Ethylene, very high pressure chemical reactions

Ethylene is quite stable at very high pressures at low temperatures unless a reachon is initiated by some chemical that acts as a catalyst to inihate the polymerizahon reaction. This is another example of a chain reachon, but now we mean it in two senses of the word. 

It all started with a chance observation on 27 March 1933, by Eric William Fawcett and Reginald Oswald Gibson of ICI Research in Winnington, Cheshire, England, who were investigating the effects of very high pressures—above 1000 atmospheres—on chemical reactions [8]. They had started an experiment on Friday 24 March, to react ethylene and benzaldehyde (one of 50 reactions suggested by Sir Robert Robinson, consultant to ICI, Nobel Prize in Chemistry 1947) at 170 °C and a pressure of 1900 atmospheres. On Monday 27 March, 1933, the reactor bomb ... 

Polyethyiene was discovered accidentally by British chemists at imperiai Chemicals Industries (I.C.I.) as an unexpected resuit of experiments on chemical reactions at very high pressures. In 1933, a reaction of benzaidehyde and ethyiene at 170 °C and 1400 atmospheres gave no adducts involving the two reagents and was considered a compiete failure. However, an observant chemist noticed a thin layer of white waxy soiid on the waiis of the reaction vessel used for the experiment. This was recognized as a polymer of ethylene, but additional experiments with ethylene alone to produce the same polymer only resulted in violent decompositions that destroyed the equipment. 

In principle, the chemical reactions of macromolecules should be similar to those of low-molecular-weight substances. Experimentally, however, either degradation is found to occur at very much lower temperatures or, occasionally, there is degradation into different products. The decomposition of poly(ethylene), for example, begins at 200°C lower than that of hexadecane. At 450°C, poly(methyl methacrylate) will be almost completely depolymerized into monomer, methyl methacrylate (Table 23-2). At this temperature, on the other hand, low-molecular-weight primary esters decompose into olefins and acids. The nature of the product also depends on whether the experiment is carried out at atmospheric pressure under nitrogen or under high vacuum (Table 23-3). 

H. R. Linden High temperature pyrolysis of coal with high energy sources seems to follow readily predictable paths similar to hydrocarbon pyrolysis. The effects of pressure, gas atmosphere, reaction time, and the volatile matter" content of the coal bear the same relationship to yields of methane, ethane, ethylene, acetylene, and hydrogen as for simple hydrocarbons. Effective reaction temperature, although not directly measurable, could be estimated by means of a suitable chemical thermometer, such as the C-. H-. -C. H4-H. system which approaches equilibrium very rapidly. As Dr. Given also noted, equating the volatile matter" to the reactive portion of the coal is an oversimplification but adequate for empirical purposes the C H ratio of the coal would probably be more suitable. 

Flammable gas. Very dangerous fire hazard when exposed to heat, flame, or powerful oxidizers. Moderate explosion hazard when exposed to flame and sparks. Explodes on contact with interhalogens (e.g., bromine trifluoride, bromine pentafluoride), magnesium and alloys, potassium and alloys, sodium and alloys, zinc, Potentially explosive reaction with aluminum when heated to 152° in a sealed container. Mixtures with aluminum chloride + ethylene react exothermically and then explode when pressurized to above 30 bar. May ignite on contact with aluminum chloride or powdered aluminum. To fight fire, stop flow of gas and use CO2, dry chemical, or water spray. When heated to decomposition it emits highly toxic fumes of cr. See also CHLORINATED HYDROCARBONS, ALIPHATIC. 

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