Aldehydes are functional derivatives of hydrocarbons in the structure of which there is a CO group (carbonyl group). For simple aldehydes, trivial (historical) names are traditionally preserved, derived from the name of carboxylic acids, into which aldehydes are converted during oxidation. If we talk about the IUPAC nomenclature, then the longest chain containing the aldehyde group is taken as the basis. The numbering of the hydrocarbon chain starts from the carbon atom of the carbonyl group (CO), which itself gets the number 1. The ending “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.
Aldehydes are obtained in several ways: oxosynthesis, hydration of alkynes, oxidation and dehydrogenation of alcohols. The preparation 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 dehydration of the corresponding alcohols in the presence of copper. One of the main industrial methods for producing aldehydes is the oxosynthesis reaction, 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. The indicated reaction proceeds in the liquid or in the gas phase according to the scheme: RCH = CH2 + C0 + H2 - RCH2CH2C0H + RCH (CH) 3C0H. Aldehydes can be prepared by hydrolysis of dihalogenated hydrocarbons. In the process of substitution of halogen atoms for OH groups, the so-called hemi-diol is formed in an intermediate form, which is unstable and turns into a carboxyl compound with H20 cleavage.
The chemical property of aldehydes is a 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 a silver mirror is used to identify aldehydes. The specified group of organic substances can be oxidized not only under the action of special oxidizing agents, but also simply when stored under the influence of atmospheric oxygen. The ease with which aldehydes are oxidized to carboxylic acids has made it possible to develop high-quality reactions (silver mirror reactions) to these organic compounds, which makes it possible to quickly and clearly determine the presence of aldehyde in a particular solution.
When heated with an ammonia solution of silver oxide, the aldehyde oxidizes to acid. In this case, silver is reduced to metallic and deposited on the walls of the test tube in the form of a dark layer with a characteristic mirror shine - the reaction of a silver mirror. It should be noted that there are a huge number of substances that are not related to aldehydes, but they are also able to enter into this reaction. To identify these compounds, another qualitative reaction to aldehydes is used - the reaction of a copper mirror. When aldehydes interact with the Feling reagent, which has a blue color (an aqueous solution of copper hydroxide, alkali and salts of tartrate acid), copper from bivalent is reduced to monovalent. In this case, a red-brown precipitate of copper oxide precipitates.
So, how is the reaction of the silver mirror? It would seem that there is nothing simpler: it is enough to heat an ammonia solution of silver with any of the aldehydes in a dish (for example, glucose solution or formaldehyde), but this approach is not always crowned with victory. Sometimes we observe the formation of a black suspension of silver in the solution, rather than a mirror coating on the walls of glassware. What is the main reason for failure? To obtain a 100% result, it is necessary to adhere to the reaction conditions, as well as carefully prepare the glass surface.