Publication date 01/27/2013 17:10
Acetaldehyde (other names: acetaldehyde, methyl formaldehyde, ethanal) is an organic compound belonging to the class of aldehydes. This substance is important for humans and is found in coffee, bread, ripe fruits and vegetables. Synthesized by plants. Occurs naturally and is produced in large quantities by humans. Formula of acetaldehyde: CH3-CHO.
Physical properties of acetaldehyde
1. Acetaldehyde is a colorless liquid with a strong, unpleasant odor.
2. 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. 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.
Preparation of acetaldehyde
1. The main method of obtaining this substance is the oxidation of ethylene (the so-called Wacker process). This is what the reaction looks like:
2CH2 = C2H4 (ethylene) + O2 (oxygen) = 2CH3CHO (methyl formaldehyde)
2. Also, acetaldehyde can 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 above process was introduced. It was carried out by oxidation or dehydrogenation of ethyl alcohol on a silver or copper catalyst.
Applications of acetaldehyde
To obtain what substances is acetaldehyde needed? Acetic acid, butadiene, aldehyde polymers and some other organic substances.
Used as a precursor (a substance that participates in a reaction leading to the creation of the target substance) to acetic acid. However, they soon stopped using the substance we are considering in this way. This was because acetic acid was easier and cheaper to produce from methalon using the Kativa and Monsanto processes.
Methyl formaldehyde 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. A recent demonstration showed that the synergistic relationship of acetic acid with nicotine increases addiction (especially in individuals under thirty years of age).
Alzheimer's disease and acetaldehyde
Those people who do not have the genetic factor for the conversion of methyl formaldehyde 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 methyl formaldehyde
Presumably, the substance we are considering is a carcinogen for humans, since today there is evidence of the carcinogenicity of acetaldehyde in various experiments on animals. In addition, methyl formaldehyde damages DNA, thereby causing development of the muscular system disproportionate to body weight, which is associated with impaired 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, such patients are at greater risk of developing cancer of the kidneys and upper liver.
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 separation (with the help of 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 b-hydroxypropionic acid nitrile:
CH3CHO + HCN CH3 - CH - CN
2.3 The addition of sodium hydrosulfite gives a crystalline substance - a derivative of acetaldehyde:
CH3CHO + HSO3NaCH3 - C - SO3Na
2.4 Interaction with ammonia leads to the formation of acetaldimine:
CH3CHO + NH3CH3-CH=NH
2.5 With hydroxylamine, acetaldehyde releases water to form acetaldoxime:
CH3CHO + H2NOH H2O + CH3-CH =NOH
2.6 Of particular interest are the reactions of acetaldehyde with hydrazine and its substitutes:
CH3CHO + H2N - NH2 + OCHCH3 CH3-CH=N-N=CH-CH3 + 2H2O
Aldazine
2.7 Acetaldehyde is capable of adding water at the carbonyl group to form a hydrate - geminal glycol. At 20°C, 58% of acetaldehyde in aqueous solution exists in the form of hydrate -C- + HOH HO-C-OH
2.8 When acetaldehyde reacts with alcohols, hemiacetals are formed:
CH3CHO + HOR CH3-CH
In the presence of traces of 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 CH3CHСl2 + 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 slightly heated with aldehydes, oxidizes them into 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 the silver lies in a thin layer on its inner surface - a silver mirror is formed:
CH3 CHO + 2OHCH3COONH4 + 3NH3 + H2O + 2Ag
4. Polymerization reactions
When acetaldehyde is exposed to acids, it trimerizes and 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 environment (in the presence of potassium acetate, carbonate or sulfite), acetaldehyde undergoes aldol condensation according to A.P. Borodin to form an 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 with the cleavage of the C-H bond in the b-position to the carbonyl:
CH3CHO + CH3CHO CH3-CHOH-CH2-CHO
When heated, aldol (without water-removing substances) splits off water to form 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 relative to the carbonyl group (superconjugation), and, as in many other cases, the p-bond in relation to the carbonyl group is broken.
7.2 Ester condensation
Proceeds with the formation of acetic ethyl ether upon the action of aluminum alcoholates on 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 of the base-catalyzed condensation of an aromatic or other aldehyde lacking hydrogen atoms with an aliphatic aldehyde or ketone. For example, cinnamaldehyde can be prepared by shaking a mixture of benzaldehyde and acetaldehyde with about 10 parts of dilute alkali and leaving 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 a 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 react directly with halogens, krypton, xenon, gold and platinum metals, and their compounds are obtained indirectly. Oxygen combines directly with all other elements. 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 only oxidize 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 accelerates oxidation. Thus, iron under normal conditions oxidizes slowly. At a red-hot temperature (400 °C), the iron wire burns in oxygen:
3Fe + 2O2 = Fe3 O4
Fine iron powder (pyrophoric iron) spontaneously ignites in air even at ordinary temperatures.
With hydrogen, oxygen forms water:
When heated, sulfur, carbon and phosphorus burn in oxygen. The interaction of oxygen with nitrogen begins only at 1200 °C or in an electrical discharge:
Hydrogen compounds burn in oxygen, for example:
2H2S + 3О2 = 2SO2 + 2Н2О (with excess O2)
2H2S + O2 = 2S + 2H2O (with a lack of O2)
Ethanal (acetic aldehyde)- 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. Used for the production of cellulose acetates, acetic acid, butanol, etc.
Structure
In ethanal, like any other aldehyde, three atoms are connected to a central trigonal atom (namely, an oxygen atom, a hydrogen atom and a carbon atom). They all lie in the same plane as this trigonal atom. All bond angles of the trigonal atom with these atoms are close to 120°.
In a carbonyl group, there is a very large difference in electronegativity between the carbon and oxygen atoms. This is reflected in the large dipole moment of acetaldehyde. The bond electrons are unevenly distributed, so the ethanal molecule is highly polar. To qualitatively describe the nature of the bond in a carbonyl group, the concept of a double bond containing σ- and π-components with two pairs of unbonded (n) electrons at the oxygen atom is usually used. It is accepted that the trigonal carbon atom is in the sp 2 hybridization state and forms a σ bond with hydrogen and another carbon atom.
Physical properties
Ethanal, like all aldehydes, is not capable of forming hydrogen bonds, so its boiling point is only 20.16 ° C. Under normal conditions, it is a colorless liquid with a sharp suffocating odor; when diluted with water, it acquires a fruity odor. It dissolves well in water, alcohol and ether.
Receipt
Wacker process
The main industrial method for producing acetaldehyde is the Wacker process. It consists of the oxidation of ethylene, which is obtained by cracking hydrocarbons. This method is of much greater importance than oxidation, catalytic dehydrogenation of ethanol or hydration of acetylene. In the Wacker process, ethylene in an aqueous solution, copper(II) chloride and palladium(II) chloride are oxidized. In the one-stage version, the catalyst is regenerated with oxygen under continuous synthesis conditions; in the two-stage version, the catalyst is regenerated with air in a separate reactor. The reaction is catalyzed by palladium.
From dihalogen-based
As a result of the hydrolysis of dihalogen compounds 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.
From ethanol
When ethanol is oxidized with atmospheric oxygen at a temperature of 300-500 ° C in the presence of catalysts, as well as with 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.
Ethanol can be obtained from ethanol by dehydrogenation. For this evaporation of alcohol it is necessary to pass over catalysts (zinc, copper) at high temperatures.
From 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 cyanide salts, hydroxynitriles are formed. Hydrocyanic acid itself is slightly dissociated. Therefore, the reaction is carried out in an alkaline environment, where cyanide ion is formed, which is the active nucleophilic part.
The reaction is very important in organic chemistry. Firstly, it allows you to extend the carbon chain of the original compound 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
Acetaldehyde undergoes a reversible hydration reaction, forming the corresponding hydrate.
Ethanal in aqueous solution is hydrated by 51%.
Interaction with alcohols
Alcohols, like water, reversibly combine with ethanal to form pivacetals. In alcohol solutions, pivacetals are in equilibrium with acetaldehyde. Thus, an ethanol solution of ethanal contains about 30% pivacetal (1-ethoxyethanol) (calculated as aldehyde).
When interacting with a second alcohol molecule under acid catalysis, piva acetals are converted to acetals.
Interaction with amines
At the first stage of the reaction, the nucleophilic addition of the amine occurs at the double bond of the carbonyl group. The primary product of the addition is a bipolar ion, which is stabilized as a result of intramolecular proton transfer from a nitrogen atom to an 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. In this case, a water molecule is split off from an amino alcohol molecule and an imine (Schiff base) is formed.
Similar to the interactions with primary amines, ethanal reacts with such ammonia derivatives as hydroxylamine, hydrazine, phenylhydrazine C 6 H 5 NHNH 2, etc. The resulting derivatives of acetaldehyde - 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 H - hydride ions, which are nucleophilic particles and are added via a double bond. To convert the initially formed alkoxide ion into alcohol, water is added to the reaction medium after the reduction is complete.
In industry, ethanal is converted into 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 of two ethanal molecules in an alkaline environment, 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, since 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 temperatures.
Oxidation reactions
The “silver mirror” reaction
One of the qualitative reactions for determining the aldehyde group is the “silver mirror” reaction - the oxidation of aldehyde argentum (I) oxide. Silver oxide is always prepared immediately before the experiment by adding a solution of alkali metal hydroxide to a solution of argentum (I) nitrate. In ammonia solution, argentum(I) oxide forms a complex compound called diamineribble hydroxide or Tollens reagent. When this compound acts on ethanal, a redox reaction occurs. Acetaldehyde is oxidized to acetic acid, and the Argentum cation is reduced to metallic silver, which gives a shiny 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 is light blue in color, is reduced to copper(I) hydroxide, which is yellow in color. This process takes place at room temperature. If the research solution is heated, 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 the hydrogen atoms located at the carbon atoms in the α-position. They are capable of being replaced by halogen atoms.
Polymerization
Acetaldehyde, like formaldehyde, can polymerize in the presence of traces of acid. The polymerization of three ethanal molecules produces paraldehyde, a liquid with a boiling point of 124.5 ° C. When heated in the presence of acids, it depolymerizes to form the original acetaldehyde.
Interaction with ammonia
Acetaldehyde 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, ethanal is oxidized to acetic acid and perocic acid with air. To obtain acetic acid, oxidation is usually carried out in vapors and at elevated temperatures. To obtain peroctic acid, the reaction is carried out at 0 °C or lower temperature in a solvent. 1-hydroxyethyl peracetate is formed as an intermediate product, which decomposes to form peroctic acid and acetaldehyde. The latter is returned to the loop.
Application
Ethanal is used industrially for the production of cellulose acetates, acetic and perocic acids, acetic anhydride, ethyl acetate, glyoxal, 2-ethylhexanol, alkylamines, butanol, pentaerythritol, alkylpyridinium, 1,3-butylene glycol, chloral. Also used as a reducing agent in the production of mirrors.
World production in 1982 was 2 million tons/year (excluding USSR).
Physiological action
Animals
For white mice, with a 2-hour exposure, LC 50 = 21.8 mg/l, when administered into the stomach, LD 50 = 1232 mg/kg. The main symptoms of poisoning are respiratory distress and irritation of the mucous membranes. Inhalation of ethanal at a concentration of 0.5 mg/l for seven hours causes noticeable irritation of the mucous membranes in cats. At 2 mg/l - severe irritation, and 20 mg/l causes death after 1-2 hours. An autopsy shows swelling and inflammation of the lungs. Rats and guinea pigs tolerated a dose of 100 mg/kg for 6 months. In this case, there was a violation of conditioned reflex activity and an increase in blood pressure. The same changes were caused by a dose of 10 mg/kg after 2-3 months.
Human
The odor threshold is 0.0001 mg/l, and already at 0.004 mg/l a pungent odor is felt. Apart from mild irritation of the mucous membranes from 0.1-0.4 mg/l with chronic exposure to ethanal, no other pathological changes were noted. At high concentrations, increased heart rate and night sweats are observed. With very large ones - suffocation, sharp cough, headaches, bronchitis, pneumonia. It is possible to get used to small concentrations.
Entry into the body and transformations
It is retained in the respiratory tract of a rabbit by 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 into i. The metabolic rate is high and in rabbits 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 hemiketals with one alcohol molecule, and stable acetals and ketals with two alcohol molecules. Reactions to form hemiacetals are catalyzed by acids and bases. This reaction is reversible - acetals are hydrolyzed by acids.
The reaction mechanism is the reverse of the mechanism of hydrolysis of acetals.
Acetals are formed by the action of excess 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 the reaction is not possible. This property - the stability of acetals in an alkaline environment - is used when it is necessary to protect the carbonyl group.
5. Write reaction 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. Are the resulting compounds capable of hydrolyzing? Write the schemes for hydrolysis reactions.
Solution
Imines and oximes can undergo hydrolysis with aqueous acids by reactions reverse to their formation. Hydrolysis can be thought of as the acid-catalyzed addition of water to a heteroanalog of a carbonyl compound.
Thioacetals can also be hydrolyzed.
The carbonyl group contains a carbon-oxygen double bond; Since mobile π electrons are strongly attracted to oxygen, the carbon of the carbonyl group is an electron-deficient center, and the oxygen of the carbonyl group 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 would be nucleophilic addition.
In the transition state, oxygen begins to gain electrons and the negative charge it will have in the final product. It is the tendency of oxygen to acquire electrons, or more precisely 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 the 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, aldol condensation, is based on the addition of a conjugated carbanion generated from an aldehyde or ketone to a carbonyl group (it would be more correct to call this reaction aldol addition):
In some cases, aldol addition occurs in the presence of an acid catalyst. In this case, a neutral and weak C-nucleophile - enol - attaches to the activated carbonyl group.
To carry out the reactions, a slightly alkaline medium is used.
Ionization of 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 a carbonyl group
Resonance of this type is impossible for carbanions formed during 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 the same way as it affects the acidity of carboxylic acids: the C=O group is involved 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 are acidic enough to be detached by 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, like nucleophiles.
7. Write diagrams of intramolecular transformations that occur in an acidic environment:
- 4-hydroxy - 3-methylpentanal
— 5-hydroxyhexanal
Describe the reaction mechanism. What is the reason for this intramolecular interaction? Are the resulting compounds capable of hydrolyzing?
Solution
γ- and δ-Hydroxycarbonyl compounds easily form products of intramolecular interaction of the hydroxyl group with the carbonyl group - cyclic hemiacetals. These compounds can exist in open-chain and cyclic hemiacetal forms. This 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 the tetrahydropyran cycle, more precisely 2-hydroxytetrahydropyran derivatives, in which an asymmetric carbon atom appears.
These are intramolecular nucleophilic addition reactions with acid catalysis.
Hydrolysis of these compounds cannot occur, since no water was formed during the reaction (water was not split off).
8. Write the reaction schemes for the preparation:
- full ethyl ester of butanedioic acid from butanedioic acid
- complete amide of butanedioic acid from the complete 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 of chemical compounds are known. 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 look at a representative of this class - acetaldehyde.
Definition
Acetaldehyde is an organic compound of the aldehyde class. It can also be called differently: acetaldehyde, ethanal or methyl formaldehyde. The formula of acetaldehyde is CH 3 -CHO.
Properties
The substance in question has the appearance 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 o C), only its trimer, paraldehyde, can be stored and transported. Acetaldehyde is obtained by heating the mentioned substance with an inorganic acid. This is a typical aliphatic adhehyde, and it can take part in all reactions that are characteristic of this group of compounds. The substance tends to tautomerize. 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 it and its salts can react. The latter, for example, when interacting with the Grignard reagent and organolithium compounds, form hydroxethyl derivatives. Acetaldehyde upon condensation is distinguished by its chirality. Thus, during the Strecker reaction, it can condense with ammonia and cyanides, and the product of hydrolysis will be the amino acid alanine. Acetaldehyde also enters into the same type of reaction with other compounds - amines, then the reaction product becomes imines. In the synthesis of heterocyclic compounds, acetaldehyde is a very important component, the basis of all experiments performed. Paraldehyde, a cyclic trimer of this substance, is obtained by the condensation of three ethanal molecules. Also, acetaldehyde can form stable acetals. This occurs during the interaction of the chemical substance in question with ethyl alcohol, taking place under anhydrous conditions. 
Receipt
Acetaldehyde is mainly produced by the oxidation of ethylene (Wacker process). Palladium chloride acts as an oxidizing agent. This substance can also be obtained during the hydration of acetylene, which contains mercury salts. The reaction product is enol, which isomerizes into the desired substance. Another method for producing acetaldehyde, which was 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 is formed.
Application
Using 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 human, animal and plant organisms, acetaldehyde is a participant in some complex reactions. It is also part of cigarette smoke.
Conclusion
Acetaldehyde can be both beneficial and harmful. It is bad for 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 into 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 in an open cup for a while, and then check the reaction with litmus. To obtain table vinegar, they still mainly use acetic acid fermentation of alcohol or low-grade wines (wine vinegar). To do this, the alcohol solution is slowly passed through sawdust from beech wood under intensive air supply. 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 retail chain 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 classified as a poison. You can buy it at a pharmacy or chemical store. Already at 16.6 °C it hardens into a crystalline mass similar to ice. Synthetically, acetic acid is obtained from ethyne through 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 industrially by adding water to ethyne. 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 (This reaction was discovered by the Russian scientist M. G. Kucherov in 1881 - Note translation). Since mercury salts are very poisonous, we will not synthesize ethanal from ethyne ourselves. 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. Heat the mixture to a boil over a low flame and pass the resulting vapors through ice water. The resulting ethanal dissolves in water and can be detected using the reactions described above for the determination of alkanals. In addition, the solution exhibits an acidic reaction because oxidation easily proceeds further with the formation of acetic acid.
To obtain ethanal in larger quantities and more pure, we will assemble, guided by the drawing, a more complex installation. However, this experiment can only be performed in a circle or if the reader has extensive experience. Ethanal is poisonous and very volatile!
The left side of the installation is designed to pass a current of carbon dioxide (carbon dioxide). The latter is necessary to remove the evolved ethanal from the reaction sphere before it is oxidized further to acetic acid. Let's place pieces of marble in a flask and add dilute hydrochloric acid to them in small portions. To do this, you need a drip funnel with a long outlet tube (at least 25 cm). You can tightly attach such a tube to a regular drip funnel using a rubber hose. This tube must be filled with acid at all times so that carbon dioxide can overcome the excess resistance of the subsequent part of the installation and does not escape in the opposite direction (You can also use a dropping funnel without a long outlet tube. In this case, you need to insert another We insert one short glass 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 translation).
How to ensure equalization of pressure in the gas release device is shown in the figure on page 45.
First, pour 20 ml of denatured alcohol into another vessel that serves as a reactor - a 250 ml round-bottomed flask. Then dissolve 40 g of finely ground potassium or sodium bichromate (Poison!) in 100 ml of diluted sulfuric acid (Add 20 ml of concentrated sulfuric acid to 80 ml of water.) Due to the higher density of sulfuric acid, it is imperative to add it to water, and not vice versa. Sulfuric acid is always added gradually and only while wearing safety glasses. Under no circumstances should you 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's insert a tube outlet into the reactor connecting it to a device for releasing carbon dioxide. This tube must be immersed in liquid.
Finally, the cooling system deserves special attention. In a tube that extends upward from the reactor at an angle, vapors of alcohol and acetic acid should condense. It is best to cool this tube using an external lead coil running running water through it. In extreme cases, we can do without refrigeration, but then we will get a dirtier product. To condense ethanal, which already boils at 20.2 °C, we use a direct refrigerator. It is, of course, advisable to take an efficient refrigerator - coil, ball or with internal cooling. In extreme cases, a not too short Liebig refrigerator will do. In any case, the cooling water must be very cold. Tap water is only suitable for this in winter. At other times of the year, you can pass ice water from a large tank installed at a sufficient height. We cool the receivers - two test tubes connected to each other - by immersing them in a cooling mixture of equal (by weight) quantities 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 toxic, the experiment must be carried out in a fume hood or in the open air.
Only now, when the installation is charged and assembled, will we begin the experiment. First, let's check the operation of the gas release device 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. We will stop the gas evolution, turn on the entire cooling system and heat the contents of the reactor to a boil. Since the oxidation of alcohol now releases heat, the burner can be removed. After this, 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 flow slowly from the dropping funnel into the reactor.
At the end of the reaction, each of the two receivers contains several milliliters of almost pure ethanal. We plug the test tubes with cotton wool and store them in the cold for the next experiments. Long-term storage of ethanal is impractical and dangerous, since it evaporates too easily and, when in a bottle with a ground-in stopper, can forcefully knock out the stopper. Ethanal is sold only in sealed thick-walled glass ampoules.
Experiments with ethanal
In addition to the qualitative reactions described above, we can conduct a number of other experiments with small amounts of ethanal,
In a test tube, carefully add 1 drop of concentrated sulfuric acid to 1-2 ml of ethanal (wearing safety glasses and at a distance from you) using a glass rod. 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 ethanal, does not mix with water and boils only at 124 °C. It is obtained by combining three ethanal molecules to form a ring:
This ethanal polymer 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 a concentrated solution of sodium hydroxide. A yellow “aldehyde resin” is released. It also arises due to the addition 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 ethanal is cold treated with hydrogen chloride gas. Previously, it found some use as a solid fuel ("dry alcohol").
Dilute approximately 0.5 ml of ethanal with 2 ml of water. Add 1 ml of a diluted solution of sodium hydroxide or soda and heat for several minutes. We will smell an exceptionally pungent odor of crotonaldehyde. (Conduct the experiment in a fume hood or in the open air!).
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 eliminating water, the aldol turns into crotonaldehyde:
studopedia.org
Acetaldehyde (other names: acetaldehyde, methyl formaldehyde, ethanal) is an organic compound belonging to the class of aldehydes. This substance is important for humans and is found in coffee, bread, ripe fruits and vegetables. Synthesized by plants. Occurs naturally and is produced in large quantities by humans. Formula of acetaldehyde: CH3-CHO.
Physical properties
1. Acetaldehyde is a colorless liquid with a strong, unpleasant odor.
2. 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. 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.
Preparation of acetaldehyde
1. The main method of obtaining this substance is the oxidation of ethylene (the so-called Wacker process). This is what the reaction looks like:
2CH2 = C2H4 (ethylene) + O2 (oxygen) = 2CH3CHO (methyl formaldehyde)
2. Also, acetaldehyde can 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 above process was introduced. It was carried out by oxidation or dehydrogenation of ethyl alcohol on a silver or copper catalyst.
Applications of acetaldehyde
— To obtain what substances is acetaldehyde needed? Acetic acid, butadiene, aldehyde polymers and some other organic substances.
- Used as a precursor (a substance that participates in a reaction leading to the creation of the target substance) to acetic acid. However, they soon stopped using the substance we are considering in this way. This was because acetic acid was easier and cheaper to produce from methalon using the Kativa and Monsanto processes.
— Methyl formaldehyde 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. A recent demonstration showed that the synergistic relationship of acetic acid with nicotine increases addiction (especially in individuals under thirty years of age).
Alzheimer's disease and acetaldehyde
Those people who do not have the genetic factor for the conversion of methyl formaldehyde 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 methyl formaldehyde
Presumably, the substance we are considering is a carcinogen for humans, since today there is evidence of the carcinogenicity of acetaldehyde in various experiments on animals. In addition, methyl formaldehyde damages DNA, thereby causing development of the muscular system disproportionate to body weight, which is associated with impaired 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, such patients are at greater risk of developing cancer of the kidneys and upper liver.
Safety
This substance is toxic. It is an air pollutant when smoked or from exhaust in traffic jams.
fb.ru
ACETALDEHYDE (acetic aldehyde, ethanal) CH3CHO - colorless liquid with a pungent suffocating odor, b.p. 20.8° C, miscible with water, alcohol, ether in all respects. A. is obtained by hydration of acetylene in the presence of mercury salts (Kucherov’s method), oxidation of ethyl alcohol and other methods. Used to produce acetic acid, butadiene, acetylene, acetal, synthetic resins, etc.
Synthesis was carried out at room temperature using equimolecular amounts of nitromethane and α-naphthaldehyde in an ethanal solution. The resulting 1-(a-naphthyl)-2-nitroethylene did not differ in elemental composition and properties from that synthesized using the described procedure.
Only now, when the installation is charged and assembled, will we begin the experiment. First, let's check the operation of the gas release device 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. Let's stop the gas evolution, turn on the entire cooling system and heat the contents of the reactor to a boil. Since the oxidation of alcohol now releases heat, the burner can be removed. After this, 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 flow slowly 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. Let's select a stopper with two holes for the test tube. Into one of them we will insert a small dropping funnel or just a small funnel with an elongated tube, the exit from which will first be closed using a piece of rubber hose and a clamp. Using the second hole in the stopper, we attach a device for cooling the vapor to the test tube - the same as when producing ethanal (p. 144). The receiver must be cooled with ice and water, because ether already boils at 34.6 °C. Due to its unusually easy flammability, the refrigerator must be as long as possible (at least 80 cm) so that there is sufficient distance between the fire source and the receiver. For the same reason, we will conduct the experiment away from flammable objects, in the open air or in a fume hood. Pour about 5 more 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 ester is used industrially to produce other substances, including ethanal (by acid hydrolysis).
The oxidation of ethanal released 2.7 g of sulfur. Calculate how many liters of acetylene were required to obtain the required mass of ethanal CH3-CH=0 (i.u.).
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 fractions of aldehydes in the mixture,
In these reactions, a carbanion (88), obtained by the action of a base (usually 0H), on the a-H atom of one molecule of a 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 alcohol obtained by the Grignard reaction from ethanal and propylmagnesium bromide.
Acetaldehyde (ethanal) is an intermediate in the biological degradation of carbohydrates (see section 3.8.1). It was first derived in 1782 by Scheele, the structure having been 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 into 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 in an open cup for a while, and then check the reaction with litmus. To obtain table vinegar, they still mainly use acetic acid fermentation of alcohol or low-grade wines (wine vinegar). To do this, the alcohol solution is slowly passed through sawdust from beech wood under intensive air supply. 5% or 10% table vinegar or 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 classified as a poison. You can buy it at a pharmacy or chemical store. Already at 16.6 °C it hardens into a crystalline mass similar to ice. Synthetically, acetic acid is obtained from ethyne through ethanal.
Saturated and monounsaturated five- and six-membered rings can be metalated in the same way as their acyclic counterparts. However, in the case of tetrahydrofuran, heating with n-butyllithium produces a lithium derivative which undergoes cycloreversion to generate ethylene and lithium ethanal enolate. This process seems to be the most convenient method for obtaining such an enolate, but it is necessary to take into account the possibility of such an undesirable side process when carrying out metalation reactions using tetrahydrofuran as a solvent.
Ethanal can be obtained from acetylene as a result
XIII.26. Saturated ketone A with a molecular weight of 100, the NMR spectrum of which consists of only 3, ax singlets at 1.08 and 2.15 ppm, is treated with PCL and then the resulting compound is exposed to potash. This produces compound B, which is then treated with sodium amide in a solution of liquid ammonia and the reaction product is introduced into condensation with ethanal. 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 industrially by adding water to ethyne. In the GDR, at the synthetic butadiene rubber plant in Schkopau, this process is carried out in powerful reactors.
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 important for the production of plastics, synthetic rubber, drugs and solvents. For example, when hydrogen chloride is added to ethyne, vinyl chloride (vinyl chloride) is formed - the starting material for the production of polyvinyl chloride (PVC) and plastics based on it. Ethanal is obtained from ethyne, which we will get to know later, and from it many other products are obtained.
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 industrially by adding water to ethyne. 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 ethylene is introduced into heated dilute sulfuric acid, in which catalysts - mercury salts and other substances - are dissolved. Since mercury salts are very poisonous, we will not synthesize ethanal from ethine ourselves. Let's choose a simpler method - careful oxidation of ethanol.
Acetaldehyde (ethanal), CH3-CHO, was first prepared by Fourcroy 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 received
Acetaldehyde (acetic aldehyde, ethanal) is a lightly boiling liquid with a green leafy odor. In industry, it is obtained from acetylene by the Kucherov reaction (see 38), oxidation of ethyl alcohol, isomerization of ethylene oxide (see Scheme 5). The most modern method of producing 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 starting material in this method is inorganic raw materials - coal and lime.
Ethanal (acetaldehyde) (CH3.CHO). Obtained from the oxidation of ethanol or acetylene. A mobile, colorless liquid with a pungent, fruity odor, caustic, very volatile, flammable, miscible with water, alcohol and ether. It is used in organic synthesis to produce plastics, oil varnishes, or in medicine as an antiseptic.
Acetaldehyde, acetaldehyde, ethanal is an extremely volatile liquid with a boiling point of 20° and a peculiar strong odor. It is 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 diluted (50%) sulfuric acid containing a little mercury sulfate (Kucherov). This method is the main one for obtaining acetaldehyde. During normal fermentation, acetaldehyde is formed as an intermediate product.
See pages where the term is mentioned Ethanal obtaining: Basic principles of organic chemistry volume 1 (1963) - [ p.167, p.264, p.380, p.395, p.453, p.454, p.487]
Basic principles of organic chemistry Volume 1 Edition 6 (1954) - [ p.207, p.226, p.243, p.269, p.339, p.372, p.409, p.410, p.413, c .516 ]
Organic Chemistry Vol. 3 (1980) - [p.79, p.179, p.183]
chem21.info
Acetaldehyde (other names: acetaldehyde, methyl formaldehyde, ethanal) - belonging to the class of aldehydes. This substance is important for humans and is found in coffee, bread, ripe fruits and vegetables. Synthesized by plants. Occurs naturally and is produced in large quantities by humans. Formula of acetaldehyde: CH3-CHO.
Physical properties
1. Acetaldehyde is a colorless liquid with a strong, unpleasant odor.
2. Soluble in ether, alcohol and water.
3. is 44.05 grams/mol.
4. Density is 0.7 grams/centimeter³.
Thermal properties
1. Melting point is -123 degrees.
2. The boiling point is 20 degrees.
3. equal to -39 degrees.
4. Auto-ignition temperature is 185 degrees.
Preparation of acetaldehyde
1. The main method of obtaining this substance is (the so-called Wacker process). This is what the reaction looks like:
2CH2 = C2H4 (ethylene) + O2 (oxygen) = 2CH3CHO (methyl formaldehyde)
2. Also, acetaldehyde can 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 above process was introduced. It was performed by oxidation or dehydrogenation on a silver or copper catalyst.
Applications of acetaldehyde
To obtain what substances is acetaldehyde needed? Acetic acid, butadiene, aldehyde polymers and some other organic substances.
- Used as a precursor (a substance that participates in a reaction leading to the creation of the target substance) to acetic acid. However, they soon stopped using the substance we are considering in this way. This was because acetic acid was easier and cheaper to produce from methalon using the Kativa and Monsanto processes.
- Methyl formaldehyde 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. A recent demonstration showed that the synergistic relationship of acetic acid with nicotine increases addiction (especially in individuals under thirty years of age).
Alzheimer's disease and acetaldehyde
Those people who do not have the genetic factor for the conversion of methyl formaldehyde to acetic acid have a high risk of predisposition to diseases such as Alzheimer's disease, which usually occurs in old age.
Alcohol and methyl formaldehyde
Presumably, the substance we are considering is a carcinogen for humans, since today there is evidence of the carcinogenicity of acetaldehyde in various experiments on animals. In addition, methyl formaldehyde damages DNA, thereby causing development of the muscular system disproportionate to body weight, which is associated with impaired 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, such patients are at greater risk of developing cancer of the kidneys and upper liver.
Safety
This substance is toxic. It is an air pollutant when smoked or from exhaust in traffic jams.
(at 20 °C)
Acetaldehyde (acetaldehyde, ethanal, methyl formaldehyde) is an organic compound of the aldehyde class with the chemical formula CH 3 -CHO. It is one of the most important aldehydes, widely occurring in nature and produced in large quantities industrially. Acetaldehyde is found in coffee, ripe fruits, bread, and is synthesized by plants as a result of their metabolism. Also produced by oxidation of ethanol.
Physical properties
The substance is a colorless liquid with a pungent odor, soluble in water, alcohol, and ether. Due to its very low boiling point (20.2 °C), acetaldehyde is stored and transported in the form of a trimer - paraldehyde, from which it can be obtained by heating with mineral acids (usually sulfuric acid).
Receipt
In 2003, global production was about a million tons per year. The main production method is ethylene oxidation (Wacker process):
As an oxidizing agent, the Wacker process uses palladium chloride, which is regenerated by oxidation with copper chloride in the presence of atmospheric oxygen:
Acetaldehyde is also prepared by hydration of acetylene in the presence of salts (Kucherov reaction), producing enol, which isomerizes to aldehyde:
This method used to dominate until the advent of the Wacker process by oxidation or dehydrogenation of ethyl alcohol, over a copper or silver catalyst.
Reactivity
In terms of its chemical properties, acetaldehyde is a typical aliphatic aldehyde and is characterized by reactions of this class of compounds. Its reactivity is determined by two factors - the activity of the carbonyl of the aldehyde group and the mobility of the hydrogen atoms of the methyl group due to the inductive effect of the carbonyl. Like other carbonyl compounds with hydrogen atoms at the α-carbon atom, acetaldehyde tautomerizes to form enol vinyl alcohol, the equilibrium is almost completely shifted towards the aldehyde form (the equilibrium constant is only 6 10 −5 at room temperature):
Condensation reaction
Due to its small size and availability as an anhydrous monomer (as opposed to formaldehyde), it is a widely used electrophile in organic synthesis. As far as condensation reactions are concerned, the aldehyde is prochiral. Used primarily as a source of the "CH 3 C + H(OH)" synthon in aldol and related condensation reactions. Grignard reagent and organolithium compounds react with MeCHO to form hydroxethyl derivatives. In one very interesting condensation reaction, three equivalents of formaldehyde add and one reduces the resulting aldehyde, forming pentaerythritol (C(CH 2 OH) 4 .) from MeCHO.
The aldol condensation reaction is caused by the mobility of hydrogen in the alpha position in the radical and is carried out in the presence of dilute alkalis. It can be considered as a reaction of nucleophilic addition of one aldehyde molecule to another: CH 3 -CH 2 -CH=O + CH 3 -CH 2 -CH=O → CH 3 -CH 2 -CH(OH)-CH(CH 3)- CH=O +(OH)- The product is 2-methyl-3-hydroxypentanal.
Acetal derivatives
Three molecules of acetaldehyde condense to form “paraldelhyde,” a cyclic trimer containing single C-O bonds. The condensation of four molecules produces a cyclic compound called metaldehyde.
Acetaldehyde forms stable acetals when reacting with ethanol under dehydration conditions. The product CH 3 CH(OCH 2 CH 3) 2 is called an "acetal", although the term is used to describe a broader group of compounds with the general formula RCH(OR") 2.
Application
Acetaldehyde is used to produce acetic acid, butadiene, some organic substances, and aldehyde polymers.
Traditionally, acetaldehyde was mainly used as a precursor to acetic acid. This application was rejected due to the fact that acetic acid is more efficiently produced from methanol using the Monsanto and Kativa processes. In terms of condensation reaction, acetaldehyde is an important precursor to the pyridine derivatives, pentaerythrol and crotonaldehyde. Urea and acetaldehyde condense to form resins. Acetic anhydride reacts with acetaldehyde to give ethylidene diacetate, from which vinyl acetate, the monomer polyvinyl acetate, is obtained.
Biochemistry
Alzheimer's disease
People who lack the genetic factor for the conversion of acetaldehyde to acetic acid may be at greater risk of developing Alzheimer's disease. "These results indicate that the absence of ALDH2 is a risk factor for late-onset Alzheimer's disease."
Alcohol problem
Acetaldehyde, derived from ingested ethanol, binds enzymes to form adducts associated with organ disease. The drug disulfiram (Antabuse) prevents the oxidation of acetaldehyde to acetic acid. This gives an unpleasant feeling when drinking alcohol. Antabuse is used when the alcoholic himself wants to recover.
Carcinogen
Acetaldehyde is a suspected human carcinogen. “There is ample evidence of the carcinogenicity of acetaldehyde (the main metabolite of ethanol) in animal experiments,” in addition, acetaldehyde damages DNA and causes muscle development disproportionate to overall body weight, associated with an imbalance in the body’s protein balance. As a result of a study of 818 alcoholics, scientists concluded that those patients who were exposed to acetaldehyde to a greater extent had a defect in the gene for the enzyme alcohol dehydrogenase. Therefore, such patients are at greater risk of developing cancers of the upper gastrointestinal tract and liver.
Safety
Congenital alcohol intolerance
One of the mechanisms of congenital alcohol intolerance is the accumulation of acetaldehyde.
Notes
- en:Wacker process
- March, J. "Organic Chemistry: Reactions, Mechanisms, and Structures" J. Wiley, New York: 1992. ISBN 0-471-58148-8.
- Sowin, T. J.; Melcher, L. M. "Acetaldehyde" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI:10.1002/047084289
- en: Strecker amino acid synthesis
- Kendall, E. C. McKenzie, B. F. (1941), "dl-Alanine", Org. Synth.; Coll. Vol. 1:21
- Wittig, G.; Hesse, A. (1988), "Directed Aldol Condensations: β-Phenylcinnamaldehyde", Org. Synth.; Coll. Vol. 6:901
- Frank, R. L.; Pilgrim, F. J.; Riener, E. F. (1963), "5-Ethyl-2-Methylpyridine", Org. Synth.; Coll. Vol. 4:451
- Adkins, H.; Nissen, B. H. (1941), "Acetal", Org. Synth.; Coll. Vol. 1:1
- en:Monsanto process
- en:Cativa process
- NAD+ to NADH Hipolito, L.; Sanchez, M. J.; Polache, A.; Granero, L. Brain metabolism of ethanol and alcoholism: An update. Curr. Drug Metab. 2007, 8, 716-727
- Study Points to Acetaldehyde-Nicotine Combination in Adolescent Addiction
- Nicotine’s addictive hold increases when combined with other tobacco smoke chemicals, UCI study finds
- "Mitochondrial ALDH2 Deficiency as an Oxidative Stress." Annals of the New York Academy of Sciences 1011: 36-44. April 2004. doi:10.1196/annals.1293.004. PMID 15126281. Retrieved 2009-08-13.
- Nakamura, K.; Iwahashi, K.; Furukawa, A.; Ameno, K.; Kinoshita, H.; Ijiri, I.; Sekine, Y.; Suzuki, K.; Iwata, Y.; Minabe, Y.; Mori, N. Acetaldehyde adducts in the brain of alcoholics. Arch. Toxicol. 2003, 77, 591.
- Chemical Summary For Acetaldehyde, US Environmental Protection Agency
- DNA and chromosome damage induced by acetaldehyde in human lymphocytes in vitro
- ^ Nicholas S. Aberle, II, Larry Burd, Bonnie H. Zhao and Jun Ren (2004). "Acetaldehyde-induced cardiac contractile dysfunction may be alleviated by vitamin B1 but not by vitamins B6 or B12." Alcohol & Alcoholism 39 (5): 450-454. doi:10.1093/alcalc/agh085.
- Nils Homann, Felix Stickel, Inke R. König, Arne Jacobs, Klaus Junghanns, Monika Benesova, Detlef Schuppan, Susanne Himsel, Ina Zuber-Jerger, Claus Hellerbrand, Dieter Ludwig, Wolfgang H. Caselmann, Helmut K. Seitz Alcohol dehydrogenase 1C* 1 allele is a genetic marker for alcohol-associated cancer in heavy drinkers International Journal of Cancer Volume 118, Issue 8, Pages 1998-2002
- Smoking. (2006). Encyclopædia Britannica. Accessed 27 Oct 2006.
