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Fluoroboric acid

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Fluoroboric acid
Canonical, skeletal formula of fluoroboric acid
Names
Preferred IUPAC name Tetrafluoroboric acid
Other names Borofluoric acid

Hydrofluoroboric acid

Hydrogen Tetrafluoroborate
Identifiers
CAS Number
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.037.165 Edit this at Wikidata
EC Number
  • 240-898-3
Gmelin Reference 21702
MeSH Fluoroboric+acid
PubChem CID
RTECS number
  • ED2685000
UN number 1775
CompTox Dashboard (EPA)
InChI
  • InChI=1S/BF4H/c2-1(3,4)5/h2HKey: YKRRMQXMWYXWJW-UHFFFAOYSA-N
SMILES
  • ..F(F)F
Properties
Chemical formula BF4H
Molar mass 87.81 g·mol
Appearance Colourless liquid
Melting point −90 °C (−130 °F; 183 K)
Boiling point 130 °C (266 °F; 403 K)
Acidity (pKa) -0.4
Basicity (pKb) 14.4
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3 0 0
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). ☒N verify (what is  ?) Infobox references
Chemical compound

Fluoroboric acid or fluoboric acid (systematically named oxonium tetrafluoroboranuide or oxonium tetrafluoridoborate(1-)) is an inorganic compound with the chemical formula H
3OBF
4. As fluoroboric acid has not been isolated, its descriptive properties remain largely unknown. It is mainly produced as a precursor to other fluoroborate salts. It is classified as a strong acid, fluoroboric acid is corrosive and attacks the skin.

It is available commercially as a solution in water and other solvents such as diethyl ether. With a strength comparable to nitric acid, fluoroboric acid is a strong acid with a weakly coordinating, non-oxidizing conjugate base.


Production

Pure fluoroboric acid has never been produced but aqueous solutions of HBF4 can be produced by dissolving boric acid in aqueous hydrofluoric acid solution at 20-25 °C. Three equivalents of HF react to give the intermediate boron trifluoride and the fourth gives fluoroboric acid.

B(OH)3 + 4 HF → H3O + BF4 + 2 H2O

Aqueous solutions of fluoroboric acid can also be prepared by treating impure hexafluorosilicic acid with solid boric acid followed by removal of precipitated silicon dioxide. Anhydrous solutions can be prepared by treatment with acetic anhydride.

Salts

Main article: Tetrafluoroborate

Fluoroboric acid is the principal precursor to fluoroborate salts, which are typically prepared by acid-base reactions. The inorganic salts are intermediates in the manufacture of flame-retardant materials and glazing frits, and in electrolytic generation of boron. HBF4 is also used in aluminum etching and acid pickling.

Applications

Organic chemistry

HBF4 is used as a catalyst for alkylations and polymerizations. In carbohydrate protection reactions, ethereal fluoroboric acid is an efficient and cost-effective catalyst for transacetalation and isopropylidenation reactions. Acetonitrile solutions cleave acetals and some ethers, while neat fluoroboric acid removes tert-butoxycarbonyl groups.

Galvanic cells

Aqueous HBF4 is used as an electrolyte in galvanic cell oxygen sensor systems, which consist of an anode, cathode, and oxygen-permeable membrane. The solution of HBF4 is able to dissolve lead(II) oxide from the anode in the form of lead tetrafluoroborate while leaving the rest of the system unchanged.

Metal plating

A mixture of CrO3, HBF4, and sulfonic acids in conjunction with a cathode treatment give tin-plated steel. Tin(I) fluoroborate/fluoroboric acid mixtures and organic reagents are used as the electrolyte in the cathode treatment of the tin plating process. Similar processes of electrodeposition and electrolytic stripping are used to obtain specific metal alloys.

Other fluoroboric acids

A series of fluoroboric acids is known in aqueous solutions. The series can be presented as follows:

  • H
  • H
  • H
  • H
  • H

See also

References

  1. Flood, D. T. (1933). "Fluorobenzene" (PDF). Organic Syntheses. 13: 46; Collected Volumes, vol. 2, p. 295.
  2. Friestad, G. K.; Branchaud, B. P. (2001). "Tetrafluoroboric Acid". Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289X.rt035.{{cite encyclopedia}}: CS1 maint: multiple names: authors list (link)
  3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  • Albert, R.; Dax, K.; Pleschko, R.; Stütz, A. E. (1985). "Tetrafluoroboric acid, an efficient catalyst in carbohydrate protection and deprotection reactions". Carbohydrate Research. 137: 282–290. doi:10.1016/0008-6215(85)85171-5.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Bandgar, B. P.; Patil, A. V.; Chavan, O. S. (2006). "Silica supported fluoroboric acid as a novel, efficient and reusable catalyst for the synthesis of 1,5-benzodiazepines under solvent-free conditions". Journal of Molecular Catalysis A: Chemical. 256 (1–2): 99–105. doi:10.1016/j.molcata.2006.04.024.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Heintz, R. A.; Smith, J. A.; Szalay, P. S.; Weisgerber, A.; Dunbar, K. R. (2002). "Homoleptic Transition Metal Acetonitrile Cations with Tetrafluoroborate or Trifluoromethanesulfonate Anions". Inorganic Syntheses. 33: 75–83. doi:10.1002/0471224502.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 307. ISBN 978-0-13-039913-7.
  • Meller, A. (1988). "Boron". Gmelin Handbook of Inorganic Chemistry. Vol. 3. New York: Springer-Verlag. pp. 301–310.
  • Perry, D. L.; Phillips, S. L. (1995). Handbook of Inorganic Compounds (1st ed.). Boca Raton: CRC Press. p. 1203. ISBN 9780849386718.{{cite book}}: CS1 maint: multiple names: authors list (link)
  • Wamser, C. A. (1948). "Hydrolysis of Fluoboric Acid in Aqueous Solution". Journal of the American Chemical Society. 70 (3): 1209–1215. doi:10.1021/ja01183a101.
  • Wilke-Dörfurt, E.; Balz, G. (1927). "Zur Kenntnis der Borfluorwasserstoffsäure und ihrer Salze". Zeitschrift für Anorganische und Allgemeine Chemie. 159 (1): 197–225. doi:10.1002/zaac.19271590118.{{cite journal}}: CS1 maint: multiple names: authors list (link)

External links

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