PBS-1 (mono), PBS-4 (tetra)
|Jmol 3D model||Interactive image|
|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|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Sodium perborate (PBS) 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.
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.
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 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).
- B.J Brotherton Boron: Inorganic Chemistry Encyclopedia of Inorganic Chemistry (1994) Ed. R. Bruce King, John Wiley & Sons ISBN 0-471-93620-0
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
- Carrondo, M. A. A. F. de C. T.; Skapski, A. C. (1978). "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 B 34: 3551. doi:10.1107/S0567740878011565.