Physical Properties of Benzoic Acid

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Benzoic acid, C6H5COOH, a white crystalline powder, the simplest of aromatic carboxylic acids, has a melting point of 122°C, a boiling point of 249°C and a molecular weight of 122.12. Widely occurring in many plants and resins, its uses are many: as a food preservative, germicide or antifungal agent; to season tobacco and to enhance perfume; and in the production of cosmetics, dyes, plastics and insect repellant.

Carboxylic Acid

  • A carboxylic acid is any organic compound with a formula including "COOH" wherein a carbon (C) atom is double bonded to an oxygen (O) atom to make what is called a carbonyl group (―C=O) and where this same carbon atom is singled bonded to a hydroxyl group (―OH). Carboxylic acids are considered to be "stronger" acids because they donate their hydrogen ion (H+) more readily than most other groups of organic compounds. (Acids are hydrogen ion (H+) donors; bases are hydrogen ion receivers (OH-)).

Properties

  • Carboxylic acids have much higher boiling points than organic compounds of similar molecular weight. They are distinctive, too, for their foul odor. The water solubility of carboxylic acids, however, is similar to that of other organic compounds unless the carboxylic acids are converted into a salt. Then they are highly soluble in water. Salts are created by adding a strong base such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) to the acid.

Functions

  • The sodium salt of benzoic acid is sodium benzoate, C7H5NaO2. A white, odorless powder, highly soluble in water, sodium benzoate is an effective antimicrobial agent against most yeast and bacterial strains. It also has a sweet, astringent taste. Because of these characteristics, according to Science Encyclopedia Online, "[i]t is the most widely used food preservative in the world." Foodstuffs that rely on sodium benzoate include jams, jellies, preserves, pickles, salsas, maple syrups, margarine, diet soft drinks, fruit juices and wine coolers. Sodium benzoate is also used in personal products such as toothpaste and mouthwash and as an antiseptic and as a tableting lubricant in pharmaceutical preparations.

Industrial Applications

  • Sodium benzoate is used to inhibit corrosion and as an antifreeze additive in automobile engines. It is used as a nucleating agent for ethylene, propylene, butane, polyethylene and polypropylene, as a photographic processing stabilizer, and as a dye intermediate. Benzoic acid esters (compounds formed by reactions with alcohols in the presence of either hydrochloric or sulfuric acid) are used as pesticides, disinfectant additives, solvents, dye carriers and in the manufacture of other compounds.

Warnings

  • The material safety data sheet for benzoic acid posts substantive warnings regarding the handling of this substance. While benzoic acid is readily biodegradable and it is not carcinogenic, potentially adverse health effects include irritation to the respiratory tract upon inhalation; abdominal pain, sore throat, nausea and vomiting upon ingestion of large doses; and painful irritation with redness upon contact with the eyes or skin. There is, as well, a fire hazard. If benzoic acid fine dust collects in the air in sufficient concentrations, in the presence of an igniting source, there could be a dust explosion. Further, in an enclosed area the vapors from molten benzoic acid could potentially explode.

References

  • Photo Credit "DNA Molecule display, Oxford University" is Copyrighted by Flickr user: net_efekt (Christian Guthier) under the Creative Commons Attribution license.
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