Homologues of carboxylic acids. Carboxylic acids
.
O
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The group of -C atoms is called a carboxyl group or carboxyl.
\
OH
Organic acids containing one carboxyl group in the molecule are monobasic. The general formula of these acids is RCOOH.
Carboxylic acids containing two carboxyl groups are called dibasic. These include, for example, oxalic and succinic acids.
There are also polybasic carboxylic acids containing more than two carboxyl groups. These include, for example, tribasic citric acid. Depending on the nature of the hydrocarbon radical, carboxylic acids are divided into saturated, unsaturated, and aromatic.
Saturated, or saturated, carboxylic acids are, for example, propanoic (propionic) acid or the already familiar succinic acid.
Obviously, saturated carboxylic acids do not contain P-bonds in a hydrocarbon radical.
In molecules of unsaturated carboxylic acids, the carboxyl group is associated with an unsaturated, unsaturated hydrocarbon radical, for example in molecules of acrylic (propenoic) CH2=CH-COOH or oleic CH3-(CH2)7-CH=CH-(CH2)7-COOH and other acids.
As can be seen from the formula of benzoic acid, it is aromatic, since it contains an aromatic (benzene) ring in the molecule.
Nomenclature and isomerism
We have already considered the general principles of the formation of the names of carboxylic acids, as well as other organic compounds. Let us dwell in more detail on the nomenclature of mono- and dibasic carboxylic acids. The name of a carboxylic acid is formed from the name of the corresponding alkane (alkane with the same number of carbon atoms in the molecule) with the addition of the suffix -ov, the ending -aya and the word acid. The numbering of carbon atoms begins with the carboxyl group. For example:
Many acids also have historically established, or trivial, names (Table 6). 
After our first acquaintance with the diverse and interesting world of organic acids, we will consider in more detail the saturated monobasic carboxylic acids.
It is clear that the composition of these acids will be reflected by the general formula C n H 2n O2, or C n H 2n +1 COOH, or RCOOH.
Physical properties of saturated monobasic carboxylic acids
Lower acids, i.e. acids with a relatively small molecular weight containing up to four carbon atoms per molecule, are liquids with a characteristic pungent odor (remember the smell of acetic acid). Acids containing from 4 to 9 carbon atoms are viscous oily liquids with an unpleasant odor; containing more than 9 carbon atoms per molecule - solids that do not dissolve in water. The boiling points of saturated monobasic carboxylic acids increase with increasing number of carbon atoms in the molecule and, consequently, with increasing relative molecular weight. For example, the boiling point of formic acid is 101 °C, acetic acid is 118 °C, and propionic acid is 141 °C.
The simplest carboxylic acid, formic HCOOH, having a small relative molecular weight (46), under normal conditions is a liquid with a boiling point of 100.8 °C. At the same time, butane (MR(C4H10) = 58) under the same conditions is gaseous and has a boiling point of -0.5 °C. This discrepancy between boiling points and relative molecular weights is explained by the formation of carboxylic acid dimers, in which two acid molecules are linked by two hydrogen bonds. The occurrence of hydrogen bonds becomes clear when considering the structure of carboxylic acid molecules.
Molecules of saturated monobasic carboxylic acids contain a polar group of atoms - carboxyl (think about what causes the polarity of this functional group) and a practically non-polar hydrocarbon radical. The carboxyl group is attracted to water molecules, forming hydrogen bonds with them.
Formic and acetic acids are unlimitedly soluble in water. It is obvious that with an increase in the number of atoms in a hydrocarbon radical, the solubility of carboxylic acids decreases.
Knowing the composition and structure of carboxylic acid molecules, it will not be difficult for us to understand and explain the chemical properties of these substances.
Chemical properties
The general properties characteristic of the class of acids (both organic and inorganic) are due to the presence in the molecules of a hydroxyl group containing a highly polar bond between hydrogen and oxygen atoms. These properties are well known to you. Let us consider them again using the example of water-soluble organic acids.
1. Dissociation with the formation of hydrogen cations and anions of the acid residue. More accurately, this process is described by an equation that takes into account the participation of water molecules in it.
The dissociation equilibrium of carboxylic acids is shifted to the left; the vast majority of them are weak electrolytes. Nevertheless, the sour taste of, for example, formic and acetic acids is explained by the dissociation into hydrogen cations and anions of acidic residues.
It is obvious that the presence of “acidic” hydrogen in the molecules of carboxylic acids, i.e., the hydrogen of the carboxyl group, also determines other characteristic properties.
2. Interaction with metals in the electrochemical voltage range up to hydrogen. Thus, iron reduces hydrogen from acetic acid:
2CH3-COOH + Fe -> (CHgCOO)2Fe + H2
3. Interaction with basic oxides to form salt and water:
2R-COOH + CaO -> (R-COO)2Ca + H20
4. Reaction with metal hydroxides to form salt and water (neutralization reaction):
R-COOH + NaOH -> R-COONa + H20 3R-COOH + Ca(OH)2 -> (R-COO)2Ca + 2H20
5. Interaction with salts of weaker acids, with the formation of the latter. Thus, acetic acid displaces stearic acid from sodium stearate and carbonic acid from potassium carbonate.
6. The interaction of carboxylic acids with alcohols to form esters is the esterification reaction already known to you (one of the most important reactions characteristic of carboxylic acids). The interaction of carboxylic acids with alcohols is catalyzed by hydrogen cations.
The esterification reaction is reversible. The equilibrium shifts towards the formation of the ester in the presence of dewatering agents and the removal of ester from the reaction mixture.
In the reverse reaction of esterification, called ester hydrolysis (reacting an ester with water), an acid and an alcohol are formed. It is obvious that polyhydric alcohols, for example glycerol, can also react with carboxylic acids, i.e., enter into an esterification reaction: 
All carboxylic acids (except formic acid), along with the carboxyl group, contain a hydrocarbon residue in their molecules. Of course, this cannot but affect the properties of acids, which are determined by the nature of the hydrocarbon residue.
7. Addition reactions at a multiple bond - unsaturated carboxylic acids enter into them; for example, the reaction of hydrogen addition is hydrogenation. When oleic acid is hydrogenated, saturated stearic acid is formed.
Unsaturated carboxylic acids, like other unsaturated compounds, add halogens via a double bond. For example, acrylic acid discolors bromine water.
8. Substitution reactions (with halogens) - saturated carboxylic acids can enter into it; for example, by reacting acetic acid with chlorine, various chlorinated acids can be obtained:
When halogenating carboxylic acids containing more than one carbon atom in the hydrocarbon residue, the formation of products with different positions of the halogen in the molecule is possible. When a reaction occurs via a free radical mechanism, any hydrogen atoms in the hydrocarbon residue can be replaced. If the reaction is carried out in the presence of small amounts of red phosphorus, then it proceeds selectively - hydrogen is replaced only in A-position (at the carbon atom closest to the functional group) in the acid molecule. You will learn the reasons for this selectivity when studying chemistry at a higher educational institution.
Carboxylic acids form various functional derivatives when replacing the hydroxyl group. When these derivatives are hydrolyzed, carboxylic acid is formed again.
Carboxylic acid chloride can be prepared by reacting phosphorus(III) chloride or thionyl chloride (SOCl 2) with acid. Carboxylic acid anhydrides are prepared by reacting chlorine anhydrides with carboxylic acid salts. Esters are formed by the esterification of carboxylic acids with alcohols. Esterification is catalyzed by inorganic acids.
This reaction is initiated by protonation of the carboxyl group - the interaction of a hydrogen cation (proton) with the lone electron pair of the oxygen atom. Protonation of a carboxyl group entails an increase in the positive charge on the carbon atom in it:
Methods of obtaining
Carboxylic acids can be obtained by oxidation of primary alcohols and aldehydes.
Aromatic carboxylic acids are formed by the oxidation of benzene homologues.
Hydrolysis of various carboxylic acid derivatives also produces acids. Thus, the hydrolysis of an ester produces an alcohol and a carboxylic acid. As mentioned above, acid-catalyzed esterification and hydrolysis reactions are reversible. Hydrolysis of the ester under the influence of an aqueous solution of alkali proceeds irreversibly; in this case, not an acid, but its salt is formed from the ester. During the hydrolysis of nitriles, amides are first formed, which are then converted into acids. Carboxylic acids are formed by the interaction of organic magnesium compounds with carbon monoxide (IV).
Individual representatives of carboxylic acids and their significance
Formic (methane) acid HCOOH is a liquid with a pungent odor and a boiling point of 100.8 °C, highly soluble in water. Formic acid is poisonous and causes burns if it comes into contact with the skin! The stinging fluid secreted by ants contains this acid. Formic acid has disinfectant properties and therefore finds its use in the food, leather and pharmaceutical industries, and medicine. It is also used in dyeing fabrics and paper.
Acetic (ethanoic) acid CH3COOH is a colorless liquid with a characteristic pungent odor, miscible with water in any ratio. Aqueous solutions of acetic acid are marketed under the name vinegar (3-5% solution) and vinegar essence (70-80% solution) and are widely used in the food industry. Acetic acid is a good solvent for many organic substances and is therefore used in dyeing, tanning, and the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, substances used to control weeds - herbicides - are obtained from it. 
Acetic acid is the main component of wine vinegar, the characteristic smell of which is due to it. It is a product of ethanol oxidation and is formed from it when wine is stored in air.
The most important representatives of higher saturated monobasic acids are palmitic C15H31COOH and stearic C17H35COOH acids. Unlike lower acids, these substances are solid and poorly soluble in water.
However, their salts - stearates and palmitates - are highly soluble and have a detergent effect, which is why they are also called soaps. It is clear that these substances are produced on a large scale.
Of the unsaturated higher carboxylic acids, oleic acid C17H33COOH, or (CH2)7COOH, is of greatest importance. It is an oil-like liquid without taste or smell. Its salts are widely used in technology.
The simplest representative of dibasic carboxylic acids is oxalic (ethanedioic) acid HOOC-COOH, the salts of which are found in many plants, for example, sorrel and sorrel. Oxalic acid is a colorless crystalline substance that is highly soluble in water. It is used for polishing metals, in the woodworking and leather industries.
1. Unsaturated elaidic acid C17H33COOH is a trans-isomer of oleic acid. Write the structural formula of this substance.
2. Write an equation for the hydrogenation reaction of oleic acid. Name the product of this reaction.
3. Write an equation for the combustion reaction of stearic acid. What volume of oxygen and air (n.a.) will be required to burn 568 g of stearic acid?
4. A mixture of solid fatty acids - palmitic and stearic - is called stearin (it is from this that stearin suppositories are made). What volume of air (n.a.) will be required to burn a two-hundred-gram stearic candle if stearin contains equal masses of palmitic and stearic acids? What volume of carbon dioxide (n.o.) and mass of water are formed in this case?
5. Solve the previous problem provided that the candle contains equal amounts (same number of moles) of stearic and palmitic acids.
6. To remove rust stains, treat them with a solution of acetic acid. Make up molecular and ionic equations for the reactions occurring in this case, taking into account that rust contains iron(III) oxide and hydroxide - Fe2O3 and Fe(OH)3. Why are such stains not removed with water? Why do they disappear when treated with an acid solution?
7. Baking (baking) soda NaHC03 added to the yeast-free dough is first “quenched” with acetic acid. Do this reaction at home and write its equation, knowing that carbonic acid is weaker than acetic acid. Explain the formation of foam.
8. Knowing that chlorine is more electronegative than carbon, arrange the following acids: acetic, propionic, chloroacetic, dichloroacetic and trichloroacetic acids in order of increasing acidic properties. Justify your result.
9. How can we explain that formic acid reacts in a “silver mirror” reaction? Write an equation for this reaction. What gas can be released in this case?
10. When 3 g of saturated monobasic carboxylic acid reacted with excess magnesium, 560 ml (n.s.) of hydrogen were released. Determine the formula of the acid.
11. Give reaction equations that can be used to describe the chemical properties of acetic acid. Name the products of these reactions.
12. Suggest a simple laboratory method by which you can recognize propanoic and acrylic acids.
13. Write an equation for the reaction of producing methyl formate - an ester of methanol and formic acid. Under what conditions should this reaction be carried out?
14. Make up structural formulas of substances with the composition C3H602. What classes of substances can they be classified into? Give the reaction equations characteristic of each of them.
15. Substance A - an isomer of acetic acid - is insoluble in water, but can undergo hydrolysis. What is the structural formula of substance A? Name the products of its hydrolysis.
16. Make up the structural formulas of the following substances:
a) methyl acetate;
b) oxalic acid;
c) formic acid;
d) dichloroacetic acid;
e) magnesium acetate;
f) ethyl acetate;
g) ethyl formate;
h) acrylic acid.
17*. A sample of saturated monobasic organic acid weighing 3.7 g was neutralized with an aqueous solution of sodium bicarbonate. By passing the liberated gas through lime water, 5.0 g of sediment was obtained. What acid was taken and what was the volume of gas released?
Carboxylic acids in nature
Carboxylic acids are very common in nature. They are found in fruits and plants. They are present in needles, sweat, urine and nettle juice. You know, it turns out that the bulk of acids form esters, which have odors. Thus, the smell of lactic acid, which is contained in human sweat, attracts mosquitoes; they sense it at quite a considerable distance. Therefore, no matter how much you try to drive away the annoying mosquito, it still feels its victim well. In addition to human sweat, lactic acid is found in pickles and sauerkraut.
And female monkeys, in order to attract a male, secrete acetic and propionic acid. A dog's sensitive nose can smell butyric acid, which has a concentration of 10–18 g/cm3.
Many plant species are capable of producing acetic and butyric acid. And some weeds take advantage of this and, by releasing substances, eliminate their competitors, suppressing their growth, and sometimes causing their death.
The Indians also used acid. To destroy the enemy, they soaked the arrows with a deadly poison, which turned out to be a derivative of acetic acid.
And here a natural question arises: do acids pose a danger to human health? After all, oxalic acid, which is widespread in nature and is found in sorrel, oranges, currants and raspberries, for some reason has not found application in the food industry. It turns out that oxalic acid is two hundred times stronger than acetic acid, and can even corrode dishes, and its salts, accumulating in the human body, form stones.
Acids have found wide application in all spheres of human life. They are used in medicine, cosmetology, food industry, agriculture and for household needs.
For medical purposes, organic acids such as lactic, tartaric, and ascorbic are used. Probably each of you used vitamin C to strengthen the body - this is precisely ascorbic acid. It not only helps strengthen the immune system, but also has the ability to remove carcinogens and toxins from the body. Lactic acid is used for cauterization, as it is highly hygroscopic. But tartaric acid acts as a mild laxative, as an antidote for alkali poisoning, and as a component necessary for preparing plasma for blood transfusions.
But fans of cosmetic procedures should know that fruit acids contained in citrus fruits have a beneficial effect on the skin, as, penetrating deep, they can accelerate the process of skin renewal. In addition, the smell of citrus fruits has a tonic effect on the nervous system.
Have you noticed that berries such as cranberries and lingonberries are stored for a long time and remain fresh. Do you know why? It turns out that they contain benzoic acid, which is an excellent preservative.
But in agriculture, succinic acid has found wide use, since it can be used to increase the productivity of cultivated plants. It can also stimulate plant growth and accelerate their development.
DEFINITION
Carboxylic acids– organic compounds whose molecules contain one or more functional carboxyl groups – COOH, associated with a hydrocarbon radical.
The carboxyl group consists of a carbonyl group > C= O and the associated hydroxyl group –OH.
The general formula of carboxylic acids is R–COOH.
The acidic properties of carboxylic acids are due to a shift in electron density to the carbonyl oxygen, which causes the appearance of a partial positive charge on the atom.
As a result, the polarity of the O–H bond increases, and the dissociation process becomes possible:
The resulting anion is stabilized due to charge delocalization:
Lower carboxylic acids containing up to 3 carbon atoms are colorless liquids with a characteristic pungent odor, miscible with water in any ratio. Most acids containing 4–9 atoms are oily liquids with an unpleasant odor. Acids containing more than 10 hydrogen atoms are solids that are insoluble in water.
The solubility of carboxylic acids in water and high boiling points are associated with the formation of intermolecular hydrogen bonds. In the solid state, carboxylic acids exist mainly in the form of cyclic dimers, and in the liquid state linear association also occurs:
Types of carboxylic acids
Depending on the structure of the hydrocarbon radical, carboxylic acids are divided into:
- aromatic (benzoic acid)
- aliphatic (saturated (caproic acid) and unsaturated (acrylic acid))
- alicyclic (quinic acid)
- heterocyclic (nicotinic acid).
Based on the number of carboxyl groups, carboxylic acids are divided into:
- monobase()
- dibasic (oxalic acid)
- polybasic (citric acid).
When other functional groups (–OH, =CO, –NH2, etc.) are introduced into the acid molecule, other classes of compounds are formed: hydroxy, keto acids, etc.
General formula of saturated monobasic carboxylic acids:
WITH n H2nO2 (n= 1,2,3...) or Cn H 2n+1 COOH (n = 0,1,2…)
General formula of unsaturated monobasic carboxylic acids:
WITH n H 2 n –2 O 2 (n= 1,2,3...) or CnH 2 n –1 COOH (n = 0,1,2…)
General formula of saturated dibasic carboxylic acids:
C n H 2n–2 O 4 (n = 2,3…)
Names and formulas of some carboxylic acids
|
Carboxylic acid formula |
IUPAC name |
Trivial name |
|---|---|---|
|
Saturated monobasic carboxylic acids |
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Unsaturated monobasic carboxylic acids |
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Dibasic carboxylic acids |
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Examples of problem solving
EXAMPLE 1
| Exercise | Three identical test tubes without signatures contain three acids: formic, acetic and hydrochloric. Based on the differences in their chemical properties, how can you determine which acid is in each test tube? |
| Solution | Formic acid also exhibits some properties (reductive). Therefore, it can be determined, for example, by the reaction with copper (II) hydroxide; in the case of formic acid, red copper (I) oxide is formed: The remaining acids can be distinguished by reaction with silver nitrate. In the case of hydrochloric acid, a white precipitate of silver chloride precipitates: Silver acetate dissolves in water, so no changes will occur in the test tube. Thus, the remaining test tube contains acetic acid. |
EXAMPLE 2
| Exercise | Determine if, upon hydrolysis of a sample weighing 2.64 g, 1.38 g of alcohol and 1.8 g of monobasic carboxylic acid are released. |
| Solution | The general formula of an ester consisting of an alcohol and an acid with different numbers of carbon atoms is: Thus, the alcohol formula is: and the formula of the acid is: Let us write the equation for ester hydrolysis: In accordance with the law of conservation of mass of substances, the mass of reaction products is equal to the mass of the starting substances. Let's calculate the mass: M(acid) + m(alcohol) – m(ether) g Let's calculate the amount of water substance: According to the reaction equation n(acid) = n(alcohol) mol |
General formula of saturated monobasic carboxylic acids C n H 2 n +1 COOH.
Nomenclature of carboxylic acids
For carboxylic acids, trivial names are more accepted, the occurrence of which is usually associated with the natural sources from which they are isolated or synthesized. Thus, formic acid is found in the secretions of ants, butyric acid in cow butter, oxalic acid in a number of plants; nicotinic acid was obtained for the first time by oxidation of nicotine, succinic acid from amber, o-phthalic acid from naphthalene, etc.
International names of carboxylic acids are formed from the name of the corresponding hydrocarbon with the addition of the ending “ -oic acid". But such names are used quite rarely and only in cases where the acid does not have a trivial name.
| Number of C atoms | Carboxylic acid | Acid name | |
| Trivial | IUPAC nomenclature | ||
| UNDC | ant | methane | |
| CH 3 – COOH | vinegar | ethane | |
| CH 3 – CH 2 – COOH | propionic | propane | |
| CH 3 – CH 2 – CH 2 – COOH | oil | butane | |
| CH 3 – (CH 2) 2 – CH 2 – COOH | valerian | pentane | |
| CH 3 – (CH 2) 3 – CH 2 – COOH | nylon | hexane | |
| CH 3 – (CH 2) 4 – CH 2 – COOH | heptane | ||
| CH 3 – (CH 2) 5 – CH 2 – COOH | caprylic | octane | |
| CH 3 – (CH 2) 6 – CH 2 – COOH | pelargonium | nonane | |
| CH 3 – (CH 2) 7 – CH 2 – COOH | capric | dean's | |
| CH 3 – (CH 2) 8 – CH 2 – COOH | undecyl | undecane | |
| CH 3 – (CH 2) 9 – CH 2 – COOH | lauric | dodecane | |
| CH 3 – (CH 2) 10 – CH 2 – COOH | tridecyl | tridecane | |
| CH 3 – (CH 2) 11 – CH 2 – COOH | myristic | tetradecane | |
| CH 3 – (CH 2) 12 – CH 2 – COOH | pentadecyl | pentadecane | |
| CH 3 – (CH 2) 13 – CH 2 – COOH | palmitic | hexadecane | |
| CH 3 – (CH 2) 14 – CH 2 – COOH | margarine | heptadecane | |
| CH 3 – (CH 2) 15 – CH 2 – COOH | stearic | octadecane | |
| CH 3 – (CH 2) 17 – CH 2 – COOH | arachine | eicosan | |
| CH 3 – (CH 2) 19 – CH 2 – COOH | Behenaceae | ||
| CH 3 – (CH 2) 21 – CH 2 – COOH | lignoceric | ||
| CH 3 – (CH 2) 23 – CH 2 – COOH | cerotinic | ||
| CH 3 – (CH 2) 25 – CH 2 – COOH | montana | ||
| CH 3 – (CH 2) 27 – CH 2 – COOH | lemon balm |
Chain numbering starts from the carboxyl group:
CH 3 – CH – CH 2 – CH – C = O
CH 3 CH 3 OH
2,4-dimethylpentanoic acid
The acidic residues of some carboxylic acids also have their own individual names.
Isomerism of carboxylic acids
1. Isomerism of the radical
CH 3 – CH 2 – CH 2 – C = O CH 3 – CH – C = O
OH CH 3 OH
butanoic acid 2-methylpropanoic acid
(oil) (iso-oil)
2. Interclass isomerism with esters
CH 3 – CH 2 – CH 2 – C = O CH 3 – CH 2 – C = O
OH O – CH 3
butanoic acid methyl ester
propanoic acid
Physical properties of carboxylic acids
The lower representatives of carboxylic acids (C 1 – C 3) are easily mobile liquids with a pungent acidic odor, capable of crystallizing upon cooling. Mixes with water in all proportions. Starting with butyric acid (C 4) - oily liquids, sparingly soluble in water. Higher acids (> C 10) are solid substances, insoluble in water and odorless. All carboxylic acids are soluble in organic solvents.
In the class of acids, as well as in the class of alcohols, the phenomenon of association of molecules occurs due to the formation of hydrogen bonds, and these bonds are stronger than in alcohols.
Formic acid is found in free form in the body and caustic secretions of ants, stinging nettles and in small quantities in the urine and sweat of animals. Formic acid is a caustic substance: drops of it cause blisters on the skin.
Acetic acid has been known in the form of vinegar since ancient times. Anhydrous acetic acid can exist in the solid state in the form of a transparent mass or crystals resembling ice, with a melting point of 16.6 0 C. Therefore, anhydrous acetic acid is often called glacial acetic acid.
Free butyric acid is found in rancid oil and sweat. An ester of glycerol and butyric acid is part of cow butter. Since other fats do not contain butyric acid esters, in doubtful cases, to prove the authenticity of cow butter, the product is analyzed for butyric acid.
Valeric acid is found in valerian root, and in the form of an ester is a component of the drug validol.
The names of the three subsequent even acids - caproic, caprylic and capric - have a common root. “Capra” in Latin means “goat”; These acids are actually found in goat milk fat.
Pelargonic acid is contained in the volatile oil of rose pelargonium and other plants of the geranium family, lauric acid (in old books it was called laurel) - in laurel oil. Myristic acid is found in the aromatic seeds of the nutmeg tree - nutmeg. Palmitic acid is isolated from palm oil, which is extracted from coconut kernels. “Stear” in ancient Greek means “fat, lard.” Hence the name stearic acid. Together with palmitic acid, it is one of the most important fatty acids and makes up the main part of most vegetable and animal fats. Arachidic acid is found in groundnut oil - peanuts.
Methods for producing carboxylic acids
1. Carboxylic acids are found in free form in nature and in the form of their derivatives, for example, esters. From esters, carboxylic acids can be obtained by hydrolysis.
2. Oxidation of aldehydes (alcohols)
CH 3 – CH 2 – C = O + [O]¾¾® CH 3 – CH 2 – C = O
propanal propanoic acid
3. Industrial method – oxidation of saturated hydrocarbons
CH 4 + O 2 ¾¾® H – C = O
formic acid
Other acids are obtained similarly by oxidation of alkanes.
4. Formic acid is obtained from carbon monoxide (II).
CO + NaOH ¾¾® HCOONa
sodium formate
HCOONa + H 2 SO 4 ¾¾® HCOOH + Na 2 SO 4
ant
5. Preparation of acetic acid from carbon monoxide (II) and methanol
CH 3 OH + CO ¾¾® CH 3 COOH
methanol acetic acid
Chemical properties of carboxylic acids
1. Properties of hydroxyl hydrogen
1.1 Interaction with active metals:
2CH 3 – CH 2 – C = O +2Na ® 2CH 3 – CH 2 – C = O + H 2
propanoic acid
1.2. Interaction with basic oxides (metals of groups I–II):
2CH 3 – CH 2 – COOH + CaO ® (CH 3 – CH 2 – COO) 2 Ca + H 2 O
propanoic acid calcium salt
propanoic acid
1.3. Interaction with alkalis:
CH 3 – CH 2 – COOH + KOH ® CH 3 – CH 2 – COOK + H 2 O
propanoic acid potassium salt
propanoic acid
1.4. Interaction with sodium carbonate is a qualitative reaction to the carboxyl group (emission of carbon dioxide).
CH 3 – CH 2 – COOH + Na 2 CO 3 ® CH 3 – CH 2 – COONa + H 2 O + CO2
propanoic acid sodium salt
propanoic acid
2. Properties of the hydroxyl group
2.1. Interaction with alcohols – esterification reaction – formation of esters:
H 2 SO 4 conc.
CH 3 – CH 2 – C – OH + OH – CH 2 – CH 3 ¾¾® CH 3 – CH 2 – C – O– CH 2 – CH 3 + H 2 O
propanoic acid ethanol ethyl ester propanoic acid
acids (ethyl propanoate)
3. Interaction with halogens. The hydrogen atom is replaced at the second carbon atom of the chain (in the a-position).
CH 3 – CH 2 – C – OH + Br 2 ® CH 3 – CH – C – OH + HBr
propanoic acid 2-bromopropanoic acid
(a-bromopropionic acid)
4. Oxidation reactions. Complete oxidation – combustion:
C 3 H 6 O 2 + 3.5O 2 ® 3CO 2 + 3H 2 O
5. Special properties of formic acid
The reducing properties of formic acid are due to the presence of an aldehyde group
The oxidation of formic acid produces carbonic acid, which decomposes into carbon dioxide and water:
H – C = O + [O] ® H 2 CO 3 ® H 2 O + CO 2
The reducing properties of formic acid are used in practice to discover it (and distinguish it from other acids).
Carboxylic acids- organic substances whose molecules contain one or more carboxyl groups.
The carboxyl group (abbreviated as COOH) is a functional group of carboxylic acids and consists of a carbonyl group and an associated hydroxyl group.
Based on the number of carboxyl groups, carboxylic acids are divided into monobasic, dibasic, etc.
The general formula of monobasic carboxylic acids is R—COOH. An example of a dibasic acid is oxalic acid HOOC—COOH.
Based on the type of radical, carboxylic acids are divided into saturated (for example, acetic acid CH 3 COOH), unsaturated [for example, acrylic acid CH 2 =CH—COOH, oleic acid CH 3 —(CH 2) 7 —CH=CH—(CH 2) 7 -COOH] and aromatic (for example, benzoic C 6 H 5 -COOH).
Isomers and homologues
Monobasic saturated carboxylic acids R-COOH are isomers of esters (abbreviated R"-COOR") with the same number of carbon atoms. The general formula for both is C n H 2 n O2.
| G | HCOOH methane (ant) |
||||
| CH3COOH ethane (acetic) | HCOOCH 3 formic acid methyl ester |
||||
| CH3CH2COOH propane (propionic) |
HCOOCH 2 CH 3 ethyl formic acid |
CH 3 COOCH 3 acetic acid methyl ester | |||
| CH3(CH2)2COOH butane (oil) |
2-methylpropane |
HCOOCH 2 CH 2 CH 3 propyl ester of formic acid |
CH 3 COOCH 2 CH 3 ethyl acetate |
CH 3 CH 2 COOCH 3 propionic acid methyl ester |
|
| isomers | |||||
Algorithm for composing the names of carboxylic acids
- Find the carbon backbone - this is the longest chain of carbon atoms, including the carbon atom of the carboxyl group.
- Number the carbon atoms in the main chain, starting with the carboxyl carbon atom.
- Name the compound using the algorithm for hydrocarbons.
- At the end of the name, add the suffix “-ov”, the ending “-aya” and the word “acid”.
In molecules of carboxylic acids p-electrons of the oxygen atoms of the hydroxyl group interact with electrons of the -bond of the carbonyl group, as a result of which the polarity of the O-H bond increases, the -bond in the carbonyl group strengthens, the partial charge (+) on the carbon atom decreases and the partial charge (+) on the hydrogen atom increases .
The latter promotes the formation of strong hydrogen bonds between carboxylic acid molecules.
The physical properties of saturated monobasic carboxylic acids are largely due to the presence of strong hydrogen bonds between molecules (stronger than between alcohol molecules). Therefore, the boiling points and solubility in water of acids are higher than those of the corresponding alcohols.
Chemical properties of acids
Strengthening the -bond in the carbonyl group leads to the fact that addition reactions are uncharacteristic for carboxylic acids.
- Combustion:
CH 3 COOH + 2O 2 2CO 2 + 2H 2 O
- Acidic properties.
Due to the high polarity of the O-H bond, carboxylic acids in an aqueous solution noticeably dissociate (more precisely, react reversibly with it):HCOOH HCOO - + H + (more precisely HCOOH + H 2 O HCOO - + H 3 O +)
All carboxylic acids are weak electrolytes. As the number of carbon atoms increases, the strength of acids decreases (due to a decrease in the polarity of the O-H bond); on the contrary, the introduction of halogen atoms into the hydrocarbon radical leads to an increase in the strength of the acid. Yes, in a rowHCOOH CH 3 COOH C 2 H 5 COOH
the strength of acids decreases, and in the seriesIncreasing.
Carboxylic acids exhibit all the properties inherent in weak acids:
Mg + 2CH 3 COOH (CH 3 COO) 2 Mg + H 2
CaO + 2CH 3 COOH (CH 3 COO) 2 Ca + H 2 O
NaOH + CH 3 COOH CH 3 COONa + H 2 O
K 2 CO 3 + 2CH 3 COOH 2CH 3 COOK + H 2 O + CO 2 - Esterification (reaction of carboxylic acids with alcohols leading to the formation of an ester):
Polyhydric alcohols, such as glycerol, can also enter into the esterification reaction. Esters formed by glycerol and higher carboxylic acids (fatty acids) are fats.Fats are mixtures of triglycerides. Saturated fatty acids (palmitic C 15 H 31 COOH, stearic C 17 H 35 COOH) form solid fats of animal origin, and unsaturated fatty acids (oleic C 17 H 33 COOH, linoleic C 17 H 31 COOH, etc.) form liquid fats (oils) of plant origin.
- Substitution in a hydrocarbon radical:
Substitution occurs in the - position.The peculiarity of formic acid HCOOH is that this substance is a bifunctional compound; it is both a carboxylic acid and an aldehyde:
Therefore, formic acid, among other things, reacts with an ammonia solution of silver oxide (silver mirror reaction; qualitative reaction):HCOOH + Ag 2 O (ammonia solution) CO 2 + H 2 O + 2Ag
Preparation of carboxylic acids
Chemical compounds based on one or more COOH groups are defined as carboxylic acids.
The compounds are based on the COOH group, which has two components - carbonyl and hydroxyl. A group of COOH atoms is called a carboxyl group (carboxyl). The interaction of elements is ensured by the combination of two oxygen atoms and a carbon atom.
In contact with
Classmates
Structure of carboxylic acids
Hydrocarbon radical in monobasic saturated acids combines with one COOH group. The general formula of carboxylic acids looks like this: R-COOH.
The structure of the carbon group affects the chemical properties.
Nomenclature
In the names of carbon compounds, the carbon atom of the COOH group is numbered first. The number of carboxyl groups is denoted by the prefixes di-; three-; tetra-.
For example, CH3-CH2-COOH is the formula for propanoic acid.
Carbon compounds have and familiar names: formic, acetic, citric... All these are names of carboxylic acids.
The names of salts of carbonic compounds are obtained from the names of the hydrocarbon with the addition of the suffix “-oat” (COOC)2-potassium ethanediot.
Classification of carboxylic acids
Carboxylic acids classification.
By the nature of the hydrocarbon:
- limit;
- unsaturated;
- aromatic.
According to the number of COUN groups there are:
- monobasic (acetic acid);
- dibasic (oxalic acid);
- polybasic (citric acid).
Saturated carboxylic acids- compounds in which the radical is connected to one carbonyl.
The classification of carboxylic acids also divides them according to the structure of the radical to which the carbonyl is bonded. According to this criterion, compounds are aliphatic and alicyclic.
Physical properties
Let's look at the physical properties of carboxylic acids.
Carbon compounds have different numbers of carbon atoms. Depending on this number, the physical properties of these compounds differ.
Compounds containing from one to three carbon atoms are considered lower. These are colorless liquids with a pungent odor. Lower compounds dissolve easily in water.
Compounds containing from four to nine carbon atoms are oily liquids with an unpleasant odor.
Compounds containing more than nine carbon atoms are considered superior and the physical properties of these compounds are as follows : they are solids, they cannot be dissolved in water.
The boiling and melting points depend on the molecular weight of the substance. The higher the molecular weight, the higher the boiling point. Boiling and melting require a higher temperature than alcohols.
There are several ways to obtain carboxylic acids.
Chemical reactions exhibit the following properties:
Application of carboxylic acids
Carbon compounds are common in nature. Therefore, they are used in many areas: in industry (light and heavy) , in medicine and agriculture, as well as in the food industry and cosmetology.
Aromatic compounds are found in large quantities in berries and fruits.
In medicine, lactic, tartaric and ascorbic acid are used. Dairy is used as a cauterization, and tartar is used as a mild laxative. Ascorbic acid strengthens the immune system.
Fruit and aromatic ones are used in cosmetology. Thanks to them, cells renew themselves faster. The aroma of citrus fruits can have a tonic and calming effect on the body. Benzoic acid is found in balms and essential oils; it dissolves well in alcohol.
High molecular weight unsaturated compounds are found in dietetics. Oleic is the most common in this area.
Polyunsaturated with double bonds (linoleic and others) have biological activity. They are also called active fatty acids. They are involved in metabolism, affect visual function and immunity, as well as the nervous system. The absence of these substances in food or their insufficient consumption inhibits the growth of animals and has a negative impact on their reproductive function.
Sorbic acid is obtained from rowan berries. It is an excellent preservative.
Acrylic has a pungent odor. It is used to produce glass and synthetic fibers.
Based on the ethyrification reaction, fat is synthesized, which is used in the manufacture of soap and detergents.
Formicidum is used in medicine, in beekeeping, and also as preservatives.
Acetic is a colorless liquid with a pungent odor; mixes easily with water. It is widely used in the food industry as a seasoning. It is also used for preservation. It also has solvent properties. Therefore, it is widely used in the production of varnishes and paints, and in dyeing. On its basis, raw materials are made to combat insects and weeds.
Stearic and palmitic(higher monobasic compounds) are solids and do not dissolve in water. But their salts are used in soap production. They make soap bars hard.
Since the compounds are capable of imparting homogeneity to masses, they are widely used in the manufacture of medicines.
Plants and animals also produce carbon compounds. Therefore, it is safe to consume them internally. The main thing is to follow the dosage. Exceeding the dose and concentration leads to to burns and poisoning.
The corrosiveness of the compounds is beneficial in metallurgy, as well as for restorers and furniture makers. Mixtures based on them allow you to level surfaces and remove rust.
Esters obtained from the esterification reaction have found their use in perfumery. They are also used as components of varnishes and paints, and solvents. And also as aromatic additives.
