Sodium Perborate

KEY FACTS

OTHER NAMES:

Perboric acid, sodium salt

FORMULA:

NaBO₃

ELEMENTS:

Sodium, boron, oxygen

COMPOUND TYPE:

Salt (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

81.80 g/mol

MELTING POINT:

Not available; See Overview

BOILING POINT:

Not applicable

SOLUBILITY:

Soluble in water, with decomposition

OVERVIEW

Sodium perborate (SO-dee-um per-BOR-ate) is a white amorphous powder commonly available as the monohydrate (NaBO₃·H₂O) or the tetrahydrate (NaBO₃·₄H₂O). The most frequently available form of the compound, the tetraborate, is a white crystalline solid with a salty taste that melts at 63°C (145°F) and loses its water of hydration when heated above 130°C (270°F). When dissolved in water, all forms of sodium tetraborate decompose to yield hydrogen peroxide (H₂O₂) and sodium borate (Na₂B₄O₇). The formation of hydrogen peroxide, which is itself unstable and breaks down to release nascent oxygen (O), makes sodium tetraborate an excellent source of 'active' oxygen. The terms nascent and active refer to individual atoms of oxygen that have a strong tendency to react with other elements and compounds. Since sodium tetraborate is more stable than hydrogen peroxide, it can be used for the same purposes as the peroxide, but is safer and easier to handle. The most common applications of sodium tetraborate are in detergents, bleaches, hair care products, and disinfectants.

HOW IT IS MADE

Anhydrous sodium perborate can be made by heating the tetrahydrate:

NaBO₃·₄H₂O → NaBO₃ + 4H₂O

or by reacting hydrogen peroxide with sodium metaborate:

H₂O₂ + NaBO₂ → NaBO₃ + H₂O

Sodium perborate tetrahydrate is prepared by reacting hydrogen peroxide with borax (Na₂B₄O₇).

COMMON USES AND POTENTIAL HAZARDS

Sodium perborates' uses are based on the fact that it is a mild and relatively safe oxidizing agent. An oxidizing agent is a substance that supplies oxygen to other substances. The oxidation of a material may cause bleaching or the destruction of disease-causing microogranisms. For example, sodium perborate is added to some detergents to improve their bleaching capability. It makes the detergents more effective in removing stains, keeping white fabrics white, and preserving the original colors of colored cloth. The compound is also added to some automatic dishwasher powders to improve the product's ability to loosen left-on food and to sterilize dishes, silverware, and cookware. Sodium perborate is also used as an ingredient in a variety of home- and personal-care products, such as deodorants, mouthwashes, denture cleaners, and toothpastes.

Sodium perborate is an irritant to the skin, eyes, and respiratory tract. If ingested, it may cause nausea, vomiting, diarrhea, abdominal pain, and bleeding. Exposure to large quantities of the pure compound can produce severe skin rashes, permanent eye damage, breathing difficulties, unconsciousness, and kidney failure. Despite these concerns, people who use personal- and home-care products containing sodium perborate are at low risk for health problems. The compound degrades during machine washing, and home users rarely ingest, inhale, or come into contact with significant quantities of the compound. The European Union Scientific Committee on Toxicity, Ecotoxicity, and the Environment issued a report in May 2004 stating that manufacturers and consumers do not need to take steps beyond those already in place to protect themselves from exposure to sodium perborate.

Interesting Facts

• Because of concerns about the hazard that boron compounds may pose to the environment, sodium perborate is being replaced in many applications by a similar but safer oxidizing agent, sodium percarbonate.

Words to Know

AMORPHOUS

Without crystalline structure.

FOR FURTHER INFORMATION

"Material Safety Data Sheet." Solvay Interox. http://www.solvayinterox.com.au/solvay/uploadfile/SOL030%20-%20PBST.doc (accessed on November 10, 2005).

"Opinion on the Results of the Risk Assessment of Sodium Perborate." Scientific Committee on Toxicity, Ecotoxicity, and the Environment (CSTEE), 28 May 2004. http://europa.eu.int/comm/health/ph_risk/committees/sct/documents/out225_en.pdf (accessed on November 10, 2005).

"Sodium Perborate Information." PAN Pesticides Database. http://www.pesticideinfo.org/Detail_Poisoning.jsp?Rec_Id=PC34416 (accessed on November 10, 2005).

"Sodium Perborate Monohydrate." Shangyuchem. http://www.chem-world.com/sodium-perborate.htm (accessed on November 10, 2005).