Carboxylic acids contain one or more. Chemical properties of carboxylic acids and methods of preparation

Date: 11.10.2019

Obtaining carboxylic acids

I... In industry

1. Allocated from natural products

(fats, waxes, essential and vegetable oils)

2. Oxidation of alkanes:

2CH 4 + + 3O 2 t, kat→ 2HCOOH + 2H 2 O

methane formic acid

2CH 3 -CH 2 -CH 2 -CH 3 + 5O 2 t, kat, p→ 4CH 3 COOH + 2H 2 O

n-butane acetic acid

3. Oxidation of alkenes:

CH 2 = CH 2 + O 2 t, kat→ CH 3 COOH

ethylene

WITH H 3 -CH = CH 2 + 4 [O] t, kat→ CH 3 COOH + HCOOH (acetic acid + formic acid )

4. Oxidation of benzene homologues (obtaining benzoic acid):

C 6 H 5 -C n H 2n + 1 + 3n [O] KMnO4, H +→ C 6 H 5 -COOH + (n-1) CO 2 + nH 2 O

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

toluene benzoic acid

5.Production of formic acid:

Stage 1: CO + NaOH t , p→ HCOONa (sodium formate - salt )

2 stage: HCOONa + H 2 SO 4 → HCOOH + NaHSO 4

6. Obtaining acetic acid:

CH 3 OH + CO t, p→ CH 3 COOH

Methanol

II... In the laboratory

1. Hydrolysis of esters:

2. From salts of carboxylic acids :

R-COONa + HCl → R-COOH + NaCl

3. By dissolving carboxylic acid anhydrides in water:

(R-CO) 2 O + H 2 O → 2 R-COOH

4. Alkaline hydrolysis of halogen derivatives of carboxylic acids:

III... General methods for the production of carboxylic acids

1. Oxidation of aldehydes:

R-COH + [O] → R-COOH

For example, the Silver Mirror reaction or oxidation with copper (II) hydroxide are qualitative reactions of aldehydes

2. Oxidation of alcohols:

R-CH 2 -OH + 2 [O] t, kat→ R-COOH + H 2 O

3. Hydrolysis of halogenated hydrocarbons containing three halogen atoms at one carbon atom.

4. From cyanides (nitriles) - the method allows you to build up a carbon chain:

WITH H 3 -Br + Na-C≡N → CH 3 -CN + NaBr

CH 3 -CN - methyl cyanide (acetic acid nitrile)

WITH H 3 -CN + 2H 2 O t→ CH 3 COONH 4

acetate ammonium

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

5. Usage reagent Grignard

R-MgBr + CO 2 → R-COO-MgBr H2O→ R-COOH + Mg (OH) Br

APPLICATION OF CARBONIC ACIDS

Formic acid- in medicine - formic alcohol (1.25% alcohol solution formic acid), in beekeeping, in organic synthesis, in the production of solvents and preservatives; as a strong reducing agent.

Acetic acid- in the food and chemical industries (production of cellulose acetate, from which acetate fiber, organic glass, film is obtained; for the synthesis of dyes, medicines and esters). In the household as a flavoring and preservative.

Butyric acid- to obtain flavoring additives, plasticizers and flotation reagents.

Oxalic acid- in the metallurgical industry (descaling).

Stearic C 17 H 35 COOH and palmitic acid C 15 H 31 COOH - as surfactants, lubricants in metalworking.

Oleic acid C 17 H 33 COOH - flotation reagent and collector for beneficiation of non-ferrous metal ores.

Individual representatives

monobasic saturated carboxylic acids

Formic acid was first isolated in the 17th century from red forest ants. Also found in stinging nettle juice. Anhydrous formic acid is a colorless liquid with a pungent odor and a pungent taste that causes burns on the skin. It is used in the textile industry as a mordant for dyeing fabrics, for tanning leather, as well as for various syntheses.
Acetic acid widespread in nature - found in animal secretions (urine, bile, feces), in plants (in green leaves). Formed during fermentation, decay, souring wine, beer, is found in sour milk and cheese. The melting point of anhydrous acetic acid is + 16.5 ° C, its crystals are transparent as ice, therefore it is called glacial acetic acid. First received in late XVIII century by the Russian scientist T. E. Lovits. Natural vinegar contains about 5% acetic acid. A vinegar essence is prepared from it, which is used in the food industry for canning vegetables, mushrooms, and fish. Acetic acid is widely used in the chemical industry for various syntheses.

Representatives of aromatic and unsaturated carboxylic acids

Benzoic acid C 6 H 5 COOH is the most important representative of aromatic acids. Distributed in nature in the plant world: in balms, incense, essential oils... In animal organisms, it is contained in the breakdown products of protein substances. it crystalline substance, melting point 122 ° C, sublimes easily. V cold water dissolves poorly. It dissolves well in alcohol and ether.

Unsaturated unsaturated acids with one double bond in the molecule have the general formula C n H 2 n -1 COOH.

High molecular weight unsaturated acids often referred to by nutritionists (they call them unsaturated). The most common one is oleic CH 3 - (CH 2) 7 –CH = CH– (CH 2) 7 –COOH or C 17 H 33 COOH. It is a colorless liquid that solidifies in the cold.
Polyunsaturated acids with multiple double bonds are especially important: linoleic CH 3 - (CH 2) 4 - (CH = CH – CH 2) 2 - (CH 2) 6 –COOH or C 17 H 31 COOH with two double bonds, linolenic CH 3 –CH 2 - (CH = CH – CH 2) 3 - (CH 2) 6 –COOH or C 17 H 29 COOH with three double bonds and arachidonic CH 3 - (CH 2) 4 - (CH = CH – CH 2) 4 - (CH 2) 2 –COOH with four double bonds; they are often referred to as essential fatty acids. 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, support the structure of cell membranes, are necessary for the functioning of the visual apparatus and nervous system affect immunity. The absence of these acids in food inhibits the growth of animals, inhibits their reproductive function, causes various diseases... The human body cannot synthesize linoleic and linolenic acids on its own and must receive them ready-made with food (like vitamins). For the synthesis of arachidonic acid in the body, linoleic acid is needed. Polyunsaturated fatty acids with 18 carbon atoms in the form of glycerin esters are found in the so-called drying oils - flaxseed, hemp, poppy, etc. Linoleic acid C 17 H 31 COOH and linolenic acid C 17 H 29 COOH are part of vegetable oils. For example, linseed oil contains about 25% linoleic acid and up to 58% linolenic.

Sorbic (2,4-hexadienoic) acid CH 3 –CH = CH – CH = CHCOOH was obtained from rowan berries (in Latin - sorbus). This acid is an excellent preservative, so rowan berries do not grow moldy.

The simplest unsaturated acid, acrylic CH 2 = SNSOON, has a pungent odor (in Latin acris - pungent, pungent). Acrylates (esters of acrylic acid) are used to obtain organic glass, and its nitrile (acrylonitrile) - for the manufacture of synthetic fibers.

Calling newly isolated acids, chemists often give free rein to their imaginations. So, the name of the closest homologue of acrylic acid, crotonic

CH 3 -CH = CH-COOH, does not come from a mole, but from a plant Croton tiglium from the oil of which it was isolated. The synthetic isomer of crotonic acid is very important - methacrylic acid CH 2 = C (CH 3) -COOH, from the ether of which (methyl methacrylate), as well as from methyl acrylate, make transparent plastic - plexiglass.

Unlimited carbon acids are capable of addition reactions:

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

CH 2 = CH-COOH + Cl 2 → CH 2 Cl -CHCl -COOH

VIDEO:

CH 2 = CH-COOH + HCl → CH 2 Cl -CH 2 -COOH

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

The last two reactions run against Markovnikov's rule.

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

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KGOU SPO "Kamensk Pedagogical College"

Carboxylic acids

(Abstract in chemistry)

Completed:

student of group 212 Chebakov D.S.

Checked:

Chemistry teacher S.A. Merzlova

Stone-on-Obi

1.Determination of carboxylic acids

2 isomerism and nomenclature

3 being in nature

4.Receiving

5.Physical properties

6.Chemical properties

7.Application

Bibliography

Definition of carbon acids

CARBONIC ACIDS- organic compounds containing one or more carboxyl groups —COOH. The name comes from lat. carbo - coal and Greek. oxys - sour By the number of these groups, mono-, di, tri- and tetracarboxylic acids are distinguished (a larger number of -COOH groups in one molecule is rare). Carboxylic acids can be aliphatic - with a normal and branched chain, cyclic and aromatic, saturated and unsaturated, contain halogen atoms and various functional groups: OH (hydroxy acids), NH2 (amino acids), CO (keto acids), etc. Many carboxylic acids in a free state, as well as in the form of various derivatives (salts, esters), are widespread in nature and play an important role in the life of plants and animals.

Isomerism and nomenclature

The isomerism of saturated monobasic carboxylic acids is similar to the isomerism of aldehydes. Most often, the historically established names of acids (formic, acetic, etc.) are used. According to the international nomenclature, they are formed from the names of the corresponding hydrocarbons with the addition of the ending - new and the words "Acid", for example: methanoic acid, ethanoic acid.

Isomerism is characteristic of carboxylic acids:

1.Carbon skeleton

CH3 - CH2 - CH2 - CH2 -COOH

CH2 - CH2 -COOH

carboxylic acid organic chemical

2.Radical

CH3 - CH2 - CH2 - CH2 -COOH 3 methylethane

CH3 - CH2 - CH2 - CH2 -COOH 4 methylpentane

3.Multiple connections

CH2 = CH - CH2 -COOH butenoic acid 3

CH2 - CH = CH2 -COOH butenoic acid 2

Being in nature

Natural sources contain many unsaturated acids in the form of esters. Higher unsaturated acids, as a rule, contain an even number of carbon atoms and are named after natural sources. Naming the newly isolated acids, chemists often give free rein to their imaginations. So, the name of the closest homologue of acrylic acid, crotonic CH3-CH = CH-COOH, does not come from a mole at all, but from the Croton tiglium plant, from whose oil it was isolated. The synthetic isomer of crotonic acid is very important - methacrylic acid CH2 = C (CH3) -COOH, from the ether of which (methyl methacrylate), as well as from methyl acrylate, they make transparent plastic - plexiglass. When two isomeric acids with the structure CH3-CH = C (CH3) -COOH were discovered, they were called angelic and tiglinic. Angelic acid was isolated from angelic oil obtained from the angelic (angelica) root of the Angelica officinalis plant. And tiglinic - from the same Croton tiglium oil as crotonic acid, only named after the second part of this botanical term. Another way to come up with a new name is to rearrange the letters in an already known name.

Arachidic acid found in peanut oil. In terms of production scale, it occupies one of the first places among all edible oils, but there is little actually arachidic acid in it - only a few percent. Behenic acid is found in behenic oil, which is squeezed from the large, nut-like seeds of a plant of the Moringa family common in Indonesia. Almost pure lignoceric acid (in its name it is easy to see the Latin lignum - wood, wood and cera - wax) is extracted from the resin of a beech tree. Previously, this acid was also called carnauba, because there is quite a lot of it in carnauba wax, which covers the leaves of the Brazilian wax palm.

Fatty acids in oils and fats are extracted by humans in huge quantities, measured annually in millions of tons. So chemists have never had a shortage of natural fatty acids to study them.

Formic acid became known in the 17th century, when it was discovered in the caustic secretions of red ants. Most of the other acids, which have their "own" historically formed names, were obtained mainly in the 19th century. and named for the natural source in which they are found in significant quantities or were first discovered. For example, butyric acid is found in oils, including regular oils. butter- only not in a free state, but in the form of an ester with glycerin. Free butyric acid, like all carboxylic acids, with a small number of carbon atoms, has a pungent odor, when the oil deteriorates (rancid), butyric and other acids are released in a free state and give it bad smell and taste.

Russian roots are used in the names of the three acids considered. For derivatives of these acids (salts, esters, etc.), it is customary to use Latin roots: formate - for formic acid (Latin formica - ant), acetate - for acetic acid (Latin acetum - vinegar), butyrate - for butyric acid (Greek. butyron - oil); these names, including for the acids themselves, are also adopted in Western European languages.

Other carboxylic acids occur naturally in esters with glycerin and other polyhydric alcohols - in the form of fats, oils, waxes, and rarely - in a free state.

Valeric acid found in valerian root. The names of the next three even acids (caproic, caprylic and capric) have a common root (Capra in Latin - goat), these acids are indeed contained in fat goat milk(as, however, and cow), and in a free state "smell like a goat." The content of these acids in milk fats is not very high - from 7 to 14% of the total of all fatty acids.

Pelargonic acid is found in the volatile oil of Pelargonium rosea and other plants of the geranium family. Lauric acid (in the old books it was called laurel) is contained in large quantities in laurel oil (up to 45%). Myristic acid is predominant in the oil of plants of the myristic family, for example, in the aromatic nutmeg seeds - nutmeg.

Palmitic acid easy to isolate from palm oil squeezed from kernels coconut(copra). This oil is almost entirely composed of palmitic acid glyceride. The name stearic acid comes from the Greek. stear - fat, lard. Together with palmitic acid, it belongs to the most important fatty acids and constitutes the main part of most vegetable and animal fats. Candles were made from a mixture of these acids (stearin).

Receiving

In the laboratory, carboxylic acids, like inorganic ones, can be obtained from their salts by acting on them with sulfuric acid when heated:

In industry, carboxylic acids are produced in various ways.

The general method for producing carboxylic acids is the oxidation of hydrocarbons with atmospheric oxygen. The reaction is carried out as in the gas phase at high blood pressure and temperature without catalysts, and in solutions. In this case, cracking of carbon chains occurs, so that the acids obtained in this way always contain fewer carbon atoms than the starting hydrocarbons. For example, acetic acid is produced by the oxidation of N-butane in an acetic acid solution:

Mn, Co, 6-8 MPa

2CH3 - CH2 - CH2 - CH3 + 5O2 4СH3COOH + 2H2O

Physical properties

Lower carboxylic acids are liquids with a pungent odor, readily soluble in water. With an increase in the relative molecular weight, the solubility of acids in water decreases, and the boiling point increases. Higher acids, starting with pelargonic (n-nonane) CH3- (CH2) 7-COOH, are solid, odorless, insoluble in water. Lower carboxylic acids in anhydrous form and in concentrated solutions irritate the skin and cause burns, especially formic acid and acetic acid.

Chemical properties

The general properties of carboxylic acids are similar to those of inorganic acids.

Carboxylic acids also have some specific properties due to the presence of radicals in their molecules. So, for example, acetic acid reacts with chlorine:

monochloroacetic acid

The chemical properties of formic acid are somewhat different from other carboxylic acids.

1. Of the monobasic carboxylic acids, formic acid is the strongest acid.

2. Due to the peculiarities of the structure of the molecules, formic acid is similar to aldehydes easily oxidized (reaction of the "silver mirror"):

carbonic acid.

3. When heated with concentrated sulfuric acid, formic acid splits off water and carbon monoxide (II) is formed:

This reaction is sometimes used to produce carbon monoxide (II) in the laboratory.

As already noted, the strongest of the monobasic carboxylic acids is formic acid.

Acetic acid much weaker. Consequently, the methyl CH3 - radical (and other radicals) affects the carboxyl group. As a result, the bond between the hydrogen and oxygen atoms in the carboxyl group becomes less polar and the elimination of the hydrogen ion becomes more difficult. In radicals of carboxylic acids, hydrogen atoms can be replaced by halogens. In this case, the substitution occurs more easily in the hydrocarbon unit, which is closer to the carboxyl group. Consequently, the carboxyl group acts on the hydrocarbon radical, that is, their influence is mutual.

Application

Formic acid is used industrially as a strong reducing agent. Its 1.25% solution in alcohol (formic alcohol) is used in medicine. Highest value has acetic acid, it is necessary for the synthesis of dyes (for example indigo), medicines (for example, aspirin), esters, acetic anhydride, monochloroacetic acid, etc. Large quantities of it are consumed for the production of acetate fiber, non-combustible film, organic glass that transmits UV rays.

Its salts - acetates are widely used. Lead (II) acetate is used for the manufacture of lead white and lead lotion in medicine, iron (III) and aluminum acetates - as mordants for crumbling tissues, copper (II) acetate - for plant pest control. 3-9% aqueous solution of acetic acid - vinegar - flavoring and preserving agent. Certain compounds that use acetic acid, such as sodium salt 2,4-dichlorophenoxyacetic acid, are herbicides for weed control. Sodium and potassium salts of higher carboxylic acids are the main constituents of soap.

Formic acid esters are used as solvents and fragrances

Bibliography

G.E. Rudzitis, F.G. Feldman Chemistry: Organic Chemistry: Textbook for 10 cl. educational institutions. - 5th ed. - M .: Education, 1998 .-- 160 p.

O.S.Gabrielyan Chemistry. Grade 10: Textbook for educational institutions / O.S. Gabrielyan.-11th ed., Revised-M. : Bustard, 2006.- 267, p.

L.S. Guzei Chemistry. Grade 11: Textbook for educational institutions / R.P. Surovtseva, G.G. Lysov - 7th ed., Stereotype. M.: Bustard, 2006 .-- 223, p.

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Chemical properties of carboxylic acids

1. Reactions with the participation of hydrogen of the carboxyl group.

1.1. Some acids significantly dissociate with the elimination of the H + cation.

N – UNSD ⇄ НСОО  + Н +

As noted earlier, carboxylic acids are characterized by relatively high dissociation constants. For formic acid we have:

NSOO  formate ion; CH 3 COO  acetate ion.

1.2. Interaction with metals

2RCOOH + Mg  (RCOO) 2  Mg + H 2

1.3. Interaction with alkalis.

RCOOH + NaOH  RCOONa + H 2 O

1.4. Interaction with basic oxides.

2CH 3 COOH + MgO (CH 3 COO) 2 Mg + H 2 O

1.5. Interaction with salts of weaker (similar in strength) acids.

2СН 3 СООН + Na 2 CO 3  2СН 3 СООNa + H 2 CO 3

2. Reactions involving a carboxyl group.

2.1. Reactions with phosphorus halides.

2.2. Reactions with ammonia. When acid and ammonia are mixed, an ammonium salt is first formed, which is then subjected to dry distillation:

A special case.

2.3. Reactions with alcohols

2.4. Dimerization with the formation of acid anhydrides.

H special case:

3. Reactions involving hydrogen -carbon atom.

3.1. Halogenation.

Chlorination as a special case of halogenation.

4. Oxidation reactions.

NSOOH + [O]  HO  COOH  H 2 O + CO 2 

Properties of individual representatives of the homologous series

Formic acid HCOOH is found in needles, nettles, and in the secretions of ants. It is a colorless liquid with a pungent unpleasant odor. Causes skin burns, mixes up with water, ethers, alcohols in any relationship. d = 1.21 g / cm 3.

Acetic (ethanic, methylcarboxylic) acid CH 3 COOH. At normal temperature, it is a colorless liquid with a pungent odor. Miscible with water, ethanol, diethyl and dimethyl ethers, benzene in all respects. Insoluble in CS 2. Acetic essence - 70-80% solution of CH 3 COOH. Food vinegar - 5% solution. T pl = 17C, T bale = 118.1C, d = 1.05 g / cm 3. It is used in dyeing, in the leather industry, in the food industry, for the production of esters (acetates).

Acetic anhydride. T pl = 73.1С, T bale = 139.5С. Has a pungent odor, soluble in benzene, dimethyl ether, chloroform. Dipole moment 2.82D, H 2 O 1.84D. It is used on a large scale for the production of cellulose acetate, pharmaceuticals.

Tasks by topic

Objective 1. Calculate the mass fraction of salt in a solution of a monobasic saturated carboxylic acid with its initial mass of 200 g and a mass fraction of hydrogen in the acid of 8.1%, if the salt is obtained by absorbing a solution of 5.6 liters of ammonia (normal conditions).

Let's write down the reaction equation.

С k H 2k + 1 COOH + NH 3 = С k H 2k + 1 COONH 4. (1)

Let's establish the molecular formula of the acid.

;
;

200k + 200 = 113.4k + 372.6;
.

The refined reaction equation has the form:

C 2 H 5 COOH + NH 3 = C 2 H 5 COONH 4,

from which follows:

n (NH 3) = n (C 2 H 5 COONH 4);

m (C 2 H 5 COONH 4) = n (C 2 H 5 COONH 4)  M (C 2 H 5 COONH 4) =

N (NH 3)  M (C 2 H 5 COONH 4) =

m (NH 3) = n (NH 3)  M (NH 3) =

m 2 (solution) = m 1 (solution) + m (NH 3);

m 2 (solution) = 200 + 4.25 = 204.25 g.

Objective 2. When a mixture of monobasic carboxylic acids with a total weight of 50 g interacted with an excess of silver oxide, 16.8 liters of gas were released (normal conditions). Then, an excess of ammonia was passed through the resulting solution. Find the mass of the formed salt if the reduced mass fraction of oxygen in an equimolar mixture of acids is 60.4%.

Let us write the equation for the reaction of the interaction of the initial substances with silver oxide, taking into account that of the saturated monobasic carboxylic acids, only formic acid reacts with it.

HCOOH + Ag 2 O = CO 2 + H 2 O + 2Ag (1)

For others

With k H 2 k +1 COOH + Ag 2 Oreaction does not proceed. (2)

Using the reaction equation (1), we find the mass of formic acid:

n (HCOOH) = n (CO 2); m (HCOOH) = n (HCOOH) M (HCOOH) =

N (CO 2) M (НСООН) =
G.

Let's find the molecular formula of the unknown carboxylic acid.

;
;

6400 = 845.6k + 5556.8;
.

The molecular formula of the acid is CH 3 COOH.

As a result of the interaction of HCOOH with silver oxide, only acetic acid remains in the solution, which, when interacting with an excess of ammonia, forms a salt according to the reaction equation:

CH 3 COOH + NH 3 = CH 3 COONH 4. (3)

m (CH 3 COOH) = m (mixture) –m (HCOOH) = 50 - 34.5 = 15.5 g.

From the reaction equation (3) we have:

n (CH 3 COOH) = n (CH 3 COONH 4);

m (CH 3 COONH 4) = n (CH 3 COONH 4)  M (CH 3 COONH 4) =

Methods of obtaining... 1 . Oxidation of aldehydes and primary alcohols is a common method for producing carboxylic acids. The oxidizing agents used are /> K M n O 4 and K 2 C r 2 O 7.

2 Another general method is the hydrolysis of halogenated hydrocarbons containing three halogen atoms on one carbon atom. In this case, alcohols are formed containing OH groups at one carbon atom - such alcohols are unstable and split off water with the formation of a carboxylic acid: />

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

3. The production of carboxylic acids from cyanides (nitriles) is an important method for building up a carbon chain in the production of the starting cyanide. An additional carbon atom is introduced into the molecule using the reaction of replacing the halogen in the halogenated hydrocarbon molecule with sodium cyanide, for example: />

CH 3 -B r + NaCN→ CH 3 - CN + NaBr.

The resulting nitrile of acetic acid (methyl cyanide), when heated, is easily hydrolyzed to form ammonium acetate:

CH 3 CN + 2H 2 O → CH 3 COONH 4.

Acidification of the solution produces acid:

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

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

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

5 . Hydrolysis of esters: />

R - COOR 1 + KOH → R - COOK + R 'OH,

R - COOK + HCl → R— COOH + KCl .

6. Hydrolysis of acid anhydrides: />

(RCO) 2 O + H 2 O → 2 RCOOH.

7. For individual acids, there are specific methods of obtaining ./>

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

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

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

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

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

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

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

RCOOH RCOO - + H +

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

The substituents present in the carboxylic acid molecule strongly affect its acidity due to the inductive effect... Substituents such as chlorine or phenyl radical pull off the electron density and, therefore, have a negative inductive effect (- /). Pulling the electron density away 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, + I. They lower the acidity. Effect of substituents on the acidity of carboxylic acidsclearly manifests itself in the values of the dissociation constants K a for a number of acids. In addition, the strength of acidis influenced by the presence of a conjugate multiple connection.

Carboxylic Acids Formula K a

Propionic CH 3 CH 2 COOH 1,3 * 10 -5

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

Acetic CH 3 COOH 1.7 * 10 -5

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

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

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

Formic HCOOH 6.1 * 10 -4

Benzoic C 6 H 5 COOH 1.4 * 10 -4

Chloroacetic CH 2 ClCOOH 2.2 * 10 -3

Tetron CH 3 - C ≡ C - COOH 1,3 * 10 -3

Dichloroacetic CHCl 2 COOH 5.6 * 10 -2

Oxalic HOOC - COOH 5.9 * 10 -2

TrichloroaceticCCl 3 COOH 2.2 * 10 -1

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

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

2 RCOOH + М g → (RCOO) 2 Mg + Н 2,

2 RCOOH + CaO → (RCOO) 2 Ca + H 2 O,

RCOOH + NaOH → RCOONa+ H 2 O,

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

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

CH 3 COONa + HCl→ CH 3 COOH + NaCl.

Salts of carboxylic acids in aqueous solutions are hydrolyzed:

CH 3 SOOK + H 2 O CH 3 COOH + KOH.

The difference between carboxylic acids and mineral acids lies in the possibility of the formation of a number of functional derivatives.

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

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

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

Connection examples

Acid

Ethanic (acetic) Benzoic acid

acid chloride

Etanoyl Chloride Benzoyl Chloride

(acetyl chloride)

acid anhydride

Ethanic (acetic) benzoic anhydrite

Anhydrite

ester

Ethyl ethanoate (ethyl acetate) Methyl benzoate

amide

Ethanamide (acetamide) Benzamide

Nitrile

Ethanolnitrile Benzonitrile

(acetonitrile)

Anhydrides are formed from carboxylic acids by the action of dehydrating agents:

2 R - CO - OH + Р 2 О 5 → (R - CO -) 2 O + 2НРО 3.

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

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

Esters can also be obtained by the interaction of acid chlorides and alkali metal alcoholates:

R-CO-Cl + Na-O-R '→ R-CO-OR' + NaCl.

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

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

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

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

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

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

R-CO-X + H 2 O → R-CO-OH + HX.

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

R-CO-OR ‘+ NaOH → R-CO-ONa + R'OH.

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

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

Unsaturated carboxylic acids are capable of addition reactions:

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

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

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

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

The last two reactions run against Markovnikov's rule.

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

5 . Redox reactions of carboxylic acids ./>

Carboxylic acids under the action of reducing agents in the presence of catalysts are capable of converting to aldehydes, alcohols and even hydrocarbons:

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

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

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

or in a simplified way:

C H 3 HCOOH + Ag 2 O → 2Аg + СО 2 + Н 2 О.

In addition, formic acid is oxidized by chlorine:

НСООН + Сl 2 → CO 2 + 2 HCl.

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

CH 3 COOH + 2O 2 → 2CO 2 + 2H 2 O.

6. Reactions decarboxing... Saturated unsubstituted monocarboxylic acids due to their high strength communication C-C decarboxylated with difficulty when heated. This requires the fusion of an alkali metal salt of a carboxylic acid with an alkali: />

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

Dibasic carboxylic acids easily remove CO 2 when heated:

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

Carboxylic acid class: 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 -UNON. Thus, general formula, which all saturated monobasic carboxylic acids have, looks like this: R-COOH, where R is a radical particle that can include any number of carbon atoms.

Accordingly, the definition of this class of compounds can be given as follows. Carboxylic acids are organic oxygen-containing molecules that contain one or more functional groups —COOH — carboxyl groups.

The fact that these substances refer specifically to acids is explained by the mobility of the hydrogen atom in the carboxyl. The electron density is unevenly distributed, since oxygen is the most electronegative in the group. From this communication O-N strongly polarizes, and the hydrogen atom becomes extremely vulnerable. It is easily cleaved off by entering into chemical interactions. Therefore, acids in the corresponding indicators give a similar reaction:

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

Classification

Several main features can be distinguished according to which carboxylic acids are divided into groups. The first is the nature of the radical. For this factor, there are:

Alicyclic acids. Example: cinchona.
Aromatic. Example: benzoic.
Aliphatic. Example: acetic, acrylic, oxalic and others.
Heterocyclic. Example: nicotine.

If we talk about bonds in a molecule, then two groups of acids can also be distinguished:

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

Monobasic - only one -COOH-group. Example: formic, stearic, butane, valerian and others.
Bibasic- respectively, two groups -COOH. Example: oxalic, malonic and others.
Multi-base- lemon, milk and others.

Discovery history

Winemaking has flourished since antiquity. And, as you know, one of its products is acetic acid. Therefore, the history of the popularity of this class of compounds goes back to the times of Robert Boyle and Johann Glauber. However, at the same time chemical nature find out these molecules long time failed.

After all, for a long time the views of vitalists dominated, who denied the possibility of the formation of organics without living beings. But already in 1670 D. Ray managed to get 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 distilling charcoal). As a result, acetic acid was obtained. Thus, carboxylic acids (physical properties, structure) were studied and the foundation was laid for the discovery of all other representatives of a number of aliphatic compounds.

Physical properties

All their representatives have been studied in detail today. For each of them, you can find a characteristic in all parameters, including use in industry and being in nature. We will consider what carboxylic acids are, their and other parameters.

So, there are several main characteristic parameters.

If the number of carbon atoms in the chain does not exceed five, then these are pungent, mobile and volatile liquids. Above five - heavy oily substances, even more - solid, paraffin-like.
The density of the first two representatives exceeds one. All others are lighter than water.
Boiling point: the larger the chain, the higher the value. The more ramified the structure, the lower.
Melting point: Depends on the parity of the number of carbon atoms in the chain. For even ones it is higher, for odd ones 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 hence the structure crystal lattice, its strength. The simpler and more structured the molecules are, the higher the rates that carboxylic acids give. The physical properties of these compounds make it possible to define their areas and ways of using them in industry.

Chemical properties

As we have already indicated above, these acids can exhibit different properties. The reactions with their participation 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 +.
Shows, that is, interacts with basic oxides, as well as their hydroxides. It interacts with simple metals by standard scheme(that is, only with those that stand up to hydrogen in the series of voltages).
With stronger acids (inorganic) it behaves like a base.
It is capable of being reduced to primary alcohol.
A special reaction is esterification. This is the interaction with alcohols with the formation of a complex product - an ether.
The reaction of decarboxylation, that is, the elimination of a carbon dioxide molecule from the compound.
Able to interact with halides of elements such as phosphorus and sulfur.

It's 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 an acid, 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, the synthesis is carried out by the 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

Carboxylic acid salts - important connections used in industry. They are obtained as a result of the interaction of the latter with:

metals;
basic oxides;
alkalis;
amphoteric hydroxides.

Especially essential among them are those that are formed between the alkali metals sodium and potassium and the higher limit acids - palmitic, stearic. After all, the products of such an 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 a common laundry soap used for washing clothes.

If you replace the acid with palmitic acid, and the metal with potassium, you get potassium palmitate - a liquid soap for washing hands. Therefore, it is safe to say that carboxylic acid salts are in fact important organic compounds. Their industrial production and use is simply colossal in its scale. If you imagine how much soap every person on Earth spends, then it is easy to imagine these scales.

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. General form can be represented by the equation:

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

The product with two radicals is the ester. Obviously, as a result of the reaction, the carboxylic acid, alcohol, ester and water have undergone significant changes. So, hydrogen leaves the acid molecule in the form of a cation and meets with the hydroxo group, 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;
a constituent component of a perfume;
solvents;
components of varnishes, paints, plastics;
medicines and so on.

It is clear that the areas of their use are wide enough to justify the volume of production in industry.

Ethanic acid (acetic)

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

She is a food additive under the code E-260.
Used in the food industry for preservation.
It is used in medicine for the synthesis of drugs.
Component in the preparation of aromatic compounds.
Solvent.
Participant in the process of printing, dyeing fabrics.
An essential component in the reactions of chemical synthesis 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.