Diammonium phosphate

Diammonium phosphate (DAP; IUPAC name diammonium hydrogen phosphate; chemical formula (NH4)2(HPO4) is one of a series of water-soluble ammonium phosphate salts that can be produced when ammonia reacts with phosphoric acid.

Diammonium phosphate[1]
Names
IUPAC name
diammonium hydrogen phosphate
Other names
ammonium monohydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate dibasic
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.029.079
E number E342(ii) (antioxidants, ...)
UNII
  • InChI=1S/2H3N.H3O4P/c;;1-5(2,3)4/h2*1H3;(H3,1,2,3,4) checkY
    Key: MNNHAPBLZZVQHP-UHFFFAOYSA-N checkY
  • InChI=1/2H3N.H3O4P/c;;1-5(2,3)4/h2*1H3;(H3,1,2,3,4)/p-1
    Key: MNNHAPBLZZVQHP-REWHXWOFAG
  • [NH4+].[NH4+].OP([O-])([O-])=O
Properties
(NH4)2HPO4
Molar mass 132.06 g/mol
Appearance colorless monoclinic crystals
Density 1.619 g/cm3
Melting point 155 °C (311 °F; 428 K) decomposes
57.5 g/100 mL (10 °C)
106.7 g/100 mL (70 °C)
Solubility insoluble in alcohol, acetone and liquid ammonia
1.52
Thermochemistry
−1566.91 kJ/mol
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
2
0
1
Flash point Non-flammable
Safety data sheet (SDS) ICSC 0217
Related compounds
Other anions
 Monoammonium phosphate
Triammonium phosphate
Other cations
 Disodium phosphate
Dipotassium phosphate
Related compounds
 Ammonium nitrate
Ammonium sulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references

Solid diammonium phosphate shows a dissociation pressure of ammonia as given by the following expression and equation:[2]

(NH4)2HPO4(s) ⇌ NH3(g) + (NH4)H2PO4(s)

At 100 °C, the dissociation pressure of diammonium phosphate is approximately 5 mmHg.[3]

According to the diammonium phosphate MSDS from CF Industries, Inc., decomposition starts as low as 70 °C: "Hazardous Decomposition Products: Gradually loses ammonia when exposed to air at room temperature. Decomposes to ammonia and monoammonium phosphate at around 70 °C (158 °F). At 155 °C (311 °F), DAP emits phosphorus oxides, nitrogen oxides and ammonia."

Uses

DAP is used as a fertilizer.[4] When applied as plant food, it temporarily increases the soil pH, but over a long term the treated ground becomes more acidic than before, upon nitrification of the ammonium. It is incompatible with alkaline chemicals because its ammonium ion is more likely to convert to ammonia in a high-pH environment. The average pH in solution is 7.5–8.[5] The typical formulation is 18-46-0 (18% N, 46% P2O5, 0% K2O).[5]

DAP can be used as a fire retardant. It lowers the combustion temperature of the material, decreases maximum weight loss rates, and causes an increase in the production of residue or char.[6] These are important effects in fighting wildfires as lowering the pyrolysis temperature and increasing the amount of char formed reduces that amount of available fuel and can lead to the formation of a firebreak. It is the largest component of some popular commercial firefighting products and is the ingredient in "fire retardant" cigarettes.[7]

DAP is also used as a yeast nutrient in winemaking and mead-making; as an additive in some brands of cigarettes purportedly as a nicotine enhancer; to prevent afterglow in matches, in purifying sugar; as a flux for soldering tin, copper, zinc and brass; and to control precipitation of alkali-soluble and acid-insoluble colloidal dyes on wool.[1]

Natural occurrence

The compound occurs in the nature as the exceedingly rare mineral phosphammite.[8][9] The related dihydrogen compound occurs as the mineral biphosphammite.[10][9] Both are related to guano deposits.[8][10]

References
  1. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. John R Van Wazer (1958). Phosphorus And Its Compounds - Volume I: Chemistry. New York: Interscience Publishers, Inc. p. 503.
  3. McKetta Jr, John J., ed. (1990). Encyclopedia of Chemical Processing and Design (Chemical Processing and Design Encyclopedia). New York: Marcel Dekker, Inc. p. 478. ISBN 0-8247-2485-2.
  4. IPNI. "Diammonium Phosphate" (PDF). www.ipni.net. International Plant Nutrition Institute. Archived (PDF) from the original on 24 September 2015. Retrieved 21 July 2014.
  5. International Plant Nutrition Institute. "Nutrient Source Specifics: Diammonium Phosphate" (PDF). Archived (PDF) from the original on 2012-10-21. Retrieved 2012-12-10.
  6. George, C.W.; Susott, R.A. (April 1971). "Effects of Ammonium Phosphate and Sulfate on the Pyrolysis and Combustion of Cellulose". Research Paper INT-90. Intermountain Forest and Range Experiment Station: USDA Forest Service. OL 16022833M.
  7. Phos-Chek MSDS, Phos-Chek website
  8. "Phosphammite". www.mindat.org. Retrieved 8 November 2020.
  9. "List of Minerals". www.ima-mineralogy.org. 21 March 2011. Retrieved 8 November 2020.
  10. "Biphosphammite". www.mindat.org. Retrieved 8 November 2020.
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