Purification of Sodium Tetrametaphosphate

Three hundred grams of crude sodium tetrametaphosphate 4-hydrate (ca. 0.63 mol) is dissolved in 2 1. of water at room temperature and the solution filtered if necessary. The solution is stirred vigorously, and a total of 11. of 95% ethanol is added, the first part of the alcohol in a steady stream until precipitation begins and the remainder more slowly over a period of at least 30 minutes. The crystals are removed by filtering and are washed successively with 300 ml. of 35% ethanol and 300 ml. of 50% ethanol. Ethanol on the crystals is allowed to evaporate, and the crystals are dissolved in 1 1. of water, t The compound is reprecipitated as before by adding 500 ml. of 95% ethanol. J Two such precipitations eliminate phosphate impurities which give multiple end points in acid-base titrations.1 The yield of the air-dried product is 195 to 

A 10 to 15% aqueous solution is prepared from the purified sodium tetrametaphosphate. The solution is cooled to room temperature, and sufficient cold concentrated sodium hydroxide solution to give a final concentration of 8.5 to 10% tetrametaphosphate and a mol ratio of hydroxide to tetrametaphosphate of 3 1 is added. The temperature is not permitted to rise above 40° during this addition. The resulting solution is stored at constant temperature, and aliquots are titrated periodically for excess sodium hydroxide to pH 10. When 1.90 to 1.95 mols of sodium hydroxide has been consumed, f giving a 9.8 to 11.5% solution of sodium tetraphosphate, an equal volume of 95% ethanol is added and the system allowed to stand until two clear liquid layers are formed. The upper layer is discarded, and the sirupy lower layer, containing about 46% sodium tetraphosphate, is reserved for procedure C.f 

The product is purified by dissolving 45 g. of it and 5 g. of guanidonium chloride in 75 ml. of water, diluting with sufficient formamide (ca. 70 ml.) to produce permanent turbidity, and crystallizing as outlined above. 

The product is washed and dried as in its preparation. About 85% of the guanidonium tetraphosphate is recovered in each recrystallization. Anal, (after one recrystallization). Calcd. for [(NH2)2C=NH-H]6P40i3-H20 P, 17.46 N, 35.5 H20, 2.54 [(NH2)2C=NH-H]6P40i3, 97.5. Found P, 17.2, 17.7 N, 34.6, 36.0 H20, 2.8, 2.9 [(NH2)2C= NH-H]6P40i3,t 97.98. An acid-paper chromatogramj on a sample 2 years old indicated 2% of the total phosphorus as orthophosphate, 2% as pyrophosphate, none as triphosphate, and 96% as tetraphosphate. An alkaline-paper chromatogram J revealed no ring compounds. 

Submitted by Stanley K. Yasuda and Jack L. Lambert Checked by L. E. NETHERTONf and Vincent R. WiederkehrI1 

---