In today's world, Fluoroboric acid is a topic that has captured the attention of millions of people around the world. Whether due to its historical relevance, its impact on contemporary society or its influence on popular culture, Fluoroboric acid is a topic that continues to generate interest and debate. Over the years, Fluoroboric acid has been the subject of countless research, discussions and analysis, leading to a greater understanding of its complexities and the identification of multiple perspectives on it. In this article, we will explore some key aspects related to Fluoroboric acid, with the aim of delving into its meaning and scope in different contexts.
Hydronium tetrafluoroborate
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Preferred IUPAC name | |||
Other names
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3D model (JSmol)
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ChEBI | |||
ChemSpider | |||
ECHA InfoCard | 100.037.165 | ||
EC Number |
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21702 | |||
MeSH | Fluoroboric+acid | ||
PubChem CID
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RTECS number |
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UNII | |||
UN number | 1775 | ||
CompTox Dashboard (EPA)
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Properties | |||
H[BF4] | |||
Molar mass | 87.81 g·mol−1 | ||
Appearance | Colourless liquid | ||
Melting point | −90 °C (−130 °F; 183 K) | ||
Boiling point | 130 °C (266 °F; 403 K) | ||
Acidity (pKa) | ~1.8 (MeCN solution) | ||
Hazards | |||
GHS labelling: | |||
Danger | |||
H314 | |||
P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501 | |||
NFPA 704 (fire diamond) | |||
Safety data sheet (SDS) | External MSDS | ||
Related compounds | |||
Related compounds
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa).
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Fluoroboric acid or tetrafluoroboric acid (archaically, fluoboric acid) is an inorganic compound with the simplified chemical formula H+[BF4]−. Solvent-free tetrafluoroboric acid (H[BF4]) has not been reported. The term "fluoroboric acid" usually refers to a range of compounds including hydronium tetrafluoroborate ([H3O]+[BF4]−), which are available as solutions. The ethyl ether solvate is also commercially available, where the fluoroboric acid can be represented by the formula [H((CH3CH2)2O)n]+[BF4]−, where n is 2.
It is mainly produced as a precursor to other fluoroborate salts. It is 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. It is a strong acid with a weakly coordinating, non-oxidizing conjugate base. It is structurally similar to perchloric acid, but lacks the hazards associated with oxidants.
Pure H[BF4] has not been described. The same holds true for the superacids that are known by the simplified formulas H[PF6] and H[SbF6]. However, a solution of BF3 in HF is highly acidic, having an approximate speciation of [H2F]+[BF4]− (fluoronium tetrafluoroborate) and a Hammett acidity function of −16.6 at 7 mol % BF3, easily qualifying as a superacid. Although the solvent-free H[BF4] has not been isolated, its solvates are well characterized. These salts consist of protonated solvent as a cation, e.g., H3O+ and H5O+2, and the tetrahedral BF−4 anion. The anion and cations are strongly hydrogen-bonded.
Aqueous solutions of H[BF4] are produced by dissolving boric acid in aqueous hydrofluoric acid. Three equivalents of HF react to give the intermediate boron trifluoride and the fourth gives fluoroboric acid:
An anhydrous fluoroboric acid solution can be prepared by adding aqueous fluoroboric acid to an excess of acetic anhydride at 0°C, which produces a solution of fluoroboric acid, acetic acid, and residual acetic anhydride.
The acidity of fluoroboric acid is complicated by the fact that its name refers to a range of different compounds, e.g. [H(CH3CH2)2O]+[BF4]− (dimethyloxonium tetrafluoroborate), [H3O]+[BF4]− (oxonium tetrafluoroborate), and HF·BF3 (hydrogen fluoride-boron trifluoride 1:1 adduct) – each with a different acidity. The aqueous pKa is quoted as −0.44. Titration of [N((CH2)3CH3)4]+[BF4]− (tetrabutylammonium tetrafluoroborate) in acetonitrile solution indicates that H[BF4], i.e., HF·BF3, has a pKa of 1.6 in that solvent. Its acidity is thus comparable to that of fluorosulfonic acid.
Fluoroboric acid is the principal precursor to fluoroborate salts, which are typically prepared by treating the metal oxides with fluoroboric acid. The inorganic salts are intermediates in the manufacture of flame-retardant materials and glazing frits, and in electrolytic generation of boron. H[BF4] is also used in aluminum etching and acid pickling.
H[BF4] 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. Many reactive cations have been obtained using fluoroboric acid, e.g. tropylium tetrafluoroborate (C7H7+[BF4]−), triphenylcarbenium tetrafluoroborate (Ph3C]+[BF4]−), triethyloxonium tetrafluoroborate (Et3O]+[BF4]−), and benzenediazonium tetrafluoroborate ([PhN2]+[BF4]−).
Solutions of H[BF4] are used in the electroplating of tin and tin alloys. In this application, methanesulfonic acid is displacing the use of H[BF4]. Fluoroboric acid is also used for high-speed electroplating of copper in fluoroborate baths.
Fluoroboric acid is toxic and attacks skin and eyes. It attacks glass. It hydrolyzes, releasing corrosive, volatile hydrogen fluoride.
A series of fluoroboric acids is known in aqueous solutions. The series can be presented as follows:
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