OXYGEN-CONTAINING COMPOUNDS
CARBONYL COMPOUNDS
ALDEHYDE AND
Organic compounds whose molecules contain a carbonyl groupare called carbonyl compounds. Depending on the nature of the substituents associated with the carbonyl group, carbonyl compounds are divided into aldehydes, ketones, carboxylic acids and their functional derivatives.
ALDEHYDES
Aldehydes are organic compounds containing a carbonyl group in which a carbon atom is bonded to a radical and one hydrogen atom, that is, the general formula of aldehydes. An exception is formic aldehyde., in which, as can be seen,R= H.
isomerism
Aldehydes are characterized by isomerism of the hydrocarbon radical, which can have both a normal (unbranched) chain and a branched one, as well as interclass isomerism with ketones. For instance ,
|
O |
O |
O |
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|
butyric aldehyde |
isobutyric |
methyl ethyl ketone or |
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Receipt
1.
The most commonly used methods for obtaining aldehydes are the oxidation and catalytic dehydrogenation of primary alcohols.
a) Oxidation of primary alcohols.
As can be seen, acids are formed upon further oxidation. These reactions were already given when considering the chemical properties of alcohols.
b) Dehydrogenation of primary alcohols. The reaction is carried out by passing alcohol vapor over heated to 200-300° With a catalyst, which uses copper, nickel, cobalt, etc.
2. A method has been developed for the production of acetaldehyde by the oxidation of ethylene with atmospheric oxygen in the presence of copper and palladium salts.
3. Acetic aldehyde is obtained by hydration of acetylene according to the Kucherov reaction.
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O |
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HC º CH + H 2 O –– HgSO 4 ® –– ® CH 3 –C |
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I |
The Kucherov reaction has already been considered in detail when studying the chemical properties of acetylenic hydrocarbons.
4. Aldehydes are obtained by hydrolysis of dihalogen derivatives of hydrocarbons, but only those in which both halogen atoms are located at one of the terminal carbon atoms.
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CH 3 -CH 2 - |
2H 2 O ® + 2 HCl |
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1,1-dichloropropane |
1,1-propanediol |
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Under the action of water on a dihaloalkyl in an alkaline or acidic medium, the reaction of its hydrolysis goes through the stage of formation of a dihydric alcohol containing two hydroxyl groups at one carbon atom.
Such alcohols, due to their instability at the time of formation, lose water and form aldehydes.
Physical Properties
The simplest aldehyde formic - a gas with a very pungent odor. Other lower aldehydes are liquids that are readily soluble in water. Aldehydes have a suffocating odor, which, with repeated dilution, becomes pleasant, reminiscent of the smell of fruits. Aldehydes boil at a lower temperature than alcohols with the same number of carbon atoms. This c due to the absence of hydrogen bonds in aldehydes. At the same time, the boiling point of aldehydes is higher than that of hydrocarbons corresponding in molecular weight, which is associated with the high polarity of aldehydes.
The physical properties of some aldehydes are presented in the table.
table . Physical properties of some aldehydes
|
Name |
Formula |
t ° boiling, |
t ° square, |
d4 20 |
|
Formic |
O |
92,0 |
21,0 |
0,815 |
|
Acetic |
O |
123,5 |
21,0 |
0,780 |
|
propionic |
O |
102,0 |
48,8 |
0,807 |
|
Oil |
O |
99,0 |
75,7 |
0,817 |
|
isobutyric |
O |
65,9 |
64,0 |
0,794 |
Chemical properties
Aldehydes are characterized by high reactivity. Most of their reactions are due to the presence of a carbonyl group. The carbon atom in the carbonyl group is in the state sp2- hybridization and forms three s - connections (one of them is connection C–O ), which are located in the same plane at an angle of 120° to each other.
Scheme of the structure of the carbonyl group
The double bond of the carbonyl group is similar in physical nature to the double bond between carbon atoms, i.e. this combination s- and p - bonds, the last of which is formed by p-electrons of carbon and oxygen atoms. Due to the greater electronegativity of the oxygen atom compared to the carbon atom, the bond C=O strongly polarized due to electron density shift p - bonds to the oxygen atom, as a result of which a partial negative ( d-) , and on the carbon atom - partial positive ( d + ) charges: .
Due to polarization, the carbon atom of the carbonyl group has electrophilic properties and is able to react with nucleophilic reagents. The most important reactions of aldehydes are nucleophilic addition reactions at the double bond of the carbonyl group.
1. One of the typical nucleophilic addition reactions of aldehydesis an addition of hydrocyanic (hydrocyanic) acid leading to the formation a - oxynitriles.
This reaction is used to extend the carbon chain and produce a - hydroxy acids.
2.
Addition of sodium hydrosulfitegives crystalline substances commonly referred to as hydrosulfite derivatives of aldehydes.
The mentioned derivatives are easily hydrolyzed in any environment, leading to the original carbonyl compound. So, when heated with a solution of soda, a hydrosulfite derivative of acetaldehyde, acetaldehyde itself is formed.
This property is used to purify aldehydes and isolate them from mixtures.
3.
Addition of alcoholsto aldehydes leads to the formation of hemiacetals - compounds,in which the carbon atom is bonded to both hydroxyl (–OH) and alkoxy (–O R ) groups.
When hemiacetals are treated with an excess of alcohol in an acidic medium, acetals are formed - compounds in which the carbon atom is bonded to two alkoxy groups (the reaction resembles the synthesis of ethers from alcohols).
Unlike ethers, acetals are hydrolyzed by acids to form an alcohol and an aldehyde.
4. Addition of hydrogento aldehydes is carried out in the presence of catalysts ( Ni, Co, Pd etc.) and leads to the formation of primary alcohols.
Lithium aluminum hydride is increasingly being used as a reducing agent. LiAlH 4 and sodium borohydride NaBH4.
In addition to addition reactions at the carbonyl group, aldehydes are also characterized by oxidation reactions.
5. Oxidation . Aldehydes are easily oxidized to form the corresponding carboxylic acids.
a) ammonia solution of silver oxide[ Ag (NH 3 ) 2 ] OH when heated with aldehydes, it oxidizes the aldehyde to an acid (in the form of its ammonium salt) with the formation of free metallic silver. The reduced silver is deposited in a thin layer on the walls of the chemical vessel in which the reaction takes place, and a silver mirror is obtained. This reaction, which is therefore called the "silver mirror", serves as a qualitative reaction to aldehydes.
b) another characteristic reaction is the oxidation of aldehydes with copper hydroxide ( II).
When blue copper hydroxide is heated ( II ) with a solution of acetaldehyde, a red precipitate of copper oxide ( I ). In this case, acetaldehyde is oxidized to acetic acid, and copper with an oxidation state of +2 is reduced to copper with an oxidation state of +1. Formic aldehyde (formaldehyde) occupies a special place among the aldehydes. Due to the absence of formic aldehyde radical, it has some specific properties. Oxidation of formaldehyde, for example, is carried out to carbon dioxide CO 2 .
Formaldehyde readily polymerizes to form cyclic and linear polymers. So, in an acidic environment, it forms a cyclic trimer - trioxymethylene.
Dry gaseous formaldehyde in the presence of catalysts forms high molecular weight polyformaldehyde. The polymerization of formaldehyde resembles the polymerization of alkenes.
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O –– kat® |
H |
H |
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…–H 2 C–O (H 2 C–O) n H 2 C–O–… |
In aqueous solutions, formaldehyde forms a polymer called paraform.
n CH 2 \u003d O + H 2 O ® HOCH 2 ( OCH 2 ) n-2 OCH 2 OH
(paraform)
Of particular practical importance is the polycondensation reaction of formaldehyde with phenol to form phenol-formaldehyde resins. Under the action of alkaline or acidic catalysts on a mixture of phenol and formaldehyde, condensation occurs in the ortho and para positions.
The growth of the molecule due to the condensation of phenol with formaldehyde is carried out at normal temperature in a linear direction.
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CH2OH |
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etc.
In total, the polycondensation reaction of phenol with formaldehyde can be represented as follows:
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O+(n+1) |
catalyst |
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NH2O |
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–––––––– ® |
Phenol-formaldehyde resins are the first industrial synthetic resins, their production under the name "Bakelite" was first started in 1909. Phenol-formaldehyde resins are used in the production of various plastics. In combination with various fillers, such plastics are called phenolics. In addition, phenol-formaldehyde resins are used in the manufacture of various adhesives and varnishes, thermal insulation materials, wood plastics, molds, etc.
Application
Much has already been said about the use of formaldehyde. In addition, it is used to obtain carbamide resins by interaction with urea, on the basis of which plastics are produced, which are necessary for the needs of electrical engineering. Solutions of formaldehyde (formalin) are used in the leather industry for tanning leather, for disinfecting grain and vegetable stores, greenhouses, hotbeds, for dressing seeds before sowing, for storing anatomical preparations, and also in the production of certain drugs.
Acetic aldehyde is the feedstock for the production of acetic acid, acetic anhydride, ethyl alcohol, ethyl acetate and other valuable products on an industrial scale, and various synthetic resins when condensed with amines and phenols.
KETONES
Ketones are compounds in which the carbonyl group is bonded to two hydrocarbon radicals. General formula of ketones, where R may match with R".
isomerism
Ketones are characterized by isomerism of hydrocarbon radicals, isomerism of the position of the carbonyl group, and interclass isomerism with aldehydes.
Receipt
Almost all the preparation methods given earlier for aldehydes (see "") are also applicable to ketones.
1. Oxidation of secondary alcohols.
2. Dehydrogenation of secondary alcohols.
3. Hydration of acetylene homologues (Kucherov reaction).
4. Hydrolysis of dihalogenated hydrocarbonscontaining both halogen atoms at one of the middle carbon atoms in the chain.
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CH 3 - |
Cl |
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CH 3 - |
O |
5.
Ketones are also obtained by pyrolysis of calcium salts of carboxylic acids when they are heated.O
II
CH 3 -C
I
O
Physical Properties
Lower ketones are liquids that are easily soluble in water. In general, ketones have a pleasant smell, reminiscent of the smell of flowers. Like aldehydes, ketones boil at a lower temperature than the corresponding alcohols, but higher than hydrocarbons. The physical properties of some ketones are presented in the table.
Table. Physical properties of some ketones
|
Name |
Formula |
t ° square, |
t ° boiling, |
d4 20 |
|
Acetone (dimethyl ketone) 42,0 |
102,7 |
0,816 |
Chemical properties
Like aldehydes, ketones are highly reactive. The chemical activity of aldehydes and ketones is the higher, the greater the positive charge on the carbon atom of the carbonyl group. Radicals that increase this positive charge sharply increase the reactivity of aldehydes and ketones, while radicals that reduce the positive charge have the opposite effect. In ketones, two alkyl groups are electron-donating, which makes it clear why ketones are less active in nucleophilic addition reactions compared to aldehydes.
Examples of reactions of this type for aldehydes were considered in detail earlier (see ""), therefore, giving some examples of nucleophilic addition reactions at the carbonyl group of ketones, we will pay attention only to the differences in their chemical properties from aldehydes.
1. Accession of hydrocyanic acid.
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R |
Oh |
It should be noted that only methyl ketones react with sodium hydrosulfite, i.e. ketones having the grouping CH3.
3.
Compared to aldehydes, ketones do not react with alcohols.
4. Addition of hydrogen. The addition of hydrogen to ketones leads to the formation of secondary alcohols.
5. Ketones are much more difficult to oxidize than aldehydes. Air oxygen and weak oxidizing agents do not oxidize ketones. Ketones do not give a "silver mirror" reaction and do not react with copper hydroxide ( II ). Under the action of strong oxidizing agents under harsh conditions, the carbon chain of the ketone molecule is destroyed near the carbonyl group and acids (sometimes ketones, depending on the structure of the original ketone) are formed with a smaller number of carbon atoms.
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Application
Acetone, the simplest representative of ketones, has the widest industrial application. Acetone is a valuable solvent used in the paint and varnish industry, in the production of rayon, film, and smokeless powder. It also serves as a feedstock in the production of methacrylic acid, methyl methacrylate (production of unbreakable organic glass), methyl isobutyl ketone, etc.
END OF SECTION
Aldehydes and ketones are characterized by the presence of a carbonyl group in the molecule. In aldehydes, the carbonyl group is bonded to one hydrogen atom and one hydrocarbon radical. All aldehydes contain a group
called the aldehyde group.
General formula of aldehydes:
An aldehyde molecule contains two fewer hydrogen atoms than the corresponding alcohol molecule.
i.e., an aldehyde is a dehydrogenated (oxidized) alcohol. Hence the name "aldehyde" - from the combination of two abbreviated Latin words alcohol dehydrogenatus (dehydrogenated alcohol).
Limit aldehydes and ketones have the same total formula
Nomenclature and isomerism. The names of aldehydes come from the names of the saturated acids into which they are converted during oxidation. This is due to the fact that many acids were discovered and named earlier than their corresponding aldehydes.
The names and formulas of some of the simplest aldehydes are given below:
To compile the names of aldehydes according to the Geneva nomenclature, the ending al is added to the name of a hydrocarbon with the same number of carbon atoms. In complex cases, the position of the aldehyde group is indicated by a number that is placed after this ending:
The isomerism of aldehydes is due to the isomerism of the chain of carbon atoms of the hydrocarbon radical:
The names of ketones according to rational nomenclature are derived from the names of the radicals included in their molecule, with the addition of the ending ketone, for example:
Some ketones have historical names, for example, dimethyl ketone is called acetone.
According to the Geneva nomenclature, the names of ketones are produced by adding the ending he to the name of the corresponding hydrocarbon. In the case of a branched ketone chain, the numbering of carbon atoms starts from the end closest to the branch (according to the rules for numbering hydrocarbons). Place
occupied by a carbonyl group is indicated in the name by a diphra after the end, for example:
physical properties. The first member of the homologous series of aldehydes is formic aldehyde - gas; medium representatives of the liquid; higher aldehydes are solids. Lower aldehydes have a pungent odor and mix well with water. Medium aldehydes are sparingly soluble in water; higher aldehydes are insoluble. All aldehydes are readily soluble in alcohol and ether.
Lower ketones are liquids with a characteristic odor that are easily mixed with water. Higher ketones are solids. All ketones are highly soluble in alcohol and ether.
Chemical reactions of aldehydes and ketones. Aldehydes and ketones are extremely reactive organic compounds. Many of their reactions proceed without heating and pressure. Especially characteristic of aldehydes and ketones are reactions that occur with the participation of a carbonyl group. There are, however, some differences in the reactions of aldehydes and ketones. Generally, aldehydes are more reactive than ketones.
Addition reactions: A number of different substances can add to the carbonyl group of aldehydes and ketones. In this case, one of the bonds connecting the oxygen and carbon atoms in the carbonyl group breaks, and parts of the reactant are added to the free valences formed. If the joining substance contains hydrogen, then the latter is always directed towards carbonyl oxygen; the carbonyl group is converted into a hydroxyl group:
From an electronic point of view, this "reactive feature of carbonyl oxygen in aldehydes and ketones is explained by the fact that the electron clouds that form a bond between carbon and oxygen atoms in the carbonyl group are shifted to the oxygen atom, since the latter attracts electrons more strongly than the carbon atom. As a result, the double bond is highly polarized:
Different substances are added to a polarized double bond in a certain direction. Consider some addition reactions characteristic of aldehydes and ketones.
Hydrocyanic acid addition The bond in the hydrocyanic acid molecule is also polarized, and therefore hydrogen, which has some positive charge, is attached to the oxygen atom, and the group to the carbon atom:
The media resulting in this case are called cyanogiorins (or oxynitriles) and are "compounds with mixed functions (containing both hydroxyl and cyano group). Oxynitriles serve as starting materials for the synthesis of various organic compounds.
The addition of sodium bisulfite (acid sodium sulfite
The resulting compounds (bisulfite compounds) are crystalline substances. They are used in laboratory practice to isolate aldehydes and ketones in a pure state from their mixtures with other substances, since they easily decompose when
boiling with soda or dilute acids to form initial aldehydes and ketones.
The addition of organometallic compounds to the carbonyl group of aldehydes and ketones is discussed on page 165.
The reduction of aldehydes and ketones can be viewed as the addition of a hydrogen molecule to a carbonyl group. When aldehydes are reduced, primary alcohols are formed, and when ketones are reduced, secondary ones are formed:
Substitution reactions in the series of aldehydes and ketones lead to the replacement of the oxygen of the carbonyl group with other atoms or radicals.
The action of pentahalide phosphorus. Under the action of, for example, phosphorus pentachloride, the carbonyl oxygen is replaced by two chlorine atoms and a dihaloid hydrocarbon is formed:
These dihalides, reacting with water, are able to give the original aldehydes and ketones again.
Action of hydroxylamine. Under the action of hydroxylamine on aldehydes and ketones, respectively, aldoximes and ketoximes are formed (hydroxylamine can be considered as ammonia, in which one hydrogen atom is replaced by hydroxyl):
The oximes resulting from this reaction are in most cases crystalline substances and serve to discover and isolate pure aldehydes and ketones.
Oxidation reactions. Aldehydes are easily oxidized by various oxidizing agents, turning into carboxylic acids:
For example, aldehydes easily take away oxygen from the oxides of certain metals. The so-called silver mirror reaction is based on this property. It lies in the fact that by heating the aldehyde with an ammonia solution of silver oxide, the aldehyde is oxidized to acid and the silver oxide is reduced to metallic silver:
Metallic silver settles on the walls of the vessel and forms a shiny mirror surface.
Ketones are much more difficult to oxidize. Only with very vigorous oxidation does their carbon chain break, two acids are formed, for example:
Reactions involving a hydrogen atom in the -position relative to the carbonyl group.
action of halogens. The carbonyl group of aldehydes and ketones strongly affects the mobility of hydrogen atoms located at the carbon next to the carbonyl group - position). So, for example, when bromine or chlorine acts on aldehydes or ketones, they easily replace hydrogen atoms in the -position:
Halogen atoms that have entered the - position to the carbonyl group of aldehydes or ketones also have a very high reactivity.
Condensation reactions. Condensation reactions are called compaction reactions in which new carbon-carbon bonds are formed. Condensation reactions can proceed without the release of simple molecules (water, ammonia, hydrogen chloride, etc.) or with their release.
Aldehydes easily enter into condensation reactions. So, for example, a molecule of acetaldehyde under the action of small amounts of dilute alkali in the cold condenses with another molecule of the same aldehyde:
The resulting compound containing aldehyde and alcohol groups was called aldol (short for aldehyde alcohol), and the above reaction was called aldol condensation. As can be seen from the reaction equation, aldol condensation occurs due to the mobile hydrogen atom in the -position to the carbonyl group.
Under somewhat different conditions, condensation can proceed with the formation of a new carbon-carbon double bond:
The resulting compound is called crotonic aldehyde, and the reaction is called crotonic condensation.
Ketongs are also capable of condensation reactions, which are somewhat more complicated than for aldehydes.
Typical reactions of aldehydes. For aldehydes, as compounds more reactive than ketones, the following reactions are also characteristic:
The formation of esters. If a small amount of aluminum alcoholate is added to the aldehyde, then an energetic reaction occurs, in which, as it were, the oxidation of one aldehyde molecule occurs due to the reduction of another aldehyde molecule, and an ester is formed:
This reaction is called the Tishchenko reaction, after the name of the Russian scientist who discovered it.
formation of acetals. When aldehydes are heated with alcohols in the presence of small amounts of mineral acids, the following reaction occurs:
The resulting compound is called acetal and is, as it were, a simple ether of an unstable dihydric alcohol:
The acetal formation reaction is reversible. Upon hydrolysis in the presence of acids, acetals readily decompose to form the starting aldehydes and alcohols. 4
Polymerization. Aldehydes can form linear or cyclic polymers, and in both cases, the residues of the aldehyde molecules are linked together through an atom
Mineral acids are used as substances that accelerate the polymerization of aldehydes. Cyclic polymers, when heated, split into molecules of the initial aldehydes.
Ways to get. Alcohol oxidation. As we already know, aldehydes are formed during the oxidation of primary alcohols, and ketones are formed during the oxidation of secondary ones. Oxidation can be carried out using various oxidizing agents, for example, potassium bichromate in an acidic environment or air oxygen in the presence of catalysts - platinum, copper, etc. In both cases, the reactions proceed according to the scheme:
Obtaining from dihalogenated hydrocarbons. If both halogen atoms are at the same carbon atom, then when such halogen derivatives are heated with water or better with alkali, aldehydes or ketones are formed:
Action of water on acetylenic hydrocarbons (Kucherov's reaction). When water acts on acetylene in the presence of divalent mercury salts, acetaldehyde is obtained:
Acetylene homologues under these conditions form ketones:
Oxosynthesis. Oxosynthesis is a method of obtaining oxygen-containing organic compounds by reacting unsaturated hydrocarbons with carbon monoxide and hydrogen at elevated temperature, in the presence of a cobalt catalyst and at pressure. As a result of this process, aldehydes are formed containing one more carbon atom than the original olefin:
Formic aldehyde (formaldehyde) Colorless gas with a pungent, specific odor; well soluble in water. An aqueous solution of formaldehyde containing formaldehyde in solution is called formalin. When the solution is evaporated, formaldehyde polymerizes with the formation of a solid mixture of low molecular weight polyoxymethylenes (paraformaldehyde), which again gives formaldehyde under the action of acids.
Formaldehyde is the first member of the homologous series of aldehydes. In the general formula
formaldehyde has a hydrogen atom instead of an alkyl radical. Therefore, some chemical properties of formaldehyde differ sharply from the properties of other aldehydes of this series. So, nayrimer, under the action of alkalis, formaldehyde, unlike other aldehydes of the fatty series, which are resinous with alkalis, forms methyl alcohol and a salt of formic acid;
In this reaction, one molecule of formaldehyde is reduced to alcohol, while the other is oxidized to acid.
Formaldehyde is used in huge quantities for the production of phenol-formaldehyde, urea and other synthetic polymers. Exceptionally valuable properties are possessed by a high-molecular polymer of formaldehyde - polyformaldehyde (p. 327).
A significant amount of formaldehyde goes to the preparation of isoprene (2-methylbutadiene-1,3) - the starting material for synthetic rubber.
The process of obtaining isoprene from formaldehyde and isobutylene proceeds in two stages according to the scheme:
The second stage of the process takes place at 200–220°C in the presence of phosphoric acid derivatives as a catalyst.
Formaldehyde is used as a starting material for the production of dyes, pharmaceuticals, synthetic rubber, explosives and many other organic compounds. Formaldehyde is poisonous and even in small concentrations irritates the mucous membranes.
Formalin (an aqueous solution of formaldehyde) is widely used as an antiseptic (disinfectant). Interestingly, the preservative effect of smoke when smoking food (fish, meat) is explained by the strong antiseptic effect of formaldehyde, which is formed as a result of incomplete combustion of fuel and is contained in smoke in a small amount.
An industrial method for obtaining formaldehyde is the catalytic oxidation of methanol. Methanol is oxidized in the gas phase with atmospheric oxygen at 500-600 °C:
Metallic copper or silver deposited on an inert porous carrier or in the form of a metal mesh are used as catalysts. (Recently, they began to use a more efficient iron oxide-molybdenum
catalyst.) To lower the temperature of the process, which favors the oxidation reaction and an increase in the yield of formaldehyde, 10-12% water is added to methanol.
On fig. 15 shows a schematic diagram of the production of formaldehyde by the oxidation of methanol.
The evaporator 2 receives methanol from the measuring tank 1 and purified air through the blower 4. In the evaporator, liquid methanol evaporates and mixes with air, resulting in the formation of a vapor-air mixture with a methanol content in the mixture. The steam-air mixture heated to 100 °C enters contact apparatus 6, in which methanol is oxidized at
Rice. 15. Scheme of the production of formaldehyde by the oxidation of methanol: 1 - dipstick; 2 - evaporator; 3 - filter; 4 - blower; 5 - heater; 6 - contact device; 7 - refrigerator; 8, 10 - absorbers; 9 - intermediate cooler.
The reaction products are sent to refrigerator 7, where they are cooled to 100-130 °C. Then they enter absorbers 8 and 10, in which the formed formaldehyde is absorbed. Absorber 8 is irrigated with a dilute formaldehyde solution coming from absorber 10, irrigated with water. Thus, the resulting formaldehyde exits the absorber as an aqueous solution containing 37.6% formaldehyde and about 10% methanol. The output of formaldehyde is about 80%. Exhaust gases from the absorber 10 contain nitrogen (about 70%), hydrogen (about 20%) and small amounts of methane, oxygen, carbon monoxide and carbon dioxide.
Recently, a method for the synthesis of formaldehyde has received industrial application by incomplete oxidation of concentrated methane with atmospheric oxygen:
Nitrogen oxides serve as a catalyst. (Oxidation is carried out., at a temperature of about 600 ° C.
Acetic aldehyde (acetaldehyde) CH3-CHO. Colorless liquid with a pungent odor, highly soluble in water; pace. bale +21°С. Under the action of acids, it easily polymerizes into cyclic polymers - paraldehyde (liquid), and metaldehyde (solid).
Acetic aldehyde is the most important starting compound for the production of acetic acid, synthetic polymers, medicinal compounds, and many other substances.
In industry, the following methods for the production of acetaldehyde are most widely used:
1. Direct hydration of acetylene with water vapor in the presence of liquid mercury catalysts (according to the Kucherov reaction).
3. Direct oxidation of ethylene with atmospheric oxygen in the presence of liquid palladium catalysts.
Hydration of acetylene in the presence of mercury catalysts is carried out by passing acetylene, mixed with water vapor at 90-100 ° C, into a hydrator filled with a catalyst, the so-called "contact" acid (a solution of mercury sulfate in sulfuric acid). The hydrator also receives continuously or periodically) metallic mercury, which forms mercury sulphate with sulfuric acid. A mixture of acetylene and steam bubbles through the acid layer; in this case, hydration of acetylene and the formation of acetaldehyde occur. The gas-vapor mixture leaving the hydrator is condensed and the separated acetaldehyde is separated from impurities. The yield of acetaldehyde (calculated as acetylene) reaches 95%.
When acetylene is hydrated in the presence of non-mercury catalysts, acetylene is diluted with nitrogen, mixed with steam, and the resulting gas-vapor mixture is passed at high temperature over a non-mercury catalyst, such as oxides of zinc, cobalt, chromium, or other metals. The duration of contact of the gas-vapor mixture with the catalyst is a fraction of a second; as a result, there are no side reactions, which leads to an increase in the yield of acetaldehyde and a more pure product.
A very promising industrial method for the production of acetaldehyde is the direct oxidation of ethylene with atmospheric oxygen in the presence of liquid palladium catalysts:
The reaction proceeds according to a much more complex scheme than shown above, and a number of by-products are formed. The process is carried out in tubular reactors at a temperature of about 120 ° C and pressure.
Acetone (dimethyl ketone) Colorless liquid with a characteristic odor, soluble in water, temp. bale 56.1 °C.
Acetone is an excellent solvent for many organic substances, and therefore is widely used in various industries (manufacturing of artificial fibers, drugs, etc.). Acetone is also used for the synthesis of various organic compounds.
A. E. Favorsky obtained isoprene from acetone and acetylene. The reaction proceeds in three stages:
The main industrial method for producing acetone is to obtain it from isopropylbenzene simultaneously with phenol (p. 234).
Some acetone is obtained by oxidative dehydrogenation or dehydrogenation of isopropyl alcohol.
Oxidative dehydrogenation of isopropyl alcohol can be carried out over a silver catalyst at 450-500 °C:
Carbon dioxide, propylene and acetic acid are formed as by-products. This process can also be carried out in the liquid phase at atmospheric pressure and a temperature of about 150 °C:
The resulting hydrogen peroxide is used for various syntheses, for example, to obtain glycerol from acrolein (p. 96).
Dehydrogenation of isopropyl alcohol is carried out in the vapor phase at 350-400 °C in the presence of a copper catalyst:
Characteristic chemical properties of saturated monohydric and polyhydric alcohols, phenol
Limit monohydric and polyhydric alcohols
Alcohols (or alkanols) are organic substances whose molecules contain one or more hydroxyl groups ($—OH$ groups) connected to a hydrocarbon radical.
According to the number of hydroxyl groups (atomicity), alcohols are divided into:
- monoatomic, for example:
$(CH_3-OH)↙(methanol(methyl alcohol))$ $(CH_3-CH_2-OH)↙(ethanol(ethyl alcohol))$
— diatomic (glycols), For example:
$(OH-CH_2-CH_2-OH)↙(ethanediol-1,2(ethylene glycol))$
$(HO-CH_2-CH_2-CH_2-OH)↙(propanediol-1,3)$
— triatomic, For example:
According to the nature of the hydrocarbon radical, the following alcohols are distinguished:
— marginal containing only saturated hydrocarbon radicals in the molecule, for example:
— unlimited containing multiple (double and triple) bonds between carbon atoms in the molecule, for example:
$(CH_2=CH-CH_2-OH)↙(propen-2-ol-1 (allylic alcohol))$
— aromatic, i.e. alcohols containing a benzene ring and a hydroxyl group in the molecule, connected to each other not directly, but through carbon atoms, for example:
Organic substances containing hydroxyl groups in the molecule, directly bonded to the carbon atom of the benzene ring, differ significantly in chemical properties from alcohols and therefore stand out in an independent class of organic compounds - phenols. For instance:
There are also polyhydric (polyhydric) alcohols containing more than three hydroxyl groups in the molecule. For example, the simplest six-hydric alcohol hexaol (sorbitol):
Nomenclature and isomerism
When forming the names of alcohols, a generic suffix is added to the name of the hydrocarbon corresponding to the alcohol. -ol. The numbers after the suffix indicate the position of the hydroxyl group in the main chain, and the prefixes di-, tri-, tetra- etc. - their number:
In the numbering of carbon atoms in the main chain, the position of the hydroxyl group takes precedence over the position of multiple bonds:
Starting from the third member of the homologous series, alcohols have an isomerism of the position of the functional group (propanol-1 and propanol-2), and from the fourth - the isomerism of the carbon skeleton (butanol-1, 2-methylpropanol-1). They are also characterized by interclass isomerism - alcohols are isomeric to ethers:
$(CH_3-CH_2-OH)↙(ethanol)$ $(CH_3-O-CH_3)↙(dimethyl ether)$
alcohols
physical properties.
Alcohols can form hydrogen bonds both between alcohol molecules and between alcohol and water molecules.
Hydrogen bonds arise from the interaction of a partially positively charged hydrogen atom of one alcohol molecule and a partially negatively charged oxygen atom of another molecule. It is due to hydrogen bonds between molecules that alcohols have abnormally high boiling points for their molecular weight. Thus, propane with a relative molecular weight of $44$ is a gas under normal conditions, and the simplest of alcohols is methanol, with a relative molecular weight of $32$, under normal conditions it is a liquid.
The lower and middle members of the series of saturated monohydric alcohols, containing from $1$ to $11$ carbon atoms, are liquids. Higher alcohols (beginning with $C_(12)H_(25)OH$) are solids at room temperature. Lower alcohols have a characteristic alcoholic smell and a burning taste, they are highly soluble in water. As the hydrocarbon radical increases, the solubility of alcohols in water decreases, and octanol is no longer miscible with water.
Chemical properties.
The properties of organic substances are determined by their composition and structure. Alcohols confirm the general rule. Their molecules include hydrocarbon and hydroxyl radicals, so the chemical properties of alcohols are determined by the interaction and influence of these groups on each other. The properties characteristic of this class of compounds are due to the presence of a hydroxyl group.
1. Interaction of alcohols with alkali and alkaline earth metals. To reveal the effect of a hydrocarbon radical on a hydroxyl group, it is necessary to compare the properties of a substance containing a hydroxyl group and a hydrocarbon radical, on the one hand, and a substance containing a hydroxyl group and not containing a hydrocarbon radical, on the other. Such substances can be, for example, ethanol (or other alcohol) and water. Hydrogen of the hydroxyl group of alcohol molecules and water molecules can be reduced by alkali and alkaline earth metals (replaced by them):
$2Na+2H_2O=2NaOH+H_2$,
$2Na+2C_2H_5OH=2C_2H_5ONa+H_2$,
$2Na+2ROH=2RONa+H_2$.
2. Interaction of alcohols with hydrogen halides. Substitution of a hydroxyl group for a halogen leads to the formation of haloalkanes. For instance:
$C_2H_5OH+HBr⇄C_2H_5Br+H_2O$.
This reaction is reversible.
3. Intermolecular dehydration of alcohols- splitting of a water molecule from two alcohol molecules when heated in the presence of water-removing agents:
As a result of intermolecular dehydration of alcohols, ethers. So, when ethyl alcohol is heated with sulfuric acid to a temperature of $100$ to $140°C$, diethyl (sulfuric) ether is formed:
4. Interaction of alcohols with organic and inorganic acids to form esters ( esterification reaction):
The esterification reaction is catalyzed by strong inorganic acids.
For example, when ethyl alcohol and acetic acid react, acetic ethyl ester is formed - ethyl acetate:
5. Intramolecular dehydration of alcohols occurs when alcohols are heated in the presence of dehydrating agents to a temperature higher than the intermolecular dehydration temperature. As a result, alkenes are formed. This reaction is due to the presence of a hydrogen atom and a hydroxyl group at neighboring carbon atoms. An example is the reaction of obtaining ethene (ethylene) by heating ethanol above $140°C$ in the presence of concentrated sulfuric acid:
6. Alcohol oxidation usually carried out with strong oxidizing agents, for example, potassium dichromate or potassium permanganate in an acidic medium. In this case, the action of the oxidizing agent is directed to the carbon atom that is already associated with the hydroxyl group. Depending on the nature of the alcohol and the reaction conditions, various products can be formed. Thus, primary alcohols are first oxidized to aldehydes and then in carboxylic acids:
When secondary alcohols are oxidized, ketones are formed:
Tertiary alcohols are quite resistant to oxidation. However, under severe conditions (strong oxidizing agent, high temperature), oxidation of tertiary alcohols is possible, which occurs with the breaking of carbon-carbon bonds closest to the hydroxyl group.
7. Dehydrogenation of alcohols. When alcohol vapor is passed at $200-300°C$ over a metal catalyst, such as copper, silver or platinum, primary alcohols are converted into aldehydes, and secondary alcohols into ketones:
The presence of several hydroxyl groups in an alcohol molecule at the same time determines the specific properties polyhydric alcohols, which are capable of forming water-soluble bright blue complex compounds when interacting with a fresh precipitate of copper (II) hydroxide. For ethylene glycol, you can write:
Monohydric alcohols are not able to enter into this reaction. Therefore, it is a qualitative reaction to polyhydric alcohols.
Phenol
The structure of phenols
The hydroxyl group in the molecules of organic compounds can be connected directly to the aromatic nucleus, or it can be separated from it by one or more carbon atoms. It can be expected that, depending on this property, substances will differ significantly from each other due to the mutual influence of groups of atoms. Indeed, organic compounds containing the aromatic phenyl radical $C_6H_5$— directly bonded to the hydroxyl group exhibit special properties that differ from those of alcohols. Such compounds are called phenols.
Phenols are organic substances whose molecules contain a phenyl radical associated with one or more hydroxo groups.
Like alcohols, phenols are classified by atomicity, i.e. by the number of hydroxyl groups.
Monatomic phenols contain one hydroxyl group in the molecule:
Polyhydric phenols contain more than one hydroxyl group in the molecules:
There are other polyhydric phenols containing three or more hydroxyl groups in the benzene ring.
Let's get acquainted in more detail with the structure and properties of the simplest representative of this class - phenol $C_6H_5OH$. The name of this substance formed the basis for the name of the entire class - phenols.
Physical and chemical properties.
physical properties.
Phenol is a solid, colorless, crystalline substance, $t°_(pl.)=43°С, t°_(boiling)=181°С$, with a sharp characteristic odor. Poisonous. Phenol is slightly soluble in water at room temperature. An aqueous solution of phenol is called carbolic acid. It causes burns on contact with skin, so phenol must be handled with care!
Chemical properties.
acid properties. As already mentioned, the hydrogen atom of the hydroxyl group has an acidic character. The acidic properties of phenol are more pronounced than those of water and alcohols. Unlike alcohols and water, phenol reacts not only with alkali metals, but also with alkalis to form phenolates:
However, the acidic properties of phenols are less pronounced than those of inorganic and carboxylic acids. For example, the acidic properties of phenol are about $3000$ times weaker than those of carbonic acid. Therefore, by passing carbon dioxide through an aqueous solution of sodium phenolate, free phenol can be isolated:
Adding hydrochloric or sulfuric acid to an aqueous solution of sodium phenolate also leads to the formation of phenol:
Qualitative reaction to phenol.
Phenol reacts with iron(III) chloride to form an intensely purple complex compound.
This reaction makes it possible to detect it even in very limited quantities. Other phenols containing one or more hydroxyl groups in the benzene ring also give a bright blue-violet color when reacted with iron (III) chloride.
Reactions of the benzene ring.
The presence of a hydroxyl substituent greatly facilitates the course of electrophilic substitution reactions in the benzene ring.
1. Bromination of phenol. Unlike benzene, phenol bromination does not require the addition of a catalyst (iron(III) bromide).
In addition, the interaction with phenol proceeds selectively (selectively): bromine atoms are sent to ortho- and para positions, replacing the hydrogen atoms located there. The selectivity of the substitution is explained by the features of the electronic structure of the phenol molecule discussed above.
So, when phenol reacts with bromine water, a white precipitate is formed 2,4,6-tribromophenol:
This reaction, as well as the reaction with iron (III) chloride, serves for the qualitative detection of phenol.
2. Phenol nitration also occurs more easily than the nitration of benzene. The reaction with dilute nitric acid proceeds at room temperature. The result is a mixture ortho- and pair- isomers of nitrophenol:
When concentrated nitric acid is used, an explosive is formed - 2,4,6-trinitrophenol(picric acid):
3. Hydrogenation of the aromatic ring of phenol in the presence of a catalyst occurs easily:
4.Polycondensation of phenol with aldehydes, in particular with formaldehyde, occurs with the formation of reaction products - phenol-formaldehyde resins and solid polymers.
The interaction of phenol with formaldehyde can be described by the scheme:
You probably noticed that “mobile” hydrogen atoms are preserved in the dimer molecule, which means that the reaction can continue further with a sufficient amount of reagents:
Reaction polycondensation, those. the polymer production reaction, proceeding with the release of a low molecular weight by-product (water), can continue further (until one of the reagents is completely consumed) with the formation of huge macromolecules. The process can be described by the overall equation:
The formation of linear molecules occurs at ordinary temperature. Carrying out this reaction when heated leads to the fact that the resulting product has a branched structure, it is solid and insoluble in water. As a result of heating a linear phenol-formaldehyde resin with an excess of aldehyde, solid plastic masses with unique properties are obtained. Polymers based on phenol-formaldehyde resins are used for the manufacture of varnishes and paints, plastic products that are resistant to heating, cooling, water, alkalis and acids, and have high dielectric properties. Polymers based on phenol-formaldehyde resins are used to make the most critical and important parts of electrical appliances, power unit cases and machine parts, the polymer base of printed circuit boards for radio devices. Adhesives based on phenol-formaldehyde resins are able to reliably connect parts of various nature, maintaining the highest bond strength in a very wide temperature range. Such glue is used to fasten the metal base of lighting lamps to a glass bulb. Now you understand why phenol and products based on it are widely used.
Characteristic chemical properties of aldehydes, saturated carboxylic acids, esters
Aldehydes and ketones
Aldehydes are organic compounds whose molecules contain a carbonyl group. 
, connected to a hydrogen atom and a hydrocarbon radical.
The general formula for aldehydes is:
In the simplest aldehyde, formaldehyde, the second hydrogen atom plays the role of a hydrocarbon radical:
A carbonyl group bonded to a hydrogen atom is called aldehyde:
Organic substances in the molecules of which the carbonyl group is bonded to two hydrocarbon radicals are called ketones.
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 bonded to two methyl radicals:
Nomenclature and isomerism
Depending on the structure of the hydrocarbon radical associated with the aldehyde group, limiting, unsaturated, aromatic, heterocyclic and other aldehydes are distinguished:
In accordance with the IUPAC nomenclature, the names of aldehydes are formed from the name of an alkane with the same number of carbon atoms in the molecule using the suffix -al. For instance:
The numbering of carbon atoms of the main chain starts from the carbon atom of the aldehyde group. Therefore, the aldehyde group is always located at the first carbon atom, and it is not necessary to indicate its position.
Along with the 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 name of ketones according to the systematic nomenclature, the keto group is denoted 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 instance:
For aldehydes, only one type of structural isomerism is characteristic - isomerism of the carbon skeleton, which is possible from butanal, and for ketones - also isomerism of the position of the carbonyl group. In addition, they are also characterized by interclass isomerism (propanal and propanone).
Trivial names and boiling points of some aldehydes.
Physical and chemical properties
physical properties.
In an aldehyde or ketone molecule, due to the greater electronegativity of the oxygen atom compared to the carbon atom, the $C=O$ bond is strongly polarized due to the shift in the electron density of the $π$ bond to oxygen:
Aldehydes and ketones are polar substances with excess electron density on the oxygen atom. The lower members of the series of aldehydes and ketones (formaldehyde, acetaldehyde, acetone) are infinitely 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 from four to six carbon atoms in the chain have an unpleasant odor; higher aldehydes and ketones have floral odors and are used in perfumery.
Chemical properties
The presence of an aldehyde group in a molecule determines the characteristic properties of aldehydes.
recovery reactions.
Addition of hydrogen to aldehyde molecules occurs at the double bond in the carbonyl group:
Aldehydes are hydrogenated as primary alcohols, while ketones are secondary alcohols.
So, when acetaldehyde is hydrogenated on a nickel catalyst, ethyl alcohol is formed, and when acetone is hydrogenated, propanol-2 is formed:
Hydrogenation of aldehydes recovery reaction, at which the oxidation state of the carbon atom in the carbonyl group decreases.
Oxidation reactions.
Aldehydes are able not only to recover, but also oxidize. When oxidized, aldehydes form carboxylic acids. Schematically, this process can be represented as follows:
From propionaldehyde (propanal), for example, propionic acid is formed:
Aldehydes are oxidized even by atmospheric oxygen and such weak oxidizing agents as an ammonia solution of silver oxide. In a simplified form, this process can be expressed by the reaction equation:
For instance:
More precisely, this process is 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 with an even thin film. Therefore, this reaction is called the reaction "silver mirror". It is widely used for making mirrors, silvering decorations and Christmas decorations.
Freshly precipitated copper (II) hydroxide can also act as an oxidizing agent for aldehydes. 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, like the "silver mirror" reaction, is used to detect aldehydes.
Ketones are not oxidized either by atmospheric oxygen or by such a weak oxidizing agent as an ammonia solution of silver oxide.
Individual representatives of aldehydes and their meaning
Formaldehyde(methanal, formic aldehyde$HCHO$ ) - a colorless gas with a pungent odor and a boiling point of $ -21C ° $, we will readily dissolve in water. Formaldehyde is poisonous! A solution of formaldehyde in water ($40%$) is called formalin and is used for disinfection. In agriculture, formalin is used for dressing seeds, in the leather industry - for processing leather. Formaldehyde is used to obtain urotropin - a medicinal substance. Sometimes compressed in the form of briquettes, urotropin is used as a fuel (dry alcohol). A large amount of formaldehyde is consumed in the production of phenol-formaldehyde resins and some other substances.
Acetic aldehyde(ethanal, acetaldehyde$CH_3CHO$ ) - a liquid with a sharp unpleasant odor and a boiling point of $ 21 ° C $, we will dissolve well in water. Acetic acid and a number of other substances are obtained from acetaldehyde on an industrial scale, it is used for the production of various plastics and acetate fibers. Acetic aldehyde is poisonous!
carboxylic acids
Substances containing one or more carboxyl groups in a molecule are called carboxylic acids.
group of atoms 
called carboxyl group, or carboxyl.
Organic acids containing one carboxyl group in the molecule are monobasic.
The general formula for 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 limiting, unsaturated, aromatic.
Limiting, or saturated, carboxylic acids are, for example, propanoic (propionic) acid:
or already familiar to us succinic acid.
Obviously, saturated carboxylic acids do not contain $π$-bonds in the hydrocarbon radical. In molecules of unsaturated carboxylic acids, the carboxyl group is bonded to an unsaturated, unsaturated hydrocarbon radical, for example, in acrylic (propene) $CH_2=CH—COOH$ or oleic $CH_3—(CH_2)_7—CH=CH—(CH_2)_7—COOH molecules $ 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:
Nomenclature and isomerism
The general principles for the formation of names of carboxylic acids, as well as other organic compounds, have already been considered. Let us dwell in more detail on the nomenclature of mono- and dibasic carboxylic acids. The name of a carboxylic acid is formed from the name of the corresponding alkane (an alkane with the same number of carbon atoms in the molecule) with the addition of the suffix -ov-, ending -and I and the words acid. The numbering of carbon atoms begins with the carboxyl group. For instance:
The number of carboxyl groups is indicated in the name by prefixes di-, tri-, tetra-:
Many acids also have historically developed, or trivial, names.
Names of carboxylic acids.
| Chemical formula | Systematic name of the acid | Trivial name for an acid |
| $H—COOH$ | methane | Formic |
| $CH_3—COOH$ | Ethane | Acetic |
| $CH_3—CH_2—COOH$ | propane | propionic |
| $CH_3—CH_2—CH_2—COOH$ | Butane | oily |
| $CH_3—CH_2—CH_2—CH_2—COOH$ | Pentane | Valerian |
| $CH_3—(CH_2)_4—COOH$ | Hexane | Nylon |
| $CH_3—(CH_2)_5—COOH$ | Heptanoic | Enanthic |
| $NEOS-UNSD$ | Ethandium | sorrel |
| $HOOS—CH_2—COOH$ | Propandioic | Malonic |
| $HOOS—CH_2—CH_2—COOH$ | Butane | Amber |
After getting acquainted with the diverse and interesting world of organic acids, let us consider in more detail the limiting monobasic carboxylic acids.
It is clear that the composition of these acids is expressed by the general formula $C_nH_(2n)O_2$, or $C_nH_(2n+1)COOH$, or $RCOOH$.
Physical and chemical properties
physical properties.
Lower acids, i.e. acids with a relatively small molecular weight, containing up to four carbon atoms in a molecule, are liquids with a characteristic pungent odor (remember the smell of acetic acid). Acids containing from $4$ to $9$ of carbon atoms are viscous oily liquids with an unpleasant odor; containing more than $9$ carbon atoms in a molecule - solid substances that do not dissolve in water. The boiling points of limiting monobasic carboxylic acids increase with an increase in the number of carbon atoms in the molecule and, consequently, with an increase in the relative molecular weight. For example, 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, formic $HCOOH$, having a small relative molecular weight $(M_r(HCOOH)=46)$, under normal conditions is a liquid with a boiling point of $100.8°С$. At the same time, butane $(M_r(C_4H_(10))=58)$ under the same conditions is gaseous and has a boiling point of $-0.5°С$. This discrepancy between boiling points and relative molecular masses is explained by the 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 a substantially non-polar hydrocarbon radical. The carboxyl group is attracted to water molecules, forming hydrogen bonds with them:
Formic and acetic acids are infinitely soluble in water. Obviously, with an increase in the number of atoms in the hydrocarbon radical, the solubility of carboxylic acids decreases.
Chemical properties.
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 bond 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:
$CH_3-COOH⇄CH_3-COO^(-)+H^+$
More precisely, this process is described by an equation that takes into account the participation of water molecules in it:
$CH_3-COOH+H_2O⇄CH_3COO^(-)+H_3O^+$
The equilibrium of dissociation 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 the dissociation into hydrogen cations and anions of acidic residues.
Obviously, the presence of “acidic” hydrogen in the molecules of carboxylic acids, i.e. hydrogen carboxyl group, due to other characteristic properties.
2. Interaction with metals standing in the electrochemical series of voltages up to hydrogen: $nR-COOH+M→(RCOO)_(n)M+(n)/(2)H_2$
So, iron reduces hydrogen from acetic acid:
$2CH_3-COOH+Fe→(CH_3COO)_(2)Fe+H_2$
3. Interaction with basic oxides with the formation of salt and water:
$2R-COOH+CaO→(R-COO)_(2)Ca+H_2O$
4. Interaction with metal hydroxides with the formation of salt and water (neutralization reaction):
$R—COOH+NaOH→R—COONa+H_2O$,
$2R—COOH+Ca(OH)_2→(R—COO)_(2)Ca+2H_2O$.
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:
$CH_3COOH+C_(17)H_(35)COONa→CH_3COONa+C_(17)H_(35)COOH↓$,
$2CH_3COOH+K_2CO_3→2CH_3COOK+H_2O+CO_2$.
6. Interaction of carboxylic acids with alcohols with the formation of esters - the 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 towards ester formation in the presence of dewatering agents and when the ester is removed from the reaction mixture.
In the reverse esterification reaction, which is called ester hydrolysis (reaction of an ester with water), an acid and an alcohol are formed:
Obviously, to react with carboxylic acids, i.e. polyhydric alcohols, such as glycerol, can also enter into an esterification reaction:
All carboxylic acids (except formic), along with a 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. Multiple bond addition reactions- unsaturated carboxylic acids enter into them. For example, the hydrogen addition reaction is hydrogenation. For an acid containing one $π$-bond in the radical, the equation can be written in general form:
$C_(n)H_(2n-1)COOH+H_2(→)↖(catalyst)C_(n)H_(2n+1)COOH.$
So, when oleic acid is hydrogenated, saturated stearic acid is formed:
$(C_(17)H_(33)COOH+H_2)↙(\text"oleic acid")(→)↖(catalyst)(C_(17)H_(35)COOH)↙(\text"stearic acid") $
Unsaturated carboxylic acids, like other unsaturated compounds, add halogens to the double bond. For example, acrylic acid decolorizes bromine water:
$(CH_2=CH—COOH+Br_2)↙(\text"acrylic(propenoic) acid")→(CH_2Br—CHBr—COOH)↙(\text"2,3-dibromopropanoic acid").$
8. Substitution reactions (with halogens)- saturated carboxylic acids are able to enter into them. For example, by reacting acetic acid with chlorine, various chlorine derivatives of acids can be obtained:
$CH_3COOH+Cl_2(→)↖(Р(red))(CH_2Cl-COOH+HCl)↙(\text"chloroacetic acid")$,
$CH_2Cl-COOH+Cl_2(→)↖(Р(red))(CHCl_2-COOH+HCl)↙(\text"dichloroacetic acid")$,
$CHCl_2-COOH+Cl_2(→)↖(Р(red))(CCl_3-COOH+HCl)↙(\text"trichloroacetic acid")$
Individual representatives of carboxylic acids and their significance
Formic(methane) acid HCOOH— a liquid with a pungent odor and a boiling point of $100.8°C$, highly soluble in water. Formic acid is poisonous Causes burns on contact with skin! The stinging fluid secreted by ants contains this acid. Formic acid has a disinfectant property and therefore finds its application in the food, leather and pharmaceutical industries, and medicine. It is used in dyeing textiles and paper.
Acetic (ethane)acid $CH_3COOH$ is a colorless liquid with a characteristic pungent odor, miscible with water in any ratio. Aqueous solutions of acetic acid are sold under the name of vinegar ($3-5%$ solution) and vinegar 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, in the leather industry, and in the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, it is used to obtain substances used to control weeds - herbicides.
Acetic acid is the main ingredient wine vinegar, the characteristic smell of which is due precisely to it. It is a product of the oxidation of ethanol and is formed from it when wine is stored in air.
The most important representatives of the highest limiting monobasic acids are palmitic$C_(15)H_(31)COOH$ and stearic$C_(17)H_(35)COOH$ acids. Unlike lower acids, these substances are solid, 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 $CH_3 - (CH_2)_7 - CH=CH -(CH_2)_7COOH$. It is an oil-like liquid without taste or smell. Its salts are widely used in technology.
The simplest representative of dibasic carboxylic acids is oxalic (ethanedioic) acid$HOOC—COOH$, salts of which are found in many plants, for example, in sorrel and oxalis. Oxalic acid is a colorless crystalline substance, highly soluble in water. It is used in the polishing of metals, in the woodworking and leather industries.
Esters
When carboxylic acids interact with alcohols (esterification reaction), esters:
This reaction is reversible. The reaction products can interact with each other to form the initial substances - alcohol and acid. Thus, the reaction of esters with water—hydrolysis of the ester—is the reverse of the esterification reaction. The chemical equilibrium, which is established when the rates of direct (esterification) and reverse (hydrolysis) reactions are equal, can be shifted towards the formation of ether by the presence of water-removing agents.
Fats- derivatives of compounds that are esters of glycerol and higher carboxylic acids.
All fats, like other esters, undergo hydrolysis:
When hydrolysis of fat is carried out in an alkaline medium $(NaOH)$ and in the presence of soda ash $Na_2CO_3$, it proceeds irreversibly and leads to the formation of not carboxylic acids, but their salts, which are called soaps. Therefore, the hydrolysis of fats in an alkaline environment is called saponification.
Aldehydes are a class of organic compounds containing a carbonyl group -СОН. The name of aldehydes comes from the name of hydrocarbon radicals with the addition of the suffix -al. The general formula of saturated aldehydes is CnH2n + 1COH. Nomenclature and isomerism
The nomenclature of these two groups of compounds is built differently.. Trivial names for aldehydes associate them with the trivial names of acids into which they pass during oxidation
From ketones only a few have trivial names (for example, acetone). They are widely used radical-functional nomenclature, in which the names of ketones are given using the names of the radicals associated with the carbonyl group. According to the IUPAC nomenclature, the names of aldehydes derived from the name of a hydrocarbon with the same number of carbon atoms by adding an ending –al.For ketones, this nomenclature requires an end -he. The number indicates the position of the functional group in the ketone chain.
| Compound | Names according to trivial and radical-functional nomenclature | Names according to IUPAC nomenclature |
| formic aldehyde; formaldehyde | methanal | |
| acetaldehyde; acetaldehyde | ethanal | |
| propionaldehyde | propional | |
| butyric aldehyde | butanal | |
| isobutyric aldehyde | methylpropanal | |
 | valeraldehyde | pentanal |
 | isovaleraldehyde | 3-methylbutanal |
| acetone; dimethyl ketone | propanone | |
| methyl ethyl ketone | butanone | |
| methylpropylketone | pentanone-2 | |
 | methylisopropylketone | 3-methylbutanone-2 |
Isomerism of aldehydes and ketones is fully reflected in the nomenclature and does not require comment. Aldehydes and ketones with the same number of carbon atoms are isomers. For instance:
Production methods - Oxidation or catalytic dehydrogenation of primary alcohols to aldehydes, secondary - to ketones. These reactions have already been mentioned when considering the chemical properties of alcohols.
- Pyrolysis of calcium or barium salts of carboxylic acids, one of which is a salt of formic acid, gives aldehydes.
– Hydrolysis of geminal ( substituents on one carbon ) dihaloalkanes
– Hydration of acetylene and its homologues proceeds in the presence of mercury sulfate (Kucherov reaction) or over a heterogeneous catalyst
physical properties. Formic aldehyde is a gas. The remaining lower aldehydes and ketones are liquids that are poorly soluble in water. Aldehydes have a pungent smell. Ketones usually smell good. 1. R. Oxidation. Aldehydes are easily oxidized to carboxylic acids. Copper (II) hydroxide, silver oxide, atmospheric oxygen can serve as oxidizing agents:
Aromatic aldehydes are more difficult to oxidize than aliphatic ones. Ketones, as mentioned above, are more difficult to oxidize than aldehydes. The oxidation of ketones is carried out under harsh conditions, in the presence of strong oxidizing agents. Formed as a result of a mixture of carboxylic acids. In this case, metallic silver is formed. The silver oxide solution is prepared immediately before the experiment:
Aldehydes also reduce a freshly prepared ammonia solution of copper (II) hydroxide, which has a light blue color (Fehling's reagent), to yellow copper (I) hydroxide, which decomposes when heated, releasing a bright red precipitate of copper (I) oxide. CH3-CH=O + 2Cu(OH)2 - CH3COOH+2CuOH+H2O 2CuOH->Cu2O+H2O
2. R. Accessions. Hydrogenation is the addition of hydrogen. Carbonyl compounds are reduced to alcohols with hydrogen, lithium aluminum hydride, and sodium borohydride. Hydrogen is added at the C=O bond. The reaction is more difficult than the hydrogenation of alkenes: heating, high pressure and a metal catalyst (Pt, Ni
Lecture No. 11
ALDEHYDES AND KETONES
Plan
1. Receiving methods.
2. Chemical properties.
2.1. Nucleophilic reactions
accessions.
2.2. Reactions for a -carbon atom.
2.3.
Lecture No. 11
ALDEHYDES AND KETONES
Plan
1. Receiving methods.
2. Chemical properties.
2.1. Nucleophilic reactions
accessions.
2.2. Reactions for 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 C=O bond has significant polarity
( m C=O =2.5-2.8 D). Carbonyl carbon atom
group carries an effective positive charge and is the object of attack
nucleophiles. The main type of reactions of aldehydes and ketones is reactions
nucleophilic addition Ad N. In addition, the carbonyl group has an effect on
C-H bond reactivity in a position, increasing its acidity.
Thus, the molecules of aldehydes and ketones
contain two main reaction centers - the C=O bond and the C-H bond in a-position:
2.1. Nucleophilic reactions
accessions.
Aldehydes and ketones easily add nucleophilic reagents to the C=O bond.
The process begins with the attack of the nucleophile at the carbonyl carbon atom. Then
the tetrahedral intermediate formed at the first stage adds a proton and
gives the product of addition:
The activity of carbonyl compounds in
Ad N -reactions depends on the magnitude
effective positive charge on the carbonyl carbon atom and volume
substituents on the carbonyl group. Electron donating and bulky substituents
hinder the reaction, electron-withdrawing substituents increase the reaction
the ability of a carbonyl compound. Therefore, aldehydes
Ad N -reactions are more active than
ketones.
The activity of carbonyl compounds increases in
the 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 of the type
NH 2 X. All addition reactions
go quickly, in mild conditions, however, the resulting products, as a rule,
thermodynamically unstable. Therefore, the reactions proceed reversibly, and the content
addition products in an equilibrium mixture can be low.
Water connection.
Aldehydes and ketones add water to
the formation of hydrates. The reaction is reversible. Formed hydrates
thermodynamically unstable. Equilibrium is skewed towards products
addition only in the case of active carbonyl compounds.
Hydration product of trichloroacetic aldehyde
chloral hydrate is a stable crystalline compound that is used in
medicine as a sedative and hypnotic.
The addition of alcohols and
thiols.
Aldehydes add alcohols to form hemiacetals. With an excess of alcohol and in the presence of an acid catalyst
the reaction goes further - to the formation acetals
The hemiacetal formation reaction proceeds as
nucleophilic addition and is accelerated in the presence of acids or
grounds.
The process of acetal formation proceeds as
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. V
in an acidic environment, hemiacetals and acetals are easily hydrolyzed. In an alkaline environment
hydrolysis does not occur. The reactions of formation and hydrolysis 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.
Accession of hydrocyanic
acids
Hydrocyanic acid is added to a carbonyl compound under conditions
basic catalysis to form cyanohydrins.
The reaction has a preparative value and
used in synthesis a-hydroxy- and a -amino acids (see lek. No. 14). The fruits of some plants
(e.g. bitter almonds) contain cyanohydrins. Standing out when they
cleavage hydrocyanic acid has a toxic effect.
Addition of bisulfite
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 an excess of sodium bisulfite solution.
The reaction is used to isolate carbonyl compounds from mixtures. carbonyl
the compound can be easily regenerated by treatment of the bisulfite derivative
acid or lye.
Interaction with common connections
NH formulas 2x.
Reactions proceed according to the general scheme as a process
attachment-detachment. The addition product formed at the first stage does not
stable and easily splits off water.
According to the above 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 intermediates
products in many enzymatic processes (transamination under the action of
coenzyme pyridoxal phosphate; reductive amination of keto acids at
participation of the coenzyme NADN). During the catalytic hydrogenation of imines,
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 lek. No. 16)
2.2. Reactions by a -carbon atom.
Keto-enol tautomerism.
Hydrogen in a -position to the carbonyl group has acidic
properties, since the anion formed during its elimination is stabilized for
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 -positions to the oxygen atom of the carbonyl group.
Ketone and enol are tautomers.
Tautomers are isomers capable of rapidly and reversibly converting into each other.
due to the migration of some group (in this case, a proton). Balance between
called ketone and enol keto-enol tautomerism.
The enolization process is catalyzed by acids and
grounds. Enolization under the action of a base can be represented
with the following scheme:
Most carbonyl compounds exist
predominantly in the 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
conjugation.
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
form is stabilized due to the presence in it of a system of conjugate p -bonds and intramolecular
hydrogen bond.
If the compound in enol form is
a conjugated system with a high stabilization energy, then the enol form
prevails. For example, phenol exists only in the enol form.
Enolization and the formation of enolate anions are
the first stages of the reactions of carbonyl compounds proceeding through a -carbon atom. The most important
of which are halogenation and aldol-crotonic
condensation
.
Halogenation.
Aldehydes and ketones easily react with halogens (Cl 2,
Br2, I2 ) with education
exclusively a -halogen derivatives.
The reaction is catalyzed by acids or
grounds. 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). So the halogen
involved in speed—defining stage
process.
If the 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 action of an electron-withdrawing influence
halogen. In an alkaline environment, acetaldehyde and methyl ketones give
trihalogen derivatives, which are then cleaved under the action of an excess of alkali with
the formation of trihalomethanes ( haloform reaction)
.
The cleavage of triiodoacetone proceeds as a reaction
nucleophilic substitution. CI groups 3 — hydroxide anion, like S N -reactions in the carboxyl group (see Lec. No. 12).
Iodoform precipitates from the reaction mixture in the form
pale yellow crystalline precipitate with a characteristic odor. iodoform
the reaction is used for analytical purposes to detect compounds of the type
CH 3 -CO-R, including in
clinical laboratories for the diagnosis of diabetes mellitus.
Condensation reactions.
In the presence of catalytic amounts of acids
or alkali carbonyl compounds containing a - hydrogen atoms,
undergo condensation to form b -hydroxycarbonyl compounds.
Carbonyl is involved in the formation of the C-C bond
carbon atom of one molecule ( carbonyl component) and a - another carbon atom
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 is easily
dehydrated to form a,b - unsaturated carbonyl
connections.
This type of condensation is called crotonic(by the name of the condensation product of acetaldehyde - crotonic
aldehyde).
Consider the mechanism of aldol condensation in
alkaline environment. In the first step, the hydroxide anion abstracts a proton from a - carbonyl positions
compounds to form the 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 a strong
base and further detaches a proton from a water molecule.
In aldol condensation of two different
carbonyl compounds (cross-aldol condensation) possible
formation of 4 different products. However, this can be avoided if one of
does not contain carbonyl compounds a -hydrogen atoms (for example, aromatic aldehydes
or formaldehyde) and cannot act as the methylene component.
As a methylene component in reactions
condensation can be not only carbonyl compounds, but also other
CH-acids. Condensation reactions are of preparative value, as they allow
build up a chain of carbon atoms. According to the type of aldol condensation and
retroaldol decay (reverse process), many biochemical processes occur
processes: glycolysis, synthesis of citric acid in the Krebs cycle, synthesis of neuraminic
acids.
2.3. Oxidation reactions and
recovery
Recovery
Carbonyl compounds are reduced to
alcohols as a result of catalytic hydrogenation or under the action of
reducing agents that are hydride anion donors.
[H]: H2 / cat., cat. – Ni, Pt,
Pd;
LiAlH 4 ; NaBH4.
Recovery of carbonyl compounds
complex metal hydrides includes nucleophilic attack of the carbonyl group
hydride anion. Subsequent hydrolysis yields alcohol.
Recovery is similar
carbonyl group in vivo under the action of the coenzyme NADH, which is
hydride ion donor (see Lec. No. 19).
Oxidation
Aldehydes oxidize very easily
any oxidizing agents, even such weak ones as atmospheric 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 (Cannicaro reaction).
2HCHO + NaOH ® HCOONa + CH 3 OH
This is the reason why the aqueous solution
formaldehyde (formalin) during long-term storage becomes acidic
reaction.
Ketones are resistant to the action of oxidizing agents in
neutral environment. In acidic and alkaline environments under the action of strong
oxidizers(KMnO 4 ) they
oxidized with cleavage of the C-C bond. The splitting of the carbon skeleton occurs along
the carbon-carbon double bond of the enol form of the carbonyl compound, similar to
oxidation of double bonds in alkenes. This results in a mixture of products
containing carboxylic acids or carboxylic acids and ketones.