The chemical properties of the aldehydes: silver mirror reaction

aldehydes are functional derivatives of hydrocarbons, in the structure where there is a group CO (carbonyl group).For simple aldehydes trivial traditionally stored (historic) name, produced from the name of carboxylic acids which are converted to aldehydes by oxidation.Speaking of the IUPAC nomenclature, the basis for taking the longest chain containing the aldehyde group.Start numbering hydrocarbon chain produced from a carbon atom of a carbonyl group (CO), which itself is the number 1. To name the main hydrocarbon chain is added to the end of the "Al."Since aldegidogruppa located at the chain end, the numeral 1, are generally not written.Isomers of the present compounds due to isomerism hydrocarbon skeleton.

Aldehydes are prepared by several methods: oxo process, alkynes hydration, oxidation and dehydrogenation of alcohols.Preparation of aldehydes from primary alcohols require special conditions, since the organic compounds formed are easily oxidised to carboxylic acid.Aldehydes can also be synthesized by dehydrating the corresponding alcohols in the presence of copper.One major industrial methods for producing aldehydes is the reaction of the oxo synthesis, which is based on the reaction of an 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 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 digalogenoproizvodnyh hydrocarbons.During substitution of halogen atoms on the OH groups of the intermediate is formed so-called heme-diol, which is unstable and is converted in the carboxylic compound with the cleavage of H20.

Chemical property aldehydes - a quality response to silver.During oxidation the aldehydes are converted to carboxylic acid (e.g., S5N11SON + O - S5N11SOON).In any specialized tutorial information can be found that the silver mirror reaction is used for identifying aldehydes.This group of organic substances can be oxidized not only by the action of specific oxidants, but just when stored under the influence of atmospheric oxygen.The ease with which the aldehydes oxidised to carboxylic acid allowed to develop qualitative reactions (silver mirror reaction) to these organic compounds, which makes it possible to quickly and clearly identify the presence of aldehyde in a given solution.

When heated with an ammoniacal solution of silver oxide to the acid aldehyde is oxidized.When this is reduced to metallic silver and is deposited on the walls of the tubes in a dark layer with a characteristic gloss - silver mirror reaction.It should be noted that there are many substances that are not aldehydes but are also able to engage in the above reaction.For the identification of these compounds used another qualitative reaction for aldehydes - the reaction of a copper mirror.When reacting aldehydes with Fehling reagent having a blue color (an aqueous solution of cupric hydroxide, an alkali and acid tartrate salts) of divalent copper is reduced to monovalent.This drops a red-brown precipitate of copper oxide.

So, how the reaction is carried silver mirror?It would seem that nothing could be simpler: just heat in a pot of silver ammonia solution with any of the aldehydes (for example, glucose or formaldehyde), but this approach is not always crowned with victory.Sometimes we see the formation of the black suspension of silver in the solution, not the mirror coating on the walls of the glassware.What is the main reason for failure?For 100% result must adhere to the reaction conditions, and carefully prepare the glass surface.