organic chemical compound, the molecules of which have in their structure at least one carboxyl group (containing a carbonyl aligned - functional group of aldehydes and ketones, and hydroxyl - alcohol functional group) received common name - carboxylic acid.Formula them can be represented as R-COOH, where R is a monovalent hydrocarbon functional group.Any carboxylic acid, in contrast to most inorganic acids, weak and incompletely dissociated into ions.
As the simplest examples the formic (methane) acid H-COOH.The name refers to the history of the first of its receipt in 1670 of red ants English naturalist John Ray.The carboxylic acid having two or more carboxyl groups will be called diacid (or di), tribasic (or tri) and so on.The simplest example is oxalic acid and its formula C2H2O4, in a molecule containing two carboxylic acid groups.As a result, you can shestiosnovnoy Mellitic (geksakarbonovuyu) acid, its formula C12H6O12.The molecule contains six carboxyl groups are replaced in a benzene ring hydrogen atoms.
organic acid usually found in nature.For example, geksakarbonovaya acid is found in honey stone discovered in brown coal).
There are many important natural compounds in this class.These include citric acid C6H8O7 (a few food additives E330-E333), which was first obtained from the juice of unripe lemons in 1784 by the Swedish chemist K. Scheele.Tartaric acid C4H6O6 is a food additive E334).This carboxylic acid is widely distributed in nature.It is contained in the fresh juice of many fruits.
If you consider any homologous series of organic compounds, in it there are regular changes of properties with increasing molecular weight.The properties of each compound depend on the structure of the molecules, that is largely defines their isomerism carboxylic acids.The first representatives of the homologous series formed from formic acid including acetic and propionic relate to liquids.They are distinguished by a pungent odor, and are readily soluble in water.Senior representatives are solids that do not dissolve in water.
chemical properties of carboxylic acids are mainly determined by the influence of the carbonyl group to a hydroxyl group.Therefore, these compounds, in contrast to the alcohols, have a pronounced acid character.
example, in aqueous solutions, they can dissociate into ions, which proves dyeing liquid after addition litmus red.This suggests the presence of hydrogen cations.That is, the medium of their aqueous solutions is acidic (pH less than 7).
When interacting with metals or bases capable of forming a carboxylic acid salt: 2CH3-COOH + Mg → (CH3-COO) 2Mg + H2 ↑.
Organic acids also enter into chemical reactions with carbonates, forcing carbonic acid: 2CH3-COOH + MgCO3 → (CH3-COO) 2Mg + H2O + CO2 ↑.
They readily react with ammonia to form salts: CH3-COOH + NH3 → CH3-COONH4.
acidic properties of organic acids are amplified in the presence of their radical substituents with a negative inductive effect.For example, the action of chlorine to acetic acid is gradually replacing one hydrogen atom of chlorine atoms and receiving chloroacetic acid, dichloroacetic acid, and then trichloroacetic acid, there is a sharp increase in their acidic properties.
Any carboxylic acid can be obtained in several ways.The most common is a method which is based on the oxidation reaction.As the initial charge of reactants alcohols or aldehydes.Another method of producing organic acids is the hydrolysis of nitriles of flowing when heated with dilute mineral acids.
