Fluoroboric acid

Fluoroboric acid
Preferred IUPAC name Tetrafluoroboric acid
Other names Borofluoric acid Hydrofluoroboric acid Hydrogen Tetrafluoroborate
Identifiers
CAS number	16872-11-0 Y
PubChem	28118
ChemSpider	26156 N
EC number	240-898-3
UN number	1775
MeSH	Fluoroboric+acid
ChEBI	CHEBI:38902 N
RTECS number	ED2685000
Gmelin Reference	21702
Jmol-3D images	Image 1
SMILES [H+].[F--].F[B+](F)F
InChI InChI=1S/BF4H/c2-1(3,4)5/h2H N Key: YKRRMQXMWYXWJW-UHFFFAOYSA-N N
Properties
Molecular formula	HBF4
Molar mass	87.81 g mol−1
Exact mass	88.010743318 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 Triflic acid
N (verify) (what is: Y/N?) 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 1 Production 1.1 Salts 2 Applications 2.1 Organic chemistry 2.2 Galvanic cells 2.3 Metal plating 3 Other fluoroboric acids 4 See also 5 References 6 External links

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.^[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. Anhydrous solutions can be prepared by treatment with acetic anhydride.^[2]

Salts

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 in 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^[3]:

• H[B(OH)₄]
• H[BF(OH)₃]
• H[BF₂(OH)₂]
• H[BF₃(OH)]
• H[BF₄]

See also

• Fluorosulfuric acid
• Fluoroantimonic acid

References

• Albert, R.; Dax, K.; Pleschko, R.; Stutz, A. E. Carbohydr. Res. 1985, 137, 282-290.
• Bandgar, B. P.; Patil, A. V.; Chavan, O.S. J. Mol. Catal. A: Chem. 2006, 256, 99-105.
• Heintz, R. A.; Smith, J. A.; Szalay, P. S.; Weisgerber, A.; Dunbar, K. R. Inorg. Synth. 2002, 33, 75.
• Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 307. ISBN 978-0130399137. 
• Meller, A. Gmelin Handbook of Inorganic Chemistry: Boron. Vol. 3. New York: Springer-Verlag, 1988. 301-310.
• Perry, D. L.; Phillips, S. L. Handbook of Inorganic Compounds. Boca Raton: CRC Press, 1995. 1203.
• Wamser, C. A. J. Am. Chem. Soc. 1948, 70, 1209-1215.
• Wilke-Doerfurt, E.; Balz, G. Z. Z. Anorg. Allg. Chem. 1927, 159, 224.

1. ^ Flood, D. T., "Fluorobenzene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV2P0295 ; Coll. Vol. 2: 295 
2. ^ Gregory K. Friestad, Bruce P. Branchaud, "Tetrafluoroboric Acid" in "Encyclopedia of Reagents for Organic Synthesis" 2001 John Wiley & Sons. DOI: 10.1002/047084289X.rt035.
3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 

External links

• INCHEM: Fluoroboric Acid (ICSC)

Hydrogen compounds H3AsO3 H3AsO4 HAt HSO3F HBF4 HBr HBrO HBrO2 HBrO3 HBrO4 HCl HClO HClO2 HClO3 HClO4 HCN HCNO H2CrO4/H2Cr2O7 H2CO3 H2CS3 HF HFO HI HIO HIO2 HIO3 HIO4 H2MoO4 HNC HNCO HNO HNO3 H2N2O2 HNO5S H3NSO3 H2O H2O2 H2O3 H3PO2 H3PO3 H3PO4 H4P2O7 H5P3O10 H2PtCl6 H2S H2Se H2SeO3 H2SeO4 H4SiO4 H2SiF6 H2SO3 H2SO4 H2SO5 H2S2O3 H2S2O6 H2S2O7 H2S2O8 CF3SO3H H2Te H2TeO3 H6TeO6 H4TiO4 H2Po H3VO4 HCo(CO)4