Organic acids characterization of their properties. organic acids

A large number of compounds known modern world are classified as organic acids. In nature, they are obtained mainly from sugars as a result of complex biochemical reactions. Their role in all life processes is invaluable. For example, in the biosynthesis of glycosides, amino acids, alkaloids and other biologically reactive substances; in carbohydrate, fat and protein metabolism... Vital necessary processes with the participation of organic acids a great many.

What is special about them? Organic acids acquire unique chemical and biological properties due to their own elemental and functional composition of molecules. A certain sequence of connecting atoms of different nature and the specificity of their combination give the substance individual characteristics and features of interaction with others.

Qualitative composition of organic substances

The main brick, a kind of monometer of all living things, is carbon, or, as it is also called, carbon. All "skeletons" are built from it - basic structures, skeletons - organic compounds and acids as well. In second place in terms of prevalence is hydrogen, another name for the element is hydrogen. It fills the valences of carbon free from connection with other atoms, gives the molecules volume and density.

The third is oxygen, or oxygen, it combines with carbon as part of groups of atoms, giving a simple aliphatic or aromatic substance completely new characteristics, for example, oxidizing ability. Next in the range of prevalence is nitrogen, its contribution to the properties of organic acids is special, there is a separate class of amine-containing compounds. Also in organic compounds there are sulfur, phosphorus, halogens and some other elements in much smaller quantities.

Other organic substances are also separated into a separate class. Nucleic acids are phosphorus- and nitrogen-containing biological polymers built from monomers - nucleotides, forming complex structures DNA and RNA.

Substantiation of chemical identity

The determining factor of difference from other substances is the presence in the compound of such an association of atoms, which has a strict sequence of their binding to each other and carries a kind of genetic code of the class, like a functional group of organic acids. It is called carboxyl, consists of one carbon atom, hydrogen and two oxygen, and, in fact, combines carbonyl (-C=O) and hydroxyl (-OH) groups.

The constituent parts interact at the electronic level, generating the individual properties of acids. In particular, carbonyl addition reactions are not inherent in them, and the ability to donate a proton is several times higher than that of alcohols.

Structural features

What happens at the electronic level of mutual influence in the functional group of the organic acid class? The carbon atom has a partially positive charge due to the pulling of the bond density to oxygen, in which the ability to hold it is much higher. The oxygen from the hydroxyl part has an unshared pair of electrons, which now begins to be attracted to carbon. This reduces the density of the oxygen-hydrogen bond, as a result of which the hydrogen becomes more mobile. For the compound, acid-type dissociation becomes possible. A decrease in the positive charge of carbon causes the termination of the addition processes, as already mentioned above.

The role of specific fragments

Each functional group has individual properties and gives them to the substance in which it is contained. The presence of several in one excludes the possibility of giving certain reactions that previously distinguished specific fragments separately. This is important feature, which is characterized organic chemistry. Acids can contain groups containing nitrogen, sulfur, phosphorus, halogens, etc.

Class of carboxylic acids

The most famous group of substances from the entire family. It should not be assumed that only compounds of this class are all organic acids. Carbon representatives are the most numerous group, but not the only one. There are, for example, sulfonic acids, they have a different functional fragment. Of these, aromatic derivatives, actively involved in chemical production phenols.

There is another significant class belonging to such a section of chemistry as organic substances. Nucleic acids are separate compounds that require individual consideration and description. They have already been briefly mentioned above.

Carbonic representatives of organic substances contain in their composition a characteristic functional group. It is called carboxyl, the specifics of its electronic structure is described earlier. It is the functional group that determines the presence of strong acidic properties, due to the mobile hydrogen proton, which is easily split off during dissociation. The weakest of this series is only acetate (acetic).

Classification of carboxylic acids

According to the type of structure of the hydrocarbon skeleton, aliphatic (rectilinear) and cyclic are distinguished. For example, propionic, heptanoic, benzoic, trimethylbenzoic carboxylic organic acids. By the presence or absence of multiple bonds - limiting and unsaturated - butyric, acetic, acrylic, hexene, etc. Depending on the length of the skeleton, there are lower and higher (fatty) carboxylic acids, the category of the latter begins with a chain of ten carbon atoms.

The quantitative content of a structural unit, such as a functional group of organic acids, is also the principle of classification. There are one-, two-, three- and multi-base ones. For example, formic carboxylic acid, oxalic, citric and others. Representatives containing, in addition to the main group, also specific groups are called heterofunctional.

Modern nomenclature

To date, in chemical science, two methods are used to name compounds. Rational and systematic nomenclature have largely the same rules, but differ in some details of naming. Historically, there have been trivial "names" of compounds that were given to substances based on their inherent chemical properties, location in nature, and other points. For example, butanoic acid is called butyric, propenoic - acrylic, diureidoacetic - allantoic, pentanoic - valeric, etc. Some of them are now allowed to be used in rational and systematic nomenclature.

Stepwise Algorithm

The way of constructing the names of substances, including such as organic acids, is as follows. First you need to find the longest hydrocarbon chain and number it. The first number must be in close proximity to the branching of the end so that the substituents of hydrogen atoms in the skeleton receive the smallest locants - numbers indicating the numbers of carbon atoms with which they are associated.

Next, you need to find the main functional group, and then identify the rest, if any. So, the name consists of: listed in alphabetical order and with the corresponding substituents locants, the main part speaks of the length of the carbon skeleton and its saturation with hydrogen atoms, in the penultimate turn, belonging to the class of substances is determined, indicating a special suffix and the prefix di- or tri- for polybasic , for example, for carboxylic it is “-ovaya” and the word acid is written at the end. Ethanoic, methanedioic, propenoic, butic acid, hydroxyacetic, pentanedioic, 3-hydroxy-4-methoxybenzoic, 4-methylpentanoic and so on.

Main functions and their meaning

Many acids, both organic and inorganic, are invaluably important for people and their activities. Acting from the outside or being produced inside, they initiate many processes, participate in biochemical reactions, ensuring proper operation human body and are also used in many other areas.

Hydrochloric (or hydrochloric) acid is the base gastric juice and a neutralizer of most unnecessary and dangerous bacteria that have entered the gastrointestinal tract. Sulfuric acid is an indispensable raw material in the chemical industry. The organic part of the representatives of this class is even more significant - milk, ascorbic, acetic and many others. Acids change the pH environment digestive system to the alkaline side, which is essential to maintain normal microflora. In many other aspects, they have an irreplaceable positive impact on human health. It is absolutely impossible to imagine industry without the use of organic acids. All this works only thanks to their functional groups.

DEFINITION

acids- electrolytes, during the dissociation of which only H + ions are formed from positive ions:

HNO 3 ↔ H + + NO 3 -

CH 3 COOH ↔ H + + CH 3 COO -

Acid classification

Acids are primarily classified into inorganic and organic (carboxylic). Weak acidic properties are exhibited by such organic compounds as alcohols and phenols. Inorganic and carboxylic acids, in turn, have their own classifications. So, all inorganic acids can be classified:

• according to the number of hydrogen atoms capable of splitting off in an aqueous solution (monobasic -HCl, HNO 2, dibasic -H 2 SO 4, H 2 SiO 3, tribasic -H 3 PO 4)
• by acid composition (oxygen-free - HI, HF, H 2 S and oxygen-containing - HNO 3, H 2 CO 3)

Carboxylic acids are classified:

• by the number of carboxyl groups (monobasic - HCOOH, CH 3 COOH and dibasic -H 2 C 2 O 4)

Physical properties of acids

At n.o. most inorganic acids exist in a liquid state, some in a solid state (H 3 PO 4, H 3 BO 3).

organic acids with the number of carbon atoms up to 3 are easily mobile colorless liquids with a characteristic pungent odor; acids with 4-9 carbon atoms - oily liquids with bad smell, and acids with a large number of carbon atoms are solids that are insoluble in water.

The structure of the carboxyl group

DEFINITION

carboxyl group- -COOH consists of a carbonyl group -> C=O and a hydroxyl group -OH, which mutually influence each other. The lone pair of electrons of the oxygen atom in the hydroxide ion is shifted towards the carbon atom of the carbonyl group, which weakens the –OH bond and causes the presence of acidic properties (Fig. 1).

Rice. 1 The structure of the carboxyl group

Obtaining acids

Inorganic and organic acids are different ways. So, inorganic acids can be obtained:

• by the reaction of acid oxides with water

  SO 3 + H 2 O \u003d H 2 SO 4

• by the reaction of the combination of non-metals with hydrogen

  H 2 + S ↔ H 2 S

• by the exchange reaction between salts and other acids

  K 2 SiO 3 + 2HCl → H 2 SiO 3 ↓ + 2KCl

Organic acids are obtained by:

• oxidation of aldehydes and primary alcohols (KMnO 4 and K 2 Cr 2 O 7 act as oxidizing agents)

  R - CH 2 -OH → R -C (O) H → R-COOH,

  where R is a hydrocarbon radical.

Chemical properties of acids

To general chemical properties and organic and inorganic acids include:

- the ability to change the color of indicators, for example, litmus becomes red when it enters an acid solution (this is due to the dissociation of acids);

— interaction with active metals

2RCOOH + Mg = (RCOO) 2 Mg + H 2

Fe + H 2 SO 4 (p - p) \u003d FeSO 4 + H 2

— interaction with basic and amphoteric oxides

2RCOOH + CaO = (RCOO) 2 Ca + H 2 O

6RCOOH + Al 2 O 3 = 2(RCOO) 3 Al + 3H 2 O

2HCl + FeO = FeCl 2 + H 2 O

6HNO 3 + Al 2 O 3 \u003d 2Al (NO 3) 3 + 3H 2 O

- interaction with bases

RCOOH + NaOH = RCOONa + H 2 O

H 2 SO 4 + 2NaOH \u003d Na 2 SO 4 + H 2 O

- interaction with salts of weak acids

RCOOH + NaHCO 3 \u003d RCOONa + H 2 O + CO 2

CH 3 COONa + HCl \u003d CH 3 COOH + NaCl

Specific properties of inorganic acids

The specific properties of inorganic acids include redox reactions associated with the properties of acid anions:

H 2 SO 3 + Cl 2 + H 2 O \u003d H 2 SO 4 + 2HCl

Pb + 4HNO 3 (conc) = Pb (NO 3) 2 + 2NO 2 + 2H 2 O

Specific properties of organic acids

The specific properties of organic acids include the formation of functional derivatives by substitution of the hydroxyl group (1, 2, 3, 4), as well as halogenation (5), reduction (6) and decarboxylation (7).

R -C (O) -OH + PCl 5 \u003d R -C (O) -Cl (acid chloride) + POCl 3 + HCl (1)

R –C(O)-OH + H-O-C(O)-R = R – C(O) – O – C(O) – R (anhydride) (2)

CH 3 COOH + CH 3 -CH 2 -OH \u003d CH 3 -C (O) -O-C 2 H 5 (ethyl acetate (ester)) + H 2 O (3)

CH 3 COOH + CH 3 -NH 2 \u003d CH 3 -C (O) -NH-CH 3 (amide) + H 2 O (4)

CH 3 -CH 2 -COOH + Br 2 \u003d CH 3 - CHBr -COOH + HBr (catalyst - P cr) (5)

R-COOH + LiAlH 4 ( water solution, acidified with HCl) = R-CH 2 -OH + AlCl 3 + LiCl (6)

CH 2 \u003d CH-CH 2 -COOH \u003d CO 2 + CH 2 \u003d CH-CH 3 (7)

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

A group of substances with various properties contained in products of plant and animal origin is called. This group is one of the six groups that make up plant phytonutrients. characterized by the presence of one or more carboxyl groups in the molecule. Organic acids are most widely found in food plant origin. Often such acids are called fruit acids. They give a certain taste to the fruit. The most common fruit acids include citric, malic, oxalic, tartaric, pyruvic, salicylic, acetic, etc. Data biological substances different in their structure, as well as in their biological role in living organisms. readily soluble in water and alcohol.

Groups of organic acids

According to their inherent properties, they are divided into two different groups- volatile (easily evaporating) and non-volatile (forming a precipitate). Volatile acids include acetic, butyric, lactic, propionic, formic, valeric, etc. characteristic feature volatile acids is the presence of odor, they are distilled with steam.

Non-volatile acids are citric, tartaric, oxalic, malic, glycolic, glyoxylic, pyruvic, malonic, succinic, fumaric, isocitric, etc.

The role of organic acids in the body

Maintain the acid-base balance of the human body. key, very important function these acids is the alkalization of the body. take a direct part in the processes of digestion, in energy metabolism, activate intestinal motility, slow down the development of putrefactive bacteria and fermentation processes in the large intestine, normalize daily stools, stimulate the secretion of gastric juice in gastrointestinal tract. Thus, they improve digestion, reduce the acidity of the environment (alkaline the body), reduce the risk of developing gastrointestinal diseases. Speaking about the role of organic acids in the human body, one must take into account the fact that certain functions are inherent in each organic acid. Of the known organic acids, the following can be noted:
- benzoic and salicylic acids have an antiseptic effect
- ursolic and oleic acids prevent atrophy skeletal muscle, lower blood sugar levels, dilate the venous vessels of the heart, contribute to weight loss
- uronic acids utilize salts heavy metals, radionuclides, contribute to the formation ascorbic acid
- tartronic acid inhibits the conversion of carbohydrates into fats, thereby preventing obesity and atherosclerosis
- gallic acid has an antifungal and antiviral effect
- hydroxycinnamic acids have a choleretic and anti-inflammatory effect
- malic, citric, tartaric and hydroxycarboxylic acids reduce the risk of the formation of nitrosamines (carcinogenic substances) in the body, and also alkalize the body
- lactic acid has anti-inflammatory and antimicrobial effects and is also nutrition for beneficial bacteria intestines

Lack of organic acids in the body

Violation of the acid-base balance of the body leads to serious illnesses. For example, increased acidity in the body reduces the efficiency of assimilation of vital trace elements (potassium, magnesium, calcium, sodium). The lack of the above substances usually leads to diseases of cardio-vascular system, causes disease Bladder and kidneys. Due to a lack of calcium, pain in muscles and joints occurs, and the body's immunity decreases. Increased acidity in the body can occur when malnutrition. Such nutrition is associated with a lack of fruits and vegetables in the daily menu, an excess of meat and an increased intake of refined carbohydrates. At hyperacidity in the body (such a disease is called acidosis), a person is gaining excess weight, as excess lactic acid accumulates in his muscles (not processed lactose - milk sugar). An increased risk of developing diabetes. Microelement deficiency leads to joint pain, osteoporosis and bone fragility, and metabolism is disturbed. In some cases, acidosis can lead to oncological diseases. Special attention people with diabetes need to pay attention to the acid-base balance of the body - this disease disrupts the correct balance of substances.

Main sources of organic acids

are contained in the fruits of plants in a free state, and in other parts of plants - in bound forms, in the form of salts and esters. The concentration of organic acids in plants is different. In sorrel and spinach, the content of oxalic acid reaches 16%, in apples the level of malic acid reaches 6%, in lemons - 9% is the level citric acid. The main sources for the content of certain types of organic acids are:

1. Benzoic and salicylic acids - the fruits of cranberries, lingonberries, plums, pears, cinnamon
2. Ursolic and oleic acids - raspberry, sea buckthorn, hawthorn fruit, apple peel, lavender herb, lingonberry, pomegranate, mountain ash
3. Uronic acids - apples, pears, plums, peaches, cherry plums, carrots, beets, cabbage
4. Tartronic acid - zucchini, cucumbers, cabbage, quince, eggplant
5. Gallic acid - oak bark, tea
6. Hydroxycinnamic acids - coltsfoot, plantain leaves, Jerusalem artichoke and artichoke shoots
7. Lactic acid - sour milk, wine, beer

For the full functioning of the human body are extremely necessary. Therefore, they should take their rightful place in your daily menu.

Be healthy and cheerful!

Organic acids are important parts of biological machines. They act in processes that are associated with the use of energy of food substances; with the participation of acids in enzyme systems, the stages of gradual rearrangement and oxidation of molecules of carbohydrates, fats and amino acids proceed. Some of the carboxylic acids are obtained and consumed in metabolic processes (metabolism) in very impressive quantities. So, within a day, 400 G acetic acid. This amount would be enough to make 8 l regular vinegar. The rise and fall of anyon such a large scale, of course, means that this substance is necessary to perform some important functions. The analysis detects a number of other acids in the cells of organisms, and most of them are compounds with a mixed function, i.e., in addition to the COOH group, these acids contain other groups, such as CO, OH, etc.

The variety of inorganic acids is not so great: only phosphoric, carbonic and hydrochloric acids (and partly silicic) are found in most organisms both in the form of salts and in a free state (for example, gastric juice).

Carboxylic acids are important primarily because, acting together with special enzymes, they form a closed system of reactions (the Krebs cycle) that oxidizes pyruvic acid. Pyruvic acid itself is a rearrangement product of food molecules, such as carbohydrates.

When studying the Krebs cycle, the following acids will be encountered: pyruvic, acetic, citric, cis-aconitic, isocitric, oxalo-succinic, α-ketoglutaric, succinic, fumaric, malic, oxaloacetic.

Enzymatic reactions were observed in the cells of various microorganisms (molds), showing how easily these acids are converted into each other. So, oxaloacetic acid is formed from carbon monoxide (IV) and pyruvic acid:

CH 3 -CO-COOH + CO 2 → HOOS-CH 2 -CO-COOH

From acetic acid, by removing hydrogen, succinic and fumaric acids can be obtained.

From acetic acid, glycolic acid CH 2 OHCOOH, glyoxylic acid CHO-COOH and oxalic acid COOH-COOH are also formed. Fumaric acid can be converted to malic acid, oxaloacetic acid, etc.

Thanks to such chemical flexibility - the ability to turn into each other under the influence of enzymes, adding or giving away low molecular weight (CO 2, H 2 O, H), organic acids (especially di- and tricarboxylic acids) have become biologically valuable compounds - permanent parts of biological machines.

There is another group of organic acids, which cannot be dispensed with in the creation of biological structures - these are fatty acids. Fatty acid molecules arerelatively long chains, at one end of which there is a polar group - carboxyl COOH. In nature, there are most often fatty acids with a straight chain and an even number of carbon atoms; in plants, fatty acids containing cycles have been found (in particular, chaulmuric acid has a cyclopentene ring in the molecule).

Saturated fatty acids include: butyric, caproic, caprylic, palmitic, stearic, etc. Unsaturated fatty acids include crotonic, oleic, linoleic, linolenic.

Unsaturated acids appear to be essential for the normal functioning of the body, although their specific functions are not entirely clear. Fatty acids are commonly found in foods as esters of glycerol (fats and oils) called triglycerides. In these esters, three glycerol hydroxyls form ester bonds with three acid residues R 1 , R 2 , R3.

Some fats are associated with cell proteins; most of the fat forms deposits, which are the body's fuel reserve. Fats (triglycerides) are also found in the blood, where they enter from the intestinal mucosa through the lymphatic pathways. In the blood, fats with a small admixture of protein and some lipids form small particles (chylomicrons), the size of which is about 50 mk. When fats are oxidized, a lot of heat is released (twice as much as when the same amount of carbohydrates is oxidized), so fat is an energy substance.

Oxidation of fats occurs mainly in the kidneys, liver, but can also occur in the tissues of other organs.

In the process of oxidation, catalyzed by a number of enzymes, “fragments” containing only two carbon atoms are sequentially split off from a long fatty acid molecule. In order for this reaction to start, repeat the required number of times and turn fatty acid in water, carbon monoxide (IV), acetoacetic acid, the participation of a special one - coenzyme A (CoA) and adenosine triphosphoric acid (ATP) turned out to be necessary. We will return to this issue later.

Fats are insoluble in water, but can be obtained in the form of thin emulsions. Fat emulsification is facilitated by bile salts (glycocholic and taurocholic).

Article on organic acids

Found in pure form in plants, as well as taking the form of salts or esters - organic compounds

In the free state, such polybasic hydroxy acids are found quite often in fruits, while compounds are characteristic primarily of other elements of plants, such as stems, leaves, and so on. If you look at organic acids, their list is constantly growing and, on the whole, is not closed, that is, regularly replenished. Already discovered such acids as:

adipic,

benzoic,

dichloroacetic,

Valerian,

Glycolic,

Glutaric,

Lemon,

Maleic,

margarine,

oil,

Dairy,

Monochloroacetic,

Ant,

propionic,

salicylic,

Trifluoroacetic,

Fumarovaya,

Acetic,

sorrel,

Apple,

Succinic and many other organic acids.

Often such substances can be found in fruit and berry plants. Fruit plants include apricots, quince, cherry plum, grapes, cherries, pears, citrus fruits and apples, while berry plants include lingonberries, cherries, blackberries, cranberries, gooseberries, raspberries, black currants. They are based on tartaric, citric, salicylic, oxalic and organic acids, including many

To date, many properties of acids have been studied directly in the field of pharmacology and biological effects on the human body. For example:

• firstly, organic acids are quite significant components of metabolism (metabolism, namely proteins, fats and carbohydrates);
• secondly, they cause secretory work salivary glands; promote acid-base balance;
• thirdly, they take a significant part in increasing the separation of bile, gastric and pancreatic juices;
• and finally, they are antiseptics.

Their acidity ranges from four whole to five and five.

In addition, organic acids play an important role in the food industry, acting as a direct indicator of the quality or poor quality of products. For the latter, the ion chromatography method is very often used, in which not only organic acids, but also inorganic ions can be detected at a time. With this method, conductometric detection with suppression of background electrical conductivity shows a result almost ten times more accurate than detection with low rates wavelength ultraviolet radiation.
Identification of the profile of organic acids in fruit juices is necessary not only to establish the quality of the drink, its acceptability for consumption, but also contributes to the identification of counterfeit.
If we consider the properties of carboxylic acids directly, then they primarily include:

Giving red color to litmus paper;

Easy solubility in water;

Present sour taste.

They are also an important electrical conductor. According to the strength of decomposition, absolutely all acids belong to the weak group of electrolytes, with the exception, of course, of formic acid, which, in turn, occupies an average value in terms of intensity. The height of the molecular weight of a carboxylic acid affects the strength of decomposition and has an inverse relationship. With the help of specifically defined metals, it becomes possible to isolate hydrogen and salt from acids, which occurs much more slowly than when interacting with something like sulfuric or hydrochloric. Salts also appear when exposed to basic oxides and bases.