Benzoic acid is the simplest member of the class of carboxylic or organic acids with the chemical formula C6H5COOH. We can say about this chemical compound that it was formed due to the replacement of 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. 2.9 g of the substance C6H5COOH can dissolve in 1 liter of water. The acidity is 4.202, the refractive index is 1.5397.
The name comes from benzoic resin, from which in the 16th century (which was first described by Nostradamus in 1556, and then Blaise de Vigener 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. Liebig described the structure of benzoic acid for the first time, and in 1875 its antifungal and antiseptic properties were studied by the German physiologist Ernst Leopold Zalkovsky. 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 today use the unique abilities of this carboxylic acid for long-term storage of lingonberry without additional preservatives (even without the addition of sugar) or special processing methods.
Esters and salts of benzoic acid are known as benzoates. Qualitative characteristics of aromatic compounds and carboxylic acids combines 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 relative to the carboxyl group.
The second scheme of the substitution reaction occurs at the site of hydrogen in the carboxyl group and proceeds more slowly.
All reactions mentioned for carboxylic acids are also characteristic of C6H5COOH.
Due to its unique antiseptic and antifungal 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. Thanks 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 antimicrobial activity only in acidic foods. If the pH inside the cells is less than or equal to 5, then anaerobic fermentation of glucose will decrease by 95%. The effectiveness of acid and benzoates depends on the pH of food. Fruit juices (contain citric acid), sparkling drinks (contain CO2), soft drinks (contain phosphoric acid), pickles (acetic acid) or other acidified foods are preserved by acid and its salts. The optimal concentration during food preservation is in the range from 0.05-0.1%.
Based on toluene, benzoic acid is most often synthesized. Its preparation proceeds according to the reaction scheme for the oxidation of methylbenzene with potassium permanganate. On a commercial basis, this unique organic compound is produced through the partial oxidation of toluene with oxygen. The process proceeds 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 food preservative 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.