Tetrasodium Imidodiphosphate

The crystals effloresce slowly when exposed to air and are decomposed by carbon dioxide. Consequently, they must be kept sealed off from air. This compound is, moreover, very soluble in water. 

When anhydrous disodium monoamidophosphate is heated to 210° under vacuum, anhydrous tetrasodium imi-dodiphosphate is formed.1 

To get a good yield, the disodium monoamidophosphate has to be absolutely free from water. The freshly prepared, crystal, water-containing salt is kept at room temperature in a desiccator over sodium hydroxide or calcium chloride 

Then 10 to 15 g. of the anhydrous disodium monoamido-phosphate is weighed in a 50-ml. flask with a glass joint. The flask is attached to a high-vacuum system, via a stopcock and a trap filled with solid sodium hydroxide, and evacuated. The flask is then heated in an oil bath to 80° and this temperature maintained for 6 hours. The temperature is then raised, and pressure builds up from the ammonia liberated. This gas is pumped off at intervals and the temperature increased to 210°. The formation of ammonia slows down after some time, and the reaction comes to an end after about 7 days. 

In order to purify the crude product, tetrasodium imido-diphosphate, 10 g. of it is put in small portions into 100 ml. of ice-cold water with continuous stirring. Because of hydration the temperature of the solution goes up to 10 to 15°. The clear liquid is immediately precipitated in fractions by acetone. Schematically  

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Then la is discarded and the three fractions lb", 2a, and 26, which contain pure tetrasodium imidodiphosphate, are united. Finally, the crystals are washed with acetone and air-dried. ... 

Tetrasodium imidodiphosphate occurs as colorless crystals, easily soluble in water. It is isomorphous with Na4P2-O7TOH2O. The water solution has a pH of 11 (0.1 M). At the boiling point a cleavage into monoamidophosphate and monohydrogen phosphate occurs ... 

When anhydrous dlsodlum monoamldophosphate is heated In vacuum to 210°C, anhydrous tetrasodium Imidodiphosphate is formed (Klement and Blberacher) ... 

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