Tetraammonium Pyrophosphate

Submitted by C. Swanson and F. McCollough Checked by Ralph K. BranwHisTELLf 

Tetraammonium pyrophosphate has been prepared by bubbling ammonia into an ice-water solution of pyrophos- 

Fifty grams (0.28 mol) of solid pyrophosphoric acid is dissolved, with stirring, in 2 1. of 95% ethanol maintained at 5° in a 3-1. beaker, A small quantity of decolorizing charcoal is added and the solution is filtered by suction into another 3-1. beaker which is kept in a salt-ice-water bath. The pyrophosphoric acid solution is agitated vigorously while ammonia is bubbled through a gas inlet tube of 1 cm. i.d. into the solution. The ammonia is added at a rate such that the temperature of the solution does not rise above 10°. Almost immediately, diammonium dihydrogen pyrophosphate precipitates from solution however, continued ammoniation converts this substance to the tetraammonium salt. 

Ammoniation is complete when a 1 % solution of a portion of the solid product (which has been washed thoroughly with fresh ethanol) has a pH of approximately 8.2. (For complete reaction, ammonia must be added for 2 to 4 hours.) When conversion to the tetraammonium salt has been completed, passage of ammonia is discontinued, but stirring is maintained until the temperature of the reaction mixture reaches 20°. The product is then filtered under suction onto a Buchner funnel and air is pulled through the filter cake for one hour. The product is placed on a large dish and vacuum-dried at 25°. Yields of 90 to 95 % are obtained. Anal. Calcd. for (NH4)4P207 P, 25.2 N, 22.8. Found P, 25.6 N, 22.8. 

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Tetraammonium pyrophosphate is a colorless, water-soluble crystalline compound which loses ammonia very slowly when exposed to the atmosphere. 

P20j(NH4)2H2 Diammonium dihydrogen pyrophosphate, 7 66 P207(NH4)4 Tetraammonium pyrophosphate, 7 65 P207Na2H2 Disodium dihydrogen pyrophosphate, 3 99 P207Na4 Tetrasodium pyrophosphate, 3 100... 

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