Aldehydes and ketones. Properties and synthesis of carbonyl compounds

Organic compounds containing in their molecular structure a carbonyl group of the following type:> C = O, - are called oxo compounds and are divided into two large categories - aldehydes and ketones. By the structure of hydrocarbon radicals, these substances are classified into aliphatic, aromatic and alicyclic. The first and second are characterized by the presence in the molecules of the carbonyl group, which is bonded directly to the benzene ring or side chain. Aldehydes and ketones with a molecular bond of the aromatic series that have a functional group in the side chain are considered as derivatives of aliphatic carbonyl compounds.

Aromatic aldehydes are synthesized in two main ways: the introduction of a carbonyl group into a benzene ring during the electrophilic substitution process and the conversion of substituents already present in the structure. Aldehydes and ketones among all organic compounds are the most reactive. And in the chemical plan, the former are much more active than the latter. For aldehydes, oxidation, substitution, polymerization, addition and condensation are very characteristic. Ketones do not support the polymerization reaction.

The preparation of aldehydes of an aromatic series, especially benzaldehyde, by oxidation of hydrocarbon compounds with an air mixture is made by an industrial method. Such reactions are carried out in chemical plants using oxides of various metals, for example, vanadium oxide. In addition, for the synthesis of aromatic aldehyde, methods used in the preparation of aliphatic compounds can be used.

Aromatic aldehydes are mostly liquid-insoluble liquids with a peculiar sharp smell of bitter almonds. The more they have a carbonyl group more distant from the benzene ring, the sharper becomes their smell. Aromatic aldehydes, whose chemical properties are similar in many respects to analogous compounds of the aliphatic series due to the mutual influence of the benzene ring and the carbonyl group, have some specific chemical properties and physical characteristics. For example, they can be easily oxidized to carboxylic acids, followed by reduction to the corresponding alcohols and hydrocarbons. A propionic aldehyde, which perfectly mixes with many kinds of organic solvents, is converted to propionic acid in the presence of the corresponding catalysts, and to propanol during hydrogenation.

Many methods can be used to synthesize ketones of the aromatic series. For example, the process of alkaline hydrolysis of geminal dihalides, dehydrogenation, oxidation of the corresponding monatomic secondary alcohol compounds, and others. However, the main method of obtaining these substances is the acylation of aromatic compounds. All aldehydes and ketones, having an electrophilic center, perfectly interact with the reagents of the nucleophilic series.

Such aromatic compounds with electron-donor substituents also readily enter acylation reactions. Ketones of this molecular structure are liquid or solid substances with a pleasant floral odor, insoluble in water, which allows them to be widely used in the perfume industry.