Copper acetylenide is an organometallic binary compound. This formula has been known to science since at least 1856. In crystals, forms a monohydrate with the formula Cu 2 C 2 Ć H 2 O. Thermally unstable, explodes when heated.
Structure
Copper acetylenide is a binary compound. It is possible to conditionally distinguish in it a negatively charged part ā the C 2ā2 anion, and a positively charged ā Cu + Cu cations. In fact, such a division is arbitrary: in the compound there is only a fraction of the ionic bond, although it is larger in comparison with the HCā” bond. But this bond also has a very strong polarity (as for covalent bonds) due to the fact that a carbon atom with a triple bond is in sp hybridization - its relative electronegativity is greater than in hybridizations sp 3 (single bond) or sp 2 (double bond ) This is what allows carbon in acetylene to relatively easily detach a hydrogen atom from itself and replace it with a metal atom, that is, exhibit properties inherent in acids.
Getting
The most common method for producing copper acetylenide in a laboratory is by passing gaseous acetylene through an ammonia solution of copper (I) chloride. The result is an insoluble precipitate of reddish acetylide.
Instead of copper (I) chloride, its hydroxide Cu 2 O can also be used. In both cases, it is important that the reaction actually proceeds with the ammonia complex of copper.
Physical properties
Pure copper acetylide is dark red-brown crystals. In fact, it is a monohydrate - in the precipitate, one molecule of water corresponds to each acetylide molecule (written as Cu 2 C 2 Ć H 2 O). Dry copper acetylenide is explosive: it can detonate when heated (it is less thermally stable than silver acetylenide), as well as under mechanical stress, for example, upon impact.
On this occasion, there is an assumption that copper pipes in chemical plants carry a great danger, since acetylenide is formed inside during prolonged use, which can then lead to a strong explosion. This is especially true for the field of petrochemistry, where copper, as well as its acetylenides, are also used as catalysts, which increases the level of risk.
Chemical properties
We have already said that carbon with a triple bond in acetylene is much more electronegative than, for example, carbon with a double bond (as in ethylene) or single (in ethane). The ability of acetylene to react with certain metals, giving off a hydrogen ion and replacing it with a metal ion (for example, the reaction of the formation of sodium acetylenide during the interaction of acetylene with metallic sodium) confirms this. We call this ability of acetylene one of the acid properties in accordance with the Bronsted-Lowry theory: according to it, the acidity of a substance is determined by its ability to detach a proton from itself. The acidity of acetylene (also in copper acetylenide) can be considered relative to ammonia and water: during the interaction of the metal amide with acetylene, acetylenide and ammonia are formed. That is, acetylene gives off a proton, which characterizes it as a stronger acid than ammonia. In the case of water, copper acetylenide decomposes, forming acetylene - it takes the proton of water, showing itself to be a less strong acid than water. So, in the relative range of acidity (according to Bronsted - Lowry), acetylene is a weak acid, located somewhere between water and ammonia.
Copper (I) acetylenide is unstable: in water (as we already know) and in acid solutions it decomposes with the release of acetylene gas and a red-brown precipitate - copper oxide (I) or a white precipitate of copper (I) chloride if diluted with hydrochloric acid solution .
To avoid explosion, the decomposition of acetylenide is carried out by gentle heating in the wet form in the presence of a strong mineral acid, for example diluted nitric acid.
Using
The reaction of the formation of copper (I) acetylenide can be of high quality for the detection of terminal (with a triple bond at the end) alkynes. An indicator is the precipitation of an insoluble red-brown precipitate of acetylenide.
In large-scale production - for example, in petrochemistry - copper (I) acetylenide is not used, since it is explosive and unstable in water. However, several specific reactions in the so-called subtle synthesis are associated with it.
Copper (I) acetylenide can also be used as a nucleophilic reagent in organic synthesis. In particular, it plays an important role in the synthesis of polyins - compounds with several alternating triple and single bonds. Acetylenides of copper (I) in an alcohol solution are oxidized by atmospheric oxygen, condensing with the formation of diines. This is the Glaser-Ellington reaction, discovered in 1870 and later improved. Copper (I) here plays the role of a catalyst, since it is not consumed in the process.
Later, instead of oxygen, potassium hexacyanoferrate (III) was proposed as an oxidizing agent.
Ellington has improved the method of producing polyins. Instead of the alkynes and salts of copper (I) initially introduced into the solution, for example, chloride, he proposed taking copper (II) acetate, which would oxidize the alkine in the medium of another organic solvent, pyridine, at a temperature of 60-70 Ā° .
Such a modification made it possible to obtain much larger and more stable molecules ā macrocycles ā from dyins.