Acetic Acid
Overview
Acetic acid (uh-SEE-tik AS-id) is a clear, colorless liquid with a sharp odor. In its pure form, the compound is also known as glacial acetic acid. Acetic acid is the primary active ingredient of vinegar, which typically consists of about five parts of acetic acid mixed with 95 parts of water. The compound's name comes from the Latin word for vinegar, acetum.
Key Facts
Other Names:
Ethanoic acid; methanecarboxylic acid; vinegar acid
Formula:
CH3COOH
Elements:
Carbon, hydrogen, oxygen
Compound Type:
Carboxylic acid (organic)
State:
Liquid
Molecular Weight:
60.05 g/mol
Melting Point:
16.6°C (61.9°F)
Boiling Point:
117.9°C (244.2°F)
Solubility:
Soluble in water, alcohol, ether, acetone, benzene, and other organic solvents
Acetic acid, in the form of vinegar, has been known to humans for centuries. When fruit juices are allowed to stand for too long, or when they are fermented to make wine, vinegar forms. The use of vinegar as a condiment is mentioned a number of times in the Bible, and was described by the Greek natural philosopher Theophrastus (c. 372–c. 287 BCE). The first person to extract acetic acid from vinegar was the Muslim alchemist Jabir ibn Hayyan Geber (c. 721–815). The pure compound was not produced, however, for another ten centuries when the German chemist Georg Ernst Stahl (1660–1734) extracted acetic acid from vinegar in 1700 by distillation.
More than 1.4 million metric tons (1.5 million short tons) of acetic acid are produced in the United States annually. The largest fraction of that amount is used as a raw material in the manufacture of plastics.
How It Is Made
The most common method of making acetic acid is one developed by the Monsanto chemical corporation. In this process, synthesis gas (a mixture of carbon monoxide [CO] and hydrogen [H2]) is heated over a catalyst of copper metal mixed with zinc oxide to make methanol (methyl alcohol; CH3OH). The methanol is then treated with carbon monoxide (CO) to make acetic acid. Acetic acid can also be made by the fermentation of any material that contains sugar or some other carbohydrate. Although this method is of interest from a historical standpoint, it is not sufficiently efficient to use industrially.
Researchers are constantly looking for new, more efficient, more environmentally-friendly methods for making acetic acid. In 2003, for example, chemists at the University of Southern California reported on a new method for making acetic acid directly from methane gas (CH4) using a catalyst of palladium and sulfuric acid. Other researchers are looking for ways to oxidize the waste gases produced from industrial processes to acetic acid.
Interesting Facts
Ancient Romans boiled fermented wine (vinegar) in lead pots to make a sweet syrup called sapa. The acetic acid in the vinegar dissolved a small amount of lead from which the pots were made, producing lead acetate (Pb[C2H3O2]). When they used sapa as a sweetening agent in their foods, the Romans ingested the lead acetate which, over long periods of time, caused the lead poisoning from which so many of them died.
Common Uses and Potential Hazards
Acetic acid is probably best known to most people as vinegar. In this form, it is used as a condiment and a food preservative. The greatest volume of acetic acid is used, however, in a variety of chemical processes, especially the manufacture of plastic materials such as polyvinyl acetate (PVA), polyethylene terephthalate (PET), and cellulose acetate. A more recent use of acetic acid is in the manufacture of calcium magnesium acetate (CMA), a deicer. Traditionally, roads, highways, and airport runways have been treated with calcium chloride (CaCl2) or some other salt to remove snow and ice. These compounds have serious environmental effects, however, and researchers have long been looking for alternatives that are as effective in removing snow and ice, but less harmful to the environment. CMA has been the most promising of these alternatives, and its production has produced a growing demand for acetic acid. Some other applications of acetic acid include:
- As a cleaning agent;
- In the manufacture of photographic materials;
- For the production of a variety of organic compounds, such as those used in the manufacture of packaging materials, paints, adhesives and artificial fibers;
- As a fumigant (pesticide) to preserve fruits and grains;
- In the printing of textiles; and
- As an acidifier to improve the flow of oil from wells.
Dilute acetic acid in the form of vinegar is harmless and has been consumed by humans for centuries. Prolonged contact with the skin or eyes may, however, produce irritation of tissues and should be avoided. Concentrated forms of acetic acid pose more serious health risks, such as irritation of the gastrointestinal system, respiratory system, and eyes. Most people do not come into contact with the concentrated acid, and safety precautions are of importance only to individuals who handle the material in their work.
Words to Know
An ancient field of study from which the modern science of chemistry evolved. A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure. A process of separating two or more substances by boiling the mixture of which they are composed and condensing the vapors produced at different temperatures.For Further Information
"Acetic Acid." Chemical of the Week. http://scifun.chem.wisc.edu/chemweek/AceticAcid/AceticAcid.html (accessed on September 16, 2005).
"Acetic Acid and CMA." https://netfiles.uiuc.edu/mcheryan/www/cma.htm (accessed on September 16, 2005).
"Acetic Acid and Derivatives." Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed. Vol. 1. New York: John Wiley & Sons, 1991, pp. 121-175.
See Also
Amyl Acetate; Butyl Acetate; Ethyl Acetate; Isoamyl Acetate
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