Wurtz reaction
The Wurtz reaction is of limited use because it leads to the combination of two alkyl groups and thus to an alkane with more carbon atoms than in the starting materials. In this way, ethane can be obtained from methyl bromide, n-butane from ethyl bromide, and 2,3-dimethylbutane from isopropyl bromide.
The Wurtz reaction is only suitable for the synthesis of symmetrical R-R alkanes. For example, propane cannot be obtained with a good yield by this method. If sodium reacts with a mixture of methyl bromide and ethyl bromide, then propane is indeed formed; but it will be mixed with ethane, formed by the combination of two methyl groups, and n-butane, formed by two ethyl groups. A significant amount of reagents is spent on the formation of unnecessary products; in addition, there is a problem of separation. Therefore, the Wurtz reaction is unsuitable for the synthesis of R-R unsymmetrical alkanes (R and R are different alkyl groups).
Although many reactions of simple alkyl halides can be extended to more complex halogenated compounds, this is not the case for the Wurtz reaction. Sodium metal is a very reactive substance, and will react not only with the halogen, but with any other group that may be in a more complex compound. For example, the Wurtz reaction cannot be applied to compounds in which, in addition to the halogen, there is a HO group, since sodium will react with the hydroxyl group faster than with the halogen.
The mechanism of the Wurtz reaction is complex and has not yet been fully elucidated, but it is clear that sodium is formed first in the reaction. organic compound, analogous to the organomagnesium compound described above, RX + +2Na = RNa + NaX, which then reacts with a second alkyl halide molecule RNa + RX = R?R + NaX organic compounds.)
microcrystalloscopy
The reaction of the environment is of great, sometimes even decisive importance for the course of the experiment. It is necessary to choose the medium taking into account the properties of the substance. Some reactions proceed only at a certain pH value, others fluctuate in sensitivity ...
salt world
Acid and base solutions are mixed in the desired molar ratio. After evaporation of water, a crystalline salt is obtained ...
salt world
This method is suitable, for example, if an insoluble salt is formed...
salt world
Only alkalis (soluble bases) are suitable for such reactions. These reactions produce another base and another salt. It is important that the new base is not alkaline and cannot react with the formed salt...
Metabolism of carbohydrates in the body
С6Н12О6 + 2ATP + 2Фn 2С3Н6О3 + 2ATP Glucose lactic acid Therefore ...
Transformations of potassium and cesium tungstate antimonates
Samples No. 2 and No. 3 were placed in nitric acid for 7 days. As a result, a change in the color of sample No. 3 was observed, it became lemon-colored. With sample No. 2, such changes did not occur. Samples were washed with distilled water to remove acid...
Acylation reactions
Consider the reaction of alkyl-d-halogenation (conversion of acyl halides to ketones with the help of organometallic compounds). Acyl halides interact smoothly and under mild conditions with lithium dialkyl cuprates...
Acylation reactions
Also of interest is the reaction of alkyl-deacyloxy substitution (conversion of anhydrides, esters and amides carboxylic acids into ketones using organometallic compounds), which can be used to obtain ketones from compounds of other classes ...
Synthesis of organohalogen compounds. haloform cleavage reaction
In the case of halogenation of ketones induced by a base, namely: if a b-haloketone is formed ...
Synthesis of isobutyl ester of acetic acid by esterification reaction
Obtaining isobutyl ester of acetic acid. To magnesium ethyl bromide, prepared from 8.2 g of magnesium, 37 g of ethyl bromide and 200 cm3 of ether, 25 g of isobutyl alcohol are slowly poured while cooling. The mixture is then boiled gently for 30 minutes....
Synthesis of unsaturated carbonyl compounds
Cross (mixed) aldol condensation of aromatic aldehydes with ketones, leading to the formation of b, c-unsaturated fatty aromatic ketones...
Synthesis of six-membered oxygen-containing heterocyclic compounds
Synthesis of flavones and isoflavones. 2.2 Auwers reaction Conversion of coumaranones to flavones. Dehydrobromination of 2-bromo-2-(b-bromobenzyl)-coumarone by the action of an alcoholic solution of alkali...
Thermodynamic calculation of the polymerization reaction of dimethylol urea
The analysis will be carried out on the example of methacrolein and isoprene. Monomer 1 Monomer 2 Table 4 - Composition of monomers Monomer e Q methacrolein 0 1.75 isoprene -1.2 3.3 f1=0.95 f2=0.05 Table 5 - Composition of the copolymer with different proportions of monomers...
Phenols: methods of synthesis and chemical properties
The original method of introducing a carboxyl group into an aromatic ring was discovered by G. Kolbe in 1860. When dry sodium or lithium phenolates are heated with CO2 at 150-180 ° C and a pressure of 5 atm, sodium or lithium salts of salicylic acid are formed ...
Chemical properties simple cyclic ethers on the example of ethyloxirane
When ethylene oxide is heated at a temperature of about 400 ° C or 150--300 ° C in the presence of catalysts (Al2O3, H3PO4, etc.), isomerization to acetaldehyde occurs: A radical mechanism proposed by Benson to explain the reaction ...
WURZ REACTION– a chemical reaction that makes it possible to obtain the simplest organic compounds - saturated hydrocarbons. The Wurtz reaction itself consists in the condensation of alkyl halides under the action of metallic Na, Li, or less commonly K: 2RHal + 2Na = R–R + 2NaHal.Sometimes it is interpreted as the interaction of RNa or RLi with R "Hal.
The reaction was discovered by the French organic chemist Charles Wurtz (1817-1884) in 1855 while trying to obtain ethyl sodium from ethyl chloride and sodium metal. Despite the fact that the Wurtz reaction leads to the formation of a new carbon-carbon bond, it is rarely used in organic synthesis. Basically, it is used to obtain saturated hydrocarbons with a long carbon chain, it is especially useful in obtaining individual large hydrocarbons. molecular weight, and, as can be seen from the above scheme, to obtain a given hydrocarbon, only one alkyl halide should be taken, since the condensation of two alkyl halides results in a mixture of all three possible combination products.
Therefore, if an alkyl halide and sodium are used, only hydrocarbons with an even number of carbon atoms can be obtained by the Wurtz reaction. The Wurtz reaction proceeds most successfully with primary alkyl iodides. Very low yields of the target product are obtained using the Wurtz method for secondary alkyl halides. The reaction is usually carried out in diethyl ether. The use of hydrocarbons as solvents reduces the selectivity of the reaction.
However, if a pre-prepared organometallic compound, such as alkyllithium, is used, then unsymmetrical condensation products can also be obtained:
RLi + R"Hal = R - R" + LiHal
In both cases, the reaction is accompanied by the formation a large number by-products through side processes. This illustrates an example of the interaction of ethyllithium with 2-bromoctane:
.
In this case, 3-methylnonane and a number of side products in the indicated molar ratios are formed as a product of the Wurtz reaction.
In addition to sodium, metals such as silver, zinc, iron, copper, and indium were used in the Wurtz reaction.
The Wurtz reaction has been successfully used for intramolecular condensations to build carbocyclic systems. Thus, cyclopropane can be obtained from 1,3-dibromopropane under the action of metallic zinc and sodium iodide (as a reaction promoter):
Other strained carbocyclic systems can also be constructed. For example, from 1,3-dibromoadamantane, using a sodium-potassium alloy, 1,3-dehydroadamantane can be obtained:
.And the interaction of 1-bromo-3-chloro-cyclobutane with sodium leads to bicyclobutane:
.A number of varieties of the Wurtz reaction are known, which have received their own names. These are the Wurtz–Fittig reaction and the Ullmann reaction. The first is the condensation of an alkyl and aryl halide under the action of sodium to form an alkylaromatic derivative. In the case of the Ullmann reaction, aryl iodides are usually introduced into the condensation, and freshly prepared copper is used instead of sodium, this reaction makes it possible to obtain various biaryl derivatives in high yield, including unsymmetrical ones containing a substituent in one of the aromatic nuclei:
.The Wurtz reaction mechanism is believed to consist of two main steps:
1) the formation of an organometallic derivative (if a metal is used, and not a pre-prepared organometallic compound):
RHal + 2Na = R–Na + NaHal,
2) the interaction of the formed, in this case, sodium organic compound with another alkyl halide molecule:
RHal + R–Na = RR + NaHal.
Depending on the nature of R and the reaction conditions, the second stage of the process can proceed according to the ionic or radical mechanism.
Sources: Internet resources
http://www.krugosvet.ru/enc/nauka_i_tehnika/himiya/REAKTSIYA_VYURTSA.html
NAMED REACTIONS IN ORGANIC CHEMISTRY
1. Reaction of M.I. Konovalova
Substitution of hydrogen by a nitro group in aliphatic, acyclic, and also in the side chain of fat - aromatic compounds at high or normal pressure.
CH 3 -CH 3 + HO-NO 2 ( razb .) = (t=140 o c) CH 3 -CH 2 -NO 2 + H 2 O
2. Reaction W . BUT . wurtz (c synthesis wurtz )
If metallic sodium is added to a monohalogen-substituted hydrocarbon, then two moles of sodium halide are formed and the hydrocarbon radicals combine with each other, i.e., the carbon chain increases.
2 C 2 H 5 Cl + 2 Na = 2 NaCl + C 4 H 10
3. Kolbe-Schmidt reaction
Obtaining hydrocarbons by electrolysis of solutions of salts of carboxylic acids (electrochemical method).
2CH 3 COONa + 2H 2 O= ( electrolysis ) H 2 + 2CO 2 + C 2 H 6 + 2NaOH
4. Dumas reaction
A method for producing methane from sodium acetate by fusion with solid alkali.
CH 3 COONa + NaOH = (t o ) Na 2 CO 3 +CH 4
5. Reaction G . G . Gustavson
Preparation of cycloalkanes from dihalogen-substituted ones.
CH 2 (Cl)-CH 2 -CH 2 (Cl) + Zn = (t o ) ZnCl 2 + C 3 H 6 ( cyclopropane )
6. Rule V.V. Markovnikova
When a hydrogen halide is added to an alkene (or alkyne), hydrogen is added to a more hydrogenated (orhydrogenated) carbon atom, i.e., an atom at which there are more hydrogen atoms, and a halogen - to a less hydrogenated one.
CH 3 -CH=CH 2 + HCl = (t o , AlCl3)CH3-CH(Cl)-CH 3
7. Rule A.M. Zaitsev
With the elimination of a hydrogen atom in the reactions of dehydrohalogenation and dehydration, it occurs mainly from the least hydrogenated (or hydrogenated) carbon atom.
CH 3 -CH 2 -CH(Cl)-CH 3 +KOH ( alcohol . R - R ) = (t o ) CH 3 -CH=CH-CH 3 + KCl + H 2 O
CH 3 -CH(OH)-CH 2 -CH 3 = (t=170 o C, H2SO4 conc .) CH 3 -CH=CH-CH 3 + H 2 O
8. Reaction E . E . Wagner
Oxidation of alkenes with potassium permanganate in a slightly alkaline medium, leading to the formation of glycols.
3CH 2 =CH 2 + 2KMnO 4 + 4H 2 O=3CH 2 (OH)-CH 2 (OH) + 2MnO 2 + 2KOH
9. Reaction of S.V. Lebedev
Simultaneous dehydrogenation and dehydration ethyl alcohol in the presence of amphoteric oxides with the formation of butadiene-1,3.
2C 2 H 5 OH= (t=425 about C, Al2O3 or Cr2O3)CH 2 =CH-CH=CH 2 + 2H 2 O+H 2
10. Reaction of M.G. Kucherova
Hydration of acetylene in the presence of mercury salts to form acetaldehyde.
C 2 H 2 + H 2 O = ( hg 2+ ) CH 3 COH
11. Friedel-Crafts reaction
The reaction for obtaining benzene homologues in the presence of aluminum chloride.
C 6 H 6 +CH 3 Cl = (t o , AlCl3)C 6 H 5 -CH 3 + HCl
12. Reactions of N.D. Zelinsky (obtaining benzene)
cyclohexane dehydrogenationC 6 H 12 = ( t =300 about C , Pt . Pd ) C 6 H 6 + 3H 2
dehydrocyclization (or aromatization) of hexaneC 6 H 14 = ( t =300 about C , Pt ) C 6 H 6 + 4 H 2
trimerization of acetylene on activated carbon 3C 2 H 2 = (active coal)C 6 H 6
13. Wurtz-Fittig reaction
Reaction of sodium with a mixture of halobenzene and haloalkane to form toluene.
C 6 H 5 Cl + 2Na + CH 3 Cl = (t o ) C 6 H 5 -CH 3 + 2NaCl
14. Sergeev-Udrisome-Kruzhalov reaction
Obtaining phenol from benzene through cumene (Cumene method).
Istage. C 6 H 6 +CH 2 =CH-CH 3 = (t o , AlCl3)C 6 H 5 CH(CH 3 ) 2
IIstage. C 6 H 5 CH(CH 3 ) 2 + O 2 = (t o , H2SO4)C 6 H 5 -OH+CH 3 -C(O)-CH 3
15. Reaction of A.U. Williamson (Williamson synthesis)
Preparation of ethers by alkylation of alcoholates or phenolates with alkyl halides.
CH 3 ONa + CH 3 Cl = (t o ) NaCl + CH 3 -O-CH 3
16. Reaction of K.S. Kirchhoff
The reaction of the conversion of starch into glucose under the catalytic action of sulfuric acid.
( C 6 H 10 O 5 ) n (+ H 2 O , enzymes) ( C 6 H 10 O 5 ) x (+ H 2 O , enzymes) C 12 H 22 O 11 (+ H 2 O , enzymes) n C 6 H 12 O 6
17. Reaction N.N. Zinina
Receiving Method aromatic amines(including aniline) by reduction of nitro compounds.
C 6 H 5- NO 2 + 3H 2 = C 6 H 5- NH 2 + 2H 2 O
WURZ REACTION– a chemical reaction that makes it possible to obtain the simplest organic compounds - saturated hydrocarbons.
The Wurtz reaction itself consists in the condensation of alkyl halides under the action of metallic Na, Li, or less commonly K:
2RHal + 2Na ® R–R + 2NaHal.
Sometimes it is interpreted as the interaction of RNa or RLi with R "Hal.
The reaction was discovered by the French organic chemist Charles Wurtz (1817-1884) in 1855 while trying to obtain ethyl sodium from ethyl chloride and sodium metal.
Despite the fact that the Wurtz reaction leads to the formation of a new carbon-carbon bond, it is not often used in organic synthesis. Basically, it is used to obtain saturated hydrocarbons with a long carbon chain, it is especially useful in obtaining individual hydrocarbons of large molecular weight, and, as can be seen from the above diagram, only one alkyl halide should be taken to obtain a given hydrocarbon, since when two alkyl halides are condensed, a mixture is obtained all three possible combination products. Therefore, if an alkyl halide and sodium are used, only hydrocarbons with an even number of carbon atoms can be obtained by the Wurtz reaction. The Wurtz reaction proceeds most successfully with primary alkyl iodides. Very low yields of the target product are obtained using the Wurtz method for secondary alkyl halides. The reaction is usually carried out in diethyl ether. The use of hydrocarbons as solvents reduces the selectivity of the reaction.
However, if a pre-prepared organometallic compound, such as alkyllithium, is used, then unsymmetrical condensation products can also be obtained:
RLi + R"Hal ® R – R" + LiHal
In both cases, the reaction is accompanied by the formation of a large number of side products due to side processes. This illustrates an example of the interaction of ethyllithium with 2-bromoctane:
In this case, 3-methylnonane and a number of side products in the indicated molar ratios are formed as a product of the Wurtz reaction.
In addition to sodium, metals such as silver, zinc, iron, copper, and indium have been used in the Wurtz reaction.
The Wurtz reaction has been successfully used for intramolecular condensations to build carbocyclic systems. Thus, cyclopropane can be obtained from 1,3-dibromopropane under the action of metallic zinc and sodium iodide (as a reaction promoter):
Other strained carbocyclic systems can also be constructed. For example, from 1,3-dibromoadamantane, using a sodium-potassium alloy, 1,3-dehydroadamantane can be obtained:
And the interaction of 1-bromo-3-chloro-cyclobutane with sodium leads to bicyclobutane:
A number of varieties of the Wurtz reaction are known, which have received their own names. These are the Wurtz-Fittig reaction and the Ullmann reaction. The first is the condensation of an alkyl and aryl halide under the action of sodium to form an alkylaromatic derivative. In the case of the Ullmann reaction, aryl iodides are usually introduced into the condensation, and freshly prepared copper is used instead of sodium, this reaction makes it possible to obtain various biaryl derivatives in high yield, including unsymmetrical ones containing a substituent in one of the aromatic nuclei:
The Wurtz reaction mechanism is believed to consist of two main steps:
1) the formation of an organometallic derivative (if a metal is used, and not a pre-prepared organometallic compound):
RHal + 2Na ® R–Na + NaHal,
2) the interaction of the formed, in this case, sodium organic compound with another alkyl halide molecule:
RHal + R–Na ® RR + NaHal.
Depending on the nature of R and the reaction conditions, the second stage of the process can proceed according to the ionic or radical mechanism.
Vladimir Korolkov
In industry, a substance is usually obtained in large quantities, striving for maximum profitability. Often you can use not a pure organic compound, but a mixture. In a number of cases, it is economically advantageous to carry out the separation of even complex mixtures, especially if it is possible to isolate other useful substances at the same time. There are many cases when it turns out to be profitable to develop a unique synthesis method and build a special enterprise for the production of a highly profitable substance.
In the laboratory, it is usually necessary to synthesize small amounts of a substance (grams and fractions of a gram). In research, chemists almost always need individual substances, not mixtures. Unlike industry, time is more valuable than price. In addition, laboratory syntheses are always flexible because the researcher is not interested in repeating the learned process many times. Therefore, methods are used that allow quickly, with high yield to obtain the target product with a minimum content of impurities.
It is important that laboratory (but not industrial) methods, as a rule, can be extended to the entire class of synthesized compounds.
In the course of studying the course of organic chemistry, the main attention is directed to laboratory methods of obtaining. When solving problems, industrial methods should not be used, even if they are used to obtain exactly the substance whose synthesis must be planned. For example, if ethylene is to be synthesized during the synthesis, it should be obtained using common methods synthesis of alkenes, although this compound is in huge quantities obtained by cracking.
Alkenes and alkynes in the presence of heterogeneous catalysts, such as Pt, Pd, Ni, easily add one or two moles of hydrogen at slight heating and low pressure. In this case, alkanes with the same carbon skeleton are quantitatively formed.
Halogen derivatives of saturated hydrocarbons can be reduced to alkanes by metal in an acidic medium:
Alkanes can be obtained by hydrolysis of Grignard reagents:
The above methods make it possible to synthesize alkanes having the same carbon skeleton as in the original molecule.
For the synthesis of paraffins, the structure of the carbon chain of which differs from the starting materials, several methods are known. Monohalogenated derivatives of alkanes, when interacting with metallic sodium, are converted into saturated hydrocarbons by the Wurtz reaction. During the reaction, a carbon-carbon bond between carbon atoms bonded in the parent compound to halogens.
The Wurtz reaction can be used exclusively for the synthesis of symmetrical alkanes (R-R) with an even number of carbon atoms. To avoid the formation of mixtures of alkanes, only one halogen derivative should be introduced into this reaction.
The limitations of the Wurtz reaction are clear from the following example.
The reaction produces a mixture of propane, ethane and n-butane. Since the reaction rates are close, it is not possible to suggest conditions under which propane formation would be the predominant process. Consequently, two-thirds of the starting materials will be wasted. In addition, the difficult problem of separating the reaction products arises.
When extending the Wurtz reaction to more complex halogen derivatives, care should be taken. alkali metals have a very high reactivity. If there are functional groups in the molecule, in addition to the halogen atom, in most cases the reaction of sodium or potassium with them will go faster than with the halogen. It makes no sense to even try to carry out the Wurtz reaction if the molecule contains hydroxy- (OH), carboxy- (COOH), sulfo- (SO 3 H) and many other groups along with halogen.
One of the ways to obtain alkanes is the reaction of decarboxylation (elimination of CO 2) of salts of carboxylic acids. In some cases, this process occurs very easily even with slight heating. Saturated carboxylic acids of the aliphatic series cleave off the carboxyl group only when their salts are calcined with alkali.
As a result of decarboxylation, an alkane is formed, containing one carbon atom less than it was in the original acid.
If a salt of a carboxylic acid of the aliphatic series is subjected to electrolysis (Kolbe's anodic synthesis), then the carboxylate anion gives the electrode one electron at the anode, turning into an unstable radical. Emission of CO 2 leads to an alkyl radical. When two alkyl radicals recombine, a symmetrical alkane with an even number of carbon atoms is formed.
Lecture No. 8
hydrocarbons
· Alkenes. homologous series, nomenclature, types of isomerism. Geometric isomerism in the alkene series. cis- and trance- isomers, E,Z-nomenclature. Reasons for the lack of free rotation relative to the double bond. Physical properties, patterns of their change in the homologous series and spectral characteristics alkenes.
· Production methods: dehydrogenation of alkanes, cracking of oil, partial hydrogenation of alkynes, dehalogenation, dehydrohalogenation of haloalkanes and dehydration of alcohols (Zaitsev's rule).
Alkenes (olefins, ethylene hydrocarbons)
Alkenes - open chain hydrocarbons general formula C n H 2 n and containing one double bond in the molecule (p-bond) .
Compared to alkanes, the corresponding ethylene hydrocarbons form more isomers, which is associated not only with differences in carbon skeletons, but also with the location of the double bond and the geometry of the molecule.
Consider the isomerism of alkenes with four carbon atoms. In addition to structural isomers, there are double bond position isomers (butene-1 and butene-2). Butene-2 can exist as two isomers that differ spatial arrangement substituents on the double bond. Since free rotation relative to the p-bond is impossible (60 kcal barrier) and the entire fragment of the molecule lies in the same plane, methyl groups can be located either on one side of the double bond or on opposite sides. In the name of the first use the prefix cis- (on the one hand - lat.), on the other - trance- (through - lat.). This type of spatial isomerism is called geometric.
