Functional derivatives of carboxylic acids. Dibasic carboxylic acids. a,b-Unsaturated acids
Carboxylic acid derivatives
1. Acid halides.
When exposed to phosphorus halides or thionyl chloride, the formation of halides occurs:
CH 3 COOH + PCl 5 ® CH 3 COCl + POCl 3 + HCl
The halogen in acid halides is highly reactive. A strong inductive effect determines the ease of substitution of halogen with other nucleophiles: -OH, -OR, -NH2, -N3, -CN, etc.:
CH 3 COCl + CH 3 COOAg ® (CH 3 CO) 2 O acetic anhydride + AgCl
1. Anhydrides.
Anhydrides are formed by the reaction of acid salts with their acid halides:
CH 3 COONa + CH 3 COCl ® NaCl + (CH 3 CO) 2 O
Acid anhydrides are highly chemically active and, like acid halides, are good acylating agents.
Amides are obtained via acid halides
CH 3 COCl +2 NH 3 ® CH 3 CONH 2 acetamide + NH 4 Cl
or from ammonium salts of acids, during dry distillation of which water is split off and an acid amide is formed. Also, acid amides are formed as a by-product during the hydrolysis of nitriles. Amidation processes are important in industry for the production of a number of valuable compounds (N,N-dimethylformamide, dimethylacetamide, ethanolamides of higher acids).
4. Nitriles. The most important representatives of nitriles are acetonitrile CH 3 CN (used as a polar solvent) and acrylonitrile CH 2 =CHCN (monomer for the production of synthetic neuron fiber and for the production of divinylnitrile synthetic rubber, which is oil- and gasoline-resistant). The main method for producing nitriles is the dehydration of amides on acid catalysts:
CH 3 CONH 2 ® CH 3 C-CN + H 2 O
5. Esters. Esters of carboxylic acids are of important practical importance as solvents, hydraulic fluids, lubricating oils, plasticizers and monomers. They are obtained by esterification of alcohols with acids, anhydrides and acid halides or by the reaction of acids and alkenes:
CH 3 -CH=CH 2 + CH 3 COOH ® CH 3 COOCH(CH 3) 2
Many esters are used as aromatic substances:
| CH 3 COOCH 2 CH 3 | pear essence |
| CH 3 CH 2 CH 2 COOCH 2 CH 2 CH 2 CH 2 CH 3 | pineapple essence |
| rum essence |
Dibasic saturated acids
Dibasic saturated (saturated) acids have the general formula C n H 2 n (COOH) 2. Of these, the most important are:
HOOC-COOH - oxalic, ethanedicarboxylic acid;
HOOS-CH 2 -COOH - malonic, propanedicarboxylic acid;
NOOS-CH 2 -CH 2 -COOH - succinic, butanedicarboxylic acid;
NOOS-CH 2 -CH 2 -CH 2 -COOH - glutaric, pentanedicarboxylic acid.
Methods of obtaining
General methods the production of dibasic acids is similar to the methods for producing monobasic acids (oxidation of glycols, hydrolysis of dinitriles, Kolbe synthesis - see Lecture No. 27).
1. Oxidation of hydroxy acids:
OH-CH 2 CH 2 COOH ® HOCCH 2 COOH ® HOOC-CH 2 -COOH
2. Oxidation of cycloalkanes.
This industrial method obtaining adipic acid HOOC-CH 2 CH 2 CH 2 CH 2 -COOH from cyclohexane.
Succinic and oxalic acids are also formed as by-products. Adipic acid is used to synthesize nylon 6,6 fibers and plasticizers.
Dibasic acids are stronger than monobasic acids. This is explained by the mutual influence of carboxyl groups that facilitate dissociation:
In general, the reactions of dicarboxylic acids and their monocarboxylic analogues are almost the same. The reaction mechanism for the formation of diamides, diesters, etc. from carboxylic acids is the same as for monocarboxylic acids. The exception is dicarboxylic acids, which contain fewer than four carbon atoms between the carboxyl groups. Such acids, whose two carboxyl groups are capable of reacting with the same functional group or with each other, exhibit unusual behavior in reactions that proceed to form five- or six-membered closed activated complexes or products.
An example of the unusual behavior of carboxylic acids is the reactions that occur when heated.
At 150 o C, oxalic acid decomposes into formic acid and CO 2:
HOOC-COOH ® HCOOH + CO 2
2. Cyclodehydration.
When g-dicarboxylic acids, in which the carboxyl groups are separated by carbon atoms, are heated, cyclodehydration occurs, resulting in the formation of cyclic anhydrides:
Functional derivatives of carboxylic acids. Dibasic carboxylic acids.a , b -Unsaturated acids
Carboxylic acid derivatives
1. Acid halides.
When exposed to phosphorus halides or thionyl chloride, the formation of halides occurs:
CH 3 COOH + PCl 5 ® CH 3 COCl + POCl 3 + HCl
The halogen in acid halides is highly reactive. A strong inductive effect determines the ease of substitution of halogen with other nucleophiles: - OH, - OR, - N.H.2, - N3, - CN and etc.:
CH 3 COCl + CH 3 COOAg® (CH3CO)2O acetic anhydride + AgCl
1. Anhydrides.
Anhydrides are formed by the reaction of acid salts with their acid halides:
CH 3 COONa + CH 3 COCl ® NaCl + (CH 3 CO) 2 O
Acid anhydrides are highly chemically active and, like acid halides, are good acylating agents.
2. Amides.
Amides are obtained via acid halides
CH 3 COCl +2 NH 3® CH 3 CONH 2acetamide+NH4Cl
or from ammonium salts of acids, during dry distillation of which water is split off and an acid amide is formed. Also, acid amides are formed as a by-product during the hydrolysis of nitriles. Amidation processes are important industrially for the production of a number of valuable compounds ( N, N-dimethylformamide, dimethylacetamide, ethanolamides of higher acids).
4. Nitriles. The most important representatives of nitriles are acetonitrile CH 3 CN(used as a polar solvent) and acrylonitrile CH 2 = CHCN(monomer for the production of synthetic neuron fiber and for the production of divinylnitrile synthetic rubber, which is oil and gasoline resistant). The main method for producing nitriles is the dehydration of amides on acid catalysts:
CH 3 CONH 2 ® CH 3 C- CN + H 2 O
5. Esters. Esters of carboxylic acids are of important practical importance as solvents, hydraulic fluids, lubricating oils, plasticizers and monomers. They are obtained by esterification of alcohols with acids, anhydrides and acid halides or by the reaction of acids and alkenes:
CH 3 -CH=CH 2 + CH 3 COOH® CH 3 COOCH(CH 3) 2
Many esters are used as aromatic substances:
| CH 3 COOCH 2 CH 3 | pear essence |
| CH 3 CH 2 CH 2 COOCH 2 CH 2 CH 2 CH 2 CH 3 | pineapple essence |
| HCOOCH 2 CH 3 | rum essence |
Dibasic saturated acids
Dibasic saturated (saturated) acids have the general formula CnH 2 n(COOH) 2 . Of these, the most important are:
NOOS-SOUN- oxalic, ethanedicarboxylic acid;
NOOS-CH 2 -COOH- malonic, propanedicarboxylic acid;
NOOS-CH 2 -CH 2 -COOH- succinic, butanedicarboxylic acid;
NOOS-CH 2 -CH 2 -CH 2 -COOH- glutaric, pentanedicarboxylic acid.
Methods of obtaining
General methods for producing dibasic acids are similar to methods for producing monobasic acids (oxidation of glycols, hydrolysis of dinitriles, Kolbe synthesis - see Lecture No. 27).
1. Oxidation of hydroxy acids:
OH-CH2CH2COOH® HOCCH 2 COOH® HOOC-CH2-COOH
2. Oxidation of cycloalkanes.
This is an industrial method for obtaining adipic acid HOOC- CH 2 CH 2 CH 2 CH 2 - COOH from cyclohexane.
Succinic and oxalic acids are also formed as by-products. Adipic acid is used for fiber synthesis nylon 6.6 and plasticizers.
Chemical properties
Dibasic acids are stronger than monobasic acids. This is explained by the mutual influence of carboxyl groups that facilitate dissociation:
In general, the reactions of dicarboxylic acids and their monocarboxylic analogues are almost the same. The reaction mechanism for the formation of diamides, diesters, etc. from carboxylic acids is the same as for monocarboxylic acids. The exception is dicarboxylic acids, which contain fewer than four carbon atoms between the carboxyl groups. Such acids, whose two carboxyl groups are capable of reacting with the same functional group or with each other, exhibit unusual behavior in reactions that proceed to form five- or six-membered closed activated complexes or products.
An example of the unusual behavior of carboxylic acids is the reactions that occur when heated.
At 150 o C, oxalic acid decomposes into formic acid and CO 2:
HOOC-COOH® HCOOH + CO2
2. Cyclodehydration.
When heated g-dicarboxylic acids, in which the carboxyl groups are separated by carbon atoms, undergo cyclodehydration, resulting in the formation of cyclic anhydrides:
3. Syntheses based on malonic ester.
Dibasic acids with two carboxyl groups on one carbon atom, i.e. malonic acid and its mono- and disubstituted homologues, when heated slightly above their melting temperatures, decompose (are subjected to decarboxylation) with the elimination of one carboxyl group and the formation of acetic acid or its mono- and disubstituted homologues:
HOOCCH 2 COOH® CH 3 COOH + CO 2
HOOCCH(CH3)COOH® CH3CH2COOH + CO 2
HOOCC(CH 3) 2 COOH® (CH3) 2 CHCOOH + CO 2
The hydrogen atoms of the methylene group located between the acyl groups of malonic acid diethyl ester ( malonic ester), have acidic properties and give sodium salt with sodium ethoxide. This salt sodium malonic ester– alkylate by the mechanism of nucleophilic substitution S N2 . Based on sodium malonic ester, mono- and dibasic acids are obtained:
-Na++RBr® RCH(COOCH 2 CH 3) 2 + 2 H 2 O ®
R-CH(COOH)2 alkylmalonic acid ® R-CH2COOHalkylacetic acid+CO2
4. Pyrolysis of calcium and barium salts.
During pyrolysis of calcium or barium salts adipic (C 6), pimeline (C 7) And cork (From 8) acids are eliminated CO 2 and cyclic ketones are formed:
Unsaturated monobasic carboxylic acids
Unsaturated monobasic acids of the ethylene series have the general formula CnH 2 n -1 COOH, acetylene and diethylene series - CnH 2 n -3 COOH. Examples of unsaturated monobasic acids:
Unsaturated monobasic acids differ from saturated ones by large dissociation constants. Unsaturated acids form all the usual derivatives of acids - salts, anhydrides, acid halides, amides, esters, etc. But due to multiple bonds they enter into addition, oxidation and polymerization reactions.
Due to the mutual influence of the carboxyl group and the multiple bond, the addition of hydrogen halides to a,b-unsaturated acids occurs in such a way that hydrogen is directed to the least hydrogenated carbon atom:
CH 2 = CHCOOH + HBr ® BrCH 2 CH 2 COOH b-bromopropionic acid
Ethylene acids such as acrylic acid and their esters undergo polymerization much more easily than the corresponding hydrocarbons.
Acrylic acid obtained from ethylene (via chlorohydrin or ethylene oxide), by hydrolysis of acrylonitrile or oxidation of propylene, which is more efficient. In technology, derivatives of acrylic acid are used - its esters, especially methyl ( methyl acrylate). Methyl acrylate easily polymerizes to form transparent glassy substances, so it is used in the production of organic glass and other valuable polymers.
Methacrylic acid and its esters are prepared on a large scale by methods similar to those for the synthesis of acrylic acid and its esters. The starting product is acetone, from which acetone cyanohydrin is obtained, subjected to dehydration and saponification to form methacrylic acid. By esterification with methyl alcohol, methyl methacrylate is obtained, which, upon polymerization or copolymerization, forms glassy polymers (organic glasses) with very valuable technical properties.
Aromatic diazo compounds.
Reactions of aryldiazonium salts with the release of nitrogen.
Reactions resulting in the diazo group replaced by other groups , have great synthetic application, since they allow, under fairly mild conditions, the introduction into the aromatic ring of those functional groups, the introduction of which by other means would be fraught with significant difficulties or simply impracticable. In addition, using these reactions it is possible to obtain derivatives of aromatic hydrocarbons with such relative position functions that cannot be achieved using direct electrophilic substitution reactions. Reactions that release nitrogen can occur by ionic or radical mechanisms .
Replacing a diazo group with a hydroxyl group. When aqueous solutions of aryldiazonium salts are heated, even to room temperature, nitrogen is released and the corresponding compounds are formed phenols . In many cases, the yields in this reaction are high, so it can serve as a preparative method for the production of phenols. To avoid replacement of the diazo group by other nucleophiles, the reaction is usually carried out using sulfuric acid , the anions of which have low nucleophilicity:
The reaction proceeds according to the mechanism monomolecular aryl nucleophilic substitution S N 1 Ar which is mainly characteristic of diazonium salts. In the first, slow stage, the diazonium cation reversibly dissociates to form an aryl cation (in particular, a phenyl cation) and a nitrogen molecule. In the second stage, the extremely unstable aryl cation quickly combines with the nucleophile. The instability of the aryl cation is due to the impossibility of participation of the π-electrons of the aromatic ring in the delocalization of the positive charge, since the p-orbitals of the ring cannot interact with the vacant sp 2 hybrid orbital located in the plane of the σ-skeleton:
Replacing the diazo group with fluorine . When dry aryldiazonium borofluorides are heated, aryl fluorides ( Schiemann reaction ) :
This reaction is one of the best ways to introduce fluorine into an aromatic ring. It is believed that it flows through ionic mechanism with the formation of an intermediate aryl cation:
Replacement of diazo group with iodine . When a soluble salt of hydroiodic acid is added to solutions of aryldiazonium salts, the corresponding aryliodides . For example, p-diiodobenzene is obtained from p-phenylenediamine in almost quantitative yield, which is quite difficult to obtain by other methods:
Replacing the diazo group with chlorine or bromine. To obtain chloro- or bromine derivatives, diazonium salts are heated in the presence of copper(I) salts - CuCl or CuBr, respectively:
Both reactions proceed according to radical mechanism . The Cu + ion is easily oxidized into the Cu 2+ ion, donating one electron to the diazonium cation. The latter is converted into a free radical (I), which splits off a nitrogen molecule, forming an aryl radical (II). Upon subsequent interaction of the aryl radical (II) with the halide ion, the final ar is formed yl halide . The electron split off at the last stage is spent on the reduction of the Cu 2+ ion, due to which the catalyst is regenerated.
Replacing a diazo group with a cyano group. When solutions of aromatic diazonium salts are treated with copper cyanide, arylnitriles ( aryl cyanides ):
Replacing a diazo group with a nitro group. The reaction is carried out by adding solid aryldiazonium borofluoride to a solution of sodium nitrite in which copper powder is suspended. This method allows you to introduce a nitro group into positions of the aromatic ring that are inaccessible for direct nitration, for example:
Replacing the diazo group with hydrogen. When aryldiazonium salts are exposed to a reducing agent such as hypophosphorous acid H 3 PO 2 , the diazo group is replaced by a hydrogen atom. As an example, a scheme is given for the preparation of 2,4,6-tribromobenzoic acid, which cannot be obtained by direct bromination of benzoic acid:
Replacing a diazo group with a metal. Organic compounds of some metals can be obtained from diazonium salts. For example, when double mercury salts are reduced with copper, organomercury compounds are obtained ( Nesmeyanov's reaction ):
acids - mesotartaric is not an optical active substances. The homologue of oxalic acid is adipic acid HOOC(CH 2) 4 COOH, which is obtained by the oxidation of certain cyclic compounds. It is included in cleaning products for removing rust, and also serves as a starting material for the production of polyamide fibers (see the article “Giants organic world. Polymers").
CARBOXYLIC ACIDS AND THEIR DERIVATIVES
Although the carboxyl group consists of carbonyl and hydroxyl groups, carboxylic acids have very different properties from both alcohols and carbonyl compounds. Mutual influence OH- and -groups leads
to the redistribution of electron density. As a result, the hydrogen atom of the hydroxyl group acquires acid properties, i.e., it is easily split off when the acid is dissolved in water. Carboxylic acids change the color of indicators and exhibit all the properties characteristic of solutions of inorganic acids.
All monobasic acids that do not contain substituents (for example, formic and acetic acids) are weak - only slightly dissociated into ions. The strength of the acid can be changed by introducing to the a-position functional group halogen atom. Thus, trichloroacetic acid, formed during the chlorination of acetic acid CH 3 COOH + 3Cl 2 ®CCl 3 COOH + 3HCl, in an aqueous solution largely dissociates into ions.
Carboxylic acids can form functional derivatives, the hydrolysis of which again produces the original acids. Thus, when carboxylic acids are exposed to phosphorus(V) chloride and oxide, acid chlorides and anhydrides are formed, respectively; under the action of ammonia and amines - amides; alcohols - esters.
Crystals of monochloroacetic acid CH 2 ClCOOH.
Graph of the dependence of the boiling point of alkanes, alcohols, aldehydes and straight-chain carboxylic acids on the number of carbon atoms in the molecule.
The reaction to form esters is called esterification(from Greek"ether" - "ether"). It is usually carried out in the presence of a mineral acid, which plays the role of a catalyst. When heated, the ester (or water, if the ether boils at a temperature above 100 ° C) is distilled off from the reaction mixture, and the equilibrium shifts to the right. So, from acetic acid and ethyl alcohol get ethyl acetate - a solvent that is part of many types of glue:
Many esters are colorless liquids with a pleasant odor. Thus, isoamyl acetate smells like pear, ethyl butyrate smells like pineapple, isoamyl butyrate smells like apricot, benzyl acetate smells like jasmine, and ethyl formate smells like rum. Many esters are used as
flavoring additives in the manufacture of various drinks, as well as in perfumery. Derivatives of 2-phenylethyl alcohol have a particularly delicate odor: the ester of this alcohol and phenylacetic acid smells like honey and hyacinths. And the aroma of formic acid ester makes you remember the fragrance of a bouquet of roses and chrysanthemums. In the presence of alkali, esters can be hydrolyzed - decomposed into the original alcohol and a carboxylic acid salt. The hydrolysis of fats (esters of glycerol and higher carboxylic acids) produces the main components of soap - palmitate and sodium stearate,
NAMES OF SOME CARBOXYLIC ACIDS AND THEIR SALTS
*Ethyl acetate is a colorless, water-insoluble liquid with a pleasant ethereal odor ( t kip =77.1 °C), miscible with ethyl alcohol and other organic solvents.
**The names of esters are derived from the names of the corresponding alcohols and acids: ethyl acetate is an ester of ethyl alcohol and acetic acid (ethyl acetyl ester), isoamyl formate is an ester of isoamyl alcohol and formic acid (formic isoamyl ester).
GLACIC ACID
Vinegar, which is formed when wine sours, contains about 5% acetic acid (table vinegar is called a 3-15% solution). By distilling such vinegar, vinegar essence is obtained - a solution with a concentration of 70-80%. And pure (100 percent) acetic acid is released as a result of the action of concentrated sulfuric acid on acetates: CH 3 COOHNa + H 2 SO 4 (conc.) = CH 3 COOH + NaHSO 4.
Such pure acetic acid, which does not contain water, turns into transparent crystals resembling ice when cooled to 16.8 ° C. That's why it is sometimes called icy.
The similarity is not only external: in the crystals there are molecules of acetic acid,
Liquid at room temperature When cooled below 17 °C, glacial acetic acid turns into colorless crystals that really look like ice.
like water molecules, they form a system of hydrogen bonds. The intermolecular interaction turns out to be so strong that even acetic acid vapor contains not individual molecules, but their agglomerates.
Many salts of acetic acid are unstable to heat. Thus, the decomposition of calcium acetate produces acetone:
And when a mixture of sodium acetate and alkali is heated, methane is released:
For many centuries, the main method for the synthesis of acetic acid was fermentation. Edible vinegar is still produced this way. And for the production of esters and artificial fibers, acid is used as a raw material, which is obtained by the catalytic oxidation of hydrocarbons, for example butane:
CH 3 -CH 2 -CH 2 -CH 3 +2.5O 2 ®2CH 3 -COOH+H 2 O.
Organic compounds containing a carboxyl group –COUN, belong to the class of acids.
Biologically important carboxylic acids:
| Acids (trivial name) | Anion name | Acid formula |
| Monobase | ||
| ant | formate | HCOOH |
| vinegar | acetate | CH3COOH |
| oil | butyrate | CH3(CH2)2COOH |
| valerian | valerate | CH3(CH2)3COOH |
| Unsaturated acids | ||
| acrylic | acrylates | CH 2 = CH-COOH |
| croton | crotonate | CH 3 – CH = CH - COOH |
| Aromatic | ||
| benzoin | benzoate | C6H5COOH |
| Dicarboxylic acids | ||
| oxalic acid | oxalates | NOOS - SOON |
| malonova | malonates | NOOS-CH 2 - COOH |
| amber | succinates | NOOS-CH 2 – CH 2 -COOH |
| glutaric | glutarates | NOOS –(CH 2) 3 - COOH |
| Unsaturated dicarbonate | ||
| Fumaric (trans isomer) | fumarates | HOOS-CH=CH-COOH |
Acidic properties of carboxylic acids:
RCOOH RCOO - + H +
Upon dissociation, a carboxylate anion is formed, in which the negative charge is evenly distributed between the oxygen atoms, which increases the stability of this particle. The strength of carboxylic acids depends on the length of the radical (the larger the radical, the weaker the acid) and the substituents (electron-withdrawing substituents increase acidity). CI 3 COOH is much stronger than CH 3 COOH. Dicarboxylic acids are stronger than monobasic acids.
Functional derivatives of carboxylic acids:
Carboxylic acids exhibit high reactivity. They react with various substances and form functional derivatives, i.e. compounds obtained as a result of reactions at the carboxyl group.
1. Formation of salts. Carboxylic acids have all the properties of ordinary acids. They react with active metals, basic oxides, bases and salts of weak acids:
2RCOOH + Mg → (RCOO) 2 Mg + H 2,
2RCOOH + CaO → (RCOO) 2 Ca + H 2 O,
RCOOH + NaOH → RCOONa + H 2 O,
RCOOH + NaHCO 3 → RCOONa + H 2 O + CO 2.
Carboxylic acids are weak, so strong mineral acids displace them from the corresponding salts:
CH 3 COONa + HCl → CH 3 COOH + NaCl.
Salts of carboxylic acids in aqueous solutions hydrolyzed:
CH 3 COOC + H 2 O CH 3 COOH + CON.
The difference between carboxylic acids and mineral acids is the possibility of forming a number of functional derivatives.
2. Formation of functional derivatives of carboxylic acids. When the OH group in carboxylic acids is replaced by various groups (X), functional derivatives of acids are formed that have a common formula R-CO-X; here R means an alkyl or aryl group. Although nitriles have a different general formula (R-CN), they are usually also considered to be derivatives of carboxylic acids, since they can be prepared from these acids.
Acid chlorides obtained by the action of phosphorus chloride (V) on acids:
R-CO-OH + PCl 5 → R-CO-Cl + POCl 3 + HCl.
Anhydrides are formed from carboxylic acids under the action of water-removing agents:
2R-CO-OH + P 2 O 5 → (R-CO-) 2 O + 2HPO 3.
Esters are formed by heating an acid with an alcohol in the presence of sulfuric acid ( reversible reaction esterification):
Esters can also be obtained by reacting acid chlorides and alkali metal alcoholates:
R-CO-Cl + Na-O-R" → R-CO-OR" + NaCl.
Amides are formed by the reaction of carboxylic acid chlorides with ammonia:
CH 3 -CO-Cl + NH 3 → CH 3 -CO-NH 2 + HCl.
In addition, amides can be prepared by heating ammonium salts of carboxylic acids: t o
CH 3 -COONH 4 → CH 3 -CO-NH 2 + H 2 O
When amides are heated in the presence of dewatering agents, they dehydrate to form nitriles:
CH 3 -CO-NH 2 → CH 3 -C≡N + H 2 O
3. Properties of carboxylic acids due to the presence of a hydrocarbon radical. Thus, when halogens act on acids in the presence of red phosphorus, halogen-substituted acids are formed, and the hydrogen atom at the carbon atom (α-atom) adjacent to the carboxyl group is replaced by halogen: p cr.
CH 3 -CH 2 -COOH + Br 2 → CH 3 -CHBr-COOH + HBr
4. Unsaturated carboxylic acids capable of addition reactions:
CH 2 = CH-COOH + H 2 → CH 3 -CH 2 -COOH,
CH 2 = CH-COOH + Cl 2 → CH 2 Cl-CHCl-COOH,
CH 2 =CH-COOH + HCl → CH 2 Cl-CH 2 -COOH,
CH 2 = CH-COOH + H 2 O → HO-CH 2 -CH 2 -COOH,
The last two reactions proceed against Markovnikov's rule.
Unsaturated carboxylic acids and their derivatives are capable of polymerization reactions.
5. Redox reactions of carboxylic acids:
Carboxylic acids, under the action of reducing agents in the presence of catalysts, can be converted into aldehydes, alcohols and even hydrocarbons.
Formic acid HCOOH differs in a number of features, since it contains an aldehyde group.
Formic acid is a strong reducing agent and is easily oxidized to CO 2 . She gives the "silver mirror" reaction:
HCOOH + 2OH → 2Ag + (NH 4) 2 CO 3 + 2NH 3 + H 2 O,
or in a simplified form in an ammonia solution when heated:
HCOOH + Ag 2 O → 2Ag + CO 2 + H 2 O.
Saturated carboxylic acids are resistant to the action of concentrated sulfuric and nitric acids. The exception is formic acid:
H 2 SO 4 (conc)
HCOOH → CO + H 2 O
6. Decarboxylation reactions. Saturated unsubstituted monocarboxylic acids due to their high strength S-S connections When heated, they decarboxylate with difficulty. This requires melting the salt. alkali metal carboxylic acid with alkali:
CH 3 -CH 2 -COONa + NaOH → C 2 H 6 + Na 2 CO 3
Dibasic carboxylic acids easily split off CO 2 when heated:
HOOC-CH 2 -COOH → CH 3 COOH + CO 2
