home > Physical training > Properties of alcohols, aldehydes, acids, esters, phenol. Substituents on the benzene ring are divided into two groups Reactions of the benzene ring


Properties of alcohols, aldehydes, acids, esters, phenol. Substituents on the benzene ring are divided into two groups Reactions of the benzene ring




pyrocatechin

resorcinol

hydroquinone

phloroglucinol

pyrogallol

For the systematic name of phenols, the IUPAC substitution nomenclature is used, according to which phenols are considered as hydroxyl derivatives of benzene. So, phenol itself, the ancestor of the series, must have the strict name hydroxybenzene. However, in many cases, benzene derivatives containing a hydroxo group in the ring are considered to be phenol derivatives, which is reflected in the name. For example:

C2 H5

3-ethylphenol

3-bromo-2,4-dinitrophenol

(1-hydroxy-3-ethylbenzene)

(1-hydroxy-3-bromo-2,4-dinitrobenzene)

For aromatic alcohols, names according to substitutional nomenclature are constructed in the same way as for aliphatic ones. In this case, the parent structure is the side aliphatic chain, since the functional group is located there. For example:

CH2-OH

CH2-CH-OH

phenylmethanol

1-phenylpropan-2-ol

In addition, for the name of aromatic alcohols, as well as aliphatic, radical-functional and rational nomenclature can be used. So, phenylmethanol, the simplest representative of aromatic alcohols, according to the radical-functional nomenclature will be called ben-

zyl alcohol.

Phenols and aromatic alcohols are structural isomers (for example, cresols are isomeric to benzyl alcohol). In addition, other types of isomerism can be observed, as well as for many derivatives of hydrocarbons.

10.5.2. STRUCTURE OF PHENOL AND BENZYL ALCOHOL

In the phenol molecule, the nature and direction of the electric

tron effects is the same as in halobenzenes. That

is, the oxygen atom of the hydroxo group interacts with

benzene ring through –I- and +M-effects.

However (!) In the phenol molecule + M -effect is greater - I -

effect (modulo). A significant positive mesomeric effect is explained by the correspondence of the geometric configuration of the outer (interacting) p-orbitals of carbon and oxygen, both of these atoms are atoms of the II period of the Periodic Table of chemical elements. As a result, the total electronic effect that the hydroxo group has with respect to the benzene ring is the donor effect.

Due to p--conjugation, the degree of double bonding between carbon and oxygen increases: this bond has a 23.7% character. The structure of phenol should also be similar to the structure of non-existent vinyl alcohol (chap. 5.1.2, 5.3.1). But unlike vinyl alcohol, phenol does not isomerize due to its stable aromatic system.

The length of the C–O bond in phenol is shorter than in alcohols (in phenol 0.136 nm, in methanol 0.143 nm), and the strength of this bond is greater than in alcohols. In addition, due to p--conjugation, an electron density deficit (a partial positive charge) appears on the oxygen atom, due to which the polarity of the O–H bond increases so much that phenols exhibit the properties of weak acids.

The positive mesomeric effect of the hydroxo group leads to a significant increase in the electron density on the benzene ring and mainly in the o- and p-positions (chapter 10.1.1). This state corresponds to the meso formula

In the benzyl alcohol molecule, the oxygen atom of the hydroxo group is not directly bonded to the aromatic ring, so the conjugation between

them impossible. The hydroxo group affects the benzene

ring only by inductive effect

(–I effect), thereby reducing the magnitude of the electron

noah density on it. But -electronic system ben-

ash ring can interact with C–H bonds of the -carbon atom (superconjugation similar to that observed in toluene). Therefore, the electron density in the aromatic ring as a whole is somewhat lower than in benzene, but the ortho and especially para positions experience this decrease to a lesser extent. The length and strength of the C–O and O–H bonds differ little from those for aliphatic alcohols, since the effect of the benzene ring on the C–O–H fragment is small.

10.5.3. PHYSICAL AND CHEMICAL PROPERTIES OF PHENOLS

According to their state of aggregation, phenols are colorless solids or, more rarely, liquids with a strong peculiar odor. When stored in air, they gradually oxidize and, as a result, acquire a color from pink to yellow-brown.

Phenols are sparingly soluble in water, and their high boiling points are due to the presence of intermolecular hydrogen bonds (similar to alcohols).

The chemical properties of phenols are due to the mutual influence of the hydroxo group and the benzene ring; therefore, they are characterized by both reactions along the benzene ring and reactions involving the hydroxyl group.

10.5.3.1. Acid-base properties

The acidic properties of phenols are more pronounced than those of alcohols (aliphatic and aromatic). This is due to a much stronger polarization of the О–Н bond due to the shift of the electron density from the oxygen atom to the benzene ring:

The acidic properties of phenols can also be explained by the greater stability of the phenolate ion, which is formed during the dissociation of phenol. In the phenolate anion, the electron system of the aromatic ring takes part in the delocalization of the negative charge:

However, the acidic properties of phenols are less pronounced than those of carboxylic acids, the dissociation of phenols in aqueous solutions proceeds, but the equilibrium of this reaction is shifted to the left. The pKa value for phenol and its homologues ranges from 9.9 to 10.4, while for acetic acid pKa = 4.76, and for carbonic acid pKa = 6.35 (according to the first stage of dissociation). That is, phenol does not interact with metal bicarbonates, but can interact with medium salts of carbonic acid, turning them into acidic salts, since carbonic acid is weaker than phenol in the second stage of dissociation.

OH+NaHCO3

OH + Na2CO3 ONa + NaHCO3

Phenol salts, phenolates, when interacting with carbonic acid, turn into phenol:

ONa + H2 CO3 OH + NaHCO3

The introduction of electron-donor or acceptor substituents into the aromatic ring of phenol (especially in the o- and p-positions) respectively reduces or increases its acidic properties. This effect is analogous to the effect of substituents on the aromatic ring of sulfonic acids (chapter 10.3.3.4). Just as in arenesulfonic acids, electron-withdrawing substituents increase the acidic properties due to more complete delocalization of the negative charge in the anion; electron-donating substituents, on the contrary,

reduce the acidic properties, since in this case their electronic effect prevents delocalization of the anion charge:

For the same reasons (due to p-conjugation, in which the lone electron pair of oxygen electrons participates), the basicity of phenols is significantly reduced compared to alcohols.

10.5.3.2. Nucleophilic properties

Due to the +M effect of the hydroxyl group in the phenol molecule, both basic and nucleophilic properties are reduced. Therefore, reactions in which phenol plays the role of a nucleophile proceed with difficulty. An alkaline environment contributes to the increase in the reactivity of phenol, while the phenol molecule passes into the phenolate ion. These reactions are alkylation and acylation.

Alkylation (formation of ethers) . In the general case, more

The local environment promotes the reaction according to the S N 2 mechanism; therefore, substrates having an accessible electrophilic reaction center with a high effective positive charge should be more easily alkylated. Such substrates can be primary alkyl halides and, above all,

Derivatives of methane.

O-CH2-R

R-CH2 Br

In some cases, dimethyl sulfate is used as a methylating agent, in particular, in the synthesis of methyl esters of hydroquinone, m-cresol, 4-methyl-2-nitrophenol, etc. For example:

OCH3

(CH3 )2 SO4 / OH-

4-methyl-2-nitrophenol

4-methyl-1-methoxy-2-nitrobenzene

The same method can be used to obtain o- and p-nitroanisols from o- and p-nitrophenols.

Acylation (formation of esters) . Due to the lowered

phenols can only be attacked by highly reactive acylating agents, such as anhydrides and halides of carboxylic acids. The reaction is carried out in a slightly alkaline medium (usually in the presence of carbonates):

Na2CO3

NaCl

NaHCO3

Acylation salicylic acid acetic anhydride is used in the manufacture of the drug aspirin:

+ (CH3CO)2O

CH3COOH

O-C-CH3

salicylic acid

(O-acetylsalicylic acid)

Esterification under the action of carboxylic acids usually does not occur for phenols and becomes possible only in the presence of strong water-removing agents (PCl 3 , POCl 3 , P 2 O 5 ). This reaction is used in the manufacture of the drug salol:

10.5.3.3. Electrophilic substitution

Phenols, like many aromatic compounds, are capable of undergoing electrophilic substitution reactions (S E ). Moreover, the reactions of phenols with electrophilic reagents proceed much more easily than benzene and arenes. This is due to the large +M effect exerted by the hydroxyl group in relation to the benzene ring (chapter 10.1.1). As a result, the electron density on the ring is increased, and this increase is observed mainly in the o- and p-positions.

Therefore, the mechanism of interaction of phenol with an electrophilic particle can be represented as follows:

OH H

The entry of the electrophile into the o- and p-positions of the benzene ring can also be explained by comparing the stability of the resulting complexes.

Let us consider some examples and features of S E reactions for phenols.

Halogenation flows easily. No catalyst required. rirovanie

the end product may be pentachlorophenol. Bromination is usually carried out in dilute aqueous solutions.

3 Br2

3HBr

2,4,4,6-tetrabromocyclohex-2,5-dien-1-one

Nitration can be carried out with both concentrated and dilute nitric acid. Concentrated nitric acid nitrates phenol immediately to di- and trinitro derivatives, for example:

NO2+

in this case, a strong resinification of phenol occurs.

In the molecules of phenols and their esters, not only the substitution of the hydrogen atom, but also the spatially accessible alkyl groups can occur:

H3 C CH

H3 C CH

H3 CO

NO2+

H3 CO

NO2+

H3 C CH

CH CH3

H3 CO

H3 CO

CH(CH3 )2 +

H3 C CH

H3 CO

H3 CO

The action of dilute nitric acid on phenols at room temperature leads to ortho- and para-substituted mononitrophenols:

HNO3 +H2O

Considering that the nitronium cation is not formed in dilute acid and therefore nitration by the electrophilic mechanism is impossible, the reaction in this case is oxidative nitrosation (due to nitrogen dioxide contained in nitric acid):

2 NO 2

HNO3

HNO2

HNO3

HNO2

Therefore, instead of dilute nitric acid, a mixture of nitric and nitrous acids can be used to carry out the mononitration.

In addition, nitrosation is also used to determine phenols ( Lieberman reaction). Phenol is treated with concentrated sulfuric acid and a few drops of an aqueous solution of sodium nitrite are added. When diluted, the solution acquires a red color; when alkali is added, the color turns blue. This color reaction is explained by the formation of indophenol, the anion of which has a blue color:

N-OH2

indophenol (red color)

O N O-

Blue colour

Sulfonation of phenols leads to phenolsulfonic acids. The ratio of ortho- and para-isomers is determined by the reaction temperature. The ortho-isomer is already formed at 15°C, but at 100°C and above it rearranges into the more stable n-isomer.

288K

SO3H

H2SO4

373K

373K

SO3H

Alkylation. In addition to alkylation at the oxygen atom, which proceeds in an alkaline environment and leads to the formation of simple (alkylaryl) ethers, the reaction can proceed at the benzene ring. Alkylation in this case requires the use of acid catalysts. Alcohols and alkenes are usually used as alkylating agents in the presence of protic acids (H 2 SO 4 , H 3 PO 4 ) or Lewis acids (BF 3 ):

R+ [BF3 OH]

R-OH + BF3

5. Isomerism, characteristic of organic compounds, in the molecules of which there is a benzene ring.

This type of isomerism is possible in the presence of two substituents in the benzene ring. Depending on the location of the substituents in the benzene ring, ortho-, meta- and para-isomerism are distinguished. So, for example, if there are two substituents in the benzene ring - a methyl radical and a hydroxyl group, then such a substance is called cresol. And depending on the location of these groups in the benzene ring, there are three different substances:

It should be noted that many compounds having the same molecular formula may differ from each other in various types of isomerism, for example:

These isomeric substances differ simultaneously in the isometry of the carbon chain and the isometry of the position of the functional group - NH 2.

III. For example, sodium displaces only one hydrogen atom from an ethanol molecule. Therefore, this hydrogen atom is more mobile.

From this we can derive the structural formula of ethanol:

H-C-C-H

On the contrary, knowing the structural formula of ethanol, one can predict that sodium will displace only one hydrogen atom, which is associated with an oxygen atom.

Studying the properties of glucose, we were convinced that there are five groups in its molecule - it and one aldehyde group. On the contrary, knowing the structural formula of glucose, one can foresee that glucose will exhibit the properties of aldehydes and alcohols.

IV. The chemical properties of phenol are due to the presence of a hydroxyl group and a benzal nucleus in its molecule, which mutually influence each other. The presence of a hydroxyl group predetermines the similarity of phenol with alcohols:

1. Similarity similar to the properties of alcohols:

2C 6 H 5 OH + 2 Na → 2C 6 H 5 ONa + H 2

2. Property that differs from the properties of alcohols:

C 6 H 5 OH + NaOH → C 6 H 5 ONa + H 2 O


Bromination reaction

4. Nitration reaction


The influence of the benzene nucleus on the hydroxyl group causes a greater mobility of its hydrogen atom. Therefore, phenol, unlike alcohols, reacts with alkalis, i.e. has the properties of weak acids. It is sometimes called carbolic acid. This is due to the fact that the benzene nucleus pulls the electrons of the oxygen atom of the hydroxyl group towards itself. To compensate for this, the oxygen atom pulls the electron density away from the hydrogen atom more strongly. As a result, the cavalent bond between the oxygen and hydrogen atoms becomes more polar, and the hydrogen atom becomes more mobile. The hydroxyl group, in turn, gives the hydrogen atoms greater mobility in positions 2, 4, 6. This is one of many examples that confirm the thesis of A.M. Butlerov on the mutual influence of atoms in molecules.

The chemical properties of aniline are due to the presence of an amino group - NH 2 and a benzene nucleus in its molecule. Aniline is a weaker base. To answer this question, we need to recall the mutual influence of atoms and atomic groups in molecules. As in phenol molecules (this was discussed earlier), the benzene nucleus somewhat pulls the free electron pair away from the nitrogen atom of the amino group. As a result, the electron density on the nitrogen atom in the aniline molecule decreases and it attracts protons to itself more weakly, i.e. the basic properties of aniline are weakened. The most important properties of aniline:

1. Reacts with acids to form salts:

C 6 H 5 - NH 2 + HCl → C 6 H 5 NH 3 Cl

2. The resulting salts react with alkalis and aniline is released again:

C 6 H 5 - NH 3 Cl + NaOH → C 6 H 5 NH 2 + Na Cl + H 2 O

3. Vigorously participates in substitution reactions, for example, it reacts with bromine water to form 2, 4, 6 - tribromaniline:


Mutual influence of atoms in molecules of halogenated hydrocarbons.

The most characteristic chemical property of saturated hydrocarbons is substitution reactions. An example of such a reaction is the interaction of saturated hydrocarbons with halogens. Other saturated hydrocarbons react similarly with halogens:

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

Halogenated hydrocarbons have some features. According to the theory of A.M. Butlerov, this is due to the mutual influence of atoms and atomic groups in chemical compounds. From the point of view of modern ideas about electron clouds and their mutual overlap, taking into account the electronegativity of chemical elements, the mutual influence of atoms and atomic groups, for example, in methyl chioride, is explained as follows. Chlorine atoms have more electronegativity than carbon atoms. Therefore, the electron density of the bond is shifted from the carbon atom towards the chlorine atom. As a result, the chlorine atom acquires a partial negative charge, and the carbon atom acquires a partial positive charge. The acquired partial charges are denoted δ+ and δ-:

The influence of the chlorine atom extends not only to the carbon atom, but also to the hydrogen atoms. Because of this, the electron density of hydrogen atoms shifts towards the carbon atom and the chemical bonds between hydrogen and carbon atoms become more polar. As a result, the hydrogen atoms in the methyl chloride molecule are less strongly bonded to the carbon atom and are more easily replaced by chlorine than the first hydrogen atom in the methane molecule. Due to the shift of electron densities from the hydrogen atom to the carbon atom, the value of the positive charge of the latter decreases. Therefore, the covalent bond between carbon and chlorine atoms becomes less polar and stronger.

From the point of view of the ionic mechanism, the essence of V.V. Markovnikov during the interaction of propylene with hydrogen bromide is explained as follows: in the propylene molecule, as a result of a shift in electron density, the second carbon atom, which is associated with the methyl radical, is more positively charged than the first.

The electronegativity value of carbon atoms is greater than that of hydrogen atoms. Therefore, the third carbon atom of the methyl group, as a result of the electron density shift from three hydrogen atoms, acquires a relatively larger negative charge than other carbon atoms. This excess negative charge, in turn, shifts the mobile P-electron clouds from the second to the first carbon atom. As a result of this shift, the first carbon atom acquires a greater negative charge, and the second becomes more positive. As a result, the hydrogen atom (+) is attached to the carbon atom (-), and the halogen (-) is attached to the carbon atom (+).

Benzene is very resistant to oxidation. In contrast, aromatic hydrocarbons with side chains are oxidized relatively easily.

1. Under the action of energetic oxidants (K Mn O 4) on benzene homolone, only side chains are oxidized. If, for example, 2-3 ml of toluene is poured into a test tube, then a solution of potassium permanganate is added to it and heated, then it can be seen that the violet color of the solution gradually fades. This is because, under the action of potassium permanganate, the methyl group of toluene is oxidized and converted into a group

O
//
- C
\
Oh
O
//

C 6 H 5 -CH 3 + 3O → C 6 H 5 -C + H 2 O
\
Oh

It is known that methane and other saturated hydrocarbons are very resistant to the action of oxidizing agents. However, the methyl group in the toluene molecule is oxidized relatively easily. This is due to the influence of the benzene ring. From the above examples of substitution and oxidation reactions, it follows that not only the methyl group affects the benzene ring, but the benzene ring also affects the methyl group, i.e. their influence depends.

Characteristic chemical properties of saturated monohydric and polyhydric alcohols, phenol

Limit monohydric and polyhydric alcohols

Alcohols (or alkanols) are organic substances whose molecules contain one or more hydroxyl groups ($—OH$ groups) connected to a hydrocarbon radical.

According to the number of hydroxyl groups (atomicity), alcohols are divided into:

- monoatomic, for example:

$(CH_3-OH)↙(methanol(methyl alcohol))$ $(CH_3-CH_2-OH)↙(ethanol(ethyl alcohol))$

— diatomic (glycols), for example:

$(OH-CH_2-CH_2-OH)↙(ethanediol-1,2(ethylene glycol))$

$(HO-CH_2-CH_2-CH_2-OH)↙(propanediol-1,3)$

— triatomic, for example:

According to the nature of the hydrocarbon radical, the following alcohols are distinguished:

— marginal containing only saturated hydrocarbon radicals in the molecule, for example:

— unlimited containing multiple (double and triple) bonds between carbon atoms in the molecule, for example:

$(CH_2=CH-CH_2-OH)↙(propen-2-ol-1 (allylic alcohol))$

— aromatic, i.e. alcohols containing a benzene ring and a hydroxyl group in the molecule, connected to each other not directly, but through carbon atoms, for example:

Organic substances containing hydroxyl groups in the molecule that are directly connected to the carbon atom of the benzene ring differ significantly in chemical properties from alcohols and therefore stand out in an independent class of organic compounds - phenols. For example:

There are also polyhydric (polyhydric) alcohols containing more than three hydroxyl groups in the molecule. For example, the simplest six-hydric alcohol hexaol (sorbitol):

Nomenclature and isomerism

When forming the names of alcohols, a generic suffix is ​​added to the name of the hydrocarbon corresponding to the alcohol. -ol. The numbers after the suffix indicate the position of the hydroxyl group in the main chain, and the prefixes di-, tri-, tetra- etc. - their number:

In the numbering of carbon atoms in the main chain, the position of the hydroxyl group takes precedence over the position of multiple bonds:

Starting from the third member of the homologous series, alcohols have an isomerism of the position of the functional group (propanol-1 and propanol-2), and from the fourth - the isomerism of the carbon skeleton (butanol-1, 2-methylpropanol-1). They are also characterized by interclass isomerism - alcohols are isomeric to ethers:

$(CH_3-CH_2-OH)↙(ethanol)$ $(CH_3-O-CH_3)↙(dimethyl ether)$

alcohols

physical properties.

Alcohols can form hydrogen bonds both between alcohol molecules and between alcohol and water molecules.

Hydrogen bonds arise from the interaction of a partially positively charged hydrogen atom of one alcohol molecule and a partially negatively charged oxygen atom of another molecule. It is due to hydrogen bonds between molecules that alcohols have abnormally high boiling points for their molecular weight. Thus, propane with a relative molecular weight of $44$ is a gas under normal conditions, and the simplest of alcohols is methanol, with a relative molecular weight of $32$, under normal conditions it is a liquid.

The lower and middle members of the series of saturated monohydric alcohols, containing from $1$ to $11$ carbon atoms, are liquids. Higher alcohols (beginning with $C_(12)H_(25)OH$) are solids at room temperature. Lower alcohols have a characteristic alcoholic smell and a burning taste, they are highly soluble in water. As the hydrocarbon radical increases, the solubility of alcohols in water decreases, and octanol is no longer miscible with water.

Chemical properties.

The properties of organic substances are determined by their composition and structure. Alcohols confirm the general rule. Their molecules include hydrocarbon and hydroxyl radicals, so the chemical properties of alcohols are determined by the interaction and influence of these groups on each other. The properties characteristic of this class of compounds are due to the presence of a hydroxyl group.

1. Interaction of alcohols with alkali and alkaline earth metals. To reveal the effect of a hydrocarbon radical on a hydroxyl group, it is necessary to compare the properties of a substance containing a hydroxyl group and a hydrocarbon radical, on the one hand, and a substance containing a hydroxyl group and not containing a hydrocarbon radical, on the other. Such substances can be, for example, ethanol (or other alcohol) and water. Hydrogen of the hydroxyl group of alcohol molecules and water molecules can be reduced by alkali and alkaline earth metals (replaced by them):

$2Na+2H_2O=2NaOH+H_2$,

$2Na+2C_2H_5OH=2C_2H_5ONa+H_2$,

$2Na+2ROH=2RONa+H_2$.

2. Interaction of alcohols with hydrogen halides. Substitution of a hydroxyl group for a halogen leads to the formation of haloalkanes. For example:

$C_2H_5OH+HBr⇄C_2H_5Br+H_2O$.

This reaction is reversible.

3. Intermolecular dehydration of alcohols- splitting of a water molecule from two alcohol molecules when heated in the presence of water-removing agents:

As a result of intermolecular dehydration of alcohols, ethers. So, when ethyl alcohol is heated with sulfuric acid to a temperature of $100$ to $140°C$, diethyl (sulfuric) ether is formed:

4. Interaction of alcohols with organic and inorganic acids to form esters ( esterification reaction):

The esterification reaction is catalyzed by strong inorganic acids.

For example, when ethyl alcohol and acetic acid react, acetic ethyl ester is formed - ethyl acetate:

5. Intramolecular dehydration of alcohols occurs when alcohols are heated in the presence of dehydrating agents to a temperature higher than the intermolecular dehydration temperature. As a result, alkenes are formed. This reaction is due to the presence of a hydrogen atom and a hydroxyl group at neighboring carbon atoms. An example is the reaction of obtaining ethene (ethylene) by heating ethanol above $140°C$ in the presence of concentrated sulfuric acid:

6. Alcohol oxidation usually carried out with strong oxidizing agents, for example, potassium dichromate or potassium permanganate in an acidic medium. In this case, the action of the oxidizing agent is directed to the carbon atom that is already associated with the hydroxyl group. Depending on the nature of the alcohol and the reaction conditions, various products can be formed. Thus, primary alcohols are first oxidized to aldehydes and then in carboxylic acids:

When secondary alcohols are oxidized, ketones are formed:

Tertiary alcohols are quite resistant to oxidation. However, under harsh conditions (strong oxidizing agent, high temperature), oxidation of tertiary alcohols is possible, which occurs with the breaking of carbon-carbon bonds closest to the hydroxyl group.

7. Dehydrogenation of alcohols. When alcohol vapor is passed at $200-300°C$ over a metal catalyst, such as copper, silver or platinum, primary alcohols are converted into aldehydes, and secondary alcohols into ketones:

The presence of several hydroxyl groups in an alcohol molecule at the same time determines the specific properties polyhydric alcohols, which are capable of forming water-soluble bright blue complex compounds when interacting with a fresh precipitate of copper (II) hydroxide. For ethylene glycol, you can write:

Monohydric alcohols are not able to enter into this reaction. Therefore, it is a qualitative reaction to polyhydric alcohols.

Phenol

The structure of phenols

The hydroxyl group in the molecules of organic compounds can be connected directly to the aromatic nucleus, or it can be separated from it by one or more carbon atoms. It can be expected that, depending on this property, substances will differ significantly from each other due to the mutual influence of groups of atoms. Indeed, organic compounds containing the aromatic phenyl radical $C_6H_5$—, directly bonded to the hydroxyl group, exhibit special properties that differ from those of alcohols. Such compounds are called phenols.

Phenols are organic substances whose molecules contain a phenyl radical associated with one or more hydroxo groups.

Like alcohols, phenols are classified by atomicity, i.e. by the number of hydroxyl groups.

Monatomic phenols contain one hydroxyl group in the molecule:

Polyhydric phenols contain more than one hydroxyl group in the molecules:

There are other polyhydric phenols containing three or more hydroxyl groups in the benzene ring.

Let's get acquainted in more detail with the structure and properties of the simplest representative of this class - phenol $C_6H_5OH$. The name of this substance formed the basis for the name of the entire class - phenols.

Physical and chemical properties.

physical properties.

Phenol is a solid, colorless, crystalline substance, $t°_(pl.)=43°С, t°_(boiling)=181°С$, with a sharp characteristic odor. Poisonous. Phenol is slightly soluble in water at room temperature. An aqueous solution of phenol is called carbolic acid. It causes burns on contact with the skin, so phenol must be handled with care!

Chemical properties.

acid properties. As already mentioned, the hydrogen atom of the hydroxyl group has an acidic character. The acidic properties of phenol are more pronounced than those of water and alcohols. Unlike alcohols and water, phenol reacts not only with alkali metals, but also with alkalis to form phenolates:

However, the acidic properties of phenols are less pronounced than those of inorganic and carboxylic acids. For example, the acidic properties of phenol are about $3000$ times weaker than those of carbonic acid. Therefore, by passing carbon dioxide through an aqueous solution of sodium phenolate, free phenol can be isolated:

Adding hydrochloric or sulfuric acid to an aqueous solution of sodium phenolate also leads to the formation of phenol:

Qualitative reaction to phenol.

Phenol reacts with iron(III) chloride to form an intensely purple complex compound.

This reaction makes it possible to detect it even in very limited quantities. Other phenols containing one or more hydroxyl groups in the benzene ring also give a bright blue-violet color when reacted with iron (III) chloride.

Reactions of the benzene ring.

The presence of a hydroxyl substituent greatly facilitates the course of electrophilic substitution reactions in the benzene ring.

1. Bromination of phenol. Unlike benzene, phenol bromination does not require the addition of a catalyst (iron(III) bromide).

In addition, the interaction with phenol proceeds selectively (selectively): bromine atoms are sent to ortho- and para positions, replacing the hydrogen atoms located there. The selectivity of the substitution is explained by the features of the electronic structure of the phenol molecule discussed above.

So, when phenol reacts with bromine water, a white precipitate is formed 2,4,6-tribromophenol:

This reaction, as well as the reaction with iron (III) chloride, serves for the qualitative detection of phenol.

2. Phenol nitration also occurs more easily than the nitration of benzene. The reaction with dilute nitric acid proceeds at room temperature. The result is a mixture ortho- and pair- isomers of nitrophenol:

When concentrated nitric acid is used, an explosive is formed - 2,4,6-trinitrophenol(picric acid):

3. Hydrogenation of the aromatic ring of phenol in the presence of a catalyst occurs easily:

4.Polycondensation of phenol with aldehydes, in particular with formaldehyde, occurs with the formation of reaction products - phenol-formaldehyde resins and solid polymers.

The interaction of phenol with formaldehyde can be described by the scheme:

You have probably noticed that “mobile” hydrogen atoms are preserved in the dimer molecule, which means that further continuation of the reaction is possible with a sufficient amount of reagents:

Reaction polycondensation, those. the polymer production reaction, proceeding with the release of a low-molecular by-product (water), can continue further (until one of the reagents is completely consumed) with the formation of huge macromolecules. The process can be described by the overall equation:

The formation of linear molecules occurs at ordinary temperature. Carrying out this reaction when heated leads to the fact that the resulting product has a branched structure, it is solid and insoluble in water. As a result of heating a linear phenol-formaldehyde resin with an excess of aldehyde, solid plastic masses with unique properties are obtained. Polymers based on phenol-formaldehyde resins are used for the manufacture of varnishes and paints, plastic products that are resistant to heating, cooling, water, alkalis and acids, and have high dielectric properties. Polymers based on phenol-formaldehyde resins are used to make the most critical and important parts of electrical appliances, power unit cases and machine parts, the polymer base of printed circuit boards for radio devices. Adhesives based on phenol-formaldehyde resins are able to reliably connect parts of various nature, maintaining the highest bond strength in a very wide temperature range. Such glue is used to fasten the metal base of lighting lamps to a glass bulb. Now you understand why phenol and products based on it are widely used.

Characteristic chemical properties of aldehydes, saturated carboxylic acids, esters

Aldehydes and ketones

Aldehydes are organic compounds whose molecules contain a carbonyl group. , connected to a hydrogen atom and a hydrocarbon radical.

The general formula for aldehydes is:

In the simplest aldehyde, formaldehyde, the second hydrogen atom plays the role of a hydrocarbon radical:

A carbonyl group bonded to a hydrogen atom is called aldehyde:

Organic substances in the molecules of which the carbonyl group is bonded to two hydrocarbon radicals are called ketones.

Obviously, the general formula for ketones is:

The carbonyl group of ketones is called keto group.

In the simplest ketone, acetone, the carbonyl group is bonded to two methyl radicals:

Nomenclature and isomerism

Depending on the structure of the hydrocarbon radical associated with the aldehyde group, limiting, unsaturated, aromatic, heterocyclic and other aldehydes are distinguished:

In accordance with the IUPAC nomenclature, the names of saturated aldehydes are formed from the name of an alkane with the same number of carbon atoms in the molecule using the suffix -al. For example:

The numbering of carbon atoms of the main chain starts from the carbon atom of the aldehyde group. Therefore, the aldehyde group is always located at the first carbon atom, and it is not necessary to indicate its position.

Along with the systematic nomenclature, trivial names of widely used aldehydes are also used. These names are usually derived from the names of carboxylic acids corresponding to aldehydes.

For the name of ketones according to the systematic nomenclature, the keto group is denoted by the suffix -he and a number that indicates the number of the carbon atom of the carbonyl group (numbering should start from the end of the chain closest to the keto group). For example:

For aldehydes, only one type of structural isomerism is characteristic - isomerism of the carbon skeleton, which is possible from butanal, and for ketones - also isomerism of the position of the carbonyl group. In addition, they are also characterized by interclass isomerism (propanal and propanone).

Trivial names and boiling points of some aldehydes.

Physical and chemical properties

physical properties.

In an aldehyde or ketone molecule, due to the greater electronegativity of the oxygen atom compared to the carbon atom, the $C=O$ bond is strongly polarized due to the shift in the electron density of the $π$ bond to oxygen:

Aldehydes and ketones are polar substances with excess electron density on the oxygen atom. The lower members of the series of aldehydes and ketones (formaldehyde, acetaldehyde, acetone) are infinitely soluble in water. Their boiling points are lower than those of the corresponding alcohols. This is due to the fact that in the molecules of aldehydes and ketones, unlike alcohols, there are no mobile hydrogen atoms and they do not form associates due to hydrogen bonds. Lower aldehydes have a pungent odor; aldehydes containing from four to six carbon atoms in the chain have an unpleasant odor; higher aldehydes and ketones have floral odors and are used in perfumery.

Chemical properties

The presence of an aldehyde group in a molecule determines the characteristic properties of aldehydes.

recovery reactions.

Addition of hydrogen to aldehyde molecules occurs at the double bond in the carbonyl group:

Aldehydes are hydrogenated as primary alcohols, while ketones are secondary alcohols.

So, when acetaldehyde is hydrogenated on a nickel catalyst, ethyl alcohol is formed, and when acetone is hydrogenated, propanol-2 is formed:

Hydrogenation of aldehydes recovery reaction, at which the oxidation state of the carbon atom in the carbonyl group decreases.

Oxidation reactions.

Aldehydes are able not only to recover, but also oxidize. When oxidized, aldehydes form carboxylic acids. Schematically, this process can be represented as follows:

From propionaldehyde (propanal), for example, propionic acid is formed:

Aldehydes are oxidized even by atmospheric oxygen and such weak oxidizing agents as an ammonia solution of silver oxide. In a simplified form, this process can be expressed by the reaction equation:

For example:

More precisely, this process is reflected by the equations:

If the surface of the vessel in which the reaction is carried out was previously degreased, then the silver formed during the reaction covers it with an even thin film. Therefore, this reaction is called the reaction "silver mirror". It is widely used for making mirrors, silvering decorations and Christmas decorations.

Freshly precipitated copper (II) hydroxide can also act as an oxidizing agent for aldehydes. Oxidizing the aldehyde, $Cu^(2+)$ is reduced to $Cu^+$. The copper (I) hydroxide $CuOH$ formed during the reaction immediately decomposes into red copper (I) oxide and water:

This reaction, like the "silver mirror" reaction, is used to detect aldehydes.

Ketones are not oxidized either by atmospheric oxygen or by such a weak oxidizing agent as an ammonia solution of silver oxide.

Individual representatives of aldehydes and their meaning

Formaldehyde(methanal, formic aldehyde$HCHO$ ) - a colorless gas with a pungent odor and a boiling point of $ -21C ° $, we will readily dissolve in water. Formaldehyde is poisonous! A solution of formaldehyde in water ($40%$) is called formalin and is used for disinfection. In agriculture, formalin is used for dressing seeds, in the leather industry - for processing leather. Formaldehyde is used to obtain urotropin - a medicinal substance. Sometimes compressed in the form of briquettes, urotropin is used as a fuel (dry alcohol). A large amount of formaldehyde is consumed in the production of phenol-formaldehyde resins and some other substances.

Acetic aldehyde(ethanal, acetaldehyde$CH_3CHO$ ) - a liquid with a sharp unpleasant odor and a boiling point of $ 21 ° C $, we will dissolve well in water. Acetic acid and a number of other substances are obtained from acetaldehyde on an industrial scale, it is used for the production of various plastics and acetate fibers. Acetic aldehyde is poisonous!

carboxylic acids

Substances containing one or more carboxyl groups in a molecule are called carboxylic acids.

group of atoms called carboxyl group, or carboxyl.

Organic acids containing one carboxyl group in the molecule are monobasic.

The general formula for these acids is $RCOOH$, for example:

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 limiting, unsaturated, aromatic.

Limiting, or saturated, carboxylic acids are, for example, propanoic (propionic) acid:

or already familiar to us succinic acid.

Obviously, saturated carboxylic acids do not contain $π$-bonds in the hydrocarbon radical. In molecules of unsaturated carboxylic acids, the carboxyl group is bonded to an unsaturated, unsaturated hydrocarbon radical, for example, in acrylic (propene) $CH_2=CH—COOH$ or oleic $CH_3—(CH_2)_7—CH=CH—(CH_2)_7—COOH molecules $ 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

The general principles for the formation of names of carboxylic acids, as well as other organic compounds, have already been considered. 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 (an alkane with the same number of carbon atoms in the molecule) with the addition of the suffix -ov-, ending -and I and the words acid. The numbering of carbon atoms begins with the carboxyl group. For example:

The number of carboxyl groups is indicated in the name by prefixes di-, tri-, tetra-:

Many acids also have historically developed, or trivial, names.

Names of carboxylic acids.

Chemical formula Systematic name of the acid Trivial name for an acid
$H—COOH$ methane Formic
$CH_3—COOH$ Ethane Acetic
$CH_3—CH_2—COOH$ propane propionic
$CH_3—CH_2—CH_2—COOH$ Butane oily
$CH_3—CH_2—CH_2—CH_2—COOH$ Pentane Valerian
$CH_3—(CH_2)_4—COOH$ Hexane Nylon
$CH_3—(CH_2)_5—COOH$ Heptanoic Enanthic
$NEOS-UNSD$ Ethandium sorrel
$HOOS—CH_2—COOH$ Propandioic Malonic
$HOOS—CH_2—CH_2—COOH$ Butane Amber

After getting acquainted with the diverse and interesting world of organic acids, let us consider in more detail the limiting monobasic carboxylic acids.

It is clear that the composition of these acids is expressed by the general formula $C_nH_(2n)O_2$, or $C_nH_(2n+1)COOH$, or $RCOOH$.

Physical and chemical properties

physical properties.

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 of acetic acid). Acids containing from $4$ to $9$ of carbon atoms are viscous oily liquids with an unpleasant odor; containing more than $9$ carbon atoms in a molecule - solid substances that do not dissolve in water. The boiling points of limiting monobasic carboxylic acids increase with an increase in the number of carbon atoms in the molecule and, consequently, with an increase in the relative molecular weight. For example, the boiling point of formic acid is $100.8°C$, acetic acid is $118°C$, and propionic acid is $141°C$.

The simplest carboxylic acid, formic $HCOOH$, having a small relative molecular weight $(M_r(HCOOH)=46)$, under normal conditions is a liquid with a boiling point of $100.8°С$. At the same time, butane $(M_r(C_4H_(10))=58)$ under the same conditions is gaseous and has a boiling point of $-0.5°С$. This discrepancy between boiling points and relative molecular masses 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 and a substantially non-polar hydrocarbon radical. The carboxyl group is attracted to water molecules, forming hydrogen bonds with them:

Formic and acetic acids are infinitely soluble in water. Obviously, with an increase in the number of atoms in the hydrocarbon radical, the solubility of carboxylic acids decreases.

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 strong polar bond between hydrogen and oxygen atoms. Let us consider these properties using the example of water-soluble organic acids.

1. Dissociation with the formation of hydrogen cations and anions of the acid residue:

$CH_3-COOH⇄CH_3-COO^(-)+H^+$

More precisely, this process is described by an equation that takes into account the participation of water molecules in it:

$CH_3-COOH+H_2O⇄CH_3COO^(-)+H_3O^+$

The equilibrium of dissociation of carboxylic acids is shifted to the left; the vast majority of them are weak electrolytes. However, the sour taste of, for example, acetic and formic acids is due to the dissociation into hydrogen cations and anions of acidic residues.

Obviously, the presence of “acidic” hydrogen in the molecules of carboxylic acids, i.e. hydrogen carboxyl group, due to other characteristic properties.

2. Interaction with metals standing in the electrochemical series of voltages up to hydrogen: $nR-COOH+M→(RCOO)_(n)M+(n)/(2)H_2$

So, iron reduces hydrogen from acetic acid:

$2CH_3-COOH+Fe→(CH_3COO)_(2)Fe+H_2$

3. Interaction with basic oxides with the formation of salt and water:

$2R-COOH+CaO→(R-COO)_(2)Ca+H_2O$

4. Interaction with metal hydroxides with the formation of salt and water (neutralization reaction):

$R—COOH+NaOH→R—COONa+H_2O$,

$2R—COOH+Ca(OH)_2→(R—COO)_(2)Ca+2H_2O$.

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:

$CH_3COOH+C_(17)H_(35)COONa→CH_3COONa+C_(17)H_(35)COOH↓$,

$2CH_3COOH+K_2CO_3→2CH_3COOK+H_2O+CO_2$.

6. Interaction of carboxylic acids with alcohols with the formation of esters - the esterification reaction (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 ester formation in the presence of dewatering agents and when the ester is removed from the reaction mixture.

In the reverse esterification reaction, which is called ester hydrolysis (reaction of an ester with water), an acid and an alcohol are formed:

Obviously, to react with carboxylic acids, i.e. polyhydric alcohols, such as glycerol, can also enter into an esterification reaction:

All carboxylic acids (except formic), along with a 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. Multiple bond addition reactions- unsaturated carboxylic acids enter into them. For example, the hydrogen addition reaction is hydrogenation. For an acid containing one $π$-bond in the radical, the equation can be written in general form:

$C_(n)H_(2n-1)COOH+H_2(→)↖(catalyst)C_(n)H_(2n+1)COOH.$

So, when oleic acid is hydrogenated, saturated stearic acid is formed:

$(C_(17)H_(33)COOH+H_2)↙(\text"oleic acid")(→)↖(catalyst)(C_(17)H_(35)COOH)↙(\text"stearic acid") $

Unsaturated carboxylic acids, like other unsaturated compounds, add halogens to the double bond. For example, acrylic acid decolorizes bromine water:

$(CH_2=CH—COOH+Br_2)↙(\text"acrylic(propenoic) acid")→(CH_2Br—CHBr—COOH)↙(\text"2,3-dibromopropanoic acid").$

8. Substitution reactions (with halogens)- saturated carboxylic acids are able to enter into them. For example, by reacting acetic acid with chlorine, various chlorine derivatives of acids can be obtained:

$CH_3COOH+Cl_2(→)↖(Р(red))(CH_2Cl-COOH+HCl)↙(\text"chloroacetic acid")$,

$CH_2Cl-COOH+Cl_2(→)↖(Р(red))(CHCl_2-COOH+HCl)↙(\text"dichloroacetic acid")$,

$CHCl_2-COOH+Cl_2(→)↖(Р(red))(CCl_3-COOH+HCl)↙(\text"trichloroacetic acid")$

Individual representatives of carboxylic acids and their significance

Formic(methane) acid HCOOH— a liquid with a pungent odor and a boiling point of $100.8°C$, highly soluble in water. Formic acid is poisonous Causes burns on contact with skin! The stinging fluid secreted by ants contains this acid. Formic acid has a disinfectant property and therefore finds its application in the food, leather and pharmaceutical industries, and medicine. It is used in dyeing textiles and paper.

Acetic (ethane)acid $CH_3COOH$ is a colorless liquid with a characteristic pungent odor, miscible with water in any ratio. Aqueous solutions of acetic acid are sold under the name of 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, in the leather industry, and in the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, it is used to obtain substances used to control weeds - herbicides.

Acetic acid is the main ingredient wine vinegar, the characteristic smell of which is due precisely to it. It is a product of the oxidation of ethanol and is formed from it when wine is stored in air.

The most important representatives of the highest limiting monobasic acids are palmitic$C_(15)H_(31)COOH$ and stearic$C_(17)H_(35)COOH$ acids. Unlike lower acids, these substances are solid, 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, the most important is oleic acid$C_(17)H_(33)COOH$, or $CH_3 - (CH_2)_7 - CH=CH -(CH_2)_7COOH$. 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$HOOC—COOH$, salts of which are found in many plants, for example, in sorrel and oxalis. Oxalic acid is a colorless crystalline substance, highly soluble in water. It is used in the polishing of metals, in the woodworking and leather industries.

Esters

When carboxylic acids interact with alcohols (esterification reaction), esters:

This reaction is reversible. The reaction products can interact with each other to form the initial substances - alcohol and acid. Thus, the reaction of esters with water—hydrolysis of the ester—is the reverse of the esterification reaction. The chemical equilibrium, which is established when the rates of direct (esterification) and reverse (hydrolysis) reactions are equal, can be shifted towards the formation of ether by the presence of water-removing agents.

Fats- derivatives of compounds that are esters of glycerol and higher carboxylic acids.

All fats, like other esters, undergo hydrolysis:

When hydrolysis of fat is carried out in an alkaline medium $(NaOH)$ and in the presence of soda ash $Na_2CO_3$, it proceeds irreversibly and leads to the formation of not carboxylic acids, but their salts, which are called soaps. Therefore, the hydrolysis of fats in an alkaline environment is called saponification.

Substituents CH 3 , CH 2 R, CHR 2 , CR 3 , OH, OR, NH 2 , NHR, NR 2 , F, Cl, Br, I and others are called deputies first kind. They are capable of donating electrons are electron-donating substituents.

Substituents of the second kind capable of pulling and accepting electrons . These are electron-withdrawing substituents. These include SO 3 H, NO 2 , COOH, COOR, CHO, COR, CN, NH 3 + and others.

In its turn, attacking (replacing) groups can be electrophilic or nucleophilic. Electrophilic reagents serve as electron acceptors in the reaction. In a particular case, this cations. Nucleophilic reagents in the reaction are electron donors. In a particular case, this anions.

If the reagent acts on the nucleus with one substituent, then several options for their interaction can be distinguished:

– deputy of the first kind; electrophilic reagent.

As an example, consider the reaction of toluene nitration with a nitrating mixture (a mixture of nitric and sulfuric acids).

The methyl group in toluene is a first-class orientant. This is an electron donor particle.. That's why core as a whole due to the shift in electron density from the methyl group, it receives a fractional negative charge. The carbon atoms closest to the substituent are also negatively charged.. Subsequent carbons of the cycle acquire alternating charges(alternating effect). The reaction between nitric and sulfuric acids of the nitrating mixture gives several particles, among which is present electrophilic particle NO 2 +(shown above the arrow in brackets in the diagram), which attacks the negatively charged atoms of the cycle. Hydrogen atoms are replaced by a nitro group in ortho- and pair- positions relative to the methyl group. Since the nucleus has a negative charge and the attacking particle is electrophilic(positively charged), the reaction is facilitated and can proceed under milder conditions compared to the nitration of benzene.

– Deputy of the second kind; electrophilic reagent.

The sulfonic group (orientant of the second kind, electron-withdrawing), due to the shift of the electron density towards itself, charges the nucleus as a whole and the nearest carbons of the nucleus positively. The attacking particle is electrophilic. Orientation in meta-position. The substituent hinders the action of the reagent. Sulfonation should be carried out with concentrated sulfuric acid at elevated temperature.

– Deputy of the second kind; nucleophilic reagent.

In accordance with the charges, the nucleophilic particle OK - attacks ortho- and pair-position and substituent facilitates the action of the reagent. Nonetheless, nucleophilic substitution reactions have to be carried out under rather harsh conditions. This is explained by the energetic unfavorability of the transition state in the reaction and by the fact that π The electron cloud of the molecule repels the attacking nucleophilic particle.

– Deputy of the first kind; nucleophilic reagent.

The substituent hinders the action of the reagent. Orientation in meta-position. Such reactions are practically not realized.

If there are several different substituents in the nucleus, then the predominant guiding effect is exerted by the one that has the greatest orienting effect. For example, in electrophilic substitution reactions according to the strength of the orientational action, the substituents can be arranged in the following row:

OH > NH 2 > OR > Cl > I > Br > CH 3; The orienting ability of orientants of the second kind decreases in the following sequence: NO 2 > COOH > SO 3 H. An example is the chlorination reaction ortho-cresol (1-hydroxy-2-methylbenzene):

Both substituents are orientants of the first kind, electron donors. Judging by the charges on the carbon atoms (in parentheses, from the –OH group), the orientation does not match. Because the phenolic hydroxyl is the stronger orientant, mainly products corresponding to the orientation of this group are obtained. Both substituents facilitate the reaction. The reaction is electrophilic due to the interaction of the catalyst with molecular chlorine.

In practice, substitution rules are most often not strictly enforced. Substitution yields all possible products. But there are always more products that must be obtained according to the rules. For example, when toluene is nitrated, 62% ortho-, 33,5 % pair- and 4.5% meta-nitrotoluenes.

Changing the environment (temperature, pressure, catalyst, solvent, etc.) usually has little effect on orientation.

A number of substitution reactions are shown when explaining the orientation rules. Let's look at a few more reactions.

- When chlorine or bromine acts on benzene in the presence of catalysts - carriers of halides, for example, FeCl 3 , AlCl 3 , SnCl 4 and others, hydrogen atoms are sequentially replaced at cyclic carbons by halogen.

In the last electrophilic reaction chlorine as an orientant of the first kind directs the second chlorine atom to ortho- and pair- provisions(mainly in pair-). However, unlike other orientants of the first kind, it makes it difficult to react due to its strongly pronounced electron-acceptor properties, charging the nucleus positively. At the moment of attack of the electrophilic particle, the halogen of the initial compound returns part of the electron density to the nucleus, creating charges on its carbons corresponding to the action of the orientant of the first kind (dynamic orientation effect).

– Halogenation of alkyl-substituted benzenes in the light flows through radical mechanism. and the substitution takes place
α-carbon atom of the side chain:

– When nitrated according to Konovalov(dilute aqueous solution of nitric acid, ~140 °C), proceeding by the radical mechanism, also leads to substitution in side chain:

– Oxidation of benzene and its homologues

benzene ring very difficult to oxidize. However, in the presence of a catalyst V 2 O 5 at a temperature of 400 ° C ... 500 ° C, benzene forms maleic acid:

Benzene homologs upon oxidation give aromatic acids. Moreover, the side chain gives a carboxyl group at the aromatic ring, regardless of its length.

The selection of oxidizing agents can achieve sequential oxidation of the side chains.

Hydroperoxides are formed from alkylbenzenes in the presence of catalysts, the decomposition of which produces phenol and the corresponding ketones.