Silver hypophosphate

The mixed calcium salt is dissolved in ZN nitric acid, using 15ml of the latte for every 2g of the material The clear solution is diluted to double its volume with distilled water and fig of silver nitrate (for each 2g portion of calcium salt) is dissolved in the liquid. The mixture is stirred until the beige precipitate settles out. This is filtered, the silver hypophosphate rinsed with acetone, and the product is dried in warm air. It is only slighter photosensitive and may be stored in clear bottles in artificial light for extended periods of time. 

Silver hypophosphate, Ag4P206.—Silver nitrate gives with sodium hypophosphate, Na4P206, a white precipitate of silver hypophosphate. It is also produced in crystalline form by boiling a solution of silver nitrate in nitric acid with phosphorus. Heat decomposes it into silver metaphosphate and metallic silver 3... 

The yield is about lg for every 2g of starting material. From this result the actual hypophosphate content of the calcium salts obtained may be estimated, as the formation of the silver salt is quantitative in terms of the hypophosphate actually present in the intermediate material. 

Hypophosphates are extremely stable to alkali hydroxides. No decomposition occurs in 80% NaOH at 200°C after 1 h, but with fused caustic soda at 320°C there is rapid conversion to orthophosphate (5.244). If silver, mercury or copper hypophosphates are heated below 200°C in nitrogen, decomposition to metal, orthophosphate and a mixture of condensed phosphates occurs. Strong heating gives a mixture of metaphosphate and metal (5.245). 

Solutions of phosphites and hypophosphites with silver nitrate give initially white precipitates of silver phosphite and silver hypophosphite, respectively. Both these precipitates decompose to give metallic silver on warming (14.7) and (14.8). This test will distinguish them from hypophosphates or fully oxidised phosphates whose silver salts are relatively stable when precipitated. 

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