Benzoic acid is the simplest representativeclass 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 iscolorless 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 came from benzoic resin, from whichin the 16th century (first described by Nostradamus in 1556, and then by Blaise de Vigenère in 1596), the substance was first isolated by the sublimation method. For a long time this natural compound remained the only source of acid.
In 1832, the chemist Yu.Liebig was the first to describe 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 ability of this carboxylic acid for long-term storage of cranberries without additional preservatives (even without the addition of sugar) or special treatments.
Esters and salts of benzoic acid are known asbenzoates. 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.
For the aromatic ring, the reactions of electrophilic substitution are characteristic 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 place of hydrogen in the carboxyl group and proceeds more slowly.
All the reactions mentioned for carboxylic acids are also characteristic of C6H5COOH.
Thanks to the unique antiseptic andantifungal properties, benzoic acid is used in 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. Use benzoic acid or its sodium, potassium or calcium salts.
The substance is capable of exhibiting antimicrobialaction only in acidic foods. 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%.
Based on toluene is most often synthesizedbenzoic acid. 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 by 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 inas a preservative of food products, in medicine and organic synthesis: on its basis are obtained various organic substances, including dyes. It is also used in the chemical industry or in the practice of analytical laboratories.
