Catena-polyphosphates

Crystalline polyammonium catena-polyphosphate, (NH4) H2P 03 + 1, has been prepared by heating urea and monoammonium orthophosphate under ammonia vapor for 16 hours,1 by ammoniation of superphosphoric acid,2 by thermal condensation of urea phosphate,3 and by heating various ammonium phosphates in a current of ammonia.4,5 The procedure given below, in which crude ammonium tetrametaphosphate is reorganized and condensed to a long-chain polymer in a stream of ammonia, is straightforward and permits the use of common laboratory equipment and supplies. 

The charge is conveniently heated in a 1-L resin reaction vessel equipped with a heating mantle or in a small oven a larger oven may be used if the ammonia is passed directly over the charge. The product should be cooled below 150° under ammonia to avoid deammoniation in handling. The product weighs 32.3 g and is a crystalline solid with the optical, X-ray powder diffraction pattern, and infrared absorption pattern reported for form I polyammonium catena-polyphosphate.2,6 Anal. Calcd. for (NH4) H2P 03 +i with n = 50 N, 14.38 P, 31.81. Found N, 14.4 P, 31.8. 

Form I polyammonium catena-polyphosphate contains the shortest long-chain anions of several polymorphic forms having the same chemical composition.1 It is slightly soluble in water and gives a cloudy, viscous solution. The solubility increases with the quantity of solid phase present the apparent solubility of the pure compound at 25° has been estimated to be 0.15 g per 100 g of water.1 The compound is more soluble in hot water or in the presence of other dissolved... 

Polyphosphates occurring in water have either linear structures (catena-polyphosphates) or cyclic structures (cyclo-polyphosphates). 

The chemical formula of the rare earth metaphosphates has been presented as RP3O5 and R(P03)3. The correct name for the first formula would be cyclotriphosphate and for the second catena-polyphosphate. Most of the metaphosphates described in the literature are catena-polyphosphates, but this is not obvious from either the formulas or the names generally used. 

Tetravalent cerium behaves exceptionally upon heating with H3PO4. With low P/Ce ratio (1-3) it forms diphosphate, CePjO, and with a higher proportion of phosphorus it forms catena-polyphosphate, Ce(P03)4. Cerium may also reduce to trivalent in this system, with the formation of Ce(P03)3 at lower temperatures and the ultraphosphate CeP50j4 at higher temperatures (Tsuhako et al., 1979). 

The condensed rare earth phosphates decompose to orthophosphates, releasing P2O5. Ultraphosphates decompose via catena-polyphosphate (Bagieu-Beucher and Tranqui, 1970). The decomposition scheme for EuH(P03)4, for example, is ... 

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