Benzene ring ch2 oh. Isomerism characteristic of organic compounds whose molecules contain a benzene ring. Nomenclature and isomerism

Characteristic chemical properties of saturated monohydric and polyhydric alcohols, phenol

Saturated 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.

Based on the number of hydroxyl groups (atomicity), alcohols are divided into:

- monoatomic, for example:

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

— dihydric (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:

Based on the nature of the hydrocarbon radical, the following alcohols are distinguished:

— limit 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, connected directly to the carbon atom of the benzene ring, differ significantly in chemical properties from alcohols and therefore are classified as an independent class of organic compounds - phenols. For example:

There are also polyatomic (polyhydric) alcohols containing more than three hydroxyl groups in the molecule. For example, the simplest hexahydric 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 exhibit isomerism of the position of the functional group (propanol-1 and propanol-2), and from the fourth, 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 occur when a partially positively charged hydrogen atom of one alcohol molecule interacts with a partially negatively charged oxygen atom of another molecule. It is thanks to hydrogen bonds between molecules that alcohols have boiling points that are abnormally high for their molecular weight. Thus, propane with a relative molecular weight of $44$ is a gas under normal conditions, and the simplest of alcohols, methanol, with a relative molecular weight of $32$, is a liquid under normal conditions.

The lower and middle members of a series of saturated monohydric alcohols, containing from $1$ to $11$ carbon atoms, are liquids. Higher alcohols (starting from $C_(12)H_(25)OH$) are solids at room temperature. Lower alcohols have a characteristic alcoholic odor and pungent taste; they are highly soluble in water. As the hydrocarbon radical increases, the solubility of alcohols in water decreases, and octanol no longer mixes 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 identify 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. The 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 with 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 off 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. Thus, when ethyl alcohol is heated with sulfuric acid to a temperature from $100$ 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, ethyl acetate is formed - ethyl acetate:

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

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

The oxidation of secondary alcohols produces ketones:

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 rupture 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 the 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 freshly prepared precipitate of copper (II) hydroxide. For ethylene glycol we can write:

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

Phenol

Structure of phenols

The hydroxyl group in molecules of organic compounds can be associated with the aromatic ring directly, or 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 radical phenyl $C_6H_5$—, directly bonded to the hydroxyl group, exhibit special properties that differ from the properties of alcohols. Such compounds are called phenols.

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

Just like alcohols, phenols are classified according to their atomicity, i.e. by the number of hydroxyl groups.

Monohydric phenols contain one hydroxyl group in the molecule:

Polyhydric phenols contain more than one hydroxyl group in molecules:

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

Let's take a closer look at 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, $t°_(pl.)=43°C, t°_(boiling)=181°C$, with a sharp characteristic odor. Poisonous. Phenol is slightly soluble in water at room temperature. An aqueous solution of phenol is called carbolic acid. If it comes into contact with the skin, it causes burns, so phenol must be handled with care!

Chemical properties.

Acidic properties. As already mentioned, the hydrogen atom of the hydroxyl group is acidic in nature. 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 approximately $3000$ 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 allows it to be detected even in very limited quantities. Other phenols containing one or more hydroxyl groups on the benzene ring also produce bright blue-violet colors when reacted with iron(III) chloride.

Reactions of the benzene ring.

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

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

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

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

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

2. Nitration of phenol also occurs more easily than benzene nitration. The reaction with dilute nitric acid occurs at room temperature. As a result, a mixture is formed 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 core 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 following scheme:

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

Reaction polycondensation, those. the polymer production reaction, which occurs with the release of a low-molecular-weight 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 temperatures. 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, hard 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. The most critical and important parts of electrical appliances, power unit housings and machine parts, and the polymer base of printed circuit boards for radio devices are made from polymers based on phenol-formaldehyde resins. Adhesives based on phenol-formaldehyde resins are capable of reliably connecting parts of a wide variety of natures, maintaining the highest joint strength over a very wide temperature range. This glue is used to attach 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 substances whose molecules contain a carbonyl group , connected to a hydrogen atom and a hydrocarbon radical.

The general formula of aldehydes is:

In the simplest aldehyde, formaldehyde, the role of a hydrocarbon radical is played by the second hydrogen atom:

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

Organic substances in whose molecules a carbonyl group is linked 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 linked to two methyl radicals:

Nomenclature and isomerism

Depending on the structure of the hydrocarbon radical associated with the aldehyde group, saturated, 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 the carbon atoms of the main chain begins with the carbon atom of the aldehyde group. Therefore, the aldehyde group is always located at the first carbon atom, and there is no need to indicate its position.

Along with 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.

To name ketones according to systematic nomenclature, the keto group is designated 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:

Aldehydes are characterized by only one type of structural isomerism - isomerism of the carbon skeleton, which is possible with butanal, and for ketones - also isomerism of the position of the carbonyl group. In addition, they are 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 highly polarized due to a shift in the electron density of the $π$ bond towards 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 unlimitedly 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 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.

Hydrogen addition to aldehyde molecules occurs via a double bond in the carbonyl group:

The product of hydrogenation of aldehydes is primary alcohols, and ketones are secondary alcohols.

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

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

Oxidation reactions.

Aldehydes can not only be reduced, but also oxidize. When oxidized, aldehydes form carboxylic acids. This process can be schematically represented as follows:

From propionic aldehyde (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:

This process is more accurately reflected by the equations:

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

Formaldehyde(methanal, formicaldehyde$HCHO$ ) - a colorless gas with a pungent odor and a boiling point of $-21C°$, highly soluble in water. Formaldehyde is poisonous! A solution of formaldehyde in water ($40%$) is called formaldehyde and is used for disinfection. In agriculture, formaldehyde is used to treat seeds, and in the leather industry - for treating leather. Formaldehyde is used to produce methenamine, a medicinal substance. Sometimes methenamine compressed in the form of briquettes is used as fuel (dry alcohol). A large amount of formaldehyde is consumed in the production of phenol-formaldehyde resins and some other substances.

Acetaldehyde(ethanal, acetaldehyde$CH_3CHO$ ) - a liquid with a sharp unpleasant odor and a boiling point of $21°C$, highly soluble in water. Acetic acid and a number of other substances are produced from acetaldehyde on an industrial scale; it is used for the production of various plastics and acetate fiber. Acetaldehyde 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 of 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 saturated, unsaturated, aromatic.

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

or the already familiar succinic acid.

It is obvious that saturated carboxylic acids do not contain $π$ bonds in the 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 (propene) $CH_2=CH—COOH$ or oleic $CH_3—(CH_2)_7—CH=CH—(CH_2)_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

The general principles of the formation of the names of carboxylic acids, as well as other organic compounds, have already been discussed. Let us dwell in more detail on the nomenclature of mono- and dibasic carboxylic acids. The name of a carboxylic acid is derived 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-, endings -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 established, or trivial, names.

Names of carboxylic acids.

Chemical formula Systematic name of acid Trivial name for acid
$H—COOH$ Methane Ant
$CH_3—COOH$ Ethanova Vinegar
$CH_3—CH_2—COOH$ Propane Propionic
$CH_3—CH_2—CH_2—COOH$ Butane Oily
$CH_3—CH_2—CH_2—CH_2—COOH$ Pentanic Valerian
$CH_3—(CH_2)_4—COOH$ Hexane Nylon
$CH_3—(CH_2)_5—COOH$ Heptane Enanthic
$NOOC—COOH$ Ethanedium Sorrel
$NOOC—CH_2—COOH$ Propanedium Malonovaya
$NOOC—CH_2—CH_2—COOH$ Butanediovye Amber

After getting acquainted with the diverse and interesting world of organic acids, we will consider in more detail the saturated monobasic carboxylic acids.

It is clear that the composition of these acids 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 per molecule, are liquids with a characteristic pungent odor (remember the smell of acetic acid). Acids containing from $4$ to $9$ carbon atoms are viscous oily liquids with an unpleasant odor; containing more than $9$ carbon atoms per molecule - solids that do not dissolve in water. The boiling points of saturated monobasic carboxylic acids increase with increasing number of carbon atoms in the molecule and, consequently, with increasing relative molecular weight. For example, the boiling point of formic acid is $100.8°C$, acetic acid is $118°C$, and propionic acid is $141°C$.

The simplest carboxylic acid is formic $HCOOH$, having a small relative molecular weight $(M_r(HCOOH)=46)$, under normal conditions it is a liquid with a boiling point of $100.8°C$. At the same time, butane $(M_r(C_4H_(10))=58)$ under the same conditions is gaseous and has a boiling point of $-0.5°C$. 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 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.

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 accurately, 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 dissociation equilibrium 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 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. hydrogen of the carboxyl group, and other characteristic properties are determined.

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

Thus, 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 - 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 toward ester formation in the presence of dewatering agents and when the ester is removed from the reaction mixture.

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

It is obvious that reacting with carboxylic acids, i.e. Polyhydric alcohols, for example glycerol, can also 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 multiple bonds- they contain unsaturated carboxylic acids. 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:

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

Thus, 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 via a 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 capable of entering into them. For example, by reacting acetic acid with chlorine, various chlorinated acids can be obtained:

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

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

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

Individual representatives of carboxylic acids and their significance

Ant(methane) acid HTSOOKH- a liquid with a pungent odor and a boiling point of $100.8°C$, highly soluble in water. Formic acid is poisonous Causes burns upon contact with 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 used in dyeing fabrics and paper.

Vinegar (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 vinegar ($3-5% solution) and vinegar essence ($70-80% solution) and are widely used in the food industry. Acetic acid is a good solvent for many organic substances and is therefore used in dyeing, tanning, and the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, substances used to control weeds - herbicides - are obtained from it.

Acetic acid is the main component wine vinegar, the characteristic smell of which is due precisely 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$C_(15)H_(31)COOH$ and stearic$C_(17)H_(35)COOH$ acid. Unlike lower acids, these substances are solid and poorly soluble in water.

However, their salts - stearates and palmitates - are highly soluble and have a detergent effect, which is why they are also called soaps. It is clear that these substances are produced on a large scale. Of the unsaturated higher carboxylic acids, 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 odor. 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, such as 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.

Esters

When carboxylic acids react with alcohols (esterification reaction), they form esters:

This reaction is reversible. The reaction products can interact with each other to form the starting materials - alcohol and acid. Thus, the reaction of esters with water—ester hydrolysis—is the reverse of the esterification reaction. The chemical equilibrium established when the rates of forward (esterification) and reverse (hydrolysis) reactions are equal can be shifted towards the formation of ester 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 environment $(NaOH)$ and in the presence of soda ash $Na_2CO_3$, it proceeds irreversibly and leads to the formation not of carboxylic acids, but of 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 substituents first kind. They are capable of donating electrons are electron-donating substituents.

Substituents of the second kind capable of withdrawing 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 (replacement) groups can be electrophilic or nucleophilic. Electrophilic reagents serve as electron acceptors in the reaction. In a particular case, this is cations. Nucleophilic reagents in the reaction are electron donors. In a particular case, this is anions.

If a reagent acts on a 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 nitration of toluene with a nitrating mixture (a mixture of nitric and sulfuric acids).

The methyl group in toluene is an orienting agent of the first kind. 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 of the ring closest to the substituent are also negatively charged. Subsequent carbons in the cycle acquire alternating charges(alternating effect). The reaction between nitric and sulfuric acids of the nitrating mixture produces several particles, among which there is electrophilic particle NO 2 +(shown above the arrow in parentheses 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 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; The reagent is nucleophilic.

In accordance with the charges, the nucleophilic particle OK – attacks ortho- And pair-positions and the substituent facilitate the action of the reagent. Nevertheless, 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 the fact that π -the electron cloud of the molecule repels the attacking nucleophilic particle.

– Deputy of the first kind; The reagent is nucleophilic.

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

If the nucleus has several different substituents, then the predominant guiding effect is exerted by the one that has the greatest orienting effect. For example, in electrophilic substitution reactions Based on 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. The chlorination reaction is given as an example ortho-cresol (1-hydroxy-2-methylbenzene):

Both substituents are orientants of the first kind, electron-donating. Judging by the charges on the carbon atoms (in parentheses - from the –OH group), the orientation does not coincide. Because phenolic hydroxyl is a stronger orienting agent, products are generally obtained that correspond to the orientation of this group. Both substituents facilitate the reaction. The reaction is electrophilic due to the interaction of the catalyst with molecular chlorine.

In practice, the substitution rules are most often not strictly followed. Substitution produces all possible products. But there are always more products that must be produced according to the rules. For example, the nitration of toluene produces 62% ortho-, 33,5 % pair- and 4.5% meta-nitrotoluenes.

Changes in the external environment (temperature, pressure, catalyst, solvent, etc.) usually have little effect on orientation.

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

– When benzene is exposed to chlorine or bromine in the presence of catalysts that transport halogens, for example, FeCl 3, AlCl 3, SnCl 4 and others, the hydrogen atoms at cyclic carbons are successively replaced by halogen.

In the last electrophilic reaction chlorine as an orienting agent 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 expressed electron-acceptor properties, charging the nucleus positively. At the moment of attack electrophilic particle, the halogen of the original compound returns part of the electron density to the nucleus, creating charges on its carbons corresponding to the action of an orientant of the first kind (dynamic orientation effect).

– Halogenation of alkyl-substituted benzenes in light flows through radical mechanism and substitution occurs at
α-carbon side chain atom:

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

– Oxidation of benzene and its homologues

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

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

By selecting oxidizing agents, sequential oxidation of side chains can be achieved.

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

pyrocatechin

resorcinol

hydroquinone

phloroglucinol

pyrogallol

To systematically name phenols, the IUPAC substitutive nomenclature is used, according to which phenols are considered hydroxyl derivatives of benzene. Thus, phenol itself, the ancestor of the series, should have the strict name hydroxybenzene. However, in many cases, benzene derivatives containing a hydroxo group in the ring are considered phenol derivatives, as 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 substitutive nomenclature are constructed in the same way as for aliphatic ones. In this case, the parent structure is the aliphatic side chain, since the functional group is located there. For example:

CH2-OH

CH2-CH-OH

phenylmethanol

1-phenylpropan-2-ol

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

zyl alcohol.

Phenols and aromatic alcohols are structural isomers (for example, cresols are isomeric with benzyl alcohol). In addition, other types of isomerism may be observed, as is the case with many hydrocarbon derivatives.

10.5.2. STRUCTURE OF PHENOL AND BENZYL ALCOHOL

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

tron effects are the same as in halobenzenes. That

yes, the oxygen atom of the hydroxo group interacts with

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

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

effect (modulo). The 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 period II of the Periodic Table of Chemical Elements. As a result, the total electronic effect that the hydroxo group has on the benzene ring is the donor effect.

Due to p- conjugation, the degree of biconnectivity between carbon and oxygen increases: this bond has 23.7% - character. The structure of phenol should also be similar to the structure of non-existent vinyl alcohol (Chapter 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 (0.136 nm in phenol, 0.143 nm in methanol), and the strength of this bond is greater than in alcohols. In addition, due to p-conjugation, a deficiency of electron density (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 condition corresponds to the mesoformula

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

impossible with them. The hydroxo group affects benzene-

ring only through inductive effect

(–I -effect), thereby reducing the value of electron-

no density on it. But -electronic system ben-

the ash ring can interact with the 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 slightly reduced compared to 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 influence 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, less commonly, 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 determined by the mutual influence of the hydroxo group and the benzene ring; therefore, they are characterized by both reactions at 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 significantly stronger polarization of the O–H bond due to a shift in 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 electronic 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; dissociation of phenols in aqueous solutions occurs, but the equilibrium of this reaction is shifted to the left. The pK a value for phenol and its homologues ranges from 9.9 to 10.4, while for acetic acid pK a = 4.76, and for carbonic acid pK a = 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 acid salts, since carbonic acid is weaker than phenol in the second stage of dissociation.

OH + NaHCO3

OH + Na2 CO3 ONa + NaHCO3

Salts of phenol, phenolates, when interacting with carbonic acid, are converted into phenol:

ONa + H2 CO3 OH + NaHCO3

The introduction of electron-donating or accepting substituents into the aromatic ring of phenol (especially in the o- and p-positions) respectively decreases or increases its acidic properties. This effect is similar 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 acidic properties due to more complete delocalization of the negative charge in the anion; electron-donating substituents, on the contrary,

reduce acidic properties, since in this case their electronic effect prevents the 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 an increase in the reactivity of phenol, and the phenol molecule transforms into a phenolate ion. Such reactions are alkylation and acylation.

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

The local environment promotes the reaction to proceed via the S N 2 mechanism; therefore, substrates that have an accessible electrophilic reaction center with a high effective positive charge should be easier to alkylate. Such substrates can be primary alkyl halides and, above all,

Methane derivatives.

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-nitroanisoles from o- and p-nitrophenols.

Acylation (formation of esters) . Due to the decreased

Due to the nucleophilicity of the hydroxyl group, phenols can only be attacked by highly reactive acylating agents, such as anhydrides and acid 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 production of the drug aspirin:

+ (CH3CO)2O

CH3 COOH

O-C-CH3

salicylic acid

(O-acetylsalicylic acid)

Esterification under the influence of carboxylic acids for phenols usually does not occur 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 production of the drug salol:

10.5.3.3. Electrophilic substitution

Phenols, like many aromatic compounds, are capable of undergoing electrophilic substitution reactions (SE). 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 on 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 n-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's look at some examples and features of the S E reactions for phenols.

Halogenation flows easily. No catalyst required. rirovaniye

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

3 Br2

3 HBr

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

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

NO2+

In this case, strong resinization of phenol occurs.

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

H3 C CH

H3 C CH

H3CO

NO2+

H3CO

NO2+

H3 C CH

CH CH3

H3CO

H3CO

CH(CH3 )2 +

H3 C CH

H3CO

H3CO

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

In addition, nitrosation is also used for the determination of phenols ( Lieberman's 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 is blue in 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 formed already at 15 C, but at temperatures of 100 C and above it rearranges into the more stable p-isomer.

288 K

SO3H

H2SO4

373K

373K

SO3H

Alkylation. In addition to alkylation at the oxygen atom, which occurs in an alkaline medium and leads to the formation of simple (alkylaryl) ethers, the reaction can occur 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+[BF3OH]

R-OH + BF3
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