Sodium benzoate is a food preservative that occurs naturally in some fruits. The chemical is the sodium salt of benzoic acid and is considered safe to ingest and apply to the skin. It should not be used in certain acidic products because it may combine to form harmful compounds, but it is not toxic and does not irritate tissue. It dissolves readily in water, and its primary use is to inhibit the growth of molds and bacteria in food and cosmetics.
TL;DR (Too Long; Didn't Read)
Sodium benzoate is the sodium salt, NaC7H5O2, of benzoic acid, C7H6O2. It is produced when bezoic acid reacts with sodium hydroxide, NaOH, and the sodium ion replaces one of the hydrogen ions in the acid to produce sodium benzoate and water. The chemical is found naturally in fruits such as plums and cranberries, and it is used as a preservative in food and cosmetics because it inhibits the growth of molds and bacteria.
In some acidic foods, sodium benzoate may react with ascorbic or citric acid to produce benzene, a potential carcinogenic compound. Although it is sometimes confused with borax or sodium borate, which is a salt of boric acid, the two chemicals are completely different.
The Chemistry of Sodium Benzoate
Sodium benzoate is the sodium salt obtained when benzoic acid reacts with sodium hydroxide. This is an acid-base reaction that produces a salt, which is sodium benzoate, and water. The chemical formula is:
C7H6O2 + NaOH = NaC7H5O2 + H2O
In water, the compound dissolves and dissocates into a sodium ion and a benzoic acid ion. In its solid form it is a white, granular or crystalline powder that can be added to food or cosmetics.
Other sodium compounds with similar names are sodium borate or borax and sodium carbonate or soda. They are sometimes confused with sodium benzoate but are completely different chemicals. Borax is a salt of boric acid and contains boron while soda, distinct from baking soda or sodium bicarbonate, is a salt of carbonic acid. Neither is commonly used as a food additive because they are not as safe as sodium benzoate.
Where Is Sodium Benzoate Found?
Sodium benzoate keeps molds and bacteria from growing in food and cosmetics. It is found in many fruit drinks, in salad dressings and oils, and in jams. Cosmetic manufacturers use it in skin creams and other cosmetics to keep them fresh. It is found naturally in fruits such as plums and cranberries and in spices such as cinnamon. Use of the chemical is widespread because it is inexpensive and because small concentrations, typically 0.05 - 0.1 percent, are effective.
In solution, the benzoic acid ion is the active ingredient and acts directly on micro-organisms to limit their activity. When used in certain foods such as acid citrus drinks, the sodium benzoate may react with the other acids such as citric or ascorbic acids to form benzene, a potential carcinogenic compound. Because the levels of sodium benzoate in most foods are so low, the corresponding concentration of benzene will also be below dangerous levels. In general, sodium benzoate is a safe, common, inexpensive and effective food additive with possibly some restrictions for a high consumption of certain acid foods.
About the Author
Bert Markgraf is a freelance writer with a strong science and engineering background. He has written for scientific publications such as the HVDC Newsletter and the Energy and Automation Journal. Online he has written extensively on science-related topics in math, physics, chemistry and biology and has been published on sites such as Digital Landing and Reference.com He holds a Bachelor of Science degree from McGill University.