Boric Acid

OVERVIEW

Boric acid (BORE-ik ASS-id) is a colorless, odorless, white or colorless powder or crystalline material with a slightly oily feeling that slowly decomposes with heat, changing first to metaboric acid (HBO₂), then to pyroboric acid (H₂B₄O₇), and eventually to boric oxide (B₂O₃). The compound's solubility is very much a factor of temperature. In cold water, about 5 grams (0.2 ounce) of boric acid dissolve in 100 mL (3.4 ounces) of water, while at 100°C (212°F), its solubility increases to 25 grams (0.9 ounce) in 100 mL (3.4 ounces) of water.

KEY FACTS

OTHER NAMES:

Orthoboric acid; hydrogen orthoborate; boracic acid

FORMULA:

H₃BO₃

ELEMENTS:

Hydrogen, boron, oxygen

COMPOUND TYPE:

Inorganic acid

STATE:

Solid

MOLECULAR WEIGHT:

61.83 g/mol

MELTING POINT:

170.9°C (339.6°F)

BOILING POINT:

Decomposes above its melting point

SOLUBILITY:

Somewhat soluble in water, ethyl alcohol, and glycerol

Boric acid occurs naturally in a number of locations where it has precipitated out of hot springs. It may occur then in the form of the mineral sassolite. Given its abundance in nature, it is not surprising that the compound has been known to and used by humans for many centuries. For example, the Greeks are known to have used boric acid as an antiseptic, to preserve foods, and as a cleaning agent. The first person to prepare boric acid in Europe is thought to be the German chemist Wilhelm Homberg (1652–1715), who in 1702 treated natural borax (Na₂B₄O₇·10H₂O) with acid to obtain a product he called sedative salt, probably a form of boric acid. The chemical structure of the compound was determined in 1808 by the French researchers Louis-Joseph Gay-Lussac (1778–1850) and Louis-Jacques Thénard (1777–1857).

HOW IT IS MADE

The most common method of producing boric acid is by treating the relatively abundant borax with hydrochloric or sulfuric acid and crystallizing out the boric acid that forms in the reaction. A less common method of preparation involves the treatment of borax brine solutions with a chelating agent that binds to the borates present in the brine, which can then be converted to boric acid.

COMMON USES AND POTENTIAL HAZARDS

By far the greatest amount of boric acid is used in the production of heat-resistant (borosilicate) glass, glass fibers, porcelain enamels, crockery, laboratory glassware, and other specialized types of glass and ceramic materials. In 2004, about 80 percent of all the boric acid used in the United States was applied to these purposes. Although accounting for a much smaller amount of boric acid, another well-known use of the compound is as an antiseptic in eyewashes, ointments, and mouthwashes. It is also used as a preservative in foods and as a fungicide on citrus fruit crops. In the United States, a residue of no more than 8 parts per million is permitted on fruits treated with boric acid.

Interesting Facts

• The most common sources of boric acid are hot springs and volcanic sites such as the mineral springs at Vichy and Aix-la-Chapelle in France and Wiesbaden in Germany, around the volcanic regions of Tuscany in Italy, and in dry lakes of California and Nevada, such as California's Borax Lake.
• Boric acid was once used as an ingredient in talcum and diaper powders and in salves for diaper rashes because of its antiseptic properties. The compound was eventually banned for such uses, however, when regulators decided that it was too toxic if it accidentally entered the body through an open wound or by being swallowed.

Some other important applications of boric acid include the following:

• In the production of flame retardant materials;
• As a pesticide for the treatment of cockroaches, black carpet beatles, termites, fleas, fire ants, centipedes, grasshoppers, and slugs;
• As a flux in welding and brazing;
• In the synthesis of many boron compounds;

• To provide the finishing touches on the production of leather and fur products;
• In the manufacture of latex paints; and
• In the nickel plating of metallic products.

Boric acid is toxic if swallowed. It causes nausea, vomiting, diarrhea, and stomach cramps. In extreme cases, it can cause the collapse of the circulatory system, delirium, convulsions, coma, and death. Ingestion of no more than 5 grams (0.2 ounce) of boric acid can cause death in an infant. Ingestion of 15 to 20 grams (0.5 to 0.7 ounce) by an adult can also be fatal. Boric acid can also cause irritation of the skin, which, in extreme cases, can result in a condition known as borism. Borism is characterized by dry skin, eruptions of the skin and mucous membranes, and gastric disturbances.

Words to Know

BRINE SOLUTION

A solution that is saturated with or nearly saturated with sodium chloride or other inorganic salts.

CHELATING AGENT

An organic compound that binds ("grabs on to") some specific compound or compounds present in a mixture.

FLUX

A material that lowers the melting point of another substance or mixture of substances or that is used in cleaning a metal.

FOR FURTHER INFORMATION

"Borax; Boric Acid, and Borates." IPM of Alaska. http://www.ipmofalaska.com/files/Borates.html (accessed on October 12, 2005).

"Boric Acid: Technical Description." Manufacturas Los Andes. http://www.mandes.com.ar/technic-boric-acid.php (accessed on October 12, 2005).

Potter, Mike. "Cockroach Elimination." University of Kentucky Entomology. http://www.uky.edu/Agriculture/Entomology/entfacts/struct/ef614.htm (accessed on October 12, 2005).

Boric acid

Boric acid, also known as boracic acid and arthoboric acid, is a very weak acid with the formula H₃ BO₃, often used as a mild antiseptic. Chemically, it acts as a tribasic acid—an acid that can dissociate successively to produce three hydrogen ions in solution. However, because it dissociates to such a small extent, it is a very weak acid that is actually used in water solution as an eye wash. Pure boric acid is a colorless, odorless, white powder or transparent crystals that melt at about 340°F (171°C). Boric acid loses water as it is heated, changing first into metaboric acid (HBO₂) and then into pyroboric acid (H₂ B₄ O₇). The three acids can be thought of as hydrates of boric oxide (B₂ O₃). Orthoboric acid is fairly soluble in water (especially hot water), alcohol, and glycerine.

Boric acid has a wide variety of industrial applications. It is used in the manufacture of heat-resistant borosilicate glass and other ceramics, such as crockery, porcelains, enamels, and artificial gemstones. It also used in waterproofing wood and fireproofing textiles. It also finds application as an insecticide for cockroaches and black carpet beetles and as an fungicide on citrus fruits.

Its use in the last of these applications is carefully monitored, however, because of the compound’s toxicity. When swallowed, boric acid can cause nausea, vomiting, diarrhea, and other intestinal problems. In large doses, it can cause coma and death. The toxic level of boric acid in infants can be less than 0.2 ounces (5 g) and in adults, from 0.2 ounces (5 g) to 0.7 ounces (20 g).

Boric acid

Boric acid, also known as boracic acid and arthoboric acid, is a very weak acid with the formula H3BO3, often used as a mild antiseptic. Chemically, it acts as a tribasic acid—an acid that can dissociate successively to produce three hydrogen ions in solution . However, because it dissociates to such a small extent, it is a very weak acid that is actually used in water solution as an eye wash. Pure boric acid is a colorless, odorless, white powder or transparent crystals that melt at about 340°F (171°C). Boric acid loses water as it is heated, changing first into metaboric acid (HBO2) and then into pyroboric acid (H2B4O7). The three acids can be thought of as hydrates of boric oxide (B2O3). Orthoboric acid is fairly soluble in water (especially hot water), alcohol , and glycerine.

Boric acid has a wide variety of industrial applications. It is used in the manufacture of heat-resistant borosilicate glass and other ceramics , such as crockery, porcelains, enamels, and artificial gemstones. It also used in waterproofing wood and fireproofing textiles . It also finds application as an insecticide for cockroaches and black carpet beetles and as an fungicide on citrus fruits .

Its use in the last of these applications is carefully monitored, however, because of the compound's toxicity. When swallowed, boric acid can cause nausea, vomiting, diarrhea, and other intestinal problems. In large doses, it can cause coma and death. The toxic level of boric acid in infants can be less than 0.2 oz (5 g) and in adults, from 0.2 oz (5 g) to 0.7 oz (20 g).

boric acid Chemically H₃BO₄, derived from the element boron, boric acid has been used in the past as a preservative in bacon and margarine, but boron accumulates in the body. Formerly used as an anti‐infective agent and eye‐wash (boracic acid) but there was a high incidence of toxic reactions.

bo·ric ac·id • n. Chem. a weakly acid crystalline compound, B(OH)₃, derived from borax and used as a mild antiseptic and in the manufacture of heat-resistant glass and enamels.