Английская Википедия:Fluoroboric acid
Fluoroboric acid or tetrafluoroboric acid (archaically, fluoboric acid) is an inorganic compound with the simplified chemical formula Шаблон:Chem2. Unlike other strong acids like [[Sulfuric acid|Шаблон:Chem2]] or [[Perchloric acid|Шаблон:Chem2]], the pure (solvent free) tetrafluoroboric acid (more precisely, pure hydrogen tetrafluoroborate Шаблон:Chem2) does not exist. The term "fluoroboric acid" refers to a range of chemical compounds, depending on the solvent. The Шаблон:Chem2 in the simplified formula of fluoroboric acid represents the solvated proton. The solvent can be any suitable Lewis base. For instance, if the solvent is water, fluoroboric acid can be represented by the formula Шаблон:Chem2 (oxonium tetrafluoroborate), although more realistically, several water molecules solvate the proton: Шаблон:Chem2. The ethyl ether solvate is also commercially available, where the fluoroboric acid can be represented by the formula Шаблон:Chem2, where n is most likely 2.
It is mainly produced as a precursor to other fluoroborate salts.[1] 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.[2] It is structurally similar to perchloric acid, but lacks the hazards associated with oxidants.
Structure and production
Pure Шаблон:Chem2 has been described as a "nonexistent compound", as a sufficiently "naked" proton is expected to abstract a fluoride from the tetrafluoroborate ion to give hydrogen fluoride and boron trifluoride:
The same holds true for the superacids that are known by the simplified formulas [[Hexafluorophosphoric acid|Шаблон:Chem2]] and [[Hexafluoroantimonic acid|Шаблон:Chem2]].[3][4] However, a solution of Шаблон:Chem2 in HF is highly acidic, having an approximate speciation of Шаблон:Chem2 (fluoronium tetrafluoroborate) and a Hammett acidity function of −16.6 at 7 mol % Шаблон:Chem2, easily qualifying as a superacid.[5] Although the solvent-free Шаблон:Chem2 has not been isolated, its solvates are well characterized. These salts consist of protonated solvent as a cation, e.g., Шаблон:Chem2 and Шаблон:Chem2, and the tetrahedral Шаблон:Chem2 anion. The anion and cations are strongly hydrogen-bonded.[6]
Aqueous solutions of Шаблон:Chem2 are produced by dissolving boric acid in aqueous hydrofluoric acid.[7][8] Three equivalents of HF react to give the intermediate boron trifluoride and the fourth gives fluoroboric acid:
Anhydrous solutions can be prepared by treatment of aqueous fluoroboric acid with acetic anhydride.[9]
Acidity
The acidity of fluoroboric acid is complicated by the fact that its name refers to a range of different compounds, e.g. Шаблон:Chem2 (dimethyloxonium tetrafluoroborate), Шаблон:Chem2 (oxonium tetrafluoroborate), and Шаблон:Chem2 (hydrogen fluoride-boron trifluoride 1:1 adduct) – each with a different acidity. The aqueous pKa is quoted as −0.44.[1] Titration of Шаблон:Chem2 (tetrabutylammonium tetrafluoroborate) in acetonitrile solution indicates that Шаблон:Chem2, i.e., Шаблон:Chem2, has a pKa of 1.6 in that solvent. Its acidity is thus comparable to that of fluorosulfonic acid.[2]
Applications
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. Шаблон:Chem2 is also used in aluminum etching and acid pickling.
Organic chemistry
Шаблон:Chem2 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 (Шаблон:Chem2), triphenylcarbenium tetrafluoroborate (Шаблон:Chem2), triethyloxonium tetrafluoroborate (Шаблон:Chem2), and benzenediazonium tetrafluoroborate (Шаблон:Chem2).
Electroplating
Solutions of Шаблон:Chem2 are used in the electroplating of tin and tin alloys. In this application, methanesulfonic acid is displacing the use of Шаблон:Chem2.[10] Fluoroboric acid is also used for high-speed electroplating of copper in fluoroborate baths.[11]
Safety
Шаблон:Chem2 is toxic and attacks skin and eyes. It attacks glass.[1] It hydrolyzes, releasing corrosive, volatile hydrogen fluoride.[10]
Other fluoroboric acids
A series of fluoroboric acids is known in aqueous solutions. The series can be presented as follows:[12]
- Шаблон:Chem2 (hydrogen tetrahydroxyborate) (not a fluoroboric acid)
- Шаблон:Chem2 (hydrogen fluoro(trihydroxy)borate)
- Шаблон:Chem2 (hydrogen difluoro(dihydroxy)borate)
- Шаблон:Chem2 (hydrogen trifluoro(hydroxy)borate)
- Шаблон:Chem2 (hydrogen tetrafluoroborate)
See also
References
Further reading
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite book
- Шаблон:Housecroft2nd
- Шаблон:Cite book
- Шаблон:Cite book
- Шаблон:Cite journal
- Шаблон:Cite journal
External links
Шаблон:Hydrogen compounds Шаблон:Fluorine compounds
- ↑ 1,0 1,1 1,2 Gregory K. Friestad, Bruce P. Branchaud "Tetrafluoroboric Acid" E-Eros Encyclopedia of Reagents for Organic Synthesis. Шаблон:Doi
- ↑ 2,0 2,1 Ошибка цитирования Неверный тег
<ref>; для сносокEstiне указан текст - ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite book
- ↑ Mootz, D.; Steffen, M. "Crystal structures of acid hydrates and oxonium salts. XX. Oxonium tetrafluoroborates H3OBF4, [H5O2]BF4, and [H(CH3OH)2]BF4", Zeitschrift für Anorganische und Allgemeine Chemie 1981, vol. 482, pp. 193-200. Шаблон:Doi
- ↑ Шаблон:Ullmann
- ↑ Шаблон:OrgSynth
- ↑ Wudl, F.; Kaplan, M. L., "2,2′-Bi-L,3-Dithiolylidene (Tetrathiafulvalene, TTF) and its Radical Cation Salts" Inorg. Synth. 1979, vol. 19, 27. Шаблон:Doi
- ↑ 10,0 10,1 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Greenwood&Earnshaw
