Sodium perborate

Sodium perborate is chemical compound whose chemical formula may be written NaH₂BO₄, Na₂H₄B₂O₈, or, more properly, [Na⁺]₂[B₂O₄(OH)₄]²⁻. Its name is sometimes abbreviated as PBS (not to be confused with phosphate-buffered saline).

The compound is commonly encountered in anhydrous form or as a hexahydrate (commonly called, respectively, "monohydrate" or PBS-1 and "tetrahydrate" or PBS-4, after the historic assumption that NaBO₃ would be the anhydrous form). They are both white, odorless, water-soluble solids.

This salt is widely used in laundry detergents, as one of the peroxide-based bleaches.

Sodium perborate was first obtained in 1898, independently, by Sebastian Tanatar and by P. Melikoff and L. Pissadewsky; the researchers prepared sodium perborate by treating sodium borate with a solution of hydrogen peroxide and sodium hydroxide, but Tanatar also obtained sodium perborate by electrolysis of a solution of sodium borate.

Structure

Unlike sodium percarbonate and sodium perphosphate, the compound is not simply an adduct with hydrogen peroxide – known only since 1961. Rather, it contains a perborate anion [(B(OH)₂OO)₂]²⁻ 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.

Hydrates

The compound also crystallizes from water as the hexahydrate, Na₂H₄B₂O₈·6H₂O, that is, Na₂H₁₆B₂O₁₄ or NaH₈BO₇.

The anhydrous compound is commonly but incorrectly called a "monohydrate" after the historical formulation NaBO₃·H₂O instead of the correct Na₂H₄B₂O₈. Likewise, the hexahydrate is usually called "tetrahydrate" and formulated as NaBO₃·4H₂O. Both forms are white, odorless, water-soluble solids. The "monohydrate" and the "tetrahydrate" are the commercially important forms.

There does exist a true tetrahydrate Na₂H₄B₂O₈·4H₂O, traditionally known as the "trihydrate", with no industrial significance. There is a CAS number for each of the three traditional "hydrates", the three "peroxyborate" versions of each (interpreted as a hydrogen peroxide adduct) and the poorly-defined "anhydrate" NaBO₃, totalling seven.

Chemistry

Sodium perborate undergoes hydrolysis in contact with water, producing hydrogen peroxide and borate.

More precisely, in solution the cyclic anion hydrolizes into two anions [B(OH)₃(OOH)]⁻, which then enter in equilibrium with boric acid B(OH)₃, hydrogen peroxide H₂O₂, the hydroperoxyl anion ⁻OOH, and the tetrahydroxyborate anion [B(OH)₄]⁻:

[(B(OH)₂OO)₂]²⁻ + 2 H₂O ⇌ 2 [B(OH)₃(OOH)]⁻

[B(OH)₃(OOH)]⁻ ⇌ B(OH)₃ + ⁻OOH

B(OH)₃ + ⁻OOH + H₂O ⇌ [B(OH)₄]⁻ + H₂O₂

As the concentration of the solution increases, other peroxoborate species become significant. With excess H₂O₂, the anions [B(OH)₂(OOH)₂]⁻, [B(OH)(OOH)₃]⁻, and eventually [B(OOH)₄]⁻ appear. At high borate concentrations, the sodium perborate with dimeric anion crystallizes out, due to its relatively low solubility.

The "monohydrate" form dissolves faster than the "tetrahydrate" and has higher heat stability; it is prepared by heating the "tetrahydrate". The commercial "anhydrate", or Oxoborate, is prepared by further heating of "monohydrate" and actually consists of sodium borate and boron–oxygen radical.

Preparation

Sodium perborate is manufactured by reaction of borax Na₂B₄O₇ and sodium hydroxide NaOH to give sodium metaborate NaBO₂, which is then reacted with hydrogen peroxide to give hydrated sodium perborate:

Na₂B₄O₇ + 2 NaOH → 4 NaBO₂ + H₂O

2 NaBO₂ + 2 H₂O₂ → Na₂B₂O₄(OH)₄

A surfactant may be added to control crystal size.

It may also be produced in the electrolysis of an aqueous solution containing borax, sodium carbonate and sodium bicarbonate (potassium dichromate is added to improve yield along with sodium silicate). A copper pipe is used as a cathode and platinum for the anode, the current being 6 amperes at 7 to 8 volts, and the temperature 10 °C.

Uses

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), one must mix it with a suitable activator, typically tetraacetylethylenediamine (TAED).

The compound 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 also used as an oxidizing reagent in organic synthesis. For example, it converts thioethers into sulfoxides and sulfones. Another use of sodium perborate in organic synthesis is as a convenient alternative to H₂O₂, for example in the 2 step conversion of an aryl halide to a phenol (the first step is a Miyaura borylation).

Dental use

Sodium perborate monohydrate is quickly hydrolyzed into hydrogen peroxide and borate on contact with water. A 1979 double-blind crossover study suggests that hydrogen peroxide, which is released during the use of this product, may prevent or retard colonization and multiplication of anaerobic bacteria, such as those that inhabit oral wounds.

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.

Safety

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.

Brands

Bocasan

Bocasan was an oral wound cleanser manufactured in the United Kingdom by Knox Laboratories Ltd of London from 1960–1975, before being rebranded as an Oral-B product

Production of Bocasan appears to have ceased by 2003. A similar product, Amosan was available for a period before also ceasing production in 2010. As of 2013, a Dutch pharmacy offers the same formulation under the name Bikosan

It was used to aid treatment, in adults or children over 5 years old, of periodontal conditions such as canker sores, denture irritation, orthodontic irritation, or after dental procedures.

Bocasan was packaged in a 1.7 gram envelope, and contained 69.72% sodium perborate monohydrate and 29.68% sodium hydrogen tartrate anhydrous. To use, the contents were dissolved in 30 cubic centimetres of warm water. Half the amount was swilled around the mouth for two minutes and discarded, and the procedure repeated with the remainder. Treatment was recommended three times a day after meals.

A 1979 double-blind crossover study suggests that hydrogen peroxide, which is released during the use of this product, may prevent or retard colonization and multiplication of anaerobic bacteria, such as those that inhabit oral wounds. A small (n=12) 1998 RCT shows that Bocasan combined with chlorhexidine mouthwash is better than chlorhexidine alone in preventing plaque. A further study (n=28) shows that Bocasan reduces the staining associated with chlorhexidine.

Drug facts

• Active ingredient: Sodium perborate monohydrate
• Inactive ingredients: Sodium hydrogen tartrate
• Purpose: Oral cleanser
• Normal use: Use up to three times daily, after meals or as directed by a dentist

Amosan

Amosan is an oral antiseptic rinse. It contains 68.635% sodium perborate monohydrate by weight. Sold as a powder customarily packaged in 1.7g envelopes, it reconstitution with warm water, after which it is used as a mouth rinse. It is used to aid in the prevention of, as well as speed the recovery from canker sores, denture irritation, orthodontic irritation, and oral injuries or after dental procedures.

History

Amosan was originally made by Oral-B; a mention of the powder appeared in the February 6, 1970 Federal Register. Between 2005 and 2010, Amosan was manufactured in Belgium and sold under the Oral-B brand, belonging to Procter & Gamble after its 2005 acquisition of Gillette. In December 2010, its use was banned in the EU, as the product is based on borate, which the union considers "carcinogenic, mutagenic, or toxic for reproduction".

Vintage Brands Limited began manufacturing and selling Amosan Oral Antiseptic Rinse in 2014 because many consumers were disappointed that it was no longer available. Product review pages on Amazon and public comment forums elsewhere indicate a high level of frustration with the discontinuation by users who could find no effective alternative treatment.

In April 2012, it was reported that Shoppers Drug Mart in Canada had produced a comparable product under their house brand: 'Life Brand Oral Wound Cleanser'. Also, Jean Coutu and Rexall has their own house brand versions.

Drug facts

• Active ingredient: Sodium perborate monohydrate 1.2 g
• Inactive ingredients: L-Tartaric acid, sodium saccharin, flavors
• Purpose: Oral wound cleanser
• Normal use: Use up to 4 times daily, after meals and before bedtime or as directed by a dentist or physician

See also

• Amosan
• Sodium percarbonate
• Persil

References

External links

• Borax Detergent Book: Bleaching
• National Pollutant Inventory - Boron and compounds
• Sodium perborate history, image Archived 2011-04-07 at the Wayback Machine
• Sodium perborate in organic synthesis