PBS-1 (mono), PBS-4 (tetra)
3D model (JSmol)
|Molar mass||99.815 g/mol (monohydrate);|
153.86 g/mol (tetrahydrate)
|Melting point||63 °C (145 °F; 336 K) (tetrahydrate)|
|Boiling point||130 to 150 °C (266 to 302 °F; 403 to 423 K) (tetrahydrate, decomposes)|
|2.15 g/100 mL (tetrahydrate, 18 °C)|
|Safety data sheet||ICSC 1046|
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
The compound is commonly encountered in anhydrous form or as a hexahydrate (commonly called "monohydrate" or PBS-1 and "tetrahydrate" or PBS-4, after the early assumption that NaBO
3 would be the anhydrous form). They are both white, odorless, water-soluble solids.
Unlike sodium percarbonate and perphosphate, the compound is not simply an adduct with hydrogen peroxide. Rather, it contains a perborate dianion [(B(OH)
consisting of a cyclic –B–O–O–B–O–O– core with two hydroxy groups attached to each boron atom. The ring adopts a chair conformation.
The compound also crystallizes from water as the hexahydrate, Na
2O, that is, Na
14 or NaH
The anhydrous compound is commonly but incorrectly called a "monohydrate" after the original formulation NaBO
2O instead of the correct Na
8. Likewise, the hexahydrate is usually called "tetrahydrate" and formulated as NaBO
More precisely, in solution the cyclic anion hydrolizes into two anions [B(OH)
, which then enter in equilibrium with boric acid B(OH)
3, hydrogen peroxide H
2, the hydroperoxyl anion HOO−
, and the tetrahydroxyborate anion [B(OH)
As the concentration of the solution increases, other peroxoborate species become significant. With excess H
2, the anions [B(OH)
, and eventually [B(OOH)
appear. At high borate concentrations, the sodium perborate with dimeric anion crystallizes out, due to its relatively low solubility.
The monohydrate form dissolves better than the tetrahydrate and has higher heat stability; it is prepared by heating the tetrahydrate.
Sodium perborate is manufactured by reaction of borax Na
7 and sodium hydroxide NaOH to give sodium metaborate NaBO
2, which is then reacted with hydrogen peroxide to give hydrated sodium perborate:
Sodium perborate serves as a stable source of active oxygen in many detergents, laundry detergents, cleaning products, and laundry bleaches. It is a less aggressive bleach than sodium hypochlorite and other chlorine-based bleaches, 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 (40–60 °C), it has to be mixed with a suitable activator, typically tetraacetylethylenediamine (TAED).
Sodium perborate is also present in some tooth bleaching formulas for non vital root treated teeth. The compound is inserted in the root canal 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. However, this use has been banned in the European Union.
In the European Union, sodium perborate, like most borates, was classified as "carcinogenic, mutagenic, or toxic for reproduction" (CMR), category 1B of Regulation (EC) 790/2009, as a result of being included in Part 3 of Annex VI of the regulation 1272/2008 on Classification, Labelling and Packaging (CLP) of substances and mixtures. As a result, their use has been automatically banned in cosmetic products in the EU, in any concentration, starting 1 December 2010. That extends to the use of perborates for tooth whitening.
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- B.J. Brotherton "Boron: Inorganic Chemistry" in Encyclopedia of Inorganic Chemistry (1994) Ed. R. Bruce King, John Wiley & Sons ISBN 0-471-93620-0
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- "Sodium Perborate REACH Consortium" (PDF). Retrieved 2012-06-07.
- J. Dugua and B.Simon (1978): "Crystallization of sodium perborate from aqueous solutions: I. Nucleation rates in pure solution and in presence of a surfactant". Journal of Crystal Growth, volume 44, issue 3, pages 265-279.doi:10.1016/0022-0248(78)90025-8
- J. Dugua and B.Simon (1978): "Crystallization of sodium perborate from aqueous solutions: II. Growth kinetics of different faces in pure solution and in the presence of a surfactant". Journal of Crystal Growth, volume 44, issue 3, pages 280-286.doi:10.1016/0022-0248(78)90026-X
- Nature Inc. (2015): "Chemical used in beauty salon teeth whitening banned by EU". BDJ Team, volume 2, article 15075, 26 June 2015. doi:10.1038/bdjteam.2015.75
- McKillop, Alexander; Kabalka, George W.; Reddy, Marepally Srinivasa (2008). "Sodium perborate". e-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.