Chemistry:Potassium fluoride

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Short description: Ionic compound (KF)
Potassium fluoride
Potassium-fluoride-3D-ionic.png
Names
IUPAC name
Potassium fluoride
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
EC Number
  • 232-151-5
RTECS number
  • TT0700000
UNII
Properties
KF
Molar mass 58.0967 g/mol (anhydrous)
94.1273 g/mol (dihydrate)
Appearance colourless
Density 2.48 g/cm3
Melting point 858 °C (1,576 °F; 1,131 K) (anhydrous)
41 °C (dihydrate)
19.3 °C (trihydrate)
Boiling point 1,502 °C (2,736 °F; 1,775 K)
anhydrous:
92 g/100 mL (18 °C)
102 g/100 mL (25 °C)
dihydrate:
349.3 g/100 mL (18 °C)
Solubility soluble in HF
insoluble in alcohol
−23.6·10−6 cm3/mol
Structure
cubic
Hazards
GHS pictograms GHS06: Toxic
GHS Signal word Danger
H301, H311, H331[1]
P261, P264, P270, P271, P280, P301+310, P302+352, P304+340, P311, P312, P321, P322, P330, P361, P363, P403+233, P405, P501
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity 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
3
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
245 mg/kg (oral, rat)[2]
Related compounds
Other anions
Potassium chloride
Potassium bromide
Potassium iodide
Other cations
Lithium fluoride
Sodium fluoride
Rubidium fluoride
Caesium fluoride
Francium fluoride
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

Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali halide salt and occurs naturally as the rare mineral carobbiite. Solutions of KF will etch glass due to the formation of soluble fluorosilicates, although HF is more effective.

Preparation

Potassium fluoride is prepared by reacting potassium carbonate with hydrofluoric acid. Evaporation of the solution forms crystals of potassium bifluoride. The bifluoride on heating yields potassium fluoride:

[math]\ce{ K2CO3 + 4HF -> 2KHF2 + CO2 ^ + H2O }[/math]
[math]\ce{ KHF2 -> KF + HF ^ }[/math]

Platinum or heat resistant plastic containers are often used for these operations.

Potassium chloride converts to KF upon treatment with hydrogen fluoride. In this way, potassium fluoride is recyclable.[3]

Crystalline properties

KF crystallizes in the cubic NaCl crystal structure. The lattice parameter at room temperature is 0.266 nm.[4]

Applications in organic chemistry

In organic chemistry, KF can be used for the conversion of chlorocarbons into fluorocarbons, via the Finkelstein (alkyl halides)[5] and Halex reactions (aryl chlorides).[3] Such reactions usually employ polar solvents such as dimethyl formamide, ethylene glycol, and dimethyl sulfoxide.[6] More efficient fluorination of aliphatic halides can be achieved with a combination of crown ether and bulky diols in acetonitrile solvent.[7]

Safety considerations

Like other sources of the fluoride ion, F, KF is poisonous, although lethal doses approach gram levels for humans. It is harmful by inhalation and ingestion. It is highly corrosive, and skin contact may cause severe burns.

References

  1. "Potassium Fluoride". https://www.sigmaaldrich.com/catalog/product/aldrich/449148?lang=en&region=US. 
  2. Chambers, Michael. "ChemIDplus - 7789-23-3 - NROKBHXJSPEDAR-UHFFFAOYSA-M - Potassium fluoride - Similar structures search, synonyms, formulas, resource links, and other chemical information.". https://chem.nlm.nih.gov/chemidplus/rn/7789-23-3. 
  3. 3.0 3.1 Siegemund, Günter; Schwertfeger, Werner; Feiring, Andrew; Smart, Bruce; Behr, Fred; Vogel, Herward; McKusick, Blaine (2002). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_349. .
  4. "Potassium fluoride". University College London. https://www.ucl.ac.uk/~ucapahh/research/crystal/kf.htm. 
  5. Vogel, A. I.; Leicester, J.; Macey, W. A. T. (1956). "n-Hexyl Fluoride". Organic Syntheses 36: 40. doi:10.15227/orgsyn.036.0040. 
  6. Han, Q.; Li, H-Y. "Potassium Fluoride" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons,New York. doi:10.1002/047084289X.rp214
  7. Silva, Samuel L.; Valle, Marcelo S.; Pliego, Josefredo R. (2020-12-04). "Nucleophilic Fluorination with KF Catalyzed by 18-Crown-6 and Bulky Diols: A Theoretical and Experimental Study". The Journal of Organic Chemistry 85 (23): 15457–15465. doi:10.1021/acs.joc.0c02229. ISSN 0022-3263. PMID 33227195. https://doi.org/10.1021/acs.joc.0c02229.