Heavy metal acetylides

Heavy metal acetylides test for terminal alkynes... 

Nitrogen halides are destroyed with cold base. Azides and fulminates-may often be destroyed with acid, while heavy metal acetylides are decomposed by ammonium sulfide. The removal of peroxides by reduction has been described above. 

Heavy metal acetylides, particularly cuprous acetylide (CuC CH), catalyze the addition of acetylene (HC=CH) to aldehydes (RCH=0). 

Alkynylsilver compounds are readily accessible from AgN03 and HC=CR in methanol or water in the presence of base. They are thermally stable. Like many heavy metal acetylides, silver compounds of unsubstituted acetylene are shock sensitive and explosive. 

If allowed to dry, these heavy metal acetylides are likely to explode. They should be destroyed while still wet by warming with nitric acid the strong mineral acid regenerates the weak acid, acetylene. 

Although stoichiometric ethynylation of carbonyl compounds with metal acetylides was known as eady as 1899 (9), Reppe s contribution was the development of catalytic ethynylation. Heavy metal acetylides, particulady cuprous acetylide, were found to catalyze the addition of acetylene to aldehydes. Although ethynylation of many aldehydes has been described (10), only formaldehyde has been catalytically ethynylated on a commercial scale. Copper acetylide is not effective as catalyst for ethynylation of ketones. For these, and for higher aldehydes, alkaline promoters have been used. 

Phenylacetylene can be distinguished from styrene by the former s ability to form a heavy metal acetylides. The acidic acetylenes such as phenylacetylene react with certain heavy metal ions, chiefly Ag and Cu+, to form insoluble acetylides. The reaction is indicated by the formation of a precipitate. Styrene will not form this precipitate if placed in a solution such as Ag(NH3)20H or Cu(NH3)20H. 

Explain why alkynes are more acidic than alkanes and alkenes. Show how to generate nucleophilic acetylide ions and heavy-metal acetylides. 

Rubber-covered electric cable, used as a makeshift handle in the effluent pit of an acetylene plant, formed copper acetylide with residual acetylene and the former detonated when disturbed and initiated explosion of the latter. All heavy metals must be rigorously excluded from locations where acetylene may be present. 

Kabanov, A. A. etal., Russ. Chem. Rev., 1975, 44, 538-551 Application of electric fields to various explosive heavy metal derivatives (silver oxalate, barium, copper, lead, silver or thallium azides, or silver acetylide) accelerates the rate of thermal decomposition. Possible mechanisms are discussed. 

This class of compounds showing explosive instability deals with heavy metals bonded to elements other than nitrogen and contains the separately treated groups GOLD COMPOUNDS LEAD SALTS OF NITRO COMPOUNDS LITHIUM PERALKYLURANATES MERCURY COMPOUNDS METAL ACETYLIDES METAL FULMINATES METAL OXALATES PLATINUM COMPOUNDS PRECIOUS METAL DERIVATIVES SILVER COMPOUNDS... 

The heavy metal salts of acetylene have the properties of primary explosives, but only cuprous acetylide was found to be satisfactory for practical use. 

Acetylene gas and the acetylide salts of heavy metals silver and copper acetyl-ides are extremely shock-sensitive. Polyacetylenes and some halogenated acetylenes. 

Cadmium propionate, 2412 Calcium acetylide Methanol, 0582 Diazomethane Calcium sulfate, 0405 3,5-Dinitrotoluamide, 2936 Lithium tetrahydroaluminate Dioxane, 0075 Magnesium perchlorate, 4078 Magnesium Methanol, 4685 Mercury(II) thiocyanate, 0975 Silicon dioxide Hydrochloric acid, 4833 Sodium azide Heavy metals, 4753 Sodium Halocarbons (reference 10), 4790... 

SAFETY PROFILE The carbon-carbon triple bond is explosively unstable in many acetylenic compounds. Both the lower alkynes (i.e., propyne, butadyne, etc.) and higher compounds may undergo explosive decomposition. The presence of halogens and heavy metal derivatives may increase these explosive tendencies. See also ACETYLENE, ACETYLIDES, and specific compounds. 

It is sometimes necessary to protect active sites of acetylenic compounds to achieve the desired reactions. Acetylenic compounds that have an active hydrogen tend to react with heavy-metal salts to form explosive metal acetylides. However, when treated with potassium mercuric tetraiodide or mercuric acetate in organic amines, monosubstituted terminal ethynyl compounds give stable crystalline mercuric salts. These mercuric salts can be purified by recrystallization in organic solvents and used for identification. They can be further converted to lithium acetylides, which are useful tools for chemical synthesis [Eq. (62) 156]. 

The acidic acetylenes react with certain heavy metal ions, chiefly Ag" and Cu, to form insoluble acetylides. Formation of a precipitate upon addition of an alkyne to a solution of AgN03 in alcohol, for example, is an indication of hydrogen attached to triply-bonded carbon. This reaction can be used to differentiate terminal alkynes (those with the triple bond at the end of the chain) from nonterminal alkynes. 

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