Sodium Tripolyphosphate → Pyrophosphate

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The industrially important pentasodium triphosphate, Na5P3O10 (sodium tripolyphosphate), is a nonhygroscopic, white, water-soluble salt which is anhydrous or crystallizes with 6H2O and has the general formula NaO—[P(O)(ONa)—O]n—Na where n=3. About 17 g of the salt free from water of crystallization dissolve in 100 g of water at room temperature, about 20 g dissolve at 60° C., and about 32 g dissolve at 100°; after heating the solution for 2 hours at 100°, about 8% orthophosphate and 15% diphosphate are produced by hydrolysis. In the case of the preparation of pentasodium triphosphate, phosphoric acid is reacted with soda solution or sodium hydroxide solution in the stoichiometric ratio and the solution is dewatered by spraying. Similarly to Graham's salt and sodium diphosphate, pentasodium triphosphate dissolves many insoluble metal compounds (including lime soaps, etc.). Pentapotassium triphosphate, K5P3O10 (potassium tripolyphosphate), is commercially available, for example, in the form of a 50% strength by weight solution (>23% P2O5, 25% K2O). The potassium polyphosphates are widely used in the detergents and cleaners industry. There also exist sodium potassium tripolyphosphates, which can likewise be used within the scope of the present invention. These form, for example, when sodium trimetaphosphate is hydrolyzed with KOH: (NaPO3)3+2KOH→Na3K2P3O10+H2O

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