Aldehydes. Properties of alcohols, aldehydes, acids, esters, phenol
Organic drugs
We study drugs divided into groups according to chemical classification. The advantage of this classification is the ability to identify and study general patterns in the development of methods for obtaining drugs that make up the group, methods of pharmaceutical analysis based on the physical and chemical properties of substances, and establishing a connection between chemical structure and pharmacological action.
All drugs are divided into inorganic and organic. Inorganic, in turn, are classified according to the position of the elements in the PS. And organic ones are divided into derivatives of the aliphatic, alicyclic, aromatic and heterocyclic series, each of which is divided into classes: hydrocarbons, halogen derivatives of hydrocarbons, alcohols, aldehydes, ketones, acids, ethers and esters, etc.
ALIPHATIC COMPOUNDS, LIKE DRUGS.
Preparations of aldehydes and their derivatives. Carbohydrates
Aldehydes
This group of compounds includes organic medicinal substances containing an aldehyde group or their functional derivatives.
General formula:
Pharmacological properties
The introduction of an aldehyde group into the structure of an organic compound gives it a narcotic and antiseptic effect. In this regard, the action of aldehydes is similar to the action of alcohols. But unlike the alcohol group, the aldehyde group increases the toxicity of the compound.
Factors influencing the structure on the pharmacological action :
elongation of the alkyl radical increases activity, but at the same time toxicity increases;
the introduction of unsaturated bonds and halogens has the same effect;
the formation of the hydrated form of aldehyde leads to a decrease in toxicity. But the ability to form a stable hydrate form is manifested only in chlorinated aldehydes. Thus, formaldehyde is a protoplasmic poison, used for disinfection, acetaldehyde and chloral are not used in medicine due to their high toxicity, and chloral hydrate is a drug used as a sleeping pill and sedative.
The strength of the narcotic (pharmacological) effect and toxicity increased from formaldehyde to acetaldehyde and chloral. The formation of the hydrate form (chloral hydrate) can dramatically reduce toxicity while maintaining the pharmacological effect.
According to physical condition aldehydes may be gaseous (low molecular weight), liquids and solids. Low molecular weight ones have a sharp unpleasant odor, high molecular weight ones have a pleasant floral odor.
Chemical properties
Chemically, these are highly reactive substances, which is due to the presence of a carbonyl group in their molecule.
The high reactivity of aldehydes is explained by:
a) the presence of a polarized double bond
b) carbonyl dipole moment
c) the presence of a partial positive charge on the carbonyl carbon atom
σ -
σ + H
The double bond between C and O, unlike the double bond between two carbons, is highly polarized, since oxygen has a much higher electronegativity than carbon, and the electron density of the π bond is shifted towards oxygen. Such high polarization determines the electrophilic properties of the carbon of the carbonyl group and its ability to react with nucleophilic compounds (to enter into nucleophilic addition reactions). The oxygen group has nucleophilic properties.
Characteristic reactions are oxidation and nucleophilic addition
I. Oxidation reactions.
Aldehydeseasily oxidize. Oxidation of aldehydes to acids occurs under the influence as strongand weak oxidizing agents .
Many metals - silver, mercury, bismuth, copper - are reduced from solutions of their salts, especially in the presence of alkali. This distinguishes aldehydes from other organic compounds capable of oxidation - alcohols, unsaturated compounds, the oxidation of which requires stronger oxidizing agents. Consequently, the oxidation reactions of aldehydes with complexly bound cations of mercury, copper, and silver in an alkaline medium can be used to prove the authenticity of aldehydes.
I. 1 .Reactionwith ammonia solution of silver nitrate (silver mirror reaction) FS is recommended to confirm the authenticity of substances with an aldehyde group. It is based on the oxidation of aldehyde to acid and the reduction of Ag + to Ag↓.
AgNO 3 + 2NH 4 OH → NO 3 +2H 2 O
NSSON+ 2NO 3 + H 2 O → HCOONH 4 + 2Ag↓+ 2NH 4 NO 3 + NH 3
Formaldehyde, oxidizing to the ammonium salt of formic acid, reduces metallic silver, which is precipitatedon the walls of the test tube in the form shiny coating "mirror" or gray sediment.
I. 2. Reactionwith Fehling's reagent (a complex compound of copper (II) with potassium-sodium salt of tartaric acid). Aldehydes reduce the copper(II) compound to copper(I) oxide, A brick-red precipitate forms. Prepare before use).
Felling's reagent 1 - CuSO 4 solution
Felling's reagent 2 – alkaline solution of potassium-sodium salt of tartaric acid
When mixing 1:1 Felling's reagents 1 and 2 a blue copper complex compound is formed (II) with potassium-sodium tartaric acid:
blue coloring
When the aldehyde is added and heated, the blue color of the reagent disappears, and an intermediate product is formed - a yellow precipitate of copper (I) hydroxide, which immediately decomposes into a red precipitate of copper (I) oxide and water.
2KNa+ R- COH+2NaOH+ 2KOH→ R- COONa+4KNaC 4 H 4 O 6 + 2 CuOH ↓ +H2O
2 CuOH ↓ →Cu 2 O ↓ +H2O
Yellow sediment brick red sediment
The textbooks have a different general reaction scheme
I. 3. Reactionwith Nessler's reagent (alkaline solution of potassium tetraiodomercurate (II). Formaldehyde reduces the mercury ion to metallic mercury - a dark gray precipitate.
R-COH + K 2 +3KOH → R-COOK + 4KI + Hg↓ + 2H 2 O
Lecture No. 11
ALDEHYDES AND KETONES
Plan
1. Receipt methods.
2.1. Nucleophilic reactions
accession.
2.2. Reactions by a -carbon atom.
2.3.
Lecture No. 11
ALDEHYDES AND KETONES
Plan
1. Receipt methods.
2. Chemical properties.
2.1. Nucleophilic reactions
accession.
2.2. Reactions by a -carbon atom.
2.3. Oxidation and reduction reactions.
Aldehydes and ketones contain a carbonyl group
C=O. General formula:
1. Methods of obtaining.
2. Chemical
properties.
Aldehydes and ketones are one of the most reactive classes
organic compounds. Their chemical properties are determined by the presence
carbonyl group. Due to the large difference in electronegativity
carbon and oxygen and high polarizability p -bonds The C=O bond has significant polarity
( m C=O =2.5-2.8 D). Carbonyl carbon atom
group carries an effective positive charge and is an object for attack
nucleophiles. The main type of reactions of aldehydes and ketones is reactions
nucleophilic addition Ad N. In addition, the carbonyl group affects
reactivity S-N connections a -position, increasing its acidity.
Thus, molecules of aldehydes and ketones
contain two main reaction centers - the C=O bond and C-H connection V a-position:
2.1. Nucleophilic reactions
accession.
Aldehydes and ketones easily add nucleophilic reagents to the C=O bond.
The process begins with an attack by a nucleophile on the carbonyl carbon atom. Then
The tetrahedral intermediate formed in the first stage adds a proton and
gives the addition product:
Activity of carbonyl compounds in
Ad N –reactions depend on the magnitude
effective positive charge on the carbonyl carbon atom and volume
substituents on the carbonyl group. Electron-donating and bulky substituents
complicate the reaction, electron-withdrawing substituents increase the reaction
carbonyl compound ability. Therefore, aldehydes in
Ad N -reactions are more active than
ketones.
The activity of carbonyl compounds increases in
presence of acid catalysts, which increase the positive charge by
carbonyl carbon atom:
Aldehydes and ketones add water, alcohols,
thiols, hydrocyanic acid, sodium hydrosulfite, compounds like
N.H. 2 X. All addition reactions
proceed quickly, under mild conditions, but the resulting products, as a rule,
thermodynamically unstable. Therefore, the reactions proceed reversibly, and the content
addition products in the equilibrium mixture may be low.
Connecting water.
Aldehydes and ketones add water to
formation of hydrates. The reaction is reversible. Forming hydrates
thermodynamically unstable. The balance is shifted towards products
addition only in the case of active carbonyl compounds.
Trichloroacetic aldehyde hydration product
chloral hydrate is a stable crystalline compound that is used in
medicine as a sedative and hypnotic.
Addition of alcohols and
thiols.
Aldehydes combine with alcohols to form hemiacetals. In excess of alcohol and in the presence of an acid catalyst
the reaction goes further - until the formation acetals
The reaction of hemiacetal formation proceeds as
nucleophilic addition and is accelerated in the presence of acids or
grounds.
The process of acetal formation goes like this:
nucleophilic substitution of the OH group in the hemiacetal and is possible only under conditions
acid catalysis, when the OH group is converted into a good leaving group
(H 2 O).
The formation of acetals is a reversible process. IN
In an acidic environment, hemiacetals and acetals are easily hydrolyzed. In an alkaline environment
hydrolysis does not occur. The reactions of formation and hydrolysis of acetals play important role V
chemistry of carbohydrates.
Ketones under similar conditions do not
give.
Thiols are stronger nucleophiles than alcohols
form addition products with both aldehydes and ketones.
Joining hydrocyanic
acids
Hydrocyanic acid adds to a carbonyl compound under conditions
basic catalysis to form cyanohydrins.
The reaction has preparative value and
used in synthesis a-hydroxy- and a -amino acids (see lecture No. 14). Fruits of some plants
(eg bitter almonds) contain cyanohydrins. Stands out when they
When broken down, hydrocyanic acid has a poisonous effect.
Bisulfite addition
sodium
Aldehydes and methyl ketones add sodium bisulfite NaHSO 3 with the formation of bisulfite derivatives.
Bisulfite derivatives of carbonyl compounds
– crystalline substances that are insoluble in excess sodium bisulfite solution.
The reaction is used to isolate carbonyl compounds from mixtures. Carbonyl
the compound can be easily regenerated by treating the bisulfite derivative
acid or alkali.
Interaction with common connections
formula NH 2 X.
Reactions proceed according to general scheme as a process
attachment-elimination. The adduct formed at the first stage is not
stable and easily removes water.
According to the given scheme with carbonyl
compounds react with ammonia, primary amines, hydrazine, substituted hydrazines,
hydroxylamine.
The resulting derivatives are
crystalline substances that are used for isolation and identification
carbonyl compounds.
Imines (Schiff bases) are intermediate
products in many enzymatic processes (transamination under the influence
coenzyme pyridoxal phosphate; reductive amination of keto acids at
participation of the coenzyme NADN). The catalytic hydrogenation of imines produces
amines The process is used to synthesize amines from aldehydes and ketones and
called reductive amination.
Reductive amination occurs in vivo
during the synthesis of amino acids (see lecture No. 16)
2.2. Reactions by a -carbon atom.
Keto-enol tautomerism.
Hydrogen in a -position to the carbonyl group is acidic
properties, since the anion formed during its elimination is stabilized by
resonance account.
The result of the proton mobility of the hydrogen atom
V a -position
is the ability of carbonyl compounds to form enol forms due to
proton migration from a -position to the oxygen atom of the carbonyl group.
Ketone and enol are tautomers.
Tautomers are isomers that can quickly and reversibly convert into each other
due to the migration of a group (in this case, a proton). Equilibrium between
ketone and enol are called keto-enol tautomerism.
The enolization process is catalyzed by acids and
reasons. Enolization under the influence of a base can be represented by
with the following diagram:
Most carbonyl compounds exist
predominantly in ketone form. The content of the enol form increases with
an increase in the acidity of the carbonyl compound, as well as in the case of
additional stabilization of the enol form due to hydrogen bonding or due to
pairing.
Table 8. Content of enol forms and
acidity of carbonyl compounds
For example, in 1,3-dicarbonyl compounds
the mobility of the protons of the methylene group increases sharply due to
electron-withdrawing effect of two carbonyl groups. In addition, enol
the form is stabilized due to the presence in it of a system of conjugate p -bonds and intramolecular
hydrogen bond.
If a compound in enol form is
is a conjugated system with high stabilization energy, then the enol form
prevails. For example, phenol exists only in the enol form.
Enolization and formation of enolate anions are
the first stages of the reactions of carbonyl compounds occurring through a -carbon atom. The most important
of which are halogenation And aldolic-crotonic
condensation
.
Halogenation.
Aldehydes and ketones easily react with halogens (Cl2,
Br 2, I 2 ) with education
exclusively a -halogen derivatives.
The reaction is catalyzed by acids or
reasons. The reaction rate does not depend on the concentration and nature of the halogen.
The process proceeds through the formation of the enol form (slow stage), which
then reacts with halogen (fast step). Thus, the halogen is not
involved in speed—defining stage
process.
If a carbonyl compound contains several a -hydrogen
atoms, then the replacement of each subsequent one occurs faster than the previous one,
due to an increase in their acidity under the influence of electron-withdrawing influence
halogen. In an alkaline environment, acetaldehyde and methyl ketones give
trihalogen derivatives, which are then decomposed by excess alkali with
formation of trihalomethanes ( haloform reaction)
.
The breakdown of triiodoacetone occurs as a reaction
nucleophilic substitution. CI groups 3 — hydroxide anion, like S N -reactions in the carboxyl group (see lecture No. 12).
Iodoform precipitates from the reaction mixture in the form
pale yellow crystalline sediment with a characteristic odor. Iodoform
the reaction is used for analytical purposes to detect compounds of the type
CH 3 -CO-R, including
clinical laboratories for the diagnosis of diabetes mellitus.
Condensation reactions.
In the presence of catalytic amounts of acids
or alkalis carbonyl compounds containing a -hydrogen atoms,
undergo condensation to form b -hydroxycarbonyl compounds.
Carbonyl is involved in the formation of the C-C bond.
carbon atom of one molecule ( carbonyl component) And a -carbon atom is different
molecules ( methylene component). This reaction is called aldol condensation(by the name of the condensation product of acetaldehyde -
aldol).
When the reaction mixture is heated, the product easily
dehydrates to form a ,b -unsaturated carbonyl
connections.
This type of condensation is called croton(by the name of the condensation product of acetaldehyde - croton
aldehyde).
Let us consider the mechanism of aldol condensation in
alkaline environment. In the first stage, the hydroxide anion abstracts a proton from a -carbonyl position
compounds to form an enolate anion. Then the enolate anion as a nucleophile
attacks the carbonyl carbon atom of another carbonyl compound molecule.
The resulting tetrahedral intermediate (alkoxide anion) is strong
base and further abstracts a proton from the water molecule.
During aldol condensation of two different
carbonyl compounds (cross-aldol condensation) possible
formation of 4 different products. However, this can be avoided if one of the
does not contain carbonyl compounds a -hydrogen atoms (for example, aromatic aldehydes
or formaldehyde) and cannot act as a methylene component.
As a methylene component in reactions
condensation can be not only carbonyl compounds, but also other
C-H-acids. Condensation reactions have preparative value, since they allow
extend the chain of carbon atoms. According to the type of aldol condensation and
retroaldol decomposition (reverse process) many biochemical reactions occur
processes: glycolysis, synthesis of citric acid in the Krebs cycle, synthesis of neuraminic acid
acids.
2.3. Oxidation reactions and
recovery
Recovery
Carbonyl compounds are reduced to
alcohols as a result of catalytic hydrogenation or under the influence
reducing agents that are donors of hydride anions.
[H]: H 2 /cat., cat. – Ni, Pt,
Pd;
LiAlH4; NaBH4.
Reduction of carbonyl compounds
complex metal hydrides involves nucleophilic attack of the carbonyl group
hydride anion. Subsequent hydrolysis produces alcohol.
Recovery occurs in the same way
carbonyl group in vivo under the influence of the coenzyme NADN, which is
donor of hydride ion (see lecture No. 19).
Oxidation
Aldehydes oxidize very easily
any oxidizing agents, even such weak ones as air oxygen and compounds
silver(I) and copper(II).
The last two reactions are used as
qualitative for the aldehyde group.
In the presence of alkalis, aldehydes that do not contain a -hydrogen atoms
disproportionate to form alcohol and acid (Cannizzaro reaction).
2HCHO + NaOH ® HCOONa + CH 3 OH
This is the reason that the aqueous solution
formaldehyde (formalin) with long-term storage becomes sour
reaction.
Ketones are resistant to oxidizing agents
neutral environment. In acidic and alkaline environments under the influence of strong
oxidizing agents(KMnO 4 ) They
oxidize by breaking the C-C bond. The carbon skeleton is broken down by
carbon-carbon double bond of enol forms of a carbonyl compound, similar to
oxidation of double bonds in alkenes. This produces a mixture of products
containing carboxylic acids or carboxylic acids and ketones.
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, related friend with a friend 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 are therefore isolated in independent class organic compounds - phenols. For example:
There are also polyhydric (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 is methanol, having a relative molecular weight$32$, under normal conditions - liquid.
The lowest and middle members of the series of limiting 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 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 is capable of being 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, heat) 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 - 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. 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, passing sodium phenolate through an aqueous solution carbon dioxide, 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 colored purple complex connection.
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 substance 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 summary 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, polymer bases are made from polymers based on phenol-formaldehyde resins printed circuit boards for radio devices. 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 characteristic properties 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 Formalin 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$CH_3CHO$ ) - liquid with pungent unpleasant smell and boiling point $21°C$, highly soluble in water. From acetaldehyde to industrial scale acetic acid and a number of other substances are obtained; 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 organic acids, let's consider saturated monobasic carboxylic acids in more detail.
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 - 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, due to other characteristic properties.
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. So, 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. Multiple addition reactions- 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 marketed under the name vinegar ($3-5% solution) and acetic essence ($70-80% solution) and are widely used in Food Industry. Acetic acid is a good solvent for many organic substances and is therefore used in dyeing, tanning, and the paint and varnish industry. In addition, acetic acid is a raw material for the production of many technically important organic compounds: for example, substances used to control weeds - herbicides - are obtained from it.
Acetic acid is the main component wine vinegar, the characteristic smell of which is due precisely to it. It is a product of ethanol oxidation and is formed from it when wine is stored in air.
The most important representatives of higher saturated monobasic acids are palmitic$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. From unsaturated higher carboxylic acids highest value It has 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.
Which are characterized by a double bond between the carbon and oxygen atoms and two single bonds of the same carbon atom with a hydrocarbon radical, designated by the letter R, and a hydrogen atom. The group of atoms >C=O is called the carbonyl group; it is characteristic of all aldehydes. Many aldehydes have a pleasant odor. They can be obtained from alcohols by dehydrogenation (removal of hydrogen), which gives them the common name aldehydes. The properties of aldehydes are determined by the presence of a carbonyl group, its location in the molecule, as well as the length and spatial branching of the hydrocarbon radical. That is, knowing the name of a substance that reflects it, one can expect certain chemical, as well as physical properties aldehydes.
There are two main ways of naming aldehydes. The first method is based on the system used by the International Union (IUPAC), often called systematic nomenclature. It is based on the fact that the longest chain in which a carbonyl group is attached to a carbon atom serves as the basis for the name of the aldehyde, that is, its name comes from the name of a related alkane by replacing the suffix -an with the suffix -al (methane - matanal, ethane - ethanal , propane - propanal, butane - butanal and so on). Another method of forming the name of aldehydes uses the name of the corresponding one into which it will turn as a result of oxidation (methanal - formic aldehyde, ethanal - acetic aldehyde, propanal - propionic aldehyde, butanal - butyric aldehyde, and so on).
It is the polarity of the >C=O group that affects the physical properties of aldehydes: boiling point, solubility, dipole moment. Hydrocarbon compounds, consisting only of hydrogen and carbon atoms, melt and boil at low temperatures. For substances with a carbonyl group they are much higher. For example, butane (CH3CH2CH2CH3), propanal (CH3CH2CHO) and acetone (CH3COCH3) have the same molecular weight of 58, and the boiling point of butane is 0 °C, while for propanal it is 49 °C, and for acetone it is equal to 56°C. The reason for the big difference is that polar molecules have a greater ability to attract each other than non-polar molecules, so it takes more energy to break them apart and therefore requires a higher temperature for these compounds to melt or boil.
As they grow, the physical properties of aldehydes change. Formaldehyde (HCHO) is a gaseous substance under normal conditions, acetaldehyde (CH3CHO) boils at room temperature. Other aldehydes (with the exception of representatives with high molecular weight) are liquids under normal conditions. Polar molecules do not mix easily with non-polar ones because polar molecules are attracted to each other, and non-polar molecules are not able to squeeze between them. Therefore, hydrocarbons do not dissolve in water, since water molecules are polar. Aldehydes, in whose molecules the number of carbon atoms is less than 5, dissolve in water, but if the number of carbon atoms is more than 5, dissolution does not occur. The good solubility of aldehydes with low molecular weight is due to the formation of hydrogen bonds between the hydrogen atom of the water molecule and the oxygen atom of the carbonyl group.
The polarity of molecules formed by different atoms can be quantified by a number called the dipole moment. Molecules formed by identical atoms are not polar and do not have a dipole moment. The dipole moment vector is directed towards the element that is to the right in the periodic table (for one period). If a molecule consists of atoms of one subgroup, then the electron density will shift towards the element with a lower atomic number. Most hydrocarbons do not have a dipole moment or its value is extremely small, but for aldehydes it is much higher, which also explains the physical properties of aldehydes.
Almost all chemicals around us are tested by humans, based on their requests and needs. Each compound has a unique set of characteristics and properties inherent only to it, from which those useful and necessary for us in life are selected. Everyday life. The aldehydes we will discuss are also no exception.
The humble child of organic chemistry
Among the carbon compounds that are commonly called organic, there are well-known ones that, as they say, “are on everyone’s lips.” For example, glucose, ethyl alcohol or plastics. Aldehydes are unlucky in this regard. Only narrow specialists, and even high school students who are intensively studying chemistry for admission to a university, know about them. In fact, such compounds (such as acetaldehyde), the chemical properties of which we will consider, are widely used both in industrial production, and in everyday life.
Apple of discord
Alas, discoveries in science quite often do not occur without clouds. Aldehydes, their chemical structure and properties were discovered as a result of lengthy debates and discussions among scientists of the 19th century. And such famous chemists as Liebig and Döbereiner even seriously quarreled, finding out who actually holds the palm in obtaining and isolating acetaldehyde in its pure form. It was extracted from ethyl alcohol vapor passed over a platinum mesh, which serves as a reaction catalyst. The only thing that could reconcile opponents was the unconditional acceptance by all chemists of the name of a new class of substances - aldehydes, which literally means “hydrogen-free alcohols”. It indicates a method for obtaining them from alcohols by the elimination of two hydrogen atoms.
Can't be confused with anything
Considering the physical and chemical properties of aldehydes, it is easy to see that they are quite specific. Thus, formaldehyde, which is a toxic gas, has a pungent, suffocating odor. Its 40% aqueous solution, called formalin, causes a special odor in anatomical laboratories and morgues, where it is used as an antiputrefactive agent that preserves the proteins of organs and tissues.
And acetaldehyde, which is next in the homologous series, is a colorless liquid that is highly soluble in water with an unpleasant odor of rotten apples. Aldehydes, whose chemical properties are characterized by oxidation and addition reactions, can be converted into substances of genetically similar classes: carboxylic acids or alcohols. Let's look at them using specific examples.
The calling card of aldehydes
In organic chemistry, as well as in inorganic chemistry, there is such a concept as “ qualitative reaction" It can be compared to a beacon signaling that we are dealing with substances of a specific class, for example, aldehydes. The chemical properties of aldehydes are confirmed by reactions with an ammonia solution of silver oxide and with copper hydroxide when heated (silver mirror reaction)
The reaction product will be pure silver, released in the form of a mirror layer on the walls of the test tube.
As a result of the reaction, a brick-colored precipitate forms - copper oxide.
Twin substances
Now the time has come to deal with such a phenomenon, characteristic of all organic substances, including aldehydes, as isomerism. It is completely absent in the world of inorganic chemistry. Everything is simple there: one chemical formula corresponds to only one specific compound with its inherent physical and chemical properties. For example, the formula HNO 3 corresponds to one substance called nitrate acid, which has a boiling point of 86 ° C, with a pungent odor, and is very hygroscopic.
In the kingdom of organic chemistry, isomer substances live and live, whose formulas are the same but their properties are different. For example, the formula C 4 H 8 O has two completely different aldehydes: butanal and 2-methylpropanal.
Their formulas:
Isomeric aldehydes, whose chemical properties depend on their composition and structure, serve as excellent evidence of the ingenious theory of the structure of organic compounds created by the Russian scientist M. Butlerov. His discovery is of the same fundamental importance for chemistry as Mendeleev’s periodic law.
Unique carbon
Excellent evidence confirming M. Butlerov’s theory is the chemical properties of aldehydes. Organic chemistry, thanks to the research of a Russian scientist, was finally able to answer the question that has plagued more than one generation of scientists with its complexity, namely: how to explain the amazing diversity of organic compounds, which is based on the phenomenon of isomerism. Let's consider the structure of the molecules of two aldehyde isomers: butanal and 2-methylpropanal, which have the same molecular formula - C 4 H 8 O, but different structural ones, and therefore differ from each other in physical and chemical properties.
Let's pay attention to two the most important features carbon atom, which were introduced as postulates into the theory of M. Butlerov:
1. Carbon in organic compounds is always tetravalent.
2. Carbon atoms are capable of connecting with each other and forming various spatial configurations: unbranched and branched chains or cycles.
On them, according to valency, atoms of other chemical elements: hydrogen, oxygen, nitrogen, thus forming the entire gigantic arsenal of existing organic compounds (and there are more than 10 million of them). In addition, the number is constantly increasing due to new substances obtained in the chemistry of organic synthesis.
The more polar the better
Continuing to study aldehydes, their chemical structure and properties, we will dwell on the phenomenon of polarity of the atoms that make up the molecules of aldehydes. Thus, the carbon atom of the aldehyde group in the acetaldehyde molecule acquires a partial positive charge, and the oxygen atom acquires a partial negative charge. The reason for their occurrence is as follows: the electron density of the π bond is more mobile than the σ bond.
IN general formula aldehydes, where R is a hydrocarbon radical associated with an aldehyde group, a partial negative charge is formed on the oxygen atom, and a partial positive charge is formed on the carbon atom. Thus, the functional group of aldehydes becomes highly polarized, which causes greater reactivity of these substances. Simply put, the more polarized the atoms in a molecule of a substance are, the better and faster it enters into chemical reactions. The rapid oxidizing ability of the hydrogen atom in the aldehyde group and the reactivity of the carbonyl group provide aldehydes with their characteristic addition and polymerization reactions.
Life in a plastic world
It was aldehydes, whose chemical properties are determined by the ability to undergo polycondensation and polymerization reactions, that became the ancestors of phenoplasts and aminoplasts - the basic materials of the modern polymer industry. The raw materials for its enterprises are formaldehyde and acetaldehyde. Thus, phenol-formaldehyde resins are used to produce phenol plastics - the most important substitutes for ferrous and non-ferrous metals. Formaldehyde is produced by the oxidation of methane when heated to 600°C in a mixture with air, as well as by the oxidation of methanol heated to 300°C over a copper catalyst. Thus, the aldehydes, their preparation and chemical properties, which we consider, are important raw materials in organic synthesis reactions.
Drawing conclusions
As we can see, the track record of aldehydes contains quite a few necessary and important substances, such as, for example, formaldehyde and acetaldehydes, the chemical properties of which people successfully use in various areas of their life.