Acetylene hydrogenation, heat

In industry, methane is used to make methanol, halogenated methanes, ethylene, carbon tetrachloride, chloroform, acetylene, hydrogen cyanide, and methyl chloride. In the form of natural gas, methane is used as a fuel, as a source of carbon black, and as a starting material for the manufacture of synthetic proteins. It is also used in gas-fired utilities and in the home (home heating, gas dryers, and gas cooking). 

Acetylides and fulminates form highly explosive shock- and heat-sensitive salts with many metals. Acetylides are the metal derivatives of acetylene. Hydrogen attached to carbon atoms bearing a triple bond is acidic in nature. It can be substituted by a metal ion to form acetylides, with the general structure M-C=C-M. These substances are made from acetylene, HC=CH, or alkyl acetylene, RC=CH, by passing acetylene gas or aUcyl acetylene vapors over the aqueous solutions of ammoniacal metal salts, as shown in the following reactions ... 

Becently, Skinner et 23,65) have made a series of measurements of the heats of hydrogenation of acetylenic compounds. heats of hydrogenation of some of these compounds containing two acetylenic bonds (diynes) are shown in Table 2. The measurements were made in solution, but have been corrected to the liquid phase, for both reactants and products. 

Compressed or hquefied gases present hazards in the event of fire because the heat wOl cause the pressure to increase and the contama" may rupture (Braka" and Mossman, 1980 Braker et al., 1988 Matheson Gas Products, 1983). Leakage or escape of flammable gases can produce an explosive atmosphrae in the laboratory. Acetylene, hydrogen, ammonia, hydrogen sulfide, propane, and carbon monoxide are especially hazardous. 

In the first method, acetylene is heated with hydrogen fluoride in the presence of a catalyst of mercuric chloride on charcoal at about 40°C to yield vinyl fluoride directly. In the second method, acetylene is treated with an excess of hydrogen fluoride to form difluoroethane which is then pyrolyzed at about 700 C in a platinum tube to give vinyl fluoride, which is separated by distillation under pressure. Vinyl fluoride is a gas, b.p. 72°C. 

There are many compounds in existence which have a considerable positive enthalpy of formation. They are not made by direct union of the constituent elements in their standard states, but by some process in which the necessary energy is provided indirectly. Many known covalent hydrides (Chapter 5) are made by indirect methods (for example from other hydrides) or by supplying energy (in the form of heat or an electric discharge) to the direct reaction to dissociate the hydrogen molecules and also possibly vaporise the other element. Other known endothermic compounds include nitrogen oxide and ethyne (acetylene) all these compounds have considerable kinetic stability. 

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