Chemical properties of unsaturated carboxylic acids. Chemical properties of carboxylic acids and methods of preparation

It all started with vinegar, at least discovery of carboxylic acids. The name combines organic compounds containing the carboxyl group COOH.

The arrangement of the atoms in this order is important, since there are other oxygen-containing compounds.

The acetic carbonate was the first to be discovered, but its structure remained a mystery for many centuries. The substance was known as a product of wine souring.

As a combination of 2 atoms, 4 atoms and 2 oxygen, it became known to the world only in the 18th century.

Afterwards, they opened a whole range of carbon ones. Let's get acquainted with their classification, general properties and areas of application.

Properties of carboxylic acids

Differing from other organics in the presence of carboxyl groups, carboxylic acids classified according to their number.

There are one-, two-, and polybasic compounds. Monobasic carboxylic acids are distinguished by the bond between the carboxyl group and the hydrocarbon radical.

Accordingly, the general formula of the substances of the group is: - C n H 2 n +1 COOH. Acetic - monobasic. Its chemical notation is: - CH 3 COOH. The structure of the compound is even simpler: - COCOOH.

It is also classified as the simplest with the formula C 2 H 5 COOH. The remaining compounds of the monobasic series have isomers, that is, different structural options.

Formic acid, acetic acid and propionic acid have only one structural plan.

If carboxylic acid formula with two carboxyl groups, it can be called dibasic.

General entry of category substances: - COOH-R-COOH. As you can see, the carboxyl groups are located on opposite sides of the linear molecule.

In polybasic carboxyl radicals there are at least three. Two are located at the edges of the molecule, and the rest are attached to the central carbon atoms. This is, for example, lemon. Spatial recording of its formula: -

Carbon compounds are also divided according to the nature of the hydrocarbon radical. Chemical bonds between its atoms can be single.

In this case, we have before us saturated carboxylic acids. The presence of double bonds indicates unsaturated substances.

Formula of unsaturated carboxylic acids may at the same time be a record of the highest representatives of the class.

Higher compounds are those with more than 6 carbon atoms. Accordingly, from 1 to 5 carbon atoms is a sign of lower substances.

Higher carboxylic acids- these are, for example, linolenic, palmitic and arichidonic. Half of the last one has 21 carbon atoms, the rest have 18.

Being organic in origin, most carbons have at least a slight odor. However, there is a group of especially fragrant ones.

They contain a benzene ring. That is, the groups are derivatives of benzene. Its formula: - C 6 H 6 .

The substance has a sweetish odor. Therefore, carbonaceous compounds with a benzene ring are called aromatic. Moreover, a direct connection between the nucleus and carboxyl groups is required.

According to their physical state, carbon fibers are either liquid or crystalline. This refers to the aggregation of substances under normal conditions.

Some of the compounds are soluble in water, the other part is mixed only with organic matter. The nuances of chemical behavior depend on the number of carboxyl groups in the molecules.

Yes, typical reaction of carboxylic acids single-basic category - litmus staining in color.

The interaction with halogens is also considered a classic, while dicarbonic compounds can form esters of carboxylic acids. They are “born” in interaction with alcohols.

Carboxylic acid with two bases always contains a methylene group, that is, divalent CH 2.

Its presence between carboxyl groups increases the acidity of the hydrogen atoms. Therefore, condensation of derivatives is possible. This is another explanation for the appearance of ethers.

Dibasic compounds also form salts of carboxylic acids. They are used in the production of detergents, in particular soap.

However, we’ll talk separately about where carboxylic acids and their compounds come in handy.

Application of carboxylic acids

Stearic and palmitic acids are especially important in soap production. That is, higher compounds are used.

They make soap briquettes hard and allow fractions to be mixed, separating without the presence of acids.

The ability to make masses homogeneous is also useful in the production of drugs. Most of the connecting elements in them are carboxylic acids.

Accordingly, the use of reagents internally, as well as externally, is safe. The main thing is to know the maximum dosage.

Exceeding the dose or concentration of acids leads to devastating consequences. Possible chemical burns and poisoning.

But the causticity of the compounds is to the advantage of metallurgists, furniture makers, and restorers. Carboxylic acids and mixtures with them help polish and clean uneven, rusty surfaces.

By dissolving the top layer of metal, reagents improve its appearance and performance characteristics.

Chemical carboxylic acids can be refined, or technical. The latter are also suitable for working with metals.

But, only highly purified compounds are used as cosmetics and medicines. These are also needed in the food industry.

About a third of carboxylic acids are officially registered additives, known to ordinary people as eshki.

On the packages they are marked with the letter E and a serial number next to it. Acetic acid, for example, is written as E260.

Carboxylic acids can also serve as food for plants, being part of fertilizers. At the same time, it is possible to create poisons for harmful insects and weeds.

The idea is borrowed from nature. A number of plants independently produce carboxylic acids so that there are no other herbs nearby that compete for the soil and its resources. At the same time, plants that produce poison are themselves immune to it.

About a third of carbon compounds are used as mordants for fabrics. Processing is necessary so that the fabrics are evenly colored. For the same purpose, reagents are used in the leather industry.

Extraction of carboxylic acids

Since carboxylic acids are biogenic, about 35% of them are obtained from natural products. But chemical synthesis is more profitable.

Therefore, if possible, switch to it. Thus, hyaluronic acid, used for rejuvenation, has long been extracted from the umbilical cords of babies and cattle.

Now, the compound is obtained biochemically by growing bacteria on a wheat substrate that continuously produce acid.

Preparation of carboxylic acids purely chemically - this is the oxidation of alcohols and aldehydes.

The latter concept refers to alcohols devoid of hydrogen. The reaction proceeds as follows: - CH 3 - CH 2 OH → CH 3 - SON → CH 3 - COOH.

A number of carboxylic acids are obtained by hydrolysis of esters. When they receive water, they transform into heroines.

They can also be formed from monohalogen derivatives. Acids are obtained from them under the action of cyanide. The reaction intermediate must be decomposed with water.

The cost of the final products largely depends on the production scheme, the number of its stages, and consumables. Let's find out what the price tag is for carboxylic acids in their pure form.

Price of carboxylic acids

Most carboxylic acids are sold in large quantities. They are usually packaged in 25-35 kilograms. Liquids are poured into cans.

Powders are poured into plastic bags, and stearic acid is generally wrapped in. The price tag is usually set per kilo.

So, 1000 grams of citric acid costs around 80 rubles. They charge the same amount for formic and sorrel.

The cost of oleic is about 130 rubles per kilogram. Salicylic acid is already valued at 300. Stearic acid is 50-70 rubles cheaper.

A number of carboxylic acids are valued in dollars, since the main supplies are from the United States and the European Union.

This is where hyaluronic acid comes from, for example. They no longer pay a couple of hundred rubles per kilogram, but several hundred bucks.

The domestic product is present, but it is not trusted, first of all, by beauty clients.

They know that rejuvenation with hyaluronic acid is an American invention, practiced by them for half a century.

Accordingly, there is a great practice of producing a drug that must be of high quality, because it gets into the skin and the body.

Chemical compounds based on one or more COOH groups are defined as carboxylic acids.

The compounds are based on the COOH group, which has two components - carbonyl and hydroxyl. A group of COOH atoms is called a carboxyl group (carboxyl). The interaction of elements is ensured by the combination of two oxygen atoms and a carbon atom.

Structure of carboxylic acids

Hydrocarbon radical in monobasic saturated acids combines with one COOH group. The general formula of carboxylic acids looks like this: R-COOH.

The structure of the carbon group affects the chemical properties.

Nomenclature

In the names of carbon compounds, the carbon atom of the COOH group is numbered first. The number of carboxyl groups is denoted by the prefixes di-; three-; tetra-.

For example, CH3-CH2-COOH is the formula of propanoic acid.

Carbon compounds have and familiar names: formic, acetic, citric... All these are names of carboxylic acids.

The names of salts of carbonic compounds are obtained from the names of the hydrocarbon with the addition of the suffix “-oat” (COOC)2-potassium ethanediot.

Classification of carboxylic acids

Carboxylic acids classification.

By the nature of the hydrocarbon:

• limit;
• unsaturated;
• aromatic.

According to the number of COUN groups there are:

• monobasic (acetic acid);
• dibasic (oxalic acid);
• polybasic (citric acid).

Saturated carboxylic acids– compounds in which the radical is connected to one carbonyl.

The classification of carboxylic acids also divides them according to the structure of the radical to which the carbonyl is bonded. According to this criterion, compounds are aliphatic and alicyclic.

Physical properties

Let's look at the physical properties of carboxylic acids.

Carbon compounds have different numbers of carbon atoms. Depending on this number, the physical properties of these compounds differ.

Compounds containing from one to three carbon atoms are considered lower. These are colorless liquids with a pungent odor. Lower compounds dissolve easily in water.

Compounds containing from four to nine carbon atoms are oily liquids with an unpleasant odor.

Compounds containing more than nine carbon atoms are considered superior and the physical properties of these compounds are as follows : they are solids, they cannot be dissolved in water.

The boiling and melting points depend on the molecular weight of the substance. The higher the molecular weight, the higher the boiling point. Boiling and melting require a higher temperature than alcohols.

There are several ways to obtain carboxylic acids.

Chemical reactions exhibit the following properties:

Application of carboxylic acids

Carbon compounds are common in nature. Therefore, they are used in many areas: in industry (light and heavy) , in medicine and agriculture, as well as in the food industry and cosmetology.

Aromatic compounds are found in large quantities in berries and fruits.

In medicine, lactic, tartaric and ascorbic acid are used. Dairy is used as a cauterization, and tartar is used as a mild laxative. Ascorbic acid strengthens the immune system.

Fruit and aromatic ones are used in cosmetology. Thanks to them, cells renew themselves faster. The aroma of citrus fruits can have a tonic and calming effect on the body. Benzoic acid is found in balms and essential oils; it dissolves well in alcohol.

High molecular weight unsaturated compounds are found in dietetics. Oleic is the most common in this area.

Polyunsaturated with double bonds (linoleic and others) have biological activity. They are also called active fatty acids. They are involved in metabolism, affect visual function and immunity, as well as the nervous system. The absence of these substances in food or their insufficient consumption inhibits the growth of animals and has a negative impact on their reproductive function.

Sorbic acid is obtained from rowan berries. It is an excellent preservative.

Acrylic has a pungent odor. It is used to produce glass and synthetic fibers.

Based on the ethyrification reaction, fat is synthesized, which is used in the manufacture of soap and detergents.

Formicidum is used in medicine, in beekeeping, and also as preservatives.

Acetic is a colorless liquid with a pungent odor; mixes easily with water. It is widely used in the food industry as a seasoning. It is also used for preservation. It also has solvent properties. Therefore, it is widely used in the production of varnishes and paints, and in dyeing. On its basis, raw materials are made to combat insects and weeds.

Stearic and palmitic(higher monobasic compounds) are solids and do not dissolve in water. But their salts are used in soap production. They make soap bars hard.

Since the compounds are capable of imparting homogeneity to masses, they are widely used in the manufacture of medicines.

Plants and animals also produce carbon compounds. Therefore, it is safe to consume them internally. The main thing is to follow the dosage. Exceeding the dose and concentration leads to to burns and poisoning.

The corrosiveness of the compounds is beneficial in metallurgy, as well as for restorers and furniture makers. Mixtures based on them allow you to level surfaces and remove rust.

Esters obtained from the esterification reaction have found their use in perfumery. They are also used as components of varnishes and paints, and solvents. And also as aromatic additives.

Carboxylic acids are compounds that contain a carboxyl group:

Carboxylic acids are distinguished:

• monobasic carboxylic acids;
• dibasic (dicarboxylic) acids (2 groups UNS).

Depending on their structure, carboxylic acids are distinguished:

• aliphatic;
• alicyclic;
• aromatic.

Examples of carboxylic acids.

Preparation of carboxylic acids.

1. Oxidation of primary alcohols with potassium permanganate and potassium dichromate:

2. Hybrolysis of halogen-substituted hydrocarbons containing 3 halogen atoms per carbon atom:

3. Preparation of carboxylic acids from cyanides:

When heated, the nitrile hydrolyzes to form ammonium acetate:

When acidified, acid precipitates:

4. Use of Grignard reagents:

5. Hydrolysis of esters:

6. Hydrolysis of acid anhydrides:

7. Specific methods for obtaining carboxylic acids:

Formic acid is produced by heating carbon(II) monoxide with powdered sodium hydroxide under pressure:

Acetic acid is produced by the catalytic oxidation of butane with atmospheric oxygen:

Benzoic acid is obtained by oxidation of monosubstituted homologues with a solution of potassium permanganate:

Canniciaro's reaction. Benzaldehyde is treated with 40-60% sodium hydroxide solution at room temperature.

Chemical properties of carboxylic acids.

In an aqueous solution, carboxylic acids dissociate:

The equilibrium is shifted strongly to the left, because carboxylic acids are weak.

Substituents affect acidity due to an inductive effect. Such substituents pull electron density towards themselves and a negative inductive effect (-I) occurs on them. The withdrawal of electron density leads to an increase in the acidity of the acid. Electron-donating substituents create a positive inductive charge.

1. Formation of salts. Reaction with basic oxides, salts of weak acids and active metals:

Carboxylic acids are weak, because mineral acids displace them from the corresponding salts:

2. Formation of functional derivatives of carboxylic acids:

3. Esters when heating an acid with an alcohol in the presence of sulfuric acid - esterification reaction:

4. Formation of amides, nitriles:

3. The properties of acids are determined by the presence of a hydrocarbon radical. If the reaction occurs in the presence of red phosphorus, it forms the following product:

4. Addition reaction.

8. Decarboxylation. The reaction is carried out by fusing an alkali with an alkali metal salt of a carboxylic acid:

9. Dibasic acid is easily eliminated CO 2 when heated:

Additional materials on the topic: Carboxylic acids.

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Carboxylic acids

(Abstract on chemistry)

Completed:

student of group 212 Chebakov D.S.

Checked:

chemistry teacher Merzlova S.A.

Stone-on-Obi

1.Determination of Carboxylic Acids

2.Isomerism and nomenclature

3.Being in nature

4.Receipt

5.Physical properties

6.Chemical properties

7.Application

Bibliography

Definition of carbon acids

CARBOXYLIC ACIDS- organic compounds containing one or more carboxyl groups -COOH. The name comes from Lat. carbo - coal and Greek. oxys - sour. Based on the number of these groups, mono-, di-, tri- and tetracarboxylic acids are distinguished (a larger number of -COOH groups in one molecule is rare). Carboxylic acids can be aliphatic - with normal and branched chains, cyclic and aromatic, saturated and unsaturated, contain halogen atoms and various functional groups: OH (hydroxy acids), NH2 (amino acids), CO (keto acids), etc. Many carboxylic acids in the free state, as well as in the form of various derivatives (salts, esters), are widespread in nature and play a vital role in the life of plants and animals.

Isomerism and nomenclature

The isomerism of saturated monobasic carboxylic acids is similar to the isomerism of aldehydes. Most often, historically established names of acids are used (formic, acetic, etc.). According to international nomenclature, they are formed from the names of the corresponding hydrocarbons with the addition of the ending - new and the words “Acid”, for example: methanoic acid, ethanoic acid.

Carboxylic acids are characterized by isomerism:

1.Carbon skeleton

CH3 - CH2 - CH2 - CH2 -COOH

CH2 - CH2 -COOH

carboxylic acid organic chemical

2.Radical

CH3 - CH2 - CH2 - CH2 -COOH 3 methylethane

CH3 - CH2 - CH2 - CH2 -COOH 4 methylpentane

3.Multiple connections

CH2 = CH - CH2 -COOH butenoic acid 3

CH2 - CH = CH2 -COOH butenoic acid 2

Being in nature

Natural sources contain many unsaturated acids in the form of esters. Higher unsaturated acids, as a rule, contain an even number of carbon atoms and are named after natural sources. When naming newly isolated acids, chemists often give free rein to their imagination. Thus, the name of the closest homologue of acrylic acid, crotonic CH3-CH=CH-COOH, does not come from the mole at all, but from the plant Croton tiglium, from whose oil it was isolated. A very important synthetic isomer of crotonic acid is methacrylic acid CH2=C(CH3)-COOH, from the ester of which (methyl methacrylate), as well as from methyl acrylate, transparent plastic is made - plexiglass. When two isomeric acids with the structure CH3-CH=C(CH3)-COOH were discovered, they were called angelic and tiglinic. Angelic acid has been isolated from angelic oil, obtained from the angelica (angelica) root of the plant Angelica officinalis. And tiglic acid is from the same Croton tiglium oil as crotonic acid, only named after the second part of this botanical term. Another way to come up with a new name is to rearrange the letters in an already known name.

Arachidic acid found in groundnut oil - peanuts. In terms of scale of production, it occupies one of the first places among all edible oils, but it contains little arachidic acid itself - only a few percent. Behenic acid is found in behenic oil, which is extracted from the large, nut-like seeds of a plant from the Moringaceae family, common in Indonesia. Almost pure lignoceric acid (in its name it is easy to see the Latin lignum - wood, wood and cera - wax) is extracted from beech tree resin. Previously, this acid was also called carnaubic acid, because there is quite a lot of it in carnauba wax, which covers the leaves of the Brazilian wax palm.

Fatty acids in oils and fats are extracted by humans in huge quantities, measured annually in millions of tons. So chemists have never had a shortage of natural fatty acids to study.

Formic acid became known in the 17th century, when it was discovered in the caustic secretions of red ants. Most other acids, which have their own “own” historical names, were obtained mainly in the 19th century. and are named after the natural source in which they are found in significant quantities or were first discovered. For example, butyric acid is found in oils, including regular butter - just not in a free state, but in the form of an ester with glycerin. Free butyric acid, like all carboxylic acids with a small number of carbon atoms, has a pungent odor; when the oil spoils (goes rancid), butyric and other acids are released in a free state and give it an unpleasant odor and taste.

The names of the three acids considered use Russian roots. For derivatives of these acids (salts, esters, etc.), it is customary to use Latin roots: formate - for formic acid (Latin formica - ant), acetate - for acetic acid (Latin acetum - vinegar), butyrate - for butyric acid (Greek butyron - oil); these names, including those for the acids themselves, are also accepted in Western European languages.

Other carboxylic acids occur in nature as esters with glycerol and other polyhydric alcohols - in the form of fats, oils, waxes and rarely in a free state.

Valeric acid found in valerian root. The names of the three subsequent even-numbered acids (caproic, caprylic and capric) have a common root (Capra in Latin - goat), these acids are actually contained in the fat of goat's milk (as well as cow's milk), and in the free state they “smell like a goat” " The content of these acids in milk fats is not very high - from 7 to 14% of the total fatty acids.

Pelargonic acid is found in the volatile oil of rosea pelargonium and other plants of the geranium family. Lauric acid (in old books it was called laurel) is found in large quantities in bay oil (up to 45%). Myristic acid predominates in the oil of plants of the myristic family, for example, in the aromatic seeds of the nutmeg tree - nutmeg.

Palmitic acid easily isolated from palm oil extracted from coconut kernels (copra). This oil consists almost entirely of palmitic acid glyceride. The name stearic acid comes from the Greek. stear - fat, lard. Together with palmitic acid, it is one of the most important fatty acids and makes up the main part of most vegetable and animal fats. Candles were previously made from a mixture of these acids (stearin).

Receipt

In the laboratory, carboxylic acids, like inorganic acids, can be obtained from their salts by treating them with sulfuric acid when heated:

In industry, carboxylic acids are produced in various ways.

The general method for producing carboxylic acids is the oxidation of hydrocarbons with atmospheric oxygen. The reaction is carried out both in the gas phase at elevated pressure and temperature without catalysts, and in solutions. In this case, cracking of carbon chains occurs, so that the acids obtained in this way always contain fewer carbon atoms than the original hydrocarbons. For example, acetic acid is obtained by oxidation of N-butane in a solution of acetic acid:

Mn, Co, 6-8 MPa

2CH3 - CH2 - CH2 - CH3 + 5O2 4СH3COOH+2H2O

Physical properties

Lower carboxylic acids are liquids with a pungent odor, highly soluble in water. As the relative molecular weight increases, the solubility of acids in water decreases and the boiling point increases. Higher acids, starting with pelargonic (n-nonanoic) CH3-(CH2)7-COOH, are solid, odorless, insoluble in water. Lower carboxylic acids in anhydrous form and in the form of concentrated solutions irritate the skin and cause burns, especially formic acid and acetic acid.

Chemical properties

The general properties of carboxylic acids are similar to the corresponding properties of inorganic acids.

Carboxylic acids also have some specific properties due to the presence of radicals in their molecules. For example, acetic acid reacts with chlorine:

monochloroacetic acid

Formic acid's chemical properties are somewhat different from other carboxylic acids.

1. Of the monobasic carboxylic acids, formic acid is the strongest acid.

2. Due to the structural features of its molecules, formic acid is similar to aldehydes and is easily oxidized (the “silver mirror” reaction):

carbonic acid.

3. When heated with concentrated sulfuric acid, formic acid splits off water and carbon monoxide (II) is formed:

This reaction is sometimes used to produce carbon(II) monoxide in the laboratory.

As already noted, the strongest of the monobasic carboxylic acids is formic acid.

Acetic acid much weaker. Therefore, the methyl CH3 - radical (and other radicals) affects the carboxyl group. As a result, the bond between the hydrogen and oxygen atoms in the carboxyl group becomes less polar and the removal of the hydrogen ion is more difficult. In carboxylic acid radicals, hydrogen atoms can be replaced by halogens. In this case, substitution occurs more easily in the hydrocarbon unit, which is closer to the carboxyl group. Consequently, the carboxyl group acts on the hydrocarbon radical, that is, their influence is mutual.

Application

Formic acid is used in industry as a strong reducing agent. Its 1.25% solution in alcohol (formic alcohol) is used in medicine. Acetic acid is of greatest importance; it is necessary for the synthesis of dyes (for example, indigo), medicines (for example, aspirin), esters, acetic anhydride, monochloroacetic acid, etc. Large quantities of it are consumed for the production of acetate fiber, non-flammable film, and organic glass that transmits UV rays.

Its salts, acetates, are widely used. Lead (II) acetate is used to make lead white and lead lotion in medicine, iron (III) and aluminum acetates are used as mordants for crumbling fabrics, and copper (II) acetate is used to control plant pests. A 3-9% aqueous solution of acetic acid - vinegar - is a flavoring and preservative. Some compounds that are produced using acetic acid, such as the sodium salt of 2,4-dichlorophenoxyacetic acid, are herbicides - a means of controlling weeds. Sodium and potassium salts of higher carboxylic acids are the main components of soap.

Formic acid esters are used as solvents and fragrances

Bibliography

G.E. Rudzitis, F.G. Feldman Chemistry: Organic chemistry: Textbook for 10th grade. educational institutions. - 5th ed. - M.: Education, 1998. - 160 p.

O.S.Gabrielyan Chemistry. 10th grade: Textbook for general educational institutions / O.S.Gabrielyan.-11th ed., revised-M. : Bustard, 2006.- 267, p.

L.S. Guzey Chemistry. Grade 11: Textbook for educational institutions / R.P. Surovtseva, G.G. Lysova - 7th ed., stereotype. M.: Bustard, 2006. - 223, p.

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1. Classification of carboxylic acids.

2. Nomenclature, receipt.

3. Isomerism, structure.

4. Monocarboxylic acids (saturated, unsaturated, aromatic).

5. Dicarboxylic acids.

6. Derivatives of carboxylic acids.

Hydrocarbon derivatives containing the carboxyl group -COOH are called carboxylic acids.

Carboxylic acids are classified according to two structural characteristics:

a) according to the nature of the radical, there are aliphatic R(COOH)n (saturated, unsaturated) and aromatic acids Ar(COOH)n;

b) according to the number of carboxyl groups, they distinguish between monocarboxylic (n = 1), di- and polycarboxylic (n ≥ 2) acids.

Nomenclature. According to the IUPAC nomenclature, the names of acids are formed from the name of the hydrocarbon, adding the ending - oic acid, for example, CH 3 COOH - ethanoic acid. Trivial names of acids are widespread: acetic, butyric, oleic, tartaric, oxalic, etc.

Receipt.

a) O oxidation of alkenes, alkynes, primary alcohols and aldehydes (see “Chemical properties” of the corresponding classes of compounds):

R-CH = CH-CH 3 + [O] → R-COOH + CH 3 -COOH

R-CH 2 -OH + [O] → R-CH=O + [O] → R-COOH

alcohol aldehyde acid

Oxidizing agents - KMnO 4, K 2 Cr 2 O 7 in an acidic environment.

b) Oxidation of alkanes: R-CH 2 -CH 2 -R" + [O] → R-COOH + R"-COOH + H 2 O Oxidation is carried out in the presence of catalysts - cobalt or manganese salts.

V) Oxidation of alkylbenzenes (see “Chemical properties of aromatic hydrocarbons”). G) Hydrolysis of nitriles, derivatives of carboxylic acids in an acidic or alkaline environment: R-C≡N + 2H 2 O + HCl → R-COOH + NH 4 Cl

R-C≡N + H 2 O + NaOH → R-COONa + NH 3

X: -OR, -Hal, -OCOR, -NH 2.

d ) Organometallic synthesis:

Structure. The carbon and oxygen atoms of the carboxyl group are in a state of sp 2 hybridization. σ- the C-O bond is formed by the overlap of sp 2 -sp 2 hybridized orbitals, σ- O-H bond - overlapping sp 2 - s-orbitals, π- C-O bond - by overlapping unhybridized p-p orbitals. The carboxyl group is planar p,π- coupled system:

As a result of conjugation, the C-O bond becomes shorter compared to a similar bond in alcohols, the C=O bond becomes longer compared to a similar bond in carbonyl compounds, i.e. there is a noticeable alignment of bond lengths in the carboxyl group.

The intermolecular interaction of carboxylic acids is characterized by strong hydrogen bonds, resulting in the formation of linear associates and cyclic dimers:

And

The hydrogen bond in carboxylic acids is stronger than in alcohols. This causes higher solubility in water, boiling and melting points of carboxylic acids compared to alcohols of similar molecular weight.

The mutual influence of the carbonyl and hydroxyl groups in the carboxyl group determines chemical properties that differ from the properties of carbonyl compounds and alcohols. Reactions involving the carboxyl group proceed in the following main directions: acid-base interaction, nucleophilic substitution, decarboxylation.

The chemical properties of carboxylic acids are discussed below using the example of saturated monocarboxylic acids.

Monocarboxylic acids(saturated, unsaturated, aromatic acids).

General molecular formula saturated monocarboxylic acids

СnН2nО2.

Table 4.

Homologous series of saturated monocarboxylic acids

The table shows the names of acyl (R-CO-) and acidic (R-COO-) residues of some monocarboxylic acids of the limiting series.

Isomerism. Saturated monocarboxylic acids are characterized by structural isomerism (different structure of the carbon chain and different arrangement of the functional group). For example, the molecular formula C 4 H 8 O 2 corresponds to the isomers: CH 3 -CH 2 -CH 2 -COOH (butanoic acid), (CH 3) 2 CH-COOH (2-methylpropanoic or isobutanoic acid), CH 3 -CH 2 -COOCH 3 (methylpropanoate) (for details, see the “Isomerism” section).

Physical properties. Acids with the number of carbon atoms from 1 to 9 are colorless liquids with unpleasant odors; those with C≥ 10 are odorless solids. Acids with the number of carbon atoms from 1 to 3 are highly soluble in water, with C≥ 4 - substances insoluble in water, but highly soluble in organic solvents (alcohol, ether).

Chemical properties.

a) acidic properties

Aqueous solutions of carboxylic acids have an acidic reaction:

acid carboxylate ion

Delocalization of electron density ( p,π- conjugation) in the carboxylate ion leads to a complete alignment of the orders of length of both C-O bonds, increasing its stability compared to alcoholate and phenolate ions. Therefore, carboxylic acids are stronger than alcohols and phenols, carbonic acid, but inferior to such mineral acids as hydrochloric, sulfuric, nitric and phosphoric.

The strength of carboxylic acids is significantly influenced by the nature of the radical at the carboxyl group: electron-donating groups destabilize the carboxylate ion and, therefore, reduce acidic properties, electron-withdrawing groups stabilize the carboxylate ion and increase acidic properties.

In the homologous series of saturated monocarboxylic acids, with an increase in the number of carbon atoms in the acid composition, the acidic properties decrease. The strongest acid is formic acid.

Carboxylic acids form salts when interacting with active metals, metal oxides, bases, and salts. For example, CH 3 -COOH + Na 2 CO 3 → CH 3 -COONa + CO 2 + H 2 O

Salts of lower carboxylic acids are highly soluble in water, while higher ones - only sodium and potassium salts are soluble. Salts of carboxylic acids and alkali metals undergo hydrolysis and their aqueous solutions have an alkaline environment:

R-COO - Na + + HOH ↔ R-COOH + NaOH

Salts of carboxylic acids are used to obtain derivatives of carboxylic acids, hydrocarbons, and surfactants.

Sodium and potassium salts of higher fatty acids - soaps - are of great importance in the national economy. Ordinary solid soap is a mixture of sodium salts of various acids, mainly palmitic and stearic: C 15 H 31 COONa (sodium palmitate) and C 17 H 35 COONa (sodium stearate). Potassium soaps are liquid.

In ancient times, soap was made from fat and beech ash. During the Renaissance, they returned to the forgotten craft, the recipes were kept secret. Nowadays soaps are produced mainly from vegetable and animal fats.

Soaps are surfactants, a chemical hybrid consisting of a hydrophilic (carboxylate ion) and a hydrophobic (fear) end (hydrocarbon radical). Soaps sharply reduce the surface tension of water, cause wetting of particles or surfaces that have a water-repellent effect, and promote the formation of stable foam.

In hard water, the washing ability of soap sharply decreases; soluble sodium or potassium salts of higher fatty acids enter into an exchange reaction with soluble acidic carbonates of alkaline earth metals, mainly calcium, present in hard water:

2C 15 H 31 COONa + Ca(HCO 3) 2 → (C 15 H 31 COO) 2 Ca + 2NaHCO 3

The resulting insoluble calcium salts of higher fatty acids form precipitates.

Huge quantities of soap are used in everyday life for hygienic purposes, for washing, etc., as well as in various industries, especially for washing wool, fabrics and other textile materials.

b) nucleophilic substitution- S N (formation of functional derivatives of carboxylic acids)

The main type of reactions of carboxylic acids is nucleophilic substitution at the sp 2 -hybridized carbon atom of the carboxyl group, as a result of which the hydroxyl group is replaced by another nucleophile. Due to r,π-s Since in the carboxyl group the mobility of the hydroxyl group is much lower compared to alcohols, therefore nucleophilic substitution reactions are carried out in the presence of a catalyst - a mineral acid or alkali.

The reactions are accompanied by the formation of functional derivatives of carboxylic acids - acid halides (1), anhydrides (2), esters (3), amides (4):

V)decarboxylation

Decarboxylation is the removal of a carboxyl group in the form of CO 2 . Depending on the reaction conditions, compounds of different classes are formed. Electron-withdrawing groups in the radical at the carboxyl group facilitate the occurrence of reactions of this type.

Examples of decarboxylation reactions:

1) thermal decomposition of sodium or potassium salts in the presence of soda lime

R-COONa + NaOH → R-H + Na 2 CO 3

2) thermal decomposition of calcium or barium salts

R-COO-Ca-OOS-R → R-CO-R + CaCO 3

3) electrolysis of sodium or potassium salts (Kolbe synthesis)

2R-COONa + 2НН → R-R + 2NaОН +2CO 2 + Н 2

d) replacement of hydrogen atomsα-carbon atom

Halogen atom in α -halogenated acids are easily replaced by nucleophilic reagents. Therefore, α-halogen-substituted acids are starting materials in the synthesis of a wide range of substituted acids, including α-amino and α-hydroxy acids:

propionic acid α-chloropropionic acid

As a result of the influence of the halogen atom on the carboxyl group, halogenated acids (for example, trichloroacetic acid) are many times stronger acids and approach strong inorganic acids in this regard.

e) specific properties of formic acid

In the composition of formic acid, along with the carboxyl group, a carbonyl group can be distinguished, therefore formic acid exhibits the properties of both carboxylic acids and aldehydes:

1. oxidation

HCOOH + [O]→ CO 2 + H 2 O

oxidizing agents: Cu(OH) 2, OH ("silver mirror" reaction)

2. dehydration

HCOOH + H 2 SO 4 (conc.) → CO + H 2 O

Occurrence in nature and use of acids:

a) formic acid- colorless liquid with a pungent odor, miscible with water. It was first isolated in the 17th century from red ants by steam distillation. In nature, free formic acid is found in the secretions of ants, in nettle juice, and in the sweat of animals. In industry, formic acid is produced by passing carbon monoxide through heated alkali:

NaOH + CO → H-COONa

H-COONa + H 2 SO 4 → H-COOH + NaHSO 4

Formic acid is used in dyeing fabrics, as a reducing agent, and in various organic syntheses.

b) acetic acid

Anhydrous acetic acid (glacial acetic acid) is a colorless liquid with a characteristic pungent odor and sour taste, freezes at a temperature of +16 0 C, forming a crystalline mass resembling ice. A 70-80% aqueous solution of acid is called acetic essence.

It is widespread in nature, found in animal excretions, in plant organisms, and is formed as a result of fermentation and putrefaction processes in sour milk, cheese, souring wine, cooking butter, etc. They are used in the food industry as a flavoring and preservative, widely in the production of artificial fibers, solvents, and in the production of medicines.

c) butyric acid- colorless liquid, acid solutions have an unpleasant odor of old butter and sweat. Occurs in nature in the form of esters; esters of glycerin and butyric acid are found in fats and butter. Used in organic synthesis to obtain aromatic esters.

c) isovaleric acid - colorless liquid with a pungent odor, in diluted solutions it has the smell of valerian. Found in the roots of valerian, it is used to obtain medicinal substances and essences.

d) palmitic, stearic acids

These are solids with faint odors and are poorly soluble in water. Widely distributed in nature, they are found in fats in the form of esters with glycerol. Used to produce suppositories and surfactants.

Unsaturated acids

Unsaturated acids are carboxylic acids containing multiple bonds (double or triple) in the hydrocarbon radical. The most important are unsaturated mono- and dicarboxylic acids with double bonds.

Nomenclature and isomerism.

The names for unsaturated acids are compiled according to the IUPAC nomenclature, but most often trivial names are used:

CH 2 =CH-COOH - 2-propenoic or acrylic acid

CH 3 -CH=CH-COOH - 2-butenoic or crotonic acid

CH 2 =C(CH 3)-COOH - 2-methylpropenoic or methacrylic acid

CH 2 =CH-CH 2 -COOH - 3-butenoic or vinyl acetic acid

CH 3 -(CH 2) 7 -CH=CH-(CH 2) 7 -COOH - oleic acid

CH 3 -(CH 2) 4 -CH=CH-CH 2 -CH=CH-(CH 2) 7 -COOH - linoleic acid

CH 3 -CH 2 -CH=CH-CH 2 -CH=CH-CH 2 -CH=CH-(CH 2) 7 -COOH-linolenic acid.

The structural isomerism of unsaturated acids is due to the isomerism of the carbon skeleton (for example, crotonic and methacrylic acids) and the isomerism of the position of the double bond (for example, crotonic and vinyl acetic acids).

Unsaturated acids with a double bond, as well as ethylene hydrocarbons, are also characterized by geometric or cis-trans isomerism.

Chemical properties. In terms of chemical properties, unsaturated acids are similar to mono- and dicarboxylic acids, but have a number of distinctive features due to the presence of multiple bonds and a carboxyl group in the molecule and their mutual influence.

Unsaturated acids, especially those containing a multiple bond in the α-position to the carboxyl group, are stronger acids than saturated acids. Thus, unsaturated acrylic acid (K=5.6*10 -5) is four times stronger than propionic acid (K=1.34*10 -5).

Unsaturated acids enter into all reactions at the site of multiple bonds characteristic of unsaturated hydrocarbons.

A)Eelectrophilic addition:

1. halogenation

β CH 2 = α CH-COOH + Br 2 → CH 2 Br-CHBr-COOH

propenoic acid α,β-dibromopropionic acid

This is a qualitative reaction to unsaturated acids; the number of multiple bonds can be determined by the amount of halogen (bromine or iodine) consumed .

2. hydrohalogenation

α CH 2 δ+ = β CH δ- →COOH+ H δ+ - Br δ- → CH 2 Br-CH 2 -COOH

For α,β-unsaturated acids, the addition reaction proceeds against Markovnikov's rule.

b)Ghydrogenation

In the presence of catalysts (Pt, Ni), hydrogen is added at the site of the double bond and unsaturated acids become saturated:

CH 2 =CH-COOH + H 2 → CH 3 -CH 2 -COOH

acrylic acid propionic acid

Hydrogenation process ( hydrogenation) has great practical importance, especially for the conversion of higher unsaturated fatty acids into saturated ones; This is the basis for the transformation of liquid oils into solid fats.

V)ABOUTacidification

Under the conditions of the Wagner reaction (see “Alkenes”), unsaturated acids are oxidized to dihydroxy acids, and during vigorous oxidation - to carboxylic acids.

a) acrylic CH 2 =CH-COOH and methacrylic CH 2 =C(CH 3 )-COOH acid - colorless liquids with pungent odors. Acids and their methyl esters easily polymerize, which is the basis for their use in the polymer materials industry (organic glass).

Acrylic acid nitrile - acrylonitrile CH 2 =CH-C≡N is used in the production of synthetic rubber and high-molecular polyacrylonitrile (PAN) resin, from which synthetic fiber nitron (or orlon) is produced - one of the types of artificial wool.

b) higher unsaturated acids

-cis-oleic acid in the form of an ester with glycerin is part of almost all fats of animal and vegetable origin, the content of oleic acid in olive (“Provence”) oil is especially high - up to 80%, potassium and sodium salts of oleic acid are soaps;

-cis, cis-linoleic and cis, cis- Linolenic acid in the form of an ester with glycerin is part of many vegetable oils, for example soybean, hemp, and flaxseed oil. Linoleic and linolenic acids are called essential acids because they are not synthesized in the human body. It is these acids that have the greatest biological activity: they are involved in the transfer and metabolism of cholesterol, the synthesis of prostaglandins and other vital substances, maintain the structure of cell membranes, are necessary for the functioning of the visual apparatus and nervous system, and affect the immune system. The absence of these acids in food inhibits the growth of animals, inhibits their reproductive function, and causes various diseases.

Acid esters are used in the production of varnishes and paints (drying oils).

Aromatic monocarboxylic acids

TO Islots are colorless crystalline substances, some of them have a faint, pleasant odor. They are characterized by a conjugate (π, π) system:

The most important representatives:

benzoic acid

phenylacetic acid

trance-cinnamic acid

Aromatic acids are stronger acids than saturated acids (except formic acid). Acids of this type are characterized by all reactions of saturated carboxylic acids in the carboxyl group and reactions of electrophilic substitution in the benzene ring (the carboxyl group is a substituent of the 2nd kind, m-orientator).

Occurrence in nature and use of acids:

Aromatic acids are used to produce dyes, fragrances and medicinal substances; Acid esters are found in essential oils, resins and balms. Benzoic acid and its sodium salt are found in the fruits of viburnum, rowan, lingonberries, cranberries, give them a bitter taste, have bactericidal properties, and are widely used in food preservation.

O-sulfobenzoic acid amide is called saccharin, it is 400 times sweeter than sugar.

Derivatives of carboxylic acids.

General formula of carboxylic acid derivatives:

Where X: - Hal, -OOS-R, -OR, -NH 2.

For derivatives of carboxylic acids, nucleophilic substitution reactions (S N) are most characteristic. Since the products of these reactions contain an acyl group R-C=O, the reactions are called acylation, and carboxylic acids and their derivatives are called acylating reagents.

In general, the acylation process can be represented by the following scheme:

According to their acylating ability, derivatives of carboxylic acids are arranged in the following series:

salt< амиды < сложные эфиры <ангидриды <галогенангидриды

In this series, previous members can be obtained from subsequent ones by acylation of the corresponding nucleophile (for example, alcohol, ammonia, etc.). All functional derivatives can be obtained directly from acids and are converted to them by hydrolysis.

Amides, unlike other derivatives of carboxylic acids, form intermolecular hydrogen bonds and are solids (formic acid amide HCONH 2 is a liquid).

Esters

Receipt methods. The main method for producing esters is through nucleophilic substitution reactions:

a) esterification reaction R-CO HE + RABOUT-H ↔ R-CO-O R + H 2 O

The reaction is carried out in the presence of a catalyst - mineral acid. Esterification reactions are reversible. To shift the equilibrium towards the formation of an ester, an excess of one of the reactants or the removal of products from the reaction sphere is used.

b) acylation of alcohols with acid halides and anhydrides

c) from salts of carboxylic acids and alkyl halides

R-COONa + RCl → RCOOR + NaCl Nomenclature. According to IUPAC nomenclature, the names of esters are as follows:

CH 3 -SN 2 -SN 2 -WITH O-O CH 3

hydrocarbon radical

radical + hydrocarbon + oate - methyl butanoate.

If trivial names of acyl residues are indicated, then the name of this ester - methyl butyrate. Esters can be called by radical functional nomenclature - butyric acid methyl ester.

Physical properties. Esters are colorless liquids, insoluble in water and have low boiling and melting points compared to parent acids and alcohols, which is due to the absence of intermolecular hydrogen bonds in esters. Many esters have a pleasant odor, often the smell of berries or fruits (fruit essences).

Chemical properties. For esters, the most characteristic reactions are nucleophilic substitution (S N), occurring in the presence of an acid or base catalyst. The most important S N reactions are hydrolysis, ammonolysis and transesterification.

Acid hydrolysis of esters is a reversible reaction, alkaline hydrolysis is irreversible.

RCOOR + H 2 O(H +) ↔ RCOOH + ROH

RCOOR + NaOH → RCOO - Na + + ROH

Fats

Fats (triglycerides) are esters formed by glycerol and higher saturated and unsaturated acids.

Several dozen different saturated and unsaturated acids have been isolated from fats; almost all of them contain unbranched chains of carbon atoms, the number of which is usually even and ranges from 4 to 26. However, it is the higher acids, mainly with 16 and 18 carbon atoms, that are the main component of all fats. Of the saturated higher fatty acids, the most important are palmitic C 15 H 31 COOH and stearic C 17 H 35 COOH; among unsaturated fatty acids - oleic C 17 H 33 COOH (with one double bond), linoleic C 17 H 31 COOH (with two double bonds) and linolenic C 17 H 29 COOH (with three double bonds). Unsaturated acids containing a fragment (-CH 2 -CH=CH-) in the radical are called essential.

Simple triglycerides contain residues of identical fatty acids and mixed residues of different fatty acids. The names are based on the names of the acyl residues included in their composition of fatty acids:

tripalmitin dioleostearin

The importance of fats is extremely high. First of all, they are the most important component of human and animal food, along with carbohydrates and proteins. Vegetable oils have the greatest nutritional value, which, along with essential fatty acids, contain phospholipids, vitamins, and beneficial phytosterols (precursors of vitamin D) necessary for the body. The daily requirement of an adult for fats is 80-100g.

Fats are practically insoluble in water, but are highly soluble in alcohol, ether and other organic solvents. The melting point of fats depends on what acids they contain. Fats containing predominantly residues of saturated acids (animal fats - beef, lamb or lard) have the highest T pl. and are solid or ointment-like substances. Fats containing predominantly residues of unsaturated acids (vegetable oils - sunflower, olive, flaxseed, etc.), liquids with lower melting points.

Chemical properties triglycerides are determined by the presence of an ester bond and unsaturation:

a) hydrogenation (hydrogenation) of fats

The addition of hydrogen at the site of double bonds in acid residues is carried out in the presence of a catalyst - finely crushed metallic nickel at 160-240 0 C and a pressure of up to 3 atm. In this case, liquid fats and oils are converted into solid saturated fats - lard, which is widely used in the production of margarine, soap, and glycerin.

b) hydrolysis of fats

Alkaline hydrolysis (saponification) of fats produces salts of fatty acids (soaps) and glycerol, while acid hydrolysis produces fatty acids and glycerol.

c) addition and oxidation

Trilglycerides containing unsaturated fatty acid residues undergo addition reactions at the double bond (bromination, iodination) and oxidation with potassium permanganate. Both reactions allow you to determine the degree of unsaturation of fats.

All fats are flammable substances. When they burn, a large amount of heat is released: 1 g of fat when burned gives 9300 cal.

Do you know that

In 1906, Russian scientist S.A. Fokin developed it, and in 1909. He also implemented the method of hydrogenation (hardening) of fats on an industrial scale.

Margarine (from Greek - “pearls”) was obtained in 1869. Its various varieties are obtained by mixing lard with milk, and in some cases with egg yolk. The resulting product is reminiscent of butter in appearance; the pleasant smell of margarine is achieved by introducing special flavors into its composition - complex compositions of various substances, an indispensable component of which is diacetyl (butanedione), a yellow liquid found in cow butter.

However, there are also animal fats that contain a significant amount of unsaturated acids and are liquid substances (blue, cod oil or fish oil).

Vegetable fats and oils are extracted from the seeds and pulp of fruits of various plants. They are distinguished by a high content of oleic and other unsaturated acids and contain only a small amount of stearic and palmitic acids (sunflower, olive, cottonseed, linseed and other oils). Only in some vegetable fats are saturated acids predominant, and they are solids (coconut oil, cocoa butter, etc.).

Esters of fruit essences have a pleasant smell of fruits and flowers, for example isoamyl acetate - the smell of pears, amyl formate - cherries, ethyl formate - rum, isoamyl butyrate - pineapples, etc. They are used in the confectionery industry, in the production of soft drinks, and in perfumery.

An extremely valuable synthetic material - organic glass (plexiglass) - is prepared from polymethyl methacrylate. The latter is superior to silicate glass in transparency and ability to transmit UV rays. It is used in mechanical and instrument making, in the manufacture of various household and sanitary items, dishes, jewelry, and watch glasses. Due to its physiological indifference, polymethyl methacrylate has found application in the manufacture of dentures, etc.

Vinyl acetate is an ester of vinyl alcohol and acetic acid. It is obtained, for example, by passing a mixture of acetic acid and acetylene vapors over cadmium and zinc acetates at 180-220 o C:

CH 3 -COOH + CH≡CH → CH 3 -CO-O-CH=CH 2

Vinyl acetate is a colorless liquid that easily polymerizes, forming a synthetic polymer - polyvinyl acetate (PVA), used for the manufacture of varnishes, adhesives, and artificial leather.

Dicarboxylic acids

Dicarboxylic acids contain two carboxyl groups. The best known are linear acids containing from 2 to 6 carbon atoms:

NOOS-COON - ethane diova (IUPAC nomenclature) or oxalic acid (trivial nomenclature)

NOOS-CH 2 -COOH - propanedioic or malonic acid

NOOS-CH 2 -CH 2 -COOH - butanedioic or succinic acid

NOOS-CH 2 -CH 2 -CH 2 -COOH - pentanedioic or glutaric acid

NOOS-CH 2 -CH 2 -CH 2 -COOH - adipinoic acid

Physical properties. Dibasic acids are crystalline substances with high melting points, and for acids with an even number of carbon atoms it is higher; lower acids are soluble in water.

Chemical properties. In terms of chemical properties, dibasic acids are similar to monocarboxylic acids, but have a number of distinctive features due to the presence of two carboxyl groups in the molecules and their mutual influence.

Dicarboxylic acids are stronger acids than monocarboxylic acids with the same number of carbon atoms: Kion. oxalic acid (H 2 C 2 O 4) - 5.9 10 -2, 6.4 10 -5, acetic acid - 1.76 10 -5. As the distance between carboxylic groups increases, the acidic properties of dicarboxylic acids decrease. Dicarboxylic acids can form two series of salts - acidic, for example HOOC-COONa, and average - NaOOC-COONa.

Dicarboxylic acids have a number of specific properties, which are determined by the presence of two carboxyl groups in the molecule. For example, the ratio of dicarboxylic acids to heat.

Transformations of dicarboxylic acids upon heating depend on the number of carbon atoms in their composition and are determined by the possibility of the formation of thermodynamically stable five- and six-membered cycles.

When oxalic and malonic acids are heated, decarboxylation occurs to form monocarboxylic acids:

HOOC-CH 2 -COOH → CH 3 -COOH + CO 2

When heated, succinic and glutaric acids easily split off water to form five- and six-membered cyclic anhydrides:

When heated, adipic acid decarboxylates to form a cyclic ketone - cyclopentanone:

Dicarboxylic acids react with diamines and diols to form polyamides and polyesters, respectively, which are used in the production of synthetic fibers.

Along with saturated dicarboxylic acids, unsaturated, aromatic dicarboxylic acids are known.

Occurrence in nature and use of acids:

Oxalic acid widespread in the plant world. It is found in the form of salts in the leaves of sorrel, rhubarb, and sorrel. In the human body it forms sparingly soluble salts (oxalates), for example calcium oxalate, which are deposited in the form of stones in the kidneys and bladder. Used as a bleaching agent: removing rust, paints, varnish, ink; in organic synthesis.

Malonic acid (esters and salts - malonoates) found in some plants, such as sugar beets. Widely used in organic synthesis for the production of carboxylic acids.

succinic acid (salts and esters are called succinates) participates in metabolic processes occurring in the body. It is an intermediate compound in the tricarboxylic acid cycle. In 1556, the German alchemist Agricola first isolated amber from the products of dry distillation. The acid and its anhydride are widely used in organic synthesis.

Fumaric acid (HOOC-CH=CH-COOH - trans- butenedioic acid), Unlike cis- maleic , widespread in nature, found in many plants, many in mushrooms, and participates in the metabolic process, in particular in the tricarboxylic acid cycle.

Maleic acid(cis- butenedioic acid) does not occur in nature. The acid and its anhydride are widely used in organic synthesis.

Ortho-phthalic acid, acid derivatives - phthalic anhydride, esters - phthalates (repellents) are widely used.

Terephthalic acid is a large-scale industrial product used to produce a number of polymers - for example, lavsan fiber, polyethylene terephthalate (PET), from which plastic dishes, bottles, etc. are made.