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) into a solution of mercury oxide in strong (45%) sulfuric acid, heated no higher than 50 °, acetylene is passed with strong stirring; the resulting acetaldehyde and paraldehyde are periodically siphoned off or distilled off in a vacuum. The best, however, is the method claimed by the French patent 455370, according to which the plant of the Consortium of the Electrical Industry in Nuremberg operates.
There, acetylene is passed into a hot weak solution (not higher than 6%) of sulfuric acid containing mercury oxide; the acetaldehyde formed during the course of the process is continuously distilled and condensed in certain receivers. According to the Grisheim-Electron method, some of the mercury formed as a result of partial oxide reduction is lost, because it is in an emulsified state and cannot be recovered. The method of the Consortium is of great advantage in this regard, since here the mercury is easily separated from the solution and then electrochemically converted into an oxide. The yield is almost quantitative and the resulting acetaldehyde is very pure. Acetaldehyde is a volatile, colorless liquid, boiling point 21°, specific gravity 0.7951. It is miscible with water in any ratio; it is released from aqueous solutions after the addition of calcium chloride. From chemical properties 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 an 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) 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 (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 of the chemical industry. Its cheap preparation from acetylene in Lately allowed the implementation of a number of new synthetic industries, of which the method of producing 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.
ACETALDEHYDE
- an intermediate product of the oxidation of ethyl alcohol (chemical formula C2H4O), containing an aldehyde group (H-C=O); in the body is formed with the participation of the enzyme alcohol dehydrogenase. Highly toxic, its de
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- ACETALDEHYDE in Medical terms:
see Acetic aldehyde ... - ACETALDEHYDE in the Big Encyclopedic Dictionary:
(acetic aldehyde) CH3CHO, colorless liquid with a pungent odor, bp = 20.2 °C. Raw material in the production of acetic acid, acetic anhydride, … - ACETALDEHYDE in big Soviet encyclopedia, TSB:
acetaldehyde, CH3CHO, organic compound, colorless liquid with a pungent odor; boiling point 20.8|C. Melting point - 124|С, density 783 kg/m3", … - ACETALDEHYDE in the Encyclopedic Dictionary of Brockhaus and Euphron:
cm. … - ACETALDEHYDE in the Big Russian Encyclopedic Dictionary:
ACETALDEHID (acetic aldehyde), CH 3 CHO, colorless. liquid with a pungent odor, bp 20.2 °C. Raw materials in the production of acetic acid, ... - ACETALDEHYDE in the Encyclopedia of Brockhaus and Efron:
? cm. … - ACETALDEHYDE in the New Dictionary of Foreign Words:
(see acet...) organic compound, aldehyde of acetic acid; liquid boiling at 20 s; obtained from acetylene or ethyl alcohol; … - ACETALDEHYDE in the Dictionary of Foreign Expressions:
[cm. ocet...] organic compound, aldehyde of acetic acid; liquid boiling at 20 s; obtained from acetylene or ethyl alcohol; appl. For … - ACETALDEHYDE in the Dictionary of the Russian Language Lopatin:
acetaldehyde, ... - ACETALDEHYDE in the Complete Spelling Dictionary of the Russian Language:
acetaldehyde... - ACETALDEHYDE in the Spelling Dictionary:
acetaldehyde, ... - ACETALDEHYDE in the Modern Explanatory Dictionary, TSB:
(acetic aldehyde), CH3CHO, colorless liquid with a pungent odor, bp = 20.2 °C. Raw material in the production of acetic acid, acetic anhydride, … - Teturam in the Medicines Directory:
TETURAM (Teturamum). Tetraethylthiuram disulfide. Synonyms: Antabus, Abstinyl, Alcophobin, Antabus, Antaethan, Antaethyl, Anticol, Aversan, Contrapot, Crotenal, Disetil, Disulfiramum, Espenal, Exhorran, Hoca, Noxal, … - FUSEL OIL in the Encyclopedia of a sober lifestyle:
- is a mixture (C3-C10) of monohydric aliphatic alcohols, ethers and other compounds (about 40 components in total, 27 of which are identified), ... - in the Medical Dictionary:
- ENZYME DEFICIENCY in the Medical Dictionary.
- ALCOHOLISM in the Medical Dictionary:
- HYPOGLYCEMIA in the Medical Dictionary:
- ACUTE ALCOHOL SURROGATE POISONING
Acute poisoning with alcohol surrogates is associated with the intake of ethyl alcohol containing impurities of various substances prepared on the basis of ethanol or other monohydric ... - ENZYME DEFICIENCY in the big medical dictionary.
- HYPOGLYCEMIA in the Medical Big Dictionary:
Hypoglycemia - a decrease in blood glucose less than 3.33 mmol / l. Hypoglycemia can be diagnosed in healthy individuals after a few days of fasting... - ALCOHOLISM in the Medical Big Dictionary:
Alcoholism - a pronounced violation of social, psychological and physiological adaptation due to regular alcohol consumption; disease gradually leads to physical, intellectual, emotional… - ANTABUS V explanatory dictionary psychiatric terms:
A drug for the treatment of alcoholism by the method of sensitization, in which not only the craving for alcohol is suppressed, but the intake itself is done ... - ACETEC ALDEHYDE in Medical terms:
(syn.: acetaldehyde, ethanal) the simplest natural aldehyde of the acyclic series, an intermediate product of alcoholic fermentation; participates in the cycle of tricarboxylic to-t; U.'s derivatives and. …
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 reducing aldehydes or ketones with hydrogen at the time of isolation (using alkali metals or amalgamated magnesium) are formed along with the corresponding alcohols in small quantities, glycols are also formed:
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 aqueous solution 58% exists as 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 takes 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. An 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. It interacts directly with most simple substances, 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 under normal conditions oxidize 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. So, iron under 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)
DEFINITION
Ethanal(acetaldehyde, acetaldehyde) is a mobile, colorless, easily evaporating liquid with a characteristic odor (the structure of the molecule is shown in Fig. 1).
It is highly soluble in water, alcohol and ether.
Rice. 1. The structure of the ethanal molecule.
Table 1. Physical properties of ethanal.
Obtaining ethane
The most popular way to obtain ethanol is the oxidation of ethanol:
CH 3 -CH 2 -OH + [O] →CH 3 -C(O)H.
In addition, other reactions are used:
- hydrolysis of 1,1-dihaloalkanes
CH 3 -CHCl 2 + 2NaOH aq →CH 3 -C (O) -H + 2NaCl + H 2 O (t o).
- pyrolysis of calcium (barium) salts of carboxylic acids:
H-C(O)-O-Ca-O-C(O)-CH 3 → CH 3 -C(O)-H + CaCO 3 (t o).
- hydration of acetylene and its homologues (Kucherov reaction)
- catalytic oxidation of acetylene
2CH 2 \u003d CH 2 + [O] → 2CH 3 -C (O) -H (kat \u003d CuCl 2, PdCl 2).
Chemical properties of ethanal
Typical reactions characteristic of ethanal are nucleophilic addition reactions. All of them proceed mainly with splitting:
- p-bonds in the carbonyl group
– hydrogenation
CH 3 -C (O) -H + H 2 → CH 3 -CH 2 -OH (kat \u003d Ni).
- addition of alcohols
CH 3 -C (O) -H + C 2 H 5 OH ↔ CH 3 -CH 2 -C (OH) H-O-C 2 H 5 (H +).
- addition of hydrocyanic acid
CH 3 -C (O) -H + H-C≡N → CH 3 -C (CN) H-OH (OH -).
- addition of sodium hydrosulfite
CH 3 -C (O) -H + NaHSO 3 → CH 3 -C (OH) H-SO 3 Na ↓.
- C-H bonds in the carbonyl group
- oxidation of silver oxide with ammonia solution ("silver mirror" reaction) - qualitative reaction
CH 3 -(O)H + 2OH → CH 3 -C(O) -ONH 4 + 2Ag↓ + 3NH 3 + H 2 O
or simplified
CH 3 -(O)H + Ag 2 O → CH 3 -COOH + 2Ag ↓ (NH 3 (aq)).
- oxidation with copper (II) hydroxide
CH 3 -(O)H + 2Cu(OH) 2 → CH 3 -COOH + Cu 2 O↓ + 2H 2 O (OH -, t o).
- bonds C α -H
– halogenation
CH 3 -(O)H + Cl 2 → CH 2 Cl-C(O)-H + HCl.
Ethanal application
Ethanal is used primarily for the production of acetic acid and as a feedstock for the synthesis of many organic compounds. In addition, ethanal and its derivatives are used in the manufacture of certain drugs.
Examples of problem solving
EXAMPLE 1
| Exercise | An equimolecular mixture of acetylene and ethanal reacts completely with 69.6 g of Ag 2 O dissolved in ammonia. Determine the composition of the initial mixture. |
| Solution | Let's write the equations of the reactions specified in the condition of the problem: HC≡CH + Ag 2 O → AgC≡Cag + H 2 O (1); H 3 С-C(O)H + Ag 2 O →CH 3 COOH + 2Ag (2). Calculate the amount of silver oxide (I) substance: n(Ag 2 O) = m(Ag 2 O) / M(Ag 2 O); M(Ag 2 O) = 232 g/mol; n (Ag 2 O) \u003d 69.6 / 232 \u003d 2.6 mol. According to equation (2), the amount of ethanal substance will be equal to 0.15 mol. According to the condition of the problem, the mixture is equimolecular, therefore, acetylene will also be 0.15 mol. Find the masses of the substances that make up the mixture: M(HC≡CH) = 26 g/mol; M(H 3 C-C(O)H) = 44 g/mol; m(HC≡CH) = 0.15 x 26 = 3.9 g; m (H 3 C-C (O) H) \u003d 0.15 × 44 \u003d 6.6 g. |
| Answer | The mass of acetylene is 3.9 g, ethanal - 6.6 g. |
Acetaldehyde (ethanal, acetaldehyde) CH 3 CHO is a colorless, low-boiling liquid with a sharp, suffocating odor, with a boiling point of 20.2 ° C, a melting point of -123.5 ° C and a density of 0.783 t / m3. The critical temperature of acetaldehyde is 188 o C, the ignition temperature is 156 o C. In air, acetaldehyde forms explosive mixtures with flammability limits at 400 o C of 3.97 and 57% vol. Mixtures with oxygen ignite at a lower temperature - about 140 ° C. Toxic, MPC is 5 mg / m3.
Acetaldehyde is miscible in all respects with water, ethanol, diethyl ether and other organic solvents, with some forming azeotropic mixtures.
Acetaldehyde is a compound in the molecule of which the carbonyl group is bonded to a hydrocarbon radical and a hydrogen atom (CH 3 - CH \u003d O). Acetaldehyde does not form hydrogen bonds, so its boiling point is much lower than that of the corresponding alcohols.
1.1.1 Physical properties of acetylene
Acetylene (ethyne) C2H2 is a colorless gas with a slight ethereal odor in its pure form, with a boiling point of -83.8°C, a melting point of -80.8°C (at 0.17 MPa) and a density of 1.09 kg/m3. The critical temperature of acetylene is 35.5°C.
When heated to 500 ° C and compressed to pressures above 2 * 105 Pa, acetylene, even in the presence of oxygen, decomposes with an explosion. Decomposition is initiated by spark and friction. The explosiveness of acetylene increases in contact with metals capable of forming acetylides, such as copper. This must be taken into account when choosing the material of the apparatus. With air, acetylene forms explosive mixtures with ignition limits of 2.3 and 80.7% vol. At the same time, the explosiveness of mixtures decreases when they are diluted with inert gases (nitrogen, methane) or vapors.
Acetylene is much better than other gaseous hydrocarbons, soluble in water. At a temperature of 15°C and a pressure of 105 Pa, 1.15 volumes dissolve in one volume of water. In other solvents, the solubility of acetylene is: in acetone 25, ethanol 6, benzene 4, acetic acid 6 volumes. Solubility in acetone increases with increasing pressure and at 1.25 MPa is already 300 volumes in one volume. The solubility of acetylene in various solvents is of great importance for its separation from mixtures with other gases, as well as for storage in cylinders as a solution and in acetone.
Acetylene is an endothermic compound with an enthalpy of formation of +227.4 kJ/mol. Therefore, when it is burned in oxygen, a large amount of heat is released and a high temperature develops, reaching 3150 ° C.
1.2. Chemical properties
1. Under the influence of mineral acids, acetaldehyde polymerizes with the formation of a liquid cyclic trimer - paraldehyde with a boiling point of 124.4 ° C and a melting point of 12.6 ° C:
3CH 3 CHO CH 3 CH - O-CH (CH 3) - O- CH (CH 3) -O
acetaldehyde trimer-paraldehyde
and crystalline tetramer - metaldehyde:
4CH 3 CHO (CH 3 CHO) 4,
acetaldehyde tetramer metaldehyde
which, when heated with sulfuric acid, depolymerize to the original acetaldehyde. This is the basis for the use in many cases of paraldehyde instead of monomeric acetaldehyde, since it is more convenient for storage and transportation.
2. Addition of hydrocyanic (hydrocyanic) acid. Acetaldehyde interacting with hydrocyanic acid forms hydroxy acid:
CH 3 CHO + HCNCH 3 CHOH-CN
acetaldehyde hydrocyanic hydroxy acid
This reaction is a nucleophilic addition reaction at the C=O double bond, it is used to extend the carbon chain and produce hydroxy acids
3. Hydrogenation is a chemical process associated with the addition of a hydrogen molecule to acetaldehyde. In this reaction, hydrogen is added along unsaturated bonds to form ethanol:
CH 3 CHO + H 2 CH 3 CH 2 OH
acetaldehyde ethyl alcohol (ethanol)
4. The reaction of the "silver mirror" - the oxidation of acetaldehyde with an ammonia solution of silver oxide, with the formation of a salt of acetic acid (acetate), silver (in the form of a precipitate), ammonia and water:
CH 3 CHO + 2OHCH 3 COOHNH 4 + 2Ag + 3NH 3 + H 2 O
acetaldehyde ammonia solution acetate ammonia
silver oxide
5. Oxidation with copper (II) hydroxide. Acetaldehyde reacts with copper hydroxide to form acetic acid copper oxide and water:
CH 3 CHO + 2Cu (OH) 2 CH 3 COOH + CuO + 2H 2 O
acetaldehyde hydroxide acetic oxide
copper acid copper
СuO is a red precipitate.
6. Interaction with alcohols to form acetals and hemiacetals. Hemiacetals are compounds in which the carbon atom is bonded to hydroxyl and alkoxy groups. Acetals are compounds in which the carbon atom is bonded to two alkoxy groups:
CH 3 -CH \u003d O + 2CH 3 OHCH 3 -CH-OCH 3 + H 2 O
acetaldehyde methanol
7. Addition of sodium hydrosulfite (NaHSO 3) with the formation of hydrosulfite derivatives of aldehydes:
C \u003d O + HSO 3 Na C
hydrosulfite derivative of ethanal
1.2.1 Chemical properties of acetylene
The acetylene molecule contains two active fragments: a triple bond -СС- and a mobile "acetylene" hydrogen atomС-Н. Accordingly, acetylene reactions can be reduced to two main types: vinylation reactions; reactions involving the "acetylenic" hydrogen atom.
1. Addition reactions are common to all alkynes. The Kucherov reaction leads to the formation of acetaldehyde:
HC CH + H 2 O [CH 2 \u003d CH-OH] CH 3 -CH \u003d O.
2. Weak acid properties:
2 HCCH + 2Na2NaССna + H 2
HCCH + 2OHAgCCAg + 4NH 3 + 2H 2 O.
Salts of acetylene are called acetylenides. Acetylides are easily decomposed by the action of hydrochloric acid:
AgCCag+HClHCCH+2AgCl.
3. Polymerization:
a) dimerization under the action of an aqueous solution of CuCl and NH 4 Cl:
HCCH + HCCHCH 2 \u003d CH-CCH
Vinylacetylene
b) trimerization (Zelinsky reaction) with the formation of benzene.
