Chemical properties of carboxylic acids and methods of preparation. Carboxylic acids and their chemical properties Interaction of formic acid with chlorine

Methods of obtaining. 1. Oxidation of aldehydes and primary alcohols - general method obtaining carboxylic acids. />K M n O 4 and K 2 C r 2 O 7 are used as oxidizing agents.

2 Another common method is the hydrolysis of halogenated hydrocarbons containing three halogen atoms per carbon atom. In this case, alcohols containing OH groups on one carbon atom are formed - such alcohols are unstable and split off water to form a carboxylic acid:

	ZNaON
R-CCl 3			→	R - COOH + H 2 O
	-3NaCl

3. Obtaining carboxylic acids from cyanides (nitriles) is an important method that allows you to increase the carbon chain when obtaining the original cyanide. An additional carbon atom is introduced into the molecule using the reaction of replacing a halogen in a halocarbon molecule with sodium cyanide, for example:

CH 3 -B r + NaCN→ CH 3 - CN + NaBr.

The resulting nitrile acetic acid(methyl cyanide) readily hydrolyzes when heated to form ammonium acetate:

CH 3 CN + 2H 2 O → CH 3 COONH 4.

When the solution is acidified, acid is released:

CH 3 COONH 4 + HCl→ CH 3 COOH + NH 4 Cl.

4. Usage Grignard reagent according to the scheme:/>

H 2 O
R— MgBr+ CO 2 → R — COO — MgBr→ R - COOH + Mg (OH) Br

5. Hydrolysis of esters:/>

R - COOR 1 + KON → R - COOK + R'OH,

R - COOK + HCl → R— COOH+ KCl .

6. Hydrolysis of acid anhydrides:/>

(RCO) 2 O + H 2 O → 2 RCOOH.

7. There are specific methods of preparation for individual acids./>

Formic acid is prepared by heating carbon monoxide ( II ) with powdered sodium hydroxide under pressure and treating the resulting sodium formate with a strong acid:

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

2C 4 H 10 + 5 O 2 → 4CH 3 COOH + 2H 2 O.

To obtain benzoic acid, you can use the oxidation of monosubstituted benzene homologues with an acidic solution of potassium permanganate:

5C 6 H 5 -CH 3 + 6 KMnO 4 + 9 H 2 SO 4 = 5C 6 H 5 COOH + 3 K 2 SO 4 + 6 MnSO 4 + 14 H 2 O.

Additionally, benzoic acid can be prepared from benzaldehyde using Cannizzaro's reactions. In this reaction, benzaldehyde is treated with 40-60% sodium hydroxide solution at room temperature. Simultaneous oxidation and reduction leads to the formation benzoic acid and, accordingly, phenylmethanol (benzyl alcohol):

Chemical properties. Carboxylic acids- stronger acids than alcohols, since the hydrogen atom in the carboxyl group has increased mobility due to the influence of the CO group. In an aqueous solution, carboxylic acids dissociate:

RCOOH RCOO—+H+

However, due to the covalent nature of carbon molecules y acids, the above dissociation equilibrium is sufficient strongly shifted to the left. Thus, carboxylic acids - These are usually weak acids. For example, ethane (acetic)the acid is characterized by a dissociation constant K a = 1.7*10 -5./>

Substituents present in a carboxylic acid molecule greatly affect its acidity due to the effect they have inductive effect. Substituents such as chlorine or phenyl radical attract electron density and, therefore, cause a negative inductive effect (-/). The withdrawal of electron density from the carboxyl hydrogen atom leads to an increase in the acidity of the carboxylic acid. acids. In contrast, substituents such as alkyl groups have electron-donating properties and create a positive inductive effect, +I. They reduce acidity. Effect of substituents on the acidity of carboxylic acidsclearly manifested in the values ​​of dissociation constants K a for a number of acids. In addition, the strength of the acidis influenced by the presence of a conjugate multiple bond.

Carboxylic Acids Formula K a

Propionic CH 3 CH 2 COOH 1.3*10 -5

Oil CH 3 CH 2 CH 2 COOH 1.5*10 -5

Acetic CH 3 COOH 1.7*10 -5

Croton CH 3 - CH = CH - COOH 2.0 * 10 -5

Vinylacetic CH 2 =CH-CH 2 COOH 3.8*10 -5

Acrylic CH 2 =CH-COOH 5.6*10 -5

Formic HCOOH 6.1*10 -4

Benzoic C 6 H 5 COOH 1.4*10 -4

Chloroacetic CH 2 ClCOOH 2.2*10 -3

Tetronic CH 3 - C ≡ C - COOH 1.3*10 -3

Dichloroacetic CHCl 2 COOH 5.6*10 -2

Oxalic HOOC - COOH 5.9*10 -2

TrichloroaceticCCl 3 COOH 2.2*10 -1

The mutual influence of atoms in the molecules of dicarboxylic acids leads to the fact that they are stronger than monobasic acids.

2. Formation of salts. Carboxylic acids have all the properties of ordinary acids. They react with active metals, basic oxides, bases and salts of weak acids:

2 RCOOH + M g → (RCOO) 2 Mg + H 2,

2 RCOOH + CaO → (RCOO) 2 Ca + H 2 O,

RCOOH+ NaOH → RCOONa+ H 2 O,

RCOOH+ NaHCO 3 → RCOONa+ H 2 O + CO 2.

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

CH 3 COONa + HCl→ CH 3 COOH + NaCl.

Salts of carboxylic acids in aqueous solutions are hydrolyzed:

CH 3 COOK + H 2 O CH 3 COOH + CON.

The difference between carboxylic acids and mineral acids is the possibility of forming a number of functional derivatives.

3. Formation of functional derivatives of carboxylic acids. When replacing the OH group in carboxylic acids with various groups (/>X ) functional derivatives of acids are formed, having the general formula R-CO-X; here R means an alkyl or aryl group. Although nitriles have a different general formula ( R-CN ), they are usually also considered to be derivatives of carboxylic acids, since they can be prepared from these acids.

Acid chlorides are produced by the action of phosphorus chloride ( V) for acids:

R-CO-OH + PC l 5 → R-CO- Cl+ ROS l 3 + HCl.

Connection examples

Acid Ethanoic (acetic) Benzoic acid acid chloride Ethanoyl chloride Benzoyl chloride (acetyl chloride) acid anhydride Ethane (acetic) benzoic anhydrite Anhydrite ester Ethyl ethanoate (ethyl acetate) Methyl benzoate amide Ethanamide(acetamide) Benzamide Nitrile Ethannitrile Benzonitrile (acetonitrile)

Anhydrides are formed from carboxylic acids under the action of water-removing agents:

2 R - CO - OH + P 2 O 5 → (R - CO -) 2 O + 2HPO 3.

Esters are formed by heating an acid with an alcohol in the presence of sulfuric acid (reversible esterification reaction):

The mechanism of the esterification reaction has been established by the "labeled atoms" method.

Esters can also be obtained by reacting acid chlorides and alkali metal alcoholates:

R-CO-Cl + Na-O-R’ → R-CO-OR’ + NaCl .

Reactions of carboxylic acid chlorides with ammonia lead to the formation of amides:

CH 3 -CO-C l + CH 3 → CH 3 -CO-CH 2 + HCl.

In addition, amides can be prepared by heating ammonium salts of carboxylic acids:

When amides are heated in the presence of dewatering agents, they dehydrate to form nitriles:

	R 2 0 5
CH 3 - CO - NH 2	→	CH 3 - C ≡ N + H 2 O

Functional derivatives of lower acids are volatile liquids. All of them are easily hydrolyzed to form the parent acid:

R-CO-X + H 2 O → R-CO-OH + HX.

IN acidic environment these reactions can be reversible. Hydrolysis in an alkaline environment is irreversible and leads to the formation of carboxylic acid salts, for example:

R-CO-OR ‘ + NaOH → R-CO-ONa + R’OH.

4. A number of properties of carboxylic acids are due to the presence of a hydrocarbon radical. Thus, when halogens act on acids in the presence of red phosphorus, halogen-substituted acids are formed, and the hydrogen atom at the carbon atom (a-atom) adjacent to the carboxyl group is replaced by halogen:

	r cr
CH 3 -CH 2 -COOH + Br 2	→	CH 3 -CHBr-COOH + HBr

Unsaturated carboxylic acids are capable of addition reactions:

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

CH 2 =CH-COOH + C l 2 → CH 2 C l -SHC l -COOH,

CH 2 =CH-COOH + HCl → CH 2 C l -CH 2 -COOH,

CH 2 = CH-COOH + H 2 O → HO-CH 2 -CH 2 -COOH,

The last two reactions proceed against Markovnikov's rule.

Unsaturated carboxylic acids and their derivatives are capable of polymerization reactions.

5. Redox reactions of carboxylic acids./>

Carboxylic acids, under the action of reducing agents in the presence of catalysts, can be converted into aldehydes, alcohols and even hydrocarbons:

Formic acid HCOOH has a number of features, since it contains an aldehyde group:

Formic acid is a strong reducing agent and is easily oxidized to CO 2 . She gives "silver mirror" reaction:

HCOOH + 2OH → 2Ag + (NH 4) 2 CO 3 + 2NH 3 + H 2 O,

or in simplified form:

C H 3 HCOOH + Ag 2 O → 2Аg + CO 2 + H 2 O.

In addition, formic acid is oxidized by chlorine:

HCOOH + Cl 2 → CO 2 + 2 HCl.

In an oxygen atmosphere, carboxylic acids are oxidized to CO 2 and H 2 O:

CH 3 COOH + 2O 2 → 2CO 2 + 2H 2 O.

6. Reactions decarboxylation. Saturated unsubstituted monocarboxylic acids are difficult to decarboxylate when heated due to the high strength of the C-C bond. To do this, it is necessary to fuse the alkali metal salt of carboxylic acid with alkali:

The appearance of electron-donating substituents in the hydrocarbon radical promotes decarboxylation reactions:

Dibasic carboxylic acids easily split off CO 2 when heated:

Chemical compounds, which also consist of the carboxyl group COOH, are called carboxylic acids by scientists. There are a large number of names for these compounds. They are classified according to various parameters, for example, by the number of functional groups, the presence of an aromatic ring, and so on.

Structure of carboxylic acids

As mentioned, 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 ensured 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 determined by the increased ability of the hydrogen ion H+ to be attracted to oxygen, further polarizing O-H connection. Also, thanks to this property, organic acids are able to dissociate in aqueous solutions. The ability to dissolve decreases in inverse proportion to the increase in molecular weight of the acid.

Varieties of carboxylic acids

Chemists distinguish several groups of organic acids.

Monobasic carboxylic acids consist of carbon skeleton and only one functional carboxyl group. Every schoolchild knows chemical properties carboxylic acids. 10th grade curriculum in chemistry includes the direct study of 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 There are unsaturated and saturated carboxylic acids in the molecule. Chemical properties and their differences will be discussed below.

If an organic acid has a substituted atom in its radical, then its name includes the name of the substituent group. So, if the hydrogen atom is replaced by a halogen, then the name of the acid will contain the name of the halogen. The name will undergo the same changes if replacement occurs with aldehyde, hydroxyl or amino groups.

Isomerism of organic carboxylic acids

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

Methods for producing carboxylic acids

There are many ways and methods for producing acids with the COOH group, but the most commonly used are the following:

1. Isolation from natural substances (fats and other things).
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 importance of carboxylic acids for humans and industry

The chemical properties of carboxylic acids have great value for human life. They are extremely necessary for the body, as they are found in large quantities in every cell. The metabolism of fats, proteins and carbohydrates always passes through a stage at which one or another carboxylic acid is produced.

In addition, carboxylic acids are used in the creation of medicines. 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 cosmetics industry. The synthesis of fat for the subsequent production of soap, detergents and household chemicals is based on the esterification reaction 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 passes through a stage at which one or another carboxylic acid is produced.

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 halogenated 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 producing 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, the following product is formed:

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.

	Chemistry calculators
Chemistry online on our website to solve problems and equations.

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

General formula of saturated monobasic carboxylic acids: WITH n H 2n O 2

Classification of carboxylic acids.

1. By the number of carboxyl groups:

Single base (monocarbon)

Polybasic (dicarbonic, tricarbonic, etc.).

According to the nature of the hydrocarbon radical:

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

Unlimited CH 2 =CH-CH 2 -COOH; butene-3-oic acid.

Aromatic

para-methylbenzoic acid

Names of carboxylic acids.

Name
		its salts and
ant	methane
vinegar	ethane
propionic	propane	propionate
oil	butane		CH3(CH2)2COOH
valerian	pentane		CH3(CH2)3COOH
nylon	hexane	hexanate	CH3(CH2)4COOH
palmitic	hexadecane	palmitate	C 15 H 31 COOH
stearic	octadecane		C 17 H 35 COOH
acrylic	propene
oleic			CH 3 (CH 2) 7 CH=CH (CH 2) 7 COOH
benzoin	benzoin
sorrel	ethanedium		NOOS - COOH

ISOMERITY OF CARBOXYLIC ACIDS.

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

2. Isomerism of the position of the 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 isomers of esters:

Acetic acid CH 3 -COUN and methyl formate N-SOOSN 3

5. Isomerismpositions of functional groups at heterofunctional acids .

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

The structure of the carboxyl group.

The carboxyl group combines two functional groups - carbonyl and hydroxyl, which mutually influence 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 O–H bond. In an aqueous solution, carboxylic acids dissociate into ions:

Solubility in water and high temperatures boiling acids are caused by the formation intermolecular hydrogen bonds. With increasing molecular weight, the solubility of acids in water decreases.

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

	Esters	Acid halides	Anhydrides

OBTAINING CARBOXYLIC ACIDS.

1. Oxidation of alcohols in harsh conditions - with a solution of potassium permanganate or dichromate in an acidic environment when heated.
2.Oxidation of aldehydes: a solution of potassium permanganate or dichromate in an acidic medium when heated, the reaction of a silver mirror, copper hydroxide when heated.
3. Alkaline hydrolysis of trichlorides:	R-CCl 3 + 3NaOH  + 3NaCl unstable substance  RCOOH + H 2 O
4. Hydrolysis of esters.	R-COOR 1 + KOH  RCOOK + R 1 OH RCOOK + HCl  R-COOH + KCl
5. Hydrolysis of nitriles, anhydrides, salts.	1)nitrile: R-CN + 2H 2 O –(H +) RCOOH 2) anhydride: (R-COO) 2 O + H 2 O  2RCOOH 3) sodium salt: R-COONa+HClR-COOH + NaCl
6. Interaction of Grignard reagent withCO 2 :	R-MgBr + CO 2  R-COO-MgBr R-COO-MgBr -(+H 2 O) R-COOH +Mg(OH)Br
7. Formic acid get heating carbon(II) monoxide with sodium hydroxide under pressure:	NaOH + CO –(200 o C,p) HCOONa 2HCOONa+ H 2 SO 4 2HCOOH + Na 2 SO 4
8. Acetic acid get catalytic oxidation of butane:	2C 4 H 10 + 5O 2  4CH 3 -COOH + 2H 2 O
9. To receive benzoic acid can be used oxidation of monosubstituted benzene homologues acidic solution of potassium permanganate:	5C 6 H 5 –CH 3 +6KMnO 4 +9H 2 SO 4 5C 6 H 5 -COOH+3K 2 SO 4 + MnSO 4 + 14H 2 O

CHEMICAL PROPERTIES OF CARBOXYLIC ACIDS.

.
O

//
The group of -C atoms is called a carboxyl group or carboxyl.
\

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 n-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

General principles for the formation of names of carboxylic acids, as well as other 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 (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's consider saturated monobasic carboxylic acids in more detail.

It is clear that the composition of these acids will be reflected 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, which 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 is a discrepancy between boiling temperatures and relative molecular weights is explained by the formation of carboxylic acid dimers, in which two acid molecules are connected 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 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 an 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 obtained by treating the acid with phosphorus(III) chloride or thionyl chloride (SOCl 2). 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 the carboxyl group entails an increase 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 acetic essence (70-80% solution) and are widely used in food industry. Acetic acid is a good solvent for many organic matter 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.

From unsaturated higher carboxylic acids highest value oleic acid has C17H33COOH, or (CH2)7COOH. It is an oil-like liquid without taste or smell. Its salts are widely used in technology.

The simplest representative of dibasic carboxylic acids is oxalic (ethanedioic) acid HOOC-COOH, the salts of which are found in many plants, for example, sorrel and sorrel. Oxalic acid is a colorless crystalline substance, dissolves well 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 carbon dioxide(n.u.) and the mass of water 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. Compose molecular and ionic equations 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 weaker than vinegar. 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 substances having 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 aqueous solution 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 used for domestic 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 yield of cultivated plants. It can also stimulate plant growth and accelerate their development.