The meaning of Favorsky reaction in the Great Soviet Encyclopedia, BSE. The meaning of the Favorsky reaction in the Great Soviet Encyclopedia, BSE Favorsky method from acetylene and acetone

In 1925 Reppe developed industrial method addition of acetylene to formaldehyde based on the Favorsky reaction. At high pressure, about 100 atm, in the presence of copper acetylide, acetylene joins formaldehyde to form two important products - propargyl alcohol and butine-2-diol-1,4:

HC?CH + CH2O > HC?C-CH2OH

HC?C-CH2OH + CH2O > HOCH2C?C-CH2OH

Fischer-Tropsch process

A chemical reaction occurring in the presence of a catalyst in which carbon monoxide (CO) and hydrogen (H2) are converted into various liquid hydrocarbons. Typically catalysts containing iron and cobalt are used. The principal importance of this process is the production of synthetic hydrocarbons for use as synthetic lubricating oil or synthetic fuel.

The Fischer-Tropsch process is described by the following chemical equation

CO + 2 H2 > ?CH2? + H2O

2 CO + H2 > ?CH2? + CO2.

The mixture of carbon monoxide and hydrogen is called synthesis gas or syngas. The resulting hydrocarbons are purified to obtain the target product - synthetic oil.

Carbon dioxide and carbon monoxide are formed by the partial oxidation of coal and wood fuels. The benefit of this process lies primarily in its role in the production of liquid hydrocarbons or hydrogen from solid raw materials such as coal or solid carbon-containing wastes of various types. Non-oxidative pyrolysis of solid feedstock produces syngas that can be directly used as fuel without Fischer-Tropsch conversion. If a liquid petroleum-like fuel, lubricant or paraffin is required, the Fischer-Tropsch process can be used. Finally, if more hydrogen production is desired, water vapor shifts the equilibrium of the reaction so that only carbon dioxide and hydrogen are produced. Fortunately, it is quite easy to make the transition from gas to liquid fuel.

The synthesis of FT can be considered as a reductive oligomerization of carbon monoxide:

nCO + (2n+1)H2 > CnH2n+2 + nH2О

nCO + 2nH2 > CnH2n + nH2O

The thermal effect is significant, 165 kJ/mol CO.

Group VIII metals serve as catalysts: Ru is the most active, then Co, Fe, Ni. To increase the surface, they are often applied to porous supports, such as silica gel and alumina. Only Fe and Co have found application in industry. Ruthenium is too expensive, and its reserves on Earth are too small to be used as a catalyst in large-scale processes. On nickel catalysts at atmospheric pressure, mainly methane is formed (n=1), but with increasing pressure, nickel forms volatile carbonyl and is washed out of the reactor.

Side reactions of the synthesis of hydrocarbons from CO and H2 are:

hydrogenation of carbon monoxide to methane: CO + 3H2 > CH4 + H2O + 214 kJ/mol

Bell-Boudoir reaction (disproportionation of CO): 2CO > CO2 + C

equilibrium of water gas: CO + H2O - CO2 + H2

The last reaction is of particular importance for iron-based catalysts; it hardly occurs on cobalt. On iron catalysts, in addition, oxygen-containing compounds - alcohols and carboxylic acids - are formed in significant quantities.

Typical process conditions are: pressure from 1 atm (for Co catalysts) to 30 atm, temperature 190--240 °C (low temperature option, for Co and Fe catalysts) or 320--350 °C (high temperature option, for Fe) .

The mechanism of the reaction, despite decades of study, remains unclear in detail. However, this situation is typical for heterogeneous catalysis.

Thermodynamic laws for FT synthesis products are as follows:

It is possible to form hydrocarbons of any molecular weight, type and structure except acetylene from CO and H2.

The probability of hydrocarbon formation decreases in the order: methane > other alkanes > alkenes. The probability of forming normal alkanes decreases and normal alkenes increases with increasing chain length.

An increase in the total pressure in the system promotes the formation of heavier products, and an increase in the partial pressure of hydrogen in the synthesis gas favors the formation of alkanes.

The actual composition of the products of hydrocarbon synthesis from CO and H2 differs significantly from the equilibrium one. In most cases, the distribution of products by molecular weight under stationary conditions is described by the formula p(n) = n(1-b)Ibn-1, where p(n) is the mass fraction of hydrocarbon with carbon number n, b = k1/(k1+ k2), k1, k2 are the rate constants for chain growth and termination, respectively. This is the so-called Anderson - Schultz - Flory distribution (ASF distribution). Methane (n=1) is always present in greater quantities than predicted by the ASF distribution, since it is formed independently by direct hydrogenation reaction. The value of b decreases with increasing temperature and, as a rule, increases with increasing pressure. If the reaction produces products of different homologous series (paraffins, olefins, alcohols), then the distribution for each of them may have its own value b. The distribution of ASF imposes restrictions on the maximum selectivity for any hydrocarbon or narrow fraction. This is the second, after heat removal, problem of FT synthesis.

The use of carbanions for the formation of the carbon skeleton. Acetylenide anion (Favorsky and Reppe syntheses), cyanide anion (cyanohydrin synthesis and Strecker-Zelinsky reaction), enolate anion. Factors contributing to the stabilization of carbanions. Methods for generating carbanions.

Favorsky's reaction

1. Acetylene-allen rearrangement.

The rearrangement of alkynes into allenes and the migration of double bonds in the carbon chain catalyzed by strong bases was discovered by A.E. Favorsky in 1888. He prepared butine-1 by dehydrohalogenating 2,2-dichlorobutane under the influence of an alcoholic solution of KOH in an ampoule at 170 °C. Unexpectedly, instead of butine-1, butine-2 was obtained.

CH3-CH2-C≡CH ↔ ↔ CH3-C≡C-CH3

2. Addition of carbonyl compounds to alkynes.

In the presence strong reasons alkynes with a terminal triple bond are capable of adding carbonyl compounds to form alcohols:

CH3-C≡CH + CH3-CO-CH3 → CH3-C≡C-C(OH)(CH3)2

3. condensation of alkynes with alcohols.

The reaction of nucleophilic addition of alcohols to alkynes in the presence of alkalis with the formation of alkenyl ethers:

CH3-C≡CH + CH3CH2OH → CH3-C(OC2H5)=CH2

Favorsky-Reppe reaction In 1925, Reppe developed an industrial method for adding acetylene to formaldehyde based on the Favorsky reaction. At high pressure, about 100 atm, in the presence of copper acetylide, acetylene joins formaldehyde to form two important products - propargyl alcohol and butine-2-diol-1,4:

HC≡CH + CH2O → HC≡C-CH2OH

HC≡C-CH2OH + CH2O → HOCH2C≡C-CH2OH

Cyanohydrin synthesis, those. addition of hydrocyanic acid to aldoses, followed by hydrolysis of the nitrile group and reduction of the carboxyl group to the aldehyde group. The result of this reaction is the lengthening of the aldose carbon chain by one unit and the emergence of a new asymmetric center, as a result of which not one, but two new monosaccharides are obtained from each monosaccharide - stereoisomers at C-2. IN general view this sequence is shown in the diagram:

ORGANOLITHIUM COMPOUNDS, contain in the molecule a lithium atom directly bonded to a carbon atom. They are used as polymerization catalysts (butyllithium C4H9Li, etc.) in the production of butadiene and isoprene rubbers, in organic synthesis.

With formaldehyde RLi they give (after hydrolysis of the solution product) primary alcohols, with other aldehydes - secondary alcohols, with ketones and esters - tertiary alcohols:

CH2O + RLi: RCH2OH;

R"COX + RLi: RR"XCOH;

X = H, R:, OR": Compared to Grignard reagents, organolithium compounds have an advantage in the synthesis of sterically hindered alcohols. With nitriles R"CN and imines R2C=NR: organolithium compounds form (after hydrolysis of the product solution) respectively. RCOR" ketones and amines, e.g.:

RLi + R"2C=NR: : R"2CRNHR:

Organolithium compounds add via C=C bonds. Reaction occurs easily for conjugated multiple bonds, with 1,2-, 3,4- and 1,4-addition possible (see diagram). Butyllithium adds to isoprene stereospecifically in a 1,4-type. In the case of isolated multiple bonds, special connections are required. conditions (chelating agents, pressure).

Scope of rect.Green. 1Fig. Reactions with carbonyl compounds; 2fig. Reactions with other electrophiles.

STRECKER REACTIONS, 1) obtaining a-amino acids from aldehydes or ketones by the action of NH3 and HCN followed by hydrolysis of the resulting aminonitriles (the so-called Strecker synthesis):

ZELINSKY-STADNIKOV REACTION, synthesis of a-amino acids by action on aliphatic, alicyclic. or aromatic carbonyl compounds mixtures of KCN and NH4Cl with the following. acid hydrolysis of the resulting a-aminonitrile:

The process is carried out in an aqueous or aqueous-alcoholic medium at 0-20 ° C (in the case of low-reactive carbonyl compounds - at 50-60 ° C) for 3-5 hours. a-Aminonitriles are hydrolyzed, for example, 10-20% - aqueous solution of HCl. The output of the solution is 60-90%. When replacing NH4Cl with primary amine hydrochlorides, N-substituted a-amino acids are formed. It is assumed that the r-tion mechanism includes a trace. stages: (see picture)

It is possible that instead of the first two stages, interaction occurs. KCN and NH4Cl with the formation of unstable NH4CN, which decomposes into HCN and NH3.

FAVORSKY REACTION

reaction, synthesis of tertiary acetylene alcohols by condensation of acetylene hydrocarbons with ketones in the presence of anhydrous powdered potassium hydroxide. For example, acetylene reacts with acetone to form dimethylethynylcarbinol:

HCºCH + CH3COCH3-(CH3)2C (OH) C-CH.

The reaction is carried out in ether, benzene and other organic solvents with cooling and stirring. Of great practical importance, for example, is dimethylvinylethynylcarbinol synthesized from vinyl acetylene and acetone:

(CH3)2C (OH) СºС-СНН2,

copolymerization of which with methyl and (or) butyl methacrylate produces carbinol resins used in the production of varnishes and adhesives. The reaction was discovered by A.E. Favorsky in 1900.

Great Soviet Encyclopedia, TSB. 2012

Reaction mechanism

The reaction proceeds by the mechanism of nucleophilic addition to the carbonyl group of the resulting in situ upon deprotonation of the terminal alkyne acetylenide anion:

R 1 R 2 C=O + - C≡С-R R 1 R 2 C(O -)-C≡С-R R = H, Alk, Ar, OEt

The reaction is usually carried out in a suspension of potassium hydroxide or sodium amide in an aprotic solvent (ether, benzene, dimethylformamide, etc.) at temperatures from -70 to +40 °C, when using low-boiling compounds or acetylene - under a pressure of 0.4-0 .9 MPa. In some modifications, instead of acetylene, calcium carbide (acetylenide) is used in the presence of potassium hydroxide.

Yields are 40-60%.

Ketones and some aldehydes react; both substituted terminal alkynes (including heterosubstituted ones - for example, ethoxyacetylene) and acetylene are used as the alkyne component. In the latter case, due to the deprotonation of the resulting 1,1-substituted propargyl alcohols and their interaction with the carbonyl compound, bis-adducts - acetylene 1,4-diols - can also be formed:

R 1 R 2 C=O + - C≡СH R 1 R 2 C(O -)-C≡СH R 1 R 2 C(O -)-C≡СH + B - R 1 R 2 C(O -) -C≡С - + BH R 1 R 2 C(O -)-C≡С - + R 1 R 2 C=O R 1 R 2 C(O -)-C≡С(O -)R 1 R 2

In the case of aliphatic aldehydes, the reaction is complicated by aldol condensation under the influence of bases, however, the use of potassium hydroxide hexamethylphosphortriamide as a co-solvent makes it possible to synthesize 1-monosubstituted propargylic alcohols in yields of up to 70%.

Another modification of the Favorsky reaction, which allows for the enantioselective addition of alkynes to aldehydes, is the use of zinc triflate as a catalyst in the presence of (+)-N-methylephedrine and trimethylamine in wet toluene, yields in this case reach 96% with an enantioselectivity of 89-99%

The Favorsky reaction is reversible; under basic conditions, substituted propargyl alcohols can split into a terminal alkyne and a carbonyl compound ( Favorsky retroreaction) .

Synthetic application

Tertiary and secondary acetylene alcohols obtained in the Favorsky reaction are rearranged under acid catalysis into α,β-unsaturated ketones and aldehydes (Meyer-Schuster rearrangement):

The Favorsky retroreaction is used in the synthesis of alkynes, in particular, when introducing an acetylene group into the Sonogashira reaction, when commercially available 1,1-dimethylpropargyl alcohol is used as the alkyne component, after which acetone is cleaved from the resulting 3-substituted dimethylpropargyl alcohol to form the target alkyne:

R-X + HC≡С-C(CH 3) 2 OH R-C≡С-C(CH 3) 2 OH R-C≡С-C(CH 3) 2 OH R-C≡СH + (CH 3) 2 C=O

Industrial Application

The Favorsky reaction underlies one of the methods used in industry for the synthesis of isoprene, a raw material for the production of synthetic rubbers. The method for synthesizing isoprene from acetylene and acetone was proposed by Favorsky himself. In this method, acetylene is condensed with acetone to form 1,1-dimethylpropargyl alcohol, followed by hydrogenation to dimethylvinylcarbinol, which is further dehydrated to isoprene:

(CH 3) 2 C=O + HC≡СH HC≡С-C(CH 3) 2 OH HC≡С-C(CH 3) 2 OH + [H] H 2 C=СH-C(CH 3) 2 OH H 2 C=CH-C(CH 3) 2 OH HC=C(CH 3)-CH=CH 2

The industry uses the Snamprogetti/Enichem process, in which the condensation of acetone and acetylene is carried out in liquid ammonia at 10-40°C under a pressure of 20-25 atm with potassium hydroxide as a catalyst.

The meaning of Favorsky reaction in the Great Soviet Encyclopedia, BSE. The meaning of the Favorsky reaction in the Great Soviet Encyclopedia, BSE Favorsky method from acetylene and acetone

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Reaction mechanism

Synthetic application

Industrial Application

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