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Studies in the pyrolysis and flash photolysis of azoethane Sandhu, Harbhajam Singh

Abstract

The pyrolysis of azoethane has been studied in a static system in the temperature range 245 to 308°C., and at initial pressures between 15 and 110 mm. using gas chromatographic analysis. In the initial stages of the reaction, products identified are methane, ethane, ethylene, propane, propylene, n-butane, nitrogen and di- and tri- ethyl amines. At large extents of the reaction radical-olefin reactions occur extensively and produce a complex distribution of products. Compounds containing carbon, hydrogen and nitrogen are also formed at higher percentage decompositions. The orders of formation of major products with respect to azoethane, as well as activation energies, have been determined. The activation energy for the initiation reaction C₂H₅N₂C₂H₅ → 2 Ċ₂H₅ + N₂ has been found to be 47.2 ± 1.0 kcal per mole. The effects of additives such as cis-butene-2, butene-1 and carbon dioxide on the initial rates of formation of various products have been investigated. All the additives have a common effect of lowering the initial rate of formation of ethane. Increase in surface: volume ratio has the effect of lowering the time rate of pressure change by 10 to 20% and this has been attributed to the increased surface recombination of radicals. The rate of formation of ethane is also decreased in the packed reaction vessel. This study has pointed out that there is a short chain in the thermal decomposition of azoethane due to the formation and subsequent decomposition of CH₃ĊH-N=N-CH₂CH₃ radical. A mechanism has been proposed for the pyrolysis of azoethane which accounts qualitatively for the nature and distribution of products. The flash photolysis of azoethane has also been investigated at room temperature in pyrex and quartz reaction vessels. Thermally equilibrated radicals are produced in the pyrex cell with outer pyrex jacket. Addition of large amounts of carbon dioxide in the flash photolysis of azoethane decreases the product yields indicating the collisional deactivation of excited azoethane molecules. The ratio of ethyl radicals disproportionation to combination has been found to be 0.12 ± 0.02. Reactions have been postulated to account for the products of flash photolysis of azoethane.

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