Chemical organic compounds, molecules of which receive the common name carboxylic acid – have at least one carboxyl group (carbonyl – aldehyde and ketone, and the hydroxyl functional group of the alcohol functional group it combine) in its structure. Formula they can be represented as R-COOH, where R is a monovalent hydrocarbon functional group. Any carboxylic acid dissociates into weak and incomplete ions, unlike most inorganic acids.
Simple examples are formic acid (methane) acid H-COOH. The name is explained by the history of the first receipt of red ants in 1670 by the English naturalist John Ray. Carboxylic acids with two or more carboxyl groups are called dibasic (or dicarboxylic), tribasic (or tricarboxylic), and so on. The simplest example is oxalic acid with the formula C2H2O4, the molecule containing two carboxyl groups. Hexaphic acid, its formula C12H6O12, may be mentioned as hexafic acid. The molecule contains six carboxyl groups, which replace hydrogen atoms in the benzene ring.
Organic acids, as a rule, are found in nature. For example, hexacarboxylic acid is in the honeystone found in brown coals).
There are several important natural compounds of this class. These include citric acid C6H8O7 (represents several food additives E330-E333), which was originally obtained from the juice of unripe lemons in 1784 by Swedish pharmacist K. Scheele. C4H6O6 Tartaric Acid is food additive E334). This carboxylic acid is widely distributed in nature. It is contained in the fresh juice of many fruits.
If we consider the homologous series of any of these organic compounds, then there are regular changes in properties with increasing molecular weight. The properties of each compound depend on the structure of their molecules, that is, they are largely determined by the isomerism of carboxylic acids. The first representatives of the homologous series, including acetic and propionic, refer to liquids made from formic acid. They are characterized by a pungent odor and are readily soluble in water. Higher representatives are solids, which do not dissolve in water.
The chemical properties of carboxylic acids in the maindetermined by the effect of the carbonyl group on the hydroxyl group. Therefore, these compounds, unlike alcohols, have a pronounced acidic character.
For example, in aqueous solutions they candissociate into ions, which after adding to the red color of the liquid prove to be staining of the liquid. This indicates the presence of hydrogen associations. That is, the medium of their aqueous solution is acidic (pH less than 7).
When interacting with metals or bases, carboxylic acids are able to form salts: 2CH3-COOH + Mg → (CH 3-COO) 2Mg + H 2 .
2CH3-COOH + MgCO3 → (CH3-COO) 2mg + H2O + CO 2: organic acids also enter into chemical reactions with carbonates, displacing carbonic acid.
They readily react with ammonia, forming salts: CH 3-COOH + NH 3 → CH 3-COOH 4.
The acidic properties of organic acids are enhanced by the presence in them of radical constituents with a negative induction effect. For example, the chlorine in acetic acid was gradually replaced by a hydrogen atom of the chlorine atom and the action of chloroacetic acid, to obtain dichloroacetic acid, and then trichloroacetic acid, there is a rapid increase in their acidic properties.
Any carboxylic acid can be obtained in many ways. The most common method is based on the oxidation reaction. As starting reagents, alcohols or aldehydes are taken. Another way to produce organic acids is by hydrolysis of nitriles, which occurs when they are heated with dilute mineral acids.