Saturated hydrocarbons have in their molecules only low-polarity and weakly polarizing bonds, which are distinguished by high strength, therefore, under normal conditions, they are substances that are slightly chemically active with respect to polar reagents: they do not interact with concentrated acids, integers, alkali metals, oxidizers. This was the reason for their name - paraffins. Parumaffinus is Latin for unrelated. Their chemical transformations proceed mainly at elevated temperatures and under the action of UV irradiation.
There are three main types of reactions of saturated hydrocarbons: substitution, oxidation and elimination. These reactions can proceed either by breaking the C-C bond (energy 83.6 kcal) or by breaking the C-H bond (energy 98.8 kcal/mol). Reactions often go with a break in the C-H bond, tk. it is more accessible to the action of the reagent, although the C-C bond requires less energy for cleavage. As a result of such reactions, very active species are intermediately formed - aliphatic hydrocarbon radicals.
Preparation and properties of aliphatic radicals
1. Formation of free radicals during homolytic cleavage C-C connections or C-H occurs at a temperature of 300-700 about C or under the action of free radical reagents.
2. The lifetime of free radicals (resistance) increases from primary to secondary and tertiary radicals:
b) Interaction with unsaturated compounds: addition occurs with the formation of a new radical as well:
CH3. + CH 2 \u003d CH 2 CH 3 -CH 2 -CH 2.
c) -decay - radicals with a long carbon chain decompose with a break in the C-C bond in the -position to carbon with an unpaired electron.
CH 3 - CH 2: CH 2 - CH 2 . CH 3 -CH 2 . + CH 2 \u003d CH 2
d) Disproportionation - redistribution of hydrogen associated with -decay along the C-H bond:
| + CH 3 -CH 2. | + CH 3 -CH 3 |
e) Recombination - the combination of free radicals with each other
CH 3 . + CH 3 . CH 3 -CH 3
Knowing the features of the behavior of free radicals, it is easier to understand the basic laws of specific reactions of saturated hydrocarbons.
I type. substitution reaction
1. Halogenation reactions. The most energetic reagent is fluorine. Direct fluorination results in an explosion. The reactions chlorination. They can proceed under the action of chlorine molecules in the light already at room temperature. The reaction proceeds according to the free-radical chain mechanism and includes the following main stages:
a) the first slow stage - chain initiation:
Cl:ClCl. +Cl.
R: H + . Cl HCl + R.
b) chain development - the formation of reaction products with the simultaneous formation of free radicals that continue the chain process:
R. + Cl: Cl RCl + Cl.
R:H+Cl. HCl+R.
c) open circuit:
Since CI. the reagent is active, it can attack the molecule of the already obtained chlorine derivative, as a result, a mixture of mono- and polyhalogenated compounds is formed. For example:
CH 4 + Cl 2 HCl + CH 3 Cl CH 2 Cl 2 CHCl 3 CCl 4
methyl chloride –HCl -HCl -HCl
methylene chloride chloroform four-
carbon chloride
Bromination reaction proceeds much more difficult, because bromine is less active than chlorine and reacts mainly with the formation of more stable tertiary or secondary radicals. In this case, the second bromine atom usually enters a position adjacent to the first, mainly at the secondary carbon.
iodination reactions practically do not leak, because HI reduces the resulting alkyl iodides.
2. Nitration- substitution of the H atom by the NO 2 group under the action of nitric acid. It goes under the action of dilute nitric acid (12%) at a high temperature of 150 ° C under pressure (Konovalov's reaction). Paraffins of isostructure react more easily, tk. substitution occurs more easily at the tertiary carbon atom:
The mechanism of the nitration reaction is associated with the intermediate formation of free radicals. The initiation is facilitated by a partially occurring oxidation process:
RH + HONO 2 ROH + HONO
nitrous acid
HONO + HONO 2 HOH + 2 . NO 2
| + . NO 2 |
CH 3 -C-CH 3 +. NO 2 CH 3 -C-CH 3 + HNO 2
CH 3 -C-CH 3 +. NO 2 CH 3 -C-CH 3
those. the radical reaction of nitration of hydrocarbons does not have a chain character.
II type. Oxidation reactions
Under normal conditions, paraffins are not oxidized either by oxygen or by strong oxidizing agents (KMnO 4 , HNO 3 , K 2 Cr 2 O 7 , etc.).
When an open flame is introduced into a mixture of hydrocarbon with air, complete oxidation (combustion) of the hydrocarbon to CO 2 and H 2 O occurs. Heating saturated hydrocarbons in a mixture with air or oxygen in the presence of catalysts for the oxidation of MnO 2 and others to a temperature of 300 ° C leads to their oxidation with the formation of peroxide compounds. The reaction proceeds by a chain free radical mechanism.
And: R: H R . +H. circuit initiation
R:R. + O: :O: R-O-O .
R-O-O. + R: H R-O-O-H + R .
alkane hydroperoxide
O:R-O-O. +R. R-O-O-R open circuit
alkane peroxide
The tertiary units are most easily oxidized, the secondary ones are more difficult, and the primary ones are even more difficult. The resulting hydroperoxides decompose.
Primary hydroperoxides when decomposed, they form aldehydes or a primary alcohol, for example:
CH 3 -C-C-O: O-H CH 3 -C-O. + . OH CH 3 -C \u003d O + H 2 O
ethane hydroperoxide acetaldehyde
CH 3 -CH 3
side
CH 3 -CH 2 OH + CH 3 -CH 2.
Secondary hydroperoxides form ketones or secondary alcohols upon decomposition, for example:
CH 3 -C-O:OH CH 3 -C-O. + . OH H 2 O + CH 3 -C \u003d O
CH 3 CH 3 CH 3
propane hydroperoxide
CH 3 -CH 2 -CH 3
side
CH 3 -CH-OH + CH 3 -. CH-CH 3
isopropyl alcohol
Tertiary hydroperoxides form ketones, as well as primary and tertiary alcohols, for example:
CH 3 CH 3 CH 3
CH 3 -C-CH 3 CH 3 -C: CH 3 +. OH CH 3 OH + CH 3 -C \u003d O
isobutane hydroperoxide
CH 3 -CH-CH 3
side
Isobutane
CH 3 -C-CH 3 + CH 3 -C-CH 3
tert-butyl alcohol
Any hydroperoxide can also decompose with the release of atomic oxygen: CH 3 -CH 2 -O-O-H CH 3 CH 2 -OH + [O],
which goes to further oxidation:
CH 3 -C + [O] CH 3 -C-OH
Therefore, in addition to alcohols, aldehydes and ketones, carboxylic acids are formed.
By choosing the reaction conditions, it is possible to obtain one of any product. For example: 2 CH 4 + O 2 2 CH 3 OH.
Electronic and spatial structures In benzene, all carbon atoms are in the second valence state (sp 2 hybridization). As a result, three sigma bonds with carbon and hydrogen atoms are formed on the plane. (Six p-electrons that did not participate in hybridization form a common 6p-electron cloud, which contracts the benzene ring, making it stronger, since as a result of overlapping, a single delocalized six-electron -system (4n + 2 = 6, where n = 1) The electron density -> bonds are evenly distributed throughout the cycle, which leads to the uniformity of the C-C bond lengths (0.1397 nm).Single-substituted benzenes do not have isomers.
Main Chemical properties. Substitution reactions: 
Task. In which direction will the reaction of toluene with bromine go: - a) in the presence of a catalyst;
- b) when illuminating a mixture of substances?
b) Under illumination, substitution will occur in the methyl group: 
This is due to the mutual influence of the benzene ring and the substituent. Task. Give examples of reactions showing the similarity of benzene: - a) with saturated hydrocarbons;
- b) with unsaturated hydrocarbons.
Similarity with unsaturated hydrocarbons - addition reactions (chlorine or hydrogen): 
hexachloro-cyclohexane Substitution reactions are easier for benzene than for saturated hydrocarbons, and addition reactions are more difficult than for unsaturated ones. Task. Write the equations of chemical syntheses using the scheme: Indicate the reaction conditions. Solution. 
Task. Which of the following compounds is cistransisomeric? 1. a) butene-1, b) pentene-2, 3) 2-methylbutene-2, d) 2-methyl-propene, e) oleic acid, f) isoprene rubber. 2. Lead structural formulas cis, trans isomers. 3. What explains the presence of cis-, trans-isomerism in substances? Solution. 1) a), c), d) do not have, b), e), f) have cis-, trans-isomers: 
cis form of isoprene rubber 
trans-form of isoprene rubber 3) The presence of cis-trans isomerism is explained by the absence of free rotation of the molecule relative to the double bond. It is difficult because the molecule in this place has a planar structure (sp 2 is the hybridization of two carbon atoms forming a double bond). A necessary condition for the presence of cis-, trans-isomers is also the presence of different substituents at the carbon atoms that form a double bond. the basis of all organic matter are compounds that consist of two elements - carbon and hydrogen. From such a fairly simple composition, they got their name - hydrocarbons. This is a class of compounds, diverse in structure, chemical bonds, properties. They, in turn, are divided into groups - rows:
1) Saturated hydrocarbons
a) Alkanes
2) Unsaturated hydrocarbons:
a) Alkenes
b) Alkynes
All hydrocarbons are colorless. Under normal conditions, they can be in solid, liquid or gaseous states. Their state of aggregation depends on the mass of the molecules of the substance. The greater the mass of molecules, the more difficult it is to break the bonds between them, since with an increase in mass, as a rule, the attraction between molecules increases, and the processes of melting and evaporation become more difficult. The molecular weight also affects the density of the substance: with its increase, the density of the hydrocarbon increases.
A common property of all hydrocarbons, as well as all organic compounds, is combustion - oxidation by oxygen. For example, one of the components of natural gas, propane, burns in gas stoves.
When burning plastic items, many toxic substances are released that pollute the atmosphere. Inhaling the smoke of a fire in which polymers and plastics are burned is extremely harmful.
The source of natural alkanes is oil, associated and natural gases. Natural gas contains over 90% methane. In addition to methane, it contains ethane, propane, butane, some nitrogen, carbon dioxide, and sometimes hydrogen sulfide.
Oil
Oil is a mixture of various alkanes and other compounds. It contains liquid, solid, and often gaseous hydrocarbons. Gaseous hydrocarbons dissolved in oil are under pressure in the bowels of the Earth, and when they reach the surface, they are separated from liquid oil and form the so-called associated gases. They contain less methane, and the share of ethane, propane, butane in them is much higher than in natural gas. It is clear that associated gases are no less valuable than natural gas. Nevertheless, associated gases have been burned in the fields since ancient times. As a result, valuable raw materials are not only destroyed, but the environment is also damaged.
Alkenes and alkynes are almost never found in nature. They are obtained from aclanes by splitting off hydrogen in the presence of a catalyst such as nickel. Such reactions are called dehydrogenation.
Natural gas is the most economical and environmentally friendly fuel. It is used at thermal power plants, factories, at home. Liquid hydrocarbons are used as fuel.
Both saturated and unsaturated hydrocarbons are needed not only in the energy sector, but also in the chemical industry. They serve as raw materials for the production of many necessary substances: plastics, synthetic fibers, varnishes and paints, medicines, acetone, alcohol, soot, hydrogen, and others.
To obtain combustible fuel, oil is subjected to processing by distillation. Its essence lies in the fact that when oil is heated to a certain temperature, hydrocarbons evaporate one after another and then condense. This is how they get fuel. And the distillation residues are used in the chemical industry and to cover roads.
Chemical properties of alkanes
Alkanes (paraffins) are non-cyclic hydrocarbons, in the molecules of which all carbon atoms are connected only by single bonds. In other words, there are no multiple, double or triple bonds in the molecules of alkanes. In fact, alkanes are hydrocarbons containing the maximum possible number of hydrogen atoms, and therefore they are called limiting (saturated).
Due to saturation, alkanes cannot enter into addition reactions.
Since carbon and hydrogen atoms have fairly close electronegativity, this leads to the fact that the CH bonds in their molecules are extremely low polarity. In this regard, for alkanes, reactions proceeding according to the mechanism of radical substitution, denoted by the symbol S R, are more characteristic.
1. Substitution reactions
In reactions of this type carbon-hydrogen bonds are broken
RH + XY → RX + HY
Halogenation
Alkanes react with halogens (chlorine and bromine) under the action of ultraviolet light or with strong heat. In this case, a mixture of halogen derivatives with different degrees of substitution of hydrogen atoms is formed - mono-, di-tri-, etc. halogen-substituted alkanes.
On the example of methane, it looks like this:
By changing the halogen/methane ratio in the reaction mixture, it is possible to ensure that any particular methane halogen derivative predominates in the composition of the products.
reaction mechanism
Let us analyze the mechanism of the free radical substitution reaction using the example of the interaction of methane and chlorine. It consists of three stages:
- initiation (or chain initiation) - the process of formation of free radicals under the action of energy from the outside - irradiation with UV light or heating. At this stage, the chlorine molecule undergoes a homolytic cleavage of the Cl-Cl bond with the formation of free radicals:
Free radicals, as can be seen from the figure above, are called atoms or groups of atoms with one or more unpaired electrons(Cl, H, CH 3 , CH 2 etc.);
2. Chain development
This stage consists in the interaction of active free radicals with inactive molecules. In this case, new radicals are formed. In particular, when chlorine radicals act on alkane molecules, an alkyl radical and hydrogen chloride are formed. In turn, the alkyl radical, colliding with chlorine molecules, forms a chlorine derivative and a new chlorine radical:
3) Break (death) of the chain:
Occurs as a result of the recombination of two radicals with each other into inactive molecules:
2. Oxidation reactions
Under normal conditions, alkanes are inert with respect to such strong oxidizing agents as concentrated sulfuric and nitric acids, permanganate and potassium dichromate (KMnO 4, K 2 Cr 2 O 7).
Combustion in oxygen
A) complete combustion with an excess of oxygen. Leads to the formation of carbon dioxide and water:
CH 4 + 2O 2 \u003d CO 2 + 2H 2 O
B) incomplete combustion with a lack of oxygen:
2CH 4 + 3O 2 \u003d 2CO + 4H 2 O
CH 4 + O 2 \u003d C + 2H 2 O
Catalytic oxidation with oxygen
As a result of heating alkanes with oxygen (~200 o C) in the presence of catalysts, a wide variety of organic products can be obtained from them: aldehydes, ketones, alcohols, carboxylic acids.
For example, methane, depending on the nature of the catalyst, can be oxidized to methyl alcohol, formaldehyde, or formic acid:
3. Thermal transformations of alkanes
Cracking
Cracking (from the English to crack - to tear) is a chemical process that occurs at high temperature, as a result of which the carbon skeleton of alkane molecules breaks down to form molecules of alkenes and alkanes with smaller molecular weights compared to the parent alkanes. For example:
CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 → CH 3 -CH 2 -CH 2 -CH 3 + CH 3 -CH \u003d CH 2
Cracking can be thermal or catalytic. For the implementation of catalytic cracking, due to the use of catalysts, significantly lower temperatures are used compared to thermal cracking.
Dehydrogenation
The elimination of hydrogen occurs as a result of the rupture C-H connections; carried out in the presence of catalysts at elevated temperatures. Dehydrogenation of methane produces acetylene:
2CH 4 → C 2 H 2 + 3H 2
Heating methane to 1200 ° C leads to its decomposition into simple substances:
CH 4 → C + 2H 2
Dehydrogenation of other alkanes gives alkenes:
C 2 H 6 → C 2 H 4 + H 2
When dehydrogenating n-butane, butene-1 and butene-2 are formed (the latter in the form cis- And trance-isomers):
Dehydrocyclization
Isomerization
Chemical properties of cycloalkanes
The chemical properties of cycloalkanes with more than four carbon atoms in the cycles are generally almost identical to those of alkanes. For cyclopropane and cyclobutane, oddly enough, addition reactions are characteristic. This is due to the high tension within the cycle, which leads to the fact that these cycles tend to break. So cyclopropane and cyclobutane easily add bromine, hydrogen or hydrogen chloride:
Chemical properties of alkenes
1. Addition reactions
Since the double bond in alkene molecules consists of one strong sigma bond and one weak pi bond, they are quite active compounds that easily enter into addition reactions. Alkenes often enter into such reactions even under mild conditions - in the cold, in aqueous solutions and organic solvents.
Hydrogenation of alkenes
Alkenes are able to add hydrogen in the presence of catalysts (platinum, palladium, nickel):
CH 3 -CH \u003d CH 2 + H 2 → CH 3 -CH 2 -CH 3
Hydrogenation of alkenes proceeds easily even at normal pressure and slight heating. An interesting fact is that the same catalysts can be used for the dehydrogenation of alkanes to alkenes, only the dehydrogenation process proceeds at a higher temperature and lower pressure.
Halogenation
Alkenes easily enter into an addition reaction with bromine both in aqueous solution and in organic solvents. As a result of the interaction, initially yellow solutions of bromine lose their color, i.e. discolor.
CH 2 \u003d CH 2 + Br 2 → CH 2 Br-CH 2 Br
Hydrohalogenation
It is easy to see that the addition of a hydrogen halide to an unsymmetrical alkene molecule should theoretically lead to a mixture of two isomers. For example, when hydrogen bromide is added to propene, the following products should be obtained:
Nevertheless, in the absence of specific conditions (for example, the presence of peroxides in the reaction mixture), the addition of a hydrogen halide molecule will occur strictly selectively in accordance with the Markovnikov rule:
The addition of a hydrogen halide to an alkene occurs in such a way that hydrogen is attached to a carbon atom with a larger number of hydrogen atoms (more hydrogenated), and a halogen is attached to a carbon atom with a smaller number of hydrogen atoms (less hydrogenated).
Hydration
This reaction leads to the formation of alcohols, and also proceeds in accordance with the Markovnikov rule:
As you might guess, due to the fact that the addition of water to the alkene molecule occurs according to the Markovnikov rule, the formation of primary alcohol is possible only in the case of ethylene hydration:
CH 2 \u003d CH 2 + H 2 O → CH 3 -CH 2 -OH
It is by this reaction that the main amount of ethyl alcohol is carried out in the large-capacity industry.
Polymerization
A specific case of the addition reaction is the polymerization reaction, which, unlike halogenation, hydrohalogenation and hydration, proceeds through a free radical mechanism:
Oxidation reactions
Like all other hydrocarbons, alkenes burn easily in oxygen to form carbon dioxide and water. The equation for the combustion of alkenes in excess oxygen has the form:
C n H 2n + (3/2)nO 2 → nCO 2 + nH 2 O
Unlike alkanes, alkenes are easily oxidized. When acting on alkenes aqueous solution KMnO 4 discoloration, which is a qualitative reaction to double and triple CC bonds in organic molecules.
Oxidation of alkenes with potassium permanganate in a neutral or slightly alkaline solution leads to the formation of diols (dihydric alcohols):
C 2 H 4 + 2KMnO 4 + 2H 2 O → CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH (cooling)
In an acidic environment, a complete cleavage of the double bond occurs with the transformation of the carbon atoms that formed the double bond into carboxyl groups:
5CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5C 2 H 5 COOH + 8MnSO 4 + 4K 2 SO 4 + 17H 2 O (heating)
If the double C=C bond is at the end of the alkene molecule, then carbon dioxide is formed as the oxidation product of the extreme carbon atom at the double bond. This is due to the fact that the intermediate oxidation product, formic acid, is easily oxidized by itself in an excess of an oxidizing agent:
5CH 3 CH=CH 2 + 10KMnO 4 + 15H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 10MnSO 4 + 5K 2 SO 4 + 20H 2 O (heating)
In the oxidation of alkenes, in which the C atom at the double bond contains two hydrocarbon substituents, a ketone is formed. For example, the oxidation of 2-methylbutene-2 produces acetone and acetic acid.
The oxidation of alkenes, which breaks the carbon skeleton at the double bond, is used to establish their structure.
Chemical properties of alkadienes
Addition reactions
For example, the addition of halogens:
bromine water discolored.
Under normal conditions, the addition of halogen atoms occurs at the ends of the butadiene-1,3 molecule, while π bonds are broken, bromine atoms are attached to the extreme carbon atoms, and free valences form a new π bond. Thus, as if there is a "movement" of the double bond. With an excess of bromine, one more bromine molecule can be added at the site of the formed double bond.
polymerization reactions
Chemical properties of alkynes
Alkynes are unsaturated (unsaturated) hydrocarbons and therefore are capable of entering into addition reactions. Among the addition reactions for alkynes, electrophilic addition is the most common.
Halogenation
Since the triple bond of alkyne molecules consists of one stronger sigma bond and two weaker pi bonds, they are able to attach either one or two halogen molecules. The addition of two halogen molecules by one alkyne molecule proceeds by the electrophilic mechanism sequentially in two stages:
Hydrohalogenation
The addition of hydrogen halide molecules also proceeds by the electrophilic mechanism and in two stages. In both stages, the addition proceeds in accordance with the Markovnikov rule:
Hydration
The addition of water to alkynes occurs in the presence of ruthium salts in an acidic medium and is called the Kucherov reaction.
As a result of the hydration of the addition of water to acetylene, acetaldehyde (acetic aldehyde) is formed:
For acetylene homologues, the addition of water leads to the formation of ketones:
Alkyne hydrogenation
Alkynes react with hydrogen in two steps. Metals such as platinum, palladium, nickel are used as catalysts:
Alkyne trimerization
When acetylene is passed over activated carbon at high temperature, a mixture of various products is formed from it, the main of which is benzene, a product of acetylene trimerization:
Dimerization of alkynes
Acetylene also enters into a dimerization reaction. The process proceeds in the presence of copper salts as catalysts:
Alkyne oxidation
Alkynes burn in oxygen:
C n H 2n-2 + (3n-1) / 2 O 2 → nCO 2 + (n-1) H 2 O
The interaction of alkynes with bases
Alkynes with a triple C≡C at the end of the molecule, unlike other alkynes, are able to enter into reactions in which the hydrogen atom in the triple bond is replaced by a metal. For example, acetylene reacts with sodium amide in liquid ammonia:
HC≡CH + 2NaNH 2 → NaC≡CNa + 2NH 3,
and also with an ammonia solution of silver oxide, forming insoluble salt-like substances called acetylenides:
Thanks to this reaction, it is possible to recognize alkynes with a terminal triple bond, as well as to isolate such an alkyne from a mixture with other alkynes.
It should be noted that all silver and copper acetylenides are explosive substances.
Acetylides are able to react with halogen derivatives, which is used in the synthesis of more complex organic compounds with a triple bond:
CH 3 -C≡CH + NaNH 2 → CH 3 -C≡CNa + NH 3
CH 3 -C≡CNa + CH 3 Br → CH 3 -C≡C-CH 3 + NaBr
Chemical properties of aromatic hydrocarbons
The aromatic nature of the bond affects the chemical properties of benzenes and other aromatic hydrocarbons.
A single 6pi electron system is much more stable than conventional pi bonds. Therefore, for aromatic hydrocarbons, substitution reactions are more characteristic than addition reactions. Arenes enter into substitution reactions by an electrophilic mechanism.
Substitution reactions
Halogenation
Nitration
The nitration reaction proceeds best under the action of not pure nitric acid, but its mixture with concentrated sulfuric acid, the so-called nitrating mixture:
Alkylation
The reaction in which one of the hydrogen atoms at the aromatic nucleus is replaced by a hydrocarbon radical:
Alkenes can also be used instead of halogenated alkanes. As catalysts, aluminum, ferric halides or inorganic acids.<
Addition reactions
hydrogenation
Accession of chlorine
It proceeds by a radical mechanism under intense irradiation with ultraviolet light:
Similarly, the reaction can proceed only with chlorine.
Oxidation reactions
Combustion
2C 6 H 6 + 15O 2 \u003d 12CO 2 + 6H 2 O + Q
incomplete oxidation
The benzene ring is resistant to oxidizing agents such as KMnO 4 and K 2 Cr 2 O 7 . The reaction does not go.
Division of substituents in the benzene ring into two types:
Consider the chemical properties of benzene homologues using toluene as an example.
Chemical properties of toluene
Halogenation
The toluene molecule can be considered as consisting of fragments of benzene and methane molecules. Therefore, it is logical to assume that the chemical properties of toluene should to some extent combine the chemical properties of these two substances taken separately. In particular, this is precisely what is observed during its halogenation. We already know that benzene enters into a substitution reaction with chlorine by an electrophilic mechanism, and catalysts (aluminum or ferric halides) must be used to carry out this reaction. At the same time, methane is also capable of reacting with chlorine, but by a free radical mechanism, which requires irradiation of the initial reaction mixture with UV light. Toluene, depending on the conditions under which it undergoes chlorination, is able to give either the products of substitution of hydrogen atoms in the benzene ring - for this you need to use the same conditions as in the chlorination of benzene, or the products of substitution of hydrogen atoms in the methyl radical, if on it, how to act on methane with chlorine when irradiated with ultraviolet light:
As you can see, the chlorination of toluene in the presence of aluminum chloride led to two different products - ortho- and para-chlorotoluene. This is due to the fact that the methyl radical is a substituent of the first kind.
If the chlorination of toluene in the presence of AlCl 3 is carried out in excess of chlorine, the formation of trichlorine-substituted toluene is possible:
Similarly, when toluene is chlorinated in the light at a higher chlorine / toluene ratio, dichloromethylbenzene or trichloromethylbenzene can be obtained:
Nitration
The substitution of hydrogen atoms for nitrogroup, during the nitration of toluene with a mixture of concentrated nitric and sulfuric acids, leads to substitution products in the aromatic nucleus, and not in the methyl radical:
Alkylation
As already mentioned, the methyl radical is an orientant of the first kind, therefore, its Friedel-Crafts alkylation leads to substitution products in the ortho and para positions:
Addition reactions
Toluene can be hydrogenated to methylcyclohexane using metal catalysts (Pt, Pd, Ni):
C 6 H 5 CH 3 + 9O 2 → 7CO 2 + 4H 2 O
incomplete oxidation
Under the action of such an oxidizing agent as an aqueous solution of potassium permanganate, the side chain undergoes oxidation. The aromatic nucleus cannot be oxidized under such conditions. In this case, depending on the pH of the solution, either a carboxylic acid or its salt will be formed.
Alkanes
Limit hydrocarbons - alkanes- enter into substitution reactions and do not enter into addition reactions. While for almost all unsaturated compounds, i.e. substances containing double and triple bonds, this type of reaction is the most characteristic.
1. Substitution reactions
A) Halogenation:
Where hv is the formula for the quantum of light chloromethane
With a sufficient amount of chlorine, the reaction continues further and leads to the formation of a mixture of products of substitution of two, three, and four hydrogen atoms:
The halogenation reaction of alkanes proceeds according to the radical chain mechanism, i.e. as a chain of successive transformations involving free radical particles.
Consider the mechanism of radical substitution using the example of methane monochlorination:
Stage 1 - the origin of the chain- the appearance of free radicals in the reaction zone. Under the action of light energy, the bond in the Cl:Cl molecule is homolytically destroyed into two chlorine atoms with unpaired electrons (free radicals):
Stage 2 - chain growth (development). Free radicals, interacting with molecules, give rise to new radicals and develop a chain of transformations:
Stage 3 - open circuit. Radicals, connecting with each other, form molecules and break the chain of transformations:
When chlorinating or brominating an alkane with secondary or tertiary carbon atoms, the easiest way is to replace hydrogen at the tertiary atom, more difficult for the secondary, and even more difficult for the primary. This is explained by the greater stability of tertiary and secondary hydrocarbon radicals compared to primary ones due to the delocalization of the unpaired electron. Therefore, for example, during the chlorination of propane, the main reaction product is 2-chloropropane:
b) Nitration of alkanes (Konovalov reaction)
Alkanes are affected by dilute nitric acid under heating (140-150 °C) and pressure. As a result, the hydrogen atom is replaced by a nitric acid residue - the NO 2 nitro group. This reaction is called the nitration reaction, and the reaction products are called nitro compounds.
Reaction scheme:
2. Oxidation reactions
a) all alkanes burn to form carbon dioxide and water:
b) partial oxidation of alkanes at a relatively low temperature and with the use of catalysts is accompanied by the breaking of only part of the C-C and C-H bonds:
As a result of oxidation reactions, depending on the structure of the alkane, other substances can be obtained: ketones, aldehydes, alcohols.
3. Isomerization reactions(with AlCl 3 catalyst):
4. Decomposition reactions:
Cycloalkanes
The chemical properties of cycloalkanes largely depend on the number of carbon atoms in the cycle. Three- and four-membered cycles ( small cycles), being saturated, nevertheless sharply differ from all other saturated hydrocarbons. The bond angles in cyclopropane and cyclobutane are much smaller than the normal tetrahedral angle of 109 ° 28 ", characteristic of the sp 3 -hybridized carbon atom. This leads to a high tension of such cycles and their tendency to open under the action of reagents. Therefore, cyclopropane, cyclobutane and their derivatives enter into addition reactions, showing the character of unsaturated compounds. The ease of addition reactions decreases with decreasing cycle intensity in the series:
cyclopropane > cyclobutane >> cyclopentane.
The most stable are 6-member cycles, in which there are no angular and other types of stress.
Small cycles(С 3 -С 4) quite easily enter into hydrogenation reactions:
Cyclopropane and its derivatives add halogens and hydrogen halides:
For cycloalkanes (C 5 and higher), due to their greater stability, reactions are characteristic in which the cyclic structure is preserved, i.e. substitution reactions.
Chlorination cyclohexane follows a chain mechanism (similar to substitution in alkanes):
These compounds, like alkanes, also enter into dehydrogenation reactions in the presence of a catalyst, etc.
Dehydrogenation cyclohexane and its alkyl derivatives:
Alkenes
Alkenes are unsaturated hydrocarbons. Their molecules contain one double bond (σ-bond and π-bond). It is with the breaking of the weaker π-bond that the addition reactions proceed.
Alkenes undergo a variety of addition reactions. Hydrogen molecules can act as reactants ( hydrogenation reaction), halogens ( halogenation reaction), hydrogen halides ( hydrohalogenation reaction), water ( hydration reaction). Due to the rupture of the π-bond, the polymerization reaction also proceeds. In general, the schemes of these processes can be written as follows.
Let us consider the mechanism of the hydration reaction occurring in the presence of mineral acids according to the mechanism of electrophilic addition 1:
In the interaction of unsymmetrical alkenes with molecules of hydrogen halides or water, the rule of V.V. Markovnikov: the addition of a hydrogen atom to an unsymmetrical alkene molecule occurs predominantly to a more hydrogenated carbon atom (already connected to a large number of hydrogen atoms).
A variation of the addition reaction is polymerization reaction, during which the formation of a high molecular weight compound (polymer) occurs by sequential addition of molecules of a low molecular weight substance (monomer) according to the scheme:
The number n in the polymer formula (M n) is called degree of polymerization. The polymerization reactions of alkenes are due to the addition of multiple bonds:
Alkenes enter into oxidation reactions, for example, with potassium permanganate.
In a neutral and acidic environment, the reactions proceed differently.
Alkadienes (dienes)
The properties of alkadienes (dienes) are similar to those of alkenes. The main difference in their properties is due to the presence of two double bonds in the molecules, and it is their location that plays an important role. Of greatest interest are the conjugated alkadienes (i.e. those having conjugate double bonds (separated by one σ-bond). They differ in characteristic properties due to the electronic structure of the molecules, namely, a continuous sequence of four sp 2 carbon atoms, for example, butadiene-1,3: CH 2 \u003d CH - CH \u003d CH 2
Consider the chemical properties of dienes.
1. hydrogenation
Hydrogenation of butadiene-1,3 gives butene-2, i.e. 1,4 addition occurs. In this case, double bonds are broken, hydrogen atoms are attached to the extreme carbon atoms C 1 and C 4, and free valences form a double bond between C 2 and C 3 atoms:
In the presence of a Ni catalyst, a complete hydrogenation product is obtained:
2. Halogenation- proceeds similarly to the hydrogenation reaction. Preferably, halogen atoms are attached to the first and fourth carbon atoms (addition-1,4):
As a side process, 1,2-addition occurs:
With an excess of chlorine, one more of its molecules is added at the site of the remaining double bond to form 1,2,3,4-tetrachlorobutane.
The addition of halogens, hydrogen halides, water and other polar reagents occurs by an electrophilic mechanism (as in alkenes).
Addition reactions include reactions polymerization characteristic of dienes. This process is essential in the production of synthetic rubbers.
The polymerization of 1,3-dienes can proceed either by the 1,4-addition type or by a mixed 1,2- and 1,4-addition type. The direction of addition depends on the reaction conditions.
The first synthetic rubber obtained by the method of S.V. Lebedev during the polymerization of divinyl under the action of metallic sodium, was an irregular polymer with a mixed type of 1,2- and 1,4-addition units:
Alkynes
The main type of reaction for alkynes, as well as for alkenes and dienes, is the addition reaction.
1. hydrogenation
In the presence of metal catalysts (Pt, Ni), alkynes add hydrogen (the first π-bond breaks) to form alkenes, and then the second π-bond breaks, and alkanes are formed:
When other (less active catalysts) are used, hydrogenation stops at the stage of alkene formation.
2. Halogenation
The electrophilic addition of halogens to alkynes proceeds more slowly than for alkenes (the first π-bond is more difficult to break than the second):
Alkynes decolorize bromine water (qualitative reaction).
3. Hydrohalogenation
The addition of hydrogen halides to amines also proceeds by the electrophilic mechanism. The products of addition to unsymmetrical alkynes are determined by the rule of V.V. Markovnikov:
Hydrochlorination of acetylene is used in one of the industrial methods for producing vinyl chloride:
Vinyl chloride is the starting material (monomer) in the production of polyvinyl chloride (PVC).
4. Hydration (Kucherov reaction)
The addition of water to alkynes occurs in the presence of a mercury(II) salt catalyst and proceeds through the formation of an unstable unsaturated alcohol, which isomerizes into acetaldehyde (in the case of acetylene):
or to a ketone (in the case of other alkynes):
5. Polymerization
a) Dimerization under the action of an aqueous ammonia solution of CuCl:
b) Trimerization of acetylene over activated carbon leads to the formation of benzene (Zelinsky reaction):
6. Acidic properties of acetylene
Acetylene and its homologues with a terminal triple bond R-C ≡ C-H (alkynes-1) exhibit weak acidic properties due to the polarity of the C(sp)-H bond: hydrogen atoms can be replaced by metal atoms. As a result, salts are formed acetylenides:
Acetylides of alkali and alkaline earth metals are used to obtain acetylene homologues.
When acetylene (or R-C ≡ C-H) interacts with ammonia solutions of silver oxide or copper(I) chloride, precipitates of insoluble acetylenides precipitate:
7. Oxidation of alkynes
Acetylene and its homologues are easily oxidized by various oxidizing agents (potassium permanganate in an acidic and alkaline medium, potassium dichromate in an acidic medium, etc.). The structure of the oxidation products depends on the nature of the oxidizing agent and the reaction conditions.
For example, when acetylene is oxidized in an alkaline medium, oxalate is formed:
At tough Oxidation (heating, concentrated solutions, acidic environment) splits the carbon skeleton of the alkyne molecule along the triple bond and carboxylic acids are formed:
Alkynes discolour dilute potassium permanganate solution, which is used to prove their unsaturation. Under these conditions, there soft oxidation without breaking the σ-bond С-С (only π-bonds are destroyed). For example, when acetylene interacts with a dilute solution of KMnO 4 at room temperature, the following transformations are possible with the formation of oxalic acid HOOC-COOH:
When alkynes are burned, they complete oxidation to CO 2 and H 2 O. The combustion of acetylene is accompanied by the release of a large amount of heat:
A qualitative reaction to unsaturated hydrocarbons is the decolorization of bromine water and potassium permanganate solution (see Section 4).
