§12. Carboxylic acids. Carboxylic acids: physical properties. Salts of carboxylic acids The simplest carboxylic acid is formic

DEFINITION

Organic substances whose molecules contain one or more carboxyl groups connected to a hydrocarbon radical are called carboxylic acids.

The first three members of the homologous series of carboxylic acids, including propionic acid, are liquids that have a pungent odor and are highly soluble in water. The following homologues, starting with butyric acid, are also liquids that have a strong unpleasant odor, but are poorly soluble in water. Higher acids, with the number of carbon atoms 10 or more, are solid, odorless, insoluble in water. In general, in a series of homologues, with increasing molecular weight, solubility in water decreases, density decreases, and boiling point increases (Table 1).

Table 1. Homologous series of carboxylic acids.

Preparation of carboxylic acids

Carboxylic acids are obtained by the oxidation of saturated hydrocarbons, alcohols, and aldehydes. For example, acetic acid - by oxidizing ethanol with a solution of potassium permanganate in an acidic environment when heated:

Chemical properties of carboxylic acids

The chemical properties of carboxylic acids are determined primarily by the peculiarities of their structure. Thus, water-soluble acids can dissociate into ions:

R-COOH↔R-COO - + H + .

Due to the presence of H + ion in water, they have a sour taste, are able to change the color of indicators and conduct electric current. In aqueous solution, these acids are weak electrolytes.

Carboxylic acids have chemical properties characteristic of solutions of inorganic acids, i.e. interact with metals (1), their oxides (2), hydroxides (3) and weak salts (4):

2CH 3 -COOh + Zn → (CH 3 COO) 2 Zn + H 2 (1);

2CH 3 -COOH + CuO→ (CH 3 COO) 2 Cu + H 2 O (2);

R-COOH + KOH → R-COOK + H 2 O (3);

2CH 3 -COOH + NaHCO 3 → CH 3 COONa + H 2 O + CO 2 (4).

A specific property of saturated and unsaturated carboxylic acids, manifested by the functional group, is interaction with alcohols.

Carboxylic acids react with alcohols when heated and in the presence of concentrated sulfuric acid. For example, if ethyl alcohol and a little sulfuric acid are added to acetic acid, then when heated, the smell of ethyl acetic acid (ethyl acetate) appears:

CH 3 -COOH + C 2 H 5 OH ↔CH 3 -C(O)-O-C 2 H 5 + H 2 O.

A specific property of saturated carboxylic acids, manifested by the radical, is the halogenation (chlorination) reaction.

Application of carboxylic acids

Carboxylic acids serve as feedstock for the production of ketones, acid halides, vinyl esters and other important classes of organic compounds.

Formic acid is widely used to obtain esters used in perfumery, in the leather industry (tanning leather), in the textile industry (as a mordant for dyeing), as a solvent and preservative.

An aqueous solution (70-80%) of acetic acid is called vinegar essence, and a 3-9% aqueous solution is called table vinegar. The essence is often used to obtain vinegar at home by dilution.

Examples of problem solving

EXAMPLE 1

Exercise

What chemical reactions can be used to carry out the following transformations:

a) CH 4 → CH 3 Cl → CH 3 OH → HCHO → HCOOH → HCOOK.

Write the reaction equations and indicate the conditions for their occurrence.

Answer

a) Chlorination of methane in the light leads to the production of chloromethane:

CH 4 + Cl 2 →CH 3 Cl + HCl.

Halogen derivatives of alkanes undergo hydrolysis in an aqueous or alkaline medium to form alcohols:

CH 3 Cl + NaOH → CH 3 OH + NaCl.

As a result of the oxidation of primary alcohols, for example, with potassium dichromate in an acidic environment in the presence of a catalyst (Cu, CuO, Pt, Ag), aldehydes are formed:

CH 3 OH+ [O] →HCHO.

Aldehydes are easily oxidized to the corresponding carboxylic acids, for example, with potassium permanganate:

HCHO + [O] →HCOOH.

Carboxylic acids exhibit all the properties inherent in weak mineral acids, i.e. capable of interacting with active metals to form salts:

2HCOOH+ 2K→2HCOOK + H 2 .

EXAMPLE 2

Exercise

Write the reaction equations between the following substances: a) 2-methylpropanoic acid and chlorine; b) acetic acid and propanol-2; c) acrylic acid and bromine water; d) 2-methylbutanoic acid and phosphorus (V) chloride. Specify the reaction conditions.

Answer

a) as a result of the reaction between 2-methylpropanoic acid and chlorine, the hydrogen atom is replaced in the hydrocarbon radical located in the a-position; 2-methyl-2-chloropropanoic acid is formed

H 3 C-C(CH 3)H-COOH + Cl 2 → H 3 C-C(CH 3)Cl-COOH + HCl (kat = P).

b) as a result of the reaction between acetic acid and propanol-2, an ester is formed - isopropyl ester of acetic acid.

CH 3 -COOH + CH 3 -C(OH)H-CH 3 → CH 3 -C(O)-O-C(CH 3)-CH 3 .

c) as a result of the interaction reaction between acrylic acid and bromine water, the addition of a halogen at the site of the double bond in accordance with Markovnikov’s rule; 2,3-dibromopropanoic acid is formed

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

d) as a result of the reaction between 2-methylbutanoic acid and phosphorus (V) chloride, the corresponding acid chloride is formed

CH 3 -CH 2 -C(CH 3)H-COOH + PCl 5 →CH 3 -CH 2 -C(CH 3)H-COOCl + POCl 3 + HCl.

Carboxylic acids- organic substances whose molecules contain one or more carboxyl groups.

The carboxyl group (abbreviated as COOH) is a functional group of carboxylic acids and consists of a carbonyl group and an associated hydroxyl group.

Based on the number of carboxyl groups, carboxylic acids are divided into monobasic, dibasic, etc.

The general formula of monobasic carboxylic acids is R—COOH. An example of a dibasic acid is oxalic acid HOOC—COOH.

Based on the type of radical, carboxylic acids are divided into saturated (for example, acetic acid CH 3 COOH), unsaturated [for example, acrylic acid CH 2 =CH—COOH, oleic acid CH 3 —(CH 2) 7 —CH=CH—(CH 2) 7 -COOH] and aromatic (for example, benzoic C 6 H 5 -COOH).

Isomers and homologues

Monobasic saturated carboxylic acids R-COOH are isomers of esters (abbreviated R"-COOR") with the same number of carbon atoms. The general formula for both is C n H 2 n O2.

G	HCOOH methane (ant)
	CH3COOH ethane (acetic)		HCOOCH 3 formic acid methyl ester
	CH3CH2COOH propane (propionic)		HCOOCH 2 CH 3 ethyl formic acid	CH 3 COOCH 3 acetic acid methyl ester
	CH3(CH2)2COOH butane (oil)	2-methylpropane	HCOOCH 2 CH 2 CH 3 propyl ester of formic acid	CH 3 COOCH 2 CH 3 ethyl acetate	CH 3 CH 2 COOCH 3 propionic acid methyl ester
	isomers

Algorithm for composing the names of carboxylic acids

Find the carbon backbone - this is the longest chain of carbon atoms, including the carbon atom of the carboxyl group.
Number the carbon atoms in the main chain, starting with the carboxyl carbon atom.
Name the compound using the algorithm for hydrocarbons.
At the end of the name, add the suffix “-ov”, the ending “-aya” and the word “acid”.

In molecules of carboxylic acids p-electrons of the oxygen atoms of the hydroxyl group interact with electrons of the -bond of the carbonyl group, as a result of which the polarity of the O-H bond increases, the -bond in the carbonyl group strengthens, the partial charge (+) on the carbon atom decreases and the partial charge (+) on the hydrogen atom increases .

The latter promotes the formation of strong hydrogen bonds between carboxylic acid molecules.

The physical properties of saturated monobasic carboxylic acids are largely due to the presence of strong hydrogen bonds between molecules (stronger than between alcohol molecules). Therefore, the boiling points and solubility in water of acids are higher than those of the corresponding alcohols.

Chemical properties of acids

Strengthening the -bond in the carbonyl group leads to the fact that addition reactions are uncharacteristic for carboxylic acids.

Combustion:
CH 3 COOH + 2O 2 2CO 2 + 2H 2 O
Acidic properties.
Due to the high polarity of the O-H bond, carboxylic acids in an aqueous solution noticeably dissociate (more precisely, react reversibly with it):
HCOOH HCOO - + H + (more precisely HCOOH + H 2 O HCOO - + H 3 O +)

All carboxylic acids are weak electrolytes. As the number of carbon atoms increases, the strength of acids decreases (due to a decrease in the polarity of the O-H bond); on the contrary, the introduction of halogen atoms into the hydrocarbon radical leads to an increase in the strength of the acid. Yes, in a row
HCOOH CH 3 COOH C 2 H 5 COOH

the strength of acids decreases, and in the series
Increasing.
Carboxylic acids exhibit all the properties inherent in weak acids:
Mg + 2CH 3 COOH (CH 3 COO) 2 Mg + H 2
CaO + 2CH 3 COOH (CH 3 COO) 2 Ca + H 2 O
NaOH + CH 3 COOH CH 3 COONa + H 2 O
K 2 CO 3 + 2CH 3 COOH 2CH 3 COOK + H 2 O + CO 2
Esterification (reaction of carboxylic acids with alcohols leading to the formation of an ester):

Polyhydric alcohols, such as glycerol, can also enter into the esterification reaction. Esters formed by glycerol and higher carboxylic acids (fatty acids) are fats.
Fats are mixtures of triglycerides. Saturated fatty acids (palmitic C 15 H 31 COOH, stearic C 17 H 35 COOH) form solid fats of animal origin, and unsaturated fatty acids (oleic C 17 H 33 COOH, linoleic C 17 H 31 COOH, etc.) form liquid fats (oils) of plant origin.
Substitution in a hydrocarbon radical:

Substitution occurs in the - position.
The peculiarity of formic acid HCOOH is that this substance is a bifunctional compound; it is both a carboxylic acid and an aldehyde:

Therefore, formic acid, among other things, reacts with an ammonia solution of silver oxide (silver mirror reaction; qualitative reaction):
HCOOH + Ag 2 O (ammonia solution) CO 2 + H 2 O + 2Ag

Preparation of carboxylic acids

.
O

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The group of -C atoms is called a carboxyl group or carboxyl.
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OH
Organic acids containing one carboxyl group in the molecule are monobasic. The general formula of these acids is RCOOH.

Carboxylic acids containing two carboxyl groups are called dibasic. These include, for example, oxalic and succinic acids.

There are also polybasic carboxylic acids containing more than two carboxyl groups. These include, for example, tribasic citric acid. Depending on the nature of the hydrocarbon radical, carboxylic acids are divided into saturated, unsaturated, and aromatic.

Saturated, or saturated, carboxylic acids are, for example, propanoic (propionic) acid or the already familiar succinic acid.

Obviously, saturated carboxylic acids do not contain P-bonds in a hydrocarbon radical.

In molecules of unsaturated carboxylic acids, the carboxyl group is associated with an unsaturated, unsaturated hydrocarbon radical, for example in molecules of acrylic (propenoic) CH2=CH-COOH or oleic CH3-(CH2)7-CH=CH-(CH2)7-COOH and other acids.

As can be seen from the formula of benzoic acid, it is aromatic, since it contains an aromatic (benzene) ring in the molecule.

Nomenclature and isomerism

We have already considered the general principles of the formation of the names of carboxylic acids, as well as other organic compounds. 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 (alkane with the same number of carbon atoms in the molecule) with the addition of the suffix -ov, the ending -aya and the word acid. The numbering of carbon atoms begins with the carboxyl group. For example:

Many acids also have historically established, or trivial, names (Table 6).

After our first acquaintance with the diverse and interesting world of organic acids, we will consider in more detail the saturated monobasic carboxylic acids.

It is clear that the composition of these acids will be reflected by the general formula C n H 2n O2, or C n H 2n +1 COOH, or RCOOH.

Physical properties of saturated monobasic carboxylic acids

Lower acids, i.e. acids with a relatively small molecular weight containing up to four carbon atoms per molecule, are liquids with a characteristic pungent odor (remember the smell of acetic acid). Acids containing from 4 to 9 carbon atoms are viscous oily liquids with an unpleasant odor; containing more than 9 carbon atoms per molecule - solids that do not dissolve in water. The boiling points of saturated monobasic carboxylic acids increase with increasing number of carbon atoms in the molecule and, consequently, with increasing relative molecular weight. For example, the boiling point of formic acid is 101 °C, acetic acid is 118 °C, and propionic acid is 141 °C.

The simplest carboxylic acid, formic HCOOH, having a small relative molecular weight (46), under normal conditions is a liquid with a boiling point of 100.8 °C. At the same time, butane (MR(C4H10) = 58) under the same conditions is gaseous and has a boiling point of -0.5 °C. This discrepancy between boiling points and relative molecular weights 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 (think about what causes the polarity of this functional group) and a practically non-polar hydrocarbon radical. The carboxyl group is attracted to water molecules, forming hydrogen bonds with them.

Formic and acetic acids are unlimitedly soluble in water. It is obvious that with an increase in the number of atoms in a hydrocarbon radical, the solubility of carboxylic acids decreases.

Knowing the composition and structure of carboxylic acid molecules, it will not be difficult for us to understand and explain the chemical properties of these substances.

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 highly polar bond between hydrogen and oxygen atoms. These properties are well known to you. Let us consider them again using the example of water-soluble organic acids.

1. Dissociation with the formation of hydrogen cations and anions of the acid residue. More accurately, this process is described by an equation that takes into account the participation of water molecules in it.

The dissociation equilibrium of carboxylic acids is shifted to the left; the vast majority of them are weak electrolytes. Nevertheless, the sour taste of, for example, formic and acetic acids is explained by the dissociation into hydrogen cations and anions of acidic residues.

It is obvious that the presence of “acidic” hydrogen in the molecules of carboxylic acids, i.e., the hydrogen of the carboxyl group, also determines other characteristic properties.

2. Interaction with metals in the electrochemical voltage range up to hydrogen. Thus, iron reduces hydrogen from acetic acid:

2CH3-COOH + Fe -> (CHgCOO)2Fe + H2

3. Interaction with basic oxides to form salt and water:

2R-COOH + CaO -> (R-COO)2Ca + H20

4. Reaction with metal hydroxides to form salt and water (neutralization reaction):

R-COOH + NaOH -> R-COONa + H20 3R-COOH + Ca(OH)2 -> (R-COO)2Ca + 2H20

5. Interaction with salts of weaker acids, with the formation of the latter. Thus, acetic acid displaces stearic acid from sodium stearate and carbonic acid from potassium carbonate.

6. The interaction of carboxylic acids with alcohols to form esters is the esterification reaction already known to you (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 the formation of the ester in the presence of dewatering agents and the removal of ester from the reaction mixture.

In the reverse reaction of esterification, called ester hydrolysis (reacting an ester with water), an acid and an alcohol are formed. It is obvious that polyhydric alcohols, for example glycerol, can also react with carboxylic acids, i.e., enter into an esterification reaction:

All carboxylic acids (except formic acid), along with the carboxyl group, contain a hydrocarbon residue in their molecules. Of course, this cannot but affect the properties of acids, which are determined by the nature of the hydrocarbon residue.

7. Addition reactions at a multiple bond - unsaturated carboxylic acids enter into them; for example, the reaction of hydrogen addition is hydrogenation. When oleic acid is hydrogenated, saturated stearic acid is formed.

Unsaturated carboxylic acids, like other unsaturated compounds, add halogens via a double bond. For example, acrylic acid discolors bromine water.

8. Substitution reactions (with halogens) - saturated carboxylic acids can enter into it; for example, by reacting acetic acid with chlorine, various chlorinated acids can be obtained:

When halogenating carboxylic acids containing more than one carbon atom in the hydrocarbon residue, the formation of products with different positions of the halogen in the molecule is possible. When a reaction occurs via a free radical mechanism, any hydrogen atoms in the hydrocarbon residue can be replaced. If the reaction is carried out in the presence of small amounts of red phosphorus, then it proceeds selectively - hydrogen is replaced only in A-position (at the carbon atom closest to the functional group) in the acid molecule. You will learn the reasons for this selectivity when studying chemistry at a higher educational institution.

Carboxylic acids form various functional derivatives when replacing the hydroxyl group. When these derivatives are hydrolyzed, carboxylic acid is formed again.

Carboxylic acid chloride can be prepared by reacting phosphorus(III) chloride or thionyl chloride (SOCl 2) with acid. Carboxylic acid anhydrides are prepared by reacting chlorine anhydrides with carboxylic acid salts. Esters are formed by the esterification of carboxylic acids with alcohols. Esterification is catalyzed by inorganic acids.

This reaction is initiated by protonation of the carboxyl group - the interaction of a hydrogen cation (proton) with the lone electron pair of the oxygen atom. Protonation of a carboxyl group entails an increase in the positive charge on the carbon atom in it:

Methods of obtaining

Carboxylic acids can be obtained by oxidation of primary alcohols and aldehydes.

Aromatic carboxylic acids are formed by the oxidation of benzene homologues.

Hydrolysis of various carboxylic acid derivatives also produces acids. Thus, the hydrolysis of an ester produces an alcohol and a carboxylic acid. As mentioned above, acid-catalyzed esterification and hydrolysis reactions are reversible. Hydrolysis of the ester under the influence of an aqueous solution of alkali proceeds irreversibly; in this case, not an acid, but its salt is formed from the ester. During the hydrolysis of nitriles, amides are first formed, which are then converted into acids. Carboxylic acids are formed by the interaction of organic magnesium compounds with carbon monoxide (IV).

Individual representatives of carboxylic acids and their significance

Formic (methane) acid HCOOH is a liquid with a pungent odor and a boiling point of 100.8 °C, highly soluble in water. Formic acid is poisonous and causes burns if it comes into contact with the skin! The stinging fluid secreted by ants contains this acid. Formic acid has disinfectant properties and therefore finds its use in the food, leather and pharmaceutical industries, and medicine. It is also used in dyeing fabrics and paper.

Acetic (ethanoic) acid CH3COOH is a colorless liquid with a characteristic pungent odor, miscible with water in any ratio. Aqueous solutions of acetic acid are marketed under the name vinegar (3-5% solution) and 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, tanning, and the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, substances used to control weeds - herbicides - are obtained from it.

Acetic acid is the main component of wine vinegar, the characteristic smell of which is due to it. It is a product of ethanol oxidation and is formed from it when wine is stored in air.

The most important representatives of higher saturated monobasic acids are palmitic C15H31COOH and stearic C17H35COOH acids. Unlike lower acids, these substances are solid and poorly soluble in water.

However, their salts - stearates and palmitates - are highly soluble and have a detergent effect, which is why they are also called soaps. It is clear that these substances are produced on a large scale.

Of the unsaturated higher carboxylic acids, oleic acid C17H33COOH, or (CH2)7COOH, is of greatest importance. 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, the salts of which are found in many plants, for example, sorrel and sorrel. Oxalic acid is a colorless crystalline substance that is highly soluble in water. It is used for polishing metals, in the woodworking and leather industries.

1. Unsaturated elaidic acid C17H33COOH is a trans-isomer of oleic acid. Write the structural formula of this substance.

2. Write an equation for the hydrogenation reaction of oleic acid. Name the product of this reaction.

3. Write an equation for the combustion reaction of stearic acid. What volume of oxygen and air (n.a.) will be required to burn 568 g of stearic acid?

4. A mixture of solid fatty acids - palmitic and stearic - is called stearin (it is from this that stearin suppositories are made). What volume of air (n.a.) will be required to burn a two-hundred-gram stearic candle if stearin contains equal masses of palmitic and stearic acids? What volume of carbon dioxide (n.o.) and mass of water are formed in this case?

5. Solve the previous problem provided that the candle contains equal amounts (same number of moles) of stearic and palmitic acids.

6. To remove rust stains, treat them with a solution of acetic acid. Make up molecular and ionic equations for the reactions occurring in this case, taking into account that rust contains iron(III) oxide and hydroxide - Fe2O3 and Fe(OH)3. Why are such stains not removed with water? Why do they disappear when treated with an acid solution?

7. Baking (baking) soda NaHC03 added to the yeast-free dough is first “quenched” with acetic acid. Do this reaction at home and write its equation, knowing that carbonic acid is weaker than acetic acid. Explain the formation of foam.

8. Knowing that chlorine is more electronegative than carbon, arrange the following acids: acetic, propionic, chloroacetic, dichloroacetic and trichloroacetic acids in order of increasing acidic properties. Justify your result.

9. How can we explain that formic acid reacts in a “silver mirror” reaction? Write an equation for this reaction. What gas can be released in this case?

10. When 3 g of saturated monobasic carboxylic acid reacted with excess magnesium, 560 ml (n.s.) of hydrogen were released. Determine the formula of the acid.

11. Give reaction equations that can be used to describe the chemical properties of acetic acid. Name the products of these reactions.

12. Suggest a simple laboratory method by which you can recognize propanoic and acrylic acids.

13. Write an equation for the reaction of producing methyl formate - an ester of methanol and formic acid. Under what conditions should this reaction be carried out?

14. Make up structural formulas of substances with the composition C3H602. What classes of substances can they be classified into? Give the reaction equations characteristic of each of them.

15. Substance A - an isomer of acetic acid - is insoluble in water, but can undergo hydrolysis. What is the structural formula of substance A? Name the products of its hydrolysis.

16. Make up the structural formulas of the following substances:

a) methyl acetate;
b) oxalic acid;
c) formic acid;
d) dichloroacetic acid;
e) magnesium acetate;
f) ethyl acetate;
g) ethyl formate;
h) acrylic acid.

17*. A sample of saturated monobasic organic acid weighing 3.7 g was neutralized with an aqueous solution of sodium bicarbonate. By passing the liberated gas through lime water, 5.0 g of sediment was obtained. What acid was taken and what was the volume of gas released?

Carboxylic acids in nature

Carboxylic acids are very common in nature. They are found in fruits and plants. They are present in needles, sweat, urine and nettle juice. You know, it turns out that the bulk of acids form esters, which have odors. Thus, the smell of lactic acid, which is contained in human sweat, attracts mosquitoes; they sense it at quite a considerable distance. Therefore, no matter how much you try to drive away the annoying mosquito, it still feels its victim well. In addition to human sweat, lactic acid is found in pickles and sauerkraut.

And female monkeys, in order to attract a male, secrete acetic and propionic acid. A dog's sensitive nose can smell butyric acid, which has a concentration of 10–18 g/cm3.

Many plant species are capable of producing acetic and butyric acid. And some weeds take advantage of this and, by releasing substances, eliminate their competitors, suppressing their growth, and sometimes causing their death.

The Indians also used acid. To destroy the enemy, they soaked the arrows with a deadly poison, which turned out to be a derivative of acetic acid.

And here a natural question arises: do acids pose a danger to human health? After all, oxalic acid, which is widespread in nature and is found in sorrel, oranges, currants and raspberries, for some reason has not found application in the food industry. It turns out that oxalic acid is two hundred times stronger than acetic acid, and can even corrode dishes, and its salts, accumulating in the human body, form stones.

Acids have found wide application in all spheres of human life. They are used in medicine, cosmetology, food industry, agriculture and for household needs.

For medical purposes, organic acids such as lactic, tartaric, and ascorbic are used. Probably each of you used vitamin C to strengthen the body - this is precisely ascorbic acid. It not only helps strengthen the immune system, but also has the ability to remove carcinogens and toxins from the body. Lactic acid is used for cauterization, as it is highly hygroscopic. But tartaric acid acts as a mild laxative, as an antidote for alkali poisoning, and as a component necessary for preparing plasma for blood transfusions.

But fans of cosmetic procedures should know that fruit acids contained in citrus fruits have a beneficial effect on the skin, as, penetrating deep, they can accelerate the process of skin renewal. In addition, the smell of citrus fruits has a tonic effect on the nervous system.

Have you noticed that berries such as cranberries and lingonberries are stored for a long time and remain fresh. Do you know why? It turns out that they contain benzoic acid, which is an excellent preservative.

But in agriculture, succinic acid has found wide use, since it can be used to increase the productivity of cultivated plants. It can also stimulate plant growth and accelerate their development.

1.Carboxylic acids – these are oxygen-containing organic substances whose molecules contain one or more carboxyl groups

(-C OOH ), connected to a carbon radical or hydrogen atom.

The carboxyl group contains two functional groups - carbonyl >C=O and hydroxyl -OH, directly bonded to each other:

2. Classification

A) By the number of carboxyl groups in the molecule

Name	Examples
1) Monobasic	Methane *new* , formic acid Ethane *new* , acetic acid
2) Dibasic	HOOC-COOH Oxalic acid
3) Polybasic

B) By the nature of the hydrocarbon radical

Name	Examples
1) Limit (saturated)	HCOOH Methane *new* , formic acid CH3COOH Ethane *new* , acetic acid
2) Unlimited	Acrylic acid CH 2 = CHCOOH Crotonic acid CH 3 –CH=CH–COOH Oleic CH 3 –(CH 2) 7 –CH=CH–(CH 2) 7 –COOH Linoleic CH 3 –(CH 2) 4 –(CH=CH–CH 2) 2 –(CH 2) 6 –COOH Linolenic CH 3 –CH 2 –(CH=CH–CH 2) 3 –(CH 2) 6 –COOH
3) Aromatic	C 6 H 5 COOH – benzoic acid NOOS–C 6 H 4 –COOH Pair-terephthalic acid

3. Isomerism and nomenclature

I . Structural

A) Isomerism of the carbon skeleton (starting from C 4 )

B) Interclass with esters R - CO – O - R 1 (starting from C 2)

For example: for C 3 H 6 O 2

CH 3 -CH 2 -COOH propionic acid

WITH H 3 -CO -OCH 3 methyl ester of acetic acid

II . Spatial

A) Optical

For example:

B) Cis-trans isomerism for unsaturated acids

Example:

4. Nomenclature of carboxylic acids

Systematic names of acids are given by the name of the corresponding hydrocarbon with the addition of a suffix -new and words acid.

To indicate the position of the substituent (or radical), the numbering of the carbon chain starts from the carbon atom of the carboxyl group. For example, a compound with a branched carbon chain (CH 3) 2 CH-CH 2 -COOH is called 3-methylbutanoic acid. Trivial names are also widely used for organic acids, which usually reflect the natural source where the compounds were first discovered.

Some monobasic acids

Formula	Acid name R-COOH		Residue name RCOO -
Formula	systematic	trivial	Residue name RCOO -
HCOOH	methane	ant	formate
CH3COOH	ethane	vinegar	acetate
C2H5COOH	propane	propionic	propionate
C3H7COOH	butane	oil	butyrate
C4H9COOH	pentane	valerian	valerate
C5H11COOH	hexane	nylon	caprat
C15H31COOH	hexadecane	palmitic	palmitate
C17H35COOH	octadecane	stearic	stearate
C6H5COOH	benzenecarbonic	benzoin	benzoate
CH 2 =CH-COOH	propene	acrylic	acrylate

Suffixes are used for polybasic acids -diovaya, -triovaya etc.

For example:

HOOC-COOH- ethanedioic (oxalic) acid;

HOOC-CH 2 -COOH - propanedioic (malonic) acid.

LIMIT MONOBASIS CARBOXYLIC ACIDS

CnH 2 n +1 - COOHorCnH 2 nO 2

Homologous series

Name		Formula acids	t pl. °C	t kip. °C	ρ g/cm 3
acids		Formula acids	t pl. °C	t kip. °C	ρ g/cm 3
ant	methane	HCOOH		100,5	1,22
vinegar	ethane	CH3COOH	16,8		1,05
propionic	propane	CH3CH2COOH			0,99
oil	butane	CH3(CH2)2COOH			0,96

The structure of the carboxyl group

The carboxyl group combines two functional groups - carbonyl >C = O and hydroxyl -OH, which mutually influence each other:

The acidic properties of carboxylic acids are due to a shift in electron density to carbonyl oxygen and the resulting additional (compared to alcohols) polarization of the O–H bond.
In an aqueous solution, carboxylic acids dissociate into ions:

Solubility in water and high boiling points of acids are due to the formation of intermolecular hydrogen bonds.

With increasing molecular weight, the solubility of acids in water decreases.

Physical properties of saturated monobasic acids

The lower members of this series, under normal conditions, are liquids with a characteristic pungent odor. For example, ethanoic (acetic) acid has a characteristic “acetic” odor. Anhydrous acetic acid is a liquid at room temperature; at 17 °C it freezes, turning into an icy substance called “glacial” acetic acid. The middle representatives of this homologous series are viscous, “oily” liquids; starting from C 10 - solids.

The simplest representative is formic acid HCOOH - a colorless liquid with bp. 101 °C, and pure anhydrous acetic acid CH 3 COOH, when cooled to 16.8 °C, turns into transparent crystals resembling ice (hence its name glacial acid).
The simplest aromatic acid - benzoic acid C 6 H 5 COOH (mp 122.4 ° C) - easily sublimes, i.e. turns into a gaseous state, bypassing the liquid state. When cooled, its vapors sublimate into crystals. This property is used to purify a substance from impurities.

DEFINITION

Carboxylic acids– organic compounds whose molecules contain one or more functional carboxyl groups – COOH, associated with a hydrocarbon radical.

The carboxyl group consists of a carbonyl group > C= O and the associated hydroxyl group –OH.

The general formula of carboxylic acids is R–COOH.

The acidic properties of carboxylic acids are due to a shift in electron density to the carbonyl oxygen, which causes the appearance of a partial positive charge on the atom.

As a result, the polarity of the O–H bond increases, and the dissociation process becomes possible:

The resulting anion is stabilized due to charge delocalization:

Lower carboxylic acids containing up to 3 carbon atoms are colorless liquids with a characteristic pungent odor, miscible with water in any ratio. Most acids containing 4–9 atoms are oily liquids with an unpleasant odor. Acids containing more than 10 hydrogen atoms are solids that are insoluble in water.

The solubility of carboxylic acids in water and high boiling points are associated with the formation of intermolecular hydrogen bonds. In the solid state, carboxylic acids exist mainly in the form of cyclic dimers, and in the liquid state linear association also occurs:

Types of carboxylic acids

Depending on the structure of the hydrocarbon radical, carboxylic acids are divided into:

aromatic (benzoic acid)
aliphatic (saturated (caproic acid) and unsaturated (acrylic acid))
alicyclic (quinic acid)
heterocyclic (nicotinic acid).

Based on the number of carboxyl groups, carboxylic acids are divided into:

monobase()
dibasic (oxalic acid)
polybasic (citric acid).

When other functional groups (–OH, =CO, –NH2, etc.) are introduced into the acid molecule, other classes of compounds are formed: hydroxy, keto acids, etc.

General formula of saturated monobasic carboxylic acids:

WITH n H2nO2 (n= 1,2,3...) or Cn H 2n+1 COOH (n = 0,1,2…)

General formula of unsaturated monobasic carboxylic acids:

WITH n H 2 n –2 O 2 (n= 1,2,3...) or CnH 2 n –1 COOH (n = 0,1,2…)

General formula of saturated dibasic carboxylic acids:

C n H 2n–2 O 4 (n = 2,3…)

Names and formulas of some carboxylic acids

methane

ant

ethane

vinegar

propane

propionic

butane

oil

pentanoic acid

valeric acid

hexanoic acid

caproic acid

octadecane

stearic

2-propene

acrylic

CH 3 –CH=CH–COOH

2-butene

croton

CH 2 =CH–CH 2 –COOH

3-butene

vinyl acetic

CH 2 =C(CH 3)COOH

2-methyl-2-propene

methacrylic

ethanedium

sorrel

COOH–CH2–COOH

propandium

malonova

COOH–(CH 2) 2 –COOH

butanedia

amber

COOH–(CH 2) 3 –COOH

pentanediovy

glutaric

COOH–(CH 2) 4 –COOH

hexanediate

adipic

Carboxylic acid formula	IUPAC name	Trivial name
Saturated monobasic carboxylic acids
Unsaturated monobasic carboxylic acids
Dibasic carboxylic acids

Examples of problem solving

EXAMPLE 1

Exercise

Three identical test tubes without signatures contain three acids: formic, acetic and hydrochloric. Based on the differences in their chemical properties, how can you determine which acid is in each test tube?

Solution

Formic acid also exhibits some properties (reductive). Therefore, it can be determined, for example, by the reaction with copper (II) hydroxide; in the case of formic acid, red copper (I) oxide is formed:

The remaining acids can be distinguished by reaction with silver nitrate. In the case of hydrochloric acid, a white precipitate of silver chloride precipitates:

Silver acetate dissolves in water, so no changes will occur in the test tube.

Thus, the remaining test tube contains acetic acid.

EXAMPLE 2

Exercise

Determine if, upon hydrolysis of a sample weighing 2.64 g, 1.38 g of alcohol and 1.8 g of monobasic carboxylic acid are released.

Solution

The general formula of an ester consisting of an alcohol and an acid with different numbers of carbon atoms is:

Thus, the alcohol formula is:

and the formula of the acid is:

Let us write the equation for ester hydrolysis:

In accordance with the law of conservation of mass of substances, the mass of reaction products is equal to the mass of the starting substances. Let's calculate the mass:

M(acid) + m(alcohol) – m(ether) g

Let's calculate the amount of water substance:

According to the reaction equation

n(acid) = n(alcohol) mol