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The most common preservative in food – benzoic acid

food preservative benzoic acid

Benzoic acid is an aromatic acid organic compound and the simplest aromatic acid. Its chemical formula is C7H6O2. It was originally made from benzoin gum, so it is called benzoic acid. The melting point is 122.13 ℃, the boiling point is 249.2 ℃, and the relative density (15/4 ℃) is 1.2659. The appearance is white needle-like or scaly crystals. It will sublimate when the temperature is above 100℃. Slightly soluble in cold water and hexane, soluble in hot water, ethanol, ether, chloroform, benzene, carbon disulfide and turpentine, etc.

Benzoic acid is widely found in nature in the form of free acid, ester or its derivatives. It is mainly used to prepare sodium benzoate preservatives, and is used to synthesize drugs and dyes. It is also used to make plasticizers, mordants, fungicides and spices. It can be prepared by direct oxidation of toluene in the presence of manganese dioxide, or by decarboxylation of phthalic anhydride with water vapor.

The physical structure of benzoic acid:

Benzoic acid is a compound in which one hydrogen on the benzene ring is replaced by a carboxyl group (—COOH). When the carbonyl group of benzoic acid and the plane of the benzene ring are 15° respectively, the atom (group) has the lowest spatial interaction energy and becomes a dominant conformation. The meta position has a higher charge density. In the electrophilic substitution reaction, the carbonyl group (—COR) is meta Positioning base.

Physical properties of benzoic acid:

Benzoic acid is a shiny, white, monoclinic flake or needle-like crystal. It is light, odorless or has a slight odor similar to benzoin or benzaldehyde. Its vapor is highly irritating and can easily cause coughing after inhalation. Can evaporate with water vapor. Sublimation begins at about 100°C.

1 g benzoic acid was dissolved in 2.3 mL cold ethanol, 1.5 mL boiling ethanol, 4.5 mL chloroform, 3 mL diethyl ether, 3 mL acetone, 30 mL carbon tetrachloride, 10 mL benzene, 30 mL carbon disulfide, and 23 mL turpentine. Solubility in water increases with the presence of alkaline substances (such as borax, trisodium phosphate).

Chemical properties of benzoic acid:

Benzoic acid is the simplest aromatic carboxylic acid. It is aromatic and has the properties of carboxylic acid. Therefore, two major types of chemical reactions can occur. One is the substitution reaction on the benzene ring, and the other is the reaction of the carboxyl group. Benzoic acid is a weak acid, stronger than fatty acids. They have similar chemical properties and can form salts, esters, acid halides, amides, acid anhydrides, etc., and are not easily oxidized. Electrophilic substitution reaction can occur on the benzene ring of benzoic acid, mainly obtaining meta-substitution products.


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