Cupric acetylide

During the preparatiOTi and processing of cuprous acetylide, attention should be paid to potential contamination by cupric acetylide. This substance is produced by a reaction of acetylene with certain copper salts which may be present as an impurity in the initial cuprous chloride. The material is unstable and highly sensitive to mechanical stimuli, exploding upon heating to 50-70 °C (see Sect. 12.3) [33]. 

Cuprous acetylide may also form spontaneously at places where copper or its alloys come to contact with acetylene. The acetylide does not form with any alloy containing copper but only when the content exceeds maximum allowable copper COTitent specific for the particular alloy. The explosions of laboratory and industrial apparatuses as a result of copper acetylide formation are a subject of many reports [12]. 

Cuprous acetylide is the only acetylide which has been practically used, due to the ease with which it can be ignited by hot wire and by electric charges. It was therefore used as a component of fuse head compositions [13, 33, 51, 52]. Cuprous acetylide was also designed as a catalyst in ethynylation reactions (direct condensation of acetylene and aldehydes or ketones) [53-57]. 

The creation of cuprous acetylide has been suggested as a quantitative method for determination of copper in analytical chemistry [33]. Cuprous acetylide is produced in ammoniacal environments in the presence of hydroxylamine, even at very low concentrations of acetylene gas. It is on the basis of the formation of a brown precipitate of cuprous acetylide that a sensitive method for detection of acetylene was devised [58]. 

According to Fedoroff and Sheffield cupric acetylide was first prepared by Soderbaum by the introduction of acetylene into ammoniacal copper salts [2, 59]. 

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The substance is stable at ordinary temperatures and up to 100°C. Like cupric acetylide it decomposes on being heated in hydrochloric acid (Berthelot [102], Sabaneyev [107]). A solution of potassium cyanide also causes decomposition with the loss of acetylene. Makowka [108] showed that aldehyde-like compounds are formed from cuprous acetylide on reaction with a 30% solution of hydrogen peroxide. 

Care should be taken that cuprous acetylide is not contaminated with cupric acetylide which may occur if the cuprous chloride used for the reaction contains cupric salt. This is of importance since cupric acetylide is unstable and explodes on heating even between 50 and 70°C. It is also more sensitive to impact and friction than cuprous acetylide. The pure cupric acetylide is black or brown. 

Many authors recommend the precipitation of cuprous acetylide in the presence of reducing substances such as hydroxylamine (Ilosvay [111]), S02 (Rupe[112]), hydrazine sulphate (Cattelain [113]), so as to avoid contamination with cupric acetylide. 

The precipitation of cuprous acetylide was introduced into analytical chemistry for the quantitative determination of copper. Since cupric acetylide was dangerous to handle, Makowka [108] worked out a method in which cupric salts are previously reduced, e.g. with hydroxylamine, to cuprous salts, when the acetylide is precipitated. Cuprous salts in a solution of hydroxylamine are employed as reagents for acetylene (e. g. Pietsch and Kotowski [114]). 

The type b) cupric acetylides expl on gentle tapping (sometimes even when touched under soln) with a bright flash and report Co form metallic Cu. This type includes acetylides from Cu borate in strongly alkaline soln and from Cu acetate in acidic and strongly ammoniacal solns Refs l)Beil 1,241 [217] 2)H.G.Soder-... 

Cupric Acetylide. See under ACETYLIDES AND CARBIDES, Vol 1, p A74-R and in this Volume under List of Copper Compounds,pC 516-L... 

Cupric acetylide detonates on heating. However, if the symmetry of its surface film is increased by a partial oxidation of CuC2 into CuO, the compound decomposes on heating without detonation (23). 

Cupric acetylide is used as a detonator. Its applications are very limited, however, because of its high sensitivity to impact or friction. It is susceptible to form and build up upon prolong contact of copper metal with organic vapors. 

Cupric acetylide is much more sensitive to impact and friction than the cuprous salt. Friction heating or mild impact can result in violent explosion. In dry state, its sensitivity is much greater to impact and is flammable. 

Cuprous acetylide darkens when it is stored in the open. The change of color is accompanied by a significant increase in its sensitivity to mechanical stimuli. It is believed that both these phenomena are caused by oxidation of cuprous acetylide to cupric acetylide by oxygen in the atmosphere [45]. 

This reaction was proposed by Polyakov for quantitative analysis of copper acetylides (both cuprous and cupric). In the case of a mixture of cuprous and cupric acetylide only total acetylide content is determined. The analyzed substance is dissolved in a solution of potassium cyanide (cupric acetylide is also dissolved... 

Cupric acetylide is a gray-black colored substance. Depending on the method of preparation it may be produced as an amorphous substance, or as the so-called metallic, an extremely sensitive form. Cupric acetylide explosively decomposes if... 

Unlike cuprous acetylide, both forms of cupric acetylide are highly sensitive substances. Cupric acetylide may be initiated by a weak mechanical stimulus such as tapping [50]. It retains a high level of sensitivity even under water [45]. Cupric acetylide is further unstable and can explode on heating, even at temperatures as low as 50-70 °C according to Urbahski [33] or at 100-120 °C according to Morita [45]. 

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