Everything about Borates totally explained
Borates in
chemistry are
chemical compounds containing
boron bonded to three
oxygen atoms written as B(OR)
3. In B(OR)
4− anions, this number increases to four.
The borate
ion is BO
33−. it forms
salts with metallic elements. Boron found in nature is commonly as a borate mineral. Boron is also found combined with
silicate to form complex
borosilicate minerals such as the
tourmalines.
Borate exists in many forms. In acid and near-neutral conditions, it's
boric acid, commonly written as H
3BO
3 but more correctly B(OH)
3. The p
Ka of boric acid is 9.14 at 25C. Boric acid doesn't dissociate in aqueous solution, but is acidic due to its interaction with
water molecules, forming
tetrahydroxyborate:
» :B(OH)
3 + H
2O ⇌ B(OH)
4− + H
+
::
Ka = 5.8x10
−10 mol/l; p
Ka = 9.24.
Polyborate anions are formed at pH 7–10 if the boron concentration is higher than about 0.025 mol/L. The best known of these is the tetraborate ion, found in the mineral
borax:
» :4B(OH)
4− + 2H
+ ⇌ B
4O
72− + 9H
2O
Even though boric acid adds hydroxide to form B(OH)
4−, you may find for pKa values and other calculations, the fictitious ions are easier to use. Thus for a typical polyprotic acid, the deprotonation series dihydrogen borate [H
2BO
3−;], hydrogen borate [HBO
32−] and borate [BO
33−] may be written as pH increases.
Boric acid can be used to form many polymeric ions. The tetraborate ion, B
4O
72−, is very common; the hydrogen tetraborate ion, HB
4O
7−, as well as triborate and pentaborate, are also seen. The various metaborate ions have an
empirical formula of BO
2−, and form metaborate compounds. Formation of these complicated, potentially infinite network structures is extensive, perhaps surpassed only by the
silicates.
Common borate salts include sodium metaborate, NaBO
2, and sodium tetraborate, Na
2B
4O
7. The latter also occurs naturally as the hydrous mineral
borax, Na
2B
4O
7·10H
2O.
Boron,
California contains large borax deposits and is used extensively for borate mining. The
Atacama Desert in
Chile also contains mineable borate concentrations.
Various forms of borate are used as
wood preservatives or fungicides such as
disodium octaborate tetrahydrate.
Borate esters
Borate esters are
organic compounds of the type B(OR)
3 where R is an organic residue (for example
alkyl or
aryl). Borate esters include
trimethyl borate, B(OCH
3)
3, which is used as a precursor to
boronic esters for Suzuki couplings.
Further Information
Get more info on 'Borates'.
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