Carboxylic acid plus hydrogen. Chemical properties of carboxylic acids and methods of preparation

CARBOXYLIC ACIDS

Carboxylic acids are hydrocarbon derivatives containing one or more carboxyl groups.

The number of carboxyl groups characterizes the basicity of the acid.

Depending on the number of carboxyl groups, carboxylic acids are divided into monobasic carboxylic acids (contain one carboxyl group), dibasic (contain two carboxyl groups) and polybasic acids.

Depending on the type of radical associated with the carboxyl group, carboxylic acids are divided into saturated, unsaturated and aromatic. Saturated and unsaturated acids are combined under common name aliphatic or fatty acids.

Monobasic carboxylic acids

1.1 Homologous series and nomenclature

The homologous series of monobasic saturated carboxylic acids (sometimes called fatty acids) begins with formic acid

Formula homologous series

The IUPAC nomenclature allows many acids to retain their trivial names, which usually indicate natural spring, from which one or another acid was isolated, for example, formic, acetic, butyric, valeric, etc.

For more complex cases the names of acids are derived from the names of hydrocarbons with the same number carbon atoms, as in the acid molecule, with the addition of the ending -new and words acid. Formic acid H-COOH is called methanoic acid, acetic acid CH 3 -COOH is called ethanoic acid, etc.

Thus, acids are considered as derivatives of hydrocarbons, one unit of which is converted to carboxyl:

When compiling the names of branched-chain acids according to rational nomenclature, they are considered as derivatives of acetic acid, in the molecule of which hydrogen atoms substituted by radicals, for example, trimethylacetic acid (CH 3) 3 C – COOH.

1.2 Physical properties of carboxylic acids

Only from a purely formal standpoint can the carboxyl group be considered a combination of carbonyl and hydroxyl functions. In fact, their mutual influence on each other is such that it completely changes their properties.

The polarization of the C=0 double bond, usual for carbonyl, increases greatly due to the additional contraction of a free electron pair from the neighboring oxygen atom of the hydroxyl group:

The consequence of this is a significant weakening O-N connections in hydroxyl and the ease of abstraction of a hydrogen atom from it in the form of a proton (H +). The appearance of a reduced electron density (δ+) on the central carbon atom of the carboxyl also leads to the contraction of σ-electrons of the neighboring S-S connections to the carboxyl group and the appearance (as in aldehydes and ketones) of reduced electron density (δ +) on the α-carbon atom of the acid.

All carboxylic acids are acidic (detected by indicators) and form salts with hydroxides, oxides and carbonates of metals and with active metals:

Carboxylic acids in most cases in an aqueous solution are dissociated only to a small extent and are weak acids, significantly inferior to such acids as hydrochloric, nitric and sulfuric. Thus, when one mole is dissolved in 16 liters of water, the degree of dissociation of formic acid is 0.06, acetic acid is 0.0167, while hydrochloric acid with such a dilution is almost completely dissociated.

For most monobasic carboxylic acids rK A = 4.8, only formic acid has a lower pKa value (about 3.7), which is explained by the absence of the electron-donating effect of alkyl groups.

In anhydrous mineral acids, carboxylic acids are protonated at oxygen to form carbocations:

The shift in electron density in the molecule of an undissociated carboxylic acid, which was mentioned above, lowers the electron density on the hydroxyl oxygen atom and increases it on the carbonyl oxygen atom. This shift is further increased in the acid anion:

The result of the shift is complete equalization of charges in the anion, which actually exists in form A - carboxylate anion resonance.

The first four representatives of the series of carboxylic acids are mobile liquids, miscible with water in all respects. Acids, the molecule of which contains from five to nine carbon atoms (as well as isobutyric acid), are oily liquids, their solubility in water is low.

Higher acids (from C 10) - solids, are practically insoluble in water; when distilled under normal conditions, they decompose.

Formic, acetic and propionic acids have a pungent odor; The middle members of the series have an unpleasant odor; the higher acids have no odor.

On physical properties carboxylic acids are affected by a significant degree of association due to the formation of hydrogen bonds. Acids form strong hydrogen bonds because the O-H bonds in them are highly polarized. In addition, carboxylic acids are capable of forming hydrogen bonds with the participation of the oxygen atom of the carbonyl dipole, which has significant electronegativity. Indeed, in solid and liquid states, carboxylic acids exist mainly in the form of cyclic dimers:

Such dimeric structures are retained to some extent even in the gaseous state and in dilute solutions in nonpolar solvents.

Chemical properties

Acids are characterized by three types of reactions: substitution of the hydrogen ion of the carboxyl group (formation of salts); with the participation of a hydroxyl group (formation of esters, acid halides, acid anhydrides); substitution of hydrogen in the radical.

Formation of salts. Carboxylic acids easily form salts when interacting with metals, their oxides, with alkalis or bases, under the action of ammonia or amines:

Salts of carboxylic acids are widely used in national economy. They are used as catalysts, stabilizers for polymer materials, in the manufacture of paints, etc.

Formation of esters. Acid alcohols give esters:

Formation of acid halides. When phosphorus halides or SOC1 2 act on acids, acid halides are obtained:

Acid halides are highly reactive substances that are used in a variety of syntheses.

Formation of acid anhydrides. If one molecule of water is removed from two molecules of carboxylic acids (in the presence of water-removing substances P 2 O 5, etc.), a carboxylic acid anhydride is formed:

Acid anhydrides, like acid halides, are very reactive; they decompose by various compounds with active hydrogen, forming acid derivatives and free acid:

Halogenation of carboxylic acids. Hydrogen atoms of hydrocarbon radicals in acids reactivity similar to the hydrogen atoms in alkanes. The exception is the hydrogen atoms located at the α-carbon atom (directly bonded to the carboxyl). Thus, when chlorine and bromine act in the presence of halogen carriers (PC1 3, 1 2, etc.) on carboxylic acids or their acid chlorides, it is the α-hydrogen atoms that are replaced:

Action of oxidizing agents. Monobasic carboxylic acids are usually resistant to oxidizing agents. Only formic acid (to CO 2 and H 2 O) and acids with a tertiary carbon atom in the α position are easily oxidized. When the latter are oxidized, α-hydroxy acids are obtained:

In animal organisms, monobasic carboxylic acids are also capable of oxidation, and the oxygen atom is always directed to the β-position. For example, in the body of diabetic patients, butyric acid is converted into β-hydroxybutyric acid:

Ketone formation Dry distillation of calcium and barium salts of carboxylic acids (except formic acid) leads to the formation of ketones. So, when distilling calcium acetate obtained from CaCO 3 and CH 3 COOH, dimethyl ketone is formed, when distilling calcium propionic acid - diethyl ketone:

Formation of amides. When ammonium salts of acids are heated, amides are obtained:

Formation of hydrocarbons. When fusing salts alkali metals carboxylic acids with alkalis (pyrolysis), the carbon chain is split and decarboxylated, resulting in the formation of the corresponding hydrocarbon from the hydrocarbon radical of the acid, for example:

The most important representatives

Formic acid - colorless liquid with a pungent odor. It is a strong reducing agent and oxidizes to carbonic acid. In nature, free formic acid is found in the secretions of ants, in nettle juice, and in the sweat of animals. Formic acid is used in textile dyeing as a reducing agent, in leather tanning, in medicine, and in various organic syntheses.

Acetic acid - colorless liquid with a pungent odor. Aqueous solution (70 - 80 %) acetic acid is called vinegar essence, and a 3-5% aqueous solution is called table vinegar.

Acetic acid occurs widely in nature. It is found in urine, sweat, bile and skin of animals and plants. It is formed during acetic acid fermentation of liquids containing alcohol (wine, beer, etc.).

Widely used in chemical industry for the production of silk acetate, dyes, esters, acetone, acetic anhydride, salts, etc. In the food industry, acetic acid is used to preserve food; some esters of acetic acid are used in the confectionery industry.

Butyric acid is a liquid with an unpleasant odor. Contained as an ester in cow butter. IN free state is in rancid oil.

2. Dibasic carboxylic acids

General formula of the homologous series of saturated dibasic acids

Examples include:

Saturated dibasic acids are crystalline solids. Just as was noted for monobasic acids, saturated dibasic acids with an even number of carbon atoms melt at a higher temperature than neighboring homologues with an odd number of carbon atoms. The solubility in water of acids with an odd number of carbon atoms is significantly higher than the solubility of acids with an even number of carbon atoms, and with increasing chain length, the solubility of acids in water decreases.

Dibasic acids dissociate sequentially:

They are stronger than the corresponding monobasic acids. The degree of dissociation of dibasic acids decreases with increasing molecular weight.

The molecule of dibasic acids contains two carboxyl groups, so they give two series of derivatives, for example, middle and acid salts, middle and acid esters:

When oxalic and malonic acids are heated, CO 2 is easily split off:

Dibasic acids with four and five carbon atoms in the molecule, i.e., succinic and glutaric acids, when heated, eliminate water elements and give internal cyclic anhydrides:

3. Unsaturated carboxylic acids

The composition of unsaturated monobasic acids with one double bond can be expressed by the general formula C n H 2 n -1 COOH. As with any bifunctional compounds, they are characterized by reactions of both acids and olefins. α.β-Unsaturated acids are somewhat stronger than the corresponding fatty acids, since the double bond located next to the carboxyl group enhances its acidic properties.

Acrylic acid. The simplest unsaturated monobasic acid

Oleic, linoleic and linolenic acids.

Oleic acid C 17 H 33 COOH in the form of glycerol ether is extremely common in nature. Its structure is expressed by the formula

Oleic acid is a colorless oily liquid, lighter than water, and in the cold it hardens into needle-shaped crystals that melt at 14 °C. In air it quickly oxidizes and turns yellow.

The oleic acid molecule is capable of attaching two halogen atoms:

In the presence of catalysts, such as Ni, oleic acid adds two hydrogen atoms, becoming stearic acid.

Oleic acid is a cis isomer (all natural unsaturated high molecular weight acids, as a rule, belong to the cis series).

Linoleic C 17 H 31 COOH and linolenic C 17 H 29 COOH acids are even more unsaturated than oleic acid. In the form of esters with glycerin - glycerides- they are the main component of flaxseed and hemp oils:

There are two double bonds in the linoleic acid molecule. It can add four hydrogen or halogen atoms. The linoleic acid molecule has three double bonds, so it adds six hydrogen or halogen atoms. Both acids add hydrogen to form stearic acid.

Sorbic acid

It has two double bonds conjugated with each other and with the carboxyl group, having a trans configuration; is an excellent preservative for many food products: canned vegetables, cheese, margarine, fruits, fish and meat products.

Maleic and fumaric acids. The simplest of dibasic acids containing an ethylene bond are two structural isomers:

In addition, for the second of these acids two spatial configurations are possible:

Fumaric acid is found in many plants: it is especially common in mushrooms. Maleic acid is not found in nature.

Both acids are usually prepared by heating malic (hydroxysuccinic) acid:

Slow, gentle heating produces mainly fumaric acid; with stronger heating and distillation of malic acid, maleic acid is obtained.

Both fumaric and maleic acid, when reduced, give the same succinic acid.

Classification

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

Monobasic (monocarbon) RCOOH; For example:

CH 3 CH 2 CH 2 COOH;

NOOS-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 = CHCOOH propenoic (acrylic) acid

Alicyclics, for example:

Aromatic, for example:

Saturated monocarboxylic acids

(monobasic saturated carboxylic acids) – carboxylic acids in which a saturated hydrocarbon radical is connected to one carboxyl group -COOH. They all have 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 - ova 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

Skeletal isomerism in the hydrocarbon radical manifests itself, starting with butanoic acid, which has two isomers:

Interclass isomerism appears 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

Trivial name	IUPAC name
Formic acid	Methane acid
Acetic acid	Ethanoic acid
Propionic acid	Propanic acid
Butyric acid	Butanoic acid
Valeric acid	Pentanoic acid
Caproic acid	Hexanoic acid
Enanthic acid	Heptanoic acid
Caprylic acid	Octanoic acid
Pelargonic acid	Nonanoic acid
Capric acid	Decanoic acid
Undecylic acid	Undecanoic acid

Palmitic acid	Hexadecanoic acid
Stearic acid	Octadecanoic acid

Acidic residues and acid radicals

	Acid residue	Acid radical (acyl)
UNDC ant	NSOO- formate
CH 3 COOH vinegar	CH 3 COO- acetate
CH 3 CH 2 COOH propionic	CH 3 CH 2 COO- propionate
CH 3 (CH 2) 2 COOH oil	CH 3 (CH 2) 2 COO- butyrate
CH 3 (CH 2) 3 COOH valerian	CH 3 (CH 2) 3 COO- valeriat
CH 3 (CH 2) 4 COOH nylon	CH 3 (CH 2) 4 COO- capronate

Electronic structure of carboxylic acid molecules

The shift in electron density towards the carbonyl oxygen atom shown in the formula causes a strong polarization of the O-H bond, as a result of which the abstraction of a 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 -) there is p, π-conjugation of the lone pair of electrons of the oxygen atom of the hydroxyl group with p-clouds forming a π-bond, resulting in delocalization of the π-bond and a uniform distribution of negative charge between the two oxygen atoms:

In this regard, carboxylic acids, unlike aldehydes, are not characterized by addition reactions.

Physical properties

The boiling points of acids are significantly 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 following order:

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

1. Neutralization reactions

CH 3 COOH + KOH → CH 3 COOC + 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 + 2СO 2 + 2H 2 O

(HCOOH + HCO 3 - → HCOO - + CO2 +H2O)

5. Reactions with ammonia

CH 3 COOH + NH 3 → CH 3 COONH 4

II. Substitution of -OH group

1. Interaction with alcohols (esterification reactions)

2. Interaction with NH 3 upon heating (acid amides are formed)

Acid amides hydrolyze to form acids:

or their salts:

3. Formation of acid halides

Acid chlorides are of 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 reaction of acid chlorides with anhydrous salts of carboxylic acids; in this case it is possible to obtain mixed anhydrides of various acids; For example:

III. Reactions of substitution of hydrogen atoms at the α-carbon atom

Features of the structure and properties of formic acid

Molecule structure

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

Chemical properties

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

In particular, HCOOH is oxidized by an ammonia solution of Ag 2 O and copper (II) hydroxide Cu(OH) 2, i.e. it gives qualitative reactions to 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 because the carboxyl group in it is bonded to a hydrogen atom rather than to an electron-donating alkyl radical.

Methods for obtaining saturated monocarboxylic acids

1. Oxidation of alcohols and aldehydes

General scheme of oxidation of alcohols and aldehydes:

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

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. Reaction of carbon monoxide (II) with sodium hydroxide

CO + NaOH → HCOONa sodium formate

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

2. Decarboxylation of oxalic acid

Methods for producing 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 edible acetic acid is obtained.

Preparation of higher carboxylic acids

Hydrolysis of natural fats

Unsaturated monocarboxylic acids

The most important representatives

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

CH 2 =CH-COOH propenoic (acrylic) acid

Higher unsaturated acids

Radicals of these acids are part of vegetable oils.

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

Trance The -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 general properties carboxylic acids, unsaturated acids are characterized by addition reactions at multiple bonds in the hydrocarbon radical. Thus, unsaturated acids, like alkenes, are hydrogenated and decolorize bromine water, for example:

Selected representatives of dicarboxylic acids

Saturated dicarboxylic acids HOOC-R-COOH

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

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

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

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

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 neutral:

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:

Carboxylic acids are compounds that contain a carboxyl group:

Carboxylic acids are distinguished:

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

Depending on their structure, carboxylic acids are distinguished:

aliphatic;
alicyclic;
aromatic.

Examples of carboxylic acids.

Preparation of carboxylic acids.

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

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

3. Preparation of carboxylic acids from cyanides:

When heated, the nitrile hydrolyzes to form ammonium acetate:

When acidified, acid precipitates:

4. Use of Grignard reagents:

5. Hydrolysis of esters:

6. Hydrolysis of acid anhydrides:

7. Specific methods for obtaining carboxylic acids:

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

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

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

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

Chemical properties of carboxylic acids.

In an aqueous solution, carboxylic acids dissociate:

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

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

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

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

2. Formation of functional derivatives of carboxylic acids:

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

4. Formation of amides, nitriles:

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

4. Addition reaction.

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

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

Additional materials on the topic: Carboxylic acids.

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1. Classification of carboxylic acids.

2. Nomenclature, receipt.

3. Isomerism, structure.

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

5. Dicarboxylic acids.

6. Derivatives of carboxylic acids.

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

Carboxylic acids are classified according to two structural characteristics:

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

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

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

Receipt.

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

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

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

alcohol aldehyde acid

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

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

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

R-C≡N + H 2 O + NaOH → R-COONa + NH 3

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

d ) Organometallic synthesis:

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

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

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

And

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

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

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

Monocarboxylic acids(saturated, unsaturated, aromatic acids).

General molecular formula saturated monocarboxylic acids

СnН2nО2.

Table 4.

Homologous series of saturated monocarboxylic acids

		T pl., С	T kip. , С	Acyl residue - acid residue
Ant (methane)				formyl - formates
Vinegar (ethane)				acetyl - acetates
propionic (propane)	CH3-CH2-COOH			propionyl - propionates
oil (butane)	CH3-(CH2)2-COOH			butyryl - butyrates
valerian	CH3-(CH2)3-COOH			valeryl - valerates
nylon	CH3-(CH2)4-COOH			capronoyl
lauric	CH3-(CH2)10-COOH
palmitic	CH3-(CH2)14-COOH			palmityl palmitates
stearic	CH3-(CH2)16-COOH			stearyl - stearates

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

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

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

Chemical properties.

a) acidic properties

Aqueous solutions of carboxylic acids have an acidic reaction:

acid carboxylate ion

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

On the strength of carboxylic acids significant influence The nature of the radical at the carboxyl group has an effect: electron-donating groups destabilize the carboxylate ion and, therefore, reduce the acidic properties, electron-withdrawing groups stabilize the carboxylate ion and increase the acidic properties.

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

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

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

R-COO - Na + + HOH ↔ R-COOH + NaOH

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

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

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

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

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

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

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

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

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

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

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

V)decarboxylation

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

Examples of decarboxylation reactions:

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

R-COONa + NaOH → R-H + Na 2 CO 3

2) thermal decomposition of calcium or barium salts

R-COO-Ca-OOS-R → R-CO-R + CaCO 3

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

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

d) replacement of hydrogen atomsα-carbon atom

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

propionic acid α-chloropropionic acid

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

e) specific properties of formic acid

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

1. oxidation

HCOOH + [O]→ CO 2 + H 2 O

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

2. dehydration

HCOOH + H 2 SO 4 (conc.) → CO + H 2 O

Occurrence in nature and use of acids:

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

NaOH + CO → H-COONa

H-COONa + H 2 SO 4 → H-COOH + NaHSO 4

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

b) acetic acid

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

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

c) butyric acid- colorless liquid, acid solutions have bad smell old butter and sweat. Occurs in nature in the form of esters; esters of glycerol and butyric acid are part of fats and butter. Used in organic synthesis to obtain aromatic esters.

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

d) palmitic, stearic acids

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

Unsaturated acids

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

Nomenclature and isomerism.

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

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

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

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

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

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

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

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

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

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

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

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

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

A)Eelectrophilic addition:

1. halogenation

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

propenoic acid α,β-dibromopropionic acid

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

2. hydrohalogenation

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

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

b)Ghydrogenation

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

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

acrylic acid propionic acid

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

V)ABOUTacidification

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

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

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

b) higher unsaturated acids

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

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

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

Aromatic monocarboxylic acids

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

The most important representatives:

benzoic acid

phenylacetic acid

trance-cinnamic acid

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

Occurrence in nature and use of acids:

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

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

Derivatives of carboxylic acids.

General formula of carboxylic acid derivatives:

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

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

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

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

salt< амиды < сложные эфиры <ангидриды <галогенангидриды

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

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

Esters

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

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

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

b) acylation of alcohols with acid halides and anhydrides

c) from salts of carboxylic acids and alkyl halides

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

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

hydrocarbon radical

radical + hydrocarbon + oate - methyl butanoate.

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

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

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

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

RCOOR + H 2 O(H +) ↔ RCOOH + ROH

RCOOR + NaOH → RCOO - Na + + ROH

Fats

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

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

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

tripalmitin dioleostearin

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

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

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

a) hydrogenation (hydrogenation) of fats

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

b) hydrolysis of fats

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

c) addition and oxidation

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

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

Did you know that

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

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

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

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

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

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

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

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

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

Dicarboxylic acids

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

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

NOOS-CH 2 -COOH - propanedioic or malonic acid

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

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

HOOS-CH 2 -CH 2 -CH 2 -COOH - adipinoic acid

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

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

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

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

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

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

HOOC-CH 2 -COOH → CH 3 -COOH + CO 2

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

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

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

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

Occurrence in nature and use of acids:

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

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

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

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

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

Ortho-phthalic acid, wide application have acid derivatives - phthalic anhydride, esters - phthalates (repellents).

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

Carbonyl compounds. Structure and chemical properties of carboxylic acids. Lipids.

Carboxylic acids. The structure of the carboxyl group. Nomenclature.

Unripe fruits, sorrel, barberry, cranberry, lemon. What do they have in common? Even a preschooler will answer without hesitation: they are sour. But the sour taste of the fruits and leaves of many plants is due to various carboxylic acids, which include one or more carboxyl groups - COOH.

The name "carboxylic" acids comes from the Latin name for carbonic acid, acidum carbonicum, which was the first carbon-containing acid studied in the history of chemistry. They are often called fatty acids because higher homologues were first obtained from natural fats.

Carboxylic acids can be considered as derivatives of hydrocarbons containing one or more functional carboxyl groups in the molecule:

The term "carboxyl" is a compound formed in accordance with the names of two groups: and hydroxyl -OH, which are part of the carboxyl group.

Classification of carboxylic acids.

Carboxylic acids, depending on the nature of the radical, are divided into

limit,

unlimited,

acyclic,

cyclical.

Based on the number of carboxyl groups, they distinguish

monobasic (with one -COOH group)

polybasic (contain two or more -COOH groups).

Alkanoic acids are derivatives of saturated hydrocarbons containing one functional carboxyl group. Their general formula is R - COOH, where R is an alkane radical. Homologous series of the simplest low molecular weight acids:

Isomerism, nomenclature .

The isomerism of saturated acids, as well as of saturated hydrocarbons, is determined by the isomerism of the radical. The simplest three acids with one, two and three carbon atoms in the molecule have no isomers. Acid isomerism begins with the fourth member of the homologous series. Thus, butyric acid C 3 H 7 - COOH has two isomers, valeric acid C 4 H 9 - COOH has four isomers.

The most common are the trivial names of acids. Many of them are related to the names of the products from which they were originally isolated or in which they were discovered. For example, formic acid was obtained from ants, acetic acid from vinegar, and butyric acid from rancid oil.

According to the IUPAC nomenclature, the ending - is added to the name of the saturated hydrocarbon corresponding to the main carbon chain, including the carboxyl carbon. oic acid. So, for example, formic acid is methanoic acid, acetic acid is ethanoic acid, propionic acid is propane acid, etc. The numbering of the carbon atoms of the main chain starts from the carboxyl group.

The remainder of the carboxylic acid molecule, formed by removing the hydroxyl group from the carboxyl structure, is called an acid residue or acyl (from the Latin acidum - acid). The acyl of formic acid (lat. acidum formicum) is called formyl, acetic acid (acidum aceticum) is called acetyl. .

Physical and chemical properties .

Physical properties.

The first three acids of the homologous series (formic, acetic, propionic) are liquids that are highly soluble in water. The following representatives are oily liquids, slightly soluble in water. Acids, starting with capric acid C 9 H 19 COOH, are solids that are insoluble in water, but soluble in alcohol and ether.

All liquid acids have their own unique odors.

High molecular weight solid acids are odorless. As the molecular weight of acids increases, their boiling point increases and their density decreases.

Chemical properties.

Dissociation of acids:

The degree of dissociation of carboxylic acids varies. The strongest acid is formic acid, in which the carboxyl is not bonded to the radical. The degree of dissociation of organic acids is significantly lower than that of inorganic acids. Therefore they are weak acids. Organic acids, as well as inorganic ones, give characteristic reactions to indicators.

Formation of salts .

When interacting with active metals (a), metal oxides (b), bases (c), the hydrogen of the carboxylic group of the acid is replaced by a metal and salts are formed:

Formation of acid halides .

When the hydroxyl of the carboxylic group of acids is replaced by a halogen, acid derivatives are formed - halides:

Formation of acid anhydrides.

When water is removed from two acid molecules in the presence of a catalyst, acid anhydrides are formed:

Formation of esters .

The so-called esterification reaction:

Amide formation:

Reactions of carboxylic acid chlorides with ammonia

CH 3 -CO-Cl + CH 3 → CH 3 -CO-CH 2 + HCl.

Halogens are capable of replacing the hydrogen of an acid radical, forming halogen acids. This replacement occurs gradually:

Halogen-substituted acids are stronger acids than the original ones. For example, trichloroacetic acid is approximately 10 thousand times stronger than acetic acid. They are used to produce hydroxy acids, amino acids and other compounds.

Dicarboxylic acids.

Dicarboxylic acids are acids that have two or three carboxyl groups.

For example.

HOOS - COOH - ethanedioic acid (oxalic acid)

HOOS - CH 2 - COOH - propanedioic acid (malonic acid)

NOOS - CH 2 - CH 2 - COOH-butanedioic acid (succinic acid)

Dicarboxylic acids are characterized by decarboxylation reactions (elimination of CO 2) when heated:

t°

NOOS-CH 2 -COOH →CH 3 COOH + CO 2

The physiologically important end product of transformations of proteins and nucleic acids in the body is urea.

Lipids. Classification.

Lipids are esters formed by higher monobasic carboxylic acids, mainly palmitic, stearic(saturated acids) and oleic(unsaturated acid) and trihydric alcohol - glycerin. The general name for such compounds is triglycerides

Natural fats are not an individual substance, but a mixture of various triglycerides.

Classification of lipids.

Lipids are divided into:

Simple:

a) acylglycerides

b) waxes

Difficult:

a) phospholipids

b) glycolipids

Higher fatty acids.

The composition of lipids in the human and animal body includes fatty acids with a paired number of carbon atoms from 12 to 24.

Higher fatty acids are saturated (marginal)

palmitic acid - C 15 H 31 COOH

stearic - C 17 H 35 COOH

Unsaturated (unsaturated)

oleic - C 17 H 33 COOH

linoleic-C 17 H 31 COOH

linolenic-C 17 H 29 COOH

arachidonic-C 19 H 31 COOH

Simple lipids are lipids that, when hydrolyzed, form alcohols and fatty acids.

Acylglycerides are lipids that are esters of glycerol and higher fatty acids.

The formation of one of the triglycerides, such as stearic acid triglyceride, can be represented by the equation

glycerin stearic acid stearic triglyceride

The composition of triglyceride molecules may include various acid radicals, which is especially typical for natural fats, but the glycerol residue is an integral part of all fats:

All fats are lighter than water and insoluble in it. They are highly soluble in gasoline, ether, carbon tetrachloride, carbon disulfide, dichloroethane and other solvents. Well absorbed by paper and skin. Fats are found in all plants and animals. Liquid fats are usually called oils. Solid fats (beef, lamb, etc.) consist mainly of triglycerides of saturated (solid) acids, liquid fats (sunflower oil, etc.) - of triglycerides of unsaturated (liquid) acids.

Liquid fats are converted to solid fats by hydrogenation reactions. Hydrogen joins at the site of double bond cleavage in hydrocarbon radicals of fat molecules:

The reaction occurs when heated under pressure and in the presence of a catalyst - finely crushed nickel. The product of hydrogenation - solid fat (artificial lard) is called salomas used for the production of soap, stearin and glycerin. Margarine is an edible fat that consists of a mixture of hydrogenated oils (sunflower, cottonseed, etc.), animal fats, milk and some other substances (salt, sugar, vitamins, etc.).

An important chemical property of fats, like all esters, is the ability to undergo hydrolysis (saponification). Hydrolysis occurs easily when heated in the presence of catalysts - acids, alkalis, oxides of magnesium, calcium, zinc:

The hydrolysis reaction of fats is reversible. However, with the participation of alkalis, it reaches almost the end - alkalis convert the resulting acids into salts and thereby eliminate the possibility of interaction of acids with glycerin (reverse reaction).

Fats are a necessary component of food. They are widely used in industry (production of glycerin, fatty acids, soap).

Soaps and detergents

Soap- these are salts of higher carboxylic acids. Conventional soaps consist primarily of a mixture of palmitic, stearic and oleic acids. Sodium salts form solid soaps, potassium salts - liquid soaps.

Soaps are obtained by hydrolysis of fats in the presence of alkalis:

triglyceride stearic glycerin sodium stearate

Acids (tristearine)(soap)

Hence the reaction, the reverse of esterification, is called the reaction saponification,

Saponification of fats can also occur in the presence of sulfuric acid ( acid saponification). This produces glycerol and higher carboxylic acids. The latter are converted into soaps by the action of alkali or soda.

The starting materials for soap production are vegetable oils (sunflower, cottonseed, etc.), animal fats, as well as sodium hydroxide or soda ash. Vegetable oils are pre-treated hydrogenation, i.e. they are converted into solid fats. Fat substitutes are also used - synthetic carboxylic fatty acids with a large molecular weight.

Soap production requires large quantities of raw materials, so the task is to obtain soap from non-food products. The carboxylic acids necessary for soap production are obtained by oxidation of paraffin. By neutralizing acids containing from 10 to 16 carbon atoms per molecule, toilet soap is obtained, and from acids containing from 17 to 21 carbon atoms, laundry soap and soap for technical purposes are obtained. Both synthetic soap and soap made from fats do not wash well in hard water. Therefore, along with soap from synthetic acids, detergents are produced from other types of raw materials, for example, from alkyl sulfates - salts of esters of higher alcohols and sulfuric acid.

These salts contain from 12 to 14 carbon atoms per molecule and have very good cleaning properties. Calcium and magnesium salts are soluble in water, and therefore such soaps can be washed in hard water. Alkyl sulfates are found in many laundry detergents.

Synthetic detergents release hundreds of thousands of tons of food raw materials - vegetable oils and fats.

Complex lipids.

These are lipids that, upon hydrolysis, release alcohol and phosphoric acid, amino alcohols, carbohydrates..

Phospholipids - the basis of phospholipids is phosphatidic acid.

Phospholipids form the lipid matrix of biological membranes.

Heterofunctional compounds.

Heterofunctional compounds include hydroxy and oxo acids.

Hydroxy acids

Hydroxy acids are characterized by the presence in the molecule, in addition to the carboxyl group, of an O–H hydroxyl group; their general formula is R(OH) n (COOH). The first representative of organic hydroxy acids will be hydroxyethanoic acid (hydroxyacetic, oxymethanecarboxylic, glycolic acid).

The most important of the hydroxy acids involved in vital processes are: