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
CAS Number	7783-28-0 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:63051
ChemSpider	22946 Y
ECHA InfoCard	100.029.079
E number	E342(ii) (antioxidants, ...)
PubChem CID	24540
UNII	10LGE70FSU Y
CompTox Dashboard (EPA)	DTXSID6029705
InChI InChI=1S/2H3N.H3O4P/c;;1-5(2,3)4/h2*1H3;(H3,1,2,3,4) Y Key: MNNHAPBLZZVQHP-UHFFFAOYSA-N Y InChI=1/2H3N.H3O4P/c;;1-5(2,3)4/h2*1H3;(H3,1,2,3,4)/p-1 Key: MNNHAPBLZZVQHP-REWHXWOFAG
SMILES [NH4+].[NH4+].OP([O-])([O-])=O
Properties
Chemical formula	(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
Solubility in water	57.5 g/100 mL (10 °C) 106.7 g/100 mL (70 °C)
Solubility	insoluble in alcohol, acetone and liquid ammonia
Refractive index (nD)	1.52
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	−1566.91 kJ/mol
Hazards
NFPA 704 (fire 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). Y verify (what is YN ?) 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 fertilizer, 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.

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.^[7][8] The related dihydrogen compound occurs as the mineral biphosphammite.^[9][8] Both are related to guano deposits.^[7][9]

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. "Phosphammite". www.mindat.org. Retrieved 8 November 2020.
8. "List of Minerals". www.ima-mineralogy.org. 21 March 2011. Retrieved 8 November 2020.
9. "DAP Fertilizer". thesciencepool.com. 3 April 2024. Retrieved 5 April 2024.

External links

• International Chemical Safety Card 0217