Acetic acid melting and boiling point. Acetic acid

Acetic acid, the formula of which is CH3COOH, is a substance that belongs to the homologous series of aliphatic (fatty) acids. This is one of the simplest and most important members of this series. Acetic acid is of great technical importance because it is widely used in industry. In this article, we will look at the main properties of acetic acid - physical and chemical.

Physical properties of acetic acid.

Pure acetic acid is a colorless liquid with a density of 1.05 g / cm2. It is able to intensively absorb moisture from the air. Reaching a temperature of 16.6 ° C, the acid crystallizes into colorless crystals, the density of which is 1.105 g / cm2.

If acetic acid is heated to 40 ° C, it will instantly ignite. Pure acetic acid has a very pungent odor, pleasant to the taste, but causes burns on the skin. It mixes well with most solvents and is itself considered an excellent solvent for many organic compounds.

Important physical constants:

• Specific heat of fusion - 95.7 kJ / kg
• Specific heat capacity of vapor at constant pressure - 6.45 kJ / kg * deg
• Boiling point at pressure - 0.1013 MPa
• Volumetric expansion coefficient of liquid - 0.001205 deg-1
• Relative mass of vapors at 18 ° and a pressure of 0.1013 MPa (air 1.0)
• Autoignition temperature of vapors mixed with air - 566 ° С
• Flash point - 41.7 ° С
• Heat of combustion of liquid (for 18 ° С and atmospheric pressure) - 14540 kJ / kg
• Critical temperature - 321.6 ° С
• Critical pressure 5,794 MPa
• Critical density 0.3506 g / cm3

Chemical properties of acetic acid.

Acetic acid is a monobasic acid whose chemical character is determined by the presence of the carboxyl COOH.

The chemical properties of acetic acid indicate its weakness, its electrolytic dissociation constant is equal to 1.82 * 10-5 mol / liter at a temperature of 18 ° C. As in the case of mineral acids, acetic acid is capable of neutralizing basic hydrates and oxides, and also displacing carbon dioxide from carbon dioxide.

A common bottle of edible vinegar, which can be found in the kitchen of any housewife, contains many other acids and vitamins. Adding a couple of drops of the product to cooked food, salads naturally enhances the taste. But few of us seriously thought about the properties and real scale of application of the main component - acetic acid.

What is this substance?

The formula for acetic acid is CH 3 COOH, which refers it to a number of fatty carboxylic acids. The presence of one carboxyl group (COOH) refers it to monobasic acids. The substance is found on the globe in organic form and is obtained synthetically in laboratories. Acid is the simplest, but no less important representative of its range. Easily soluble in water, hygroscopic.

The physical properties of acetic acid and its density vary with temperature conditions. At room temperature, 20 ° C, the acid is in a liquid state, has a density of 1.05 g / cm 3. Has a specific smell and sour taste. A solution of a substance without impurities solidifies and transforms into crystals at a temperature below 17 ° C. The boiling process of acetic acid begins at a temperature above 117 ° C. The methyl group (CH 3) of the acetic acid formula is obtained by the interaction of alcohols with oxygen: fermentation of alcohol substances and carbohydrates, souring wines.

A bit of history

The discovery of vinegar was one of the first in the series of acids and was accomplished in stages. At first, the Arab scientists of the 8th century began to extract acetic acid by distillation. However, even in ancient Rome, this substance, obtained from sour wine, was used as a universal sauce. The name itself is translated from ancient Greek as "sour". In the 17th century, European scientists managed to obtain a pure substance of a substance. At that time, they derived a formula and discovered an unusual ability - the acetic acid in the vapor state ignited with a blue fire.

Until the 19th century, scientists found the presence of acetic acid only in organic form - as part of the compounds of salts and esters. In the composition of plants and their fruits: apples, grapes. In humans and animals: sweat, bile. In the early 20th century, Russian scientists randomly extracted acetaldehyde from the reaction of acetylene with mercuric oxide. Today, the consumption of acetic acid is so great that its main extraction occurs only by a synthetic method on a huge scale.

Mining methods

Will acetic acid be of pure form or with the presence of impurities in the solution depends on the mining method. Food-grade acetic acid is produced biochemically in the ethanol fermentation process. In industry, there are several ways to extract acid. As a rule, reactions are accompanied by high temperatures and the presence of catalysts:

• Methanol in reaction with carbon (carbonylation).
• Oxidation of the oil fraction with oxygen.
• By pyrolysis of wood.
• oxygen.

The industrial method is more efficient and economical than the biochemical one. Thanks to the industrial process, the production of acetic acid in the 20th and 21st centuries increased hundreds of times compared to the 19th century. Today, the synthesis of acetic acid by carbonylation of methanol gives more than 50% of the total produced volume.

Physical properties of acetic acid and its effect on the indicator

In a liquid state, acetic acid is colorless. The acidity level of pH 2.4 is easily checked by litmus test. Acetic acid on contact with the indicator turns it red. The physical properties of acetic acid change visually. When the temperature drops below 16 ° C, the substance takes on a solid form and resembles small ice crystals. It dissolves easily in water and interacts with a wide range of solvents except hydrogen sulfide. Acetic acid reduces the total volume of the liquid when diluted with water. Describe the physical properties of acetic acid, its color and consistency, which you observe in the following image.

The substance ignites at a temperature of 455 ° C with a heat release of 876 kJ / mol. The molar mass is 60.05 g / mol. The physical properties of acetic acid as an electrolyte in reactions are weak. Dielectric constant is 6.15 at room temperature. Pressure, like density, - variable quantity of the physical property of acetic acid. At a pressure of 40 mm. rt. Art. and a temperature of 42 ° C, the boiling process will begin. But already at a pressure of 100 mm. rt. Art. boiling will occur only at 62 ° C.

Chemical properties

Reacting with metals and oxides, the substance exhibits its acidic properties. Perfectly dissolving more complex compounds in itself, the acid forms salts called acetates: magnesium, lead, potassium, etc. The pK value of the acid is 4.75.

When interacting with gases, vinegar enters into, followed by displacement and the formation of more complex acids: chloroacetic, iodoacetic. Dissolving in water, the acid dissociates with the release of acetate ions and hydrogen protons. The degree of dissociation is 0.4 percent.

The physical and chemical properties of the crystalline acetic acid molecules create hydrogen-bonded diamers. Also, its properties are necessary for the creation of more complex fatty acids, steroids and sterol biosynthesis.

Laboratory tests

Acetic acid can be detected in a solution by identifying its physical properties, such as odor. It is enough to add a stronger acid to the solution, which will begin to displace the vinegar salts with the release of its vapors. By laboratory distillation of CH 3 COONa and H 2 SO 4, it is possible to obtain dry acetic acid.

Let's carry out an experiment from the school chemistry curriculum for grade 8. The physical properties of acetic acid are clearly demonstrated by the chemical reaction of dissolution. It is enough to add copper oxide to the solution to the substance and heat it slightly. The oxide dissolves completely, making the solution bluish.

Derivatives

Qualitative reactions of substances with many solutions form: ethers, amides and salts. However, during the production of other substances, the requirements for the physical properties of acetic acid remain high. It must always have a high degree of dissolution, which means that it must not have foreign impurities.

Depending on the concentration of acetic acid in an aqueous solution, a number of its derivatives are isolated. The concentration of the substance over 96% is called glacial acetic acid. Acetic acid in 70-80% can be purchased in grocery stores, where it will be called - vinegar essence. Table vinegar has a concentration of 3-9%.

Acetic acid and daily life

In addition to nutritional features, acetic acid has a number of physical properties that humanity has found its use in everyday life. A solution of a low concentration substance easily removes plaque from metal products, surfaces of mirrors and windows. The ability to absorb moisture is also beneficial. Vinegar is good at eliminating odors in musty rooms, removes stains from vegetables and fruits on clothes.

As it turned out, the physical property of acetic acid - remove fat from the surface - can be used in folk medicine and cosmetology. A mild solution of edible vinegar is used to treat hair to give it shine. The substance is widely used to treat colds, remove warts and skin fungi. The use of vinegar in cosmetic wraps to combat cellulite is gaining momentum.

Use in production

In compounds of salts and other complex substances, acetic acid is an indispensable element:

• Pharmaceutical industry. To create: aspirin, antiseptic and antibacterial ointments, phenacetin.
• Production of synthetic fibers. Non-flammable films, cellulose acetate.
• Food industry. For successful preservation, preparation of marinades and sauces, as a food additive E260.
• Textile industry. Part of dyes.
• Manufacture of cosmetics and hygiene products. Aromatic oils, creams to improve skin tone.
• Making mordants. It is used as an insecticide and weed control.
• Manufacture of varnishes. Technical solvents, acetone production.

The production of acetic acid increases annually. Today, its volume in the world is more than 400 thousand tons per month. The acid is transported in robust steel tanks. Due to the high physical and chemical activity of acetic acid, storage in plastic containers in many industries is prohibited or limited to several months.

Safety

Acetic acid in high concentration has a third degree of flammability and emits toxic fumes. It is recommended to wear special gas masks and other personal protective equipment when working with acid. A lethal dose for the human body from 20 ml. At the moment the substance gets inside, the acid first of all burns the mucous membrane, and then affects the rest of the organs. In such cases, immediate hospitalization is required.

After getting acid on open skin areas, it is recommended to immediately rinse them with running water. A superficial acid burn can cause tissue necrosis, which also requires hospitalization.

Physiology scientists have found that a person does not need to take acetic acid at all - you can do without food additives. But for people with acid intolerance, as well as stomach problems, the substance is contraindicated.

Acetic acid is used in typography.

The substance has been found in small amounts in honey, bananas and wheat.

After cooling the acetic acid and sharply shaking the container with it, you can observe its sharp solidification.

A small concentration of acetic acid can reduce pain from insect bites and minor burns.

Eating foods low in acetic acid lowers cholesterol levels in the body. The substance is good at stabilizing sugar levels in diabetics.

Eating protein and carbohydrate foods together with a small amount of acetic acid increases their absorption by the body.

If the food is too salty, just add a couple of drops of vinegar to smooth out the saltiness.

Finally

Millennia of use of acetic acid has resulted in its physical and chemical properties being applied at every turn. Hundreds of possible reactions, thousands of useful substances, thanks to which humanity moves on. The main thing is to know all the features of acetic acid, its positive and negative qualities.

Do not forget about the benefits, but you must always remember what harm can be caused by careless handling of high concentration acetic acid. In terms of its danger, it stands next to hydrochloric acid and always remember about safety when using acid. Dilute the essence with water correctly and carefully.

DEFINITION

Acetic (ethanic) acid is a colorless liquid with a pungent irritating odor.

If it comes into contact with mucous membranes, it causes burns. Acetic acid is miscible with water in any ratio. Forms azeotropic mixtures with benzene and butyl acetate.

Acetic acid freezes at 16 o C, its crystals resemble ice in appearance, therefore 100% acetic acid is called "glacial".

Some of the physical properties of acetic acid are shown in the table below:

Obtaining acetic acid

In industry, acetic acid is obtained by catalytic oxidation of n-butane with atmospheric oxygen:

CH 3 -CH 2 -CH 2 -CH 3 + \u003d 2CH 3 -COOH.

Significant quantities of acetic acid are produced by oxidation of acetaldehyde, which in turn is obtained by oxidation of ethylene with atmospheric oxygen on a palladium catalyst:

CH 2 \u003d CH 2 + \u003d CH 3 -COH + \u003d CH 3 -COOH.

Edible acetic acid is obtained by microbiological oxidation of ethanol (acetic acid fermentation).

When butene-2 \u200b\u200bis oxidized with potassium permanganate in an acidic medium or a chromium mixture, the double bond is completely broken to form two molecules of acetic acid:

CH 3 -CH \u003d CH-CH 3 + \u003d 2CH 3 -COOH.

Acetic acid chemical properties

Acetic acid is a weak monobasic acid. In an aqueous solution, it dissociates into ions:

CH 3 COOH↔H + + CH 3 COOH.

Acetic acid has mild acidic properties, which are related to the ability of the hydrogen atom of the carboxyl group to be split off as a proton.

CH 2 COOH + NaOH \u003d CH 3 COONa + H 2 O.

The interaction of acetic acid with alcohols proceeds according to the mechanism of nucleophilic substitution. The nucleophile is an alcohol molecule that attacks the carbon atom of the carboxyl group of acetic acid, which carries a partially positive charge. A distinctive feature of this reaction (esterification) is that the substitution occurs at the carbon atom in the sp 3 -hybridization state:

CH 3 -COOH + CH 3 OH \u003d CH 3 O-C (O) -CH 3 + H 2 O.

When interacting with istionyl chloride, acetic acid is capable of forming acid halides:

CH 3 -COOH + SOCl 2 \u003d CH 3 -C (O) Cl + SO 2 + HCl.

When phosphorus (V) oxide acts on acetic acid, anhydride is formed:

2CH 3 -COOH + P 2 O 5 \u003d CH 3 -C (O) -O-C (O) -CH 3 + 2HPO 3.

The interaction of acetic acid with ammonia produces amides. First, ammonium salts are formed, which, when heated, lose water and turn into amides:

CH 3 -COOH + NH 3 ↔CH 3 -COO - NH 4 + ↔CH 3 -C (O) -NH 2 + H 2 O.

Use of acetic acid

Acetic acid has been known since ancient times, its 3 - 6% solutions (table vinegar) are used as a flavoring seasoning and preservative. The preservative effect of acetic acid is due to the fact that the acidic environment it creates inhibits the development of putrefactive bacteria and molds.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Ethanic acid is better known as acetic acid. It is an organic compound with the formula CH 3 COOH. Belongs to the class of carboxylic acids, the molecules of which contain functional monovalent carboxyl groups COOH (either one or several). You can provide a lot of information about her, but now only the most interesting facts should be noted.

Formula

How it looks can be understood from the image below. The chemical formula of acetic acid is simple. This is due to many reasons: the compound itself is monobasic, and it belongs to the carboxyl group, which is characterized by easy proton elimination (stable elementary particle). This compound is a typical representative of carboxylic acids, since it has all of their properties.

The bond between oxygen and hydrogen (−COOH) is highly polar. This causes an easy process of dissociation (dissolution, decomposition) of these compounds and the manifestation of their acidic properties.

As a result, a proton H + and an acetate ion CH3COO - are formed. What are these substances? Acetate ion is a ligand bound to a specific acceptor (an object receiving something from a donor compound), which forms stable acetate complexes with many metal cations. And a proton is, as mentioned above, a particle capable of capturing an electron from the electron M-, K- or L-shells of the atom.

Qualitative analysis

It is based precisely on the dissociation of acetic acid. Qualitative analysis, also called a reaction, is a collection of physical and chemical methods that are used to detect compounds, radicals (independent molecules and atoms) and elements (collections of particles) that make up the analyte.

With this method, it is possible to detect the salts of acetic acid. Everything looks not as complicated as it might seem. A strong acid is added to the solution. sulfuric, for example. And if the smell of acetic acid appears, then its salt is present in the solution. How it works? The remains of acetic acid, which are formed from the salt, are bound at that moment with hydrogen cations from sulfuric acid. What's the result? The appearance of more molecules of acetic acid. This is how dissociation happens.

Reactions

It should be noted that the discussed compound is capable of interacting with active metals. These include lithium, sodium, potassium, rubidium, francium, magnesium, cesium. The latter, by the way, is the most active. What happens at the moment of such reactions? Hydrogen is released, and the notorious acetates are formed. This is how the chemical formula of acetic acid, which has reacted with magnesium, looks like: Mg + 2CH 3 COOH → (CH 3 COO) 2 Mg + H 2.

There are ways to obtain dichloroacetic (CHCl 2 COOH) and trichloroacetic (CCl 3 COOH) acids. In them, the hydrogen atoms of the methyl group are replaced by chlorine. There are only two ways to get them. One is the hydrolysis of trichlorethylene. And it is less common than the other, based on the ability of acetic acid to be chlorinated by the action of chlorine gas. This method is simpler and more effective.

This is how this process looks in the form of the chemical formula of acetic acid interacting with chlorine: CH 3 COOH + Cl 2 → CH 2 CLCOOH + HCL. Only it is worth clarifying one point: it turns out just chloroacetic acid, the two above are formed with the participation of red phosphorus in small quantities.

Other transformations

It should be noted that acetic acid (CH3COOH) is able to enter into all reactions that are characteristic of the notorious carboxylic group. It can be reduced to ethanol, monohydric alcohol. For this, it is necessary to act on it with lithium aluminum hydride, an inorganic compound that is a powerful reducing agent often used in organic synthesis. Its formula is Li (AlH 4).

Also, acetic acid can be converted to acid chloride, an active acylating agent. This happens under the influence of thionyl chloride. He, by the way, is the acid chloride of sulfurous acid. Its formula is H 2 SO 3. It should also be noted that the sodium salt of acetic acid is decarboxylated when heated with alkali (the carbon dioxide molecule is excluded), resulting in the formation of methane (CH₄). And he, as you know, is the simplest hydrocarbon, which is lighter than air.

Crystallization

Glacial acetic acid - this is often the compound in question. The fact is that when it is cooled to only 15-16 ° C, it turns into a crystalline state, as if it freezes. Visually, it really looks a lot like ice. If you have several ingredients, you can experiment that will result in the conversion of acetic acid to glacial acid. It's simple. A cooling mixture must be prepared from water and ice, and then a test tube with acetic acid prepared in advance is immersed in it. After a few minutes, it crystallizes. In addition to the connection, this requires a beaker, tripod, thermometer and test tube.

Substance harm

Acetic acid, whose chemical formula and properties have been listed above, is unsafe. Its vapors are irritating to the mucous membranes of the upper respiratory tract. The threshold for the perception of the smell of this compound in the air is in the region of 0.4 mg / l. But there is also the concept of the maximum permissible concentration - the sanitary and hygienic standard, approved by law. According to it, the air can contain up to 0.06 mg / m³ of this substance. And if we are talking about working rooms, then the limit rises to 5 mg / m 3.

The destructive effect of acid on biological tissues directly depends on how strongly it is diluted with water. The most dangerous solutions are those containing more than 30% of this substance. And if a person accidentally comes into contact with a concentrated compound, then he will not be able to avoid chemical burns. This categorically cannot be allowed, since after this coagulation necrosis begins to develop - the death of biological tissues. The lethal dose is only 20 ml.

Effects

It is logical that the higher the concentration of acetic acid, the more harm it will have if it gets on the skin or inside the body. Common symptoms of poisoning include:

• Acidosis. The acid-base balance shifts towards increasing acidity.
• Thickening of blood and a violation of its coagulability.
• Hemolysis of erythrocytes, their destruction.
• Liver damage.
• Hemoglobinuria. Hemoglobin appears in the urine.
• Toxic burn shock.

Severity

It is customary to distinguish three:

1. Lightweight. It is characterized by minor burns to the esophagus and mouth. But there is no blood clotting, and the internal organs continue to function normally.
2. Average. Intoxication, shock and blood thickening are observed. The stomach is affected.
3. Heavy. The upper respiratory tract and the walls of the digestive tract are severely affected, and renal failure develops. Painful shock is maximum. The development of burn disease is possible.

Acetic acid vapor poisoning is also possible. It is accompanied by a severe runny nose, cough, and watery eyes.

Giving help

If a person is poisoned with acetic acid, then it is very important to act quickly to minimize the consequences of what happened. Consider what to do:

• Rinse out the mouth. Do not swallow water.
• Make a tube gastric lavage. You will need 8-10 liters of cold water. Even blood impurities are not a contraindication. Because in the first hours of poisoning, large vessels still remain intact. So there will be no dangerous bleeding. Before washing, you need to do anesthesia with analgesics. The probe is lubricated with vaseline oil.
• Do not induce vomiting! The substance can be neutralized with burnt magnesia or Almagel.
• None of the above? Then the victim is given ice and sunflower oil - a few sips must be taken.
• It is permissible for the victims to consume a mixture of milk and eggs.

It is important to provide first aid within two hours of the incident. After this period, the mucous membranes swell a lot, and it will already be difficult to reduce the pain of a person. And yes, in no case should you use soda. The combination of acid and alkali will produce a reaction that produces carbon dioxide and water. And such a formation inside the stomach can be fatal.

Application

Ethanic acid aqueous solutions are widely used in the food industry. These are vinegars. To obtain them, the acid is diluted with water to obtain a 3-15% solution. As an additive, they are marked with the E260 marking. Vinegars are included in various sauces, and they are also used for canning food, marinating meat and fish. In everyday life, they are widely used to remove scale, stains from clothes and dishes. Vinegar is an excellent disinfectant. They can handle any surface. It is sometimes added during washing to soften clothes.

Vinegar is also applicable in the production of odoriferous substances, medicines, solvents, in the production of acetone and cellulose acetate, for example. Yes, and acetic acid is directly involved in dyeing and printing.

In addition, it is used as a reaction medium for the oxidation of various organic substances. An example from industry is the oxidation of paraxylene (aromatic hydrocarbon) by atmospheric oxygen to terephthalic aromatic acid. By the way, since the vapors of this substance have a pungent irritating odor, it can be used as a substitute for ammonia to remove a person from a fainting state.

Synthetic acetic acid

It is a flammable liquid that belongs to the third hazard class. It is used in industry. When working with it, personal protective equipment is used. This substance is stored under special conditions and only in a specific container. As a rule, these are:

• clean railway tanks;
• containers;
• tank trucks, barrels, stainless steel tanks (capacity up to 275 dm 3);
• glass bottles;
• polyethylene barrels with a capacity of up to 50 dm 3;
• sealed stainless steel tanks.

If the liquid is stored in a polymer container, then this is a maximum of a month. Also, joint storage of this substance with such strong oxidants as potassium permanganate, sulfuric and nitric acids is strictly prohibited.

Vinegar composition

It is also worth saying a few words about him. The composition of the traditional, familiar to everyone, vinegar contains the following acids:

• Apple. Formula: NOOSSN₂CH (OH) COOH. It is a common food additive (E296) of natural origin. Found in unripe apples, raspberries, rowan berries, barberries and grapes. In tobacco and makhorka it is presented in the form of nicotine salts.
• Dairy. Formula: CH₃CH (OH) COOH. Formed by the breakdown of glucose. Food additive (E270), which is obtained by lactic acid fermentation.
• Ascorbic. Formula: C₆H₈O₆. Food additive (E300) used as an antioxidant that prevents product oxidation.

And of course, the ethane compound is also included in the vinegar - this is the basis of this product.

How to dilute?

This is a frequently asked question. Everyone saw 70% acetic acid on sale. It is bought to make mixtures for folk remedies, or to be used as a condiment, marinade, sauce, or roll. But such a powerful concentrate cannot be used. Therefore, the question arises of how to dilute acetic acid to vinegar. First you need to protect yourself - put on gloves. Then you should prepare clean water. For solutions of various concentrations, a certain amount of liquid will be required. Which one? Well, we look at the table below and dilute acetic acid taking into account the data.

In principle, nothing complicated. To get a 9% solution, you need to take the amount of water in milliliters according to this formula: multiply 100 grams of vinegar by the initial indicator (70%) and divide by 9. What happens? The number is 778. 100 is subtracted from this, since 100 grams of acid was originally taken. It turns out 668 milliliters of water. This amount is mixed with 100 g of vinegar. The result is a whole bottle of 9% solution.

Although, the act can be even easier. Many people are interested in how to make vinegar from acetic acid. Easily! The main thing is to remember that you need to take 7 parts of water for one part of a 70% solution.

Acetic acid (methane carboxylic, ethanoic acid)CH 3 COOH - colorless liquid with a pungent odor and sour taste. Anhydrous acetic acid is called"Icy". The melting point is16.75 ° C, boiling point118, 1 °; 17, 1 ° at a pressure of 10 mm. rt. pillar, 42, 4 ° at 40 mm., 62, 2 ° at 100 mm., 98, 1 ° at 400 mm. and 109 ° at 560 mm. mercury column.

The specific heat capacity of acetic acid is0, 480 cal / g. deg., Q combustion 209, 4 kcal / mol.

Acetic acid belongs to weak acids, the dissociation constant K \u003d1, 75 . 10 -5 . It is miscible in all respects with water, alcohol, ether, benzene and is insoluble in carbon disulfide. When acetic acid is diluted with water, the volume of the solution decreases. Maximum density1.0748 g / cm 3 responds to monohydrate.

Acetic acid is the first acid that has become known to mankind (in the form of vinegar, formed when wine sour). In concentrated form, it was obtained by Stahl in1700 year, and the composition was established by Berzelius in1814 year. Acetic acid is found in plants both in free form and in the form of salts and esters; it is formed during rotting and fermentation of dairy products. Converting alcoholic liquids to vinegar (3-15% acetic acid) occurs under the action of bacteria« vinegar fungus»Micoderma aceti ... From the fermented liquid, by distillation,80% acetic acid - acetic essence. Acetic acid is produced on a limited scale from« wood vinegar» - one of the products of dry distillation of wood.

The main industrial method for the preparation of acetic acid consists in the oxidation of acetaldehyde synthesizedfrom acetylene according to Kucherov reaction. Oxidation is carried out with air or oxygen at60 ° and catalysis (CH 3 COC) 2 M n. In this way, one obtains95-97% acetic acid. In the presence of acetatescobalt and copper at 40 ° a mixture of acetic acid (50-55%), acetic anhydride (30-35%) and water (~ 10%). The mixture is separated by distillation. The oxidation of ethylene, ethyl alcohol and others is also of technical importance for the production of acetic acid, as well as the actionsulfuric acid to nitroethane.

Pure acetic acid is obtained from technical products by rectification.

The hydroxyl group of acetic acid is very reactive and can be exchanged for halogens,SH, OC 2 H 5, NH 2, NHNH 2, N 3, NHOH and others with the formation of its various derivatives, for example, acetylchloride СН 3 СОС l , acetic anhydride(CH 3 CO) 2 O, acetamide CH 3 CO N H 2, azide CH 3 CO N 3 ; acetic acid is esterified with alcohols, forming esters (acetates) CH 3 СОО R , the simplest of which are highly volatile, fruity-smelling liquids (for example, amyl acetate and isoamyl acetate« pear essence»), less commonly with a floral scent (tert-butylcyclohexyl acetate).

The physical properties of some esters of acetic acid are given in the table; they are widely used as solvents (especially ethyl acetate) for nitrocellulose varnishes, glyphthalic and polyester resins, in the production of film andcelluloid , as well as in the food industry and perfumery. Artificial fibers, varnishes and adhesives based on vinyl acetate play a significant role in the production of polymers.

Acetic acid has many and varied uses. In technology, one of its most common reactions is the introduction of the acetyl group CH 3 CO, which is used to protect, for example, in aromatic aminesNH 2 - a group from oxidation during nitration; get a number of medicinal substances (aspirin , phenacetin and others).

Significant amounts of acetic acid are used in the production of acetone, cellulose acetate, synthetic dyes, used in dyeing and printing fabrics and in the food industry. Basic salts of acetic acidAl, Fe, Cr and others serve as mordants for dyeing; they provide a strong bond between the dye and the textile fiber.

Acetic acid vapors irritate the mucous membranes of the upper respiratory tract. Chronic action of vapors leads to diseases of the nasopharynx and conjunctivitis. The maximum permissible concentration of its vapors in the air0.005 mg / l. Solutions with concentration above 30% cause burns.