Ethanal is the general formula. Acetic aldehyde: physical and thermal properties, preparation and application

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 adds 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, from aqueous solutions released 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); catalytic oxidation processes are of the greatest importance; 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 obtaining it 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.

Ethanal (acetaldehyde)- the second member of the homologous series of aliphatic aldehydes. A colorless liquid with a sharp suffocating odor, when diluted with water, it acquires a fruity odor. An intermediate product of metabolism in a living organism. It is used for the production of cellulose acetates, acetic acid, butanol, etc.

Structure

In ethanal, as in any other aldehyde, three atoms are connected to the central trigonal atom (namely: an oxygen atom, a hydrogen atom and a carbon atom). They all lie in the same plane with this trigonal atom. All bond angles of a trigonal atom with these atoms are close to 120°.

In the carbonyl group, there is a very large difference in electronegativity between the carbon and oxygen atoms. This is reflected in the large dipole moment acetaldehyde. The bond electrons are unevenly distributed, so the ethanal molecule is highly polar. For a qualitative description of the nature of the bond in the carbonyl group, the concept of a double bond is usually used, containing σ- and π-components with two pairs of unbound (n) electrons at the oxygen atom. It is assumed that the trigonal carbon atom is in the state of sp 2 hybridization and forms a σ-bond with hydrogen and another carbon atom.

Physical properties

Ethanal, like all aldehydes, is not capable of hydrogen bonding, so its boiling point is only 20.16 °C. normal conditions It is a colorless liquid with a pungent, suffocating odor that acquires a fruity odor when diluted with water. It dissolves well in water, alcohol, ether.

Receipt

Wacker process

The main industrial method for obtaining acetaldehyde is the Wacker process. It consists in the oxidation of ethylene, which is obtained by cracking hydrocarbons. This method is much more important than oxidations, catalytic dehydrogenation of ethanol or hydration of acetylene. In the Wacker process, ethylene is oxidized in aqueous solution, copper (II) chloride and palladium (II) chloride. In a one-stage variant, the catalyst is regenerated with oxygen under continuous synthesis conditions; in a two-stage variant, the catalyst is regenerated with air in a separate reactor. The reaction is catalyzed by palladium.

With dihalogenated

As a result of the hydrolysis of dihalogenated alcohols with two halogen atoms at one carbon atom, dihydric alcohols are formed containing two hydroxyl groups also at one carbon atom. Such diols are extremely unstable and easily split off a water molecule. Thus, ethanal can be obtained from 1,1-dichloroethane.

With ethanol

When ethanol is oxidized with atmospheric oxygen at a temperature of 300-500 ° C in the presence of catalysts, as well as oxidizing agents such as chromium mixture, chromium (VI) oxide, manganese (IV) oxide, etc., acetaldehyde is formed.

This process is quite difficult to stop at the stage of aldehyde formation and it can last until acetic acid is obtained.

Ethanal can also be obtained from ethanol by dehydrogenation. For this evaporation of alcohol, it is necessary to pass over catalysts (zinc, copper) at high temperatures.

With acetylene

Ethanal can be obtained by hydration of acetylene. Mercury salts are used as catalysts in the process.

Chemical properties

Nucleophilic addition

Interaction with metal cyanides

When ethanal reacts with salts of cyanide acid, hydroxynitriles are formed. Hydrocyanic acid itself is slightly dissociated. Therefore, the reaction is carried out in an alkaline medium, where the cyanide ion is formed, which is the active nucleophilic part.

Reaction is very important in organic chemistry. First, it allows the carbon chain of the parent compound to be extended by one carbon atom. Secondly, the reaction product, 2-hydroxypropanonitrile, serves as the starting product for the synthesis of the corresponding hydroxycarboxylic acid.

Interaction with water

Acetic aldehyde enters into a reversible hydration reaction, forming the corresponding hydrate.

Ethanal in aqueous solution is 51% hydrated.

Interaction with alcohols

Alcohols, like water, reversibly add to ethanal to form piracetals. In alcoholic solutions, piracetals are in equilibrium with acetaldehyde. Thus, an ethanolic solution of ethanal contains about 30% pivacetal (1-ethoxyethanol) (calculated as aldehyde).

When interacting with the second molecule of alcohol under conditions of acid catalysis, pivacetals are converted into acetals.

Interaction with amines

In the first step of the reaction, the nucleophilic addition of the amine takes place at the double bond of the carbonyl group. The primary addition product is a bipolar ion, which is stabilized as a result of the intramolecular transfer of a proton from the nitrogen atom to the oxygen atom, turning into an amino alcohol. However, the reaction does not stop at this stage, because compounds containing two electron-withdrawing groups at one carbon atom are unstable and tend to stabilize by eliminating one of the groups in the form of a neutral thermodynamically stable molecule. AT this case a water molecule is cleaved from an amino alcohol molecule and an imine (Schiff base) is formed.

Similarly, interactions with primary amines are reactions of ethanal with ammonia derivatives such as hydroxylamine, hydrazine, phenylhydrazine C 6 H 5 NHNH 2, etc. The resulting acetaldehyde derivatives - oximes, hydrazones, phenylhydrazones - are usually stable crystalline substances with clear melting points.

Recovery

Ethanal is reduced to ethanol. One of the effective reducing agents is lithium aluminum hydride LiAlH 4. It plays the role of a supplier of hydride ions H -, which are nucleophilic particles and are added at the double bond. To convert the initially formed alkoxide ion into alcohol, water is added to the reaction medium after the reduction is completed.

In industry, ethanal is converted to ethanol by catalytic hydrogenation. The reaction is carried out by passing aldehyde vapor mixed with hydrogen over a nickel or palladium catalyst.

Aldol-crotonic condensation

As a result of the interaction in an alkaline medium of two molecules of ethanal, 3-hydroxybutanal is formed.

Since the reaction product contains hydroxyl and aldehyde groups in the molecule, it was called aldol (from the words aldehyde and alcohol), and the condensation reaction of oxo compounds in an alkaline medium was called aldol condensation. This reaction is of great importance in organic synthesis because it allows the synthesis of various hydroxycarbonyl compounds. Aldol condensation can be carried out in a mixed version, using various carbonyl compounds.

Often, aldol condensation is accompanied by the elimination of water and the formation of an α, β-unsaturated carbonyl compound. In this case, the reaction is called croton condensation. This often happens when the reaction is carried out at elevated temperature.

Oxidation reactions

Silver mirror reaction

One of the qualitative reactions for determining the aldehyde group is the "silver mirror" reaction - the oxidation of aldehyde argentum (I) with oxide. Silver oxide is always prepared immediately before the experiment by adding an alkali metal hydroxide solution to the Argentum (I) nitrate solution. In a solution of ammonia, argentum(I) oxide forms a complex compound called diaminsribble hydroxide or Tollens' reagent. When this compound acts on ethanal, a redox reaction occurs. Acetic aldehyde is oxidized to acetic acid, and the Argentum cation is reduced to metallic silver, which gives a brilliant coating on the walls of the test tube - a “silver mirror”.

Oxidation with copper hydroxide

Another qualitative reaction to aldehydes is their oxidation of copper (II) hydroxide. When copper (II) aldehyde is oxidized, the hydroxide, which has a light blue color, is reduced to copper (I) hydroxide yellow color. This process takes place at room temperature. If the research solution is heated, then yellow copper (I) hydroxide turns into red copper (I) oxide.

Halogenation

The presence of an electron-withdrawing oxo group in the ethanal molecule is the reason for the increased reactivity of hydrogen atoms located at carbon atoms in the α-position. They can be replaced by halogen atoms.

Polymerization

Acetic aldehyde, like formaldehyde, is able to polymerize in the presence of traces of acid. During the polymerization of three molecules of ethanal, paraldehyde is formed - a liquid with a boiling point of 124.5 ° C. When heated in the presence of acids, it depolymerizes to form the initial acetaldehyde.

Interaction with ammonia

Acetic aldehyde reacts with anhydrous ammonia in ether to give hexahydrotriazine trihydrate, which upon dehydration over sulfuric acid forms 2,4,6-trimethylhexahydro-1,3,5-triazine, the nitrogen analogue of "paraldehyde".

In industry, ethanol is oxidized to acetic acid and peracetic acid with air. To obtain acetic acid, oxidations are usually carried out in fumes and at elevated temperatures. To obtain peracetic acid, the reaction is carried out at 0 ° C or at a lower temperature in a solvent. As an intermediate product, 1-hydroxyethyl peracetate is formed, which decomposes to form peracetic acid and acetaldehyde. The latter is returned to the loop.

Application

Ethanal is used in industry for the production of cellulose acetates, acetic and peracetic acids, acetic anhydride, ethyl acetate, glyoxal, 2-ethylhexanol, alkylamines, butanol, pentaerythritol, alkylpyridine, 1,3-butylene glycol, chloral. Also used as a reducing agent in the manufacture of mirrors.

World production in 1982 amounted to 2 million tons / year (excluding the USSR).

Physiological action

Animals

For white mice with a 2-hour exposure LC 50 = 21.8 mg / l, when administered to the stomach LD 50 = 1232 mg / kg. The main symptoms of poisoning are respiratory distress, irritation of the mucous membranes. Inhalation of 0.5 mg/L ethanal for seven hours causes marked irritation of the mucous membranes in cats. At 2 mg / l - severe irritation, and 20 mg / l after 1-2 hours causes death. An autopsy shows swelling and inflammation of the lungs. Rats and guinea pigs tolerated the 100 mg/kg dose for 6 months. At the same time, there was a violation of conditioned reflex activity, an increase blood pressure. The same changes were caused by a dose of 10 mg/kg after 2-3 months.

Human

The odor perception threshold is 0.0001 mg/l, and already at 0.004 mg/l a pungent odor is felt. In addition to mild irritation of the mucous membranes from 0.1-0.4 mg/l, no other pathological changes were noted during chronic exposure to ethanal. At high concentrations, there is an increase in heart rate, night sweats. With very large - suffocation, a sharp cough, headaches, bronchitis, pneumonia. Perhaps habituation to small concentrations.

Ingestion and transformation

lingers in respiratory tract rabbit an average of 60%, about 25% is absorbed in the upper respiratory tract. In the body, it is oxidized to acetic acid, which enters into normal metabolism and burns out in and. The metabolic rate is large and in rabbits it is 7-10 mg/min. The intermediate oxidation product is acetone.

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— Propanal

— Butanal

Alcohols, as a result of addition to aldehydes and ketones, form unstable hemiacetals and semiketals with one alcohol molecule, and stable acetals and ketals with two. Hemiacetal formation reactions are catalyzed by acids and bases. This reaction is reversible - acetals are hydrolyzed by acids.

The reaction mechanism is reverse to the mechanism of hydrolysis of acetals.

Acetals are formed under the action of an excess of alcohol only in an acidic environment. The reverse reaction of hydrolysis of acetals is also catalyzed by acids.

In alkaline hydrolysis, the leaving group (RO-) is very poor and no reaction is possible. This property - the stability of acetals in an alkaline environment - is used when it is necessary to protect the carbonyl group.

5. Write interaction reaction schemes:

- benzaldehyde with methylamine

- butanal with methanethiol in a molar ratio of 1:2

- butanal with ethylamine

- propanal with hydroxylamine

Describe the reaction mechanism. Can the resulting compounds be hydrolyzed? Write hydrolysis reaction schemes.

Solution

Imines, oximes can be hydrolyzed by aqueous acids by reactions reverse to their formation. Hydrolysis can be thought of as the acid-catalyzed addition of water to a heteroanalogue of a carbonyl compound.

Thioacetals can also be subjected to hydrolysis.

The carbonyl group contains a carbon-oxygen double bond; since the mobile π-electrons are strongly attracted to oxygen, the carbonyl group carbon is an electron-deficient center, and the carbonyl group oxygen is electron-rich.

Since the most important stage in these reactions is the formation of a bond with an electron-deficient (acidic) carbonyl carbon, the carbonyl group is most prone to interact with electron-rich nucleophilic reagents, i.e., with bases. Typical reactions of aldehydes and ketones are the reactions nucleophilic addition.

In the transition state, oxygen begins to acquire electrons and the negative charge that it will have in the final product. It is the tendency of oxygen to acquire electrons, or rather its ability to carry a negative charge, that is the real reason for the reactivity of the carbonyl group towards nucleophiles.

Oximes and thioacetals are formed by this mechanism.

6. Write reaction schemes for aldol condensation

- ethanal

- 2-methylpropanal

- butanal

- pentanal

Describe the reaction mechanisms, explain the reason for the appearance of the CH-acid center.

Solution

An important reaction is based on the addition of a conjugated carbanion generated from an aldehyde or ketone to a carbonyl group - aldol condensation (it would be more correct to call this reaction aldol addition):

In some cases, the aldol addition occurs in the presence of an acid catalyst. In this case, a neutral and weak C-nucleophile - enol - is attached to the activated carbonyl group.

A slightly alkaline medium is used to carry out the reactions.

Ionization of the α-hydrogen atom

leads to carbanion I, which is a resonant hybrid of two structures (II and III), the resonance of which is possible only with the participation of the carbonyl group

A resonance of this type is impossible for carbanions formed by the ionization of β- and γ-hydrogen atoms, etc., in saturated carbonyl compounds.

Thus, the carbonyl group affects the acidity of α-hydrogen atoms in exactly the same way as it affects the acidity of carboxylic acids: the C=O group participates in the delocalization of the negative charge of the anion

The aldehyde group also has a negative inductive effect ( – I), which also affects the enhancement of the acidic properties of α-hydrogen atoms.

The α-hydrogen atoms of carbonyl compounds are still weakly acidic, although they have sufficient acidity for them to break off under the action of basic reagents. Therefore, the resulting carbanions will be strong bases and extremely reactive species. In reactions, they behave as one would expect as nucleophiles.

7. Write the schemes of intramolecular transformations that are undergone in an acidic environment:

- 4-hydroxy - 3-methylpentanal

– 5-hydroxyhexanal

Describe the reaction mechanism. What is the reason for this intramolecular interaction? Can the resulting compounds be hydrolyzed?

Solution

γ- and δ-Hydroxycarbonyl compounds easily form products of the intramolecular interaction of the hydroxyl group with the carbonyl group - cyclic hemiacetals. These compounds can exist in open chain form and in cyclic hemiacetal form. Such a phenomenon is called ring chain isomerism. In some cases, there is a balance between cyclic and open forms.

γ-Hydroxycarbonyl compounds form tetrahydrofuran derivatives.

δ-Hydroxycarbonyl compounds form a tetrahydropyran cycle, more precisely, derivatives of 2-hydroxytetrahydropyran, in which an asymmetric carbon atom appears.

These are reactions of intramolecular nucleophilic addition with acid catalysis.

The hydrolysis of these compounds cannot proceed, since no water was formed during the reaction (water was not split off).

8. Write the reaction schemes for obtaining:

- full ethyl ester of butanedioic acid from butanedioic acid

- full amide of butanedioic acid from full methyl ester of the same acid

- methyl acetate from the corresponding carboxylic acid and anhydride

- acetamide from the corresponding functional derivatives: ester and anhydride

- methyl acetate by esterification reaction

- an ester of butanoic acid and ethyl alcohol

- propanamide from various acylating agents: acid, anhydride, ester

- anhydrides of butanoic and butanedioic acids from the corresponding acids

Describe the reaction mechanisms. Explain the need for a catalyst in the esterification reaction.

Solution

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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. This 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 a 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. More given substance can 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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The oxidation of ethanol produces ethanal (acetic aldehyde) and then ethanoic acid (acetic acid). Strong oxidizing agents immediately convert ethanal to acetic acid. Oxidation by air oxygen under the influence of bacteria also leads to the same result. We can easily verify this if we dilute the alcohol a little and leave it for a while in an open cup, and then check the reaction to litmus. To obtain table vinegar, mainly acetic fermentation of alcohol or low-grade wines (wine vinegar) is still used. To do this, an alcohol solution with an intensive air supply is slowly passed through sawdust from beech wood. 5% or 10% table vinegar or the so-called vinegar essence containing 40% acetic acid goes on sale (In the USSR, the concentration of food vinegar essence supplied to the distribution network is 80%, and the concentration of table vinegar is 9%. - Note. translation). For most experiments, it will suit us. Only in some cases will you need anhydrous (glacial) acetic acid, which is one of the poisons. You can buy it at a pharmacy or chemical supply store. Already at 16.6 ° C, it solidifies into a crystalline mass similar to ice. Synthetically, acetic acid is obtained from ethine via ethanal.

The repeatedly mentioned ethanal, or acetaldehyde, is the most important intermediate product in chemical technology based on the use of calcium carbide. It can be converted into acetic acid, alcohol, or butadiene, the starting material for synthetic rubber. Ethanal itself is produced commercially by adding water to ethine. In the GDR, at the synthetic butadiene rubber plant in Schkopau, this process is carried out in powerful reactors. continuous action. The essence of the process lies in the fact that ethine is introduced into heated dilute sulfuric acid, in which catalysts are dissolved - mercury salts and other substances (This reaction was discovered by the Russian scientist M. G. Kucherov in 1881 - Note. translation). Since mercury salts are highly toxic, we will not synthesize ethane ourselves from ethine. Let's choose a simpler method - careful oxidation of ethanol.

Pour 2 ml of alcohol (denatured alcohol) into a test tube and add 5 ml of 20% sulfuric acid and 3 g of finely ground potassium bichromate. Then quickly close the test tube with a rubber stopper, into which a curved glass tube is inserted. We heat the mixture with a small flame to a boil and pass the vapors released during this through ice water. The resulting ethanal dissolves in water and can be detected using the alkanal reactions described above. In addition, the solution is acidic because the oxidation easily proceeds to form acetic acid.

In order to obtain ethanol in large quantities and more pure, we will assemble, guided by the figure, a more complex installation. However, this experiment can only be done in a circle or if the reader has a lot of experience. Ethanal is poisonous and very volatile!

The left side of the installation is designed to pass the current of carbon dioxide (carbon dioxide). The latter is necessary to remove the liberated ethanal from the reaction sphere before it is oxidized further to acetic acid. Let us place pieces of marble in a flask and add dilute hydrochloric acid to them in small portions. To do this, you need a dropping funnel with a long outlet tube (at least 25 cm). You can tightly attach such a tube to a conventional dropping funnel using a rubber hose. This tube must be filled with acid all the time so that carbon dioxide can overcome the excess resistance of the subsequent part of the installation and does not exit in the opposite direction. one short glass tube. We insert the same tube into the stopper that closes the dropping funnel, and connect both tubes with a rubber hose. It is even more convenient to use the Kipp apparatus. - Note. transl.).

See the illustration on page 45 for how to equalize the pressure in the gassing device.

In another vessel that serves as a reactor - a 250 ml round-bottom flask - first pour 20 ml of denatured alcohol. Then we dissolve 40 g of finely ground potassium or sodium dichromate (Poison!) In 100 ml of dilute sulfuric acid (Add 20 ml of concentrated sulfuric acid to 80 ml of water.) Due to the greater density of sulfuric acid, it is imperative to add it to water, and not vice versa. Sulfuric acid is always added gradually and only with goggles. Never pour water into sulfuric acid!

We immediately place one third of the prepared solution into the reactor, and the rest into a dropping funnel connected to the reactor. Let us insert into the reactor the outlet of the tube connecting it to the device for the release of carbon dioxide. This tube must be immersed in liquid.

Finally, special attention deserves a cooling system. Alcohol and acetic acid vapors should condense in the tube, which extends upward from the reactor at an angle. It is best to cool this tube with an external lead coil, passing through it running water. In extreme cases, you can do without cooling, but then we get a dirtier product. To condense ethanol, which already boils at 20.2 °C, we use a direct condenser. It is desirable, of course, to take an efficient refrigerator - coil, ball or with internal cooling. In extreme cases, a not too short Liebig refrigerator is also suitable. In any case, the cooling water must be very cold. Tap water is suitable for this only in winter. At other times of the year, ice water can be passed from a large tank installed at a sufficient height. The receivers - two test tubes connected to each other - are cooled by immersing them in a cooling mixture of equal (by weight) amounts of crushed ice or snow and table salt. Despite all these precautions, ethanal vapor still partially escapes. Since ethanal has an unpleasant pungent odor and is poisonous, the experiment must be carried out in fume hood or outdoors.

Only now, when the installation is charged and assembled, let's start the experiment. First, we will check the operation of the device for gas evolution by adding a small amount of hydrochloric acid to the marble. In this case, the installation is immediately filled with carbon dioxide. If it certainly passes through the reactor and no leaks are detected, we will proceed to the actual production of ethanal, stop the evolution of gas, turn on the entire cooling system and heat the contents of the reactor to a boil. Since heat is now released when the alcohol is oxidized, the burner can be removed. After that, we will again gradually add hydrochloric acid so that a moderate current of carbon dioxide passes through the reaction mixture all the time. At the same time, the remaining dichromate solution should slowly flow from the dropping funnel into the reactor.

At the end of the reaction, each of the two receivers contains a few milliliters of almost pure ethanol. We plug the test tubes with cotton wool and save them for the next experiments in the cold. Long-term storage of ethanol is impractical and dangerous, since it evaporates too easily and, being in a bottle with a ground stopper, can knock out the stopper with force. Ethanal goes on sale only in sealed thick-walled glass ampoules.

Experiments with ethane

In addition to the qualitative reactions described above, we can carry out a number of other experiments with small amounts of ethanol,

In a test tube, to 1-2 ml of ethanol, carefully add (in goggles and at a distance from yourself) with a glass rod 1 drop of concentrated sulfuric acid. A violent reaction begins. As soon as it subsides, dilute the reaction mixture with water and shake the test tube. A liquid is released, which, unlike ethanol, does not mix with water and boils only at 124 °C. It is obtained by combining three ethanal molecules to form a ring:

This polymer of ethanal is called paraldehyde. When distilled with dilute acids, it turns back into ethanal. Paraldehyde is used in medicine as a sleeping pill.

In the next experiment, we carefully heat a small amount of ethanal with concentrated sodium hydroxide solution. A yellow "aldehyde resin" is released. It also arises due to the attachment of ethanal molecules to each other. However, unlike paraldehyde, the molecules of this resin are built from a large number of ethanal molecules.

Another solid polymerization product, metaldehyde, is formed when ethanol is treated in the cold with gaseous hydrogen chloride. It used to find some use as a solid fuel ("dry alcohol").

Approximately 0.5 ml of ethanol is diluted with 2 ml of water. Add 1 ml of diluted sodium hydroxide or soda solution and heat for a few minutes. We will smell the exceptionally pungent smell of crotonaldehyde. (Perform the experiment in a fume hood or outdoors!).

From ethanal, as a result of the addition of two of its molecules to each other, an aldol is first formed, which is also an intermediate product in the production of butadiene. It contains both alkanal and alkanol functional groups.

By splitting off water, the aldol is converted to crotonaldehyde:

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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 man. Formula of acetaldehyde: CH3-CHO.

Physical properties

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

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 (methylformaldehyde)

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

This substance is a significant part of tobacco smoke. There has been a recent demonstration showing that the synergistic association of acetic acid with nicotine increases addiction (especially in individuals under 30 years of age).

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.

Safety

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

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ACETALDEHYDE (acetic aldehyde, ethanal) CH3CHO - colorless liquid-bone with a pungent suffocating odor, bp. 20.8°C, miscible in all respects with water, alcohol, ether. Acetylene is obtained by hydration of acetylene in the presence of mercury salts (Kucherov's method), by the oxidation of ethyl alcohol, and by other methods. It is used to obtain acetic acid, butadiene, acetal-dol, acetal, synthetic resins, etc.

Synthesis Carried out at room temperature, using equimolecular amounts of nitromethane and a-naphthaldehyde in ethanal solution. The resulting 1-(a-naphthyl)-2-nitroethylene did not differ in elemental composition and properties from that synthesized by the described method.

Only now, when the installation is charged and assembled, let's start the experiment. First, we will check the operation of the device for gas evolution by adding a small amount of hydrochloric acid to the marble. In this case, the installation is immediately filled with carbon dioxide. If it certainly passes through the reactor and no leaks are found, we will proceed to the actual production of ethanal. We will stop the evolution of gas, turn on the entire cooling system and heat the contents of the reactor to a boil. Since heat is now released when the alcohol is oxidized, the burner can be removed. After that, we will again gradually add hydrochloric acid so that a moderate current of carbon dioxide passes through the reaction mixture all the time. At the same time, the remaining dichromate solution should slowly flow from the dropping funnel into the reactor.

We get a small amount of ether. To do this, pour about 2 ml of denatured alcohol and 1.5 ml of concentrated sulfuric acid into a test tube. We select a stopper with two holes to the test tube. In one of them we insert a small dropping funnel or just a small funnel with an elongated tube, the exit from which we first close with a piece of rubber hose and a clamp. Using the second hole in the stopper, we attach a device for vapor cooling to the test tube - the same as in the case of obtaining ethanal (p. 144). The receiver must certainly be cooled with ice water, because the ether boils already at 34.6 ° C. Due to its unusually easy flammability, the refrigerator should be as long as possible (at least 80 cm) so that there is a sufficient distance between the source of fire and the receiver. For the same reason, we will carry out the experiment away from combustible objects, in the open air or in a fume hood. Pour about 5 ml of denatured alcohol into the funnel and carefully heat the test tube on an asbestos grid with a Bunsen burner to approximately 140 ° C. A very volatile distillate condenses in the receiver, and in case of insufficient cooling, we will feel the characteristic smell of ether. Carefully opening the clamp, we will gradually, small

This ether is used in industry to obtain other substances, including ethanol (with acid hydrolysis).

During the oxidation of ethanal, 2.7 g of gray were released. Calculate how many liters of acetylene were required to obtain the required mass of CH3-CH=0 ethanal (i.e.).

A solution obtained by dissolving silver oxide weighing 6.96 g in ammonia was used to oxidize a mixture of ethanal and butanal weighing 2 g. Determine the mass fraction of aldehydes in the mixture,

In these reactions, the carbanion (88), obtained by the action of a base (usually 0H), on the a-H-atom of one molecule of the carbonyl compound (87), is added to the carbonyl carbon of another molecule (87) to form a p-hydroxycarbonyl compound . For example, in the case of ethanal CH3CHO, the reaction product is 3-hydroxybutanal

Determine the structure of the alcohol obtained by the Grignard reaction from ethanal and propyl magnesium bromide.

Acetaldehyde (ethanal) is an intermediate in the biological degradation of carbohydrates (see section 3.8.1). It was first obtained in 1782 by Scheele, the structure was established by Liebig (1835). Acetaldehyde is obtained by dehydrogenation or oxidation of ethanol over silver catalysts, hydration of acetylene (see section 2.1.4), passing ethylene and oxygen into an aqueous solution of palladium (II) chloride and copper (II) chloride at 50 °C (direct oxidation of ethylene to acetaldehyde)

The oxidation of ethanol produces ethanal (acetic aldehyde) and then ethanoic acid (acetic acid). Strong oxidizing agents immediately convert ethanal to acetic acid. Oxidation by air oxygen under the influence of bacteria also leads to the same result. We can easily verify this if we dilute the alcohol a little and leave it for a while in an open cup, and then check the reaction to litmus. To obtain table vinegar, mainly acetic fermentation of alcohol or low-grade wines (wine vinegar) is still used. To do this, an alcohol solution with an intensive air supply is slowly passed through sawdust from beech wood. 5% or 10% table vinegar or the so-called vinegar essence containing 40% acetic acid goes on sale. For most experiments, it will suit us. Only in some cases will you need anhydrous (glacial) acetic acid, which is one of the poisons. You can buy it at a pharmacy or chemical supply store. Already at 16.6 ° C, it solidifies into a crystalline mass similar to ice. Synthetically, acetic acid is obtained from ethine via ethanal.

Saturated and monounsaturated five- and six-membered rings can be metallated in the same way as their acyclic counterparts. However, in the case of tetrahydrofuran, heating with n-butyllithium produces a lithium derivative which undergoes a cycloreversion that generates ethylene and ethanal lithium enolate. This process seems to be the most convenient method for obtaining such an enolate; however, it is necessary to take into account the possibility of such an undesirable side process occurring when carrying out metallation reactions using tetrahydrofuran as a solvent.

Ethanal can be obtained from acetylene as a result of

XIII.26. A saturated ketone A with a molecular weight of 100, whose 1H NMR spectrum consists of only nz, avox singlets at 1.08 and 2.15 ppm, is treated with PCb and then the resulting compound is subjected to the action of potash. In this case, compound B is obtained, which is then treated with sodium amide in a solution of liquid ammonia, and the reaction product is introduced into condensation with ethanol. After hydrolysis, substance B is isolated. This compound then undergoes two series of transformations

The repeatedly mentioned ethanal, or acetaldehyde, is the most important intermediate product in chemical technology based on the use of calcium carbide. It can be converted into acetic acid, alcohol, or butadiene, the starting material for synthetic rubber. Ethanal itself is produced commercially by adding water to ethine. In the GDR, at the synthetic butadiene rubber plant in Schkopau, this process is carried out in powerful reactors continuously.

From ethanal, as a result of the addition of two of its molecules to each other, an aldol is first formed, which is also an intermediate product in the production of butadiene. It contains both alkanal and alkanol functional groups. 169

Ethn can be converted into a wide variety of compounds, which, in particular, have become of great importance for the production of plastics, synthetic rubber, drugs and solvents. For example, when hydrogen chloride is added to ethine, vinyl chloride (vinyl chloride) is formed - the starting material for the production of polyvinyl chloride (PVC) and plastics based on it. Ethanal, which we will meet later, is obtained from ethine, and many other products are made from it.

The repeatedly mentioned ethanal, or acetaldehyde, is the most important intermediate product in chemical technology based on the use of calcium carbide. It can be converted into acetic acid, alcohol, or butadiene, the starting material for synthetic rubber. Ethanal itself is produced commercially by adding water to ethine. In the GDR, at the synthetic butadiene rubber plant in Schkopau, this process is carried out in powerful continuous reactors. The essence of the process is that ethine is introduced into heated dilute sulfuric acid, in which catalysts - mercury salts and other substances are dissolved. Since mercury salts are very toxic, we will not synthesize ethane from ethine ourselves. Let's choose a simpler method - careful oxidation of ethanol.

Acetaldehyde (ethanal), CH3-CHO, was first obtained by Fourcroix and Vauquelin in 1800. Its composition was established by Liebig in 1835. Acetaldehyde is the simplest aliphatic aldehyde, giving characteristic aldehyde reactions. Boils at 20.2°, melts at -123°. Can be obtained

Acetaldehyde (acetic aldehyde, ethanal) is an easily boiling liquid with a smell of green foliage. In industry, it is obtained from acetylene by the Kucherov reaction (see 38), the oxidation of ethyl alcohol, and the isomerization of ethylene oxide (see Scheme 5). The most modern way to obtain acetaldehyde is the direct oxidation of ethylene with atmospheric oxygen.

Ethanal, acetaldehyde, acetaldehyde, CHaCHO, a liquid boiling at 4-21°, is obtained from ethanol by oxidation with potassium dichromate and sulfuric acid or by catalytic dehydrogenation. The only production method used in industry is the addition of water to acetylene in the presence of mercury salts. The source in this method is inorganic raw materials - coal and lime.

Ethanal (acetaldehyde) (CH3.CHO). Obtained by the oxidation of ethanol or acetylene. Mobile colorless liquid with a sharp, fruity odor, caustic, very volatile, flammable, miscible with water, alcohol and ether. Used in organic synthesis to produce plastics, oil varnishes or in medicine as an antiseptic.

Acetic aldehyde, acetaldehyde, ethanal CLEAR, extremely volatile liquid with a boiling point of 20° and a peculiar strong odor. Obtained by oxidation of ethyl alcohol and purified through aldehyde ammonia. Technically, it is obtained by adding water to acetylene; for this, acetylene is passed into warm dilute (50%) sulfuric acid containing a little mercury sulfate (Kucherov). This method is the main one for obtaining acetaldehyde. In normal fermentation, acetaldehyde is produced as an intermediate.

See pages where the term is mentioned Ethanal receiving:                Basic Principles of Organic Chemistry Volume 1 (1963)

Fundamentals of Organic Chemistry Volume 1 Edition 6 (1954) .516]

Organic Chemistry Vol. 3 (1980) — [ c.79 , c.179 , c.183 ]

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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 oxidizing agents; 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...

Acetic aldehyde belongs 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 the aldehyde of acetic acid and ethanol. His structural formula looks like this: 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.

This substance is used in industry to produce acetic acid, butadiene and various organic substances.

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 man. 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.

This substance is a significant part of tobacco smoke. There has been a recent demonstration showing that the synergistic association of acetic acid with nicotine increases addiction (especially in individuals under 30 years of 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.

Safety

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

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Introduction

Millions of chemical compounds are known today. 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 a 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 chemical in question with ethyl alcohol, taking place 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 (methylformaldehyde)

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

This substance is a significant part of tobacco smoke. There has been a recent demonstration showing that the synergistic association of acetic acid with nicotine increases addiction (especially in individuals under 30 years of age).

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.

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Historically, the first industrial method for the production of 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 compound from the point of view of 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 of alcoholic beverages has a depressing effect on the human nervous system, while calming him down. It is an integral part of the 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:

1. 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%.
2. 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:

1. Poisonous toxins that poison the body and the atmosphere are not released.
2. Uncomplicated and mild conditions implementation of the reaction, there is no danger to human life.
3. The reaction produces hydrogen. It is one of the most versatile substances that can be used in a variety of ways.
4. 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 available, 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 is an extremely volatile, 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 is of 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 of it 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 by heating 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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