What is the general formula of saturated carboxylic acids. Saturated monobasic carboxylic acids. Their structure and properties using acetic acid as an example, practical application. Oxidative cleavage of double and triple bonds in alkenes and alkynes

Classification

Organic carboxylic acids are characterized by the presence of a carboxyl group –COUN. Carboxylic acids are classified according to the number of carboxyl groups and the structure of the hydrocarbon radical. Depending on the number of carboxyl groups, acids are divided into one-, two-, three- and polybasic. Depending on the structure of the hydrocarbon radical, acids are divided into saturated, unsaturated and aromatic. The radicals that make up acids can be cyclic or acyclic.

Limit monobasic acids

Monobasic saturated carboxylic acids form a homologous series with the general formula C n H 2n O 2 (n= 1,2,3...) or C n H 2n+1 COOH (n= 0,1,2...). The isomerism of saturated monobasic carboxylic acids is due only to the isomerism of the hydrocarbon radical. The formulas and names of some acids are given in the table:

Saturated carboxylic acids
FORMULA	Name
FORMULA	Trivial	according to IUPAC
	ant	methane
	vinegar	ethane
	propionic	propane
	oil	butane
	isobutyric, dimethylacetic	butane
	valerian	pentane
	isovaleric	3-methylbutane
	trimethylacetic	2,2-dimethylpropane

Physical properties

Lower acids (formic, acetic, propionic) are colorless, pungent-smelling liquids, acids with a number of carbon atoms from 4 to 9 are oily liquids with an unpleasant odor, with a number of carbon atoms greater than 10 are solids. The solubility of acids in water decreases sharply as the number of carbon atoms in the molecule increases. The boiling points of acids increase as the molecular weight increases, and the boiling points of acids containing the same number of carbon atoms and having an unbranched radical are higher than those of acids with a branched radical. Acids boil at much higher temperatures than their corresponding alcohols. This is due to a significantly greater association of acid molecules.

Chemical properties

Reactions of acids caused by a carboxyl group

The redistribution of electron density in the carboxyl group is shown in the figure:

As a result, the polarity of the O-H bond is so high that dissociation of the acid occurs relatively easily:

The resulting anion has increased stability due to resonance:

The strength of carboxylic acids depends on the radical associated with the carboxyl group and is determined by the amount of positive charge on the carboxyl carbon. With an increase in this charge, the strength of the acid increases, and with a decrease, it decreases. In turn, the magnitude of this charge is determined by the signs of the effects (inductive and mesomeric) acting on the part of the radical. Since the positive inductive effect of a hydrocarbon radical increases with increasing number of carbon atoms and with increasing branching of the radical, the strength of the corresponding carboxylic acids decreases. Formic acid is a medium-strength acid, all other monobasic saturated acids are weak. Water-soluble acids create an acidic environment in the solution, sufficient to change the color of the indicators.

1. Carboxylic acids react with metals, metal oxides and hydroxides, forming salts:

2CH 3 COOH + Zn = (CH 3 COO) 2 Zn + H 2 2CH 3 COOH + CaO = (CH 3 COO) 2 Ca + H 2 O CH 3 COOH + NaOH = CH 3 COONa + H 2 O

Carboxylic acids are stronger than carbonic acid, so they are able to decompose carbonates:

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

2. When phosphorus halides or thionyl chloride act on carboxylic acids, the hydroxyl of the carboxyl group is replaced by a halogen and acid halides are formed:

3. Carboxylic acids react with alcohols esterification, as a result of which esters are formed. The reaction occurs reversibly in an acidic environment. Mineral acids, such as sulfuric acid, serve as esterification catalysts. In the first stage of the reaction, the oxygen of the carboxyl group is protonated:

The resulting cation is then subjected to nucleophilic attack by an alcohol molecule:

The intermediate complex can reversibly lose a water molecule and a proton, resulting in an ester:

In an alkaline environment, the ester is irreversibly hydrolyzed to form an alcohol and a salt of the original acid. This reaction is called saponification ester.

4. Carboxylic acids form functional derivatives, which include acid halides, esters, anhydrides, amides and acid nitriles. Anhydrides, amides and nitriles are most often impossible to obtain directly from acids, so indirect methods are used.

Acid anhydrides are prepared by heating the acid halide and the sodium salt of the acid, for example:

Amides are formed by treating acid halides with ammonia:

during dry distillation (heating) of ammonium salts of carboxylic acids:

or with incomplete hydrolysis of acid nitriles:

Nitriles are obtained as a result of nucleophilic substitution of a halogen atom with a cyano group:

or when dehydrating an acid amide with phosphorus(V) oxide by heating:

Most reactions involving functional derivatives of carboxylic acids proceed through the mechanism of nucleophilic substitution of S N 1 and S N 2, in which the functional derivatives are substrates. For example, in dilute aqueous solutions, the hydrolysis of acid chlorides occurs predominantly according to the S N 1 mechanism, in the first, slowest stage of which (it is this stage that determines the rate of the entire process) dissociation of the original acid chloride occurs:

In the second stage, a rapid nucleophilic attack of the water molecule on the carboxylic carbon follows, and after the proton leaves, the final hydrolysis product, a carboxylic acid, is formed:

With bimolecular substitution of S N 2, the nucleophilic attack and the departure of the chlorine ion occur simultaneously:

The bimolecular mechanism predominates at low water content in the reaction system. Below are some nucleophilic substitution reactions in functional acid derivatives.

Acid halides decompose with water (hydrolysis):

react with alcohols to form esters (alcoholysis):

Esters are also obtained by reacting acid halides with alcoholates:

As a result of the interaction of acid halides with salts of carboxylic acids, anhydrides are formed; in this way, mixed anhydrides containing residues of different acids can be obtained:

When ammonia acids act on acid halides (ammonolysis), amides are formed:

Under the influence of peroxides, acid halides form acyl peroxides:

Acid anhydrides hydrolyze when heated with water:

undergo alcoholysis when heated with alcohol, resulting in the formation of an ester and an acid:

Under the influence of ammonia, ammonolysis of the anhydride occurs, resulting in an amide and a salt of the acid:

Acid amides hydrolyze when boiled with aqueous solutions of acids and alkalis:

The hydrogen atom in the amino group of the amide can be replaced by a metal, for example:

Obtaining acids

Acids can be obtained in the following ways:

1. Oxidation of primary alcohols, for example:

2. Oxidation of aldehydes with various oxidizing agents, such as chromium mixture, potassium permanganate, diammine silver hydroxide, oxygen - in the reaction scheme the oxidizing agent is shown as [O]:

3. Hydrolysis of anhydrides, acid halides and nitriles.

4. Using organometallic compounds, for example:

5. Using organomagnesium compounds:

Features of the properties of formic acid

Formic acid exhibits the properties of an aldehyde and an acid, because contains both a carboxyl group (circled in blue) and an aldehyde group (circled in red):

Formic acid is a good reducing agent:

HCOOH + OH Ag + CO 2 + H 2 O- silver mirror reaction HCOOH + HgCl 2 Hg + CO 2 + 2HCl

When heated with concentrated sulfuric acid, formic acid dehydrates to form CO:

Formic acid forms orthoesters - esters of the unstable orthoform of the acid:

The ethyl ester of orthrumic acid is called orthoformic ether:

Orthoformic ester is prepared by boiling sodium ethoxide with chloroform according to the reaction:

Ester condensation

Ester condensation (according to Claisen) occurs when alkali metal alcoholates act on esters of carboxylic acids. Alcohol anions formed as a result of dissociation:

abstract protons from the -position of the acid radical of the ester:

The resulting anion nucleophilically attacks the carboxyl carbon atom of another ester molecule:

The resulting anion splits off the alcoholate ion and becomes the condensation product:

which is an ester (in this example, ethyl) of a 3-oxo acid. In this way, acetoacetic ester (ethyl ester of 3-oxobutanoic acid) can be obtained from ethyl acetate. Under such conditions, condensation of esters and ketones occurs, in which the ketone acts as the methylene component and the ester as the carbonyl component. The Claisen condensation of ethyl acetate and acetone produces acetylacetone - pentanedione-2,4.

In table 19.10 shows some organic compounds related to carboxylic acids. A characteristic feature of carboxylic acids is the presence of carboxylic acid in them.

Table 19.10. Carboxylic acids

(see scan)

functional group. A carboxyl group consists of a carbonyl group bonded to a hydroxyl group. Organic acids with one carboxyl group are called monocarboxylic acids. Their systematic names have the suffix -ov(aya). Organic acids with two carboxyl groups are called dicarboxylic acids. Their systematic names have the suffix -diov(aya).

Saturated aliphatic monocarboxylic acids form a homologous series, which is characterized by the general formula. Unsaturated aliphatic dicarboxylic acids can exist in the form of various geometric isomers (see Section 17.2).

Physical properties

The lower members of the homologous series of saturated monocarboxylic acids under normal conditions are liquids with a characteristic pungent odor. For example, ethanoic (acetic) acid has a characteristic “vinegar” odor. Anhydrous acetic acid is a liquid at room temperature. It freezes into an icy substance called glacial acetic acid.

All dicarboxylic acids listed in table. 19.10, at room temperature they are white crystalline substances. The lower members of the series of monocarboxylic and dicarboxylic acids are soluble in water. The solubility of carboxylic acids decreases as their relative molecular weight increases.

In the liquid state and in non-aqueous solutions, molecules of monocarboxylic acids dimerize as a result of the formation of hydrogen bonds between them:

The hydrogen bond in carboxylic acids is stronger than in alcohols. This is explained by the high polarity of the carboxyl group, due to the withdrawal of electrons from the hydrogen atom towards the carbonyl oxygen atom:

As a result, carboxylic acids have relatively high boiling points (Table 19.11).

Table 19.11. Boiling points of acetic acid and alcohols with similar relative molecular weights

Laboratory methods of obtaining

Monocarboxylic acids can be obtained from primary alcohols and aldehydes by oxidation using an acidified solution of potassium dichromate taken in excess:

Monocarboxylic acids and their salts can be obtained by hydrolysis of nitriles or amides:

The preparation of carboxylic acids by reaction with Grignard reagents and carbon dioxide is described in section. 19.1.

Benzoic acid can be prepared by oxidation of the methyl side chain of methylbenzene (see Section 18.2).

Additionally, benzoic acid can be prepared from benzaldehyde using the Cannischaro reaction. In this reaction, benzaldehyde is treated with 40-60% sodium hydroxide solution at room temperature. Simultaneous oxidation and reduction leads to the formation of benzoic acid and, accordingly, phenylmethanol:

Oxidation

The Cannizzaro reaction is characteristic of aldehydes that do not have -hydrogen atoms. This is the name given to hydrogen atoms attached to a carbon atom adjacent to the aldehyde group:

Since methanal does not have -hydrogen atoms, it can undergo the Cannizzaro reaction. Aldehydes containing at least one -hydrogen atom undergo acid-catalyzed aldol condensation in the presence of sodium hydroxide solution (see above).

Chemical properties

Although the carboxyl group contains a carbonyl group, carboxylic acids do not undergo some of the reactions that occur with aldehydes and ketones. For example, they do not undergo addition or condensation reactions. This is explained by the fact that the atom

carbon in the carboxyl group has a less positive charge than in the aldehyde or keto group.

Acidity. Pulling electron density away from the carboxyl hydrogen atom weakens the O-H bond. As a result, the carboxyl group is able to abstract (lose) a proton. Therefore, monocarboxylic acids behave like monobasic acids. In aqueous solutions of these acids the following equilibrium is established:

The carboxylate ion can be considered a hybrid of two resonance structures:

Otherwise it can be thought of as

Delocalization of the electron between the atoms of the carboxylate group stabilizes the carboxylate ion. Therefore, carboxylic acids are much more acidic than alcohols. However, due to the covalent nature of carboxylic acid molecules, the above equilibrium is strongly shifted to the left. Thus, carboxylic acids are weak acids. For example, ethanoic (acetic) acid is characterized by an acidity constant

Substituents present in a carboxylic acid molecule greatly influence its acidity due to the inductive effect they provide. Substituents such as chlorine pull electron density towards themselves and, therefore, cause a negative inductive effect. Pulling electron density from the carboxyl hydrogen atom leads to an increase in the acidity of the carboxylic acid. In contrast, substituents such as alkyl groups have electron-donating properties and create a positive inductive effect. They weaken the carboxylic acid:

The effect of substituents on the acidity of carboxylic acids is clearly manifested in the values for a number of acids indicated in Table. 19.12.

Table 19.12. Carboxylic acid values

Formation of salts. Carboxylic acids have all the properties of ordinary acids. They react with reactive metals, bases, alkalis, carbonates and bicarbonates, forming the corresponding salts (Table 19.13). The reactions shown in this table are characteristic of both soluble and insoluble carboxylic acids.

Like other salts of weak acids, carboxylate salts (salts of carboxylic acids) react with mineral acids taken in excess, forming the parent carboxylic acids. For example, when a solution of sodium hydroxide is added to a suspension of insoluble benzoic acid in water, the acid dissolves due to the formation of sodium benzoate. If sulfuric acid is then added to the resulting solution, benzoic acid precipitates:

Table 19.13. Formation of salts from carboxylic acids

Esterification. When a mixture of carboxylic acid and alcohol is heated in the presence of concentrated mineral acid, an ester is formed. This process, called esterification, requires the breakdown of alcohol molecules. There are two possibilities.

1. Alkoxyhydrogen splitting. In this case, the alcohol oxygen atom (from the hydroxyl group) enters the molecule of the resulting ether:

2. Alkylhydroxyl cleavage. In this type of cleavage, the alcohol oxygen atom enters a water molecule:

Which of these cases is realized specifically can be determined experimentally by carrying out esterification using an alcohol containing isotope 180 (see Section 1.3), i.e. using an isotope tag. Determination of the relative molecular weight of the resulting ester using mass spectrometry indicates whether the oxygen-18 isotopic tag is present in it. In this way, it was discovered that esterification with the participation of primary alcohols leads to the formation of labeled esters:

This shows that the methanol molecule undergoes methoxy-hydrogen splitting during the reaction under consideration.

Halogenation. Carboxylic acids react with phosphorus pentachloride and sulfur oxide dichloride, forming acid chlorides of the corresponding acids. For example

Both benzoyl chloride and phosphorus trichloride oxide are liquids that need to be separated from each other. Therefore, for the chlorination of carboxylic acids, it is more convenient to use sulfur oxide dichloride: this makes it possible to easily remove gaseous hydrogen chloride and sulfur dioxide from the liquid carboxylic acid chloride:

By blowing chlorine through boiling acetic acid in the presence of catalysts such as red phosphorus or iodine, and under the influence of sunlight

monochloroethanoic (monochloroacetic) acid is formed:

Further chlorination leads to the formation of disubstituted and trisubstituted products:

Recovery. When reacting with lithium in dry diethyl ether, carboxylic acids can be reduced to the corresponding alcohols. First, an alkoxide intermediate is formed, the hydrolysis of which leads to the formation of alcohol:

Carboxylic acids are not reduced by many common reducing agents. These acids cannot be reduced immediately to the corresponding aldehydes.

Oxidation. With the exception of methane (formic) and ethanoic (acetic) acids, other carboxylic acids are difficult to oxidize. Formic acid and its salts (formates) are oxidized by potassium permanganate. Formic acid is capable of reducing Fehling's reagent and, when heated in a mixture with an aqueous-ammonia solution of silver nitrate, forms a “silver mirror”. The oxidation of formic acid produces carbon dioxide and water:

Ethanedioic (oxalic) acid is also oxidized by potassium permanganate, forming carbon dioxide and water:

Dehydration. Distillation of a carboxylic acid with some kind of dehydrating agent, for example an oxide, leads to the splitting of a water molecule from two acid molecules and the formation of a carboxylic acid anhydride:

Formic and oxalic acids are exceptions in this case. Dehydration of formic acid or its potassium or sodium salt with concentrated sulfuric acid leads to the formation of carbon monoxide and

Dehydration of sodium methanoate (formate) with concentrated sulfuric acid is a common laboratory method for producing carbon monoxide. Dehydration of oxalic acid with hot concentrated sulfuric acid produces a mixture of carbon monoxide and carbon dioxide:

Carboxylates

Sodium and potassium salts of carboxylic acids are white crystalline substances. They dissolve easily in water, forming strong electrolytes.

Electrolysis of sodium or potassium carboxylate salts dissolved in a water-methanol mixture leads to the formation of alkanes and carbon dioxide at the anode and hydrogen at the cathode.

At the anode:

At the cathode:

This method of producing alkanes is called electrochemical Kolbe synthesis.

The formation of alkanes also occurs when heating a mixture of sodium or potassium carboxylates with sodium hydroxide or soda lime. (Soda lime is a mixture of sodium hydroxide and calcium hydroxide.) This method is used, for example, to produce methane in the laboratory:

Aromatic sodium or potassium carboxylates under similar conditions form arenes:

When a mixture of sodium carboxylates and acid chlorides is heated, anhydrides of the corresponding carboxylic acids are formed:

Calcium carboxylates are also white crystalline substances and are generally soluble in water. When they are heated, they form

tion with low yield of the corresponding ketones:

When a mixture of calcium carboxylates and calcium formate is heated, an aldehyde is formed:

Ammonium salts of carboxylic acids are also white crystalline substances soluble in water. When heated strongly, they form the corresponding amides:

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 a carboxylic acid, 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 the O-H bond. 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.

Monocarboxylic acids consist of a carbon skeleton and only one functional carboxyl group. Every schoolchild knows the chemical properties of carboxylic acids. The 10th grade chemistry curriculum includes direct study of the properties of monobasic acids. Dibasic and polybasic acids have two or more carboxyl groups in their structure, respectively.

Also, based on 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 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:

Isolation from natural substances (fats and other things).
Oxidation of monoalcohols or compounds with a COH group (aldehydes): ROH (RCOH) [O] R-COOH.
Hydrolysis of trihaloalkanes in alkali with intermediate production of monoalcohol: RCl3 + NaOH = (ROH + 3NaCl) = RCOOH + H2O.
Saponification or hydrolysis of acid and alcohol esters (esters): R−COOR"+NaOH=(R−COONa+R"OH)=R−COOH+NaCl.
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 are of great importance 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.

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.

Almost everyone has vinegar at home. And most people know what its base is. But what is it from a chemical point of view? What other types of this series exist and what are their characteristics? Let's try to understand this issue and study saturated monobasic carboxylic acids. Moreover, not only acetic acid is used in everyday life, but also some others, and derivatives of these acids are generally frequent guests in every home.

Class of carboxylic acids: general characteristics

From the point of view of the science of chemistry, this class of compounds includes oxygen-containing molecules that have a special grouping of atoms - a carboxyl functional group. It has the form -COOH. Thus, the general formula that all saturated monocarboxylic acids have is: R-COOH, where R is a radical species that can include any number of carbon atoms.

According to this, this class of compounds can be defined as follows. Carboxylic acids are organic oxygen-containing molecules that contain one or more functional groups -COOH - carboxyl groups.

The fact that these substances belong specifically to acids is explained by the mobility of the hydrogen atom in the carboxyl. The electron density is not evenly distributed, since oxygen is the most electronegative in the group. This causes the O-H bond to become highly polarized, and the hydrogen atom becomes extremely vulnerable. It is easily split off, entering into chemical interactions. Therefore, acids in the corresponding indicators give a similar reaction:

Thanks to the hydrogen atom, carboxylic acids exhibit oxidizing properties. However, the presence of other atoms allows them to recover and participate in many other interactions.

Classification

There are several main characteristics by which carboxylic acids are divided into groups. The first of these is the nature of the radical. Based on this factor there are:

Alicyclic acids. Example: cinchona.
Aromatic. Example: benzoin.
Aliphatic. Example: vinegar, acrylic, oxalic and others.
Heterocyclic. Example: nicotine.

If we talk about the bonds in the molecule, then we can also distinguish two groups of acids:

The number of functional groups can also serve as a sign of classification. So, the following categories are distinguished.

Monobase - only one -COOH group. Example: formic, stearic, butane, valerian and others.
Dibasic- respectively, two -COOH groups. Example: oxalic acid, malonic acid and others.
Polybasic- lemon, milk and others.

History of discovery

Winemaking has flourished since ancient times. And, as you know, one of its products is acetic acid. Therefore, the history of the popularity of this class of compounds dates back to the times of Robert Boyle and Johann Glauber. However, for a long time it was not possible to determine the chemical nature of these molecules.

After all, for a long time the views of vitalists dominated, who denied the possibility of the formation of organic matter without living beings. But already in 1670, D. Ray managed to obtain the very first representative - methane or formic acid. He did this by heating live ants in a flask.

Later, the work of scientists Berzelius and Kolbe showed the possibility of synthesizing these compounds from inorganic substances (by distillation of charcoal). The result was vinegar. In this way, carboxylic acids were studied (physical properties, structure) and the beginning was laid for the discovery of all other representatives of a number of aliphatic compounds.

Physical properties

Today all their representatives have been studied in detail. For each of them, you can find characteristics in all respects, including use in industry and occurrence in nature. We will look at what carboxylic acids are, their and other parameters.

So, we can highlight several main characteristic parameters.

If the number of carbon atoms in the chain does not exceed five, then these are sharp-smelling, mobile and volatile liquids. Above five - heavy oily substances, even more - solid, paraffin-like substances.
The density of the first two representatives exceeds unity. All others are lighter than water.
Boiling point: the larger the chain, the higher the value. The more branched the structure, the lower.
Melting point: depends on the parity of the number of carbon atoms in the chain. For even numbers it is higher, for odd numbers it is lower.
They dissolve very well in water.
Capable of forming strong hydrogen bonds.

Such features are explained by the symmetry of the structure, and therefore the structure of the crystal lattice and its strength. The simpler and more structured the molecules, the higher the performance of carboxylic acids. The physical properties of these compounds make it possible to determine the areas and methods of their use in industry.

Chemical properties

As we have already indicated above, these acids can exhibit different properties. Reactions involving them are important for the industrial synthesis of many compounds. Let us designate the most important chemical properties that a monobasic carboxylic acid can exhibit.

Dissociation: R-COOH = RCOO - + H + .
It exhibits, that is, interacts with basic oxides, as well as their hydroxides. It interacts with simple metals according to the standard scheme (that is, only with those that come before hydrogen in the voltage series).
With stronger acids (inorganic) it behaves like a base.
Capable of being reduced to primary alcohol.
A special reaction is esterification. This is the interaction with alcohols to form a complex product - an ester.
The reaction of decarboxylation, that is, the removal of a carbon dioxide molecule from a compound.
Able to interact with halides of elements such as phosphorus and sulfur.

It is obvious how versatile carboxylic acids are. Physical properties, like chemical ones, are quite diverse. In addition, it should be said that in general, in terms of strength as acids, all organic molecules are quite weak compared to their inorganic counterparts. Their dissociation constants do not exceed 4.8.

Methods of obtaining

There are several main ways in which saturated carboxylic acids can be obtained.

1. In the laboratory this is done by oxidation:

alcohols;
aldehydes;
alkynes;
alkylbenzenes;
destruction of alkenes.

2. Hydrolysis:

esters;
nitriles;
amides;
trihaloalkanes.

4. In industry, synthesis is carried out by oxidation of hydrocarbons with a large number of carbon atoms in the chain. The process is carried out in several stages with the release of many by-products.

5. Some individual acids (formic, acetic, butyric, valeric and others) are obtained by specific methods using natural ingredients.

Basic compounds of saturated carboxylic acids: salts

Salts of carboxylic acids are important compounds used in industry. They are obtained as a result of the interaction of the latter with:

metals;
basic oxides;
alkalis;
amphoteric hydroxides.

Particularly important among them are those that are formed between the alkali metals sodium and potassium and higher saturated acids - palmitic and stearic. After all, the products of such interaction are soaps, liquid and solid.

Soap

So, if we are talking about a similar reaction: 2C 17 H 35 -COOH + 2Na = 2C 17 H 35 COONa + H 2,

then the resulting product - sodium stearate - is by its nature an ordinary laundry soap used for washing clothes.

If you replace the acid with palmitic acid and the metal with potassium, you get potassium palmitate - liquid soap for washing hands. Therefore, we can confidently say that salts of carboxylic acids are actually important compounds of organic nature. Their industrial production and use are simply colossal in scale. If you imagine how much soap each person on Earth spends, it is not difficult to imagine this scale.

Esters of carboxylic acids

A special group of compounds that has its place in the classification of organic substances. This is a class They are formed by the reaction of carboxylic acids with alcohols. The name of such interactions is esterification reactions. The general view can be represented by the equation:

R, -COOH + R"-OH = R, -COOR" + H 2 O.

The product with two radicals is an ester. Obviously, as a result of the reaction, the carboxylic acid, alcohol, ester and water underwent significant changes. Thus, hydrogen leaves the acid molecule in the form of a cation and meets with the hydroxo group that has been split off from the alcohol. As a result, a water molecule is formed. The group remaining from the acid attaches to itself the radical from the alcohol, forming an ester molecule.

Why are these reactions so important and what is the industrial significance of their products? The thing is that esters are used as:

nutritional supplements;
aromatic additives;
component of perfume;
solvents;
components of varnishes, paints, plastics;
medicines and so on.

It is clear that their areas of use are wide enough to justify industrial production volumes.

Ethanoic acid (acetic)

This is a limiting monobasic carboxylic acid of the aliphatic series, which is one of the most common in terms of production volumes throughout the world. Its formula is CH 3 COOH. It owes its popularity to its properties. After all, the areas of its use are extremely wide.

It is a food additive under code E-260.
Used in the food industry for preservation.
Used in medicine for the synthesis of drugs.
Component in the production of fragrant compounds.
Solvent.
Participant in the process of book printing and fabric dyeing.
A necessary component in the reactions of chemical syntheses of many substances.

In everyday life, its 80% solution is usually called vinegar essence, and if you dilute it to 15%, you get just vinegar. Pure 100% acid is called glacial acetic acid.