Soft oxidation of alkenes. Alkenes are hydrocarbons, in whose molecules there is one double C \u003d with communication. Accession of carbenes and carbenoids

In oxidative reaction reactions, organic substances More often exhibit the properties of reducing agents, and they themselves are oxidized. The ease of oxidation of organic compounds depends on the availability of electrons when interacting with the oxidizing agent. All known factors causing an increase in electron density in organic compound molecules (for example, positive inductive and mesomeric effects) will increase their ability to oxidation and vice versa.

The tendency of organic compounds to oxidation increases with their growth nucleophilicityWhat corresponds to the following rows:

Growth of nucleophilicity in a row

Consider redox reactions representatives of the most important classes organic substances with some inorganic oxidizers.

Oxidation of alkenes

With the soft oxidation of alkenes turn into glycols (diatomic alcohols). Atoms-reducing agents in these reactions - carbon atoms associated with double bond.

The response with potassium permanganate solution takes place in a neutral or weakly alkaline medium as follows:

3C 2 H 4 + 2KMNO 4 + 4H 2 O → 3CH 2 OH-CH 2 OH + 2MNO 2 + 2KOH

In more stringent conditions, oxidation leads to a discontinuation of a carbon chain for a double bond and the formation of two acids (in a strongly alkaline medium - two salts) or acid and carbon dioxide (in a strongly alkaline environment - salts and carbonate):

1) 5CH 3 CH \u003d 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

2) 5ch 3 CH \u003d CH 2 + 10KMNO 4 + 15H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 10MNSO 4 + 5K 2 SO 4 + 20H 2 O

3) CH 3 CH \u003d CHCH 2 CH 3 + 8KMNO 4 + 10KOH → CH 3 Cook + C 2 H 5 Cook + 6H 2 O + 8K 2 MNO 4

4) CH 3 CH \u003d CH 2 + 10KMNO 4 + 13KOH → CH 3 Cook + K 2 CO 3 + 8H 2 O + 10K 2 MNO 4

Potassium dichromat in the sulfuric acid medium oxidizes alkenes in similarly reactions 1 and 2.

With the oxidation of alkenes in which carbon atoms at a double bond comprise two carbon radicals, two ketones are formulated:

Oxidation of alkins

Alkins are oxidized in a somewhat stringent conditions than alkenes, so they are usually oxidized with a tip of a carbon chain along a triple bond. As in the case of alkenes, the reducing atoms here are carbon atoms associated with a multiple association. As a result of the reactions, acids and carbon dioxide are formed. Oxidation can be carried out by permanganate or potassium dichromate in an acidic environment, for example:

5CH 3 C≡CH + 8KMNO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 8MNSO 4 + 4K 2 SO 4 + 12H 2 O

Acetylene can be oxidized by potassium permanganate in a neutral medium to potassium oxalate:

3Ch≡ch + 8kmno 4 → 3kooc -Cook + 8mno 2 + 2Kon + 2N 2 o

In the acidic medium, oxidation goes to oxalic acid or carbon dioxide:

5ch≡ch + 8kmno 4 + 12h 2 SO 4 → 5Hooc -Cooh + 8mnSO 4 + 4K 2 SO 4 + 12N 2 o
CH≡CH + 2KMNO 4 + 3H 2 SO 4 → 2CO 2 + 2MNSO 4 + 4H 2 O + K 2 SO 4

Oxidation of Gomologists Benzol

Benzol is not oxidized even in fairly harsh conditions. Benzol homologs can be oxidized by potassium permanganate solution in a neutral medium to potassium benzoate:

C 6 H 5 CH 3 + 2KMNO 4 → C 6 H 5 Cook + 2mno 2 + KOH + H 2 O

C 6 H 5 CH 2 CH 3 + 4KMNO 4 → C 6 H 5 Cook + K 2 CO 3 + 2H 2 O + 4MNO 2 + KOH

The oxidation of benzene homologists with dichromate or permanganate potassium in the acidic medium leads to the formation of benzoic acid.

5C 6 H 5 CH 3 + 6Kmno 4 +9 H 2 SO 4 → 5C 6 H 5 Soam + 6mNSO 4 + 3K 2 SO 4 + 14H 2 O

5C 6 H 5 -C 2 H 5 + 12KMNO 4 + 18H 2 SO 4 → 5C 6 H 5 COOH + 5CO 2 + 12MNSO 4 + 6K 2 SO 4 + 28H 2 O

Oxidation of alcohols

The direct product of the oxidation of primary alcohols is aldehydes, and secondary - ketones.

The aldehyde alcohols formed during the oxidation are easily oxidized to acids, therefore the aldehydes from the primary alcohols are obtained by oxidation of potassium dichromate in the acidic medium at a boiling point of aldehyde. Evaporated, aldehydes do not have time to oxidize.

3C 2 H 5 OH + K 2 CR 2 O 7 + 4H 2 SO 4 → 3CH 3 CHO + K 2 SO 4 + CR 2 (SO 4) 3 + 7H 2 O

With an excess of oxidizing agent (KMNO 4, k 2 Cr 2 O 7) in any medium, primary alcohols are oxidized to carboxylic acids or their salts, and secondary to ketones.

5C 2 H 5 OH + 4KMNO 4 + 6H 2 SO 4 → 5CH 3 COOH + 4MNSO 4 + 2K 2 SO 4 + 11H 2 O

3CH 3 -CH 2 OH + 2K 2 CR 2 O 7 + 8H 2 SO 4 → 3CH 3 -COOH + 2K 2 SO 4 + 2Cr 2 (SO 4) 3 + 11H 2 O

Tertiary alcohols under these conditions are not oxidized, and methyl alcohol is oxidized to carbon dioxide.

Double-spectacular alcohol, ethylene glycol HOCH 2 -CH 2 OH, when heated in an acidic medium with a solution of KMNO 4 or k 2 Cr 2 O 7, it is easily oxidized to oxidic acid, and in neutral - to potassium oxalate.

5CH 2 (OH) - CH 2 (OH) + 8Kmno 4 + 12h 2 SO 4 → 5Hooc -Cooh + 8mnSO 4 + 4K 2 SO 4 + 22N 2 O

3CH 2 (OH) - CH 2 (OH) + 8Kmno 4 → 3KOOC -Cook + 8mno 2 + 2Kone + 8N 2 O

Oxidation of aldehydes and ketones

Aldehydes are quite strong reducing agents, and therefore are easily oxidized by various oxidizing agents, for example: KMNO 4, k 2 Cr 2 O 7, OH, CU (OH) 2. All reactions come when heated:

3CH 3 CHO + 2KMNO 4 → CH 3 COOH + 2CH 3 Cook + 2mno 2 + H 2 O

3CH 3 CHO + K 2 CR 2 O 7 + 4H 2 SO 4 → 3CH 3 COOH + CR 2 (SO 4) 3 + 7H 2 O

CH 3 CHO + 2KMNO 4 + 3KOH → CH 3 Cook + 2K 2 MNO 4 + 2H 2 O

5CH 3 CHO + 2KMNO 4 + 3H 2 SO 4 → 5CH 3 COOH + 2MNSO 4 + K 2 SO 4 + 3H 2 O

CH 3 CHO + BR 2 + 3NAOH → CH 3 Coona + 2NABR + 2H 2 O

silver Mirror Reaction

With ammonia solution of silver oxide aldehydes are oxidized to carboxylic acids that in ammonium solution give ammonium salts (the reaction of the "silver mirror"):

CH 3 CH \u003d O + 2OH → CH 3 COONH 4 + 2AG + H 2 O + 3NH 3

CH 3 -CH \u003d O + 2CU (OH) 2 → CH 3 COOH + CU 2 O + 2H 2 O

Aldehyde (formaldehyde) is oxidized, as a rule, to carbon dioxide:

5hcoh + 4kmno 4 (spin) + 6H 2 SO 4 → 4mNSO 4 + 2K 2 SO 4 + 5CO 2 + 11H 2 O

3SH 2 O + 2K 2 CR 2 O 7 + 8H 2 SO 4 → 3CO 2 + 2K 2 SO 4 + 2Cr 2 (SO 4) 3 + 11H 2 O

HCHO + 4OH → (NH 4) 2 CO 3 + 4AG ↓ + 2H 2 O + 6NH 3

HCOH + 4CU (OH) 2 → CO 2 + 2CU 2 O ↓ + 5H 2 O

Ketones are oxidized in hard conditions with strong oxidizing agents with a break connections sch and give mixtures of acids:

Carboxylic acids.Among the acids with strong reducing properties have ant and oxal, which are oxidized to carbon dioxide.

NSON + HGCL 2 \u003d CO 2 + HG + 2HCl

HCOOH + CL 2 \u003d CO 2 + 2HCl

HOOC-COOH + CL 2 \u003d 2CO 2 + 2HCL

Formic acidIn addition to acidic properties, there are also some properties of aldehydes, in particular, regenerative. At the same time it is oxidized to carbon dioxide. For example:

2kmnO4 + 5HCOOH + 3H2SO4 → K2SO4 + 2MNSO4 + 5CO2 + 8H2O

When heated with strong watering agents (H2SO4 (conc.) Or P4O10) decomposes:

HCOOH → (T) CO + H2O

Catalytic oxidation of alkanes:

Catalytic oxidation of alkenes:

Oxidation of phenols:

Alkenes - These are hydrocarbons, in whose molecules there is one double C \u003d with communication.

Nomenclature of alkenes:the title appears suffix -One.

The first member of the homologous series is C2H4 (ethen).

For the simplest alkenes, historically established names are also used:

· Ethylene (ethen),

· Propylene (Propen),

The following monovalent radicals of alkenes are often used in the nomenclature:

Types of isomerism of alkenes:

1. Male carbon skeleton: (starting with C4N8 - butene and 2-methylpropen)

2. Isomerius of a multiple communication: (starting with C4N8): butene-1 and butene-2.

3. Interclative isomeria: with cycloalkanes (Starting from Propen):

C4H8 - butene and cyclobutane.

4. Spatial isomeria of alkenes:

Due to the fact that there is no free rotation around the double bond, it becomes possible cis-transisomeria.

Alkenes having each of the two carbon atoms with a double bond various substituentsmay exist in the form of two isomers, characterized by the location of the substituents relative to the π-communication plane:

Chemical properties of alkenes.

For alkenes are characteristic:

· double connection reactions,

· oxidation reactions

· reactions of substitution in the "side chain".

Obtaining alkenes

Alkadian.

These are hydrocarbons containing two double bonds. The first member of the series is C3N4 (adapted or allen). The title appears suffix - Dien .

Types of double ties in diene:

Isomerius diennes

Electronic structure of conjugate dienes.

Butadiene-1,3 molecule CH2 \u003d CH-CH \u003d CH2contains four carbon atoms in sp.2 - hybridized state and has a flat building.

π-electrons of double bonds form a single π-electronic cloud (conjugate system ) And delocalized between all carbon atoms.

The multiplicity of bonds (the number of general electronic pairs) between carbon atoms has an intermediate value: there is no purely single and pure double bonds. The structure of butadiene more accurately reflects the formula with delocalized "one-hour" connections.

Chemical properties of conjugate alkadiennes.

Obtaining alkadiennes.

In the tasks category C3 EGE, the special difficulties cause the oxidation reaction of organic substances permanganate KMNO 4 in an acidic medium flowing with a carbon chain gap. For example, a surge oxidation reaction flowing according to the equation:

Ch 3 – Ch = Ch 2 + KMNO.4 + H. 2 SO. 4 → Ch 3 Coool + Co. 2 + MNSO. 4 + K. 2 SO. 4 + H. 2 O.

In order to place the coefficients in complex equations of redox reactions like this, the standard method is proposed to compile an electronic balance, but after another attempt it becomes obvious that this is not enough. The root of the problem here lies in the fact that the coefficient in front of the oxidizing agent taken from electronic balance, It is necessary to replace. This article offers two ways that allow you to choose the right coefficient before the oxidizing agent so that finally equalize all the elements. Method of substitution To replace the coefficient before the oxidizing agent, it is more suitable for those who are capable of long and painstakingly consider, since the coefficient arrangement of the coefficients may be long (in this example, it took 4 attempts). The substitution method is used in conjunction with the "Table" method, which is also discussed in detail in this article. Method "Algebraic" Allows no less simple and reliable, but much faster replacing the coefficient before the oxidizing agent KMNO 4.compared with the method of substitution, however, has a narrower scope. The method "algebraic" can only be used to replace the coefficient before the oxidizing agent KMNO 4.in the equations of the reactions of the oxidation of organic substances flowing with the gap of the carbon chain.

Download:

Preview:

To use the preview, create a Google account and log in to it: https://accounts.google.com

On the topic: Methodical development, presentations and abstracts

Mailing of coefficients in chemical equations

The teacher, being the main person in organizing students' cognitive activity, is constantly in finding ways to improve learning efficiency. Organization of effective training ...

The oxidation of alkenes (acyclic and cyclic) when interacting with peracid (supracillas) in a non-polar, indifferent medium is accompanied by the formation of alkene-epoxy oxides, therefore the reaction itself is called the epoxidation reaction.

According to modern nomenclature, the Jewberry, a three-membered cycle with one oxygen atom is called oxiran.
Epoxidation of alkenes should be considered as a synchronous, agreed process in which ionic intermediates of the type of oh + hydroxyl cation do not participate. Epoxidation of alkenes is a process of synticoning one oxygen atom for dual connection with the complete preservation of the substituent configuration at double bond:

For epoxidation, a mechanism was proposed characteristic of agreed processes:

Perslotes are used as epoxidizing agents: pebenzoic, m-chloropenzoic, mononadfthal, perussum, pertinterucus and permaneury. The perkislotes of the aromatic series are used in the form of individual reagents, while the percussions of the aliphatic series - CH3CO3H, CF3CO3H and HCO3H are not isolated individually and is used immediately after their formation in the interaction of 30- or 90% hydrogen peroxide and the corresponding carboxylic acid. The perbenzoic and meta-chloropenzoic acid is currently obtained by oxidation of the benzoic and meta-chlorobenzoic acids of 70% hydrogen percussion in methanesulfonic acid solutions:

or hydrogen chloride crides and hydrogen peroxide:

Mononadfthalic acid is obtained by a similar method from phthalic anhydride and 30% hydrogen peroxide in aquatic alkali:

Initially, pebnzoic or mononadfthalic acid was used to obtain oxiranes (epoxides):

Especially convenient method using mononadfthalic acid. Mononadfthalic acid is well soluble in ether, while one of the reaction products (phthalic acid) is completely dissatisfied with the air, and the progress of the reaction is easy to judge by the amount of selected crystalline phthalic acid.
Currently, meta-chloropenzoic acid is most often used for epoxidation. In contrast to other perkslot, it is stable when stored for a long time (up to 1 year) and absolutely safe when contacting. The outlets of oxyranes obtained during the oxidation of acyclic and cyclic alkenes by meta-chloroperbenzoic acid in the methylene chloride solution, usually very high.

Perkislotes are often generated directly in the reaction mixture of 90% hydrogen peroxide and carboxylic acid in methylene chloride:

Alkenes, with double bonds associated with a carbonyl and carboxyl group or another acceptor substituent, low-active, and for their oxidation, it is necessary to use stronger oxidants, such as trifluoroprucic acid, obtained from trifluoroacetic acid anhydride and 90% hydrogen peroxide in methylene chloride. The alternative epoxidation method lies in the interaction of alkin with nitrile and 90% hydrogen peroxide:

The simplest oxiran - ethylene oxide - is obtained in industry by oxidation by oxygen in the presence of silver as a catalyst:

The three-membered ring of oxyranes is easily revealed under the action of a wide variety of nucleophilic reagents. These reactions will be discussed in detail in Chapter 11 dedicated to acyclic and cyclic simple ether. Here will also be considered only hydrolysis of epoxides. The hydrolysis of epoxides is catalyzed by both acids and bases. In both cases, virgin diols are formed, i.e. Glycols. In acid catalysis in the first stage, protonation of an epoxide oxygen atom with the formation of a cyclic oxonium ion, which is revealed as a result of a nucleophilic attack of water molecule:

The key stage in the disclosure of the ring, which determines the speed of the entire process is the nucleophilic attack with water on the protonated form of epoxide. From the point of view of the mechanism, this process is similar to the disclosure of a bromonium ion with a nucleophilic attack of a bromide ion or another nucleophilic agent. From these positions, a stereochemical result should be the formation of trans-glycols when splitting cyclic epoxides. Indeed, with an acid-catalyzed hydrolysis of cyclohexenoxide or cyclopenthenoxide, exclusively trans-1,2-diols are formed:

Thus, the two-step process of alkene epoxidation with subsequent acid hydrolysis of epoxide total corresponds to the reaction of anti-hydroxylation of alkenes.
Both stages of anti-hydroxylation of alkenes can be combined if the alkene is treated with aqueous 30 - 70% hydrogen peroxide in formic or trifluoroacetic acid. Both of these acids are strong enough in order to cause an epoxy cycle disclosure, so they are usually used for anti-hydroxylation of alkenes, for example:

The disclosure of the epoxy ring catalyzed by the base also leads to the formation of trans-glycols:

Consequently, the two-step process of epoxidation of alkenes with subsequent alkaline hydrolysis of epoxides is also a reaction of anti-hydroxylation of alkenes.
Third modern method Anti-hydroxylation of alkenes was proposed and developed by K. Prej (1933). Alken is heated with iodine and a benzoate or silver acetate in anhydrous benzene or CCL4. Trans-attachment to a double bond initially leads to the formation of a iodethyr, in which iodine further is replaced by a benzoate ion, and the glycol dibenzoate is obtained:

The reaction of the narrow in anhydrous medium leads to the formation of the same diol as the epoxidation of alkenes, followed by hydrolysis:

Thus, the preaction reaction is a more expensive modification of other methods of anti-hydroxylation of alkenes. However, for sensitive acids of compounds, this method has obvious advantages Before anti-hydroxylation using percislot and subsequent acid hydrolysis of epoxide.
Some salts and oxides of transition metals of the highest degrees of oxidation are effective dual-bonding-hydroxylation reagents. The oxidation of alkenes permanganate potassium is one of the oldest methods of synth-hydroxylation of the double bond - continues to be widespread despite the limit characteristic of it. Cis-1,2-cyclohexandiol was first obtained by V.V. Markovnikov in 1878. Hydroxylation of cyclohexen with aqueous solution of potassium permanganate at 0 ° C:

This method was further developed in the works of the Russian scientist E.E., Wagner, therefore Sin-hydroxylation under the influence of aqueous solution of potassium permanganate is called the Wagner reaction. Potassium permanganate is a strong oxidizing agent that can only hydroxy the double bond, but also split the forming vicinal diol. To avoid further cleavage of glycols, it is necessary to carefully monitor the reaction conditions. The best results are achieved in hydroxylation of alkenes in a slightly alkaline medium (pH ~ 8) at 0-5 ° C diluted with ~ 1% aqueous KMNO4 aqueous solution. Nevertheless, glycol yields are usually small (30 - 60%):

Initially, in the oxidation of alkenes permanganate potassium, a cyclic ether of manganese acid is formed, which is immediately hydrolyzed to the Vicinal Diola:

The cyclic ether of manganese acid as an intermediat has never been allocated, but its education follows from experiments with Kalia's labeled 18o permanganate. K. Vaiberg with employees (1957) showed that both oxygen atoms in Glycol turn out to be labeled when the alkene was oxidized by KMN18O4. This means that both oxygen atoms are moving from the oxidant, and not from the solvent - water, which is in good according to the proposed mechanism.
Another method of symbol-hydroxylation of alkenes under the action of Osmia oxide (VIII) OSO4 was proposed by R. Kryga in 1936. Osmia tetraoxide is a colorless crystalline substance, well-soluble in ether, dioxane, pyridine and other organic solvents. When the osmium tetraoxide interacts with alkanes in the air or dioxane, a black precipitate of osmumic acid cyclic ester is formed - osmat, which can be easily isolated individually. The addition of OSO4 to the double bond is noticeably accelerated in pyridine solution. The decomposition of osmates to the vicinal diols is achieved by the action of aqueous solution of sodium hydrosulfite or hydrogen sulfide:

The exits of the products of synthesis of alkenes in this method are significantly higher than when using permanganate as an oxidizing agent. An important advantage of the curve method is the absence of alkene oxidative splitting products characteristic of permanganate oxidation:

Osmia tetraoxide - expensive and hard-to-reach reagent, and it is very toxic. Therefore, Osmia oxide (VIII) is used for the synthesis of small quantities of hard-to-reach substances in order to obtain the highest output of the diol. To simplify the synchinous hydroxylation of alkenes under the action of OSO4, a technique was developed that allows only the catalytic amounts of this reagent. Hydroxylation is carried out using hydrogen peroxide in the presence of OSO4, for example:

It is interesting to note that the highest oxides of other transition metals (V2O5, WO3, Moo3, etc.) catalyze anti-hydroxylation of alkenes.
R. Woodword in 1958 proposed an alternative three-stage method of synthesis alkenes. Initially, the alkenes is converted to trans-iodacetate as a result of interaction with iodine and silver acetate in acetic acid. Then halogen replaces on oxygraum when processing with aqueous acetic acid when heated. The last stage lies in the hydrolytic cleavage of acetate group:

In conclusion of this section, we present the stereochemical relations between the alkene of the cis-or trans configuration and the configuration of the formed Vicinal glycol, which may be a cis- or trans-isomer, erythro or treo-shape, a meso- or D-, L-form, depending from alkene deputies:

Similar stereochemical ratios are observed in other reactions of synod or anti-attachment of hydrogen, halogen breeding, water, halogen, boron hydrides and other reagents over multiple communication.

The oxidation of alkenes permanganate potassium in an alkaline medium during heating (rigid conditions) leads to the destruction of their carbon skeleton at the dual connection site. At the same time, depending on the number of alkyl groups associated with the vinyl fragment, two carboxylic acids, acid and ketone or two ketones can be obtained:

UPR.11.What product is formed during the oxidation of cyclohexien (a) dilute potassium permanganate solution in cold and (b) concentrated potassium permanganate solution with subsequent acidification.

UPR.12.What products are formed from 1,2-dimethylcyclohexen at its (A) catalytic hydrogenation, (b) the oxidation of potassium permanent potassium permanganate in the cold, (c) ozonation with subsequent reducing splitting.

6.5. Ethylene oxidation in acetaldehyde

The oxidation of ethylene air oxygen in the presence of palladium chlorides (II) and copper (II) leads to the formation of acetaldehyde ( Wheaker process):

(63)

ethanal (acetaldehyde)

6.6. Chloroising ethylene

Vinyl chloride is obtained by chlorogeneous ethylene:

6.7. Oxidative ammonolysis

The oxidation of hydrocarbons by air oxygen in the presence of ammonia leads to the transformation of the methyl group in the cyano group. Such oxidation is called oxidative ammonolysis. Acrylonitrile is obtained by oxidation of propylene.

acrylonitrile

The oxidative ammonolysis of methane is obtained by a sinyl acid:

(66)

7. Hydraulication of alkenes (oxosynthesis)

At temperatures from 30 to 250 o C and a pressure of 100-400 atm. In the presence of dicobaltoktacarbonyl, alkenes join hydrogen and carbon monoxide with the formation of aldehydes. The mixture of isomers is usually obtained:

Mechanism:

1. Decoration of Liganda

2. Attachment ethylene

3. The introduction of ethylene

4. Attaching Liganda

5. Implementation of CO

6. Oxidative hydrogen attachment

7. Recovery Pickup

8. Accession of carbnes and carbenoids

Recent years, a lot of attention in organic chemistry is paid to the compounds of bivalent carbon - carbenas. Most of the carbents are unstable and immediately after their formation react with other connections.

8.1. The structure of Karbenov

Unnoticed carben: CH 2, also called methylene, may be in a singlet or triplet form. In the singlet form of carben, two unconvisory electrons with paired spins are located on the same orbital, while in triplet form, two unpaired electrons with parallel spins are located on two orbitals of the same energy. Various electronic configurations of singlet and triplet carbenes are reflected both in different geometry of these particles and in various chemical activity. A bivalent carbon carbon atom is located in a SP 2-hybrid state, both electrons are located on SP 2-flexIDal orbitals (wave), and a p-orbital (NSMO) is free. Triplet carben is characterized by SP-hybridization of bivalent carbon; At the same time, two unpaired electrons are located on two p-orbitals, i.e., triplet carben is a biradical. The angle of H-H - H for singlet methylene, according to spectral data, is 102-105 0, and for triplet methylene, this angle increases to 135140 o. This corresponds to a higher stability of triplet methylene. According to quantum mechanical calculations, triplet methylene is truly 10 kcal / mol more stable singlet methylene.

The substituents, however, cause a change in the relative stability of these two forms of carben. For dialkyl carben, a triplet form is also more stable singlet, but for digalokarben : Chal 2, and other carbnes with substituents containing a watered pair of electrons, the main state is a singlet. The valence angle of C1-C-C1 for dichlorkarbena, equal to 106 o, is well consistent with the singlet form. Higher stability of the singlet shape of digalocarbens compared to triplet, apparently due to its stabilization due to the vapor pair of electrons heteroatom

Such stabilization of the triplet form of digokarben is impossible. According to the data of the quantum mechanical calculation, the energy of the singlet - the triplet transition for dichlorkarben is 13.5 kcal / mol.

A. Dichlorkarben

To generate digalokarbenov, developed methods based on reaction-elmination of halogen hydrogen of trigalometans under the action strong grounds. This method was historically the first, with the help of which the first of Karbenov was generated as an intermediate - dichlorkarben (J. Hein 1950). When interacting with severe bases of chloroform (RKA chloroform is ~ 16), bromoormal (RCA \u003d 9) and other trigalogomenomets are formed an anion that is stabilized by eliminating the halide ion with the formation of digocarben. Action on chloroform of strong bases is obtained by dichlorkarben:

dichlorkarben

As a base, lithiumorganic compounds in the indifferent aprotic medium can also be used. Then below -100 0 C can be fixed in the formation of trichloromethyl lithium as an intermediate.

Using strong bases such as RLi, you can generate carbered from 1,1-digalogenesis derivatives

In recent years, to generate digalokarben instead n.-Butilitia is widely used as a base of bis (trimethylsilyl) sodium amide.

At the same time, chemically inert loving [bis (trimethylsilyl) amide] is distinguished. Bis (trimethylsilyl) sodium amide, in contrast to n-butyl lithium, can be separated in an inert atmosphere in a dry form. In practice, its essential solutions can be used more often, which can be stored at room temperature for a long time.

Dichlorkarben can also be generated with thermal decarboxylation of sodium dry chloroacetate:

One of the most affordable modern methods for generating dichlorkarbena from chloroform under the action of sodium hydroxide in the conditions of interfacial catalysis will be described in detail later.

Dichlorkarben joins alkens, giving dichlorocyclopropans. The connection occurs stereospecific - the configuration of the initial alkene is preserved in the reaction product - the cyclopropane:

(69)

trance-2-buten trance-1,2-dimethyl-3,3-

dichlorcyclopropan

(70)

cis-2-buten q.with-1,2-dimethyl-3,3-

dichlorcyclopropan

(71)

7,7-dichlorubicycloheptan

When restoring 1,1-digalocyclopropans under the action of lithium in mPEM.-butyl alcohol, zinc in acetic acid or sodium in liquid ammonia Both halogen atoms are replaced by hydrogen. This is one of the general methods for producing cyclopropane derivatives.

bicyclicheptan.

UPR. eleven.Complete the reaction:

(Z) -3-methyl-2-pentene methylenecyclohexane

Answer

B. Methylene

Methylene can be obtained by decomposition of diazomethane. Diazomethane is a relatively unstable substance that decomposes when irradiation on nitrogen and methylene.

(73)

diazometan

Methylene: CH 2 with a diazomethane photolidium is formed in a less stable singlet form. Singlet methylene under the reaction conditions as a result of collisions with diazomethane or nitrogen molecules, it quickly loses energy and turns into a more stable triplet methylene.

For singlet carbenis, it is characterized by synchronous connection to the double bond of alkene with the complete preservation of the geometry at a double bond (reaction - Cycloper compound). The attachment of the singlet shape of the carbenium for a double bond occurs, thus, strictly stereospecific.

B. Reaction Simmons-Smith

Effective and experimentally, very simple method of converting alkenes in cyclopropane derivatives is based on the reaction of alkenes with iodistan methylene and zinc and copper alloy. This reaction was opened in 1958 by Simmons and Smith and immediately won wide popularity in the synthesis of cyclopropane derivatives. Active particle in this reaction is not carben : CH 2, and carbenoid - iodide iodomethyl cycling IZNCH 2 I, formed by the interaction of methylene iodide and zinc-copper pair.

diiodmethane iodomeomethylcinodide

(Real Simmons Smith)

(75)

The reaction passes through the following mechanism:

The Simmons Smith reaction is a very convenient method of converting alkenes in the cyclopropane.

UPR. 12.Complete the reaction:

Answer

(76)

methylenecyclopentan spiroheptan.

(77)

styrene cyclopropylBenzene.