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Sodium perborate

Sodium perborate (PBS) is a white, odorless, water-soluble chemical compound with chemical formula ₃. It crystallizes as the monohydrate, NaBO₃.H₂O, tetrahydrate, NaBO₃.4H₂O and trihydrate, NaBO₃.3H₂ O. The monohydrate and tetrahydrate are the commercially important forms.

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 are not simply addition compounds of hydrogen peroxide, but contain a cyclic anion with peroxo bridges and do not contain the BO₃⁻ ion. . This makes the material more stable, safer for handling and storage. The formulae of the mono and tetra hydrates can therefore be written as Na₂B₂O₈H₄ (anhydrous) and Na₂B₂O₈H₄.6H₂O respectively.

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 tooth that has had root canal treatment. The sodium perborate is placed inside the tooth and left in place for an extended period of time to allow it to difuse 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 (40-60 °C), it has to be mixed with a suitable activator, typically tetraacetylethylenediamine (TAED).