Tetrahydroxyborate

Tetrahydroxyborate
Names
IUPAC name
Tetrahydroxyborate
Systematic IUPAC name
Tetrahydroxyboranuide[1] (substitutive)
Tetrahydroxidoborate(1-)[1] (additive)
Identifiers
15390-83-7 N
ChEBI CHEBI:41132 YesY
ChEMBL ChEMBL1231419 N
ChemSpider 154612 YesY
1966
Jmol interactive 3D Image
PubChem 177595
Properties
H4BO4−
Molar mass 78.840 g mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Tetrahydroxyborate (systematically named tetrahydroxyboranuide and tetrahydroxidoborate(1−)) is an inorganic anion with the chemical formula [B(OH)
4]−
 (also written as B(OH)−
4 or BH
4O−
4). It contributes no colour to tetrahydroxyborate salts. It is found in the mineral hexahydroborite, Ca(B(OH)4)2·2H2O (originally formulated CaB2O4.6H2O).[2] It is classified as a weak base.

Chemical properties

Basicity

Tetrahydroxyborate can assimilate a proton into the anion by recombination:

B(OH)−
4 + H+
 → B(OH)
3 + H
2O

Because of this capture of a proton (H+
), tetrahydroxyborate has Arrhenius-basic character. Its protonation product is boric acid. In aqueous solution, most tetrahydroxyborate ions are undissociated.

B(OH)−
4 is in a disfavored equilibrium with B(OH)
3 + OH−

Structure

It is a boron oxoanion with a tetrahedral geometry.[3] It is isoelectronic with the hypothetical compound orthocarbonic acid.

Chemical reactions

Tetrahydroxyborate undergoes the typical chemical reactions of a hydroxyborate. Upon treatment with a standard acid, it converts to boric acid and a metal salt. Oxidation of tetrahydroxyborate gives perborate. When heated to a high temperature, tetrahydroxyborate salts decompose to produce metaborate salts and water, or to produce boric acid and a metal hydroxide:

n [B(OH)4]− → (BO−
2)n + 2n H2O
[B(OH)4]− → B(OH)3 + HO−

Production

Tetrahydroxyborate is produced by boric acid alkalinisation. In this process boric acid and hydroxide anions react to produce tetrahydroxyborate according to the following reaction:

B(OH)3 + HO− → [B(OH)4]−

This process also involves aquatrihydroxyboron as an intermediate, and occurs in two steps. No catalyst is needed for alkalinisation (step 2).

  1. B(OH)3 + H2O → [B(OH)3H2O]
  2. [B(OH)3H2O] + HO− → [B(OH)4]− + H2O

Catalytic amounts of water are used for the process. By altering the process conditions, other borate anions may also be produced on the same production site.

Uses

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

Occurrence

The tetrahydroxyborate anion is found in Na[B(OH)4],[4] Na2[B(OH)4]Cl and CuII[B(OH)4]Cl.

ball-and-stick model of the crystal
structure of sodium tetrahydroxyborate
space-filling model of the crystal
structure of sodium tetrahydroxyborate

See also

References

  1. 1 2 "Tetrahydroxoborate(1-) (CHEBI:41132)". Chemical Entities of Biological Interest (ChEBI). UK: European Bioinformatics Institute.
  2. ↑ Glossary of Geology,5th edition, 2005, ISBN 978-0922152766 ed. by Julia A. Jackson, James P. Mehl, Klaus K. E. Neuendorf, American Geological Institute
  3. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 203–205. ISBN 0-08-037941-9.
  4. ↑ L. J. Csetenyi, F. P. Glasser, R. A. Howie (June 1993). "Structure of sodium tetrahydroxyborate". Acta Crystallogr. C 49 (6): 1039–1041. doi:10.1107/S0108270193000058.
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