Carbon group. Carboxylic acids
Carbonyl compounds. Structure and chemical properties 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 Latin name 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, butyric acid from burnt 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). Acyl of formic acid (lat. acidum formicum) is called formyl, acetic acid (acidum aceticum) is called acetyl. 
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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 - more strong 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)
HOOS - 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 where the double bond is broken in the 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 goes into the production of soap, stearin and glycerin. Margarine - edible fat, 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 in a molecule, toilet soap is obtained, and from acids containing from 17 to 21 carbon atoms - laundry soap and soap for technical purposes. 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:
Lactic (2-hydroxy-ethanecarboxylic acid, 2-hydroxypropanoic acid, hydroxypropionic acid)
malic (2-hydroxy-1,2-ethanedicarboxylic acid, hydroxysuccinic acid)
tartaric (1,2-dioxy-1,2-ethanedicarboxylic acid, dioxysuccinic acid)
citric (2-hydroxy-1,2,3-propanetricarboxylic acid)
.
O
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The group of -C atoms is called a carboxyl group or carboxyl.
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OH
Organic acids containing one carboxyl group in the molecule are monobasic. The general formula of these acids is RCOOH.
Carboxylic acids containing two carboxyl groups are called dibasic. These include, for example, oxalic and succinic acids.
There are also polybasic carboxylic acids containing more than two carboxyl groups. These include, for example, tribasic citric acid. Depending on the nature of the hydrocarbon radical, carboxylic acids are divided into saturated, unsaturated, and aromatic.
Saturated, or saturated, carboxylic acids are, for example, propanoic (propionic) acid or the already familiar succinic acid.
Obviously, saturated carboxylic acids do not contain n-bonds in a hydrocarbon radical.
In molecules of unsaturated carboxylic acids, the carboxyl group is associated with an unsaturated, unsaturated hydrocarbon radical, for example in molecules of acrylic (propenoic) CH2=CH-COOH or oleic CH3-(CH2)7-CH=CH-(CH2)7-COOH and other acids.
As can be seen from the formula of benzoic acid, it is aromatic, since it contains an aromatic (benzene) ring in the molecule.
Nomenclature and isomerism
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 the first acquaintance with the diverse and interesting world organic acids, let's consider saturated monobasic carboxylic acids in more detail.
It is clear that the composition of these acids will be reflected general formula C n H 2n O2, or C n H 2n +1 COOH, or RCOOH.
Physical properties of saturated monobasic carboxylic acids
Lower acids, i.e. acids with a relatively small molecular weight containing up to four carbon atoms in a molecule, are liquids with a characteristic pungent odor(remember the smell acetic acid). Acids containing from 4 to 9 carbon atoms are viscous oily liquids with unpleasant smell; 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 with the formation of 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 position halogen in the molecule. 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 small quantities red phosphorus, then it is selective - hydrogen is replaced only in A-position (at the carbon atom closest to the functional group) in the acid molecule. You will learn the reasons for this selectivity when studying chemistry at a higher educational institution.
Carboxylic acids form various functional derivatives when replacing the hydroxyl group. When these derivatives are hydrolyzed, carboxylic acid is formed again.
Carboxylic acid chloride can be obtained by treating the acid with phosphorus(III) chloride or thionyl chloride (SOCl 2). Carboxylic acid anhydrides are prepared by reacting chlorine anhydrides with carboxylic acid salts. Esters are formed by the esterification of carboxylic acids with alcohols. Esterification is catalyzed by inorganic acids.
This reaction is initiated by protonation of the carboxyl group - the interaction of a hydrogen cation (proton) with the lone electron pair of the oxygen atom. Protonation of 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 an 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 - colorless liquid with a characteristic pungent odor, miscible with water in any ratio. Aqueous solutions of acetic acid are marketed under the name vinegar (3-5% solution) and acetic essence (70-80% solution) and are widely used in food industry. Acetic acid is a good solvent for many organic matter and is therefore used in dyeing, tanning, and the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, substances used to control weeds - herbicides - are obtained from it. 
Acetic acid is the main component wine vinegar, the characteristic smell of which is due to it. It is a product of ethanol oxidation and is formed from it when wine is stored in air.
The most important representatives of higher saturated monobasic acids are palmitic C15H31COOH and stearic C17H35COOH acids. Unlike lower acids, these substances are solid and poorly soluble in water.
However, their salts - stearates and palmitates - are highly soluble and have a detergent effect, which is why they are also called soaps. It is clear that these substances are produced on a large scale.
From unsaturated higher carboxylic acids highest value oleic acid has C17H33COOH, or (CH2)7COOH. It is an oil-like liquid without taste or smell. Its salts are widely used in technology.
The simplest representative of dibasic carboxylic acids is oxalic (ethanedioic) acid HOOC-COOH, the salts of which are found in many plants, for example, sorrel and sorrel. Oxalic acid is a colorless crystalline substance 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 (no.) will be required to burn a two hundred gram stearic candle if stearin contains equal masses palmitic and stearic acids? What volume carbon dioxide(n.u.) and the mass of water formed in this case?
5. Solve the previous problem provided that the candle contains equal quantities ( same number 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. Added to yeast-free dough Baking (baking) soda NaHC03 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 was 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. Offer something simple laboratory method, with which you can recognize propanoic and acrylic acids.
13. Write an equation for the reaction of producing methyl formate - an ester of methanol and formic acid. Under what conditions should this reaction be carried out?
14. Make up structural formulas substances having the composition C3H602. What classes of substances can they be classified into? Give the reaction equations characteristic of each of them.
15. Substance A - an isomer of acetic acid - is insoluble in water, but can undergo hydrolysis. What is the structural formula of substance A? Name the products of its hydrolysis.
16. Make up the structural formulas of the following substances:
a) methyl acetate;
b) oxalic acid;
c) formic acid;
d) dichloroacetic acid;
e) magnesium acetate;
f) ethyl acetate;
g) ethyl formate;
h) acrylic acid.
17*. A sample of saturated monobasic organic acid weighing 3.7 g was neutralized 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 moistened the arrows 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 are widely used in all areas human life. They are used in medicine, cosmetology, food industry, agriculture and used for domestic needs.
IN medical purposes organic acids such as lactic, tartaric, and ascorbic acid are used. Probably each of you used vitamin C to strengthen the body - this is exactly what it is 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 for the fans cosmetic procedures, you 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 succinic acid has found wide use in agriculture, since it can be used to increase the yield of cultivated plants. It can also stimulate plant growth and accelerate their development.
Preparation of carboxylic acids
I. In industry
1. Isolated from natural products
(fats, waxes, essential and vegetable oils)
2. Oxidation of alkanes:
2CH 4 + + 3O 2 t,kat→ 2HCOOH + 2H 2 O
methaneformic acid
2CH 3 -CH 2 -CH 2 -CH 3 + 5O 2 t,kat,p→4CH 3 COOH + 2H 2 O
n-butaneacetic acid
3. Oxidation of alkenes:
CH 2 = CH 2 + O 2 t,kat→CH3COOH
ethylene
WITH H 3 -CH=CH 2 + 4[O] t,kat→ CH 3 COOH + HCOOH (acetic acid + formic acid )
4. Oxidation of benzene homologues (production of 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
toluenebenzoic acid
5.Obtaining formic acid:
Stage 1: CO+NaOH t , p→HCOONa (sodium formate – salt )
2 stage: HCOONa + H 2 SO 4 → HCOOH + NaHSO 4
6. Preparation of acetic acid:
CH3OH+CO t,p→CH3COOH
Methanol
II. In the laboratory
1. Hydrolysis of esters:
2. From salts of carboxylic acids :
R-COONa + HCl → R-COOH + NaCl
3. 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 preparing carboxylic acids
1. Oxidation of aldehydes:
R-COH + [O] → R-COOH
For example, the “Silver Mirror” reaction or oxidation with copper (II) hydroxide - qualitative reactions 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 per carbon atom.
4. From cyanides (nitriles) - the method allows you to increase the carbon chain:
WITH H 3 -Br + Na-C≡N → CH 3 -CN + NaBr
CH3-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 CARBOXYLIC ACIDS
Formic acid– in medicine - formic alcohol (1.25% alcohol solution formic acid), in beekeeping, in organic synthesis, when obtaining solvents and preservatives; as a strong reducing agent.
Acetic acid– in food and chemical industry(production of cellulose acetate, from which acetate fiber, organic glass, film are produced; for the synthesis of dyes, medicines and esters). IN household as a flavoring and preservative substance.
Butyric acid– for the production of flavoring additives, plasticizers and flotation reagents.
Oxalic acid– in the metallurgical industry (descaling).
Stearic C17H35COOH and palmitic acid C 15 H 31 COOH – as surfactants, lubricants in metalworking.
Oleic acid C 17 H 33 COOH is a flotation reagent and collector for the enrichment 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 pungent taste that causes burns on the skin. It is used in the textile industry as a mordant for dyeing fabrics, for tanning leather, and also for various syntheses.
Acetic acid
widespread in nature - found in animal excretions (urine, bile, feces) and plants (green leaves). It is formed during fermentation, rotting, souring of wine, beer, and is found in sour milk and cheese. The melting point of anhydrous acetic acid is + 16.5°C, its crystals are as transparent as ice, which is why it is called glacial acetic acid. First received in late XVIII century by Russian scientist T. E. Lovitz. Natural vinegar contains about 5% acetic acid. Vinegar essence is prepared from it, used in the food industry for preserving 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 flora: in balms, incense, essential oils. In animal organisms it is found in the breakdown products of protein substances. This crystalline substance, melting point 122°C, easily sublimes. IN cold water does not dissolve well. 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 mentioned by nutritionists (they call them unsaturated). The most common of them 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 hardens in the cold.
Particularly important polyunsaturated acids with several double bonds: 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 called 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, maintain the structure of cell membranes, are necessary for the functioning of the visual apparatus and nervous system, affect the immune system. The absence of these acids in food inhibits the growth of animals, inhibits their reproductive function, and causes various diseases. The human body cannot synthesize linoleic and linolenic acids itself and must receive them ready-made with food (like vitamins). For the synthesis of arachidonic acid in the body, linoleic acid is necessary. Polyunsaturated fatty acids with 18 carbon atoms in the form of glycerol esters are found in the so-called drying oils - flaxseed, hemp, poppy, etc. Linoleic acid
C17H31COOH 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 acid.
Sorbic acid (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 become moldy.
The simplest unsaturated acid, acrylic CH 2 = CHCOOH, has a pungent odor (in Latin acris - pungent, pungent). Acrylates (esters of acrylic acid) are used to produce organic glass, and its nitrile (acrylonitrile) is used to produce synthetic fibers.
When naming newly isolated acids, chemists often give free rein to their imagination. Thus, the name of the closest homologue of acrylic acid, croton
CH 3 – CH = CH – COOH, does not come from a mole at all, but from a plant Croton tiglium, from whose oil it was isolated. The synthetic isomer of crotonic acid is very important - methacrylic acid CH 2 = C (CH 3) – COOH, from the ester of which (methyl methacrylate), as well as from methyl acrylate, transparent plastic is made - plexiglass.
Unsaturated 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 proceed against Markovnikov's rule.
Unsaturated carboxylic acids and their derivatives are capable of polymerization reactions.
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
Homologous series formula
The IUPAC nomenclature allows many acids to retain their trivial names, which usually indicate the natural source from which a particular acid was isolated, for example, formic, acetic, butyric, valeric, etc.
For more complex cases, the names of acids are derived from the name of hydrocarbons with the same number of 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 the hydrogen atoms are replaced 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 polymer materials, in the manufacture of paints, etc.
Formation of esters. Acids with 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. The reactivity of the hydrogen atoms of hydrocarbon radicals in acids is 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 alkali metal salts of carboxylic acids are fused 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 - with 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 to produce silk acetate, dyes, esters, acetone, acetic anhydride, salts, etc. In the food industry, acetic acid is used for food preservation; 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 a free state it is found 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, medium 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, which hardens in the cold 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 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.
Chemical compounds, which also consist of the carboxyl group COOH, are called carboxylic acids by scientists. There are a large number of names for these compounds. They are classified according to various parameters, for example, by the number of functional groups, the presence of an aromatic ring, and so on.
Structure of carboxylic acids
As mentioned, for an acid to be carboxylic, it must have a carboxyl group, which in turn has two functional parts: hydroxyl and carbonyl. Their interaction is ensured by its functional combination of one carbon atom with two oxygen atoms. The chemical properties of carboxylic acids depend on the structure of this group.
Due to the carboxyl group, these organic compounds can be called acids. Their properties are determined by the increased ability of the hydrogen ion H+ to be attracted to oxygen, further polarizing O-H connection. Also, thanks to this property, organic acids are able to dissociate into aqueous solutions. The ability to dissolve decreases in inverse proportion to the increase in molecular weight of the acid.
Varieties of carboxylic acids
Chemists distinguish several groups of organic acids.
Monocarboxylic acids consist of a carbon skeleton and only one functional carboxyl group. Every schoolchild knows the chemical properties of carboxylic acids. 10th grade curriculum in chemistry includes the direct study of the properties of monobasic acids. Dibasic and polybasic acids have two or more carboxyl groups in their structure, respectively.
Also, based on the presence or absence of double and triple bonds in a molecule, there are unsaturated and saturated carboxylic acids. Chemical properties and their differences will be discussed below.
If organic acid has a substituted atom in the radical, then its name includes the name of the substituent group. So, if the hydrogen atom is replaced by a halogen, then the name of the acid will contain the name of the halogen. The name will undergo the same changes if replacement occurs with aldehyde, hydroxyl or amino groups.
Isomerism of organic carboxylic acids
The production of soap is based on the synthesis reaction of esters of the above acids with potassium or sodium salt.
Methods for producing carboxylic acids
There are many ways and methods for producing acids with the COOH group, but the most commonly used are the following:
- Isolation from natural substances (fats and other things).
- Oxidation of monoalcohols or compounds with a COH group (aldehydes): ROH (RCOH) [O] R-COOH.
- Hydrolysis of trihaloalkanes in alkali with intermediate production of monoalcohol: RCl3 + NaOH = (ROH + 3NaCl) = RCOOH + H2O.
- Saponification or hydrolysis of acid and alcohol esters (esters): R−COOR"+NaOH=(R−COONa+R"OH)=R−COOH+NaCl.
- Oxidation of alkanes with permanganate (hard oxidation): R=CH2 [O], (KMnO4) RCOOH.
The importance of carboxylic acids for humans and industry
The chemical properties of carboxylic acids have great value for human life. They are extremely necessary for the body, since in large quantities contained in every cell. The metabolism of fats, proteins and carbohydrates always passes through a stage at which one or another carboxylic acid is produced.
In addition, carboxylic acids are used to create medicines. No pharmaceutical industry can exist without the practical application of the properties of organic acids.
Compounds with a carboxyl group also play an important role in the cosmetics industry. Synthesis of fat for subsequent production of soap, detergents And household chemicals based on the esterification reaction with a carboxylic acid.
The chemical properties of carboxylic acids are reflected in human life. They are of great importance for human body, since they are contained in large quantities in each cell. The metabolism of fats, proteins and carbohydrates always passes through a stage at which one or another carboxylic acid is produced.
