Carboxylic acid

Carboxylic acids ( also outdated carboxylic acids ) are organic compounds which carry one or more carboxyl groups (-COOH). The carboxylic acid salts are known as carboxylates and their esters, carboxylic acid ester.

• 6.1 esterification
• 6.2 dehydration

Occurrence and Nomenclature

The systematic naming of carboxylic acids is carried out in English by the ending " acid " and is preceded by the backbone, with the acids of alkanes, for example, ethanoic acid (acetic acid), formic acid ( formic acid). Many carboxylic acids bear unsystematic names ( common names ), which also end with " acid ". The trivial name refers mostly to go to the source, from which the carboxylic acid can be recovered; some examples include formic acid, malic acid, butyric acid, tartaric acid, citric acid or acetic acid.

Classification

According to the chemical structure of the group R to which the -COOH group is bound to a distinction between aliphatic, aromatic and heterocyclic carboxylic acids. The aliphatic carboxylic acids can be divided into alkanoic acids, alkenoic and alkynoic. Alkanoic acids are also called saturated carboxylic acids. Alkenoic acids, that carboxylic acids having at least one double bond in the radical and alkynoic acids with at least one triple bond in the group, it is called contrast unsaturated carboxylic acids. Besides the structure of the rest of the carboxylic acids can be distinguished according to the number of carboxyl groups. Monocarboxylic acids have one carboxyl group, while 2 dicarboxylic acids and tricarboxylic acids carry three carboxy groups.

There are also groups of carboxylic acids, which carry additional functional groups such as keto carboxylic acids, hydroxycarboxylic acids and amino acids (actually amino carboxylic acids ).

Fatty acids are straight-chain, aliphatic monocarboxylic acids having at least four carbon atoms. Resin acids are referred to as carboxylic acids, which occur in natural resins. Metallacarbonsäuren are complexes with a Carboxyligand.

Examples

Properties

The chemical and the physical properties of the carboxylic acids are significantly determined by the carboxy group. The carbonyl group (C = O) has a relatively strong electron-withdrawing effect, so that the binding of the proton in the hydroxyl group is strongly polarized. Thereby permitting the release of the carboxyl group of H ions, represented here by acetic acid:

The acidic character of carboxylic acids produced by the resonance stabilization of the carboxylate anion. The stability of the anion facilitates the deprotonated form of the carboxylic acid.

A carboxylic acid, the acidity is higher, when the alpha carbon atom is a substituent having an electron-attracting, thus with inductive effect (-I effect). The carboxy group is supplied to a positive partial charge, which compensate the negative charge of the anion more, so to stabilize. Example would be acetate in comparison to trichloroacetate.

The short-chain carboxylic acids are colorless, strong-smelling liquids. You have a polar character, which leads to relatively high boiling points due to the hydrogen bonds through the carboxyl group. Due to a particular spatial arrangement, the hydrogen-bonding results in Carbonsäuredimeren, leading to double the mass of the particles in the vapor space above the liquid. The higher mass leads to an increase of the boiling point of carboxylic acids.

With increasing chain length of the lipophilic character increases and the hydrophilic character with it. This also applies to the salts of the carboxylic acids. The molecules of the most common fatty acids having 16 or 18 carbon atoms. Your triglyceride are the fats. The sodium and potassium salts of the fatty acids show the properties of a surfactant and may be used as a soap and soap.

Production

Carboxylic acids produced by oxidation of primary alcohols, aldehydes occur as intermediates. Suitable oxidizing agents are for example potassium permanganate, chromium trioxide, potassium dichromate, nitric acid or.

• Oxidation of primary alcohols or aldehydes:

• Hydrolysis ( = " saponification " ) of esters:

• Reaction of Grignard reagents with carbon dioxide, followed by hydrolysis:

• Kolbe- nitrile haloalkanes and subsequent hydrolysis of the nitrile yields the C block to an extended carboxylic acid. Characterized hydroxyl and carboxyl groups does not need to be protected as in the Grignard method:

• Oxidation of alkylated aromatics:

• Hydrolysis of activated carboxylic acid derivatives, such as carboxylic acid chlorides or acid anhydrides:

• Hydrolysis of nitriles ( cyanides ) ( because of the stability of the nitriles under energetic conditions):

• Acidic or basic hydrolysis of amides (due to the stability of the carboxylic acid amides under energy conditions ):

• Oxidation of olefins with basic potassium permanganate ( under neutral conditions is the reaction to the vicinal diol manganese dioxide are ):

• Kolbe -Schmitt reaction:

• Benzilic rearrangement:

• Koch reaction (hydroformylation )

Spectroscopy of carboxylic acids

The most important analytical methods for structure determination of carboxylic acids are the IR and NMR spectroscopy.

In the IR spectrum, the C = O stretching vibration at about 1710-1760 cm -1 and the broad OH stretching vibration at 3000 cm -1 are characteristic.

In the 1H -NMR spectrum of the acidic hydroxyl protons are shifted to unusually low field, 10-13 ppm. The protons of the alkyl groups on the carbonyl carbon have a chemical shift in the range of approximately 2.0-2.5 ppm; the bonded directly to the carbonyl H atom of formic acid appears at 8.08 ppm. In a C- chain of a non-conjugated acid, the peaks that are further removed from the carbonyl group, with increasingly less shifted downfield, because the influence of the inductive effect of the carbonyl group decreases.

In the 13C -NMR spectrum shows the carboxyl carbon atom in the range of about 170 to 180 ppm.

Important reactions

Given by the two neighboring oxygen atoms, the electron-withdrawing effect, nucleophilic attack to the carbon atom may occur. The nucleophiles Brønsted bases, only the salt of the carboxylic acid, however, will arise under deprotonation.

Esterification

During the acid-catalyzed esterification of the carboxyl group of an organic acid with the hydroxy group of an alcohol reacts. With elimination of water thereby produced an ester. General R1 is the remainder of the acid, and R2 is the remainder of the alcohol. Then the following equilibrium reaction takes place:

Dehydration

Carboxylic acids form with elimination of water (dehydration ) at higher temperatures organic carboxylic anhydrides.

These can react with water again to the corresponding carboxylic acids back.