Sodium perborate is a white, odorless, water-soluble chemical compound with the
chemical formula NaBO3. It crystallizes as the monohydrate, NaBO3·H2O,
trihydrate, NaBO3·3H2O and tetrahydrate, NaBO3·4H2O. The monohydrate and
tetrahydrate are the commercially important forms. The elementary
structural unit of sodium perborates is a dimer anion B2O4(OH)42−, in which two
boron atoms are joined by two peroxo bridges in a chair-shaped 6-membered
ring, and the simplistic NaBO3·nH2O-type formulas are just a convenient way to
express the average chemical composition.
Preparation and chemistry Sodium perborate is manufactured by
reaction of disodium tetraborate pentahydrate, hydrogen peroxide, and
sodium hydroxide. The monohydrate form dissolves better than the tetrahydrate
and has higher heat stability; it is prepared by heating the tetrahydrate.
Sodium perborate undergoes hydrolysis in contact with water, producing hydrogen
peroxide and borate. Structure
Unlike sodium percarbonate and perphosphate, the sodium perborate is
not simply an adduct with hydrogen peroxide, and it does not contain an
individual BO3− ion. Rather, there is a cyclic dimer anion B2O4(OH)42−, in which
two boron atoms are joined by two peroxo bridges in a chair-shaped 6-membered
ring. This makes the substance more stable, and safer for handling and
storage. The formula of the sodium salt is thus Na2H4B2O8.
Uses It serves as a source of active oxygen
in many detergents, laundry detergents, cleaning products, and laundry bleaches.
It is also present in some tooth bleaching formulas. It is used as a
bleaching agent for internal bleaching of a non vital root treated tooth. The
sodium perborate is placed inside the tooth and left in place for an extended
period of time to allow it to diffuse into the tooth and bleach stains from
the inside out. It has antiseptic properties and can act as a
disinfectant. It is also used as a "disappearing" preservative in some
brands of eye drops. Sodium perborate is a less aggressive
bleach than sodium hypochlorite, causing less degradation to dyes and textiles.
Borates also have some non-oxidative bleaching properties.
Sodium perborate releases oxygen rapidly at temperatures over 60 °C. To make it
active at lower temperatures, it has to be mixed with a suitable activator,
typically tetraacetylethylenediamine. See also
Amosan Sodium percarbonate
Sodium perphosphate Persil
References ^ a b c d e f B.J Brotherton Boron:
Inorganic Chemistry Encyclopedia of Inorganic Chemistry Ed. R. Bruce King,
John Wiley & Sons ISBN 0-471-93620-0 ^ Greenwood, Norman N.; Earnshaw, Alan.
Chemistry of the Elements. Butterworth-Heinemann. ISBN
0-08-037941-9. ^ Carrondo, M. A. A. F. de C. T.;
Skapski, A. C.. "Refinement of the X-ray crystal structure of the industrial
bleaching agent disodium tetrahydroxo-di-μ-peroxo-diborate
hexahydrate, Na2[B2(O2)2(OH)4]·6H2O". Acta Crystallogr B34: 3551.
doi:10.1107/S0567740878011565. External links
Borax Detergent Book: Bleaching National Pollutant Inventory - Boron and
compounds Sodium perborate history, image
Sodium perborate in organic synthesis