Acetate Definition in Chemistry

Important for metabolism, yet may cause a hangover

This is the chemical structure of the acetate anion.
This is the chemical structure of the acetate anion. Todd Helmenstine

Acetate refers to the acetate anion and the acetate ester functional group. The acetate anion is formed from acetic acid and has a chemical formula of CH3COO-. The acetate anion is commonly abbreviated as OAc in formulas. For example, sodium acetate is abbreviated NaOAc and acetic acid is HOAc. The acetate ester group connects a functional group to the last oxygen atom of the acetate anion. The general formula for the acetate ester group is CH3COO-R.

Key Takeaways: Acetate

  • The word "acetate" refers to the acetate anion, the acetate functional group, and to compounds that include the acetate anion.
  • The chemical formula for the acetate anion is C2H3O2-.
  • The simplest compound made using acetate is hydrogen acetate or ethanoate, which is most often called acetic acid.
  • Acetate in the form of acetyl CoA is used in metabolism to yield chemical energy. However, too much acetate in the bloodstream can lead to adenosine accumulation, which causes symptoms of a hangover.

Acetic Acid and Acetates

When the negatively-charged acetate anion combines with a positively-charge cation, the resulting compound is called an acetate. The simplest of these compounds is hydrogen acetate, which is commonly called acetic acid. The systematic name of acetic acid is ethanoate, but the name acetic acid is preferred by the IUPAC. Other important acetates are acetate of lead (i.e., sugar of lead), chromium(II) acetate, and aluminum acetate. Most transition metal acetates are colorless salts that are highly soluble in water. At one time, lead acetate was used as a (toxic) sweetener. Aluminum acetate is used in dyeing. Potassium acetate is a diuretic.

Most acetic acid produced by the chemical industry is used to prepare acetates. Acetates, in turn, are primarily used to make polymers. Nearly half of acetic acid production goes to preparing vinyl acetate, which is used to make polyvinyl alcohol, an ingredient in paint. Another fraction of acetic acid is used to make cellulose acetate, which is used to make fibers for the textile industry and acetate discs in the audio industry. In biology, acetates occur naturally for use in biosynthesis of more complex organic molecules. For example, bonding two carbons from acetate to a fatty acid produces a more complex hydrocarbon.

Properties and Synthesis of Acetate Salts

Because acetate salts are ionic, they tend to dissolve well in water. One of the easiest forms of acetate to prepare at home is sodium acetate, which is also known as "hot ice." Sodium acetate is prepared by mixing vinegar (dilute acetic acid) and baking soda (sodium bicarbonate) and evaporating off the excess water.

Acetate Esters

While acetate salts are typically white, soluble powders, acetate esters are typically available as lipophilic, often volatile liquids. Acetate esters have the general chemical formula CH3CO2R, in which R is an organyl group. Acetate esters are typically inexpensive, display low toxicity, and often have a sweet odor.

Acetate Biochemistry

Methanogen archaea produce methane via a disproportionation reaction of fermentation:

CH3COO- + H+ → CH4 + CO2

In this reaction, a single electron is transferred from the carbonyl of the carboxylic group to the methyl group, releasing methane gas and carbon dioxide gas.

In animals, acetate is most commonly used in the form acetyl coenzyme A. Acetyl coenzyme A or acetyl CoA is important for lipid, protein, and carbohydrate metabolism. It delivers the acetyl group to the citric acid cycle for oxidation, which leads to energy production.

Acetate is believe to cause or at least contribute to hangovers from alcohol consumption. When alcohol is metabolized in mammals, increased levels of serum acetate lead to adenosine accumulation in the brain and other tissues. In rats, caffeine has been shown to reduce nociceptive behavior in response to adenosine. So, while drinking coffee after consuming alcohol may not increase sobriety of a person (or rat), it may reduce the likelihood of getting a hangover.

Sources

  • "Is coffee the real cure for a hangover?" by Bob Holmes, New Scientist, Jan. 15 2011, p. 17.
  • Hosea Cheung, Robin S. Tanke, G. Paul Torrence "Acetic acid" in Ullmann's Encyclopedia of Industrial Chemistry. Weinheim, Germany: Wiley-VCH, 2005. doi:10.1002/14356007.a01_045
  • March, J. Advanced Organic Chemistry. 4th Ed. J. Wiley and Sons, 1992: New York. ISBN 0-471-60180-2.
  • Nelson, D. L.; Cox, M. M. Lehninger, Principles of Biochemistry. 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.
  • Vogels, G. D.; Keltjens, J. T.; Van Der Drift, C. (1988). "Biochemistry of methane production". In Zehnder A.J.B. Biology of anaerobic microorganisms. New York: Wiley. pp. 707–770.