Acetic acid

An organic or carboxylic monobasic acid, a molecule of which contains two carbon atoms and a carboxyl group (so called because it consists of the carbonyl and carboxyl groups) is called ethane (analogous to an alkane with the same number of carbon atoms) or acetic acid. It, like all the lower aliphatic representatives of this class of organic compounds, has a sharp odor. Its chemical formula is written as: CH3COOH. Under room conditions is a colorless liquid. The density is 1.05 g / cm³. The molar mass is 60.05 g / mol. Melts at a temperature of plus 16,75 ° C (below hardens, the crystals look like ice, therefore called ice). Boils at a temperature of plus 118.1 ° C. The refractive index is 1.372.

Representatives of this class of organic compounds are weaker than sulfuric or hydrochloric, but when compared with carbonic acid, the strongest will be acetic acid. Its chemical properties are determined by the carbonyl and hydroxyl groups that make up the molecule. They influence so strongly against each other that the chemical properties of the substance only slightly resemble the properties of carbonyl compounds (aldehydes, amides, ketones, esters) or alcohols. The ionization of the O-H bond occurs due to electron pulling by the carbonyl group. Therefore, the bond dissociates much more readily than in alcohols. The displacement of electrons from the hydroxyl group to the carbonyl group partially lowers the positive charge on the carbon atom, which makes it difficult for the nucleophile to attack it. Therefore, many substances that interact easily with carbonyl compounds do not react with CH3COOH.

To a small extent, acetic acid is capable of dissociating with the formation of hydrogen ions: CH3COOH + H2O ↔ CH3CO2ˉ + H3O +. It is characterized by neutralization reactions with bases, which result in the formation of salts: NaOH + CH3COOH → CH3COONa + H2O. Salts of carboxylic acids are usually soluble in water. This property facilitates their extraction from natural sources. Therefore, the acids were among the first isolated from organic substances. For example, ethane was obtained from sour wine. Strong hydrogen bonds are formed between the molecules of CH3COOH, which is why it exists in the form of a dimer in organic solvents and in the gas phase.

Acetic acid with water is capable of mixing in any ratio. It changes its properties depending on the concentration. Moderately aggressive with respect to metals, including iron, magnesium and zinc. This produces hydrogen and salts, called acetates: Mg + 2 CH3COOH → (CH3COO) 2Mg + H2 ↑. Since aluminum forms a passivating acid-resistant aluminum oxide film , aluminum tanks, along with stainless steel tanks, are used to transport CH3COOH.

In industry, acetic acid is obtained by oxidation of the same aldehyde: 2CH3COH + O2 → 2CH3COOH. Of 800 kg of aldehyde, a ton of CH3COOH is produced. But a more modern method of production is liquid-phase oxidation of butane with air oxygen at a temperature of 150-170 ° C and a pressure of 50 atm: CH3CH2CH2CH3 + 2O2 → 2CH3COOH + 2 H2O. In fact, the reaction is much more complicated than shown in the diagram. In addition to acetic acid, a number of by-products are formed. Both these methods are superseded (due to rising oil prices) by the methanol carbonylation method: CO + CH3OH → CH3COOH. The process takes place in the presence of a catalyst, which is the salts of rhodium, and promoters (activators) - iodide ions. The ability of some microorganisms to ferment ethyl alcohol, followed by oxidation in CH3COOH, is used in biochemical production: C2H5OH + O2 → CH3COOH + H2O. The process is very complex and takes several steps.

Acetic acid is produced in accordance with GOST 19814-74 (synthetic and regenerated), GOST 18270-72 (special purity) and GOST 61-75 (reactive). It is an important chemical reagent and industrial chemical, mainly used in production, serves for the production of plastics, artificial fibers, dyes, film and others. It is the raw material for the production of vinyl acetate, which is used in the process of producing sevylene (as an ethylene comonomer). The use of acetic acid is due to its chemical and physical properties. Salts CH3COOH are mordants serving to fix dyes on the fiber.

In households, dilute acetic acid is very often used as a descaling agent. In the food industry is used under the code of food additive E260, as an acidity regulator and as a seasoning. The food additive is approved for use in the EU, USA, Australia and New Zealand. In the food industry, it is used for preserving products in the form of vinegar with a concentration of CH3COOH in water from 3 to 15% or acetic essence with a mass fraction of the basic substance equal to 70%. A number of esters of acetic acid are used in confectionery production.