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 occurring at high temperature, as a result of which the carbon skeleton of alkane molecules breaks with the formation of alkene and alkane molecules with lower molecular weights compared to the original 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 breaking the C-H bonds; 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. Under the action of an aqueous solution of KMnO 4 on alkenes, discoloration, which is a qualitative reaction to double and triple CC bonds in molecules of organic substances.
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 becomes colorless.
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. Aluminum halides, ferric iron halides or inorganic acids can be used as catalysts.<
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 radiation:
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.
Hydrocarbons, in the molecules of which the atoms are connected by single bonds and which correspond to the general formula C n H 2 n +2.
In alkane molecules, all carbon atoms are in a state of sp 3 hybridization. This means that all four hybrid orbitals of the carbon atom are identical in shape, energy and are directed to the corners of an equilateral triangular pyramid - a tetrahedron. The angles between the orbitals are 109° 28'.
Almost free rotation is possible around a single carbon-carbon bond, and alkane molecules can take on a wide variety of shapes with angles at carbon atoms close to tetrahedral (109 ° 28 ′), for example, in a molecule n-pentane.
It is especially worth recalling the bonds in the molecules of alkanes. All bonds in the molecules of saturated hydrocarbons are single. Overlapping occurs along the axis,
connecting the nuclei of atoms, i.e., these are σ-bonds. Carbon-carbon bonds are non-polar and poorly polarizable. The length of the C-C bond in alkanes is 0.154 nm (1.54 10 - 10 m). C-H bonds are somewhat shorter. The electron density is slightly shifted towards the more electronegative carbon atom, i.e., the C-H bond is weakly polar.
The absence of polar bonds in the molecules of saturated hydrocarbons leads to the fact that they are poorly soluble in water and do not interact with charged particles (ions). The most characteristic of alkanes are reactions that involve free radicals.
Homologous series of methane
homologues- substances similar in structure and properties and differing by one or more CH 2 groups.
Isomerism and nomenclature
Alkanes are characterized by the so-called structural isomerism. Structural isomers differ from each other in the structure of the carbon skeleton. The simplest alkane, which is characterized by structural isomers, is butane. 
Fundamentals of nomenclature
1. Selecting the main circuit. The formation of the name of a hydrocarbon begins with the definition of the main chain - the longest chain of carbon atoms in a molecule, which is, as it were, its basis.
2. Numbering of atoms of the main chain. The atoms of the main chain are assigned numbers. The numbering of atoms of the main chain starts from the end closest to the substituent (structures A, B). If the substituents are at an equal distance from the end of the chain, then the numbering starts from the end at which there are more of them (structure B). If different substituents are at an equal distance from the ends of the chain, then the numbering starts from the end to which the older one is closer (structure G). The seniority of hydrocarbon substituents is determined by the order in which the letter with which their name begins follows in the alphabet: methyl (-CH 3), then ethyl (-CH 2 -CH 3), propyl (-CH 2 -CH 2 -CH 3 ) etc.
Note that the name of the substitute is formed by replacing the suffix -an with the suffix - silt in the name of the corresponding alkane.
3. Name formation. Numbers are indicated at the beginning of the name - the numbers of carbon atoms at which the substituents are located. If there are several substituents at a given atom, then the corresponding number in the name is repeated twice separated by a comma (2,2-). After the number, a hyphen indicates the number of substituents ( di- two, three- three, tetra- four, penta- five) and the name of the substituent (methyl, ethyl, propyl). Then without spaces and hyphens - the name of the main chain. The main chain is referred to as a hydrocarbon - a member of the methane homologous series ( methane CH 4, ethane C 2 H 6, propane C 3 H 8, C 4 H 10, pentane C 5 H 12, hexane C 6 H 14, heptane C 7 H 16, octane C 8 H 18, nonan C 9 H 20, dean C 10 H 22).
Physical properties of alkanes
The first four representatives of the homologous series of methane are gases. The simplest of them is methane - a colorless, tasteless and odorless gas (the smell of "gas", having felt which, you need to call 04, is determined by the smell of mercaptans - sulfur-containing compounds specially added to methane used in household and industrial gas appliances so that people those near them could smell the leak).
Hydrocarbons of composition from C 4 H 12 to C 15 H 32 - liquids; heavier hydrocarbons are solids. The boiling and melting points of alkanes gradually increase with increasing carbon chain length. All hydrocarbons are poorly soluble in water; liquid hydrocarbons are common organic solvents.
Chemical properties of alkanes
substitution reactions.
The most characteristic of alkanes are free radical substitution reactions, during which a hydrogen atom is replaced by a halogen atom or some group. Let us present the equations of characteristic reactions halogenation: 
In the case of an excess of halogen, chlorination can go further, up to the complete replacement of all hydrogen atoms by chlorine: 
The resulting substances are widely used as solvents and starting materials in organic synthesis.
Dehydrogenation reaction(hydrogen splitting off).
During the passage of alkanes over the catalyst (Pt, Ni, Al 2 0 3, Cr 2 0 3) at a high temperature (400-600 ° C), a hydrogen molecule is split off and an alkene is formed:
Reactions accompanied by the destruction of the carbon chain.
All saturated hydrocarbons burn with the formation of carbon dioxide and water. Gaseous hydrocarbons mixed with air in certain proportions can explode.
1. Combustion of saturated hydrocarbons is a free radical exothermic reaction, which is very important when using alkanes as a fuel:
In general, the combustion reaction of alkanes can be written as follows:
2. Thermal splitting of hydrocarbons.
The process proceeds according to the free radical mechanism. An increase in temperature leads to a homolytic rupture of the carbon-carbon bond and the formation of free radicals.
These radicals interact with each other, exchanging a hydrogen atom, with the formation of an alkane molecule and an alkene molecule:
Thermal splitting reactions underlie the industrial process - hydrocarbon cracking. This process is the most important stage of oil refining.
3. Pyrolysis. When methane is heated to a temperature of 1000 ° C, pyrolysis of methane begins - decomposition into simple substances: 
When heated to a temperature of 1500 ° C, the formation of acetylene is possible:
4. Isomerization. When linear hydrocarbons are heated with an isomerization catalyst (aluminum chloride), substances with a branched carbon skeleton are formed: 
5. Aromatization. Alkanes with six or more carbon atoms in the chain in the presence of a catalyst are cyclized to form benzene and its derivatives: 
Alkanes enter into reactions that proceed according to the free radical mechanism, since all carbon atoms in alkane molecules are in a state of sp 3 hybridization. The molecules of these substances are built using covalent non-polar C-C (carbon - carbon) bonds and weakly polar C-H (carbon - hydrogen) bonds. They do not have areas with high and low electron density, easily polarizable bonds, i.e., such bonds, the electron density in which can be shifted under the influence of external factors (electrostatic fields of ions). Consequently, alkanes will not react with charged particles, since bonds in alkane molecules are not broken by a heterolytic mechanism. 
DEFINITION
Alkanes saturated hydrocarbons are called, the molecules of which consist of carbon and hydrogen atoms, linked to each other only by σ-bonds.
Under normal conditions (at 25 o C and atmospheric pressure), the first four members of the homologous series of alkanes (C 1 - C 4) are gases. Normal alkanes from pentane to heptadecane (C 5 - C 17) are liquids, starting from C 18 and above are solids. As the relative molecular weight increases, the boiling and melting points of alkanes increase. With the same number of carbon atoms in a molecule, branched alkanes have lower boiling points than normal alkanes. The structure of the alkanes molecule using methane as an example is shown in fig. 1.
Rice. 1. The structure of the methane molecule.
Alkanes are practically insoluble in water, since their molecules are of low polarity and do not interact with water molecules. Liquid alkanes mix easily with each other. They dissolve well in non-polar organic solvents such as benzene, carbon tetrachloride, diethyl ether, etc.
Obtaining alkanes
The main sources of various saturated hydrocarbons containing up to 40 carbon atoms are oil and natural gas. Alkanes with a small number of carbon atoms (1 - 10) can be isolated by fractional distillation of natural gas or gasoline fraction of oil.
There are industrial (I) and laboratory (II) methods for obtaining alkanes.
C + H 2 → CH 4 (kat = Ni, t 0);
CO + 3H 2 → CH 4 + H 2 O (kat \u003d Ni, t 0 \u003d 200 - 300);
CO 2 + 4H 2 → CH 4 + 2H 2 O (kat, t 0).
— hydrogenation of unsaturated hydrocarbons
CH 3 -CH \u003d CH 2 + H 2 →CH 3 -CH 2 -CH 3 (kat \u003d Ni, t 0);
— recovery of haloalkanes
C 2 H 5 I + HI → C 2 H 6 + I 2 (t 0);
- alkaline melting reactions of salts of monobasic organic acids
C 2 H 5 -COONa + NaOH → C 2 H 6 + Na 2 CO 3 (t 0);
- interaction of haloalkanes with metallic sodium (Wurtz reaction)
2C 2 H 5 Br + 2Na → CH 3 -CH 2 -CH 2 -CH 3 + 2NaBr;
– electrolysis of salts of monobasic organic acids
2C 2 H 5 COONa + 2H 2 O → H 2 + 2NaOH + C 4 H 10 + 2CO 2;
K (-): 2H 2 O + 2e → H 2 + 2OH -;
A (+): 2C 2 H 5 COO - -2e → 2C 2 H 5 COO + → 2C 2 H 5 + + 2CO 2.
Chemical properties of alkanes
Alkanes are among the least reactive organic compounds, which is explained by their structure.
Alkanes under normal conditions do not react with concentrated acids, molten and concentrated alkalis, alkali metals, halogens (except fluorine), potassium permanganate and potassium dichromate in an acidic environment.
For alkanes, reactions proceeding according to the radical mechanism are most characteristic. The homolytic cleavage of C-H and C-C bonds is energetically more favorable than their heterolytic cleavage.
Radical substitution reactions proceed most easily at the tertiary carbon atom, more easily at the secondary carbon atom, and lastly at the primary carbon atom.
All chemical transformations of alkanes proceed with splitting:
1) C-H bonds
- halogenation (S R)
CH 4 + Cl 2 → CH 3 Cl + HCl ( hv);
CH 3 -CH 2 -CH 3 + Br 2 → CH 3 -CHBr-CH 3 + HBr ( hv).
- nitration (S R)
CH 3 -C (CH 3) H-CH 3 + HONO 2 (dilute) → CH 3 -C (NO 2) H-CH 3 + H 2 O (t 0).
– sulfochlorination (S R)
R-H + SO 2 + Cl 2 → RSO 2 Cl + HCl ( hv).
– dehydrogenation
CH 3 -CH 3 → CH 2 \u003d CH 2 + H 2 (kat \u003d Ni, t 0).
— dehydrocyclization
CH 3 (CH 2) 4 CH 3 → C 6 H 6 + 4H 2 (kat = Cr 2 O 3, t 0).
2) C-H and C-C bonds
- isomerization (intramolecular rearrangement)
CH 3 -CH 2 -CH 2 -CH 3 →CH 3 -C (CH 3) H-CH 3 (kat \u003d AlCl 3, t 0).
- oxidation
2CH 3 -CH 2 -CH 2 -CH 3 + 5O 2 → 4CH 3 COOH + 2H 2 O (t 0, p);
C n H 2n + 2 + (1.5n + 0.5) O 2 → nCO 2 + (n + 1) H 2 O (t 0).
Application of alkanes
Alkanes have found application in various industries. Let us consider in more detail, using the example of some representatives of the homologous series, as well as mixtures of alkanes.
Methane is the raw material basis of the most important chemical industrial processes for producing carbon and hydrogen, acetylene, oxygen-containing organic compounds - alcohols, aldehydes, acids. Propane is used as an automotive fuel. Butane is used to produce butadiene, which is a raw material for the production of synthetic rubber.
A mixture of liquid and solid alkanes up to C 25, called vaseline, is used in medicine as the basis for ointments. A mixture of solid alkanes C 18 - C 25 (paraffin) is used to impregnate various materials (paper, fabrics, wood) to give them hydrophobic properties, i.e. water impermeability. In medicine, it is used for physiotherapeutic procedures (paraffin treatment).
Examples of problem solving
EXAMPLE 1
| Exercise | When chlorinating methane, 1.54 g of the compound was obtained, the vapor density in air of which is 5.31. Calculate the mass of manganese dioxide MnO 2 that will be required to produce chlorine if the ratio of the volumes of methane and chlorine introduced into the reaction is 1:2. |
| Solution | The ratio of the mass of a given gas to the mass of another gas taken in the same volume, at the same temperature and the same pressure, is called the relative density of the first gas over the second. This value shows how many times the first gas is heavier or lighter than the second gas. The relative molecular weight of air is taken equal to 29 (taking into account the content of nitrogen, oxygen and other gases in the air). It should be noted that the concept of "relative molecular weight of air" is used conditionally, since air is a mixture of gases. Let's find the molar mass of the gas formed during the chlorination of methane: M gas \u003d 29 × D air (gas) \u003d 29 × 5.31 \u003d 154 g / mol. This is carbon tetrachloride - CCl 4 . We write the reaction equation and arrange the stoichiometric coefficients: CH 4 + 4Cl 2 \u003d CCl 4 + 4HCl. Calculate the amount of carbon tetrachloride substance: n(CCl 4) = m(CCl 4) / M(CCl 4); n (CCl 4) \u003d 1.54 / 154 \u003d 0.01 mol. According to the reaction equation n (CCl 4) : n (CH 4) = 1: 1, then n (CH 4) \u003d n (CCl 4) \u003d 0.01 mol. Then, the amount of chlorine substance should be equal to n(Cl 2) = 2 × 4 n(CH 4), i.e. n(Cl 2) \u003d 8 × 0.01 \u003d 0.08 mol. We write the reaction equation for the production of chlorine: MnO 2 + 4HCl \u003d MnCl 2 + Cl 2 + 2H 2 O. The number of moles of manganese dioxide is 0.08 moles, because n (Cl 2) : n (MnO 2) = 1: 1. Find the mass of manganese dioxide: m (MnO 2) \u003d n (MnO 2) × M (MnO 2); M (MnO 2) \u003d Ar (Mn) + 2 × Ar (O) \u003d 55 + 2 × 16 \u003d 87 g / mol; m (MnO 2) \u003d 0.08 × 87 \u003d 10.4 g. |
| Answer | The mass of manganese dioxide is 10.4 g. |
EXAMPLE 2
