Fluoroboric acid
| Fluoroboric acid | |
|---|---|
 |
|
|
Tetrafluoroboric acid[citation needed] |
|
|
Other names
Borofluoric acid[citation needed] Hydrofluoroboric acid[citation needed] |
|
| Identifiers | |
| CAS number | 16872-11-0  |
| PubChem | 28118 |
| ChemSpider | 26156  |
| EC number | 240-898-3 |
| UN number | 1775 |
| MeSH | Fluoroboric+acid |
| ChEBI | CHEBI:38902 |
| RTECS number | ED2685000 |
| Gmelin Reference | 21702 |
| Jmol-3D images | Image 1 |
|
|
|
|
| Properties | |
| Molecular formula | HBF4 |
| Molar mass | 87.81 g mol−1 |
| Appearance | Colourless liquid |
| Melting point |
-90 °C, 183 K, -130 °F |
| Boiling point |
130 °C, 403 K, 266 °F |
| Acidity (pKa) | -0.4 |
| Basicity (pKb) | 14.4 |
| Hazards | |
| MSDS | External MSDS |
| EU Index | 009-010-00-X |
| EU classification |  C |
| R-phrases | R34 |
| S-phrases | (S1/2), S26, S27, S45 |
| NFPA 704 |
 0
3
0
|
| Related compounds | |
| Related compounds | Hydrogen fluoride |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
|
| Infobox references | |
Fluoroboric acid (also spelt fluoboric acid) is the chemical compound with the formula HBF4. It is the conjugate acid of tetrafluoroborate. 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.
Contents |
Production [edit]
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.[1] 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.[citation needed] Anhydrous solutions can be prepared by treatment with acetic anhydride.[2]
Salts [edit]
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 [edit]
Organic chemistry [edit]
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[citation needed] fluoroboric acid removes tert-butoxycarbonyl groups.
Galvanic cells [edit]
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 [edit]
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 [edit]
A series of fluoroboric acids is known in aqueous solutions. The series can be presented as follows:[3]
- H[B(OH)4]
- H[BF(OH)3]
- H[BF2(OH)2]
- H[BF3(OH)]
- H[BF4]
See also [edit]
References [edit]
- ^ Flood, D. T. (1933), "Fluorobenzene", Org. Synth. 13: 46; Coll. Vol. 2: 295
- ^ Friestad, G. K.; Branchaud, B. P. (2001). "Tetrafluoroboric Acid". Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289X.rt035.
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419.
- 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.
- 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.
- 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.
- Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 307. ISBN 978-0130399137.
- Meller, A. (1988). "Boron". Gmelin Handbook of Inorganic Chemistry 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.
- 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.
External links [edit]
- "Fluoroboric Acid ICSC: 1040". INCHEM.
