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Acetic aldehyde (other names: acetaldehyde, methylformaldehyde, ethanal) - 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 acetaldehyde:CH3-CHO.
Physical properties
1. Acetic aldehyde is a colorless liquid with a sharp bad smell.
2. Highly soluble in ether, alcohol and water.
3. 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. equals -39 degrees.
4. Auto-ignition temperature is 185 degrees.
Obtaining acetaldehyde
1. The main way to obtain this substance is (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 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 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 such a disease as (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 the development of the muscular system disproportionate to 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 more at risk of developing kidney and upper liver cancer.
Security
This substance is toxic. It is an air pollutant from smoking or from exhaust in traffic jams.
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 food products, such as coffee, bread, and also this substance is synthesized by plants in the process of 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.
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
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!
Chemical properties of acetaldehyde
1. Hydrogenation. The addition of hydrogen to occurs in the presence of hydrogenation catalysts (Ni, Co, Cu, Pt, Pd, etc.). At the same time, it turns into ethyl alcohol:
CH3CHO + H2C2H5OH
When aldehydes or ketones are reduced with hydrogen at the time of isolation (using alkali metals or amalgamated magnesium), along with the corresponding alcohols, glycols are also formed in small quantities:
2 CH3CHO + 2HCH3 - CH - CH - CH3
2. Nucleophilic addition reactions
2.1 Addition of magnesium haloalkyls
CH3 - CH2 - MgBr + CH3CHO BrMg - O - CH - C2H5
2.2 The addition of hydrocyanic acid leads to the formation of β-hydroxypropionic acid nitrile:
CH3CHO + HCN CH3 - CH - CN
2.3 The addition of sodium hydrosulfite gives crystalline substance- acetaldehyde derivative:
CH3CHO + HSO3NaCH3 - C - SO3Na
2.4 Interaction with ammonia leads to the formation of acetaldimine:
CH3CHO + NH3CH3-CH=NH
2.5 With hydroxylamine, acetaldehyde, releasing water, forms acetaldoxime:
CH3CHO + H2NOH H2O + CH3-CH =NOH
2.6 Of particular interest are the reactions of acetaldehyde with hydrazine and its substituted:
CH3CHO + H2N - NH2 + OCHCH3 CH3-CH=N-N=CH-CH3 + 2H2O
Aldazin
2.7 Acetaldehyde is capable of adding water to the carbonyl group to form a hydrate - geminal glycol. At 20°C, acetaldehyde in an aqueous solution exists by 58% in the form of a hydrate -C- + HOH HO-C-OH
2.8 Under the action of alcohols on acetaldehyde, hemiacetals are formed:
CH3CHO + HOR CH3-CH
In the presence of traces of a mineral acid, acetals are formed.
CH3 - CH + ROH CH3 - CH + H2O
2.9 Acetaldehyde, when interacting with PC15, exchanges an oxygen atom for two chlorine atoms, which is used to obtain geminal dichloroethane:
CH3CHO + PC15 CH3CHCl2 + POCl3
3. Oxidation reactions
Acetaldehyde is oxidized by atmospheric oxygen to acetic acid. The intermediate product is peracetic acid:
CH3CHO + O2 CH3CO-OOH
CH3CO-OOH + CH3CHOCH3-C-O-O-CH-CH3
An ammonia solution of silver hydroxide, when lightly heated with aldehydes, oxidizes them to acids with the formation of free metallic silver. If the test tube in which the reaction is taking place was previously degreased from the inside, then silver lays down in a thin layer on its inner surface - a silver mirror is formed:
CH3CHO + 2OHCH3COONH4 + 3NH3 + H2O + 2Ag
4. Polymerization reactions
Under the action of acids on acetaldehyde, it trimerizes, paraldehyde is formed:
3CH3CHO CH3 - CH CH - CH3
5. Halogenation
Acetaldehyde reacts with bromine and iodine at the same rate regardless of the halogen concentration. Reactions are accelerated by both acids and bases.
CH3CHO + Br2 CH2BrCHO + HBr
When heated with tris(triphenylphosphine)rhodium chloride, they undergo decarbonylation to form methane:
CH3CHO + [(C6H5)P]3RhClCH4 + [(C6H5)3P]3RhCOCl
7. Condensation
7.1 Aldol condensation
In a weakly basic medium (in the presence of acetate, carbonate or potassium sulfite), acetaldehyde undergoes aldol condensation according to A.P. Borodin with the formation of aldehyde alcohol (3-hydroxybutanal), abbreviated as aldol. The aldol is formed as a result of the addition of an aldehyde to the carbonyl group of another aldehyde molecule, breaking the C-H bond in the b-position to the carbonyl:
CH3CHO+CH3CHO CH3-CHOH-CH2-CHO
Aldol when heated (without water-removing substances) splits off water with the formation of unsaturated crotonaldehyde (2-butenal):
CH3-CHOH-CH2-CHO CH3-CH=CH-CHO + H2O
Therefore, the transition from a saturated aldehyde to an unsaturated aldehyde through an aldol is called croton condensation. Dehydration occurs due to the very high mobility of hydrogen atoms in the b-position with respect to the carbonyl group (hyperconjugation), and, as in many other cases, the p-bond with respect to the carbonyl group is broken.
7.2 Ester condensation
Passes with the formation of acetic ethyl ester when aluminum alcoholates are exposed to acetaldehyde in a non-aqueous medium (according to V. E. Tishchenko):
2CH3CHOCH3-CH2-O-C-CH3
7.3 Claisen-Schmidt condensation.
This valuable synthetic reaction consists in the base-catalyzed condensation of an aromatic or other aldehyde having no hydrogen atoms with an aliphatic aldehyde or ketone. For example, cinnamic aldehyde can be obtained by shaking a mixture of benzaldehyde and acetaldehyde with about 10 parts of dilute alkali and keeping the mixture for 8--10 days. Under these conditions, reversible reactions lead to two aldols, but one of them, in which the 3-hydroxyl is activated by the phenyl group, irreversibly loses water, turning into cinnamaldehyde:
C6H5--CHO + CH3CHO C6H5-CHOH-CH2-CHO C6H5-CH=CH-CHO
Chemical properties of oxygen
Oxygen is highly reactive, especially when heated and in the presence of a catalyst. With most simple substances, it interacts directly, forming oxides. Only in relation to fluorine does oxygen exhibit reducing properties.
Like fluorine, oxygen forms compounds with almost all elements (except helium, neon and argon). It does not directly react with halogens, krypton, xenon, gold and platinum metals, and their compounds are obtained indirectly. With all other elements, oxygen combines directly. These processes are usually accompanied by the release of heat.
Since oxygen is second only to fluorine in electronegativity, the oxidation state of oxygen in the vast majority of compounds is taken to be -2. In addition, oxygen is assigned oxidation states +2 and + 4, as well as +1 (F2O2) and -1 (H2O2).
Alkali and alkaline earth metals are most actively oxidized, and, depending on the conditions, oxides and peroxides are formed:
O2 + 2Ca = 2CaO
O2 + Ba = BaO2
Some metals in normal conditions oxidized only from the surface (for example, chromium or aluminum). The resulting oxide film prevents further interaction. An increase in temperature and a decrease in the size of metal particles always accelerate oxidation. Yes, iron normal conditions oxidizes slowly. At the same temperature of red heat (400 ° C), the iron wire burns in oxygen:
3Fe + 2O2 = Fe3 O4
Finely dispersed iron powder (pyrophoric iron) ignites spontaneously in air even at ordinary temperatures.
Oxygen combines with hydrogen to form water:
When heated, sulfur, carbon and phosphorus burn in oxygen. The interaction of oxygen with nitrogen begins only at 1200 °C or in an electric discharge:
Hydrogen compounds burn in oxygen, for example:
2H2S + 3O2 = 2SO2 + 2H2O (with excess O2)
2H2S + O2 \u003d 2S + 2H2O (with a lack of O2)
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 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 resulting acetaldehyde 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 ethyl acetate (Tishchenko's reaction): 2CH 3 CHO = CH 3 COO C 2 H 5 . This process is used to produce ethyl acetate from acetylene.
4) Especially great importance have addition reactions: a) acetaldehyde attaches an oxygen atom, while 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 in advance (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.
