Carboxylic acids - organic matter, whose molecules contain one or more carboxyl groups.

Carboxyl group (abbreviated as COOH) - functional group carboxylic acids- consists of a carbonyl group and an associated hydroxyl group.

Based on the number of carboxyl groups, carboxylic acids are divided into monobasic, dibasic, etc.

The general formula of monobasic carboxylic acids is R—COOH. An example of a dibasic acid is oxalic acid HOOC—COOH.

Based on the type of radical, carboxylic acids are divided into saturated (for example, acetic acid CH 3 COOH), unsaturated [for example, acrylic acid CH 2 =CH—COOH, oleic acid CH 3 —(CH 2) 7 —CH=CH—(CH 2) 7 -COOH] and aromatic (for example, benzoic C 6 H 5 -COOH).

Isomers and homologues

Monobasic saturated carboxylic acids R-COOH are isomers esters(abbreviated R"—COOR"") with the same number of carbon atoms. The general formula for both is C n H 2 n O2.

G HCOOH
methane (ant)
CH3COOH
ethane (acetic)		 HCOOCH 3
methyl ether formic acid
CH3CH2COOH
propane (propionic)		 HCOOCH 2 CH 3
ethyl formic acid		 CH 3 COOCH 3
acetic acid methyl ester
CH3(CH2)2COOH
butane (oil)
2-methylpropane		 HCOOCH 2 CH 2 CH 3
propyl ester of formic acid		 CH 3 COOCH 2 CH 3
ethyl acetate		 CH 3 CH 2 COOCH 3
propionic acid methyl ester
isomers

Algorithm for composing the names of carboxylic acids

  1. Find the carbon backbone - this is the longest chain of carbon atoms that includes the carbon atom of the carboxyl group.
  2. Number the carbon atoms in the main chain, starting with the carboxyl carbon atom.
  3. Name the compound using the algorithm for hydrocarbons.
  4. At the end of the name, add the suffix “-ov”, the ending “-aya” and the word “acid”.

In molecules of carboxylic acids p-electrons of the oxygen atoms of the hydroxyl group interact with electrons of the -bond of the carbonyl group, as a result of which the polarity of the O-H bond increases, the -bond in the carbonyl group strengthens, the partial charge (+) on the carbon atom decreases and the partial charge (+) on the hydrogen atom increases .

The latter promotes the formation of strong hydrogen bonds between carboxylic acid molecules.

The physical properties of saturated monobasic carboxylic acids are largely due to the presence of strong hydrogen bonds between molecules (stronger than between alcohol molecules). Therefore, the boiling points and solubility in water of acids are higher than those of the corresponding alcohols.

Chemical properties acids

Strengthening the -bond in the carbonyl group leads to the fact that addition reactions are uncharacteristic for carboxylic acids.

  1. Combustion:

    CH 3 COOH + 2O 2 2CO 2 + 2H 2 O

  2. Acidic properties.
    Due to high polarity O-H connections carboxylic acids in an aqueous solution noticeably dissociate (more precisely, they react reversibly with it):

    HCOOH HCOO - + H + (more precisely HCOOH + H 2 O HCOO - + H 3 O +)


    All carboxylic acids are weak electrolytes. As the number of carbon atoms increases, the strength of acids decreases (due to a decrease in the polarity of the O-H bond); on the contrary, the introduction of halogen atoms into the hydrocarbon radical leads to an increase in the strength of the acid. Yes, in a row

    HCOOH CH 3 COOH C 2 H 5 COOH


    the strength of acids decreases, and in the series

    Increasing.

    Carboxylic acids exhibit all the properties inherent in weak acids:

    Mg + 2CH 3 COOH (CH 3 COO) 2 Mg + H 2
    CaO + 2CH 3 COOH (CH 3 COO) 2 Ca + H 2 O
    NaOH + CH 3 COOH CH 3 COONa + H 2 O
    K 2 CO 3 + 2CH 3 COOH 2CH 3 COOK + H 2 O + CO 2

  3. Esterification (reaction of carboxylic acids with alcohols leading to the formation of an ester):

    The esterification reaction can also involve polyhydric alcohols eg glycerin. Esters formed by glycerol and higher carboxylic acids (fatty acids) are fats.

    Fats are mixtures of triglycerides. Saturated fatty acids (palmitic C 15 H 31 COOH, stearic C 17 H 35 COOH) form solid fats of animal origin, and unsaturated fatty acids (oleic C 17 H 33 COOH, linoleic C 17 H 31 COOH, etc.) form liquid fats (oils) of plant origin.

  4. Substitution in a hydrocarbon radical:

    Substitution occurs in the - position.

    The peculiarity of formic acid HCOOH is that this substance is a bifunctional compound; it is both a carboxylic acid and an aldehyde:

    Therefore, formic acid, among other things, reacts with an ammonia solution of silver oxide (silver mirror reaction; qualitative reaction):

    HCOOH + Ag 2 O (ammonia solution) CO 2 + H 2 O + 2Ag

Preparation of carboxylic acids

Carboxylic acids Compounds that contain a carboxyl group are called:

Carboxylic acids are distinguished:

  • monobasic carboxylic acids;
  • dibasic (dicarboxylic) acids (2 groups UNS).

Depending on their structure, carboxylic acids are distinguished:

  • aliphatic;
  • alicyclic;
  • aromatic.

Examples of carboxylic acids.

Preparation of carboxylic acids.

1. Oxidation of primary alcohols with potassium permanganate and potassium dichromate:

2. Hybrolysis of halogen-substituted hydrocarbons containing 3 halogen atoms per carbon atom:

3. Preparation of carboxylic acids from cyanides:

When heated, the nitrile hydrolyzes to form ammonium acetate:

When acidified, acid precipitates:

4. Use of Grignard reagents:

5. Hydrolysis of esters:

6. Hydrolysis of acid anhydrides:

7. Specific methods for producing carboxylic acids:

Formic acid is produced by heating carbon(II) monoxide with powdered sodium hydroxide under pressure:

Acetic acid is produced by the catalytic oxidation of butane with atmospheric oxygen:

Benzoic acid is obtained by oxidation of monosubstituted homologues with a solution of potassium permanganate:

Canniciaro's reaction. Benzaldehyde is treated with 40-60% sodium hydroxide solution at room temperature.

Chemical properties of carboxylic acids.

In an aqueous solution, carboxylic acids dissociate:

The equilibrium is shifted strongly to the left, because carboxylic acids are weak.

Substituents affect acidity due to an inductive effect. Such substituents pull electron density towards themselves and a negative inductive effect (-I) occurs on them. The withdrawal of electron density leads to an increase in the acidity of the acid. Electron-donating substituents create a positive inductive charge.

1. Formation of salts. Reaction with basic oxides, salts of weak acids and active metals:

Carboxylic acids are weak, because mineral acids displace them from the corresponding salts:

2. Formation of functional derivatives of carboxylic acids:

3. Esters when heating an acid with an alcohol in the presence of sulfuric acid - esterification reaction:

4. Formation of amides, nitriles:

3. The properties of acids are determined by the presence of a hydrocarbon radical. If the reaction occurs in the presence of red phosphorus, the following product is formed:

4. Addition reaction.

8. Decarboxylation. The reaction is carried out by fusing alkali with salt alkali metal carboxylic acid:

9. Dibasic acid is easily eliminated CO 2 when heated:

Additional materials on the topic: Carboxylic acids.

Chemistry calculators
Chemistry online on our website to solve problems and equations.

Methods of obtaining. 1. Oxidation of aldehydes and primary alcohols is a common method for the preparation of carboxylic acids. />K M n O 4 and K 2 C r 2 O 7 are used as oxidizing agents.

2 Another common method is the hydrolysis of halogenated hydrocarbons containing three halogen atoms per carbon atom. In this case, alcohols containing OH groups on one carbon atom are formed - such alcohols are unstable and split off water to form a carboxylic acid:

ZNaON
R-CCl 3 → R - COOH + H 2 O
-3NaCl

3. Obtaining carboxylic acids from cyanides (nitriles) is an important method that allows you to increase the carbon chain when obtaining the original cyanide. An additional carbon atom is introduced into the molecule using the reaction of replacing a halogen in a halocarbon molecule with sodium cyanide, for example:

CH 3 -B r + NaCN→ CH 3 - CN + NaBr.

The resulting acetic acid nitrile (methyl cyanide) easily hydrolyzes when heated to form ammonium acetate:

CH 3 CN + 2H 2 O → CH 3 COONH 4.

When the solution is acidified, acid is released:

CH 3 COONH 4 + HCl→ CH 3 COOH + NH 4 Cl.

4. Usage Grignard reagent according to the scheme:/>

H 2 O
R— MgBr+ CO 2 → R — COO — MgBr→ R - COOH + Mg (OH) Br

5. Hydrolysis of esters:/>

R - COOR 1 + KON → R - COOK + R'OH,

R - COOK + HCl → R— COOH+ KCl .

6. Hydrolysis of acid anhydrides:/>

(RCO) 2 O + H 2 O → 2 RCOOH.

7. There are specific methods of preparation for individual acids./>

Formic acid is prepared by heating carbon monoxide ( II ) with powdered sodium hydroxide under pressure and treating the resulting sodium formate with a strong acid:

Acetic acid is produced by the catalytic oxidation of butane with atmospheric oxygen:

2C 4 H 10 + 5 O 2 → 4CH 3 COOH + 2H 2 O.

To obtain benzoic acid, you can use the oxidation of monosubstituted benzene homologues with an acidic solution of potassium permanganate:

5C 6 H 5 -CH 3 + 6 KMnO 4 + 9 H 2 SO 4 = 5C 6 H 5 COOH + 3 K 2 SO 4 + 6 MnSO 4 + 14 H 2 O.

Additionally, benzoic acid can be prepared from benzaldehyde using Cannizzaro's reactions. In this reaction, benzaldehyde is treated with 40-60% sodium hydroxide solution at room temperature. Simultaneous oxidation and reduction leads to the formation benzoic acid and, accordingly, phenylmethanol (benzyl alcohol):

Chemical properties. Carboxylic acids are stronger acids than alcohols because the hydrogen atom in the carboxyl group has increased mobility due to the influence of the CO group. In an aqueous solution, carboxylic acids dissociate:

RCOOH RCOO—+H+

However, due to the covalent nature of carbon molecules y acids, the above dissociation equilibrium is sufficient strongly shifted to the left. Thus, carboxylic acids - These are usually weak acids. For example, ethane (acetic)the acid is characterized by a dissociation constant K a = 1.7*10 -5./>

Substituents present in a carboxylic acid molecule greatly affect its acidity due to the effect they have inductive effect. Substituents such as chlorine or phenyl radical attract electron density and, therefore, cause a negative inductive effect (-/). The withdrawal of electron density from the carboxyl hydrogen atom leads to an increase in the acidity of the carboxylic acid. acids. In contrast, substituents such as alkyl groups have electron-donating properties and create a positive inductive effect, +I. They reduce acidity. Effect of substituents on the acidity of carboxylic acidsclearly manifested in the values ​​of dissociation constants K a for a number of acids. In addition, the strength of the acidis influenced by the presence of a conjugate multiple bond.

Carboxylic Acids Formula K a

Propionic CH 3 CH 2 COOH 1.3*10 -5

Oil CH 3 CH 2 CH 2 COOH 1.5*10 -5

Acetic CH 3 COOH 1.7*10 -5

Croton CH 3 - CH = CH - COOH 2.0 * 10 -5

Vinylacetic CH 2 =CH-CH 2 COOH 3.8*10 -5

Acrylic CH 2 =CH-COOH 5.6*10 -5

Formic HCOOH 6.1*10 -4

Benzoic C 6 H 5 COOH 1.4*10 -4

Chloroacetic CH 2 ClCOOH 2.2*10 -3

Tetronic CH 3 - C ≡ C - COOH 1.3*10 -3

Dichloroacetic CHCl 2 COOH 5.6*10 -2

Oxalic HOOC - COOH 5.9*10 -2

TrichloroaceticCCl 3 COOH 2.2*10 -1

The mutual influence of the atoms in the molecules of dicarboxylic acids leads to the fact that they are stronger than monobasic acids.

2. 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:

2 RCOOH + M g → (RCOO) 2 Mg + H 2,

2 RCOOH + 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 COOK + 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.

3. Formation of functional derivatives of carboxylic acids. When replacing the OH group in carboxylic acids with various groups (/>X ) functional derivatives of acids are formed, having the general 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 are produced by the action of phosphorus chloride ( V) for acids:

R-CO-OH + PC l 5 → R-CO- Cl+ ROS l 3 + HCl.

Connection examples

Acid

Ethanoic (acetic) Benzoic acid

acid chloride

Ethanoyl chloride Benzoyl chloride

(acetyl chloride)

acid anhydride

Ethane (acetic) benzoic anhydrite

Anhydrite

ester

Ethyl ethanoate (ethyl acetate) Methyl benzoate

amide

Ethanamide(acetamide) Benzamide

Nitrile

Ethannitrile Benzonitrile

(acetonitrile)

Anhydrides are formed from carboxylic acids under the action of water-removing agents:

2 R - 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):

The mechanism of the esterification reaction has been established by the "labeled atoms" method.

Esters can also be obtained by reacting acid chlorides and alkali metal alcoholates:

R-CO-Cl + Na-O-R’ → R-CO-OR’ + NaCl .

Reactions of carboxylic acid chlorides with ammonia lead to the formation of amides:

CH 3 -CO-C l + CH 3 → CH 3 -CO-CH 2 + HCl.

In addition, amides can be prepared by heating ammonium salts of carboxylic acids:

When amides are heated in the presence of dewatering agents, they dehydrate to form nitriles:

R 2 0 5
CH 3 - CO - NH 2

→

CH 3 - C ≡ N + H 2 O

Functional derivatives of lower acids are volatile liquids. All of them are easily hydrolyzed to form the parent acid:

R-CO-X + H 2 O → R-CO-OH + HX.

In an acidic environment these reactions can be reversible. Hydrolysis in an alkaline environment is irreversible and leads to the formation of carboxylic acid salts, for example:

R-CO-OR ‘ + NaOH → R-CO-ONa + R’OH.

4. A number of properties of carboxylic acids are 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 (a-atom) adjacent to the carboxyl group is replaced by halogen:

r cr

CH 3 -CH 2 -COOH + Br 2

 →

CH 3 -CHBr-COOH + HBr

Unsaturated carboxylic acids are capable of addition reactions:

CH 2 = CH-COOH + H 2 → CH 3 -CH 2 -COOH,

CH 2 =CH-COOH + C l 2 → CH 2 C l -SHC l -COOH,

CH 2 =CH-COOH + HCl → CH 2 C l -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 has 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 "silver mirror" reaction:

HCOOH + 2OH → 2Ag + (NH 4) 2 CO 3 + 2NH 3 + H 2 O,

or in simplified form:

C H 3 HCOOH + Ag 2 O → 2Аg + CO 2 + H 2 O.

In addition, formic acid is oxidized by chlorine:

HCOOH + Cl 2 → CO 2 + 2 HCl.

In an oxygen atmosphere, carboxylic acids are oxidized to CO 2 and H 2 O:

CH 3 COOH + 2O 2 → 2CO 2 + 2H 2 O.

6. Reactions decarboxylation. Saturated unsubstituted monocarboxylic acids due to their high strength S-S connections When heated, they decarboxylate with difficulty. To do this, it is necessary to fuse the alkali metal salt of carboxylic acid with alkali:

The appearance of electron-donating substituents in the hydrocarbon radical promotes decarboxylation reactions:

Dibasic carboxylic acids easily split off CO 2 when heated:

Reduction of carboxylic acid chlorides Carboxylic acids are difficult to reduce (more difficult than aldehydes). Acid chlorides are reduced much more easily: Interaction of carboxylic acid derivatives (salts, esters, acid halides) with organometallic compounds...
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    • In table 19.10 some are indicated organic compounds related to carboxylic acids. Characteristic sign carboxylic acids - the presence of carboxylic acid in them

    Table 19.10. Carboxylic acids

    (see scan)

    functional group. A carboxyl group consists of a carbonyl group bonded to a hydroxyl group. Organic acids with one carboxyl group are called monocarboxylic acids. Their systematic names have the suffix -ov(aya). Organic acids with two carboxyl groups are called dicarboxylic acids. Their systematic names have the suffix -diov(aya).

    Saturated aliphatic monocarboxylic acids form a homologous series, which is characterized by the general formula. Unsaturated aliphatic dicarboxylic acids can exist in the form of various geometric isomers (see Section 17.2).

    Physical properties

    Inferior members homologous series saturated monocarboxylic acids at normal conditions are liquids with a characteristic pungent odor. For example, ethanoic (acetic) acid has a characteristic “vinegar” odor. Anhydrous acetic acid is a liquid at room temperature. It freezes when it turns into an icy substance called glacial acetic acid.

    All dicarboxylic acids listed in table. 19.10, at room temperature are white crystalline substances. The lower members of the series of monocarboxylic and dicarboxylic acids are soluble in water. The solubility of carboxylic acids decreases as their relative molecular weight increases.

    In the liquid state and in non-aqueous solutions, molecules of monocarboxylic acids dimerize as a result of the formation of hydrogen bonds between them:

    The hydrogen bond in carboxylic acids is stronger than in alcohols. This is explained by the high polarity of the carboxyl group, due to the withdrawal of electrons from the hydrogen atom towards the carbonyl oxygen atom:

    As a result, carboxylic acids have relatively high boiling points (Table 19.11).

    Table 19.11. Boiling points of acetic acid and alcohols with similar relative molecular weights

    Laboratory methods of obtaining

    Monocarboxylic acids can be obtained from primary alcohols and aldehydes by oxidation using an acidified solution of potassium dichromate taken in excess:

    Monocarboxylic acids and their salts can be obtained by hydrolysis of nitriles or amides:

    The preparation of carboxylic acids by reaction with Grignard reagents and carbon dioxide is described in section. 19.1.

    Benzoic acid can be prepared by oxidation of the methyl side chain of methylbenzene (see Section 18.2).

    Additionally, benzoic acid can be prepared from benzaldehyde using the Cannischaro reaction. In this reaction, benzaldehyde is treated with 40-60% sodium hydroxide solution at room temperature. Simultaneous oxidation and reduction leads to the formation of benzoic acid and, accordingly, phenylmethanol:

    Oxidation

    The Cannizzaro reaction is characteristic of aldehydes that do not have -hydrogen atoms. This is the name given to hydrogen atoms attached to a carbon atom adjacent to the aldehyde group:

    Since methanal does not have -hydrogen atoms, it can undergo the Cannizzaro reaction. Aldehydes containing at least one -hydrogen atom undergo acid-catalyzed aldol condensation in the presence of sodium hydroxide solution (see above).

    Chemical properties

    Although the carboxyl group contains a carbonyl group, carboxylic acids do not undergo some of the reactions that occur with aldehydes and ketones. For example, they do not undergo addition or condensation reactions. This is explained by the fact that the atom

    carbon in the carboxyl group has a less positive charge than in the aldehyde or keto group.

    Acidity. Pulling electron density away from the carboxyl hydrogen atom weakens O-H connection. As a result, the carboxyl group is able to abstract (lose) a proton. Therefore, monocarboxylic acids behave like monobasic acids. In aqueous solutions of these acids the following equilibrium is established:

    The carboxylate ion can be considered a hybrid of two resonance structures:

    Otherwise it can be thought of as

    Delocalization of the electron between the atoms of the carboxylate group stabilizes the carboxylate ion. Therefore, carboxylic acids are much more acidic than alcohols. However, due to the covalent nature of carboxylic acid molecules, the above equilibrium is strongly shifted to the left. Thus, carboxylic acids are weak acids. For example, ethanoic (acetic) acid is characterized by an acidity constant

    Substituents present in a carboxylic acid molecule greatly influence its acidity due to the inductive effect they provide. Substituents such as chlorine pull electron density towards themselves and, therefore, cause a negative inductive effect. Pulling electron density from the carboxyl hydrogen atom leads to an increase in the acidity of the carboxylic acid. In contrast, substituents such as alkyl groups have electron-donating properties and create a positive inductive effect. They weaken the carboxylic acid:

    The effect of substituents on the acidity of carboxylic acids is clearly manifested in the values ​​for a number of acids indicated in Table. 19.12.

    Table 19.12. Carboxylic acid values

    Formation of salts. Carboxylic acids have all the properties of ordinary acids. They react with reactive metals, bases, alkalis, carbonates and bicarbonates, forming the corresponding salts (Table 19.13). The reactions shown in this table are characteristic of both soluble and insoluble carboxylic acids.

    Like other salts of weak acids, carboxylate salts (salts of carboxylic acids) react with mineral acids taken in excess, forming the parent carboxylic acids. For example, when a solution of sodium hydroxide is added to a suspension of insoluble benzoic acid in water, the acid dissolves due to the formation of sodium benzoate. If you then add to the resulting solution sulfuric acid, benzoic acid precipitates:

    Table 19.13. Formation of salts from carboxylic acids

    Esterification. When a mixture of carboxylic acid and alcohol is heated in the presence of concentrated mineral acid, an ester is formed. This process, called esterification, requires the breakdown of alcohol molecules. There are two possibilities.

    1. Alkoxyhydrogen splitting. In this case, the alcohol oxygen atom (from the hydroxyl group) enters the molecule of the resulting ether:

    2. Alkylhydroxyl cleavage. In this type of cleavage, the alcohol oxygen atom enters a water molecule:

    Which of these cases is realized specifically can be determined experimentally by carrying out esterification using an alcohol containing isotope 180 (see Section 1.3), i.e. using an isotope tag. Determination of the relative molecular weight of the resulting ester using mass spectrometry indicates whether the oxygen-18 isotopic tag is present in it. In this way, it was discovered that esterification with the participation of primary alcohols leads to the formation of labeled esters:

    This shows that the methanol molecule undergoes methoxy-hydrogen splitting during the reaction under consideration.

    Halogenation. Carboxylic acids react with phosphorus pentachloride and sulfur oxide dichloride, forming acid chlorides of the corresponding acids. For example

    Both benzoyl chloride and phosphorus trichloride oxide are liquids that need to be separated from each other. Therefore, for the chlorination of carboxylic acids, it is more convenient to use sulfur oxide dichloride: this makes it possible to easily remove gaseous hydrogen chloride and sulfur dioxide from the liquid carboxylic acid chloride:

    By blowing chlorine through boiling acetic acid in the presence of catalysts such as red phosphorus or iodine, and under the influence of sunlight

    monochloroethanoic (monochloroacetic) acid is formed:

    Further chlorination leads to the formation of disubstituted and trisubstituted products:

    Recovery. When reacting with lithium in dry diethyl ether, carboxylic acids can be reduced to the corresponding alcohols. First, an alkoxide intermediate is formed, the hydrolysis of which leads to the formation of alcohol:

    Carboxylic acids are not reduced by many common reducing agents. These acids cannot be reduced immediately to the corresponding aldehydes.

    Oxidation. With the exception of methane (formic) and ethanoic (acetic) acids, other carboxylic acids are difficult to oxidize. Formic acid and its salts (formates) are oxidized with potassium permanganate. Formic acid is capable of reducing Fehling's reagent and, when heated in a mixture with an aqueous-ammonia solution of silver nitrate, forms a “silver mirror”. The oxidation of formic acid produces carbon dioxide and water:

    Ethanedioic (oxalic) acid is also oxidized by potassium permanganate, forming carbon dioxide and water:

    Dehydration. Distillation of a carboxylic acid with some kind of dehydrating agent, for example an oxide, leads to the splitting of a water molecule from two acid molecules and the formation of a carboxylic acid anhydride:

    Formic and oxalic acids are exceptions in this case. Dehydration of formic acid or its potassium or sodium salt with the help of concentrated sulfuric acid leads to the formation of carbon monoxide and

    Dehydration of sodium methanoate (formate) with concentrated sulfuric acid is a common laboratory method for producing carbon monoxide. Dehydration of oxalic acid with hot concentrated sulfuric acid produces a mixture of carbon monoxide and carbon dioxide:

    Carboxylates

    Sodium and potassium salts of carboxylic acids are white crystalline substances. They dissolve easily in water, forming strong electrolytes.

    Electrolysis of sodium or potassium carboxylate salts dissolved in a water-methanol mixture leads to the formation of alkanes and carbon dioxide at the anode and hydrogen at the cathode.

    At the anode:

    At the cathode:

    This method for producing alkanes is called electrochemical Kolbe synthesis.

    The formation of alkanes also occurs when heating a mixture of sodium or potassium carboxylates with sodium hydroxide or soda lime. (Soda lime is a mixture of sodium hydroxide and calcium hydroxide.) This method is used, for example, to produce methane in the laboratory:

    Aromatic sodium or potassium carboxylates under similar conditions form arenes:

    When a mixture of sodium carboxylates and acid chlorides is heated, anhydrides of the corresponding carboxylic acids are formed:

    Calcium carboxylates are also white crystalline substances and are generally soluble in water. When they are heated, they form

    tion with low yield of the corresponding ketones:

    When a mixture of calcium carboxylates and calcium formate is heated, an aldehyde is formed:

    Ammonium salts of carboxylic acids are also white crystalline substances soluble in water. When heated strongly, they form the corresponding amides: