Sodium imidodiphosphate

Sodium hypophosphate, Na2H2P2-08-6H20, 4 68 Sodium imidodiphosphate, Na4P208(NH), 6 101 Sodium iodate, 1 168... 

Sodium imidodiphosphate, Na4P20g NH can be recrystallised from water as the decahydrate, which is more soluble (7.34.8 g/100 g H2O) than sodium pyrophosphate decahydrate, Na4P207 IOH2O (11.6 g/100 g H2O) with which it is isoelectronic and isostructural (7.72). 

The action of heat on dry disodium phosphoramidate (e.g. 7 days in vacuo at 210°C) results in condensation to form imidodiphosphate with the elimination of ammonia (7.66). This process can be continued at a higher temperature to give the sodium salt of nitrilo triphosphonic acid (7.67). 

Acid imidodiphosphate salts can be precipitated when the pH of a normal salt solution is lowered by the addition of acetic acid (7.69). In boiling aqueous solutions, imido and nitrilo compounds are hydrolysed rapidly (7.70) and (7.71). Free imidodiphosphoric acid can be prepared from an aqueous solution of the sodium salt, using a weakly acidic cation exchanger. 

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