Classification

a) By basicity (i.e., the number of carboxyl groups in the molecule):

Monobasic (monocarboxylic) RCOOH; For example:

CH 3 CH 2 CH 2 COOH;

HOOS-CH 2 -COOH propanedioic (malonic) acid

Tribasic (tricarboxylic) R (COOH) 3, etc.

b) According to the structure of the hydrocarbon radical:

Aliphatic

limit; for example: CH 3 CH 2 COOH;

unsaturated; for example: CH 2 \u003d CHCOOH propenoic (acrylic) acid

Alicyclic, for example:

Aromatic, for example:

Limit monocarboxylic acids

(monobasic saturated carboxylic acids) - carboxylic acids in which a saturated hydrocarbon radical is connected to one carboxyl group -COOH. They all have the general formula C n H 2n+1 COOH (n ≥ 0); or CnH 2n O 2 (n≥1)

Nomenclature

The systematic names of monobasic saturated carboxylic acids are given by the name of the corresponding alkane with the addition of the suffix -ovaya and the word acid.

1. HCOOH methane (formic) acid

2. CH 3 COOH ethanoic (acetic) acid

3. CH 3 CH 2 COOH propanoic (propionic) acid

isomerism

The isomerism of the skeleton in the hydrocarbon radical is manifested, starting with butanoic acid, which has two isomers:

Interclass isomerism manifests itself, starting with acetic acid:

CH 3 -COOH acetic acid;

H-COO-CH 3 methyl formate (methyl ester of formic acid);

HO-CH 2 -COH hydroxyethanal (hydroxyacetic aldehyde);

HO-CHO-CH 2 hydroxyethylene oxide.

homologous series

Acid residues and acid radicals

Electronic structure of carboxylic acid molecules

The shift of the electron density shown in the formula towards the carbonyl oxygen atom causes a strong polarization O-N connections, as a result of which the detachment of the hydrogen atom in the form of a proton is facilitated - in aqueous solutions, the process of acid dissociation occurs:

RCOOH ↔ RCOO - + H +

In the carboxylate ion (RCOO -), p, π-conjugation of the lone pair of electrons of the oxygen atom of the hydroxyl group with p-clouds forming a π-bond takes place, as a result, the π-bond is delocalized and the negative charge is uniformly distributed between the two oxygen atoms:

In this regard, for carboxylic acids, in contrast to aldehydes, addition reactions are not characteristic.

Physical properties

The boiling points of acids are much higher than the boiling points of alcohols and aldehydes with the same number of carbon atoms, which is explained by the formation of cyclic and linear associates between acid molecules due to hydrogen bonds:

Chemical properties

I. Acid properties

The strength of acids decreases in the series:

HCOOH → CH 3 COOH → C 2 H 6 COOH → ...

1. Neutralization reactions

CH 3 COOH + KOH → CH 3 COOK + n 2 O

2. Reactions with basic oxides

2HCOOH + CaO → (HCOO) 2 Ca + H 2 O

3. Reactions with metals

2CH 3 CH 2 COOH + 2Na → 2CH 3 CH 2 COONa + H 2

4. Reactions with salts of weaker acids (including carbonates and bicarbonates)

2CH 3 COOH + Na 2 CO 3 → 2CH 3 COONa + CO 2 + H 2 O

2HCOOH + Mg(HCO 3) 2 → (HCOO) 2 Mg + 2CO 2 + 2H 2 O

(HCOOH + HCO 3 - → HCOO - + CO2 + H2O)

5. Reactions with ammonia

CH 3 COOH + NH 3 → CH 3 COONH 4

II. -OH group substitution

1. Interaction with alcohols (esterification reactions)

2. Interaction with NH 3 when heated (acid amides are formed)

Acid amides hydrolyzed to form acids:

or their salts:

3. Formation of acid halides

Acid chlorides are of the greatest importance. Chlorinating reagents - PCl 3 , PCl 5 , thionyl chloride SOCl 2 .

4. Formation of acid anhydrides (intermolecular dehydration)

Acid anhydrides are also formed by the interaction of acid chlorides with anhydrous salts of carboxylic acids; in this case, mixed anhydrides of various acids can be obtained; For example:

III. Substitution reactions of hydrogen atoms at the α-carbon atom

Features of the structure and properties of formic acid

The structure of the molecule

The formic acid molecule, unlike other carboxylic acids, contains an aldehyde group in its structure.

Chemical properties

Formic acid enters into reactions characteristic of both acids and aldehydes. Showing the properties of an aldehyde, it is easily oxidized to carbonic acid:

In particular, HCOOH is oxidized with an ammonia solution of Ag 2 O and copper (II) hydroxide Cu (OH) 2, i.e. gives qualitative reactions for the aldehyde group:

When heated with concentrated H 2 SO 4, formic acid decomposes into carbon monoxide (II) and water:

Formic acid is noticeably stronger than other aliphatic acids, since the carboxyl group in it is bonded to a hydrogen atom, and not to an electron-donating alkyl radical.

Methods for obtaining saturated monocarboxylic acids

1. Oxidation of alcohols and aldehydes

The general scheme for the oxidation of alcohols and aldehydes:

KMnO 4 , K 2 Cr 2 O 7 , HNO 3 and other reagents are used as oxidizers.

For example:

5C 2 H 5 OH + 4KMnO 4 + 6H 2 S0 4 → 5CH 3 COOH + 2K 2 SO 4 + 4MnSO 4 + 11H 2 O

2. Hydrolysis of esters

3. Oxidative cleavage of double and triple bonds in alkenes and alkynes

Methods for obtaining HCOOH (specific)

1. Interaction of carbon monoxide (II) with sodium hydroxide

CO + NaOH → HCOONa sodium formate

2HCOONa + H 2 SO 4 → 2HCOOH + Na 2 SO 4

2. Decarboxylation of oxalic acid

Methods for obtaining CH 3 COOH (specific)

1. Catalytic oxidation of butane

2. Synthesis from acetylene

3. Catalytic carbonylation of methanol

4. Acetic acid fermentation of ethanol

This is how food grade acetic acid is obtained.

Obtaining higher carboxylic acids

Hydrolysis of natural fats

Unsaturated monocarboxylic acids

Key Representatives

General formula of alkenoic acids: C n H 2n-1 COOH (n ≥ 2)

CH 2 \u003d CH-COOH propenoic (acrylic) acid

Higher unsaturated acids

The radicals of these acids are part of vegetable oils.

C 17 H 33 COOH - oleic acid, or cis-octadiene-9-oic acid

Trance-isomer of oleic acid is called elaidic acid.

C 17 H 31 COOH - linoleic acid, or cis, cis-octadiene-9,12-oic acid

C 17 H 29 COOH - linolenic acid, or cis, cis, cis-octadecatriene-9,12,15-oic acid

Except common properties carboxylic acids, unsaturated acids are characterized by addition reactions at multiple bonds in the hydrocarbon radical. So, unsaturated acids, like alkenes, are hydrogenated and decolorize bromine water, for example:

Individual representatives of dicarboxylic acids

Limiting dicarboxylic acids HOOC-R-COOH

HOOC-CH 2 -COOH propanedioic (malonic) acid, (salts and esters - malonates)

HOOC-(CH 2) 2 -COOH butadiic (succinic) acid, (salts and esters - succinates)

HOOC-(CH 2) 3 -COOH pentadiic (glutaric) acid, (salts and esters - glutorates)

HOOC-(CH 2) 4 -COOH hexadioic (adipic) acid, (salts and esters - adipinates)

Features of chemical properties

Dicarboxylic acids are in many ways similar to monocarboxylic acids, but are stronger. For example, oxalic acid is almost 200 times stronger than acetic acid.

Dicarboxylic acids behave like dibasic acids and form two series of salts - acidic and medium:

HOOC-COOH + NaOH → HOOC-COONa + H 2 O

HOOC-COOH + 2NaOH → NaOOC-COONa + 2H 2 O

When heated, oxalic and malonic acids are easily decarboxylated:

Chemical compounds, which also consist of the carboxyl group COOH, have received the name carboxylic acids from scientists. There are many names for these compounds. They are classified according to various parameters, such as the number of functional groups, the presence of an aromatic ring, and so on.

The structure of carboxylic acids

As already mentioned, in order for an acid to be carboxylic, it must have a carboxyl group, which, in turn, has two functional parts: hydroxyl and carbonyl. Their interaction is provided by its functional combination of one carbon atom with two oxygen atoms. The chemical properties of carboxylic acids depend on the structure of this group.

Due to the carboxyl group, these organic compounds can be called acids. Their properties are due to the increased ability of the hydrogen ion H + to attract oxygen, additionally polarizing the O-H bond. Also, due to this property, organic acids are able to dissociate in aqueous solutions. The solubility decreases in inverse proportion to the increase in the molecular weight of the acid.

Varieties of carboxylic acids

Chemists distinguish several groups of organic acids.

Monobasic carboxylic acids consist of a carbon skeleton and only one functional carboxyl group. Every student knows the chemical properties of carboxylic acids. Grade 10 curriculum in chemistry includes directly studying the properties of monobasic acids. Dibasic and polybasic acids have two or more carboxyl groups in their structure, respectively.

Also, according to the presence or absence of double and triple bonds in the molecule, there are unsaturated and saturated carboxylic acids. Chemical properties and their differences will be discussed below.

If an organic acid has a substituted atom in its radical, then the name of the substituent group is included in its name. So, if the hydrogen atom is replaced by a halogen, then the name of the halogen will be present in the name of the acid. The name will undergo the same changes if there is a substitution for aldehyde, hydroxyl or amino groups.

Isomerism of organic carboxylic acids

Soap production is based on the reaction of synthesis of esters of the above acids with potassium or sodium salt.

Methods for obtaining carboxylic acids

There are many ways and methods for obtaining acids with a COOH group, but the following are most often used:

1. Isolation from natural substances (fats and other).
2. Oxidation of monoalcohols or compounds with a COH group (aldehydes): ROH (RCOH) [O] R-COOH.
3. Hydrolysis of trihaloalkanes in alkali with intermediate production of monoalcohol: RCl3 +NaOH=(ROH+3NaCl)=RCOOH+H2O.
4. Saponification or hydrolysis of acid and alcohol esters (esters): R−COOR"+NaOH=(R−COONa+R"OH)=R−COOH+NaCl.
5. Oxidation of alkanes with permanganate (hard oxidation): R=CH2 [O], (KMnO4) RCOOH.

The value of carboxylic acids for humans and industry

The chemical properties of carboxylic acids have great importance for human life. They are extremely necessary for the body, as in in large numbers contained in each cell. The metabolism of fats, proteins and carbohydrates always goes through a stage at which this or that carboxylic acid is obtained.

In addition, carboxylic acids are used in the creation of drugs. No pharmaceutical industry can exist without the practical application of the properties of organic acids.

Compounds with a carboxyl group also play an important role in the cosmetic industry. Synthesis of fat for the subsequent production of soap, detergents and household chemicals is based on the reaction of esterification with carboxylic acid.

The chemical properties of carboxylic acids are reflected in human life. They are of great importance for the human body, as they are found in large quantities in every cell. The metabolism of fats, proteins and carbohydrates always goes through a stage at which this or that carboxylic acid is obtained.

.
O

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The -C group of atoms is called a carboxyl group or carboxyl.
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Organic acids containing one carboxyl group in the molecule are monobasic. The general formula for 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, aromatic.

Limiting, or saturated, carboxylic acids are, for example, propanoic (propionic) acid or succinic acid already familiar to us.

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

In molecules of unsaturated carboxylic acids, the carboxyl group is linked to 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, as it contains an aromatic (benzene) ring in the molecule.

Nomenclature and isomerism

General principles for the formation of names of carboxylic acids, as well as others organic compounds, we have already considered. Let us dwell in more detail on the nomenclature of mono- and dibasic carboxylic acids. The name of a carboxylic acid is formed from the name of the corresponding alkane (an alkane with the same number of carbon atoms in the molecule) with the addition of the suffix -ov, 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 the first acquaintance with the diverse and interesting world organic acids, let us consider in more detail the limiting 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 in a 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 in a molecule - solids that do not dissolve in water. The boiling points of limiting monobasic carboxylic acids increase with an increase in the number of carbon atoms in the molecule and, consequently, with an increase in the relative molecular weight. So, for example, the boiling point of formic acid is 101 °C, acetic acid - 118 °C, propionic acid - 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 dimers of carboxylic acids, 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 an almost non-polar hydrocarbon radical. The carboxyl group is attracted to water molecules, forming hydrogen bonds with them.

Formic and acetic acids are infinitely soluble in water. Obviously, with an increase in the number of atoms in the hydrocarbon radical, the solubility of carboxylic acids decreases.

Knowing the composition and structure of the molecules of carboxylic acids, 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 strongly 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 precisely, this process describes an equation that takes into account the participation of water molecules in it.

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

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

2. Interaction with metals standing in the electrochemical series of voltages up to hydrogen. So, 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. Interaction 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 ester formation in the presence of dewatering agents and removal of ether from the reaction mixture.

In the reverse reaction of esterification, which is called ester hydrolysis (reaction of an ester with water), an acid and an alcohol are formed. Obviously, they can also react with carboxylic acids, i.e., enter into an esterification reaction. polyhydric alcohols eg glycerin:

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

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

Unsaturated carboxylic acids, like other unsaturated compounds, add halogens to the double bond. For example, acrylic acid decolorizes bromine water.

8. Substitution reactions (with halogens) - saturated carboxylic acids are able to enter into it; for example, by reacting acetic acid with chlorine, various chlorine derivatives of 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 the reaction proceeds according to the 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 upon substitution of the hydroxyl group. Upon hydrolysis of these derivatives, a carboxylic acid is again formed from them.

The carboxylic acid chloride can be obtained by treating the acid with phosphorus(III) chloride or thionyl chloride (SOCl 2). Anhydrides of carboxylic acids are obtained by the interaction of anhydride chlorides with salts of carboxylic acids. Esters formed as a result of the esterification of carboxylic acids with alcohols. Etherification is catalyzed by inorganic acids.

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

How to get

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

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

Hydrolysis of various carboxylic acid derivatives also results in acids. So, during the hydrolysis of an ester, an alcohol and a carboxylic acid are formed. As mentioned above, the esterification and hydrolysis reactions catalyzed by acid are reversible. The hydrolysis of an ester under the action of an aqueous solution of alkali proceeds irreversibly, in this case, not an acid, but its salt is formed from the ester. In the hydrolysis of nitriles, amides are first formed, which are then converted to acids. Carboxylic acids are formed by the interaction of organomagnesium 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, it is 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 a disinfectant property and therefore finds its application in the food, leather and pharmaceutical industries, and medicine. It is also used in dyeing textiles 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 sold under the name of vinegar (3-5% solution) and vinegar essence (70-80% solution) and are widely used in the food industry. Acetic acid is a good solvent for many organic substances and is therefore used in dyeing, in the leather industry, and in the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, it is used to obtain substances used to control weeds - herbicides.

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

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

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

From unsaturated higher carboxylic acids highest value has oleic acid C17H33COOH, or (CH2)7COOH. It is an oil-like liquid, tasteless and odorless. Its salts are widely used in technology.

The simplest representative of dibasic carboxylic acids is oxalic (ethanedioic) acid HOOC-COOH, salts of which are found in many plants, for example, in sorrel and oxalis. Oxalic acid is colorless crystalline substance, highly soluble in water. It is used in the polishing of metals, in the woodworking and leather industries.

1. Unsaturated elaidic acid С17Н33СООН is a trans-isomer of oleic acid. Write the structural formula of this substance.

2. Write an equation for the hydrogenation 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.S.) will be required to burn 568 g of stearic acid?

4. A mixture of solid fatty acids - palmitic and stearic - is called stearin (stearin candles are made from it). What volume of air (n.a.) will be required to burn a 200 gram stearin candle if the stearin contains equal masses of palmitic and stearic acids? What volume carbon dioxide(n.a.) and the mass of water formed in this case?

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

6. To remove rust stains, they are treated with a solution of acetic acid. Make up the molecular and ionic equations of the reactions taking place in this case, given 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. The food (drinking) soda MaHC03 added to the yeast-free dough is preliminarily “quenched” with acetic acid. Do this reaction at home and make up 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 strength acid properties. Justify your result.

9. How can one explain that formic acid enters into a "silver mirror" reaction? Write an equation for this reaction. What gas can be released in this case?

10. In the interaction of 3 g of saturated monobasic carboxylic acid with an excess of magnesium, 560 ml (n.a.) 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 that can be used to recognize propanoic and acrylic acids.

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

14. Make structural formulas of substances having the composition С3Н602. What classes of substances can they be assigned to? Give the equations of the reactions characteristic of each of them.

15. Substance A - an isomer of acetic acid - does not dissolve in water, but can be hydrolyzed. What is the structural formula of substance A? Name the products of its hydrolysis.

16. Make the structural formulas of the following substances:

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

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

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 most of the acids form esters that have odors. So the smell of lactic acid, which is contained in human sweat, attracts mosquitoes, they feel it at quite a considerable distance. Therefore, no matter how much you try to drive away the annoying mosquito, he still feels good about his victim. In addition to human sweat, lactic acid is found in pickles and sauerkraut.

And female monkeys, in order to attract a male, release acetic and propionic acid. The sensitive, canine nose is able to smell butyric acid, which has a concentration of 10–18 g/cm3.

Many plant species are able to secrete acetic and butyric acid. And some weeds take advantage of this and release substances, eliminate their competitors, suppressing their growth, and sometimes causing their death.

The Indians also used acid. To destroy the enemy, they moistened 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? Indeed, oxalic acid, which is widespread in nature, which 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 found wide application in all spheres of human life. They are used in medicine, cosmetology, food industry, agriculture and used for domestic needs.

For medical purposes, organic acids such as lactic, tartaric, and ascorbic acids are used. Probably, each of you used vitamin C to strengthen the body - this is just ascorbic acid. It not only helps to 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 the preparation of plasma during blood transfusion.

But fans of cosmetic procedures should be aware that the fruit acids contained in citrus fruits have a beneficial effect on the skin, as they penetrate deep into the skin and 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 application, since it can be used to increase the yield of cultivated plants. It is also able to stimulate the growth of plants and accelerate their development.

carboxylic acids - organic matter, whose molecules contain one or more carboxyl groups.

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

According to the number of carboxyl groups, carboxylic acids are divided into monobasic, dibasic, etc.

General formula of monobasic carboxylic acids R-COOH. An example of a dibasic acid is oxalic acid HOOC-COOH.

According to the type of radical, carboxylic acids are divided into saturated (for example, acetic acid CH 3 COOH), unsaturated [for example, acrylic acid CH 2 \u003d CH - COOH, oleic acid CH 3 - (CH 2) 7 -CH \u003d 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 as R "-COOR" ") with the same number of carbon atoms. The general formula of both C n H2 n O 2 .

Algorithm for naming carboxylic acids

1. Find the main carbon chain - this is the longest chain of carbon atoms, including the carbon atom of the carboxyl group.
2. Number the carbon atoms in the main chain, starting with the carbon atom of the carboxyl group.
3. Name the compound according to the algorithm for hydrocarbons.
4. At the end of the name, add the suffix "-ov", the ending "-aya" and the word "acid".

In carboxylic acid molecules p-electrons of oxygen atoms of the hydroxyl group interact with electrons -bonds 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 contributes to the formation of strong hydrogen bonds between the molecules of carboxylic acids.

The physical properties of limiting 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 are higher for acids than for the corresponding alcohols.

Chemical properties of acids

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

1. Combustion:
   

   CH 3 COOH + 2O 2 2CO 2 + 2H 2 O

2. acid properties.
   Because of the high polarity O-H bonds carboxylic acids in aqueous solution noticeably dissociate (more precisely, reversibly react with it):

   HCOOH HCOO - + H + (more precisely HCOOH + H 2 O HCOO - + H 3 O +)

   
   All carboxylic acids are weak electrolytes. With an increase in the number of carbon atoms, 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 a row

   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

3. 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. Limit fatty acid(palmitic C 15 H 31 COOH, stearic C 17 H 35 COOH) form solid fats of animal origin, and unsaturated (oleic C 17 H 33 COOH, linoleic C 17 H 31 COOH, etc.) form liquid fats (oils) of vegetable origin.

4. Substitution in a hydrocarbon radical:
   
   The substitution proceeds in the -position.

   The peculiarity of formic acid HCOOH is that this substance is a two-functional 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

Obtaining carboxylic acids

Carboxylic acids are derivatives of hydrocarbons, the molecule of which contains one or more carboxyl groups.

The general formula of limiting monobasic carboxylic acids: With n H 2n O 2

Classification of carboxylic acids.

1. According to the number of carboxyl groups:

Single base (monocarbon)

Polybasic (dicarboxylic, tricarboxylic, etc.).

By the nature of the hydrocarbon radical:

Limit CH 3 -CH 2 -CH 2 -COOH; butanoic acid.

Unlimited CH 2 =CH-CH 2 -COOH; butenoic acid.

aromatic

para-methylbenzoic acid

Names of carboxylic acids.

Isomerism of carboxylic acids.

1. Isomerism of the carbon chain. Begins with butanoic acid (With 3 H 7 UNSD) , which exists in the form of two isomers: butyric (butanoic) and isobutyric (2-methylpropanoic) acids.

2. Isomerism of the position of a multiple bond in unsaturated acids, For example:

CH 2 =CH-CH 2 -COOH CH 3 -CH=CH-COOH

Butene-3-oic acid Butene-2-oic acid

(vinylacetic acid) (crotonic acid)

3. Cis-, trans-isomerism in unsaturated acids, For example:

4. Interclass isomerism: Carboxylic acids are isomeric to esters:

Acetic acid CH 3 -COOH and methyl formate H-COOSH 3

5. isomerismpositions of functional groups at heterofunctional acids .

For example, there are three isomers of chlorobutyric acid: 2-chlorobutanoic, 3-chlorobutanoic and 4-chlorobutanoic.

The structure of the carboxyl group.

The carboxyl group combines two functional groups - carbonyl and hydroxyl, mutually influencing each other

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

Solubility in water and high boiling points of acids are due to the formation intermolecular hydrogen bonds. As the molecular weight increases, the solubility of acids in water decreases.

DERIVATIVES OF CARBOXY ACID– in them, the hydroxo group is replaced by some other groups. All of them form carboxylic acids upon hydrolysis.

OBTAINING CARBOXIC ACIDS.

CHEMICAL PROPERTIES OF CARBOXY ACIDS.