St. Petersburg State Technological Institute

(Technical University)

Chair organic chemistry Faculty 4

Group 476

Course work

Alkene oxidation

Student……………………………………… Rytina A.I.

Lecturer………………………………... Piterskaya Yu.L.

St. Petersburg

Introduction

1. Epoxidation (reaction by N.A. Prilezhaev, 1909)

2. Hydroxylation

2.1anti-Hydroxylation

2.2syn-Hydroxylation

3. Oxidative cleavage of alkenes

4.Ozonolysis

5. Oxidation of alkenes in the presence of palladium salts

Conclusion

List of sources used

Introduction

Oxidation is one of the most important and common transformations organic compounds.

In organic chemistry, oxidation is understood as processes that lead to the depletion of a compound in hydrogen or its enrichment in oxygen. In this case, electrons are removed from the molecule. Accordingly, recovery is understood as a separation from organic molecule oxygen or the addition of hydrogen to it.

In redox reactions, oxidizing agents are compounds with a high electron affinity (electrophiles), and reducing agents are compounds that have a tendency to donate electrons (nucleophiles). The ease of oxidation of a compound increases with the growth of its nucleophilicity.

During the oxidation of organic compounds, as a rule, complete transfer of electrons and, accordingly, a change in the valence of carbon atoms does not occur. Therefore, the concept of the degree of oxidation - the conditional charge of an atom in a molecule, calculated on the basis of the assumption that the molecule consists only of ions - is only conditional, formal.

When compiling the equations of redox reactions, it is necessary to determine the reducing agent, oxidizing agent and the number of given and received electrons. As a rule, the coefficients are selected using the electron-ion balance method (half-reaction method).

This method considers the transition of electrons from one atom or ion to another, taking into account the nature of the medium (acidic, alkaline or neutral) in which the reaction takes place. To equalize the number of oxygen and hydrogen atoms, either water molecules and protons (if the medium is acidic) or water molecules and hydroxide ions (if the medium is alkaline) are introduced.

Thus, when writing the reduction and oxidation half-reactions, one must proceed from the composition of the ions actually present in the solution. Substances that are poorly dissociated, poorly soluble or evolved as a gas should be written in molecular form.

As an example, consider the process of ethylene oxidation with a dilute aqueous solution of potassium permanganate (Wagner reaction). During this reaction, ethylene is oxidized to ethylene glycol, and potassium permanganate is reduced to manganese dioxide. Two hydroxyls are added at the site of the double bond:

3C 2 H 4 + 2KMnO 4 + 4H 2 O → 3C 2 H 6 O 2 + 2MnO 2 + 2KOH

Reduction half-reaction: MnO 4 ¯ + 2H 2 O + 3 e→ MnO 2 + 4OH ¯ 2

Oxidation half-reaction: C 2 H 4 + 2OH − − 2 e → C 2 H 6 O 2 3

Finally, we have in ionic form:

2MnO 4 ¯ + 4H 2 O + 3C 2 H 4 + 6OH ¯ → 2MnO 2 + 8OH ¯ + 3C 2 H 6 O 2

After carrying out the necessary reductions of similar terms, we write the equation in molecular form:

3C 2 H 4 + 2KMnO 4 + 4 H 2 O \u003d 3C 2 H 6 O 2 + 2MnO 2 + 2KOH.

Characteristics of some oxidizing agents

Oxygen

Air oxygen is widely used in technological processes, as it is the cheapest oxidizing agent. But oxidation with air oxygen is fraught with difficulties associated with the control of the process, which proceeds in different directions. The oxidation is usually carried out at high temperature in the presence of catalysts.

Ozone

Ozone O 3 is used to obtain aldehydes and ketones, if it is difficult to obtain them in other ways. Most often, ozone is used to establish the structure of unsaturated compounds. Ozone is produced by the action of a quiet electrical discharge on oxygen. One of the significant advantages of ozonation, compared with chlorination, is the absence of toxins after treatment.

Potassium permanganate

Potassium permanganate is the most commonly used oxidizing agent. The reagent is soluble in water (6.0% at 20ºC), as well as in methanol, acetone and acetic acid. For oxidation, aqueous (sometimes acetone) solutions of KMnO 4 are used in a neutral, acidic or alkaline medium. When carrying out the process in a neutral environment, salts of magnesium, aluminum are added to the reaction mass or carbon dioxide is passed through to neutralize the potassium hydroxide released during the reaction. The oxidation reaction of KMnO 4 in an acidic environment is most often carried out in the presence of sulfuric acid. The alkaline environment during oxidation is created by the KOH formed during the reaction, or it is initially added to the reaction mass. In slightly alkaline and neutral media, KMnO 4 oxidizes according to the equation:

KMnO4+ 3 e+ 2H 2 O \u003d K + + MnO 2 + 4OH ¯

in an acidic environment:

KMnO4+ 5 e+ 8H + = K + + Mn 2+ + 4H 2 O

Potassium permanganate is used to obtain 1,2-diols from alkenes, during the oxidation of primary alcohols, aldehydes and alkylarenes to carboxylic acids, as well as for the oxidative cleavage of the carbon skeleton along multiple bonds.

In practice, a fairly large excess (more than 100%) of KMnO 4 is usually used. This is due to the fact that under normal conditions KMnO 4 partially decomposes into manganese dioxide with the release of O 2 . Explosively decomposes with concentrated H 2 SO 4 when heated in the presence of reducing agents; mixtures of potassium permanganate with organics are also explosive.

Peracids

Peracetic and performic acids are obtained by reacting 25-90% hydrogen peroxide with the corresponding carboxylic acid according to the following reaction:

RCOOH + H 2 O 2 \u003d RCOOOH + H 2 O

In the case of acetic acid, this equilibrium is established relatively slowly, and in order to accelerate the formation of peracid, it is usually added as a catalyst sulfuric acid. Formic acid is strong enough on its own to provide a quick equilibrium.

pertrifluoro acetic acid, obtained in a mixture with trifluoroacetic acid by the reaction of trifluoroacetic anhydride with 90% hydrogen peroxide, is an even stronger oxidizing agent. Similarly, peracetic acid can be obtained from acetic anhydride and hydrogen peroxide.

Solid m-chloroperbenzoic acid, because it is relatively safe to handle, quite stable and can be stored for a long time.

Oxidation occurs due to the released oxygen atom:

RCOOOH = RCOOH + [O]

Peracids are used to obtain epoxides from alkenes, as well as lactones from alicyclic ketones.

Hydrogen peroxide

Hydrogen peroxide is a colorless liquid, miscible with water, ethanol and diethyl ether. A 30% solution of H 2 O 2 is called perhydrol. A highly concentrated preparation may react explosively with organic substances. On storage, it decomposes into oxygen and water. The persistence of hydrogen peroxide increases with dilution. For oxidation, aqueous solutions of various concentrations (from 3 to 90%) are used in neutral, acidic or alkaline media.

H 2 O 2 \u003d H 2 O + [O]

By the action of this reagent on α,β-unsaturated carbonyl compounds in an alkaline medium, the corresponding epoxyaldehydes and ketones are obtained, peracids are synthesized by oxidation of carboxylic acids in an acidic medium. A 30% solution of H 2 O 2 in acetic acid oxidizes alkenes to 1,2-diols. Hydrogen peroxide is used: to obtain organic and inorganic peroxides, Na perborate and percarbonate; as an oxidizing agent in rocket fuels; upon receipt of epoxides, hydroquinone, pyrocatechol, ethylene glycol, glycerin, vulcanization accelerators of the thiuram group, etc.; for bleaching oils, fats, fur, leather, textile materials, paper; for cleaning germanium and silicon semiconductor materials; as a disinfectant for the neutralization of domestic and industrial Wastewater; in medicine; as a source of O 2 in submarines; H 2 O 2 is part of Fenton's reagent (Fe 2 + + H 2 O 2), which is used as a source of OH free radicals in organic synthesis.

Ruthenium and osmium tetroxides

Osmium tetroxide OsO 4 is a white to pale yellow powder with mp. 40.6ºС; t. kip. 131.2ºС. Sublimates already at room temperature, soluble in water (7.47 g in 100 ml at 25ºС), СCl 4 (250 g in 100 g of solvent at 20ºС). In the presence of organic compounds, it turns black due to reduction to OsO 2 .

RuO 4 is a golden yellow prism with so pl. 25.4ºС, noticeably sublimates at room temperature. Sparingly soluble in water (2.03 g in 100 ml at 20ºС), very soluble in CCl 4 . A stronger oxidizing agent than OsO 4 . Above 100ºС explodes. Like osmium tetroxide, it has high toxicity and high cost.

These oxidizing agents are used for the oxidation of alkenes to α-glycols under mild conditions.

Alkenes - These are hydrocarbons in the molecules of which there is ONE double C \u003d C bond.

Alkene nomenclature: suffix appears in the name -EN.

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

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

ethylene (ethene)

propylene (propene),

The following monovalent alkene radicals are often used in the nomenclature:

CH2-CH=CH2

Types of isomerism of alkenes:

1. Isomerism of the carbon skeleton:(starting from C4H8 - butene and 2-methylpropene)

2. Multiple bond position isomerism:(starting with C4H8): butene-1 and butene-2.

3. Interclass isomerism: With cycloalkanes(starting with propene):

C4H8 - butene and cyclobutane.

4. Spatial isomerism of alkenes:

Due to the fact that free rotation around the double bond is impossible, it becomes possible cis-trans- isomerism.

Alkenes having two carbon atoms at each double bond various substitutes, can exist in the form of two isomers that differ in the arrangement of substituents relative to the π-bond plane:

Chemical properties of alkenes.

Alkenes are characterized by:

· double bond addition reactions,

· oxidation reactions,

· substitution reactions in the "side chain".

1. Double bond addition reactions: the weaker π-bond is broken, a saturated compound is formed. These are electrophilic addition reactions - AE.	1) Hydrogenation: CH3-CH=CH2 + H2 à CH3-CH2-CH3 2) Halogenation: CH3-CH=CH2 + Br2 (solution)à CH3-CHBr-CH2Br Bleaching bromine water is a qualitative reaction to a double bond. 3) Hydrohalogenation: CH3-CH=CH2 + HBr à CH3-CHBr-CH3 (MARKOVNIKOV'S RULE: hydrogen is attached to the most hydrogenated carbon atom). 4) Hydration - water connection: CH3-CH=CH2 + HOH à CH3-CH-CH3 (attachment also occurs according to Markovnikov's rule)
2. Addition of hydrogen bromide to presence of peroxides (Harash effect) - this is a radical addition - AR	CH3-CH=CH2 + HBr -(H2O2)à CH3-CH2-CH2Br (reaction with hydrogen bromide in the presence of peroxide proceeds against Markovnikov's rule )
3. Combustion– complete oxidation alkenes with oxygen to carbon dioxide and water.	С2Н4 + 3О2 = 2СО2 + 2Н2О
4. Soft oxidation of alkenes - Wagner reaction : reaction with a cold aqueous solution of potassium permanganate.	3CH3- CH=CH2+ 2KMnO4 + 4H2O à 2MnO2 + 2KOH + 3 CH3 - CH - CH2 Oh Oh ( a diol is formed) Discoloration of an aqueous solution of potassium permanganate with alkenes is a qualitative reaction for alkenes.
5. Hard oxidation of alkenes– hot neutral or acid solution potassium permanganate. Comes with a break in the C=C double bond.	1. Under the action of potassium permanganate in an acidic environment, depending on the structure of the alkene skeleton, the following is formed: Fragment of the carbon chain at the double bond What does it turn into = CH -R R– COOHcarboxylic acid = C – R ketoneR – C – R CH3-C-1 H=C-2Н2 +2 KMn+7O4 + 3H2SO4 a CH3-C+3 Oh + C+4 O2 + 2Mn+2SO4 + K2SO4 + 4H2O 2. If the reaction proceeds in a neutral environment when heated, then, accordingly, potassium salt: Fragment of a chain near a double bond What does it turn into K2CO3 = CH -R R– COOTo- carboxylic acid salt = C – R ketoneR – C – R 3CH3C-1H=FROM-2Н2 +10 K MnO4 - ta 3 CH3 C+3OO K + + 3K 2C+4O3 + 10MnO2 +4Н2О+ K Oh
6. Oxidation ethylene oxygen in the presence of palladium salts.	CH2=CH2 + O2 –(kat)à CH3CHO (acetaldehyde)
7. Chlorination and bromination to the side chain: if the reaction with chlorine is carried out in the light or at a high temperature, hydrogen is replaced in the side chain.	CH3-CH=CH2 + Cl2 – (light)à CH2-CH=CH2 + HCl
8. Polymerization:	n CH3-CH=CH2 а(-CH–CH2-)n propylene ô polypropylene

ALKENES PRODUCTION

I . Cracking alkanes:	С7Н16 –(t)а CH3-CH=CH2 + C4H10 alkene alkane
II. Dehydrohalogenation of haloalkanes under the action of an alcohol solution of alkali - the reaction ELIMINATING.	Zaitsev's rule: The elimination of a hydrogen atom in elimination reactions occurs predominantly from the least hydrogenated carbon atom.
III. Dehydration of alcohols at an elevated temperature (above 140°C) in the presence of water-removing reagents - aluminum oxide or concentrated sulfuric acid - the elimination reaction.	CH3- CH-CH2-CH3 – (H2SO4,t>140o)à à H2O+CH3- CH=CH-CH3 (also obeys the Zaitsev rule)
IV. Dehalogenation of dihaloalkanes having halogen atoms at neighboring carbon atoms, under the action of active metals.	CH2 Br-CH Br-CH3+ mg aCH2=CH-CH3+ MgBr2 Zinc may also be used.
V. Dehydrogenation of alkanes at 500°С:
VI. Incomplete hydrogenation of dienes and alkynes	С2Н2 + Н2 (deficiency) –(kat)à С2Н4

ALKADIENES.

These are hydrocarbons containing two double bonds. The first member of the series is C3H4 (propadiene or allene). The suffix appears in the name - DIEN .

Types of double bonds in dienes:

1.Insulateddouble bonds separated in chain by two or more σ-bonds: CH2=CH–CH2–CH=CH2. Dienes of this type exhibit properties characteristic of alkenes.

2. Cumulativedouble bonds located on one carbon atom: CH2=C=CH2(allen) Such dienes (allenes) belong to a rather rare and unstable type of compounds.

3.Paireddouble bonds separated by one σ-bond: CH2=CH–CH=CH2 Conjugated dienes have characteristic properties due to electronic structure molecules, namely, a continuous sequence of four sp2 carbon atoms.

Diene isomerism

1. Isomerism double bond positions:

2. Isomerism carbon skeleton:

3. Interclass isomerism with alkynes and cycloalkenes . For example, the following compounds correspond to the formula C4H6:

4. Spatial isomerism Dienes having various substituents at carbon atoms at double bonds, like alkenes, exhibit cis-trans isomerism. (1) Cis isomer (2) Trans isomer

Electronic structure of conjugated dienes.

Molecule of butadiene-1,3 CH2=CH-CH=CH2 contains four carbon atoms sp2 - hybridized state and has a flat structure.

π-electrons of double bonds form a single π-electron cloud (adjoint system ) and are delocalized between all carbon atoms.

The multiplicity of bonds (the number of common electron pairs) between carbon atoms has an intermediate value: there are no purely single and purely double bonds. The structure of butadiene is more accurately reflected by the formula with delocalized "one and a half" bonds.

CHEMICAL PROPERTIES OF CONJUGATED ALKADIENES.

REACTIONS OF ADDITION TO CONJUGATED DIENES. The addition of halogens, hydrogen halides, water and other polar reagents occurs by an electrophilic mechanism (as in alkenes). In addition to addition at one of the two double bonds (1,2-addition), conjugated dienes are characterized by the so-called 1,4-addition, when the entire delocalized system of two double bonds participates in the reaction: The ratio of 1,2- and 1,4-addition products depends on the reaction conditions (with an increase in temperature, the probability of 1,4-addition usually increases).

1. Hydrogenation. CH3-CH2-CH=CH2 (1,2 product) CH2=CH-CH=CH2 + H2 CH3-CH=CH-CH3 (1,4 product) In the presence of a Ni catalyst, a complete hydrogenation product is obtained: CH2=CH-CH=CH2 + 2 H2 –(Ni, t)à CH3-CH2-CH2-CH3

2. Halogenation, hydrohalogenation and hydration 1,4-attachment. 1,2-attachment. With an excess of bromine, one more of its molecule is added at the site of the remaining double bond to form 1,2,3,4-tetrabromobutane.

3. polymerization reaction. The reaction proceeds predominantly by the 1,4-mechanism, with the formation of a polymer with multiple bonds, called rubber : nCH2=CH-CH=CH2 à (-CH2-CH=CH-CH2-)n polymerization of isoprene: nCH2=C–CH=CH2 à(–CH2 –C =CH –CH2 –)n CH3 CH3 (polyisoprene)

OXIDATION REACTIONS - soft, hard, as well as burning. They proceed in the same way as in the case of alkenes - mild oxidation leads to polyhydric alcohol, and hard oxidation - to a mixture of various products, depending on the structure of the diene: CH2=CH –CH=CH2 + KMnO4 + H2O à CH2 – CH – CH – CH2 + MnO2 + KOH

Alkadienes are burning to carbon dioxide and water. C4H6 + 5.5O2 à 4CO2 + 3H2O

OBTAINING ALKADIENES.

1. catalytic dehydrogenation alkanes (through the stage of formation of alkenes). In this way, divinyl is obtained in industry from butane contained in oil refining gases and associated gases: Isoprene is obtained by catalytic dehydrogenation of isopentane (2-methylbutane):

2. Lebedev's synthesis: (catalyst - a mixture of oxides Al2O3, MgO, ZnO 2 C2H5OH –(Al2O3,MgO, ZnO, 450˚C)à CH2=CH-CH=CH2 + 2H2O + H2

3. Dehydration of dihydric alcohols:

4. Action of an alcoholic solution of alkali on dihaloalkanes (dehydrohalogenation):

In tasks of category C3 USE, oxidation reactions cause particular difficulties organic matter potassium permanganate KMnO 4 in an acidic environment, proceeding with a break in the carbon chain. For example, the propene oxidation reaction proceeding according to the equation:

CH 3 – CH = CH 2 + KMnO4 + H 2 SO 4 → CH 3 COOH + CO 2 + MnSO 4 + K 2 SO 4 + H 2 Oh

To factor in complex redox equations like this one, the standard technique suggests 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 oxidizer, taken from the electronic balance, must be replaced. This article offers two ways that allow you to choose the right factor in front of the oxidizer, in order to finally equalize all the elements. Substitution method to replace the coefficient in front of the oxidizing agent, it is more suitable for those who are able to count for a long time and painstakingly, since the arrangement of the coefficients in this way can be lengthy (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 you to replace the coefficient in front of the oxidizing agent no less simply and reliably, but much faster KMnO 4 compared to the substitution method, but has a narrower scope. The "algebraic" method can only be used to replace the coefficient in front of the oxidizer KMnO 4 in the equations of oxidation reactions of organic substances proceeding with a break in the carbon chain.

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Arrangement of coefficients in chemical equations

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

The tendency of organic compounds to oxidize increases with the growth of their nucleophilicity, which corresponds to the following rows:

The growth of nucleophilicity in the series

Consider redox reactions representatives of the most important classes organic matter with some inorganic oxidizing agents.

Alkene oxidation

With mild oxidation, alkenes are converted to glycols (dihydric alcohols). The reducing atoms in these reactions are carbon atoms linked by a double bond.

The reaction with a solution of potassium permanganate proceeds in a neutral or slightly alkaline medium as follows:

3C 2 H 4 + 2KMnO 4 + 4H 2 O → 3CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH

Under more severe conditions, oxidation leads to the breaking of the carbon chain at the double bond and the formation of two acids (in a strongly alkaline medium, two salts) or an acid and carbon dioxide (in a strongly alkaline medium, a salt and a carbonate):

1) 5CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5C 2 H 5 COOH + 8MnSO 4 + 4K 2 SO 4 + 17H 2 O

2) 5CH 3 CH=CH 2 + 10KMnO 4 + 15H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 10MnSO 4 + 5K 2 SO 4 + 20H 2 O

3) CH 3 CH=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 dichromate in a sulfuric acid medium oxidizes alkenes similarly to reactions 1 and 2.

During the oxidation of alkenes, in which carbon atoms in the double bond contain two carbon radicals, two ketones are formed:

Alkyne oxidation

Alkynes oxidize under slightly more severe conditions than alkenes, so they usually oxidize with the triple bond breaking the carbon chain. As in the case of alkenes, the reducing atoms here are carbon atoms linked by a multiple bond. As a result of the reactions, acids and carbon dioxide are formed. Oxidation can be carried out with 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 with potassium permanganate in a neutral medium to potassium oxalate:

3CH≡CH +8KMnO 4 → 3KOOC –COOK +8MnO 2 +2KOH +2H 2 O

In an acidic environment, oxidation goes to oxalic acid or carbon dioxide:

5CH≡CH + 8KMnO 4 + 12H 2 SO 4 → 5HOOC -COOH + 8MnSO 4 + 4K 2 SO 4 + 12H 2 O
CH≡CH + 2KMnO 4 + 3H 2 SO 4 → 2CO 2 + 2MnSO 4 + 4H 2 O + K 2 SO 4

Oxidation of benzene homologues

Benzene does not oxidize even under fairly harsh conditions. Benzene homologues can be oxidized with a solution of potassium permanganate 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

Oxidation of benzene homologues with dichromate or potassium permanganate in an acid 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 COOH + 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

Alcohol oxidation

The direct products of the oxidation of primary alcohols are aldehydes, while those of secondary alcohols are ketones.

The aldehydes formed during the oxidation of alcohols are easily oxidized to acids; therefore, aldehydes from primary alcohols are obtained by oxidation with potassium dichromate in an acid medium at the boiling point of the aldehyde. Evaporating, 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 oxidizer (KMnO 4 , K 2 Cr 2 O 7) in any environment primary alcohols oxidized to carboxylic acids or their salts, and secondary ones 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 are not oxidized under these conditions, but methyl alcohol is oxidized to carbon dioxide.

Dihydric 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, is easily oxidized to oxalic 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 + 22H 2 O

3CH 2 (OH) - CH 2 (OH) + 8KMnO 4 → 3KOOC -COOK + 8MnO 2 + 2KOH + 8H 2 O

Oxidation of aldehydes and ketones

Aldehydes are rather 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 take place 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 an ammonia solution of silver oxide, aldehydes are oxidized to carboxylic acids, which give ammonium salts in an ammonia solution (“silver mirror” reaction):

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

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

5HCOH + 4KMnO 4 (hut) + 6H 2 SO 4 → 4MnSO 4 + 2K 2 SO 4 + 5CO 2 + 11H 2 O

3CH 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 under severe conditions by strong oxidizing agents with a gap C-C connections and give mixtures of acids:

carboxylic acids. Among the strong acids restorative properties possess formic and oxalic, which are oxidized to carbon dioxide.

HCOOH + HgCl 2 \u003d CO 2 + Hg + 2HCl

HCOOH + Cl 2 \u003d CO 2 + 2HCl

HOOC-COOH + Cl 2 \u003d 2CO 2 + 2HCl

Formic acid, Besides acid properties, also exhibits some properties of aldehydes, in particular, reducing. It is then oxidized to carbon dioxide. For example:

2KMnO4 + 5HCOOH + 3H2SO4 → K2SO4 + 2MnSO4 + 5CO2 + 8H2O

When heated with strong dehydrating agents (H2SO4 (conc.) or P4O10) it decomposes:

HCOOH →(t)CO + H2O

Catalytic oxidation of alkanes:

Catalytic oxidation of alkenes:

Phenol oxidation:

4.5.b. Oxidative cleavage of alkenes

During the oxidation of alkenes with an alkaline aqueous solution of potassium permanganate when heated or with a solution of KMnO 4 in aqueous sulfuric acid, as well as during the oxidation of alkenes with a solution of chromium (VI) oxide CrO 3 in acetic acid or potassium dichromate and sulfuric acid, the initially formed glycol undergoes oxidative degradation. The end result is the cleavage of the carbon skeleton at the site of the double bond and the formation of ketones and/or carboxylic acids as end products, depending on the substituents on the double bond. If both carbon atoms at the double bond contain only one alkyl group, the final product of exhaustive oxidation will be a mixture of carboxylic acids, the tetrasubstituted alkene at the double bond is oxidized to two ketones. Single-substituted alkenes with a terminal double bond are cleaved to carboxylic acid and carbon dioxide.

Due to the low yields of carboxylic acids and ketones, the reactions of exhaustive oxidation of alkenes in the classical version have not found wide application and were previously used mainly to determine the structure of the initial alkene from the products of destructive oxidation. Currently, the oxidation of alkenes (R-CH=CH-R and R-CH=CH 2) to carboxylic acids (RCOOH) using potassium permanganate or dichromate is carried out under conditions of phase transfer catalysis. The yields of carboxylic acids in this case exceed 90%.

4.5.c. Ozonolysis of alkenes

The reaction of alkenes with ozone is the most important method for the oxidative cleavage of alkenes at the double bond. For many decades, this reaction served as the main method for determining the structure of the initial hydrocarbon, and also found application in the synthesis of various carbonyl compounds. The reaction of alkene with ozone is carried out by passing a current of ~5% mixture of ozone and oxygen into a solution of alkene in methylene chloride or ethyl acetate at -80 0 -100 0 C. The end of the reaction is controlled by a test for free ozone with potassium iodide. The mechanism of this peculiar and complex reaction has been established mainly thanks to the work of R. Krige. The first product of the 1,3-dipolar cycloaddition to the double bond is the so-called molozonide (1,2,3-trioxolane). This adduct is unstable and then spontaneously decomposes with ring opening and formation as final product normal ozonide (1,2,4-trioxolane).

It is now generally accepted that the transformation of molozonide into ordinary ozonide occurs by the splitting-recombination mechanism. Mollozonide undergoes spontaneous opening of the unstable 1,2,3-trioxolane ring with the formation of a carbonyl compound and a bipolar ion, which then react with each other also according to the 1,3-dipolar cycloaddition scheme.

The above scheme of the rearrangement of molozonide into normal ozonide is confirmed by the fact that if another carbonyl compound is present as an "interceptor" of the bipolar ion in the reaction mixture before the complete formation of the ozonide, then the so-called "mixed ozonide" is formed. For example, in ozonization cis-stilbene in the presence of benzaldehyde labeled with the 18 O isotope, the label is part of the ether, and not the peroxide bridge of the ozonide:

This result is in good agreement with the formation of a mixed ozonide upon recombination of a bipolar ion with labeled benzaldehyde:

Ozonides are highly unstable compounds that decompose explosively. They are not isolated individually, but split under the action of a wide variety of regents. It is necessary to distinguish between reductive and oxidative cleavage. During hydrolysis, ozonides are slowly split into carbonyl compounds and hydrogen peroxide. Hydrogen peroxide oxidizes aldehydes to carboxylic acids. This is the so-called oxidative decomposition of ozonides:

Thus, during the oxidative decomposition of ozonides, carboxylic acids and (or) ketones are formed, depending on the structure of the initial alkene. Air oxygen, hydrogen peroxide, peracids or silver hydroxide can be used as oxidizing agents. Most often in synthetic practice, hydrogen peroxide in acetic or formic acid, as well as hydrogen peroxide in an alkaline medium, is used for this purpose.

In practice, the method of oxidative decomposition of ozonides is mainly used to obtain carboxylic acids.

More important is the reductive cleavage of ozonides. The most commonly used reducing agents are zinc and acetic acid, triphenylphosphine, or dimethyl sulfide. In this case, the end products of ozonolysis are aldehydes or ketones, depending on the structure of the starting alkene.

It can be seen from the above examples that an alkene tetrasubstituted at a double bond forms two ketones during ozonolysis and subsequent reductive decomposition of the ozonide, while a trisubstituted alkene gives a ketone and an aldehyde. A disubstituted symmetrical alkene forms two aldehydes during ozonolysis, and alkenes with a terminal bond form an aldehyde and formaldehyde.

An interesting modification of ozonolysis is the method where sodium borohydride is used as the ozonide reducing agent. In this case, the final reaction products are primary or secondary alcohols formed during the reduction of aldehydes and xtones, respectively.

Ozonolysis of alkenes is a complex, time-consuming and explosive process that requires the use of special equipment. For this reason, other methods have been developed for the oxidative cleavage of alkenes to carbonyl compounds and carboxylic acids, which successfully replace the ozonolysis reaction in synthetic practice.

One of the modern preparative methods for the oxidative destruction of alkenes was proposed in 1955 by R. Lemieux. This method is based on the hydroxylation of alkenes with potassium permanganate, followed by cleavage of vicinal glycol with sodium periodate NaIO 4 at pH ~ 7 8. Periodate itself does not interact with alkene. The products of this two-step oxidative cleavage are ketones or carboxylic acids, since aldehydes are also oxidized to carboxylic acids under these conditions. In the Lemieux method, the laborious problem of separating one of the reaction products, manganese dioxide, does not arise, since both dioxide and manganate are again oxidized with periodate to a permanganate ion. This allows only catalytic amounts of potassium permanganate to be used. Below are some typical examples of the oxidative cleavage of alkenes by the Lemieux method.

Citronellol, an alcohol that is part of rose oil, geranium and lemon oils, is oxidized with a mixture of potassium permanganate and sodium periodate in aqueous acetone at 5–10 0 C to 6-hydroxy-4-methylhexanecarboxylic acid with a quantitative yield.

Another variation of this method uses catalytic amounts of osmium tetroxide instead of potassium permanganate (Lemieux & Johnson 1956). A particular advantage of the combination of OsO 4 and NaIO 4 is that it allows the oxidation to be stopped at the aldehyde stage. Osmium tetroxide adds to the double bond of the alkene to form osmate, which is oxidized by sodium periodate to carbonyl compounds with the regeneration of osmium tetroxide.

Instead of osmium tetroxide, ruthenium tetroxide RuO 4 can also be used. Lemieux-Johnson oxidative degradation of alkenes leads to the same products as ozonolysis with reductive cleavage of ozonides.

In terms characteristic of modern organic chemistry, this means that the combination of OsO 4 -NaIO 4 is synthetic equivalent ozonolysis of alkenes followed by reductive cleavage. Similarly, the oxidation of alkenes with a mixture of permanganate and periodate is the synthetic equivalent of ozonolysis with oxidative degradation of ozonides.

Thus, the oxidation of alkenes is not only a set of preparative methods for obtaining alcohols, epoxides, diols, aldehydes, ketones, and carboxylic acids; it is also one of the possible ways to establish the structure of the starting alkene. So, according to the result of the oxidative degradation of the alkene, one can determine the position of the double bond in the molecule, while the stereochemical result syn- or anti- hydroxylation of an alkene makes it possible to draw a conclusion about its geometry.