Perchlorates

OVERVIEW

The perchlorates (per-KLOR-ates) are a family of compounds consisting of salts of perchloric acid, HClO₄. The family consists of dozens of compounds, the most important of which are ammonium perchlorate (NH₄ClO₄), potassium perchlorate (KClO₄), and sodium perchlorate (NaClO₄).

KEY FACTS

OTHER NAMES:

See Overview

FORMULA:

-ClO₄

ELEMENTS:

Chlorine and oxygen, in combination with other ions

COMPOUND TYPE:

Inorganic salts

STATE:

Solid

MOLECULAR WEIGHT:

117.49 to 138.55 g/mol

MELTING POINT:

Ammonium perchlorate: Decomposes explosively when heated; Potassium perchlorate: 525°C (977°F); Sodium perchlorate: 480°C (896°F)

BOILING POINT:

Not applicable; all decompose at or above melting points

SOLUBILITY:

Soluble in water; ammonium perchlorate is also soluble in methyl alcohol and slightly soluble in ethyl alcohol

Although perchlorates have been known since the early nineteenth century, they were not produced commercially until the 1890s. Even then, they were not produced in large volumes until World War II (1939–1945), when they were made for use in explosives. Perchlorate production continued to grow in the post-war period, especially during the military build-up that accompanied the Cold War (1945–1991) between the United States and the Soviet Union. In recent years, however, concerns about the presence of perchlorates in water supplies have become increasingly widespread.

HOW IT IS MADE

Each perchlorate is produced by a different method. Ammonium perchlorate, for example, is produced in a reaction among ammonium hydroxide (NH₄OH), hydrochloric acid (HCl), and sodium chlorate (NaClO₃).

Potassium perchlorate can be made in two ways. One method by electrolyzing potassium chlorate (KClO₃) in water. The other is by heating potassium chlorate (KClO₃). This results in a mixture of potassium perchlorate and potassium chloride (KCl), which is removed.

Sodium perchlorate is made by heating a mixture of sodium chlorate and sodium chloride. This reaction yields sodium chloride (NaCl) as well as the sodium perchlorate. The excess sodium chloride is removed from the reaction, leaving sodium perchlorate behind.

COMMON USES AND POTENTIAL HAZARDS

By far the most important uses of perchlorates are in the production of explosives and fireworks and as jet and rocket fuels. These uses are based on the fact that all perchlorates are very unstable oxidizing agents. An oxidizing agent is a material that supplies oxygen to some other substances or removes electrons from that substance. When used in explosives, the perchlorates supply oxygen to the fuels in the explosive (such as sulfur or carbon), causing them to burn very rapidly, producing large volumes of gases in a very short time. When used as a rocket or jet fuel, perchlorates supply the oxygen needed to burn the fuel itself, such as kerosene or hydrogen.

Interesting Facts

• Small amounts of potassium perchlorate are found naturally in Chile in deposits of sodium nitrate.
• About 9 million kilograms (20 million pounds) of perchlorates are produced each year in the United States.
• In January 2005, the U.S. Environmental Protection Agency set a standard of 0.007 milligrams per kilogram of body weight as the maximum recommended dose a person should ingest of perchlorates per day.
• Between 1997 and 2004, Lockheed Martin spent $80 million to study, clean up, and replace local water systems that had been contaminated with perchlorates used by the company in the production of military weapons and rocket fuels. The two systems were located near Riverside and Redlands, California.

Some perchlorates have other, more limited, uses. For example, potassium perchlorate was previously used to treat Graves disease, a condition in which the body produces too much thyroid hormone. It is still used to monitor the production of thyroid hormones. Potassium perchlorate is also used in emergency breathing equipment for high altitude aircraft and underwater boats. Other uses of perchlorates include:

• In nuclear reactors and electronic tubes;
• As additives in lubricating oils;
• In the tanning and finishing of leather products;

• As a fixer for fabrics and dyes;
• In electroplating;
• In the refining of aluminum metal;
• In the manufacture of rubber products;
• In the production of certain paints and enamels.

Perchlorates pose a serious risk to humans because they are unstable and have a tendency to explode spontaneously. They are also human health hazards, with harmful effects on both the brain and the thyroid. They have a tendency to prevent the uptake of iodine by the thyroid, thus interfering with the synthesis of hormones normally produced by that organ. Health officials believe that exposure to perchlorates may cause infertility in women or may have harmful effects on their newborn children. These effects include mental retardation and delays in their normal development. As a consequence, efforts are underway to locate areas where perchlorates may have entered the public water supply causing potential health problems for people living in the region.

Words to Know

ELECTROLYSIS

A process in which an electric current is used to bring about chemical changes.

SALT

An ionic compound where the anion is derived from an acid.

SYNTHESIS

A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.

FOR FURTHER INFORMATION

Perchlorate News.com. http://www.perchloratenews.com/index.html (accessed on December 10, 2005).

"Perchlorates: New Report on Widespread Rocket Fuel Pollution in Nation's Food and Water." Organic Consumers Association. http://www.organicconsumers.org/perchlorate.htm (accessed on December 10, 2005).

"Potassium Perchlorate." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/P5983.htm (accessed on December 10, 2005).

"Safety (MSDS) Data for Ammonium Perchlorate." Physical and Theoretical Chemistry Lab. http://ptcl.chem.ox.ac.uk/MSDS/AM/ammonium_perchlorate.html (accessed on December 10, 2005).

Sharp, Renee, and Bill Walker. Rocket Science: Perchlorate and the Toxic Legacy of the Cold War. Washington, D.C.: Environmental Working Group, July 2001. Also available online at http://www.ewg.org/reports_content/rocketscience/perchlorate.pdf (accessed on December 10, 2005).

"Toxicological Profile for Perchlorates." Agency for Toxic Substances and Disease Registry. http://www.atsdr.cdc.gov/toxprofiles/tp162.html (accessed on December 10, 2005).