophosphate with urea at temperatures less than 300 C,... 

KP03)3-II was first prepared by Grunze and co-workers (24). When potassium dihydrogen orthophosphate is treated with a mixed solution of acetic acid and diacetyl oxide (acetic anhydride) at 90°C. for 24 hr., almost all of it is converted into crystalline potassium trimetaphosphate (KP03)3-II. 

The silver salt, obtained by reaction (5.166), reacts with KCl to give potassium trimetaphosphate... 

Unlike the sodium systems, melt history has less influence on potassium Kurrol s salt systems mentioned above. Potassium trimetaphosphate is not a phase diagram entity. Potassium phosphate melts with R values of unity are very difficult to quench to glasses, because they crystallize very rapidly. If potassium phosphate melts are cooled slowly, long-chain polyphosphates, [KPOsln, are the only crystals to form. No other crystals are thermodynamically stable in this portion of their phase diagram and Kurrol s salts dominate a large area of this diagram. 

Other Tripolyphosphates. Potassium tripolyphosphate [24315-83-1] (KTP), K P O q, has a high aqueous solubihty (near 180 g/100 g) and has been used in place of STP for Hquid detergents. The potassium salt, however, is more expensive than STP. Sodium potassium tripolyphosphate (SKTP), Na K P O Q, is prepared by calcination of a feed Hquor having the proper Na20/K20ratio or by reaction of sodium trimetaphosphate with KOH. For some detergent or food appHcations, SKTP may provide the optimum compromise between solubihty and cost. 

Cross-linking Monostarch phosphate - Esterification with ortho-phosphoric acid, or sodium or potassium ortho-phosphate, or sodium tripolyphosphate Distarch phosphate - Esterification with sodium trimetaphosphate or phosphorus oxychloride Phosphated distarch phosphate - Combination oftreatments for monostarch phosphate and distarch phosphate... 

In the system (KII2P04—H3P04) high-molecular potassium polyphosphates are formed on heating, together with acid mono- and di-phosphate but only a little oligophosphate (363). But tertiary P04 tetrahedra occur not only in phosphates with Na P < 1. They can also be detected in Graham s and Kurrol s salt with Mr P = 1 (224, 284, 85, 86) and are also formed in melts of anhydrous trimetaphosphates, especially in a dry atmosphere (364). Their equilibrium concentration in the melt is about 2%. 

Variations of this polymerization reaction are exhibited by potassium and sodium salts because of topochemical reasons and because of the greater stability of crystalline sodium diphosphate and sodium trimetaphosphate. Of interest to this discussion is the sequence of reactions on... 

In the discussion to follow, the great differences between sodium and potassium condensed phosphate phase systems is highlighted. Where the sodium Kurrol s salt is metastable with respect to the cyclic sodium trimetaphosphate there is no cyclic metaphosphate in the potassium phosphate two component phase system and the Kurrol s salt is the only stable compound in the phase system with K2O-P2O5 ratios near unity. 

Maddrell s salt, which are interpreted as showing that kinetic effects are responsible for difficulties in converting the cyclic trimer into the linear polymeric forms. The potassium polyphosphate samples (Kurrol s salt) obtained from the fusion of potassium sulphate and phosphoric acid have chains terminated by OSOJ groups, according to i.r. spectra. Kinetic studies show a first-order dependence of polyphosphate concentration in the hydrolysis of Graham s salt to give trimetaphosphate and short-chain species. The vaporization of sodium metaphosphate from a Knudsen cell leads to predominantly monomeric, with some dimeric, species, according to mass-spectrometric data. ... 

Anhydrous trimetaphosphates MCaPaOg, where M = Na, K, or NH4, can be obtained by heating the hydrates, which crystallize from aqueous solution to 180 °C. Further heating to 500 °C converts the sodium salt into a high molecular weight polyphosphate while the potassium compound gives a second trimetaphosphate modification. The ammonium salt loses ammonia and phosphorus pentoxide to give calcium polyphosphate. 

The potassium salt cannot be prepared the same way, but if KH2PO4 is heated with acetic anhydride, the ring anion is formed. The salt can be prepared at relatively low temperature using urea (5.161). Heating the trimetaphosphate to higher temperatures results in irreversible transformation to linear polyphosphate (5.162). 

Monosodium hydrogen phosphate Disodium monohydrogen phosphate Trisodium phosphate Sodium pyrophosphate Disodium dihydrogen phosphate Sodium triphosphate Sodium polyphosphate Sodium trimetaphosphate Sodium aluminium phosphate Potassium dihydrogen phosphate Dipotassium hydrogen phosphate Potassium triphosphate Potassium polyphosphate... 

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