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Tetrahydroxyborate is an
inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistr ...
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
with the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
or . It contributes no colour to tetrahydroxyborate salts. It is found in the mineral hexahydroborite, , originally formulated . It is one of the
boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
oxoanions, and acts as a weak base. The
systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...
s are tetrahydroxyboranuide (substitutive) and tetrahydroxidoborate(1−) (additive). It can be viewed as the
conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...
of
boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolves ...
.


Structure

Tetrahydroxyborate has a symmetric
tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
,
isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in the ...
with the hypothetical compound
orthocarbonic acid Orthocarbonic acid (methanetetrol) is the name given to a hypothetical compound with the chemical formula or . Its molecular structure consists of a single carbon atom bonded to four hydroxy groups. It would be therefore a fourfold alcohol. ...
.


Chemical properties


Basicity

Tetrahydroxyborate act as a weak Brønsted–Lowry base because it can assimilate a
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mas ...
(), yielding
boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolves ...
with release of water: : + + It can also release a hydroxy anion , thus acting as a classical Arrhenius base: : + (pK = 9.14 to the left) Thus, when boric acid is dissolved in pure (neutral) water, most of it will exist as tetrahydroxyborate ions.


With diols

In aqueous solution, the tetrahydroxyborate anion reacts with cis-
vicinal diols Vicinal may refer to: * Vicinal (chemistry), stands for any two functional groups bonded to two adjacent atoms. * Vicinal (logology), a word where all letters have alphabetic neighbors. * Vicinal tramway or ''Buurtspoor'', a system of narrow gau ...
(
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...
s containing similarly-oriented
hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
groups in adjacent
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes u ...
atoms), ) such as mannitol, sorbitol,
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
and
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids know ...
, to form anion esters containing one or two five-member rings. For example, the reaction with mannitol can be written as : + + 2 : + + 2 Giving the overall reaction : + 2 (H(HCOH)2(HCO\s)2(HCOH)2H)2 + 4 These mannitoborate esters are fairly stable and thus depletes the tetrahydroxyborate from the solution. The addition of mannitol to an initially neutral solution containing boric acid or borates lowers the pH enough for the be titrated by a strong base as NaOH, including with an automated a potentiometric titrator. This is a reliable method to assay the amount of borate content present in the solution.


Other chemical reactions

Upon treatment with a strong acid, a metal tetrahydroxyborate converts to
boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolves ...
and the metal salt. Oxidation of tetrahydroxyborate gives the perborate anion : : 2 + 2 → + 2 When heated to a high temperature, tetrahydroxyborate salts decompose to produce
metaborate A metaborate is an anion (negative ion) consisting of boron and oxygen, with empirical formula ; or any salt with such anions, such as sodium metaborate, or calcium metaborate . It is one of the boron oxoanions or borates In aqueous solutio ...
salts and water, or to produce boric acid and a metal
hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...
: :''n'' → () + 2''n''  : → + HO


Production

Tetrahydroxyborate salts are produced by treating boric acid with an
alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a s ...
such as
sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and a ...
, with
catalytic Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recy ...
amounts of water. Other borate salts may be obtained by altering the process conditions.


Uses

Tetrahydroxyborate can be used as a cross-link in polymers.


Occurrence

The tetrahydroxyborate
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
is found in Na (OH)4 Na2 (OH)4l and CuII (OH)4l. File:Sodium-tetrahydroxyborate-xtal-3D-balls.png,
ball-and-stick model In chemistry, the ball-and-stick model is a molecular model of a chemical substance which displays both the three-dimensional position of the atoms and the bonds between them. The atoms are typically represented by spheres, connected by rods ...
of the crystal
structure of sodium tetrahydroxyborate File:Sodium-tetrahydroxyborate-xtal-3D-SF.png,
space-filling model In chemistry, a space-filling model, also known as a ''calotte model'', is a type of three-dimensional (3D) molecular model where the atoms are represented by spheres whose radii are proportional to the radii of the atoms and whose center-t ...
of the crystal
structure of sodium tetrahydroxyborate


See also

*
Borate A borate is any of several boron oxyanions, negative ions consisting of boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt with such anions, such as sodium metaborate, and disodium tetraborate . The name also ...
*
Tetrafluoroborate Tetrafluoroborate is the anion . This tetrahedral species is isoelectronic with tetrafluoroberyllate (), tetrafluoromethane (CF4), and tetrafluoroammonium () and is valence isoelectronic with many stable and important species including the perch ...


References

Glossary of Geology,5th edition, 2005, ed. by Julia A. Jackson, James P. Mehl, Klaus K. E. Neuendorf, American Geological Institute . Lyman F. Kebler (1894): "On the interaction of borax, carbonates and polyhydric alcohols; also on the composition of borax". ''Journal of the Franklin Institute'', volume 138, issue 3, pages 236-239. {{doi, 10.1016/0016-0032(94)90292-5 Borates Anions