Chemistry:Monopotassium phosphate

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Monopotassium phosphate
Monopotassium phosphate.png
TetragonalKH2PO4structure2.png
Two unit cells of MKP viewed close to the b axis
Kaliumdihydrogenphosphat.jpg
Names
IUPAC names
Potassium dihydrogen phosphate[1]
Other names
Potassium phosphate monobasic;
Phosphoric acid, monopotassium salt;
Potassium biphosphate
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
EC Number
  • 231-913-4
RTECS number
  • TC6615500
UNII
Properties
KH2PO4
Molar mass 136.086 g/mol
Appearance Colourless crystals or white granular or crystalline powder[2]
Odor Odorless [2]
Density 2.338 g/cm3
Melting point 252.6 °C (486.7 °F; 525.8 K) [4]
Boiling point 400 °C (752 °F; 673 K) , decomposes
22.6 g/100 mL (20 °C)
83.5 g/100 mL (90 °C)
Solubility Slightly soluble in ethanol
Acidity (pKa) 6.86[3]
Basicity (pKb) 11.9
1.4864
Structure
Tetragonal[5]
I42d
a = 0.744 nm, b = 0.744 nm, c = 0.697 nm
Hazards
Safety data sheet External MSDS
GHS pictograms GHS07: Harmful[6]
GHS Signal word Warning[6]
H315, H319[6]
P264, P280, P305+351+338, P321, P332+313, P337+313[6]
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
1
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
3200 mg/kg (rat, oral)
Related compounds
Other cations
 Monosodium phosphate
Monoammonium phosphate
Related compounds
 Dipotassium phosphate
Tripotassium phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Tracking categories (test):

Monopotassium phosphate (MKP) (also, potassium dihydrogen phosphate, KDP, or monobasic potassium phosphate) is the inorganic compound with the formula KH2PO4. Together with dipotassium phosphate (K2HPO4.(H2O)x) it is often used as a fertilizer, food additive, and buffering agent. The salt often cocrystallizes with the dipotassium salt as well as with phosphoric acid.[7]

Single crystals are paraelectric at room temperature. At temperatures below −150 °C (−238 °F), they become ferroelectric.

Structure

Monopotassium phosphate can exist in several polymorphs. At room temperature it forms paraelectric crystals with tetragonal symmetry. Upon cooling to −150 °C (−238 °F) it transforms to a ferroelectric phase of orthorhombic symmetry, and the transition temperature shifts up to −50 °C (−58 °F) when hydrogen is replaced by deuterium.[8] Heating to 190 °C (374 °F) changes its structure to monoclinic.[9] When heated further, MKP decomposes, by loss of water, to potassium metaphosphate, KPO3, at 400 °C (752 °F).

Symmetry Space
group 		№ Pearson
symbol 		a
(nm) 		b
(nm) 		c
(nm) 		Z Density
(g/cm3) 		T (°C, °F, K)
Orthorhombic[8] Fdd2 43 oF48 1.0467 1.0533 0.6926 8 2.37 < −150 °C, −238 °F, 123 K
Tetragonal[5] I42d 122 tI24 0.744 0.744 0.697 4 2.34 −150 to 190 °C, −238 to 374 °F, 123 to 463 K
Monoclinic[9] P21/c 14 mP48 0.733 1.449 0.747 8 190 to 400 °C, 374 to 752 °F, 463 to 673 K

Manufacturing

Monopotassium phosphate is produced by the action of phosphoric acid on potassium carbonate.

Applications

Fertilizer-grade MKP powder contains the equivalent of 52% P2O5 and 34% K2O, and is labeled NPK 0-52-34. MKP powder is often used as a nutrient source in the greenhouse trade and in hydroponics.

As a crystal, MKP is noted for its non-linear optical properties. It is used in optical modulators and for non-linear optics such as second-harmonic generation (SHG).

Also, to be noted is KD*P, potassium dideuterium phosphate, with slightly different properties. Highly deuterated KDP is used in nonlinear frequency conversion of laser light instead of protonated (regular) KDP due to the fact that the replacement of protons with deuterons in the crystal shifts the third overtone of the strong OH molecular stretch to longer wavelengths, moving it mostly out of the range of the fundamental line at approximately 1064 nm of neodymium-based lasers. Regular KDP has absorbances at this wavelength of approximately 4.7–6.3% per cm of thickness while highly deuterated KDP has absorbances of typically less than 0.8% per cm.

Monopotassium phosphate is also used as an ingredient in sports drinks such as Gatorade and Powerade.

In medicine, monopotassium phosphate is used for phosphate substitution in hypophosphatemia.[10]

Gallery

References

  1. ↑ "Potassium dihydrogen phosphate". https://pubchem.ncbi.nlm.nih.gov/compound/516951#section=IUPAC-Name&fullscreen=true. 
  2. ↑ 2.0 2.1 "Commission Regulation (EU) No 231/2012 of 9 March 2012 laying down specifications for food additives listed in Annexes II and III to Regulation (EC) No 1333/2008 of the European Parliament and of the Council Text with EEA relevance". E 340 (i) MONOPOTASSIUM PHOSPHATE. https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX%3A32012R0231. 
  3. ↑ Mathews, Christopher K., K. E. Van Holde, Ean R. Appling, and Spencer J. Anthony-Cahill. Biochemistry. Redwood City, CA: Benjamin/Cummings Pub., 1990. Print.
  4. ↑ King, Harold S. J. Am. Chem. Soc. 1927, 49, 6, 1511–1512 https://doi.org/10.1021/ja01405a018
  5. ↑ 5.0 5.1 Ono, Yasuhiro; Hikita, Tomoyuki; Ikeda, Takuro (1987). "Phase Transitions in Mixed Crystal System K1−x(NH4)xH2PO4". Journal of the Physical Society of Japan 56 (2): 577. doi:10.1143/JPSJ.56.577. Bibcode: 1987JPSJ...56..577O. 
  6. ↑ 6.0 6.1 6.2 6.3 "Potassium Dihydrogen Phosphate". American Elements. https://www.americanelements.com/potassium-dihydrogen-phosphate-7778-77-0. 
  7. ↑ Klaus Schrödter; Gerhard Bettermann; Thomas Staffel; Friedrich Wahl; Thomas Klein; Thomas Hofmann (2012). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3. 
  8. ↑ 8.0 8.1 Fukami, T. (1990). "Refinement of the Crystal Structure of KH2PO4 in the Ferroelectric Phase". Physica Status Solidi A 117 (2): K93–K96. doi:10.1002/pssa.2211170234. Bibcode: 1990PSSAR.117...93F. 
  9. ↑ 9.0 9.1 Itoh, Kazuyuki; Matsubayashi, Tetsuo; Nakamura, Eiji; Motegi, Hiroshi (1975). "X-Ray Study of High-Temperature Phase Transitions in KH2PO4". Journal of the Physical Society of Japan 39 (3): 843. doi:10.1143/JPSJ.39.843. Bibcode: 1975JPSJ...39..843I. 
  10. ↑ Gaasbeek, André; Meinders, A. Edo (October 2005). "Hypophosphatemia: an update on its etiology and treatment". The American Journal of Medicine 118 (10): 1094–1101. doi:10.1016/j.amjmed.2005.02.014. ISSN 0002-9343. PMID 16194637. https://pubmed.ncbi.nlm.nih.gov/16194637/. 

External links



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