Alkanes

Chemical structure (above) and 3D-model (below) of methane - the simplest alkane

Alkanes (also saturated hydrocarbons , paraffins ) are acyclic hydrocarbons of linear or branched structure, containing only simple bonds and forming a homologous series with the general formula C _n H _{2n + 2} .

All alkanes belong to a larger class of aliphatic hydrocarbons. Alkanes are saturated hydrocarbons, that is, contain the maximum possible number of hydrogen atoms for a given number of carbon atoms. Each carbon atom in alkane molecules is in a state of sp ³ - hybridization - all 4 hybrid orbitals of atom C are identical in shape and energy, 4 bonds are directed to the vertices of the tetrahedron at 109 ° 28 'angles. C – C bonds are σ-bonds characterized by low polarity and polarizability . The C – C bond length is 0.154 nm , the C – H bond length is 0.1087 nm .

The simplest member of the class is methane (CH ₄ ). The longest chain hydrocarbon — non - contatriktan C ₃₉₀ H _{782 was} synthesized in 1985 by British chemists I. Bidd and MK Whiting ^[1] .

Nomenclature

Rational

One of the atoms of the carbon chain is selected, it is considered to be substituted methane, and the name “alkyl alkyl 2 alkyl 3 alkyl 4 methane” is built up relative to it, for example:

a : n- butyl- sec- butylisobutylmethane

b : triisopropylmethane

in : triethylpropylmethane

Systematic IUPAC

According to the IUPAC nomenclature, the names of alkanes are formed using the suffix -an by adding to the corresponding root the name of the hydrocarbon. The longest unbranched hydrocarbon chain is selected, and the numbering of this chain starts from the side of the substituent nearest to the end of the chain. In the name of the compound, the number indicates the carbon atom number at which the replacement group or heteroatom is located , then the name of the group or heteroatom and the name of the main chain. If the groups are repeated, then list the numbers indicating their position, and the number of identical groups is indicated by the prefixes di-, tri-, tetra-. If the groups are not the same, their names are listed in alphabetical order. ^[2]

For example:

2,6,6-trimethyl-3-ethylheptane (from left to right) / 2,2,6-trimethyl-5-ethylheptane (from right to left)

When comparing the positions of substituents in both combinations, preference is given to the one in which the first distinct digit is the smallest. Thus, the correct name is 2, 2 , 6-trimethyl-5-ethylheptane .

Homologous series and isomerism

Alkanes form a homologous series .

Homologous series of alkanes (first 10 members)
Methane	CH ₄	CH ₄
Ethane	CH ₃ —CH ₃	C ₂ H ₆
Propane	CH ₃ —CH ₂ —CH ₃	C ₃ H ₈
Butane	CH ₃ —CH ₂ —CH ₂ —CH ₃	C ₄ H ₁₀
Pentane	CH ₃ —CH ₂ —CH ₂ —CH ₂ —CH ₃	C ₅ H ₁₂
Hexane	CH ₃ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₃	C ₆ H ₁₄
Heptane	CH ₃ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₃	C ₇ H ₁₆
Octane	CH ₃ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₃	C ₈ H ₁₈
Nonan	CH ₃ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₃	C ₉ H ₂₀
Dean	CH ₃ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₂ —CH ₃	C ₁₀ H ₂₂

Alkanes, the number of carbon atoms in which more than three, have isomers. The isomerism of saturated hydrocarbons is due to the simplest type of structural isomerism — the carbon skeleton isomerism, and, starting from C ₇ H ₁₆ , also to optical isomerism ^[3] . The number of structural isomers of alkanes C _n H _{2n + 2} depending on the number of carbon atoms n excluding stereoisomerism ^[4] ^[5] and taking into account stereoisomerism ^[6] :

n	The number of isomers	Taking into account stereoisomerism
four	2	2
five	3	3
6	five	five
7	9	eleven
eight	18	24
9	35	55
ten	75	136
eleven	159	345
12	355	900
13	802	2412
14	1858	6563
15	4347	18,127
20	366 319	3 396 844
25	36,797,588	749 329 719
thirty	4,111,846,763	182,896,187,256

The number of structural isomers of lower hydrocarbons to C ₁₄ H ₃₀ was established by direct calculation; in 1931, a recursive method for calculating the number of isomers was developed ^[7] . No simple bond was found between the number of carbon atoms n and the number of isomers ^[7] . With $n\rightarrow {\mathcal {1}}$ ${\ displaystyle n \ rightarrow {\ mathcal {1}}}$ The number of different structural isomers of alkanes can be estimated using the Redfield – Poya theorem ^[8] .

Physical Properties

Melting and boiling points increase with molecular weight and main carbon chain length.
Under standard conditions established by IUPAC ( pressure 10 ⁵ Pa , temperature 0 ° C), unbranched alkanes from CH ₄ to C ₄ H ₁₀ are gases, from C ₅ H ₁₂ to C ₁₃ H ₂₈ - from C ₁₄ H ₃₀ and further - with solid substances.
Melting and boiling points fall from less branched to more branched. For example, at 20 ° C, n- pentane is a liquid, and neopentane is a gas.
Gaseous alkanes burn with a colorless or pale blue flame with a large amount of heat.

Physical properties of normal alkanes
n	Title	T _pl , ° C	T _kip , ° C	Density , g / cm ³	Refractive index
one	Methane	−182,48	−161,5	0.416 at T _kip
2	Ethane	−183.3	−88.63	0.546 at T _kip
3	Propane	−187,7	−42,1	0.585 at T _kip
four	Butane	−138.35	−0.5	0.6 at T _kip	1.3326
four	Isobutane	−159,60	−11.73	0.5510 at T _kip
five	Pentane	−129,7	36.07	0.6262	1.3575
6	Hexane	−95.3	68.7	0.6594	1.3749
7	Heptane	−90,6	98.4	0.638	1.3876
eight	Octane	−55,8	125.7	0.7025	1.3974
9	Nonan	−54	150.8	0.718	1.4054
ten	Dean	−29,7	174.1	0.730	1.4119
eleven	Undecane	−25,6	195.9	0.7402	1.4151
12	Dodecane	−9,6	216.3	0.7487	1.4216
13	Tridecan	−5,4	235.5	0.7564	1.4256
14	Tetradecane	5.9	253.6	0.7628	1.4289
15	Pentadecane	9.9	270,6	0.7685	1.4310
sixteen	Hexadecane	18.2	286.8	0.7734	1.4345
17	Heptadecane	22.0	301.9	0.778 *	1.4369 *
18	Octadecane	28.2	316.1	0.7819 *	1.4390 *
nineteen	Nonadecan	32.1	329.76	0.7855 *	1.4409 *
20	Eykosan	36.8	342.7	0.7887 *	1,4426 *
21	Genekosan	40.5	355.1	0.7917 *	1.4441 *
22	Dokosan	44.4	367.0	0.7944 *	1.4455 *
23	Tricosane	47.6	378.3	0.7969 *	1.4468 *
24	Tetrakosan	50.9	389.2	0.7991 *	1.4480 *
25	Pentacosan	53.7	399.7	0.8012 *	1.4491 *
26	Hexacosan	57	262 (15 mmHg)	0.778
27	Heptacosan	60	270 (15 mmHg)	0.780
28	Octacosan	61.1	280 (15 mmHg)	0,807
29	Nonakosan	64	286 (15 mmHg. Art.)	0,808
thirty	Triacontan	65,8	446.4	0.897 *	1.4536 *
31	Gentriacontan	67.9	455	0.8111 *	1.4543 *
32	Dotriacontan	69.7	463	0.8124 *	1.4550 *
33	Tritriacontan	71	474	0.811
34	Tetratriacontan	73.1	478	0.8148 *	1.4563 *
35	Pentatriacontan	74.7	486	0.8159 *	1.4568 *
36	Hexatriacontan	75	265 at 130 Pa	0.814
37	Heptatriacontan	77.4	504.14	0.815
38	Octatriacontan	79	510.93	0.816
39	Nonatriacontan	78	517.51	0.817
40	Tetracontan	81.4	523.88	0.817
41	Gentetracontan	80.7	530.75	0.818
42	Dotetracontan	82.9	536.07	0.819
43	Tritetracontan	85.3	541.91	0.820
44	Tetratetracontan	86.4	547.57	0.820
45	Pentatetracontan		553.1	0.821
46	Hexatetracontan		558.42	0.822
47	Heptathetracontan		563.6	0.822
48	Octate tetracontan		568.68	0.823
49	Nonatetracontan		573.6	0.823
50	Pentacon	93	421	0.824
51	Master pentacon		583	0.824
52	Dopentakontan	94	587.6	0.825
53	Tripentacon		592	0.825
54	Tetrapentacontan	95	596.38	0.826
...	...	...	...	...	...
60	Hexacontan	98.9
...	...	...	...	...	...
70	Heptacontan	105.3
...	...	...	...	...	...
100	Hectan	115.2
...	...	...	...	...	...
150	Pentacontaghectan	123
...	...	...	...	...	...
390	Noncontrictrican	132

Note to the table: * marked values obtained for supercooled liquid.

Spectral properties

IR Spectroscopy

In the IR spectra of alkanes, the frequencies of stretching vibrations of the C – H bond in the region of 2850–3000 cm ^{– 1} are clearly manifested. The frequencies of stretching vibrations of the C – C bond are variable and often of low intensity. Characteristic deformation vibrations due to C – H in the methyl and methylene groups usually lie in the range of 1400–1470 cm ^{– 1} , but the methyl group gives a weak band in the spectra at 1380 cm ^{– 1} .

UV spectroscopy

Pure alkanes do not absorb radiation in the ultraviolet region above 2000 Å, and for this reason they are often excellent solvents for removing the UV spectra of other compounds.

Chemical Properties

Alkanes have a low chemical activity. This is explained by the fact that single C – H and C – C bonds are relatively strong and difficult to destroy. Since C – C bonds are non-polar, and C – H bonds are low-polar, both types of bonds are low-polarized and belong to the σ-form, their breaking is most probable by the homolytic mechanism, that is, with the formation of radicals.

Radical Substitution Reactions

Halogenation

Halogenation of alkanes proceeds by a radical mechanism. To initiate the reaction, a mixture of alkane and halogen must be irradiated with UV light or heated.

Chlorination of methane does not stop at the stage of methyl chloride production (if equimolar amounts of chlorine and methane are taken), but leads to the formation of all possible substitution products, from chloromethane to carbon tetrachloride . Chlorination of other alkanes leads to a mixture of hydrogen substitution products at different carbon atoms. The ratio of chlorination products depends on temperature. The rate of chlorination of primary, secondary, and tertiary atoms depends on temperature; at low temperature, the rate decreases in the order: tertiary, secondary, primary. As the temperature rises, the difference between the velocities decreases until it becomes the same. In addition to the kinetic factor, the distribution of chlorination products is influenced by the statistical factor: the probability of an attack by the chlorine of the tertiary carbon atom is 3 times less than the primary one, and 2 times less than the secondary one. Thus, chlorination of alkanes is a non-stereoselective reaction, except for the cases when only one monochlorination product is possible.

It is worth noting that the halogenation occurs the easier it is, the longer the carbon chain of the n- alkane. In the same direction, the ionization energy of a substance molecule decreases, that is, an alkane becomes easier to become an electron donor.

Halogenation is one of the substitution reactions . First of all, the least hydrogenated carbon atom is halogenated (the tertiary atom, then the secondary, the primary atoms are halogenated last). Halogenation of alkanes takes place in stages with the sequential formation of chloromethane , dichloromethane , chloroform and carbon tetrachloride : in one stage no more than one hydrogen atom is replaced:

{\mathsf {CH_{4}+Cl_{2}\rightarrow CH_{3}Cl+HCl}}

{\ displaystyle {\ mathsf {CH_ {4} + Cl_ {2} \ rightarrow CH_ {3} Cl + HCl}}}

{\mathsf {CH_{3}Cl+Cl_{2}\rightarrow CH_{2}Cl_{2}+HCl}}

{\ displaystyle {\ mathsf {CH_ {3} Cl + Cl_ {2} \ rightarrow CH_ {2} Cl_ {2} + HCl}}}

{\mathsf {CH_{2}Cl_{2}+Cl_{2}\rightarrow CHCl_{3}+HCl}}

{\ displaystyle {\ mathsf {CH_ {2} Cl_ {2} + Cl_ {2} \ rightarrow CHCl_ {3} + HCl}}}

{\mathsf {CHCl_{3}+Cl_{2}\rightarrow CCl_{4}+HCl}}

{\ displaystyle {\ mathsf {CHCl_ {3} + Cl_ {2} \ rightarrow CCl_ {4} + HCl}}}

Under the action of light, the chlorine molecule breaks down into radicals, then they attack alkane molecules, tearing off a hydrogen atom, as a result of which methyl radicals · CH _{3 are formed} , which collide with chlorine molecules, destroying them and forming new radicals.

Chain mechanism of halogenation:

1) Initiation

{\ce {\mathsf {Cl{\text{:}}Cl->[{h\nu }]Cl{\text{·}}+{\text{·}}Cl}}}

{\ displaystyle {\ ce {\ mathsf {Cl {\ text {:}} Cl -> [{h \ nu}] Cl {\ text {·}} + {\ text {·}} Cl}}}}

2) chain growth

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{-}}CH_{3}+Cl{\text{·}}\rightarrow CH_{3}{\text{-}}{\dot {CH}}{\text{-}}CH_{3}+HCl}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {-}} CH_ {3} + Cl {\ text {·}} \ rightarrow CH_ {3} {\ text {-}} {\ dot {CH}} {\ text {-}} CH_ {3} + HCl}}}

{\mathsf {CH_{3}{\text{-}}{\dot {CH}}{\text{-}}CH_{3}+Cl{\text{:}}Cl\rightarrow CH_{3}{\text{-}}CHCl{\text{-}}CH_{3}+Cl{\text{·}}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} {\ dot {CH}} {\ text {-}} CH_ {3} + Cl {\ text {:}} Cl \ rightarrow CH_ { 3} {\ text {-}} CHCl {\ text {-}} CH_ {3} + Cl {\ text {·}}}}

3) Open circuit

{\mathsf {CH_{3}{\text{-}}{\dot {CH}}{\text{-}}CH_{3}+Cl{\text{·}}\rightarrow CH_{3}{\text{-}}CHCl{\text{-}}CH_{3}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} {\ dot {CH}} {\ text {-}} CH_ {3} + Cl {\ text {·}} \ rightarrow CH_ {3 } {\ text {-}} CHCl {\ text {-}} CH_ {3}}}

Bromination of alkanes differs from chlorination by higher stereoselectivity due to the greater difference in the rates of bromination of tertiary, secondary and primary carbon atoms at low temperatures.

Alkane iodination with iodine does not occur, iodides can not be obtained by direct iodization.

With fluorine and chlorine, the reaction can proceed with an explosion, in such cases, the halogen is diluted with nitrogen or a suitable solvent.

Sulphurization

With simultaneous action on alkanes with sulfur oxide (IV) and oxygen, with ultraviolet irradiation or with the participation of substances that are donors of free radicals (diazomethane, organic peroxides), the sulfonation reaction proceeds with the formation of alkylsulfonic acids :

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{-}}CH_{2}{\text{-}}CH_{3}{\xrightarrow {O_{2};SO_{2};h\nu }}CH_{3}{\text{-}}CH_{2}{\text{-}}CH_{2}{\text{-}}CH_{2}{\text{-}}SO_{2}OH}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {-}} CH_ {2} {\ text {-}} CH_ {3} {\ xrightarrow {O_ { 2}; SO_ {2}; h \ nu}} CH_ {3} {\ text {-}} CH_ {2} {\ text {-}} CH_ {2} {\ text {-}} CH_ {2} {\ text {-}} SO_ {2} OH}}}

Sulphochlorination (Reed reaction)

When exposed to ultraviolet radiation, alkanes react with a mixture of SO ₂ and Cl _2. After an alkyl radical forms with the departure of hydrogen chloride, sulfur dioxide is added. The resulting complex radical is stabilized by the capture of a chlorine atom with the destruction of another molecule of the latter.

Chain process development:

{\mathsf {RH+Cl\cdot \rightarrow R\cdot +HCl}}

{\ displaystyle {\ mathsf {RH + Cl \ cdot \ rightarrow R \ cdot + HCl}}}

{\mathsf {R\cdot +SO_{2}\rightarrow RSO_{2}\cdot }}

{\ displaystyle {\ mathsf {R \ cdot + SO_ {2} \ rightarrow RSO_ {2} \ cdot}}}

{\mathsf {RSO_{2}\cdot +Cl_{2}\rightarrow RSO_{2}Cl+Cl\cdot }}

{\ displaystyle {\ mathsf {RSO_ {2} \ cdot + Cl_ {2} \ rightarrow RSO_ {2} Cl + Cl \ cdot}}}

It is easiest to sulfochlorinate carbohydrates of a linear structure, in contrast to the reactions of chlorination and nitration. ^[9]

The resulting sulfonyl chlorides are widely used in the production of surfactants .

Nitration

Alkanes react with a 10% solution of nitric acid or nitrous oxide NO ₂ in the gas phase at a temperature of 140 ° C and a slight pressure with the formation of nitro derivatives:

{\mathsf {RH+HNO_{3}\rightarrow RNO_{2}+H_{2}O}}

{\ displaystyle {\ mathsf {RH + HNO_ {3} \ rightarrow RNO_ {2} + H_ {2} O}}}

Available data point to a free radical mechanism. As a result of the reaction, mixtures of products are formed.

Oxidation Reactions

Auto-oxidation

The oxidation of alkanes in the liquid phase proceeds by a free-radical mechanism and leads to the formation of hydroperoxides , their decomposition products and interaction with the initial alkane. Scheme of the main auto-oxidation reaction:

{\mathsf {RH+O_{2}\rightarrow R\cdot +HOO\cdot }}

{\ displaystyle {\ mathsf {RH + O_ {2} \ rightarrow R \ cdot + HOO \ cdot}}}

{\mathsf {R\cdot +O_{2}\rightarrow ROO\cdot }}

{\ displaystyle {\ mathsf {R \ cdot + O_ {2} \ rightarrow ROO \ cdot}}}

{\mathsf {ROO\cdot +RH\rightarrow ROOH+R\cdot }}

{\ displaystyle {\ mathsf {ROO \ cdot + RH \ rightarrow ROOH + R \ cdot}}}

Combustion

The main chemical property of saturated hydrocarbons, which determine their use as a fuel, is the combustion reaction. Example:

{\mathsf {CH_{4}+2O_{2}\rightarrow CO_{2}+2H_{2}O+\Delta Q}}

{\ displaystyle {\ mathsf {CH_ {4} + 2O_ {2} \ rightarrow CO_ {2} + 2H_ {2} O + \ Delta Q}}}

The Q value reaches 46,000 - 50,000 kJ / kg .

In the case of a lack of oxygen instead of carbon dioxide, carbon monoxide (II) or carbon oxide is obtained (depending on the oxygen concentration).

Catalytic oxidation

In the reactions of catalytic oxidation of alkanes, alcohols , aldehydes , carboxylic acids can be formed.

During mild oxidation of CH ₄ in the presence of a catalyst with oxygen at 200 ° C, the following can be formed:

methanol : ${\mathsf {2CH_{4}+O_{2}\rightarrow 2CH_{3}OH}}$ ${\ displaystyle {\ mathsf {2CH_ {4} + O_ {2} \ rightarrow 2CH_ {3} OH}}}$
formaldehyde : ${\mathsf {CH_{4}+O_{2}\rightarrow HCHO+H_{2}O}}$ ${\ displaystyle {\ mathsf {CH_ {4} + O_ {2} \ rightarrow HCHO + H_ {2} O}}}$
formic acid : ${\mathsf {2CH_{4}+3O_{2}\rightarrow 2HCOOH+2H_{2}O}}$ ${\ displaystyle {\ mathsf {2CH_ {4} + 3O_ {2} \ rightarrow 2HCOOH + 2H_ {2} O}}}$

Oxidation can also be carried out by air. The process is carried out in the liquid or gaseous phase. In industry, they get higher fatty alcohols and the corresponding acids .

The reaction of the oxidation of alkanes by dimethyldioxyrane :

The mechanism of the reactions of producing acids by catalytic oxidation and cleavage of alkanes is shown below using the example of the production of acetic acid from butane :

Thermal transformations of alkanes

Decomposition

Decomposition reactions occur only under the influence of high temperatures. An increase in temperature leads to a rupture of the carbon bond and the formation of free radicals .

Examples:

{\mathsf {CH_{4}{\xrightarrow[{}]{^{o}t>1000^{o}C}}C+2H_{2}}}

{\ displaystyle {\ mathsf {CH_ {4} {\ xrightarrow [{}] {^ {o} t> 1000 ^ {o} C}} C + 2H_ {2}}}}

{\mathsf {C_{2}H_{6}\rightarrow 2C+3H_{2}}}

{\ displaystyle {\ mathsf {C_ {2} H_ {6} \ rightarrow 2C + 3H_ {2}}}

Cracking

When heated above 500 ° C, alkanes undergo pyrolytic decomposition to form a complex mixture of products, the composition and ratio of which depend on the temperature and reaction time. During pyrolysis , carbon-carbon bonds are split with the formation of alkyl radicals.

In the years 1930-1950. pyrolysis of higher alkanes was used in industry to produce a complex mixture of alkanes and alkenes containing from five to ten carbon atoms. He received the name of "thermal cracking." With the help of thermal cracking, it was possible to increase the amount of gasoline fraction by splitting alkanes contained in the kerosene fraction ( 10-15 carbon atoms in the carbon skeleton) and the fraction of solar oil ( 12-20 carbon atoms). However, the octane number of gasoline obtained by thermal cracking does not exceed 65, which does not meet the requirements of the operating conditions of modern internal combustion engines.

At present, thermal cracking is completely superseded in industry by catalytic cracking, which is carried out in the gas phase at lower temperatures - 400-450 ° C and low pressure - 10-15 atm on an aluminosilicate catalyst, which is continuously regenerated by burning coke formed on it in a current of air . During catalytic cracking in the resulting gasoline, the content of alkanes with a branched structure increases sharply.

For methane:

{\mathsf {2CH_{4}{\xrightarrow[{}]{^{o}t>1500^{o}C}}C_{2}H_{2}+3H_{2}}}

{\ displaystyle {\ mathsf {2CH_ {4} {\ xrightarrow [{}] {^ {o} t> 1500 ^ {o} C}} C_ {2} H_ {2} + 3H_ {2}}}

During cracking, one of the bonds (CC) is broken, forming two radicals. Then three processes occur simultaneously, due to which the reaction produces many different products.

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{:}}CH_{3}{\xrightarrow {1500^{\circ }C}}CH_{3}{\text{-}}CH_{2}{\text{·}}+{\text{·}}CH_{3}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {:}} CH_ {3} {\ xrightarrow {1500 ^ {\ circ} C}} CH_ {3} {\ text {-}} CH_ {2} {\ text {·}} + {\ text {·}} CH_ {3}}}

1) Recombination

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{·}}+{\text{·}}CH_{2}{\text{-}}CH_{3}\rightarrow CH_{3}{\text{-}}CH_{2}{\text{-}}CH_{2}{\text{-}}CH_{3}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {·}} + {\ text {·}} CH_ {2} {\ text {-}} CH_ { 3} \ rightarrow CH_ {3} {\ text {-}} CH_ {2} {\ text {-}} CH_ {2} {\ text {-}} CH_ {3}}}

{\mathsf {CH_{3}{\text{·}}+{\text{·}}CH_{2}{\text{-}}CH_{3}\rightarrow CH_{3}{\text{-}}CH_{2}{\text{-}}CH_{3}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {·}} + {\ text {·}} CH_ {2} {\ text {-}} CH_ {3} \ rightarrow CH_ {3} {\ text {-}} CH_ {2} {\ text {-}} CH_ {3}}}

{\mathsf {CH_{3}{\text{·}}+{\text{·}}CH_{3}\rightarrow CH_{3}{\text{-}}CH_{3}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {·}} + {\ text {·}} CH_ {3} \ rightarrow CH_ {3} {\ text {-}} CH_ {3}}}

2) Disproportionation

{\mathsf {CH_{3}{\text{·}}+{\text{·}}CH_{2}{\text{-}}CH_{3}\rightarrow CH_{4}+CH_{2}{\text{=}}CH_{2}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {·}} + {\ text {·}} CH_ {2} {\ text {-}} CH_ {3} \ rightarrow CH_ {4} + CH_ { 2} {\ text {=}} CH_ {2}}}}

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{·}}+{\text{·}}CH_{2}{\text{-}}CH_{3}\rightarrow CH_{3}{\text{-}}CH_{3}+CH_{2}{\text{=}}CH_{2}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {·}} + {\ text {·}} CH_ {2} {\ text {-}} CH_ { 3} \ rightarrow CH_ {3} {\ text {-}} CH_ {3} + CH_ {2} {\ text {=}} CH_ {2}}}

3) β-decay (bond break (CH))

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{·}}{\xrightarrow {-H{\text{·}}}}CH_{2}{\text{=}}CH_{2}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {·}} {\ xrightarrow {-H {\ text {·}}}} CH_ {2} {\ text {=}} CH_ {2}}}}

Dehydration

1) In the carbon skeleton, 2 (ethane) or 3 (propane) carbon atoms are the preparation of (terminal) alkenes, since others cannot be obtained in this case; hydrogen evolution:

Flow conditions: 400–600 ° C, Pt, Ni, Al ₂ O ₃ , Cr ₂ O ₃ catalysts, for example, ethylene formation from ethane:

{\mathsf {CH_{3}{\text{-}}CH_{3}\rightarrow CH_{2}{\text{=}}CH_{2}+H_{2}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {3} \ rightarrow CH_ {2} {\ text {=}} CH_ {2} + H_ {2}}}}

2) In the carbon skeleton, 4 (butane, isobutane) or 5 (pentane, 2-methylbutane, neopentane ) carbon atoms — production of alkadienes, for example, 1.3-butadiene and 1.3-butadiene from 1.2

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{-}}CH_{2}{\text{-}}CH_{3}\rightarrow CH_{2}{\text{=}}CH{\text{-}}CH{\text{=}}CH_{2}+2H_{2}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {-}} CH_ {2} {\ text {-}} CH_ {3} \ rightarrow CH_ {2} {\ text {=}} CH {\ text {-}} CH {\ text {=}} CH_ {2} + 2H_ {2}}}

{\mathsf {CH_{3}{\text{-}}CH_{2}{\text{-}}CH_{2}{\text{-}}CH_{3}\rightarrow CH_{2}{\text{=}}C{\text{=}}CH{\text{-}}CH_{3}+2H_{2}}}

{\ displaystyle {\ mathsf {CH_ {3} {\ text {-}} CH_ {2} {\ text {-}} CH_ {2} {\ text {-}} CH_ {3} \ rightarrow CH_ {2} {\ text {=}} C {\ text {=}} CH {\ text {-}} CH_ {3} + 2H_ {2}}}

3) In the carbon skeleton of 6 (hexane) and more carbon atoms - the production of benzene and its derivatives:

{\mathsf {CH_{3}(CH_{2})_{5}CH_{3}\rightarrow C_{6}H_{5}CH_{3}+4H_{2}}}

{\ displaystyle {\ mathsf {CH_ {3} (CH_ {2}) _ {5} CH_ {3} \ rightarrow C_ {6} H_ {5} CH_ {3} + 4H_ {2}}}

Methane Conversion

В присутствии никелевого катализатора протекает реакция:

{\mathsf {CH_{4}+H_{2}O\rightarrow CO+3H_{2}}}

{\mathsf {CH_{4}+H_{2}O\rightarrow CO+3H_{2}}}

Продукт этой реакции (смесь CO и H ₂ ) называется « синтез-газом ».

Реакции электрофильного замещения

Изомеризация:
Под действием катализатора (например, AlCl ₃ ) происходит изомеризация алкана: например, бутан (C ₄ H ₁₀ ), взаимодействуя с хлоридом алюминия (AlCl ₃ ), превращается из н -бутана в 2-метилпропан.

С марганцевокислым калием (KMnO ₄ ) и бромной водой (раствор Br ₂ в воде) алканы не взаимодействуют.

Being in nature

Нахождение в космосе

В небольших количествах алканы содержатся в атмосфере внешних газовых планет Солнечной системы: на Юпитере — 0,1 % метана , 0,0002 % этана , на Сатурне метана 0,2 %, а этана — 0,0005 %, метана и этана на Уране — соответственно 1,99 % и 0,00025 %, на Нептуне же — 1,5 % и 1,5⋅10 ⁻¹⁰ , соответственно ^[10] . На спутнике Сатурна Титане метан (1,6 %) содержится в жидком виде, причём, подобно воде, находящейся на Земле в круговороте , на Титане существуют (полярные) озёра метана (в смеси с этаном) и метановые дожди. К тому же, как предполагается, метан поступает в атмосферу Титана в результате деятельности вулкана ^[11] . Кроме того, метан найден в хвосте кометы Хиякутаке и в метеоритах ( углистых хондритах ). Предполагается также, что метановые и этановые кометные льды образовались в межзвёздном пространстве ^[12] .

Нахождение на Земле

Добыча нефти

В земной атмосфере метан присутствует в очень небольших количествах (около 0,0001 %), он производится некоторыми археями (архебактериями) , в частности, находящимися в кишечном тракте крупного рогатого скота . Промышленное значение имеют месторождения низших алканов в форме природного газа , нефти и, вероятно, в будущем — газовых гидратов (найдены в областях вечной мерзлоты и под океанами). Также метан содержится в биогазе .

Высшие алканы содержатся в кутикуле растений , предохраняя их от высыхания, паразитных грибков и мелких растительноядных организмов. Это обыкновенно цепи с нечётным числом атомов углерода , образующиеся при декарбоксилировании жирных кислот с чётным количеством углеродных атомов. У животных алканы встречаются в качестве феромонов у насекомых , в частности у мухи цеце (2-метилгептадекан C ₁₈ H ₃₈ , 17,21-диметилгептатриаконтан C ₃₉ H ₈₀ , 15,19-диметилгептатриаконтан C ₃₉ H ₈₀ и 15,19,23-триметилгептатриаконтан C ₄₀ H ₈₂ ). Некоторые орхидеи при помощи алканов-феромонов привлекают опылителей.

Getting

Главным источником алканов (а также других углеводородов) являются нефть и природный газ , которые обычно встречаются совместно.

Восстановление галогенпроизводных алканов:

При каталитическом гидрировании в присутствии палладия галогеналканы превращаются в алканы ^[13] :

{\mathsf {RCH_{2}Cl+H_{2}\rightarrow RCH_{3}+HCl}}

{\mathsf {RCH_{2}Cl+H_{2}\rightarrow RCH_{3}+HCl}}

Восстановление иодалканов происходит при нагревании последних с иодоводородной кислотой:

{\mathsf {RCH_{2}I+HI\rightarrow RCH_{3}+I_{2}}}

{\mathsf {RCH_{2}I+HI\rightarrow RCH_{3}+I_{2}}}

Для восстановления галогеналканов пригодны также амальгама натрия, гидриды металлов, натрий в спирте, цинк в соляной кислоте или цинк в спирте ^[13]

Восстановление спиртов :

Восстановление спиртов приводит к образованию углеводородов, содержащих то же количество атомов С. Так, например, проходит реакция восстановления бутанола (C ₄ H ₉ OH), проходящую в присутствии LiAlH ₄ . При этом выделяется вода ^[14] .

{\mathsf {CH_{3}CH_{2}CH_{2}CH_{2}OH{\xrightarrow[{}]{LiAlH_{4}}}CH_{3}CH_{2}CH_{2}CH_{3}+H_{2}O}}

{\mathsf {CH_{3}CH_{2}CH_{2}CH_{2}OH{\xrightarrow[{}]{LiAlH_{4}}}CH_{3}CH_{2}CH_{2}CH_{3}+H_{2}O}}

Восстановление карбонильных соединений

Реакция Кижнера — Вольфа :

Реакцию проводят в избытке гидразина в высококипящем растворителе в присутствии KOH ^[15] .

Реакция Клемменсена ^[16] :

Гидрирование непредельных углеводородов

Из алкенов

{\mathsf {C_{n}H_{2n}+H_{2}\rightarrow C_{n}H_{2n+2}}}

{\mathsf {C_{n}H_{2n}+H_{2}\rightarrow C_{n}H_{2n+2}}}

Из алкинов

{\mathsf {C_{n}H_{2n-2}+2H_{2}\rightarrow C_{n}H_{2n+2}}}

{\mathsf {C_{n}H_{2n-2}+2H_{2}\rightarrow C_{n}H_{2n+2}}}

Катализатором реакции являются соединения никеля , платины или палладия ^[17] .

Синтез Кольбе

При электролизе солей карбоновых кислот, анион кислоты — RCOO ⁻ перемещается к аноду, и там, отдавая электрон превращается в неустойчивый радикал RCOO•, который сразу декарбоксилируется. Радикал R• стабилизируется путём сдваивания с подобным радикалом, и образуется R—R ^[18] . For example:

{\mathsf {CH_{3}COO^{-}\rightarrow CH_{3}COO\cdot +e^{-}}}

{\mathsf {CH_{3}COO^{-}\rightarrow CH_{3}COO\cdot +e^{-}}}

{\mathsf {CH_{3}COO\cdot \rightarrow CH_{3}\cdot +CO_{2}}}

{\mathsf {CH_{3}COO\cdot \rightarrow CH_{3}\cdot +CO_{2}}}

{\mathsf {2CH_{3}\cdot +B\rightarrow C_{2}H_{6}}}

{\mathsf {2CH_{3}\cdot +B\rightarrow C_{2}H_{6}}}

Газификация твёрдого топлива (Процессы Бертло, Шрёдера, Бергиуса )

Проходит при повышенной температуре и давлении. Катализатор — Ni (для Бертло), Mo (для Шрёдера) или без катализатора (для Бергиуса):

{\mathsf {C+2H_{2}\rightarrow CH_{4}}}

{\mathsf {C+2H_{2}\rightarrow CH_{4}}}

Реакция Вюрца

{\mathsf {2R{\text{-}}Br+2Na\rightarrow R{\text{-}}R+2NaBr}}

{\mathsf {2R{\text{-}}Br+2Na\rightarrow R{\text{-}}R+2NaBr}}

Реакция идёт в ТГФ при температуре −80 °C ^[19] . При взаимодействии R и R` возможно образование смеси продуктов (R—R, R`—R`, R—R`)

Синтез Фишера — Тропша

{\mathsf {nCO+(2n+1)H_{2}\rightarrow C_{n}H_{2n+2}+nH_{2}O}}

{\mathsf {nCO+(2n+1)H_{2}\rightarrow C_{n}H_{2n+2}+nH_{2}O}}

Реакция Дюма

Получением алканов с помощью декарбоксилирования солей карбоновых кислот, при сплавлении со щелочью (обычно NaOH или KOH):

$CH{\scriptstyle {\text{3}}}COONa+NaOH\rightarrow Na{\scriptstyle {\text{2}}}CO{\scriptstyle {\text{3}}}+CH{\scriptstyle {\text{4}}}$ $CH{\scriptstyle {\text{3}}}COONa+NaOH\rightarrow Na{\scriptstyle {\text{2}}}CO{\scriptstyle {\text{3}}}+CH{\scriptstyle {\text{4}}}$

Гидролиз карбида алюминия ^[20]

${\mathsf {Al_{4}C_{3}+12H_{2}O\rightarrow 3CH_{4}\uparrow +4Al(OH)_{3}\downarrow }}$ ${\mathsf {Al_{4}C_{3}+12H_{2}O\rightarrow 3CH_{4}\uparrow +4Al(OH)_{3}\downarrow }}$

Биологическое действие

Низшие алканы обладают наркотическим действием . При хроническом действии алканы нарушают работу нервной системы, что проявляется в виде бессонницы, брадикардии , повышенной утомляемости и функциональных неврозов ^[21] .

Notes

↑ Bidd, Ilesh and Whiting, Mark C. The synthesis of pure n-paraffins with chain-lengths between one and four hundred. J. Chem. Soc., Chem. Commun., Issue 19, 1985, p. 543—544
↑ Дерябина Г. И., Кантария Г. В. 2.4.2. Правила построения названий алканов по систематической международной номенклатуре ИЮПАК (неопр.) . Интерактивный мультимедиа-учебник «Органическая химия» . Кафедра органической, биоорганической и медицинской химии СамГУ . Дата обращения 10 октября 2012. Архивировано 14 октября 2012 года.
↑ Химическая энциклопедия, т. 3, 1992 , с. 177.
↑ Физер Л., Физер М. Органическая химия, т. 1, 1966 , с. 125
↑ Последовательность A000602 в OEIS = Number of n-node unrooted quartic trees; number of n-carbon alkanes C(n)H(2n+2) ignoring stereoisomers
↑ Последовательность A000628 в OEIS = Number of n-node unrooted steric quartic trees; number of n-carbon alkanes C(n)H(2n+2) taking stereoisomers into account
↑ ¹ ² Henze Henry R., Blair Charles M. The number of isomeric hydrocarbons of the methane series (англ.) // Journal of the American Chemical Society. — ACS Publishers , 1931. — Vol. 53, no. 8 . — P. 3077–3085. — DOI : 10.1021/ja01359a034 .
↑ G. Pólya. Kombinatorische Anzahlbestimmungen für Gruppen, Graphen und chemische Verbindungen // Acta Mathematica . — 1937. — Vol. 68. — P. 145–254. — DOI : 10.1007/BF02546665 .
↑ Перекалин В.В., Зонис С.А. Органическая химия
↑ (англ.) Dr. David R. Williams. Jupiter Fact Sheet (англ.) (недоступная ссылка) . NASA (2007). Дата обращения 6 октября 2010. Архивировано 5 октября 2011 года.
↑ (англ.) Titan: Arizona in an Icebox? , Emily Lakdawalla, 21 January 2004, verified 28 March 2005
↑ (англ.) Mumma, MJ; Disanti, MA, dello Russo, N., Fomenkova, M., Magee-Sauer, K., Kaminski, CD, and DX Xie. Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin (англ.) // Science : journal. - 1996. - Vol. 272 , no. 5266 . — P. 1310 . — DOI : 10.1126/science.272.5266.1310 . — PMID 8650540 .
↑ ¹ ² Chemical Catalog >> Organic Chemistry page 63
↑ ALCOHOLS - an article from the encyclopedia "Krugosvet"
↑ Kizhner - Wolf reaction // The Great Soviet Encyclopedia : [in 30 t.] / Ch. ed. A. M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
↑ http://www.cnshb.ru/AKDiL/0048/base/RK/160003.shtm
Гид Hydrogenation catalysts (Unsolved) (inaccessible link) . The appeal date is June 10, 2009. Archived April 22, 2009.
↑ Kolbe reaction // The Great Soviet Encyclopedia : [in 30 t.] / Ch. ed. A. M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
↑ SUMMER RESPONSE
↑ carbide, its hydrolysis - Chemist's Handbook 21 (Unidentified) . chem21.info. The appeal date is April 12, 2018.
↑ Toxic characteristics of organic substances

Literature

Activation and catalytic reactions of alkanes / Trans. from English; by ed. K. Hill. - M .: Mir , 1992.
General toxicology / Ed. Loita A. Oh .. - SPb. : ELBI-SPb., 2006.
Petrov Al. A. Chemistry of alkanes . - M .: Science , 1974. - 243 p.
Poya D. Combinatorial computing for groups, graphs and chemical compounds (rus.) // Enumerative problems of combinatorial analysis. - M .: Mir, 1979. - P. 36-138.
Pereushanu V. Production and use of hydrocarbons. - M .: Chemistry, 1987.
Rudakov Ye. S. Reactions of alkanes with oxidizing agents, metal complexes and radicals in solutions. - Kiev: Naukova Dumka , 1985.
Fizer L., Fizer M. Organic Chemistry. In-depth course. - M. , 1966. - T. 1. - 680 p.
Heins A. Methods of oxidation of organic compounds. Alkanes, alkenes, alkynes and arenas. - M .: Mir, 1988.
Chemical Encyclopedia / Ch. ed. I. L. Knunyants. - M .: The Great Russian Encyclopedia, 1992. - T. 3: Copper sulfides - Polymeric dyes. - 640 s. - ISBN 5-85270-039-8 .
Perekalin V.V., Zonis S. А. Organic chemistry. - 4th ed., Revised. - M .: Enlightenment , 1982. - 560 p.

Links

[1] Bidd, Ilesh and Whiting, Mark C. The synthesis of pure n-paraffins with chain-lengths between one and four hundred. J. Chem. Soc., Chem. Commun., Issue 19, 1985, p. 543—544

[2] Дерябина Г. И., Кантария Г. В. 2.4.2. Правила построения названий алканов по систематической международной номенклатуре ИЮПАК (неопр.) . Интерактивный мультимедиа-учебник «Органическая химия» . Кафедра органической, биоорганической и медицинской химии СамГУ . Дата обращения 10 октября 2012. Архивировано 14 октября 2012 года.

[_971881605e00c1f6-3] Химическая энциклопедия, т. 3, 1992 , с. 177.

[_824bc64fcd7fc4ca-4] Физер Л., Физер М. Органическая химия, т. 1, 1966 , с. 125

[5] Последовательность A000602 в OEIS = Number of n-node unrooted quartic trees; number of n-carbon alkanes C(n)H(2n+2) ignoring stereoisomers

[6] Последовательность A000628 в OEIS = Number of n-node unrooted steric quartic trees; number of n-carbon alkanes C(n)H(2n+2) taking stereoisomers into account

[Henze-7] ¹ ² Henze Henry R., Blair Charles M. The number of isomeric hydrocarbons of the methane series (англ.) // Journal of the American Chemical Society. — ACS Publishers , 1931. — Vol. 53, no. 8 . — P. 3077–3085. — DOI : 10.1021/ja01359a034 .

[Polya-8] G. Pólya. Kombinatorische Anzahlbestimmungen für Gruppen, Graphen und chemische Verbindungen // Acta Mathematica . — 1937. — Vol. 68. — P. 145–254. — DOI : 10.1007/BF02546665 .

[9] Перекалин В.В., Зонис С.А. Органическая химия

[jupiter-info-10] (англ.) Dr. David R. Williams. Jupiter Fact Sheet (англ.) (недоступная ссылка) . NASA (2007). Дата обращения 6 октября 2010. Архивировано 5 октября 2011 года.

[11] (англ.) Titan: Arizona in an Icebox? , Emily Lakdawalla, 21 January 2004, verified 28 March 2005

[science-12] (англ.) Mumma, MJ; Disanti, MA, dello Russo, N., Fomenkova, M., Magee-Sauer, K., Kaminski, CD, and DX Xie. Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin (англ.) // Science : journal. - 1996. - Vol. 272 , no. 5266 . — P. 1310 . — DOI : 10.1126/science.272.5266.1310 . — PMID 8650540 .

[alkane-13] ¹ ² Chemical Catalog >> Organic Chemistry page 63

[14] ALCOHOLS - an article from the encyclopedia "Krugosvet"

[15] Kizhner - Wolf reaction // The Great Soviet Encyclopedia : [in 30 t.] / Ch. ed. A. M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.

[16] ttp://www.cnshb.ru/AKDiL/0048/base/RK/160003.shtm

[17] Гид Hydrogenation catalysts (Unsolved) (inaccessible link) . The appeal date is June 10, 2009. Archived April 22, 2009.

[18] Kolbe reaction // The Great Soviet Encyclopedia : [in 30 t.] / Ch. ed. A. M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.

[19] SUMMER RESPONSE

[20] rbide, its hydrolysis - Chemist's Handbook 21 (Unidentified) . chem21.info. The appeal date is April 12, 2018.

[21] Toxic characteristics of organic substances