An organic or carboxylic monobasic acid, the molecule of which contains two carbon atoms and a carboxyl group (received the name because it consists of a carbonyl and carboxyl groups), is called ethanoic (by analogy with an alkane with the same number of carbon atoms) or acetic acid. She, like all lower aliphatic representatives of this class of organic compounds, has a pungent odor. Its chemical formula is written as: CH3COOH. At room conditions, it is a colorless liquid. Density - 1.05 g / cm³. The molar mass is 60.05 g / mol. It melts at a temperature of plus 16.75 ° C (it hardens below, the crystals are like ice, therefore they are called ice). Boils at a temperature of plus 118.1 ° C. The refractive index is 1.372.
Representatives of this class of organic compounds is weaker than hydrochloric or sulfuric acid, but when compared with carbonic acid, the most severe is acetic acid. Its chemical properties are determined by the constituent molecules of the carbonyl and hydroxyl groups. They affect each other so strongly that the chemical properties of a substance only slightly resemble those of carbonyl compounds (aldehydes, amides, ketones, esters) or alcohols. The O – H bond is ionized due to the attraction of electrons by the carbonyl group. Therefore, the bond is much easier to dissociate than in alcohols. The shift of electrons from the hydroxyl group to the carbonyl group partially reduces the positive charge on the carbon atom, which makes it difficult to attack it with a nucleophile. Therefore, many substances that easily interact 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, as a result of which salts are formed: NaOH + CH3COOH → CH3COONa + H2O. Salts of carboxylic acids are generally soluble in water. This property facilitates their extraction from natural sources. Therefore, acids were among the first to be isolated from organic substances. So, for example, ethane was obtained from sour wine. Strong hydrogen bonds are formed between CH3COOH molecules; due to this, it exists in the form of a dimer in organic solvents and in the gas phase.
Acetic acid with water can mix in any ratio. It changes its properties depending on the concentration. Moderately aggressive towards 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 film of aluminum oxide, aluminum tanks, along with stainless steel tanks, are used to transport CH3COOH.
In industry, acetic acid is obtained by oxidation of the aldehyde of the same name: 2CH3COH + O2 → 2CH3COOH. Out of 800 kg of aldehyde, a ton of CH3COOH is obtained. But a more modern method of production is the liquid phase oxidation of butane by atmospheric oxygen at a temperature of 150-170 ° 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 of these methods were supplanted (due to higher oil prices) by methanol carbonylation: CO + CH3OH → CH3COOH. The process proceeds in the presence of a catalyst, which are rhodium salts, and promoters (activators) - ion iodide. The ability of some microorganisms to ferment ethanol, followed by oxidation in CH3COOH, is used in biochemical production: C2H5OH + O2 → CH3COOH + H2O. The process is very complex and proceeds in several stages.
Acetic acid is produced in accordance with GOST 19814-74 (synthetic and regenerated), GOST 18270-72 (high purity) and GOST 61-75 (reactive). This is an important chemical reagent and industrial chemical, mainly used in the production, is used to produce plastics, artificial fiber, dyes, film, and so on. It is a raw material for the production of vinyl acetate, which is used in the process of obtaining sevilen (as comonomer of ethylene). The use of acetic acid is due to its chemical and physical properties. CH3COOH salts are mordants used to fix dyes on fiber.
In households, diluted acetic acid is very often used as a descaler. In the food industry it is used under the code of food additive E260, as an acidity regulator and as a seasoning. Food supplement approved for use in 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 vinegar essence with a mass fraction of the main substance equal to 70%. A number of esters of acetic acid are used in the confectionery industry.