Acetylides decomposition

Silver acetylide decomposition was studied [679] by X-ray diffraction and microscopic measurements and, although the a—time relationship was not established, comparisons of intensities of diffraction lines enabled the value of E to be estimated (170 kj mole 1). The rate-limiting step is believed to involve electron transfer and explosive properties of this compound are attributed to accumulation of solid products which catalyze the decomposition (rather than to thermal deflagration). 

An ethynylation reagent obtained by decomposition of lithium aluminum hydride in ethers saturated with acetylene gives a satisfactory yield of (64), Best results are obtained with the lithium acetylide-ethylene diamine complex in dioxane-ethylenediamine-dimethylacetamide. Ethynylation of (63) with lithium acetylide in pure ethylenediamine gives (64) in 95% yield. 

Explosions involving flammable gases, vapours and dusts are discussed in Chapter 5. In addition, certain chemicals may explode as a result of violent self-reaction or decomposition when subjected to mechanical shock, friction, heat, light or catalytic contaminants. Substances containing the atomic groupings listed in Table 6.7 are known from experience to be thermodynamically unstable, or explosive. They include acetylides and acetylenic compounds, particular nitrogen compounds, e.g. azides and fulminates, peroxy compounds and vinyl compounds. These unstable moieties can be classified further as in Table 6.8 for peroxides. Table 6.9 lists a selection of potentially explosive compounds. 

A calcium carbide/stannous mixture combusted. Could it be the exothermic decomposition of a tin acetylide ... 

Alone, or Metals, or Metal compounds Mellor, 1940, Vol. 8, 327 1967, Vol. 8, Suppl. 2.2, 84, 96 It is an explosive of positive oxygen balance, less stable than ammonium nitrate, and has been studied in detail. Stable on slow heating to 300°C, it decomposes explosively on rapid heating or under confinement. Presence of zinc, copper, most other metals and their acetylides, nitrides, oxides or sulfides cause flaming decomposition above the m.p. (70°C). Commercial cobalt (cubes) causes an explosion also. 

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. 

Explosibility. Liquid ethylene oxide is stable to detonating agents, but the vapor will undergo explosive decomposition. Pure ethylene oxide vapor will decompose partially however, a slight dilution with air or a small increase in initial pressure provides an ideal condition for complete decomposition. Copper or other acetylide-forming metals such as silver, magpesium, and alloys of such metals should not be used to handle or store ethylene oxide because of the danger of the possible presence of acetylene. Acetylides detonate readily and will initiate explosive decomposition of ethylene oxide vapor. In the presence of certain catalysts, liquid ethylene oxide forms a poly-condensate. 

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. 

Muraour, Effect of Electron Impact Upon Lead Azide and Silver Acetylide-Theoretical Observations Upon the Thermal Decomposition of Explosives , Chim Ind 30, 39- 40 (1933)... 

See other IRRADIATION DECOMPOSITION INCIDENTS, SILVER COMPOUNDS See related METAL ACETYLIDES... 

Pyrophoric in air, explosive decomposition with water, and the sodium salt is similar. See entry COMPLEX ACETYLIDES... 

Violent decomposition occurred during attempted distillation. See related ALKYLMETALS, METAL ACETYLIDES... 

This replacement-of-solvent operation should not be carried out with Li- or NaC=COC2H5 and Li- or NaCsCCl (danger of vigorous decomposition or even explosion ) or acetylides with the structure MCsCChCCI R or MC=CCH=CHCH2R (increased risk of isomerization processes). 

Fig. 16.30. Pd(0)-catalyzed arytation of a copper acetytide at the beginning of a three-step synthesis of an ethynyt aromatic compound. Mechanistic details of the C,C coupling Step 1 formation of a complex between the catalytically active Pd(0) complex and the arylating agent. Step 2 oxidative addition of the arylating agent and formation of a Pd(II) complex with a cr-bonded aryl moiety. Step 3 formation of a Cu-acetylide. Step 4 trans-metalation the alkynyl-Pd compound is formed from the alkynyl-Cu compound via ligand exchange. Step 5 reductive elimination to form the -complex of the arylated alkyne. Step 6 decomposition of the complex into the coupling product and the unsaturated Pd(0) species, which reenters the catalytic cycle anew with step 1.

An alternative approach for alkynyl carboxylates involved reaction between [bis(acyloxy)iodo]benzenes and lithium acetylides [59]. Alkynyl iodonium salts afforded with sodium carboxylates in the presence of water 1-acyloxyketones heating in an excess of acetic acid gave similarly a-acetoxy ketones [60], Alkynyl tosylates and mesylates were obtained from the thermal decomposition of isolable alkynyl iodonium sulphonates. 

Copper. The compound Cu2C2 is formed readily from ethyne and sources of copper(I) in aqueous or aqueous ammoniacal solution as an explosive orange monohydrate, or from Cu2I2 and KC=CH in liquid ammonia as dark red crystals.193-195 It is also formed by decomposition of orange CuC=CH above —45°, or from the reaction between CuCl and [C6H3(CH2NMe2)2-2,6]Pt 2C2.190 The acetylide is insoluble in all solvents with which it does not react with HC1 or KCN solutions, ethyne is liberated. If copper(II) salts are used, red CuC2 is formed. 

Complexes Cu(C=C-C=CPh)(PR3),i have also been prepared and are claimed to be more stable to aerial decomposition than the mono-acetylide complexes (72). 

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. 

OSHA PEL TWA 2 mg(Sn)/m3 ACGIH TLV IW A 2 mg(SnVm3 SAFETY PROFILE Poison by ingestion, intraperitoneal, intravenous, and subcutaneous routes. Experimental reproductive effects. Human mutation data reported. Potentially explosive reaction with metal nitrates. Violent reactions with hydrogen peroxide, ethylene oxide, hydra2ine hydrate, nitrates, K, Na. Ignition on contact with bromine trifluoride. A vigorous reaction with calcium acetylide is initiated by flame. When heated to decomposition it emits toxic fumes of Cl. See also TIN COMPOUNDS. 

McCowan [38] used electron microscopic and X-ray measurements to study the thermal decomposition of silver acetylide. Although detailed or-time relationships could not be established, the value of was estimated to be 170 kJ mol in the interval 388 to 408 K. The rate-limiting step was identified as the production of an electron and an acetylide radical that react fiirther to yield amorphous carbon. Decomposition is catalyzed by the product, probably metallic silver, and explosion was ascribed to the accumulation of catalyst rather than heat. 

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