Accent placement: ALDEHI`DY
ALDEHYDES - a class of organic compounds with general formula
where R is a hydrocarbon radical (residue); in the body they are intermediate products of metabolism.
Individual representatives of aldehydes usually receive their names from the acid formed during their oxidation (for example, acetic acid - acetic acid). Depending on the type of radical, there are saturated, unsaturated, aromatic, cyclic A., etc. If the radical is an alcohol residue, a carboxylic acid, etc., aldehyde alcohols, aldehyde acids and other compounds with mixed functions are formed that have chemical properties. properties inherent in A. and the corresponding R-groups. When replacing hydrogen aldehyde group on a hydrocarbon radical we get ketones(see), giving many reactions similar to A.. One of the simplest A. is acetic, or acetaldehyde CH 3 - CHO, sometimes obtained by dehydrogenation of ethyl alcohol over heated copper.
A common method for obtaining aluminum from hydrocarbons of the acetylene series is by adding water to them in the presence of a catalyst, discovered by M. G. Kucherov:
This reaction is used in the synthetic production of acetic acid. Aromatic hydrocarbons are usually obtained by the oxidation of aromatic hydrocarbons having a side methyl group:
or by the action of carbon monoxide on the corresponding hydrocarbons in the presence of HCl and a catalyst.
Features and chemistry properties A. Associated mainly with the properties and transformations of the aldehyde group. Thus, the simplest of A. is formic, or formaldehyde
the aldehyde group is associated with hydrogen and is a gas; lower A. (eg, acetaldehyde) - liquids with a pungent odor; higher A. - insoluble in water solids.
Due to the presence of a carbonyl group and a mobile hydrogen atom, A. are among the most reactive organic compounds. Most of the versatile reactions of aluminum are characterized by the participation of a carbonyl group. These include oxidation reactions, addition and replacement of oxygen with other atoms and radicals.
A. easily polymerize and condense (see. Aldocondensation); when treating A. with alkalis or acids, aldols are obtained, for example:
When water is eliminated, the aldol turns into crotonaldehyde
capable of further addition of molecules (by polymerization). The polymers obtained as a result of condensation are collectively called aldol resins.
When studying biol. substrates (blood, urine, etc.), the positive effect of reactions based on the oxidation of the aldehyde group is given by the sum of reducing substances. Therefore, these reactions, although they are used for the quantitative determination of sugar (glucose) according to Hagedorn-Jensen, as well as the Nylander, Gaines, Benedict, etc. tests, cannot be considered specific.
A. play an important role in biol. processes, in particular, biogenic amines in the presence of amine oxidase enzymes are converted into amino acids, followed by their oxidation into fatty acids.
A. radicals of higher fatty acids are part of molecules plasmalogens(cm.). Plant organisms in the processes of photosynthesis, formic A is used to assimilate carbon. Produced by plants essential oils consist mainly of cyclic unsaturated amino acids (anise, cinnamon, vanillin, etc.).
During alcoholic fermentation, under the action of the yeast carboxylase enzyme, decarboxylation of pyruvic acid occurs with the formation of acetic acid, which is converted by reduction into ethanol.
A. are widely used in the synthesis of many organic compounds. In honey in practice they are used directly by A. (see Formalin, Paraldehyde, Citral), and synthetic derivatives obtained from A., for example, methenamine (see. Hexamethylenetetramine), chloral hydrate (see), etc.
see also Formic aldehyde. Acetaldehyde.
Aldehydes as an occupational hazard. A. are widely used in the industrial production of synthetic resins and plastics, vanilla dye and textile industries, in Food Industry and perfumes. Formaldehyde is used ch. arr. in the production of plastics and artificial resins, in the leather and fur industry, etc.; acrolein - in all production processes where fats are heated to t° 170° (foundries - drying of oil-fixed rods, electrical industry, oil mills and lard production, etc.). For more details, see articles dedicated to individual A.
All A., especially the lower ones, have a pronounced toxic effect.
A. irritate the mucous membranes of the eyes and upper respiratory tract. By the nature of their general toxic effect, A. are drugs, but their narcotic effect is significantly inferior to the irritating one. The degree of severity of intoxication is determined, along with the magnitude of the effective concentration, also by the nature of the radical and, as a consequence, by a change in physical-chemical. properties of A.: lower A. (highly soluble and highly volatile substances) have a sharp irritating effect on the upper parts of the respiratory organs and a relatively less pronounced narcotic effect; as the length of the hydrocarbon chain of the radical increases, the solubility and volatility of the radical decrease, as a result of which the irritant decreases and the narcotic effect does not increase; the irritating effect of unsaturated A. is stronger than that of limiting ones.
The mechanism of toxic action of A. is associated with the high reactivity of the carbonyl group of A., edges, interacting with tissue proteins, causes a primary irritant effect, reflex reactions c. n. pp., dystrophic changes in internal organs, etc. In addition, when entering the body, A. undergo various biochemical transformations; in this case, the toxic effect on the body is no longer exerted by the amino acids themselves, but by the products of their transformations. A. are slowly excreted from the body and are able to accumulate, which explains the development of hron. poisonings, the main manifestations of which are observed primarily in the form of pathological changes in the respiratory system.
First aid for aldehyde poisoning. Bring the victim to Fresh air. Rinse eyes with 2% alkaline solution. Alkaline and oil inhalations. In case of asphyxia - inhalation of oxygen. According to indications, drugs that stimulate cardiac activity and respiration, sedatives (bromides, valerian). For a painful cough - mustard plasters, cups, codeine preparations. In case of poisoning through the mouth - gastric lavage, orally 3% sodium bicarbonate solution, raw eggs, protein water, milk, saline laxatives. In case of contact with skin, wash with water or 5% ammonia.
See also articles on individual aldehydes.
Prevention. Sealing and automation of production processes. Ventilation of premises (see. Ventilation). Use of personal protective equipment, e.g. filter gas mask grade “A” (see. Gas masks), workwear (see. Cloth) etc.
Maximum permissible concentrations in the atmosphere of industrial premises: for acrolein - 0.7 mg/m 3, for acetaldehyde, butyraldehyde and proponealdehyde - 5 mg/m 3, for formaldehyde and croton A. - 0.5 mg/m 3 .
Determination of aldehydes. All A. are determined in total by the bisulfite method by binding with acidic sodium sulfate or colorimetrically with fuchsulfur dioxide. A polarographic method (Petrova-Yakovtsevskaya) and a spectrophotometric method (Weksler) have been developed.
see also Poisoning, Industrial poisons.
Bibliography: Bauer K. G. Analysis of organic compounds, trans. from German, M., 1953; Nesmeyanov A. N. And Nesmeyanov N. A. The beginnings of organic chemistry, book. 1-2, M., 1969-1970.
Occupational hazards - Amirkhanova G. F. And Latypova Z. V. Experimental justification of the maximum permissible concentration of acetaldehyde in the water of reservoirs, in the book: Prom. polluted reservoirs, ed. S. N. Cherkinsky, V. 9, p. 137, M., 1969, bibliogr.; Bykhovskaya M. S.., Ginzburg S. L. And Khalizova O. D. Methods for determining harmful substances in the air, p. 481, M., 1966; Wang Wen-yan, Materials on the toxicology of fatty aldehydes, in the book: Materials on toxicol. substances used in production. plastic mass and synthetic rubbers, ed. N.V. Lazarev and I.D. Gadaskina, p. 42, L., 1957, bibliogr.; Harmful substances in industry, ed. N.V. Lazareva, vol. 1, p. 375, L., 1971, bibliogr.; Gurvits S. S. And Sergeeva T. I. Determination of small amounts of aldehydes in the air of industrial premises using the method of derivative polarography, Gig. labor and prof. zabolev., No. 9, p. 44, 1960; Trofimov L. V. Comparative toxic effects of croton and butyraldehydes, ibid., No. 9, p. 34, 1962, bibliogr.; Tsai L. M. On the issue of acetaldehyde transformations in the body, ibid., No. 12, p. 33, 1962, bibliogr.; Nine S. N. A. O. Studies on the toxicity of glycid aldehyde, Arch, environm. Hlth, v. 2, p. 23, 1961, bibliogr.; Jung F. u. Onnen K. Bindung und Wirkungen des Formaldehyds an Erythrocyten, Naunyn-Schmiedeberg's Arch. exp. Path. Pharmak., Bd 224, S. 179, 1955; Nova H. a. Touraine R. G. Asthme au formol, Arch. Mai. prof., t. 18, p. 293, 1957; Skоg E. A lexicological investigation of lower aliphatic aldehydes, Actapharmacol. (Kbh.), v. 6, p. 299, 1950, bibliogr.
B.V. Kulibakin; N.K. Kulagina (prof.).
Sources:
- Big medical encyclopedia. Volume 1/Editor-in-Chief Academician B.V. Petrovsky; publishing house "Soviet Encyclopedia"; Moscow, 1974.- 576 p.
Class of organic compounds with general formula
where R is a hydrocarbon radical (residue); in the body they are intermediate products of metabolism.
Individual representatives of aldehydes usually receive their names from the acid formed during their oxidation (for example, acetic acid - acetaldehyde). Depending on the type of radical, saturated, unsaturated, aromatic, cyclic aldehydes and others are distinguished. If the radical is the remainder of an alcohol, carboxylic acid, etc., aldehyde alcohols, aldehyde acids and other compounds with mixed functions are formed, possessing the chemical properties inherent in aldehydes and the corresponding R-groups. When the hydrogen of the aldehyde group is replaced by a hydrocarbon radical, ketones are obtained (see), which give many reactions similar to aldehydes. One of the simplest aldehydes is acetic, or acetaldehyde CH 3 - CHO, sometimes obtained by dehydrogenation of ethyl alcohol over heated copper.
A common method for producing aldehyde from hydrocarbons of the acetylene series by adding water to them in the presence of a catalyst, discovered by M. G. Kucherov:
This reaction is used in the synthetic production of acetic acid. Aromatic aldehydes are usually prepared by the oxidation of aromatic hydrocarbons having a pendant methyl group:
or by the action of carbon monoxide on the corresponding hydrocarbons in the presence of HCl and a catalyst.
Features and chemical properties of aldehydes are associated mainly with the properties and transformations of the aldehyde group. Thus, the simplest of aldehydes is formic, or formaldehyde.
the aldehyde group of which is bonded to hydrogen is a gas; lower aldehydes (for example, acetaldehyde) are liquids with a pungent odor; Higher aldehydes are water-insoluble solids.
Due to the presence of a carbonyl group and a mobile hydrogen atom, aldehydes are among the most reactive organic compounds. Most of the versatile reactions of aldehydes are characterized by the participation of a carbonyl group. These include oxidation reactions, addition and replacement of oxygen with other atoms and radicals.
Aldehydes easily polymerize and condense (see Aldol condensation); When aldehydes are treated with alkalis or acids, aldols are obtained, for example:
When water is eliminated, the aldol turns into crotonaldehyde
capable of further addition of molecules (by polymerization). The polymers obtained as a result of condensation are collectively called aldol resins.
When studying biological substrates (blood, urine, etc.), the positive effect of reactions based on the oxidation of the aldehyde group is achieved by the sum of reducing substances. Therefore, these reactions, although they are used for the quantitative determination of sugar (glucose) according to Hagedorn-Jensen, as well as the Nylander, Gaines, Benedict and others tests, cannot be considered specific.
Aldehydes play an important role in biological processes, in particular, biogenic amines are converted into aldehydes in the presence of amine oxidase enzymes, followed by their oxidation into fatty acids.
Radical aldehydes of higher fatty acids are part of plasmalogen molecules (see). Plant organisms use formic aldehyde during photosynthesis to assimilate carbon. Essential oils produced by plants consist mainly of cyclic unsaturated aldehydes. (anise, cinnamon, vanillin and others).
During alcoholic fermentation, under the action of the yeast carboxylase enzyme, pyruvic acid is decarboxylated to form acetaldehyde, which is converted into ethyl alcohol by reduction.
Aldehydes are widely used in the synthesis of many organic compounds. In medical practice, both aldehydes are used directly (see Formalin, Paraldehyde, Citral), and synthetic derivatives obtained from aldehydes, for example, methenamine (see Hexamethylenetetramine), chloral hydrate (see) and others.
Aldehydes as an occupational hazard
Adeghydes are widely used in the industrial production of synthetic resins and plastics, the vanilla dye and textile industries, the food industry and perfumery. Formaldehyde is mainly used in the production of plastics and artificial resins, in the leather and fur industry and so on; acrolein - in all production processes where fats are heated to t° 170° (foundries - drying of oil-fastened rods, electrical industry, oil mills and lard production, and so on). For more details, see articles devoted to individual aldehydes.
All aldehydes, especially lower ones, have a pronounced toxic effect.
Aldehydes irritate the mucous membranes of the eyes and upper respiratory tract. By the nature of their general toxic effect, aldehydes are drugs, but their narcotic effect is significantly inferior to the irritating one. The degree of severity of intoxication is determined, along with the magnitude of the effective concentration, also by the nature of the radical and, as a consequence, by a change in the physicochemical properties of aldehydes: lower aldehydes (highly soluble and highly volatile substances) have a sharp irritating effect on the upper parts of the respiratory system and a relatively less pronounced narcotic effect; as the length of the hydrocarbon chain of the radical increases, the solubility and volatility of aldehydes decrease, as a result of which the irritating effect decreases and the narcotic effect does not increase; the irritant effect of unsaturated aldehydes is stronger than that of saturated aldehydes.
The mechanism of the toxic action of aldehydes is associated with the high reactivity of the carbonyl group of aldehydes, which, when interacting with tissue proteins, causes the primary irritant effect, reflex reactions of the central nervous system, dystrophic changes in internal organs and so on. In addition, when entering the body, aldehydes undergo various biochemical transformations; in this case, it is not the aldehydes themselves that have a toxic effect on the body, but the products of their transformations. Aldehydes are slowly eliminated from the body and can accumulate, which explains the development of chronic poisoning, the main manifestations of which are observed primarily in the form of pathological changes in the respiratory system.
First aid for aldehyde poisoning. Remove the victim to fresh air. Rinse eyes with 2% alkaline solution. Alkaline and oil inhalations. In case of asphyxia, inhale oxygen. According to indications, drugs that stimulate cardiac activity and respiration, sedatives (bromides, valerian). For a painful cough - mustard plasters, cups, codeine preparations. In case of poisoning through the mouth - gastric lavage, orally 3% sodium bicarbonate solution, raw eggs, protein water, milk, saline laxatives. In case of contact with skin, wash with water or 5% ammonia.
See also articles on individual aldehydes.
Prevention
Sealing and automation of production processes. Ventilation of premises (see Ventilation). The use of personal protective equipment, for example, a filter gas mask of grade “A” (see Gas masks), protective clothing (see Clothing) and so on.
Maximum permissible concentrations in the atmosphere of industrial premises: for acrolein - 0.7 mg/m3, for acetaldehyde, butyraldehyde and propponic aldehyde - 5 mg/m3, for formaldehyde and croton A. - 0.5 mg/m3.
Determination of aldehydes. All aldehydes are determined in total by the bisulfite method by binding with acidic sodium sulfate or colorimetrically with fuchsulfurous acid. A polarographic method (Petrova-Yakovtsevskaya) and a spectrophotometric method (Weksler) have been developed.
Bibliography
Bauer K. G. Analysis of organic compounds, trans. from German, M., 1953; Nesmeyanov A. N. and Nesmeyanov N. A. Beginnings of organic chemistry, book. 1-2, M., 1969-1970.
Occupational hazards- Amirkhanova G.F. and Latypova Z.V. Experimental justification of the maximum permissible concentration of acetaldehyde in the water of reservoirs, in the book: Prom. polluted reservoirs, ed. S. N. Cherkinsky, V. 9, p. 137, M., 1969, bibliogr.; Bykhovskaya M. S., Ginzburg S. L. and Khalizova O. D. Methods for determining harmful substances in the air, p. 481, M., 1966; Wang Wen-yan, Materials on the toxicology of fatty aldehydes, in the book: Materials on toxicol. substances used in production. plastic mass and synthetic rubbers, ed. N.V. Lazarev and I.D. Gadaskina, p. 42, L., 1957, bibliogr.; Harmful substances in industry, ed. N.V. Lazareva, vol. 1, p. 375, L., 1971, bibliogr.; Gurvits S.S. and Sergeeva T.I. Determination of small amounts of aldehydes in the air of industrial premises using the method of derivative polarography, Gig. labor and prof. zabolev., No. 9, p. 44, 1960; Trofimov L.V. Comparative toxic effects of croton and butyraldehydes, ibid., No. 9, p. 34, 1962, bibliogr.; Tsai L.M. On the issue of acetaldehyde transformations in the body, ibid., No. 12, p. 33, 1962, bibliogr.; Nine S. N. a. O. Studies on the toxicity of glycid aldehyde, Arch, environm. Hlth, v. 2, p. 23, 1961, bibliogr.; Jung F. u. Onnen K. Bindung und Wirkungen des Formaldehyds an Erythrocyten, Naunyn-Schmiedeberg's Arch. exp. Path. Pharmak., Bd 224, S. 179, 1955; Nova H. a. Touraine R. G. Asthme au formol, Arch. Mai. prof ., t. 293, 1957; A lexicological investigation of lower aliphatic aldehydes, Actapharmacol., v. 299, 1950, bibliogr.
B.V. Kulibakin; N.K. Kulagina (prof.).
Lecture No. 11
ALDEHYDES AND KETONES
Plan
1. Receipt methods.
2.1. Nucleophilic reactions
accession.
2.2. Reactions by a -carbon atom.
2.3.
Lecture No. 11
ALDEHYDES AND KETONES
Plan
1. Receipt methods.
2. Chemical properties.
2.1. Nucleophilic reactions
accession.
2.2. Reactions by a -carbon atom.
2.3. Oxidation and reduction reactions.
Aldehydes and ketones contain a carbonyl group
C=O. General formula:
1. Methods of obtaining.
2. Chemical
properties.
Aldehydes and ketones are one of the most reactive classes
organic compounds. Their chemical properties are determined by the presence
carbonyl group. Due to the large difference in electronegativity
carbon and oxygen and high polarizability p -bonds The C=O bond has significant polarity
( m C=O =2.5-2.8 D). Carbonyl carbon atom
group carries effective positive charge and is a target for attack
nucleophiles. The main type of reactions of aldehydes and ketones is reactions
nucleophilic addition Ad N. In addition, the carbonyl group affects
reactivity of the C-H bond a -position, increasing its acidity.
Thus, the molecules of aldehydes and ketones
contain two main reaction centers - the C=O bond and C-H connection V a-position:
2.1. Nucleophilic reactions
accession.
Aldehydes and ketones easily add nucleophilic reagents to the C=O bond.
The process begins with an attack by a nucleophile on the carbonyl carbon atom. Then
The tetrahedral intermediate formed in the first stage adds a proton and
gives the addition product:
Activity of carbonyl compounds in
Ad N –reactions depend on the magnitude
effective positive charge on the carbonyl carbon atom and volume
substituents on the carbonyl group. Electron-donating and bulky substituents
complicate the reaction, electron-withdrawing substituents increase the reaction
carbonyl compound ability. Therefore, aldehydes in
Ad N -reactions are more active than
ketones.
The activity of carbonyl compounds increases in
presence of acid catalysts, which increase the positive charge by
carbonyl carbon atom:
Aldehydes and ketones add water, alcohols,
thiols, hydrocyanic acid, sodium hydrosulfite, compounds like
N.H. 2 X. All addition reactions
proceed quickly, under mild conditions, but the resulting products, as a rule,
thermodynamically unstable. Therefore, the reactions proceed reversibly, and the content
addition products in the equilibrium mixture may be low.
Connecting water.
Aldehydes and ketones add water to
formation of hydrates. The reaction is reversible. Forming hydrates
thermodynamically unstable. The balance is shifted towards products
addition only in the case of active carbonyl compounds.
Trichloroacetic aldehyde hydration product
chloral hydrate is a stable crystalline compound that is used in
medicine as a sedative and hypnotic.
Addition of alcohols and
thiols.
Aldehydes combine with alcohols to form hemiacetals. In excess of alcohol and in the presence of an acid catalyst
the reaction goes further - until the formation acetals
The reaction of hemiacetal formation proceeds as
nucleophilic addition and is accelerated in the presence of acids or
grounds.
The process of acetal formation goes like this:
nucleophilic substitution of the OH group in the hemiacetal and is possible only under conditions
acid catalysis, when the OH group is converted into a good leaving group
(H 2 O).
The formation of acetals is a reversible process. IN
In an acidic environment, hemiacetals and acetals are easily hydrolyzed. In an alkaline environment
hydrolysis does not occur. The formation and hydrolysis reactions of acetals play an important role in
chemistry of carbohydrates.
Ketones under similar conditions do not
give.
Thiols are stronger nucleophiles than alcohols
form addition products with both aldehydes and ketones.
Joining hydrocyanic
acids
Hydrocyanic acid adds to a carbonyl compound under conditions
basic catalysis to form cyanohydrins.
The reaction has preparative value and
used in synthesis a-hydroxy- and a -amino acids (see lecture No. 14). Fruits of some plants
(eg bitter almonds) contain cyanohydrins. Stands out when they
hydrocyanic acid has a poisonous effect when broken down.
Bisulfite addition
sodium.
Aldehydes and methyl ketones add sodium bisulfite NaHSO 3 with the formation of bisulfite derivatives.
Bisulfite derivatives of carbonyl compounds
– crystalline substances that are insoluble in excess sodium bisulfite solution.
The reaction is used to isolate carbonyl compounds from mixtures. Carbonyl
the compound can be easily regenerated by treating the bisulfite derivative
acid or alkali.
Interaction with common connections
formula NH 2 X
Reactions proceed according to general scheme as a process
attachment-elimination. The adduct formed at the first stage is not
stable and easily removes water.
According to the given scheme with carbonyl
compounds react with ammonia, primary amines, hydrazine, substituted hydrazines,
hydroxylamine.
The resulting derivatives are
crystalline substances that are used for isolation and identification
carbonyl compounds.
Imines (Schiff bases) are intermediate
products in many enzymatic processes (transamination under the influence
coenzyme pyridoxal phosphate; reductive amination of keto acids at
participation of the coenzyme NADN). The catalytic hydrogenation of imines produces
amines. The process is used to synthesize amines from aldehydes and ketones and
called reductive amination.
Reductive amination occurs in vivo
during the synthesis of amino acids (see lecture No. 16)
2.2. Reactions by a -carbon atom.
Keto-enol tautomerism.
Hydrogen in a -position to the carbonyl group is acidic
properties, since the anion formed during its elimination is stabilized by
resonance account.
The result of the proton mobility of the hydrogen atom
V a -position
is the ability of carbonyl compounds to form enol forms due to
proton migration from a -position to the oxygen atom of the carbonyl group.
Ketone and enol are tautomers.
Tautomers are isomers that can quickly and reversibly convert into each other
due to the migration of a group (in this case, a proton). Equilibrium between
ketone and enol are called keto-enol tautomerism.
The enolization process is catalyzed by acids and
reasons. Enolization under the influence of a base can be represented by
with the following diagram:
Most carbonyl compounds exist
predominantly in ketone form. The content of the enol form increases with
an increase in the acidity of the carbonyl compound, as well as in the case of
additional stabilization of the enol form due to hydrogen bonding or due to
pairing.
Table 8. Content of enol forms and
acidity of carbonyl compounds
For example, in 1,3-dicarbonyl compounds
the mobility of the protons of the methylene group increases sharply due to
electron-withdrawing effect of two carbonyl groups. In addition, enol
the form is stabilized due to the presence in it of a system of conjugate p -bonds and intramolecular
hydrogen bond.
If a compound in enol form is
is a conjugated system with high stabilization energy, then the enol form
prevails. For example, phenol exists only in the enol form.
Enolization and formation of enolate anions are
the first stages of reactions of carbonyl compounds that occur through a -carbon atom. The most important
of which are halogenation And aldolic-crotonic
condensation
.
Halogenation.
Aldehydes and ketones easily react with halogens (Cl2,
Br 2, I 2 ) with education
exclusively a -halogen derivatives.
The reaction is catalyzed by acids or
reasons. The reaction rate does not depend on the concentration and nature of the halogen.
The process proceeds through the formation of the enol form (slow stage), which
then reacts with halogen (fast step). Therefore, the halogen is not
involved in speed—defining stage
process.
If a carbonyl compound contains several a -hydrogen
atoms, then the replacement of each subsequent one occurs faster than the previous one,
due to an increase in their acidity under the influence of electron-withdrawing influence
halogen. In an alkaline environment, acetaldehyde and methyl ketones give
trihalogen derivatives, which are then decomposed by excess alkali with
formation of trihalomethanes ( haloform reaction)
.
The breakdown of triiodoacetone occurs as a reaction
nucleophilic substitution. CI groups 3 — hydroxide anion, like S N -reactions in the carboxyl group (see lecture No. 12).
Iodoform precipitates from the reaction mixture in the form
pale yellow crystalline sediment with a characteristic odor. Iodoform
the reaction is used for analytical purposes to detect compounds of the type
CH 3 -CO-R, including
clinical laboratories for the diagnosis of diabetes mellitus.
Condensation reactions.
In the presence of catalytic amounts of acids
or alkalis carbonyl compounds containing a -hydrogen atoms,
undergo condensation to form b -hydroxycarbonyl compounds.
In education S-S connections carbonyl involved
carbon atom of one molecule ( carbonyl component) And a -carbon atom is different
molecules ( methylene component). This reaction is called aldol condensation(by the name of the condensation product of acetaldehyde -
aldol).
When the reaction mixture is heated, the product easily
dehydrates to form a ,b -unsaturated carbonyl
connections.
This type of condensation is called croton(by the name of the condensation product of acetaldehyde - croton
aldehyde).
Let us consider the mechanism of aldol condensation in
alkaline environment. In the first stage, the hydroxide anion abstracts a proton from a -carbonyl position
compounds to form an enolate anion. Then the enolate anion as a nucleophile
attacks the carbonyl carbon atom of another carbonyl compound molecule.
The resulting tetrahedral intermediate (alkoxide anion) is strong
base and further abstracts a proton from a water molecule.
During aldol condensation of two different
carbonyl compounds (cross-aldol condensation) possible
formation of 4 different products. However, this can be avoided if one of the
does not contain carbonyl compounds a -hydrogen atoms (for example, aromatic aldehydes
or formaldehyde) and cannot act as a methylene component.
As a methylene component in reactions
condensation can be not only carbonyl compounds, but also other
C-H-acids. Condensation reactions have preparative value, since they allow
extend the chain of carbon atoms. According to the type of aldol condensation and
retroaldol decomposition (reverse process) many biochemical reactions occur
processes: glycolysis, synthesis citric acid in the Krebs cycle, synthesis of neuramine
acids.
2.3. Oxidation reactions and
recovery
Recovery
Carbonyl compounds are reduced to
alcohols as a result of catalytic hydrogenation or under the influence
reducing agents that are donors of hydride anions.
[H]: H 2 /cat., cat. – Ni, Pt,
Pd;
LiAlH4; NaBH4.
Reduction of carbonyl compounds
complex metal hydrides involves nucleophilic attack of the carbonyl group
hydride anion. Subsequent hydrolysis produces alcohol.
Recovery occurs in the same way
carbonyl group in vivo under the influence of the coenzyme NADN, which is
donor of hydride ion (see lecture No. 19).
Oxidation
Aldehydes oxidize very easily
any oxidizing agents, even such weak ones as air oxygen and compounds
silver(I) and copper(II).
The last two reactions are used as
qualitative for the aldehyde group.
In the presence of alkalis, aldehydes that do not contain a -hydrogen atoms
disproportionate to form alcohol and acid (Cannizzaro reaction).
2HCHO + NaOH ® HCOONa + CH 3 OH
This is the reason that the aqueous solution
formaldehyde (formalin) with long-term storage becomes sour
reaction.
Ketones are resistant to oxidizing agents in
neutral environment. In acidic and alkaline environments under the influence of strong
oxidizing agents(KMnO 4 ) They
oxidize by breaking the C-C bond. The carbon skeleton is broken down by
carbon-carbon double bond of enol forms of a carbonyl compound, similar to
oxidation of double bonds in alkenes. This creates mixture of products,
containing carboxylic acids or carboxylic acids and ketones.
Structure of aldehydes and ketones
Aldehydes- organic substances whose molecules contain carbonyl group:
connected to a hydrogen atom and a hydrocarbon radical. The general formula of aldehydes is:
In the simplest aldehyde, another hydrogen atom plays the role of a hydrocarbon radical:
Formaldehyde A carbonyl group bonded to a hydrogen atom is often called aldehydic:
Ketones are organic substances in whose molecules a carbonyl group is linked to two hydrocarbon radicals. Obviously, the general formula for ketones is:
The carbonyl group of ketones is called keto group.
In the simplest ketone, acetone, the carbonyl group is linked to two methyl radicals:
Nomenclature and isomerism of aldehydes and ketones
Depending on the structure of the hydrocarbon radical associated with the aldehyde group, there are saturated, unsaturated, aromatic, heterocyclic and other aldehydes:
In accordance with the IUPAC nomenclature, the names of saturated aldehydes are formed from the name of an alkane with the same number of carbon atoms per molecule using a suffix -al. For example:
Numbering Main chain carbon atoms begin with the carbon atom of the aldehyde group. Therefore, the aldehyde group is always located at the first carbon atom, and there is no need to indicate its position.
Along with systematic nomenclature, trivial names of widely used aldehydes are also used. These names are usually derived from the names of carboxylic acids corresponding to aldehydes.
For the title ketones according to systematic nomenclature, the keto group is designated by the suffix -He and a number that indicates the number of the carbon atom of the carbonyl group (numbering should start from the end of the chain closest to the keto group).
For example:
For aldehydes There is only one type of structural isomerism - carbon skeleton isomerism, which is possible with butanal, and for ketones- also isomerism of carbonyl group position. In addition, they are also characterized interclass isomerism(propanal and propanone).
Physical properties of aldehydes and ketones
In an aldehyde or ketone molecule, due to the greater electronegativity of the oxygen atom compared to the carbon atom, the bond C=O is highly polarized due to a shift in the electron density of the π bond to oxygen:
Aldehydes and ketones - polar substances with excess electron density on the oxygen atom. The lower members of the series of aldehydes and ketones (formaldehyde, acetaldehyde, acetone) are unlimitedly soluble in water. Their boiling points are lower than those of the corresponding alcohols. This is due to the fact that in the molecules of aldehydes and ketones, unlike alcohols, there are no mobile hydrogen atoms and they do not form associates due to hydrogen bonds.
Lower aldehydes have a pungent odor; aldehydes containing four to six carbon atoms in the chain have an unpleasant odor; Higher aldehydes and ketones have floral odors and are used in perfumery.
The presence of an aldehyde group in a molecule determines the characteristic properties of aldehydes.
Recovery reactions.
1. Hydrogen addition to aldehyde molecules occurs via a double bond in the carbonyl group:
The product of hydrogenation of aldehydes is primary alcohols, ketones are secondary alcohols.
Thus, when hydrogenating acetaldehyde on a nickel catalyst, ethyl alcohol is formed, and when hydrogenating acetone, 2-propanol is formed.
2. Hydrogenation of aldehydes- a reduction reaction in which the oxidation state of the carbon atom included in the carbonyl group decreases.
Oxidation reactions.
Aldehydes can not only be reduced, but also oxidized. When oxidized, aldehydes form carboxylic acids. This process can be schematically represented as follows:
1. Oxidation by air oxygen. For example, propionic acid is formed from propionic aldehyde (propanal):
2. Oxidation with weak oxidizing agents(ammonia solution of silver oxide). In a simplified form, this process can be expressed by the reaction equation:
For example:
This process is more accurately reflected by the equations:
If the surface of the vessel in which the reaction is carried out was previously degreased, then the silver formed during the reaction covers it smoothly. thin film. Therefore, this reaction is called the “silver mirror” reaction. It is widely used for making mirrors, silvering decorations and Christmas tree decorations.
3. Oxidation with freshly precipitated copper(II) hydroxide. By oxidizing the aldehyde, Cu 2+ is reduced to Cu +. The copper (I) hydroxide CuOH formed during the reaction immediately decomposes into red copper (I) oxide and water.
This reaction, just like the reaction " silver mirror", is used for the detection of aldehydes.
Ketones are not oxidized either by atmospheric oxygen or by such a weak oxidizing agent as ammonia solution silver oxide.
Chemical properties of aldehydes and acids - summary
Individual representatives of aldehydes and their significance
Formaldehyde(methanal, formic aldehyde HCHO) is a colorless gas with a pungent odor and a boiling point of -21 ° C, highly soluble in water. Formaldehyde is poisonous! A solution of formaldehyde in water (40%) is called formaldehyde and is used for formaldehyde and vinegar disinfection. IN agriculture Formalin is used to treat seeds and in the leather industry to treat leather. Formaldehyde is used to produce methenamine- medicinal substance. Sometimes methenamine compressed in the form of briquettes is used as fuel (dry alcohol). A large amount of formaldehyde is consumed in the production of phenol-formaldehyde resins and some other substances.
Acetaldehyde(ethanal, acetaldehyde CH 3 CHO) - a liquid with a pungent, unpleasant odor and a boiling point of 21 ° C, highly soluble in water. Acetic acid and a number of other substances are produced from acetaldehyde on an industrial scale; it is used for the production of various plastics and acetate fiber. Acetaldehyde is poisonous!
Group of atoms -
Called carboxyl group, or carboxyl.
Organic acids containing one carboxyl group in the molecule are monobasic.
The general formula of these acids is RCOOH, for example:
Carboxylic acids containing two carboxyl groups are called dibasic. These include, for example, oxalic and succinic acids:
There are also polybasic carboxylic acids containing more than two carboxyl groups. These include, for example, tribasic citric acid:
Depending on the nature of the hydrocarbon radical, carboxylic acids are divided into saturated, unsaturated, aromatic.
Limit, or saturated, carboxylic acids are, for example, propanoic (propionic) acid:
or the already familiar succinic acid.
It is obvious that saturated carboxylic acids do not contain π bonds in the hydrocarbon radical.
In molecules of unsaturated carboxylic acids, the carboxyl group is associated with an unsaturated, unsaturated hydrocarbon radical, for example, in acrylic (propene) molecules
CH 2 =CH-COOH
or oleic
CH 3 -(CH 2) 7 -CH=CH-(CH 2) 7 -COOH
and other acids.
As can be seen from the formula of benzoic acid, it is aromatic, since it contains an aromatic (benzene) ring in the molecule:
The name of a carboxylic acid is derived from the name of the corresponding alkane (alkane with the same number of carbon atoms in the molecule) with the addition of the suffix -s— , endings -and I and words acid. Numbering of carbon atoms starts with a carboxyl group. For example:
The number of carboxyl groups is indicated in the name by prefixes di-, tri-, tetra-:
Many acids also have historically established, or trivial, names.
The composition of saturated monobasic carboxylic acids will be expressed by the general formula C n H 2n O 2, or C n H 2n+1 COOH, or RCOOH.
Physical properties of carboxylic acids
Lower acids, i.e. acids with a relatively small molecular weight containing up to four carbon atoms per molecule, are liquids with a characteristic pungent odor (for example, the smell of acetic acid). Acids containing from 4 to 9 carbon atoms are viscous oily liquids with an unpleasant odor; containing more than 9 carbon atoms per molecule - solids that do not dissolve in water. The boiling points of saturated monobasic carboxylic acids increase with increasing number of carbon atoms in the molecule and, consequently, with increasing relative molecular weight. Thus, the boiling point of formic acid is 100.8 °C, acetic acid is 118 °C, and propionic acid is 141 °C.
The simplest carboxylic acid is formic HCOOH, having a small relative molecular weight (M r (HCOOH) = 46), under normal conditions it is a liquid with a boiling point of 100.8 ° C. At the same time, butane (M r (C 4 H 10) = 58) under the same conditions is gaseous and has a boiling point of -0.5 ° C. This is a discrepancy between boiling temperatures and relative molecular weights explained formation of carboxylic acid dimers, in which two acid molecules are linked by two hydrogen bonds:
The occurrence of hydrogen bonds becomes clear when considering the structure of carboxylic acid molecules.
Molecules of saturated monobasic carboxylic acids contain a polar group of atoms - carboxyl
And practically nonpolar hydrocarbon radical. The carboxyl group is attracted to water molecules, forming hydrogen bonds with them:
Formic and acetic acids are unlimitedly soluble in water. It is obvious that with an increase in the number of atoms in a hydrocarbon radical, the solubility of carboxylic acids decreases.
Chemical properties of carboxylic acids
The general properties characteristic of the class of acids (both organic and inorganic) are due to the presence in the molecules of a hydroxyl group containing a strong polar connection between hydrogen and oxygen atoms. Let us consider these properties using the example of water-soluble organic acids.
1. Dissociation with the formation of hydrogen cations and anions of the acid residue:
More precisely, this process is described by an equation that takes into account the participation of water molecules in it:
The dissociation equilibrium of carboxylic acids is shifted to the left; the vast majority of them are weak electrolytes. However, the sour taste of, for example, acetic and formic acids is due to dissociation into hydrogen cations and anions of acidic residues.
It is obvious that the presence of “acidic” hydrogen in the molecules of carboxylic acids, i.e., the hydrogen of the carboxyl group, also determines other characteristic properties.
2. Interaction with metals, standing in the electrochemical voltage series up to hydrogen:
Thus, iron reduces hydrogen from acetic acid:
3. Interaction with basic oxides with the formation of salt and water:
4. Interaction with metal hydroxides with the formation of salt and water (neutralization reaction):
5. Interaction with salts of weaker acids with the formation of the latter. Thus, acetic acid displaces stearic acid from sodium stearate and carbonic acid from potassium carbonate:
6. Interaction of carboxylic acids with alcohols with the formation of esters - esterification reaction (one of the most important reactions characteristic of carboxylic acids):
The interaction of carboxylic acids with alcohols is catalyzed by hydrogen cations.
The esterification reaction is reversible. The equilibrium shifts toward ester formation in the presence of dewatering agents and when the ester is removed from the reaction mixture.
In the reverse reaction of esterification, called ester hydrolysis (the reaction of an ester with water), an acid and an alcohol are formed:
It is obvious that polyhydric alcohols, for example glycerol, can also react with carboxylic acids, i.e., enter into an esterification reaction:
All carboxylic acids (except formic acid), along with the carboxyl group, contain a hydrocarbon residue in their molecules. Of course, this cannot but affect the properties of acids, which are determined by the nature of the hydrocarbon residue.
7. Addition reactions at multiple bonds- they contain unsaturated carboxylic acids. For example, the reaction of hydrogen addition is hydrogenation. For an acid containing one n-bond in the radical, the equation can be written in general form:
Thus, when oleic acid is hydrogenated, saturated stearic acid is formed:
Unsaturated carboxylic acids, like other unsaturated compounds, add halogens via a double bond. For example, acrylic acid decolorizes bromine water:
8. Substitution reactions (with halogens)- saturated carboxylic acids are capable of entering into them. For example, by reacting acetic acid with chlorine, various chlorinated acids can be obtained:
Chemical properties of carboxylic acids - summary
Individual representatives of carboxylic acids and their significance
Formic (methanoic) acid HCOOH- a liquid with a pungent odor and a boiling point of 100.8 °C, highly soluble in water.
Formic acid is poisonous and causes burns if it comes into contact with the skin! The stinging fluid secreted by ants contains this acid.
Formic acid has disinfectant properties and therefore finds its use in the food, leather and pharmaceutical industries, and medicine. It is used in dyeing fabrics and paper.
Acetic (ethanoic) acid CH 3 COOH- a colorless liquid with a characteristic pungent odor, miscible with water in any ratio. Aqueous solutions of acetic acid are marketed under the name vinegar (3-5% solution) and acetic essence (70-80% solution) and are widely used in the food industry. Acetic acid is a good solvent for many organic substances and is therefore used in dyeing, tanning, and the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, substances used to control weeds - herbicides - are obtained from it. Acetic acid is the main component of wine vinegar, the characteristic smell of which is due to it. It is a product of ethanol oxidation and is formed from it when wine is stored in air.
The most important representatives of higher saturated monobasic acids are palmitic C 15 H 31 COOH and stearic C 17 H 35 COOH acids. Unlike lower acids, these substances are solid and poorly soluble in water.
However, their salts - stearates and palmitates - are highly soluble and have a detergent effect, which is why they are also called soaps. It is clear that these substances are produced on a large scale.
Of the unsaturated higher carboxylic acids, the most important is oleic acid C 17 H 33 COOH, or CH 3 - (CH 2) 7 - CH = CH - (CH 2) 7 COOH. It is an oil-like liquid without taste or odor. Its salts are widely used in technology.
The simplest representative of dibasic carboxylic acids is oxalic (ethanedioic) acid HOOC-COOH, the salts of which are found in many plants, such as sorrel and sorrel. Oxalic acid is a colorless crystalline substance, dissolves well in water. It is used in metal polishing, woodworking and leather industries.
Reference material for taking the test:
Mendeleev table
Solubility table