Tetrahydroxyborate

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Tetrahydroxyborate
Stereo, skeletal formula of tetrahydroxyborate with a dimension Ball and stick model of tetrahydroxyborate
Identifiers
CAS number 15390-83-7 N
PubChem 177595
ChemSpider 154612 YesY
ChEBI CHEBI:41132 YesY
ChEMBL CHEMBL1231419 N
Gmelin Reference 1966
Jmol-3D images Image 1
Properties
Molecular formula H4BO4-
Molar mass 78.840 g mol-1
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
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
4
O
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[edit]

Basicity[edit]

Tetrahydroxyborate can assimilate a proton into the anion by recombination:

B(OH)
4
+ H+
B(OH)
3
+ H
2
O

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[edit]

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

Chemical reactions[edit]

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[edit]

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[edit]

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

Occurrence[edit]

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

Sodium-tetrahydroxyborate-xtal-3D-balls.png
Sodium-tetrahydroxyborate-xtal-3D-SF.png
ball-and-stick model of the crystal
structure of sodium tetrahydroxyborate
space-filling model of the crystal
structure of sodium tetrahydroxyborate

See also[edit]

References[edit]

  1. ^ a b "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 0080379419. 
  4. ^ L. J. Csetenyi, F. P. Glasser, R. A. Howie (June 1993). "Structure of sodium tetrahydroxyborate". Acta Cryst. C49 (6): 1039–1041. doi:10.1107/S0108270193000058.