Fluoroboric acid is the chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 HBF₄. It is the conjugate acid of tetrafluoroborate

Tetrafluoroborate

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 is available commercially as a solution in water and other solvent

Solvent

A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

s such as diethyl ether

Diethyl ether

Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

. With a strength comparable to nitric acid

Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

, fluoroboric acid is a strong acid with a weakly coordinating, non-oxidizing conjugate base.

Production

Pure fluoroboric acid has never been produced but aqueous solutions of HBF₄ can be produced by dissolving boric acid

Boric acid

Boric acid, also called hydrogen borate or boracic acid or orthoboric acid or acidum boricum, is a weak acid of boron often used as an antiseptic, insecticide, flame retardant, as a neutron absorber, and as a precursor of other chemical compounds. It exists in the form of colorless crystals or a...

 in aqueous hydrofluoric acid

Hydrofluoric acid

Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....

 solution at 20-25 °C. Three equivalents of HF react to give the intermediate boron trifluoride

Boron trifluoride

Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...

 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

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

. Anhydrous solutions can be prepared by treatment with acetic anhydride

Acetic anhydride

Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula 2O. Commonly abbreviated Ac2O, it is the simplest isolatable acid anhydride and is a widely used reagent in organic synthesis...

.

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

Boron

Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

. HBF₄ is also used in aluminum etching and acid pickling.

Organic chemistry

HBF₄ is used as a catalyst in for alkylation

Alkylation

Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in...

s and polymerizations. In carbohydrate protection reactions, ethereal fluoroboric acid is an efficient and cost-effective catalyst for transacetalation and isopropylidenation reactions. Acetonitrile

Acetonitrile

Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...

 solutions cleave acetals and some ethers, while neat fluoroboric acid removes tert-butoxycarbonyl groups.

Galvanic cells

Aqueous HBF₄ is used as an electrolyte

Electrolyte

In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....

 in galvanic cell

Galvanic cell

A Galvanic cell, or Voltaic cell, named after Luigi Galvani, or Alessandro Volta respectively, is an electrochemical cell that derives electrical energy from spontaneous redox reaction taking place within the cell...

 oxygen sensor systems, which consist of an anode

Anode

An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

, cathode

Cathode

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

, and oxygen-permeable membrane. The solution of HBF₄ is able to dissolve lead(II) oxide

Lead(II) oxide

Lead oxide is the inorganic compound with the formula PbO. Lead oxide occurs in two polymorphs, red, having a tetragonal crystal structure and yellow, having an orthorhombic crystal structure...

 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 acid

Sulfonic acid

Sulfonic acid usually refers to a member of the class of organosulfur compounds with the general formula RS2–OH, where R is an alkyl or aryl. The formal part of acid, HS2–OH, are formally derivatives of the "parent" inorganic compound with the formula HSO2.-Preparation:Sulfonic acid is...

s 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

Electrodeposition

Electrodeposition may refer to:*Electroplating*Electrophoretic deposition*Underpotential deposition...

 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:

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

External links

• INCHEM: Fluoroboric Acid (ICSC)