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 6 H2O and has the general formula NaO—[P(O)(ONa)—O]n—Na where n=3. About 17 g of the salt which is free from water of crystallization dissolve in 100 g of water at room temperature, at 60° about 20 g, at 100° around 32 g; after heating the solution at 100° for two hours, about 8% orthophosphate and 15% diphospate are produced by hydrolysis. For the preparation of pentasodium triphosphate, phosphoric acid is reacted with sodium carbonate solution or sodium hydroxide solution in stoichiometric ratio and water is removed from the solution by spraying. In a similar way to Graham's salt and sodium diphosphate, pentasodium triphosphate dissolves numerous insoluble metal compounds (including lime soaps etc.). Penta-potassium triphosphate, K5P3O10 (potassium tripolyphosphate), is available commercially, for example, in the form of a 50% strength by weight solution (>23% P2O5, 25% K2O). The potassium polyphosphates are used widely in the washing and cleaning products industry. There are also sodium potassium tripolyphosphates which can likewise be used for the purposes of the present invention. These are formed, for example, when sodium trimetaphosphate is hydrolyzed with KOH: (NaPO3)3+2KOH→Na3K2P3O10+H2O

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