Electrophilic substitution reactions- substitution reactions in which the attack is carried out electrophile- a particle that is positively charged or has a deficit of electrons. When a new bond is formed, the outgoing particle - electrofuge split off without its electron pair. The most popular leaving group is the proton H+.
All electrophiles are Lewis acids.
General view of electrophilic substitution reactions:
(cationic electrophile)
(neutral electrophile)
There are reactions of aromatic (widespread) and aliphatic (not common) electrophilic substitution. The specificity of electrophilic substitution reactions specifically for aromatic systems is explained by the high electron density of the aromatic ring, which is capable of attracting positively charged particles.
For aromatic systems, there is actually one mechanism of electrophilic substitution - S E Ar. Mechanism S E 1(by analogy with the mechanism S N 1) is extremely rare, and S E 2(corresponding by analogy S N 2) does not occur at all.
S E Ar reactions
reaction mechanism S E Ar or aromatic electrophilic substitution reactions is the most common and most important among the substitution reactions of aromatic compounds and consists of two stages. At the first stage, the electrophile is attached, at the second stage, the electrofuge is split off:
During the reaction, an intermediate positively charged intermediate is formed (in the figure - 2b). It bears the name Weland intermediate, aronium ion or σ-complex. This complex is usually very reactive and is easily stabilized by rapidly eliminating the cation.
The rate-limiting step in the vast majority of reactions S E Ar is the first stage.
Relatively weak electrophiles usually act as an attacking particle, so in most cases the reaction S E Ar proceeds under the action of a Lewis acid catalyst. More often than others, AlCl 3, FeCl 3, FeBr 3, ZnCl 2 are used.
DECARBOXYLATION, elimination of CO 2 from the carboxyl group of carboxylic acids or the carboxylate group of their salts. It is usually carried out by heating in the presence of acids or bases. Aromatic acids are decarboxylated, as a rule, under harsh conditions, for example, when heated in quinoline in the presence of a metal. powders. By this method, in the presence of Cu, furan is obtained from pyromucic acid. DECARBOXYLATION of aromatic acids is facilitated in the presence of electrophilic substituents, for example, trinitrobenzoic acid is decarboxylated when heated to 40-45 °C. D. vapors of carboxylic acids over heated catalysts (Ca and Ba carbonates, Al 2 O 3, etc.) is one of the methods for the synthesis of ketones:
2RCOOH: RCOR + H 2 O + CO 2 .
DECARBOXYLATION of sodium salts of carboxylic acids during the electrolysis of their conc. aqueous solutions is an important method for obtaining alkanes. Halogen decarboxylation - substitution of a carboxyl group in a molecule for a halogen, proceeds under the action of LiCl and tetraacetate Pb on carboxylic acids, as well as free halogens (Cl 2, Br 2, I 2) on salts of carboxylic acids, for example:
RCOOM RHal (M = Ag, K, Hg, T1).
Silver salts of dicarboxylic acids under the action of I 2 are easily converted into lactones: 
An important role is also played by oxidative decarboxylation - the elimination of CO 2 from carboxylic acids, accompanied by oxidation. Depending on the oxidizing agent used, this DECARBOXYLATION results in alkenes, esters, and other products. So, during the decarboxylation of phenylacetic acid in the presence of pyridine-N-oxide, benzaldehyde is formed: 
Like DECARBOXYLATION of salts of carboxylic acids, DECARBOXYLATION of organoelement derivatives and esters occurs, for example: 
The reactions of decarboxylation of carboxylic acids are an energetically favorable process, since as a result, a stable CO 2 molecule is formed. Decarboxylation is characteristic of acids that have an electron-withdrawing substituent in the ά-position. Dibasic acids are the easiest to decarboxylate.
Oxalic and malonic acids are easily decarboxylated when heated, and when succinic and glutaric acids are heated, cyclic anhydrides are formed, which is due to the formation of five- or six-membered heterocycles having stable “half-chair” and “chair” conformations
In biological systems, decarboxylation reactions proceed with the participation of enzymes - decarboxylases. Decarboxylation of amino acids leads to the formation of biogenic amines.
Decarboxylation of amino acids leads to the formation of biogenic amines.
In saturated aliphatic acids, as a result of the EA influence of the carboxyl group, a CH-acid center appears at the α-carbon atom. This is well manifested in halogenation reactions.
Halogenated acids are widely used for the synthesis of biologically important compounds - hydroxy- and amino acids.
Decarboxylation
The decarboxylation reaction of carboxylic acids consists in the elimination of a carboxyl group from a carboxylic acid molecule, proceeding according to the following general scheme:
R-C(O)OH --> R-H + CO 2
The most well-known reactions are the decarboxylation of acetic and benzoic acids, which are carried out by heating a mixture of a salt of a carboxylic acid and an alkali to a high temperature:
H 3 C-C (O) ONa + NaOH --> CH 4 + Na 2 CO 3
Ph-C(O)ONa + NaOH --> PhH + Na 2 CO 3
A number of acids decarboxylate very easily with slight heating, in general, the presence of electroacceptor substituents in the organic radical of the carboxylic acid facilitates the decarboxylation reaction, for example, nitromethane and trinitrobenzene are obtained from nitroacetic and trinitrobenzoic acids, respectively:
O 2 N-CH 2 -C (O) OH --> O 2 N-CH 3 + CO 2
2,4,6-(NO 2) 3 C 6 H 2 -C(O)OH ---> 1,3,5-(NO 2) 3 C 6 H 3 + CO 2.
Decarboxylation at relatively low temperatures is a feature of aromatic carboxylic acids, in the aromatic ring of which hydroxyl groups are in the ortho- or para-position, for example, gallic acid easily turns into trihydric phenol - pyrogallol with slight heating.
Acetoacetic and malonic acids are very easily decarboxylated:
H 3 C-C(O)-CH 2 -C(O)OH --> H 3 C-C(O)-CH 3 + CO 2
HO-C(O)-CH 2 -C(O)OH --> H 3 С-C(O)OH + CO 2
The latter reaction is the basis of convenient preparative synthesis methods, called "Synthesis based on malonic and acetoacetic esters".
Decarboxylation of dicarboxylic acids is used to obtain cyclic ketones, for example, heating adipic acid with a small amount of barium oxide allows cyclopentanone to be obtained in good yield:
HO-C (O) - (CH 2) 4 -C (O) OH --> cyclo-C 4 H 8 C \u003d O + CO 2
The decarboxylation reaction is a key step in reactions such as the Kolbe (electrolysis of salts of carboxylic acids), Simonini, Marquewald, Dakin-West and Borodin-Hunsdiecker reactions.
Oxidative decarboxylation. When heated to 260-300 o With the copper salt of benzoic acid, it decomposes with the formation of phenyl benzoate, carbon dioxide and copper:
2 Cu --> C 6 H 5 -C (O) O-C 6 H 5 + CO 2 + Cu
The reaction proceeds through a cyclic intermediate state. One option for oxidative decarboxylation is the reaction of carboxylic acids with lead tetraacetate (oxidant) in the presence of calcium or lithium chloride (source of chloride anions). The reaction proceeds in boiling benzene and leads to the formation of halogen derivatives of hydrocarbons:
R-C(O)-OH + Pb 4 + 2 LiCl --> R-Cl + Pb 2 + CH 3 C(O)OLi + CH 3 C(O)OH
Decarboxylation reactions are integral and important stages of such biochemical processes as alcoholic fermentation and tricarboxylic acid cycle.
Links
Literature
- K. V. Vatsuro, Mishchenko “Nominal reactions in organic chemistry”, M .: Chemistry, 1976.
- J. J. Lee, Nominal reactions. Mechanisms of organic reactions, M.: Binom., 2006.
Wikimedia Foundation. 2010 .
Synonyms:See what "Decarboxylation" is in other dictionaries:
Cleavage of CO2 from the carboxyl group of carboxylic acids to t. Enzymatic D. can be reversible (for example, D. of oxaloacetate with the formation of pyruvate) and irreversible (for example, oxidative D. of amino acids catalyzed by decarboxylases, coenzyme to ryh ... Biological encyclopedic dictionary
Cleavage of CO2 from the carboxyl group of carboxylic acids is usually with the participation of decarboxylase enzymes. Enzymatic D. can be reversible (D. oxaloacetate to pyruvate) and irreversible (oxidative D. amino acids). Special meaning in the cell ... ... Dictionary of microbiology
- [de ... + lat. carbo charcoal + gr. sour] – cleavage from organic acids of the COOH group; is essential in the process of metabolism and during decay. A large dictionary of foreign words. Publishing house "IDDK", 2007 ... Dictionary of foreign words of the Russian language
Exist., Number of synonyms: 1 split (8) ASIS Synonym Dictionary. V.N. Trishin. 2013 ... Synonym dictionary
The process of splitting off carbon dioxide from the carboxyl group (see Carboxyl) of acids. In the absence of other non-hydrocarbon gr. in the D. molecule leads to the formation of hydrocarbons. Many hypotheses of the origin of oil attach great importance to participation in ... ... Geological Encyclopedia
decarboxylation- The reaction of splitting off the CO2 group from the carboxyl group of carboxylic acids or the carboxylate group of their salts. [Arefiev V.A., Lisovenko L.A. English Russian explanatory dictionary of genetic terms 1995 407s.] Topics genetics EN decarboxylation ... Technical Translator's Handbook
Decarboxylation- * decarboxylation * decarboxylation movement or loss by organic compounds of carboxyl groups, from which CO2 is formed. D. occurs under the action of decarboxylase enzymes that catalyze the roar of 51 positions to deoxyribose instead of ... ... Genetics. encyclopedic Dictionary
Decarboxylation decarboxylation. The reaction of elimination of the CO2 group from the carboxyl group of carboxylic acids or the carboxylate group of their salts. (
DECARBOXYLATION, elimination of CO 2 from the carboxyl group of carboxylic acids or the carboxylate group of their salts. It is usually carried out by heating in the presence of acids or bases. The decarboxylation of saturated monocarboxylic acids proceeds, as a rule, under severe conditions. Thus, the calcination of Na acetate with an excess of soda lime leads to the elimination of CO 2 and the formation of methane: CH 3 COONa + NaOH CH 4 + Na 2 CO 3. DECARBOXYLATION is facilitated for acids containing a -position of electronegative groups. Easy DECARBOXYLATION of acetoacetic (formula I) and nitroacetic acids (II) is due to the occurrence of a cyclic transition state:
Chemical encyclopedia. Volume 2 >>
D. homologues of nitroacetic acid - a preparative method for obtaining nitroalkanes.
Naib. DECARBOXYLATION of acids is easily carried out, the carboxyl group of which is directly connected with other electrophores. groups. For example, heating pyruvic acid with conc. H 2 SO 4 easily leads to acetaldehyde:
During the decarboxylation of oxalic acid under the same conditions, in addition to CO 2, H 2 O and CO are formed.
D. is also facilitated if the carboxyl group is bonded to an unsaturated C atom; so, DECARBOXYLATION of the monopotassium salt of acetylenedicarboxylic acid is a convenient method for the synthesis of propiolic acid:
D. acetylenecarboxylic acid is carried out at room temperature in the presence. Cu salts: HCCCOOH HC=CH + CO 2 . Aromatic acids are decarboxylated, as a rule, under harsh conditions, for example, when heated in quinoline in the presence of a metal. powders. By this method, in the presence of Cu, furan is obtained from pyromucic acid. Decarboxylation of aromatic acids is facilitated in the presence of electrophoresis. substituents, for example, trinitrobenzoic acid is decarboxylated when heated to 40-45 °C.
D. carboxylic acid vapors over heated catalysts (Ca and Ba carbonates, Al 2 O 3, etc.) - one of the methods for the synthesis of ketones: 2RCOOH:
RCOR + H 2 O + CO 2 . When decarboxylation of a mixture of two acids, a mixture of unsymmetrical and symmetrical ketones is formed. DECARBOXYLATION of sodium salts of carboxylic acids during the electrolysis of their conc. aqueous solutions (see Kolbe reactions) is an important method for obtaining alkanes.
DECARBOXYLATION reactions that have preparative significance include halogen decarboxylation - the replacement of a carboxyl group in a molecule by a halogen. The reaction proceeds under the action of LiCl (or N-bromosuccinimide) and tetraacetate Pb on carboxylic acids, as well as free halogens (Cl 2, Br 2, I 2) on
salts of carboxylic acids, for example: RCOOM RHal (M = Ag, K,
Hg, T1). Silver salts of dicarboxylic acids under the action of I 2 are easily converted into lactones:
Oxidize also plays an important role. DECARBOXYLATION - elimination of CO 2 from carboxylic acids, accompanied by oxidation. Depending on the oxidizing agent used, this DECARBOXYLATION results in alkenes, esters, and other products. So, during the decarboxylation of phenylacetic acid in the presence of pyridine-N-oxide, benzaldehyde is formed:
Like DECARBOXYLATION of salts of carboxylic acids, DECARBOXYLATION of organoelement derivatives and esters occurs, for example:
D. esters are also carried out under the action of bases (alcoholates, amines, etc.) in an alcoholic (aqueous) solution or Li and Na chlorides in DMSO.
Of great importance in various metabolic processes is enzymatic DECARBOXYLATION. There are two types of such reactions: simple DECARBOXYLATION (reversible reaction) and oxidative DECARBOXYLATION, in which first DECARBOXYLATION occurs, and then dehydrogenation of the substrate. According to the latter type, in the organism of animals and plants, enzymatic decarboxylation of pyruvic and a -ketoglutaric acids - intermediate products of the breakdown of carbohydrates, fats and proteins (see Tricarboxylic acid cycle). Enzymatic decarboxylation of amino acids is also widespread in bacteria and animals.
Lecture No. 12
carboxylic acids
Plan
1. Methods of obtaining.
2. Chemical properties.
2.1. acid properties.
2.3. Reactions for a -carbon atom.
2.5. Recovery.
2.6. dicarboxylic acids.
Lecture No. 12
carboxylic acids
Plan
1. Methods of obtaining.
2. Chemical properties.
2.1. acid properties.
2.2. Reactions of nucleophilic substitution.
Functional derivatives of carboxylic acids.
2.3. Reactions for a -carbon atom.
2.5. Recovery.
2.6. dicarboxylic acids.
1. Methods of obtaining
2. Chemical
properties
Carboxylic acids contain a carboxyl group which is directly bonded between
is a carbonyl group and a hydroxyl. Their mutual influence causes a new
a set of properties that are different from those of carbonyl compounds and
hydroxyl derivatives. Reactions involving carboxylic acids proceed according to
following main directions.
- Substitution of hydrogen of the COOH group under
action of bases ( acid properties). - Interaction with nucleophilic reagents
at the carbonyl carbon atom ( the formation of functional derivatives and
recovery) - Reactions for a -carbon atom
(halogenation) - Decaboxylation
2.1. Acidic
properties
Carboxylic acids are one of the strongest organic acids. Their water
solutions are acidic.
RCOOH + H 2 O \u003d RCOO - +
H3O+
Causes of high acidity of carboxylic acids and
its dependence on the nature of the substituents in the hydrocarbon radical were
discussed earlier (see Lec. No. 4).
Carboxylic acids form salts when
interaction with active metals and most bases. 
When interacting with strong inorganic
carboxylic acids can exhibit basic properties by adding
proton at the carbonyl oxygen atom. 
Protonation of carboxylic acids is used
to activate the carboxyl group in nucleophilic substitution reactions.
Due to the presence in the molecule at the same time
acid and basic centers, carboxylic acids form intermolecular
hydrogen bonds and exist mainly in the form of dimers (see Lec. No. 2).
2.2. Reactions of nucleophilic substitution.
Functional derivatives of carboxylic acids.
The main type of reactions of carboxylic acids -
interaction with nucleophiles with the formation of functional derivatives.
Interconversions linking carboxylic acids and their functionalities
derivatives are shown in the diagram.
The connections shown in the diagram contain
acyl group during
their interconversions, it passes unchanged from one compound to
another by combining with a nucleophile. Such processes are called acylation,
and carboxylic acids and their functional derivatives - acylating
reagents. In general terms, the acylation process can be represented as
the next diagram. 
So acylation is
the process of nucleophilic substitution at the carbonyl carbon atom.
Consider the reaction mechanism in general terms and
compare it with Ad N -reactions
aldehydes and ketones. As in the case of carbonyl compounds, the reaction begins
from the attack of the nucleophile on the carbonyl carbon atom bearing the effective
positive charge. At the same time it breaks p -bond carbon-oxygen and formed tetrahedral
intermediate. Ways of further transformation of the intermediate in carbonyl and
acyl compounds are different. If carbonyl compounds give a product accession, then the acyl compounds cleave off the X group and give the product substitution.
The reason for the different behavior of acyl and
carbonyl compounds - in different stability of the potential leaving group X.
In the case of aldehydes and ketones, this is the hydride anion H — or carboanion R — , which, due to their high basicity, are
extremely poor leaving groups. In the case of acyl compounds X
a significantly more stable leaving group (Cl — ,
RCOO - , RO - , NH 2 - ), which makes it possible to eliminate it as an anion
X — or conjugate acid
NH.
Reactivity with respect to
nucleophiles in carboxylic acids and their functional derivatives is less than in
aldehydes and ketones, since the effective positive charge on the carbonyl
their carbon atom is lower due to the + M- effect of the X group.
The activity of the acyl group increases under conditions
acid catalysis, since protonation increases the effective
a positive charge on the carbon atom and facilitates its attack
nucleophile. 
Derivatives according to their acylating ability
carboxylic acids are arranged in the next row in accordance with the decrease
+ M-effect of group X.
In this series, the previous terms can be obtained from
subsequent acylation of the corresponding nucleophile. The process of getting more
there are practically no active acylating reagents from less active ones due to
unfavorable equilibrium position due to higher basicity
leaving group compared to the attacking nucleophile. All functional
derivatives can be obtained directly from acids and converted into them
during hydrolysis.
Acid chlorides and anhydrides
Acquisition Methods
Acid chlorides are obtained by interaction
carboxylic acids with phosphorus and sulfur halides.
RCOOH + SOCl 2 ® RCOOCl + SO 2 +
HCl
RCOOH + PCl 5 ® RCOOH + POCl 3 +
HCl
Anhydrides are formed from carboxylic acids
the action of phosphorus (V) oxide.
Mixed anhydrides can be obtained
acylation of salts of carboxylic acids with acid chlorides.
acid chlorides and anhydrides.
X loranhydrides and anhydrides are the most reactive derivatives
carboxylic acids. Their reactions with nucleophiles proceed under mild conditions, without
catalyst and is practically irreversible.
When using mixed anhydrides with
the nucleophile combines the rest of the weaker acid, and the anion of the stronger
acid plays the role of a leaving group. 
IN
mixed anhydrides play an important role in biochemical acylation reactions
carboxylic acids and phosphoric acid - acylphosphates and substituted acylphosphates. WITH
the nucleophile combines the residue of organic acids, and the acyl phosphate anion
plays the role of a good leaving group. 
Esters
Acquisition Methods
RCOO— Na+ + RCl ® RCOOR + NaCl The most important method for obtaining esters is esterification reaction. The reaction proceeds as a nucleophilic substitution in
carboxyl group.
Carboxylic acids are weak acylating
reagents due to the significant +M effect of the OH group. Use of the strong
nucleophiles, which are also strong bases (for example,
basic catalysis), in this case it is impossible, since they transfer carboxylic
acids into even less reactive salts of carboxylic acids. The reaction is carried out
under conditions of acid catalysis. The role of the acid catalyst is, as already
said, in increasing the effective positive charge on the carbon atom
carboxyl group, and, in addition, the protonation of the OH group at the stage
splitting off turns it into a good leaving group - H 2 O. 
All steps of the esterification reaction
reversible. To shift the equilibrium towards the esterification process, use
excess of one of the reactants or removal of products from the reaction sphere.
Nucleophilic substitution reactions in
alkoxycarbonyl group.
Esters are weaker acylating
reagents than anhydrides and acid chlorides. S N -reactions in the alkoxycarbonyl group proceed in more
harsh conditions and require acid or base catalysis. The most important
reactions of this type are hydrolysis, aminolysis and
interesterification
.
Hydrolysis.
Esters are hydrolyzed to form carboxylic acids by the action of
acids or alkalis.
Acid hydrolysis of esters is a reverse esterification reaction. 
The mechanism of acid hydrolysis includes the same steps as
and the esterification process, but in reverse order.
Alkaline hydrolysis of esters requires
equimolar amounts of alkali and proceeds irreversibly.
RCOOR + NaOH ® RCOO - Na + + R OH
The essence of alkaline catalysis is to use
instead of a weak nucleophile - water, a stronger nucleophile -
hydroxide ion. 
Irreversibility of the process
provided by low reactivity towards nucleophiles
hydrolysis product - carboxylate anion.
Interesterification.
In the transesterification reaction, the role of the nucleophile
performs an alcohol molecule. The process is catalyzed by acids or
grounds. 
The reaction mechanism is similar to the hydrolysis of complex
ethers. Interesterification is a reversible process. To shift the balance to the right
it is necessary to use a large excess of the initial alcohol. Reaction
interesterification finds application in the production of fatty acid esters
from triacylglycerides (see lek. 18)
Aminolysis.
Esters acylate ammonia and amines with
formation of amides of carboxylic acids. 
Amides of carboxylic acids
The structure of the amide group
A the mid group is found in many biologically important compounds,
primarily in peptides and proteins (peptide bond). Her electronic and
spatial structure largely determines their biological
functioning.
The amide group is p-p -adjoint system in which
additional overlapping of the p-orbital of the nitrogen atom with p -communication orbital
carbon-oxygen.
Such an electron density distribution
leads to an increase in the energy barrier of rotation around the C-N bond to 60 -
90 kJ/mol. As a result, the amide bond has a planar structure, and the bond lengths
C-N and C \u003d O have values \u200b\u200brespectively less and more than their usual
quantities.
Lack of free rotation around the C-N bond
leads to the existence of amides cis- And trance-isomers. For
most amides is preferred trance-configuration.
The peptide bond also has trance-configuration in which the side radicals of amino acid residues
most distant from each other
Acquisition Methods
Nucleophilic substitution reactions in
carboxamide group.
Amides are the least reactive derivatives of carboxylic acids. For them
hydrolysis reactions are known that proceed under harsh conditions under the action of
aqueous solutions of acids or alkalis. 
The reaction mechanisms are similar to the hydrolysis of complex
ethers. However, in contrast to the hydrolysis of esters, acid and alkaline hydrolysis
amides proceed irreversibly.
2.3. Reactions for a - carbon
atom
carboxylic acids containing a - hydrogen atoms,
react with bromine in the presence of phosphorus to form exclusively a - bromo derivatives
(Gell-Forgald-Zelinsky reaction
)
Halogen in a -halo-substituted acids are easily substituted under
action of nucleophilic reagents. That's why a -halogenated acids
are starting materials in the synthesis of a wide range of substituted a - position
acids, including a-amino- and a -hydroxy acids.
2.4.
Decarboxylation
Decarboxylation is the elimination of CO 2 from carboxylic acids or their salts. Decarboxylation
carried out by heating in the presence of acids or bases. At the same time, as
As a rule, the carboxyl group is replaced by a hydrogen atom.
Unsubstituted monocarboxylic acids
decarboxylated under harsh conditions.
Decarboxylation is facilitated by the presence
electron-withdrawing substituents in a-position.
The importance of enzymatic
decarboxylation of keto-, amino- and hydroxy acids in the body (see lek. No. 14 and
16).
Decarboxylation by heating (dry
distillation) of calcium and barium salts of carboxylic acids - a method for obtaining
ketones.
2.5.
Recovery.
Carboxylic acids, acid chlorides, anhydrides and esters
are restored LiAlH 4 to primary
alcohols. 
Acid chlorides can be reduced to
aldehydes (see Lec. No. 11).
In the reduction of amides of carboxylic acids
amines are formed.
3. Dicarboxylic acids
Dicarboxylic acids contain two carboxyl groups. most accessible
are linear acids containing from 2 to 6 carbon atoms. Their
the structure and methods of obtaining are presented in table 9. bacteria
Chemical properties of dicarboxylic acids in
basically similar to the properties of monocarboxylic acids. They give all the reactions
characteristic of the carboxyl group. At the same time, one can obtain
functional derivatives (acid chlorides, anhydrides, complex, esters, amides) as
one by one and both carboxyl
groups. Dicarboxylic acids are more acidic than monocarboxylic acids.
due to the –I effect of the carboxyl group. As the distance between
carboxyl groups, the acidity of dicarboxylic acids decreases (see table.
9).
In addition, dicarboxylic acids have a number
specific properties, which are determined by the presence in the molecule of two
carboxyl groups.
The ratio of dicarboxylic acids to
heating.
Transformations of dicarboxylic acids upon heating
depend on the length of the chain that separates the carboxyl groups, and are determined
the possibility of forming thermodynamically stable five- and six-membered
cycles.
When heated oxalic and malonic acids
decarboxylation occurs.
Succinic, glutaric and maleic acids at
when heated, they easily split off water with the formation of five- and six-membered cyclic
anhydrides.
Adipic acid when heated
decarboxylated to form a cyclic ketone, cyclopentanone.
Polycondensation reactions
D icarboxylic acids interact with diamines and diols with
the formation of polyamides and polyesters, respectively, which are used in
production of synthetic fibers.
Biologically important dicarboxylic
acids.
Oxalic acid
forms insoluble salts, for example,
calcium oxalate, which are deposited as kidney and bladder stones.
succinic acid
participates in the metabolic processes taking place in
body. It is an intermediate in the tricarboxylic acid cycle.
fumaric acid,
as opposed to maleic ,
widely distributed in nature, is involved in the process
metabolism, in particular in the tricarboxylic acid cycle.
The sources of saturated hydrocarbons are oil and natural gas. The main component of natural gas is the simplest hydrocarbon, methane, which is used directly or processed. Oil extracted from the bowels of the earth is also subjected to processing, rectification, and cracking. Most hydrocarbons are obtained from the processing of oil and other natural resources. But a significant amount of valuable hydrocarbons is obtained artificially, synthetic ways.
Isomerization of hydrocarbons
The presence of isomerization catalysts accelerates the formation of branched hydrocarbons from linear hydrocarbons. The addition of catalysts makes it possible to somewhat reduce the temperature at which the reaction proceeds.
Isooctane is used as an additive in the production of gasoline, to improve their anti-knock properties, and also as a solvent.
Hydrogenation (hydrogen addition) of alkenes
As a result of cracking, a large amount of unsaturated hydrocarbons with a double bond, alkenes, is formed. Their number can be reduced by adding hydrogen to the system and hydrogenation catalysts- metals (platinum, palladium, nickel):
Cracking in the presence of hydrogenation catalysts with the addition of hydrogen is called reduction cracking. Its main products are saturated hydrocarbons. Thus, the increase in pressure during cracking ( high pressure cracking) allows you to reduce the amount of gaseous (CH 4 - C 4 H 10) hydrocarbons and increase the content of liquid hydrocarbons with a chain length of 6-10 carbon atoms, which form the basis of gasoline.
These were industrial methods for obtaining alkanes, which are the basis for the industrial processing of the main hydrocarbon raw material - oil.
Now consider several laboratory methods for obtaining alkanes.
Decarboxylation of sodium salts of carboxylic acids
Heating the sodium salt of acetic acid (sodium acetate) with an excess of alkali leads to the elimination of the carboxyl group and the formation of methane:
If instead of sodium acetate we take sodium propionate, then ethane is formed, from sodium butanoate - propane, etc.
Wurtz synthesis
When haloalkanes react with an alkali metal sodium, saturated hydrocarbons and an alkali metal halide are formed, for example:
The action of an alkali metal on a mixture of halogen hydrocarbons (for example, bromoethane and bromomethane) will lead to the formation of a mixture of alkanes (ethane, propane and butane).
!!! The Wurtz synthesis reaction leads to an elongation of the chain of saturated hydrocarbons.
The reaction on which the Wurtz synthesis is based proceeds well only with haloalkanes, in the molecules of which the halogen atom is attached to the primary carbon atom.
Hydrolysis of carbides
When processing some carbides containing carbon in the -4 oxidation state (for example, aluminum carbide), methane is formed with water.
