Fluoboric Acid

Title: Fluoboric Acid
CAS Registry Number: 16872-11-0
CAS Name: Hydrogen tetrafluoroborate
Additional Names: borofluoric acid; hydrofluoboric acid
Molecular Formula: BF4H
Molecular Weight: 87.81
Percent Composition: B 12.31%, F 86.54%, H 1.15%
Line Formula: HBF4
Literature References: Prepd from H3BO3 + HF: Fichter, Thiele, Z. Anorg. Allg. Chem. 67, 302 (1910); Mathers et al., J. Am. Chem. Soc. 37, 1516 (1915); Funk, Binder, Z. Anorg. Allg. Chem. 155, 327; 159, 121 (1926); Sheintsis, J. Appl. Chem. USSR 13, 1101 (1940); Wamser, Christian, J. Am. Chem. Soc. 70, 1209 (1948); Kwasnik in Handbook of Preparative Inorganic Chemistry vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) pp 221-222. For other methods of prepn see H. S. Booth, D. R. Martin, Boron Trifluoride and Its Derivatives (New York, 1949). Review: Sharp, Adv. Fluorine Chem. 1, 68-128 (1960).
Properties: Liquid. Poisonous! bp 130° (decompn). Miscible with water, alcohol. Strong acid. nD20 of a 20% aq soln 1.3284. Heat of formn 388.5 kcal. Undergoes limited hydrolysis in water to form hydroxyfluoborate ions; major product is BF3OH-. Pure HBF4 may be stored in glass vessels at room temps. Forms cryst salts wth metals. The heavy metal salts and LiBF4 and NaBF4 are very sol in water. See Potassium Tetrafluoborate about color phenomena appearing in concd solns of fluoboric acid.
Boiling point: bp 130° (decompn)
Index of refraction: nD20 of a 20% aq soln 1.3284
CAUTION: Strong caustic action on skin, mucous membranes. Irritating to eyes, respiratory tract. Plating solns contg fluoborates are considered toxic.
Use: As catalyst for preparing acetals, esterifying cellulose; to clean metal surfaces before welding; to brighten aluminum; as a solute in electrolytes for plating metals such as chromium, iron, nickel, copper, silver, zinc, cadmium, indium, tin, and lead (has a high throwing power). Reagent for sodium in the presence of magnesium and potassium ions; for making stabilized diazo salts (diazonium and tetrazonium fluoborates). An 0.1 to 0.5% soln retards fermentation: Homeyer, Pharm. Ztg. 34, 761 (1889).
Fluocinolone Acetonide Fluocortin Butyl Fluocortolone Fluometuron Fluorescein

The structure of the tetrafluoroborate anion, BF4

Tetrafluoroborate is the anion BF4. This tetrahedral species is isoelectronic with tetrafluoromethane, CF4 and tetrafluoroammonium NF4+, and is valence isoelectronic with many stable and important species including the closely related anion perchlorate, ClO4. It arises by the reaction of fluoride salts with the Lewis acid BF3, treatment of tetrafluoroboric acid with base, or by treatment of boric acid with hydrofluoric acid.