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Benzoic acid

Benzoic acid is the simplest representative of a class of carboxylic or organic acids with the chemical formula C6H5COOH. This chemical compound can be said to have been formed by replacing one hydrogen atom attached to the carbon atom of the benzene ring with a carboxyl group.

Benzoic acid, in appearance, is a colorless crystalline solid with a density of 1.27 g / cm³ and a molar mass of 122.1 g / mol. The melting point of C6H5COOH is 122.41 ° C, and the boiling point is 249.2 ° C. In 1 liter of water, 2.9 g of C6H5COOH can be dissolved. The acidity is 4.202, the refractive index is 1.5397.

The name originated from benzoic resin, from which, in the 16th century (first described by Nostradamus in 1556, and then by Blaise de Vigenère in 1596), the substance was first isolated by sublimation. For a long time this natural compound remained the only source of acid.

In 1832 the chemist J. Liebich first described the structure of benzoic acid, and in 1875 the German physiologist Ernst Leopold Zalkovsky investigated its antifungal and antiseptic properties. Salts are used as a food preservative, and benzoic acid itself is an important raw material for the synthesis of many other organic compounds. Many housewives still use the unique abilities of this carboxylic acid for long-term storage of cranberries without additional preservatives (even without the addition of sugar) or special treatment methods.

Esters and benzoic acid salts are known as benzoates. The qualitative characteristics of aromatic compounds and carboxylic acids combine benzoic acid. Its chemical properties are determined by the presence of an aromatic ring and a carboxyl group.

The aromatic ring is characterized by electrophilic substitution reactions mainly for the third carbon atom, the location of which is determined with respect to the carboxyl group.

The second scheme of the substitution reaction proceeds at the site of hydrogen in the carboxyl group and proceeds more slowly.

All the reactions mentioned for carboxylic acids are also characteristic of C6H5COOH.

Due to the unique antiseptic and antifungal properties, benzoic acid is used for canning. It is used as a series of food additives E210-E213. Benzoic acid blocks the work of enzymes and the metabolism of harmful unicellular organisms. Due to its action the growth of yeast, mold and many pathogenic bacteria is suppressed. Benzoic acid or its sodium, potassium or calcium salts is used.

The substance is capable of exhibiting an antimicrobial effect only in acidic food products. If the pH inside the cells is less than or equal to 5, the anaerobic fermentation of glucose will decrease by 95%. The effectiveness of acid and benzoates depends on the pH of the food. Fruit juices (containing citric acid), sparkling drinks (contain CO2), soft drinks (contain phosphoric acid), pickles (acetic acid) or other acidified food are preserved with acid and its salts. Optimal concentrations during preservation of food range from 0.05-0.1%.

On the basis of toluene, benzoic acid is most often synthesized. Its preparation proceeds according to the scheme of the reaction of methylbenzene oxidation with potassium permanganate. On a commercial basis, this unique organic compound is produced due to partial oxidation of toluene with oxygen. The process takes place on a special catalyst. For laboratories, benzoic acid is a cheap and affordable reagent. For all syntheses, it can be purified by recrystallization from an aqueous solution. In this case, the property of high solubility in hot water and poor solubility in cold water is used.

Benzoic acid is widely used as a preservative of food products, in medicine and organic synthesis: it produces various organic substances, including dyes. It is also used in the chemical industry or in the practice of analytical laboratories.

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