Acetic aldehyde chemical formula. Obtaining acetaldehyde

Engineering systems 20.09.2019

Engineering systems

Acetic aldehyde refers to organic compounds and belongs to the class of aldehydes. What properties does this substance have, and what does the formula of acetaldehyde look like?

general characteristics

Acetic aldehyde has several names: acetaldehyde, ethanal, methylformaldehyde. This compound is an aldehyde acetic acid and ethanol. Its structural formula is as follows: CH 3 -CHO.

Rice. one. Chemical formula acetaldehyde.

A feature of this aldehyde is that it occurs both in nature and is produced artificially. In industry, the volume of production of this substance can be up to 1 million tons per year.

Ethanal is found in foods such as coffee, bread, and is also synthesized by plants during metabolism.

Acetic aldehyde is a colorless liquid with a pungent odor. Soluble in water, alcohol and ether. Is poisonous.

Rice. 2. Acetic aldehyde.

The liquid boils at a fairly low temperature - 20.2 degrees Celsius. Because of this, there are problems with its storage and transportation. Therefore, the substance is stored in the form of paraldehyde, and acetaldehyde is obtained from it, if necessary, by heating with sulfuric acid (or with any other mineral acid). Paraldehyde is a cyclic trimer of acetic acid.

How to get

Acetic aldehyde can be obtained in several ways. The most common option is the oxidation of ethylene or, as this method is also called, the Wacker process:

2CH 2 \u003d CH 2 + O 2 -2CH 3 CHO

The oxidizing agent in this reaction is palladium chloride.

Acetaldehyde can also be obtained by reacting acetylene with mercury salts. This reaction bears the name of a Russian scientist and is called the Kucherov reaction. As a result chemical process an enol is formed, which isomerizes to an aldehyde

C 2 H 2 + H 2 O \u003d CH 3 CHO

Rice. 3. M. G. Kucherov portrait.

Prior to the discovery of the Wacker method in the 1960s, acetaldehyde was prepared using ethyl alcohol. Ethyl alcohol was oxidized or dehydrogenated. Copper or silver acted as a catalyst:

C 2 H 5 OH–CH 3 COH+H 2

2C 2 H 5 OH + O 2 \u003d 2CH 3 OH + 2H 2 O

According to the chemical properties, acetaldehyde is a typical representative of aldehydes.

Used in industry given substance to obtain acetic acid, butadiene and various organic substances.

Publication date 27.01.2013 17:10

Acetic aldehyde (other names: acetaldehyde, methylformaldehyde, ethanal) is an organic compound belonging to the class of aldehydes. This substance is important for humans, it is found in coffee, bread, ripe fruits and vegetables. Synthesized by plants. Found in nature and produced in large quantities man. Formula of acetaldehyde: CH3-CHO.

Physical properties of acetaldehyde

1. Acetic aldehyde is a colorless liquid with a sharp unpleasant odor.

2. Highly soluble in ether, alcohol and water.

3. The molar mass is 44.05 grams/mol.

4. Density is 0.7 grams/centimeter³.

Thermal properties of acetaldehyde

1. The melting point is -123 degrees.

2. The boiling point is 20 degrees.

3. The ignition temperature is -39 degrees.

4. Auto-ignition temperature is 185 degrees.

Obtaining acetaldehyde

1. The main way to obtain this substance is the oxidation of ethylene (the so-called Wacker process). This is what the reaction looks like:

2CH2 = C2H4 (ethylene) + O2 (oxygen) = 2CH3CHO (methyl formaldehyde)

2. Acetaldehyde can also be obtained by hydration of acetylene in the presence of mercury salts (the so-called Kucherov reaction). This produces phenol, which then isomerizes to an aldehyde.

3. The following method was popular before the advent of the above process. It was carried out by oxidation or dehydrogenation of ethyl alcohol on a silver or copper catalyst.

The use of acetaldehyde

What substances do you need acetaldehyde to obtain? Acetic acid, butadiene, aldehyde polymers and some other organic substances.

Used as a precursor (substance that participates in the reaction leading to the creation of the target substance) to acetic acid. However, the substance under consideration was soon ceased to be used in this way. This was because acetic acid is easier and cheaper to produce from methalone using the Kativa and Monsanto processes.

Methylformaldehyde is an important precursor to pentaerythrol, pyridine derivatives, and crotonaldehyde.

Getting resins as a result of the fact that urea and acetaldehyde have the ability to condense.

Obtaining ethylidene diacetate, from which polyvinyl acetate monomer (vinyl acetate) is subsequently produced.

Tobacco addiction and acetaldehyde

This substance is a significant part of tobacco smoke. A recent demonstration has shown that the synergistic association of acetic acid with nicotine increases addiction (especially in individuals under thirty).

Alzheimer's disease and acetaldehyde

Those people who do not have the genetic factor for converting methylformaldehyde to acetic acid have a high risk of predisposition to a disease such as senile dementia (or Alzheimer's disease), which usually occurs in old age.

Alcohol and methylformaldehyde

Presumably, the substance we are considering is a human carcinogen, since today there is evidence of the carcinogenicity of acetaldehyde in various animal experiments. In addition, methylformaldehyde damages DNA, thereby causing a disproportionate development of the muscular system with body weight, which is associated with a violation of protein metabolism in the body. A study of 800 alcoholics was conducted, as a result of which scientists came to the conclusion that people exposed to acetaldehyde have a defect in the gene for one enzyme - alcohol dehydrogenase. For this reason, these patients are at greater risk of developing kidney and upper liver cancer.

Acetic aldehyde (other names: acetaldehyde, methylformaldehyde, ethanal) is an organic compound belonging to the class of aldehydes. This substance is important for humans, it is found in coffee, bread, ripe fruits and vegetables. Synthesized by plants. It occurs naturally and is produced in large quantities by humans. Formula of acetaldehyde: CH3-CHO.

Physical properties

1. Acetic aldehyde is a colorless liquid with a sharp unpleasant odor.

Thermal Properties

— Methylformaldehyde is an important precursor to pentaerythrol, pyridine derivatives and crotonaldehyde.

Alcohol and methylformaldehyde

Security

This substance is toxic. It is an air pollutant from smoking or from exhaust emissions in traffic jams.

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Introduction

Today, millions are known chemical compounds. And most of them are organic. These substances are divided into several large groups, the name of one of them is aldehydes. Today we will consider a representative of this class - acetaldehyde.

Definition

Acetic aldehyde is an organic compound of the class of aldehydes. It can also be called differently: acetaldehyde, ethanal or methylformaldehyde. The formula of acetaldehyde is CH 3 -CHO.

Properties

The substance under consideration has the form of a colorless liquid with a sharp suffocating odor, which is highly soluble in water, ether and alcohol. Since the boiling point of the compound under discussion is low (about 20 ° C), only its trimer, paraldehyde, can be stored and transported. Acetic aldehyde is obtained by heating said substance with an inorganic acid.
o is a typical aliphatic aldehyde, and it can take part in all reactions that are characteristic of this group of compounds. The substance has the property of tautomerization. This process ends with the formation of enol - vinyl alcohol. Because acetaldehyde is available as an anhydrous monomer, it is used as an electrophile. Both he and his salts can enter into reactions. The latter, for example, when interacting with the Grignard reagent and lithium-organic compounds, form hydroxyethyl derivatives. Acetic aldehyde during condensation is distinguished by its chirality. So, during the Strecker reaction, it can condense with ammonia and cyanides, and the amino acid alanine will become the product of hydrolysis. Acetaldehyde also enters into the same type of reaction with other compounds - amines, then imines become the reaction product. In the synthesis of heterocyclic compounds, acetaldehyde is very important component, the basis of all ongoing experiments. Paraldehyde, the cyclic trimer of this substance, is obtained by the condensation of three ethanal molecules. Acetaldehyde can also form stable acetals. This occurs during the interaction of the considered chemical with ethyl alcohol, passing under anhydrous conditions.

Receipt

In general, acetaldehyde is produced by the oxidation of ethylene (the Wacker process). Palladium chloride acts as an oxidizing agent. This substance can also be obtained during the hydration of acetylene, in which mercury salts are present. The reaction product is enol, which isomerizes to the desired substance. Another way to obtain acetaldehyde, which was the most popular long before the Wacker process became known, is the oxidation or dehydration of ethanol in the presence of copper or silver catalysts. During dehydration, in addition to the desired substance, hydrogen is formed, and during oxidation, water.

Application

With the help of the compound under discussion, butadiene, aldehyde polymers and some organic substances, including the acid of the same name, are obtained. It is formed during its oxidation. The reaction looks like this: "oxygen + acetaldehyde = acetic acid." Ethanal is an important precursor to many derivatives and this property is widely used in synthesis
many substances. In humans, animals and plants, acetaldehyde is a participant in some complex reactions. It is also found in cigarette smoke.

Conclusion

Acetaldehyde can be both beneficial and harmful. It has a bad effect on the skin, is an irritant and possibly a carcinogen. Therefore, its presence in the body is undesirable. But some people themselves provoke the appearance of acetaldehyde by smoking cigarettes and drinking alcohol. Think about it!

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Physical properties of acetaldehyde

1. Acetic aldehyde is a colorless liquid with a sharp unpleasant odor.

2. Highly soluble in ether, alcohol and water.

3. The molar mass is 44.05 grams/mol.

4. Density is 0.7 grams/centimeter³.

Thermal properties of acetaldehyde

1. The melting point is -123 degrees.

2. The boiling point is 20 degrees.

3. The ignition temperature is -39 degrees.

4. Auto-ignition temperature is 185 degrees.

1. The main way to obtain this substance is the oxidation of ethylene (the so-called Wacker process). This is what the reaction looks like:

2CH2 = C2H4 (ethylene) + O2 (oxygen) = 2CH3CHO (methyl formaldehyde)

2. Acetaldehyde can also be obtained by hydration of acetylene in the presence of mercury salts (the so-called Kucherov reaction). This produces phenol, which then isomerizes to an aldehyde.

3. The following method was popular before the advent of the above process. It was carried out by oxidation or dehydrogenation of ethyl alcohol on a silver or copper catalyst.

The use of acetaldehyde

What substances do you need acetaldehyde to obtain? Acetic acid, butadiene, aldehyde polymers and some other organic substances.

- Used as a precursor (substance that participates in the reaction leading to the creation of the target substance) to acetic acid. However, the substance under consideration was soon ceased to be used in this way. This was because acetic acid is easier and cheaper to produce from methalone using the Kativa and Monsanto processes.

— Methylformaldehyde is an important precursor to pentaerythrol, pyridine derivatives and crotonaldehyde.

- Obtaining resins as a result of the fact that urea and acetaldehyde have the ability to condense.

- Obtaining ethylidene diacetate, from which the monomer polyvinyl acetate (vinyl acetate) is subsequently produced.

Tobacco addiction and acetaldehyde

Alzheimer's disease and acetaldehyde

Alcohol and methylformaldehyde

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Historically the first industrial method obtaining acetaldehyde was the hydration of acetylene according to Kucherov.

This method dominated the production of acetaldehyde until 1960, in the next ten years it was competed by another method based on the dehydrogenation of ethanol over a copper or silver catalyst. After 1975, both of them were supplanted by an extremely simple and cheap method, called the Wacker process, after the name of the German company where it was developed.

In the Wacker process, ethylene is oxidized in an aqueous hydrochloric acid solution containing palladium(II) and copper(II) chlorides. The reactions occurring in this case are described by the following equations:

or in total:

There are two variations of the Wacker process that have found practical application. In a one-step process, a mixture of ethylene and oxygen is passed through a solution containing HCl, PdCl 2 and CuCl 2 at 125° C. and a pressure of 3 atm. The resulting acetaldehyde, together with unreacted ethylene, is passed through a separator with water, which absorbs the acetaldehyde, and the ethylene is recycled. In a two-stage version of the Wacker process, an aqueous solution of palladium and copper chlorides circulates in two reactors. Ethylene at a pressure of 10 atmospheres is passed into the first reactor, where it is oxidized to acetaldehyde. The reduced form of the catalyst (a mixture of PdCl 2 and Cu 2 Cl 2) enters the second reactor, where it is reactivated during oxidation with atmospheric oxygen. The acetic aldehyde in the separator is taken up in water and isolated by distillation under reduced pressure. The output of acetaldehyde in both cases is 95%. Economically, the one-stage Wacker process has no advantages over the two-stage one, since in the first case pure oxygen is required, and in the second variant it is replaced by air. The production of acetic aldehyde consumes no more than 1-2% of the produced ethylene.

Acetic aldehyde is mainly used for catalytic oxidation to acetic acid.

The oxidizing agent is air, and the catalyst is cobalt (II) salts, usually mixed with copper (II) salts. Other more modern method the production of acetic acid by methanol carbonylation will be discussed in section 28.8.4 of this chapter. A certain amount of acetaldehyde is still consumed for the synthesis of butanol-1 according to the scheme:

Currently, butanol-1 is produced mainly by the hydroformylation of propylene (see section 28.8.5).

Vinyl acetate is used as a monomer to produce polymers and copolymers that have a very wide range of practical applications from gramophone records (in the form of a copolymer with vinyl chloride) to various types of adhesives, varnishes and emulsion paints based on copolymers of vinyl acetate with esters. acrylic acid. The modern method for producing vinyl acetate is essentially a special kind of Wacker process, where acetic acid is used instead of water.

A mixture of ethylene and acetic acid is oxidized in the gas phase in the presence of a palladium catalyst at 200°C and a pressure of 10 atm, the yield of vinyl acetate reaches 90-95%. Vinyl acetate production in the United States was 1.2 million tons, which corresponds to the consumption of 2.5-3% of ethylene produced.

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Essence of two basic substances

Acetic aldehyde is also called acetaldehyde, ethanal or methylformaldehyde. Its formula is: CH3-CHO.

If we consider the connection from the point of view chemical properties, then the substance is a liquid that has no color, but with a pungent pungent odor. It is highly soluble in water and has a boiling point of 20ºС.

You can get acetaldehyde by heating paraldehyde (trim) with an acid of inorganic origin. The second way, through the oxidation of ethylene, or in another way it is called the Wacker process. The oxidizing agent is palladium chloride.

The most popular method by which it is possible to obtain an aldehyde is the oxidation of ethyl alcohol, but using copper or silver as a catalyst. After dehydration, in addition to the aldehyde, hydrogen and water are also formed.

It is one of the most common compounds found in everything from baked goods to fruits of plants. He is integral part yu smoke from cigarettes and car exhaust. That is why it belongs to the category of highly toxic substances that pollute the atmosphere with toxins.

Ethanol or ethyl alcohol is a simple alcohol, denoted as C 2 H 5 OH, belongs to the category of monohydric alcohols. It is a liquid, volatile composition and combustible.

The most important component alcoholic beverages, has an inhibitory effect on nervous system person, while calming him. Is an integral part fuel liquid, many solvents and is widely used in medicine as a disinfectant and antiseptic. Tinctures are prepared from ethyl alcohol, added to household chemicals, antifreezes and washers. Toothpaste, perfume and shower gels are made from alcohol.

It is the result of chemical reactions, because. does not occur in nature.

Main ways to get:

Fermentation. Agricultural products are exposed to yeast, as a result of which ethanol is released, but its concentration is not so high, it does not even reach 15%.
Production in industrial conditions. After the unique automated stages of obtaining ethyl alcohol, a liquid with a high concentration is obtained.

Acetaldehyde production process

As already mentioned, one of the ways to obtain acetaldehyde is an oxidation reaction, which is carried out using high temperatures and copper oxide. The formula is an integral part of the production of acetic acid and is as follows:

C 2 H 5 OH + CuO (t) \u003d Cu + H 2 O + CH 3 CHO,

Undoubtedly, the process is quite convenient, but there is another way to obtain acetaldehyde.

The process of dehydrogenation of ethyl alcohol was popular 50 years ago.

This method has many positive aspects, for example:

Poisonous toxins that poison the body and the atmosphere are not released.
Uncomplicated and mild conditions implementation of the reaction, there is no danger to human life.
The reaction produces hydrogen. It is one of the most versatile substances that can be used in a variety of ways.
There is no need to use various petroleum products, since only ethyl alcohol is taken as the basis.

So, the transformation occurs under the influence of about 400 ° C, hydrogen is split off, in a catalytic way. Hydrogenation is a method of catalytic synthesis, which is based on redox processes associated with mobile equilibrium.

Formula chemical reaction looks like:

C 2 H 5 OH → CH 3 CHO + H 2

With an increase in temperature and a sharp decrease in pressure, hydrogen molecules are directed to convert acetaldehyde, but as soon as the characteristics change, the pressure will increase and the temperature will drop, H 2 will lead to the formation of ethanol. It is this effect of conditions that constitutes the hydrogenation reaction.

This method also uses a catalyst in the form of copper or zinc. Copper is a strong and active catalyst that is capable of losing activity during the reaction. Therefore, they create a mixture of copper, cobalt oxide (no more than 5%), and only 2% chromium oxide, all this is applied to asbestos. If this catalyst is present, then the reaction is carried out at only 280-300°C. The degree of transformation of ethanol in this situation is 33-50% per pass through the catalyst.

The advantage of the second method over the first is that during dehydrogenation, much less side toxic substances are formed, but at the same time, a high rate of acetaldehyde in the contact gases is recorded. The contact gases of this reaction are a pair of acetaldehyde and hydrogen, in an equal ratio (usually 1:1), but the contact gases of the oxidation process consist of alcohol diluted with nitrogen, which is introduced with air. For this reason, it is much easier to separate acetaldehyde from the contact gases of the dehydrogenation reaction, and the percentage of losses will be significantly lower than that of the oxidative reaction.

Another important advantage is that ethyl acetate appears from dehydrogenated alcohol, it is a very valuable product.

Usually, after transformation into an aldehyde, it is used to synthesize acetic acid. To obtain it, it is necessary to carry out the process of oxidation of acetaldehyde with mercury:

CH3CHO + HgSO4 + H2O = CH3COOH + H2SO4 + Hg

It should be borne in mind that mercury is not an accelerator, and in order to stop the final reaction, iron (III) sulfate is added, it is he who oxidizes mercury.

Sulfuric acid is added to prevent the hydrolysis of salts. And sometimes, if there is no mercury (II) sulfate, they prepare a solution on their own: mercury oxide is dissolved in sulfuric acid. Take approximately 4:1 ratio of sulfuric acid and mercury oxide.

It turns out a chemical solution and for the sake of splitting off acetic acid, it must be filtered and an alkali solution added.

The result of acetic acid is calculated only taking into account the fact that calcium carbide is the purest. Finding the percentage ratio of the acid obtained to the theoretical indicator is one of the ways how you can get the yield of acetic acid.

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Aldehydes. Aldehydes are called organic substances

substances whose molecules contain group -С-Н,
called aldehyde. This group includes

carbonyl group > C=0. That aldehyde

the group has such a structure is proved on the basis of
properties of aldehydes. Aldehydes are formed during the oxidation of primary alcohols.

Acetic aldehyde (acetal dehy and d). Physical and chemical properties. Acetic aldehyde - extremely volatile, easily flammable liquid with a pungent odor, highly soluble in water, alcohol and many other organic solvents.

Maximum permissible concentration of acetaldehyde vapors in the air industrial premises 5 mg/m3.

Acetaldehyde polymerizes easily to form paraldehyde, a liquid with a boiling point of 124°C and a melting point of 12°C. This property of aldehyde (the property to turn into paraldehyde)
used for transportation and storage. At the point of consumption, paraldehyde is depolymerized by heating to give acetaldehyde.

When ignited, acetaldehyde burns with a luminous flame.

Acetic aldehyde is stored in glaciers and transported in thermal containers.

Getting and using. Acetic aldehyde is obtained from acetylene by adding water to it (Kucherov reaction). To do this, a mixture of acetylene with water vapor is passed over catalysts (metal oxides, zinc vanadate) at 400 °C.

Acetic aldehyde has great importance as a raw material for the production of many chemical products: acetic acid, ethyl alcohol, ether, etc. In addition, acetaldehyde is used as an intermediate in the production of dyes, medicinal and aromatic substances.

Acetaldehyde forms synthetic resins with phenol and protein substances, which are processed into various plastic masses. Formaldehyde also enters into the same reactions.

Ketones. When secondary alcohols are oxidized, ketones are formed. For example, the oxidation of secondary propyl alcohol produces dimethyl ketone (acetone).

Acetone. Physical and chemical properties. Acetone is a colorless, flammable liquid with a characteristic ethereal odour. Its boiling point is 56.1°C, melting point minus 94.3°C, density 0.79 g/cm 15 . Acetone is highly soluble in water, alcohols, ethers, mineral and vegetable oils, turpentine and other substances, is good solvent cellulose acetate, resins and fats. Acetone vapors are poisonous, twice as heavy as air and form explosive mixtures with it. Concentration limits ignition: LEL -2.2%, ERW - 13%. Temperature limits of ignition of acetone: LEL minus 20 ° С,
ERW plus 6 o C. In the presence of an ignition source, acetone is highly flammable and burns with a luminous flame

C 3 H 6 O + 4O 2 3CO 2 + 3H 2 O + Q

During combustion, acetone is heated in depth, forming a homothermal layer; the growth rate of the heated layer is 60 cm/h. The temperature of the heated layer reaches 56°C. Acetone burnout rate from the free surface
is 20 cm/h.

certain fire hazard are aqueous solutions of acetone. An aqueous solution containing only 10% (mass.) acetone is a flammable liquid with a flash point of 11 °C. This property of acetone must be taken into account when using aqueous solutions him in technological process, as well as when extinguishing burning acetone in tanks. Acetone ignites spontaneously on contact with strong
oxidizing agents: sodium peroxide, chromic anhydride, a mixture of sulfuric acid with potassium permanganate or berthollet salt (KClO 3), etc. The autoignition temperature of acetone is 465 ° C, the calorific value is 31012.8
kJ/kg. In the presence of alkali, it reacts with iodine, chlorine, and bromine to form iodoform, chloroform, and bromoform, respectively.

Under the action of ultraviolet rays, acetone decomposes into ethane and carbon monoxide.

Getting and using acetone. In industry
Acetone is made in a variety of ways.

The first method is the oxidation of secondary propyl (isopropyl) alcohol. The reaction is carried out at 650°C and in the presence of a catalyst (copper, silver, etc.).

The second (main) industrial method consists in the decomposition of isopropylbenzene hydroperoxide when heated with sulfuric acid.

Isopropylbenzene hydroperoxide, in turn, semi-
tea by oxidation of isopropylbenzene (cumene).

The third way is the decomposition of acetic acid vapors
over a catalyst (for example, copper) at 400°C.

Acetone is one of the most widely used solvents. It is used in the production of varnishes, smokeless powder, chloroform, iodoform, artificial paints, in the manufacture of organic glass, in the production of films, celluloid, etc. It serves as a raw material for the production of synthetic rubber, indigo, sulfonic acid, is used in the production of leather, for degreasing wool and fur. Pure acetone is used for extraction food products, vitamins and medicinal substances, as well as a solvent for storing acetylene. It can be used as an additive to motor fuel to increase the octane number.

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ACETALDEHYDE, CH 3 . CH: O, acetaldehyde, found in raw wood and wine spirits, in wine, in many essential oils(camphor, anise, mint and others), as well as in young pea fruits. A. is one of the products intermediately formed in the process of alcoholic fermentation of carbohydrates (see. Fermentation). Its formation is associated with the action of carboxylase, a special enzyme found in yeast zymase, which decomposes pyro-tartaric acid(see) on A. and carbon dioxide: CH,. CO. COOH=CH, . CHO + CO 2 . As a result of further reduction-oxidation interactions, A. turns into ethyl alcohol. A. is also an intermediate product of the breakdown of glucose in animals. A. is obtained 1) by the oxidation of ethyl alcohol with chromic acid, manganese peroxide and sulfuric acid or with the help of catalysts (copper, silver, platinum): CH 3. CH s OH+ + 0=CH e. CHO+H and O; 2) hydration. A. is a volatile colorless liquid with a pleasant smell in weak dilutions; boiling point 21°, sp. in. 0.7951; A. mixes with water, alcohol, ether in any ratio; from aqueous solutions is allocated with calcium chloride. Of the chemical properties of A., the following are important. 1. The addition of a small amount of concentrated sulfuric acid causes the formation of paraldehyde, a liquid boiling at 124°, not exhibiting typical aldehyde reactions. Polymerization proceeds with a significant release of heat according to the equation: ZSN 8 . CHO=C e H a O s . When paraldehyde is heated with acids, depolymerization occurs, i.e. e. turns back A. 2. In the presence of certain substances (HC1, zinc chloride and, especially, weak alkalis), A. turns into aldols(see): 2SN 3. CHO \u003d CH 3. CH(OH). CH a. CNO. Under the action of strong alkalis on A., an aldehyde resin is formed. 3. Oxidation of A. produces acetic acid; CH3 CHO + 0 \u003d CH 3. COOH. 4. During the recovery, ethyl alcohol is formed: CH 3. CHO + H 2 \u003d CH 3. CH 2 OH. 5. Hydrocyanic acid joins A., forming lactic acid nitrile: CH 3. CHO + + HCN=CH 3 . CH(OH). CN from which saponification can be obtained lactic acid(cm.). 6. With ammonium cyanide, amino-nitrile CH 3 ■ CH (NH 2) is obtained. CN, upon saponification of which is formed ala- HUH(CM.)- S. Bears.

See also:

ACETATES, salts of acetic acid, are used in laboratory practice for the manufacture of buffer solutions. Introduced into the body, A., like other salts of fatty acids, are oxidized to carbonic salts, causing an increase in the alkalinity of the blood and ...
ACETYLENE, has a chemical the formula C2H2 (formula of the structure of HC CH) and is a colorless poisonous gas under ordinary conditions, at 0 ° and 26 atm. condensing into a liquid. 1 l A. ...
ACETOSONE, benzozone, С6Н6С0.02.СОСН „ benzoyl-acetyl peroxide, white crystal-lich. powder, melt, at 40°, soluble in water; aqueous solutions, like hydrogen peroxide, are strong oxidizers; alkalis and organic substances acetozone decomposes; when heated...
ACETIMETER(from Latin acetum - vinegar and Greek metron - measure), a device invented by Otto to determine the amount of free acetic acid in vinegar in cases where the presence of foreign acids is not expected and ...
ACETONE, CH3-CO-CH3 (dimethyl ketone), colorless, flammable liquid with a specific gravity of 0.79 at 18 °, with a pleasant smell, burning taste. Boils at 56.5°, easily soluble in water, alcohol and ether. Acetone comes out...

ACETALDEHYDE, acetaldehyde, ethanal, CH 3 CHO, is found in raw wine alcohol (formed during the oxidation of ethyl alcohol), as well as in the first shoulder straps obtained during the distillation of wood alcohol. Previously, acetaldehyde was obtained by oxidation of ethyl alcohol with dichromate, but now they switched to the contact method: a mixture of ethyl alcohol and air vapors is passed through heated metals (catalysts). Acetaldehyde, obtained by distillation of wood alcohol, contains about 4-5% of various impurities. Of some technical importance is the method of obtaining acetaldehyde by decomposition of lactic acid by heating it. All these methods for the production of acetaldehyde are gradually losing their significance in connection with the development of new, catalytic methods for the production of acetaldehyde from acetylene. In countries with a developed chemical industry (Germany), they gained predominance and made it possible to use acetaldehyde as a starting material for the production of other organic compounds: acetic acid, aldol, etc. The basis of the catalytic method is the reaction discovered by Kucherov: acetylene in the presence of mercury oxide salts attaches one particle of water and turns into acetaldehyde - CH: CH + H 2 O \u003d CH 3 · CHO. To obtain acetaldehyde according to a German patent (Griesheim-Electron chemical factory in Frankfurt am Main), acetylene is passed into a solution of mercury oxide in strong (45%) sulfuric acid, heated no higher than 50 °, with strong stirring; the resulting acetaldehyde and paraldehyde are periodically siphoned off or distilled off in a vacuum. The best, however, is the method claimed by the French patent 455370, according to which the plant of the Consortium of the Electrical Industry in Nuremberg operates.

There, acetylene is passed into a hot weak solution (not higher than 6%) of sulfuric acid containing mercury oxide; the acetaldehyde formed during the course of the process is continuously distilled and condensed in certain receivers. According to the Grisheim-Electron method, some of the mercury formed as a result of partial oxide reduction is lost, because it is in an emulsified state and cannot be recovered. The method of the Consortium is of great advantage in this regard, since here the mercury is easily separated from the solution and then electrochemically converted into an oxide. The yield is almost quantitative and the resulting acetaldehyde is very pure. Acetaldehyde is a volatile, colorless liquid, boiling point 21°, specific gravity 0.7951. It is miscible with water in any ratio; it is released from aqueous solutions after the addition of calcium chloride. Of the chemical properties of acetaldehyde, the following are of technical importance:

1) The addition of a drop of concentrated sulfuric acid causes polymerization to form paraldehyde:

The reaction proceeds with a large release of heat. Paraldehyde is a liquid that boils at 124°C and does not show typical aldehyde reactions. When heated with acids, depolymerization occurs, and acetaldehyde is obtained back. In addition to paraldehyde, there is also a crystalline polymer of acetaldehyde, the so-called metaldehyde, which is probably a stereoisomer of paraldehyde.

2) In the presence of some catalysts (hydrochloric acid, zinc chloride, and especially weak alkalis), acetaldehyde is converted to aldol. Under the action of strong caustic alkalis, the formation of an aldehyde resin occurs.

3) Under the action of aluminum alcoholate, acetaldehyde is converted into acetic ethyl ether (Tishchenko's reaction): 2CH 3 CHO = CH 3 COO C 2 H 5. This process is used to produce ethyl acetate from acetylene.

4) Addition reactions are especially important: a) acetaldehyde attaches an oxygen atom, turning into acetic acid: 2CH 3 CHO + O 2 \u003d 2CH 3 COOH; oxidation is accelerated if a certain amount of acetic acid is added to acetaldehyde (Grisheim-Electron); highest value have catalytic oxidation methods; catalysts are: iron oxide, vanadium pentoxide, uranium oxide, and especially manganese compounds; b) by attaching two hydrogen atoms, acetaldehyde turns into ethyl alcohol: CH 3 CHO + H 2 = CH 3 CH 2 OH; the reaction is carried out in a vapor state in the presence of a catalyst (nickel); under certain conditions, synthetic ethyl alcohol successfully competes with the alcohol produced by fermentation; c) hydrocyanic acid combines with acetaldehyde, forming lactic acid nitrile: CH 3 CHO + HCN = CH 3 CH (OH) CN, from which lactic acid is obtained by saponification.

These diverse transformations make acetaldehyde one of the important products chemical industry. Its cheap production from acetylene has recently made it possible to carry out a number of new synthetic industries, of which the method for the production of acetic acid is a strong competitor to the old method of its extraction by dry distillation of wood. In addition, acetaldehyde is used as a reducing agent in the production of mirrors and is used to prepare quinaldine, a substance used to obtain paints: quinoline yellow and red, etc.; in addition, it serves to prepare paraldehyde, which is used in medicine as a hypnotic.