Acetylene refers to unsaturated hydrocarbons. Its chemical properties are determined by the triple bond. It is able to enter into reactions of oxidation, substitution, addition and polymerization. Ethan - saturated hydrocarbon, for which the nature of the substitution reaction by radical type, dehydrogenation and oxidation. At about 600 degrees Celsius, it decomposes into hydrogen and ethene.

You will need

• - chemical equipment;
• - catalysts;
• - bromine water.

Instruction

• Acetylene, ethylene and ethane are normally colorless combustible gases. Therefore, first familiarize yourself with the safety precautions when working with volatile substances. Do not forget to repeat the molecular structure and chemical properties of alkynes (unsaturated hydrocarbons), alkenes and alkanes. See how they are similar and how they differ. To make ethane, you need acetylene and hydrogen.
• To produce acetylene in laboratory conditions, carry out the decomposition of calcium carbide CaC2. You can take it ready-made or get it by sintering quicklime with coke: CaO + 3C \u003d CaC2 + CO - the process proceeds at a temperature of 2500 ° C, CaC2 + 2H2O \u003d C2H2 + Ca (OH) 2. Conduct qualitative reaction on acetylene - discoloration of bromine water or potassium permanganate solution.
• You can get hydrogen in several ways: - by the interaction of metals with an acid: Zn + 2 HCl \u003d ZnCl2 + H2 - during the reaction of alkali with metals, the hydroxides of which have amphoteric properties: Zn + 2 NaOH + 2 H2O \u003d Na2 + H2 - by electrolysis of water, to increase the electrical conductivity of which alkali is added. In this case, hydrogen is formed at the cathode, and oxygen is formed at the anode: 2 H2O = 2 H2 + O2.
• To receive from acetylene ethane, it is necessary to carry out a hydrogen addition reaction (hydrogenation), taking into account the properties chemical bonds: first from acetylene ethylene is obtained, and then, with further hydrogenation, ethane. For a visual expression of the processes, compose and write down the reaction equations: C2H2 + H2 \u003d C2H4C2H4 + H2 \u003d C2H6 The hydrogenation reaction proceeds at room temperature in the presence of catalysts - finely crushed palladium, platinum or nickel.

DEFINITION

Acetylene (ethyne)- colorless and odorless gas, has a weak narcotic effect (the structure of the molecule is shown in Fig. 1).

Slightly soluble in water and very good in acetone. In the form of an acetone solution, it is stored in steel cylinders filled with some inert porous material. Mixtures of acetylene with air are explosive.

Rice. 1. The structure of the acetylene molecule.

Table 1. Physical Properties acetylene.

Getting acetylene

Allocate industrial and laboratory methods for producing acetylene. So, in industry, acetylene is obtained by high-temperature cracking of methane:

2CH 4 → CH≡CH +3H 2.

In the laboratory, acetylene is obtained by hydrolysis of calcium carbide:

CaC 2 + 2H 2 O \u003d Ca (OH) 2 + C 2 H 2.

In addition to the above reactions, to obtain acetylene, the reactions of dehydrogenation of alkanes and alkenes are used:

CH 3 -CH 3 → CH≡CH +2H 2;

CH 2 \u003d CH 2 → CH≡CH + H 2.

Chemical properties of acetylene

Acetylene enters into addition reactions proceeding according to the nucleophilic mechanism, such as:

– hydrogenation

СH≡CH +H 2 O→ → CH 3 -CH=O (H 2 SO 4 (18%), t = 90 o C);

– halogenation

CH≡CH +Br 2 →CHBr=CHBr + Br 2 →CHBr 2 -CHBr 2 ;

– hydrohalogenation

СH≡CH + HСl → CH 2 \u003d CHCl + HCl → CH 3 -CHCl 2.

In addition, acetylene is able to form salts when interacting with active metals (1) and silver oxide (2):

2CH≡CH +2Na→2CH≡C-Na + H 2 (1);

СH≡CH + Ag 2 O → Ag- С≡C-Ag↓ + H 2 O (2).

It is able to trimerize:

3C 2 H 2 → C 6 H 6 (t = 600 o C, kat = C active).

Application of acetylene

Acetylene is an initial product for many major chemical industries. For example, various halogen derivatives are obtained from acetylene, such as tetrachloroethane and trichlorethylene, which are good solvents, as well as vinyl chloride, which serves as a monomer for the production of polyvinyl chloride. In addition, acetylene is used to produce synthetic rubbers.

Examples of problem solving

EXAMPLE 1

The task	An equimolecular mixture of acetylene and formaldehyde reacts completely with 69.6 g of Ag 2 O dissolved in ammonia. Determine the composition of the initial mixture.
Solution	Let's write the equations of the reactions specified in the condition of the problem: HC≡CH + Ag 2 O → AgC≡Cag + H 2 O (1); H-C(O)H + 2 Ag 2 O → CO 2 + H 2 O + 4Ag (2). Calculate the amount of silver oxide (I) substance: n(Ag 2 O) = m(Ag 2 O) / M(Ag 2 O); M(Ag 2 O) = 232 g/mol; n (Ag 2 O) \u003d 69.6 / 232 \u003d 0.3 mol. According to equation (2), the amount of formaldehyde substance will be equal to 0.1 mol. According to the condition of the problem, the mixture is equimolecular, therefore, acetylene will also be 0.1 mol. Find the masses of the substances that make up the mixture: M(HC≡CH) = 26 g/mol; M(H-C(O)H) = 30 g/mol; m(HC≡CH) = 0.1 x 26 = 2.6 g; m(H-C(O)H) = 0.1 × 30 = 3 g.
Answer	The mass of acetylene is 2.6 g, formaldehyde - 3 g.

EXAMPLE 2

The task	When a mixture of propane and acetylene was passed through a flask with bromine water, the mass of the flask increased by 1.3 g. With complete combustion of the same amount of the initial mixture of hydrocarbons, 14 l (N.O.) of carbon monoxide (IV) were released. Determine the mass fraction of propane in the initial mixture.
Solution	When a mixture of propane and acetylene is passed through a bottle of bromine water, acetylene is absorbed. Let us write the chemical reaction equation corresponding to this process: HC ≡ CH + 2Br 2 → NSVr 2 -SNVr 2. Thus, the value by which the mass of the bottle (1.3 g) has increased is the mass of acetylene. Find the amount of acetylene substance (molar mass - 26 g / mol): n (C 2 H 2) \u003d m (C 2 H 2) / M (C 2 H 2); n (C 2 H 2) \u003d 1.3 / 26 \u003d 0.05 mol. We write the reaction equation for the combustion of acetylene: 2C 2 H 2 + 5O 2 \u003d 4CO 2 + 2H 2 O. According to the reaction equation, 2 mol of acetylene entered it, however, it is known that 0.05 mol of this amount was absorbed by bromine water. Those. stood out: 2-0.05 \u003d 0.1 mol CO 2. Find the total amount of carbon monoxide (IV): n sum (CO 2) \u003d V (CO 2) / V m; n sum (CO 2) \u003d 14 / 22.4 \u003d 0.625 mol. We write the equation for the propane combustion reaction: C 3 H 8 + 5O 2 \u003d 3CO 2 + 4H 2 O. Considering that 0.1 mol of carbon monoxide (IV) was released in the combustion reaction of acetylene, the amount of carbon monoxide (IV) substance released during the combustion of propane is equal to: 0.625 - 0.1 \u003d 0.525 mol CO 2. Find the amount of propane substance that entered into the combustion reaction. According to the reaction equation n(CO 2) : n(C 3 H 8) = 3: 1, i.e. n (C 3 H 8) \u003d n (CO 2) / 3 \u003d 0.525 / 3 \u003d 0.175 mol. Calculate the mass of propane (molar mass 44 g/mol): m (C 3 H 8) \u003d n (C 3 H 8) × M (C 3 H 8); m (C 3 H 8) \u003d 0.175 × 44 \u003d 7.7 g. Then, the total mass of the mixture of hydrocarbons will be: m mixture \u003d m (C 2 H 2) + m (C 3 H 8) \u003d 1.3 + 7.7 \u003d 9.0 g. Find the mass fraction of propane in the mixture: ω = m / m mixture × 100%; ω (C 3 H 8) \u003d m (C 3 H 8) / m mixture × 100%; ω (C 3 H 8) \u003d 7.7 / 9.0 × 100% \u003d 0.856 × 100% \u003d 85.6%.
Answer	Mass fraction of propane 85.6%.

am. Its chemical properties are determined by the triple bond. It is able to enter into reactions of oxidation, substitution, addition and polymerization. Ethane- saturated hydrocarbon, for which the nature of the substitution reactions of the radical type, dehydrogenation and oxidation. At about 600 degrees Celsius, it decomposes into hydrogen and ethene.

You will need

• - chemical equipment;
• - catalysts;
• - bromine water.

Instruction

Acetylene, ethylene and ethane are normally colorless combustible gases. Therefore, first familiarize yourself with the safety precautions when working with volatile substances. Do not forget to repeat the molecular structure and chemical properties of alkynes (unsaturated hydrocarbons), alkenes and alkanes. See how they are similar and how they differ. To make ethane, you need acetylene and hydrogen.

To produce acetylene in the laboratory, decompose calcium carbide CaC2. You can take it ready-made or get it by sintering quicklime with coke: CaO + 3C \u003d CaC2 + CO - the process proceeds at a temperature of 2500 ° C, CaC2 + 2H2O \u003d C2H2 + Ca (OH) 2. Carry out a qualitative reaction for acetylene - decolorization of bromine water or potassium permanganate solution.

You can get hydrogen in several ways: - by the interaction of metals with an acid: Zn + 2 HCl \u003d ZnCl2 + H2 - during the reaction of alkali with metals whose hydroxides have amphoteric properties: Zn + 2 NaOH + 2 H2O \u003d Na2 + H2 - by electrolysis of water, to increase the electrical conductivity of which alkali is added. In this case, hydrogen is formed at the cathode, and oxygen is formed at the anode: 2 H2O = 2 H2 + O2.

To receive from acetylene ethane, it is necessary to carry out a hydrogen addition reaction (hydrogenation), taking into account the properties of chemical bonds: first, from acetylene ethylene is obtained, and then, with further hydrogenation, ethane. For a visual expression of the processes, compose and write down the reaction equations: C2H2 + H2 \u003d C2H4C2H4 + H2 \u003d C2H6 The hydrogenation reaction proceeds at room temperature in the presence of catalysts - finely crushed palladium, platinum or nickel.

note

Observe safety precautions while working. Remember that these gases burn well and are explosive when mixed with air or oxygen.

Useful advice

Note that hydrogen is lighter than air, so it must be collected in a test tube turned upside down. You can determine the receipt of ethane by exposing it to bromine water (its color will remain unchanged).

Attention, only TODAY!

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Please help =) 1) Make up the reaction equations with which you can carry out transformations according to the scheme:

ethanol---ethene---ethyn--ethanal.

Make up the reaction equations with which you can carry out transformations according to the scheme:

С2Н2---->

A 1. General formula of alkadienes: 1) Cn H2n 3) CnH2n-2 2) CnH2n+2 4) CnH2n-6 A 2. The name of the substance whose formula is CH3─CH2─CH2─CH(CH3)─CH 1)

2-methylpentanal 3) 4-methylpentanal 2) 2-methylpentanol 4) pentanal A 3. A type of hybridization of the electron orbitals of the carbon atom indicated by an asterisk in a substance whose formula is CH3─C∗≡CH 1) sp3 3) sp 2) sp2 4) not hybridized A 4. Only σ-bonds are present in the molecule 1) acetylene 3) 2-mtylbutene-2 ​​2) isobutane 4) methylbenzene A 5. Homologs are 1) ethyne and ethene 3) cyclobutane and butane 2) propane and butane 4) ethene and methane A 6. The isomers are: 1) pentane and pentadiene 3) ethanol and ethanal 2) acetic acid and methyl formate 4) ethane and acetylene A 7. The color of the mixture of protein with copper hydroxide (ΙΙ) 1) blue 3) red 2) blue 4) violet A 8. Aniline from nitrobenzene can be obtained using the reaction: 1) Wurtz 3) Kucherov 2) Zinin 4) Lebedev A 9. What substances can be used for the successive implementation of the following transformations С2Н5ОН → С2Н5Сl → С4Н10 1) O2, Na 3) HCl, NaOH 2) HCl, Na 4) NaCl, Na A 10. The volume of ethane required to obtain 4 l carbon dioxide 1) 2l 3) 10l 2) 4l 4) 6l B 1. Match the molecular formula organic matter and the class to which it belongs A) C4H6 1) arenes B) C4H8O2 2) carbohydrates C) C7H8 3) aldehydes D) C5H10O5 4) esters 5) alkynes B 2. Phenol reacts with 1) sodium 2) oxygen 3) hydroxide sodium 4) silicon oxide (ΙV) 5) benzene 6) hydrogen chloride B 3. Both methane and propene are characterized by 1) bromination reactions 2) sp-hybridization of carbon atoms in molecules 3) the presence of π-bonds in molecules 4) hydrogenation reaction 5) combustion in air 6) low solubility in water B 4. Molecular formula of hydrocarbon, mass fraction hydrogen in which 15.79%, and the relative vapor density in air is 3.93 ________ С mass ester, obtained by the interaction of 46 g of a 50% solution of formic acid and ethyl alcohol, if the yield of the reaction product is 80% of the theoretically possible.

Please help TASK 1 For a substance whose formula is C (3rd bond) \u003d -C-CH2-CH3, | CH3 make up

structural formulas of two isomers and two homologues. Give the names of all substances according to the systematic nomenclature.

TASK 2

With which of the following substances: bromine, hydrogen bromide, water, sodium hydroxide, ethane - will acetylene react? Write the reaction equations, indicate the conditions for their implementation, make the names of the starting materials and reaction products.

Alkynes are aliphatic unsaturated hydrocarbons, in the molecules of which there is one triple bond between carbon atoms.

Hydrocarbons of the acetylene series are even more unsaturated compounds than their corresponding alkenes (with the same number of carbon atoms). This can be seen from a comparison of the number of hydrogen atoms in the series:

C2H6 C2H4 C2H2

ethane ethylene acetylene

(ethene) (ethine)

Alkynes form their homologous series with the general formula, as in diene hydrocarbons СnH2n-2

1. The structure of alkynes

First and main representative homologous series alkyne is acetylene (ethyne) C2H2. The structure of its molecule is expressed by the formulas:

N-S? S-N or N: S::: S: N

structural electronic

formula formula

By the name of the first representative of this series - acetylene - these unsaturated hydrocarbons are called acetylenic.

In alkynes, carbon atoms are in the third valence state (sp-hybridization). In this case, a triple bond occurs between carbon atoms, consisting of one s- and two p-bonds. The length of the triple bond is 0.12 nm, and the energy of its formation is 830 kJ/mol. Models of the spatial structure of acetylene are shown in Figs. one.

Fig.1. Models of the spatial structure of the acetylene molecule:

a - tetrahedral; b - ball-and-stick; in - according to Brigleb

2. Nomenclature and isomerism

Nomenclature. According to the systematic nomenclature, acetylenic hydrocarbons are named by replacing the suffix -an with the suffix -in in alkanes. The composition of the main chain must include a triple bond, which determines the beginning of the numbering. If a molecule contains both a double and a triple bond, then the preference for numbering is given to the double bond:

H-C? C-CH2-CH3 H3C-C? C-CH3 H2C \u003d C-CH2-C? CH

butyn-1 butyn-2 2-methylpenten-1-in-4

(ethylacetylene) (dimethylacetylene)

According to rational nomenclature, alkyne compounds are called acetylene derivatives.

Unsaturated (alkyne) radicals have trivial or systematic names:

H-C? C- - ethinyl;

HC?C-CH2- -propargyl

Isomerism. The isomerism of alkyne hydrocarbons (as well as alkene hydrocarbons) is determined by the structure of the chain and the position of the multiple (triple) bond in it:

H-C? C-CH-CH3 H-C? C-CH2-CH2-CH3 H3C-C=C-CH2-CH3

3-methylbutyn-1 pentyn-1 pentyn-2

3. Obtaining alkynes

Acetylene in industry and in the laboratory can be obtained in the following ways:

1. High-temperature decomposition (cracking) of natural gas - methane:

2CH4 1500°C® HC?CH + 3H2

or ethane:

C2H6 1200°C® HC?CH + 2H2

2. Water decomposition of calcium carbide CaC2, which is obtained by sintering quicklime CaO with coke:

CaO + 3C 2500°C® CaC2 + CO

CaC2 + 2H2O ® HC?CH + Ca(OH)2

3. In the laboratory, acytylene derivatives can be synthesized from dihalogen derivatives containing two halogen atoms at one or adjacent carbon atoms by the action of an alcoholic solution of alkali:

H3C-CH-CH-CH3 + 2KOH ® H3C-C?C-CH3 + 2KBr + 2H2O

2,3-dibromobutane butyn-2

(dimethylacetylene)

4. Physical and chemical properties

physical properties. Acetylene hydrocarbons containing from two to four carbon atoms in a molecule (under normal conditions) are gases, starting with C5H8 - liquids, and higher alkynes (with C16H30 and above) - solids. The physical properties of some alkynes are shown in table. one.

Table 1. Physical properties of some alkynes
Name
Formula
t pl, ° С
t bale, ° С
d204

Acetylene (ethane)
HC-CH
- 81,8
-84,0
0,6181*

Methylacetylene (propyne)
HC?C-CH3
-101,5
-23,2
0,7062**

Ethyl acetylene (butyn-1)
HC?C-C2H5
-125,7
+8,1
0,6784

s-Dimethylacetylene

(butin-2)
H3C-C?C-CH3
-32,3
+27,0
0,6510

Propylacetylene (Pentin-1)
HC? C- (CH2) 2-CH3
-90,0
+40,2
0,6900

Methylethylacetylene (Pentin-2)
H3C-C? C-C2H5
-101,0
+56,1
0,7107

Butylacetylene (hexine-1)
HC? C- (CH2) 3-CH3
-131,9
+71,3
0,7155

*At -32 °C,

**At temperature - 50 °С.

Chemical properties. The chemical properties of alkynes are determined by the triple bond, the features of its structure. Alkynes are capable of entering into addition, substitution, polymerization and oxidation reactions.

Addition reactions. Being unsaturated compounds, alkynes are primarily involved in addition reactions. These reactions proceed in steps: with the addition of one molecule of the reagent, the triple bond first turns into a double bond, and then, as the addition proceeds, into a single bond. It would seem that alkynes, having two p-bonds, should be much more active in electrophilic addition reactions. But it is not so. The carbon atoms in alkynes are closer together than in alkenes and are more electronegative. This is due to the fact that the electronegativity of a carbon atom depends on its valence state. Therefore, p-electrons, being closer to carbon nuclei, exhibit somewhat less activity in electrophilic addition reactions. In addition, the proximity of positively charged atomic nuclei that can repel approaching electrophilic reagents (cations) affects. At the same time, alkynes can enter into nucleophilic addition reactions (with alcohols, ammonia, etc.).

1. Hydrogenation. The reaction proceeds under the same conditions as in the case of alkenes (catalysts Pt, Pd, Ni). When alkynes are reduced, alkenes are formed first, and then alkanes:

HC?CH -® H2C=CH2 -® H3C-CH3

acetylene ethylene ethane

2. Halogenation. This reaction proceeds at a lower rate than in the series of ethylene hydrocarbons. The reaction also proceeds in steps:

HC?CH -®CHBr=CHBr -®CHBr2-CHBr2

1,2-dibromoethane 1,1,2,2-tetrabromoethane

3. Hydrohalogenation. The addition reactions of hydrogen halides, like halogens, proceed mainly according to the mechanism of electrophilic addition:

HC?CH + HCl -® H2C=CHCl -® H3C-CHCl2

chloroethene 1,1-dichloroethane

(vinyl chloride)

The second hydrogen halide molecule is added in accordance with Markovnikov's rule.

4. Accession of water (reaction of M.G. Kucherov,. 1881). Catalyst - salt of mercury:

HC?CH + HOH --® u H2C=CH-OHu ® H3C-C=O

vinyl acetic

alcohol aldehyde

(intermediate

unstable product)

An unstable intermediate, vinyl alcohol, rearranges to form acetaldehyde.

5. Accession of hydrocyanic acid:

HC?CH + HCN cat.® H2C=CH-CN

acrylonitrile

Acrylonitrile is a valuable product. It is used as a monomer to produce a synthetic fiber - nitron.

6. Accession of alcohol. As a result of this reaction, vinyl ethers are formed (the reaction of A. E. Favorsky):

HC?CH + HO-C2H5 KOH® H2C=CH-O-C2H5

ethyl vinyl ether

The addition of alcohols in the presence of alcoholates - typical reaction nucleophilic addition.

substitution reactions. Hydrogen atoms in acetylene can be replaced by metals (metalation reaction). As a result, metal derivatives of acetylene - acetylenides are formed. This ability of acetylene can be explained as follows. The carbon atoms of acetylene, being in the state of sp-hybridization, are known to be distinguished by increased electronegativity (compared to carbons in other hybrid states). Therefore, the electron density C-H bonds slightly shifted towards carbon and the hydrogen atom acquires some mobility:

But this "mobility", of course, is incomparable with the "freedom" of the proton in real acids: hydrochloric acid, for example, is almost 1033 times stronger in acidity than acetylene. But even such a mobility of hydrogen is sufficient for it to be replaced by a metal in an alkaline environment. So, under the action of an ammonia solution of silver oxide on acetylene, silver acetylenide is formed:

HC?CH + 2OH ® Ag-C?C-Ag + 4NH3 + 2H2O

silver acetylenide

Dry acetylides must be handled with great care: they are highly explosive.

isomerization reaction. Acetylene hydrocarbons, like alkanes and alkenes, are capable of isomerization with triple bond displacement:

H3C-CH2-C?CH Na(alcohol solution)® H3C-C?C-CH3

butyn-1 butyn-2

polymerization reactions. Acetylene, depending on the reaction conditions, is able to form various polymerization products - linear or cyclic:

HC?CH + HC?CH -®HC?CH-CH=CH2

vinylacetylene

(butene-1-in-3)

These substances are of great interest. For example, when hydrogen chloride is added to vinylacetylene, chloroprene is formed, which is used as a monomer in the production of chloroprene rubber:

H2C=CH-C?CH + 2HCl ® H2C=C-CH==CH2

vinylacetylene chloroprene

Oxidation reaction. Acetylenes are easily oxidized. In this case, the molecule breaks at the site of the triple bond. If acetylene is passed through an oxidizing agent ( water solution potassium permanganate), the solution quickly becomes colorless. This reaction is qualitative for multiple (double and triple) bonds:

3HC?CH + 10KMnO4 + 2H2O ® 6CO2 + 10KOH + 10MnO2

With the complete combustion of acetylene in air, two products are formed, carbon monoxide (IV) and water:

2HC?CH + 5O2 ® 4CO2 + 2H2O

Incomplete combustion produces carbon (soot):

HC?CH + O2 ® C + CO + H2O

5. Individual representatives

Acetylene (ethyne) HC?CH is a colorless gas, odorless (technical acetylene has an unpleasant odor due to the presence of various impurities). Acetylene is slightly soluble in water, well - in acetone. In air, it burns with a very smoky flame [high (in percent) carbon content in the molecule]. When burning in oxygen, acetylene creates a high-temperature flame (up to 3000 °C). This is used for welding and cutting metals. Mixtures of acetylene with oxygen or air are explosive, therefore acetylene is stored and transported in special cylinders (marking: white cylinder with a red inscription "Acetylene"). This balloon is filled with a porous material that is impregnated with acetone.

Acetylene is a valuable product for the chemical industry. Synthetic rubber, acetic aldehyde and acetic acid, ethyl alcohol and many other substances are obtained from it.

Vinylacetylene (butene-1-in-3) HC? C-CH \u003d CH 2 - a gas with an unpleasant odor. Upon reduction, it forms butadiene-1,3, and upon addition of hydrogen chloride, it forms 2-chlorobutadiene-1,3 (chloroprene).

Materials from the site http://chemistry.narod.ru/ were used for preparation.