Aldehydes are functional derivativeshydrocarbons, in the structure of which there is a CO group (carbonyl group). For simple aldehydes, trivial (historical) names, traditionally derived from the name of carboxylic acids, which aldehydes turn into on oxidation, are traditionally preserved. If we talk about the IUPAC nomenclature, then the longest chain containing the aldehyde group is taken as the basis. The beginning of the numbering of the hydrocarbon chain is produced from the carbon atom of the carbonyl group (CO), which itself receives the number 1. The end of the "al" is added to the name of the main hydrocarbon chain. Since the aldehyde group is at the end of the chain, the number 1, as a rule, is not written. The isomerism of the compounds presented is due to the isomerism of the hydrocarbon skeleton.
Альдегиды получают несколькими способами:oxosynthesis, hydration of alkynes, oxidation and dehydrogenation of alcohols. The production of aldehydes from primary alcohols requires special conditions, since the resulting organic compounds are easily oxidized to carboxylic acids. Aldehydes can also be synthesized by dehydrating the corresponding alcohols in the presence of copper. One of the main industrial methods for producing aldehydes is the reaction of oxosynthesis, which is based on the interaction of alkene, C0 and H2 in the presence of catalysts containing Co at a temperature of 200 degrees and a pressure of 20 MPa. This reaction takes place in the liquid or in the gas phase according to the scheme: RCH = CH2 + C0 + H2 - RCH2CH2C0H + RCH (CH) 3C0H. Aldehydes can be obtained by hydrolysis of dihalogen derivatives. In the process of replacing halogen atoms with OH groups, the so-called heme diol is intermediately formed, which is unstable and turns into a carboxyl compound with H20 cleavage.
The chemical property of aldehydes is qualitative.reaction to silver. In the process of oxidation, aldehydes are converted to carboxylic acids (for example, C5H11CON + O - C5H11COOH). In any specialized textbook, you can find information that the reaction of the silver mirror is used to identify aldehydes. This group of organic substances can oxidize not only under the action of special oxidizing agents, but also simply during storage under the influence of atmospheric oxygen. The ease with which aldehydes are oxidized to carboxylic acids has made it possible to develop qualitative reactions (the reaction of a silver mirror) to these organic compounds, which makes it possible to quickly and visually determine the presence of aldehyde in a particular solution.
При нагревании с аммиачным раствором оксида silver aldehyde is oxidized to acid. At the same time, silver is reduced to metallic and is deposited on the walls of the tube in the form of a dark layer with a characteristic specular gloss - the reaction of the silver mirror. It should be noted that there are a huge number of substances that do not belong to aldehydes, but they are also able to enter the specified reaction. To identify these compounds, another qualitative reaction to aldehydes is used — the reaction of the copper mirror. In the interaction of aldehydes with Fehling's reagent having a blue color (an aqueous solution of copper hydroxide, alkali and salts of tartrate acid), the divalent copper is reduced to monovalent. When this falls red-brown precipitate of copper oxide.
Итак, как же осуществляется реакция серебряного mirrors? It would seem that there is nothing simpler: it is enough to heat the ammonia solution of silver with any of the aldehydes (for example, a glucose solution or formaldehyde) in a dish, but this approach is not always crowned with victory. Sometimes we observe the formation of a black suspension of silver in solution, rather than a mirror coating on the walls of glassware. What is the main reason for failure? To obtain 100% of the result, it is necessary to adhere to the reaction conditions, as well as carefully prepare the glass surface.
