Ethane from thermal decomposition

It has been generally accepted that the thermal decomposition of paraffinic hydrocarbons proceeds via a free radical chain mechanism [2], In order to explain the different product distributions obtained in terms of experimental conditions (temperature, pressure), two mechanisms were proposed. The first one was by Kossiakoff and Rice [3], This R-K model comes from the studies of low molecular weight alkanes at high temperature (> 600 °C) and atmospheric pressure. In these conditions, the unimolecular reactions are favoured. The alkyl radicals undergo successive decomposition by [3-scission, the main primary products are methane, ethane and 1-alkenes [4], The second one was proposed by Fabuss, Smith and Satterfield [5]. It is adapted to low temperature (< 450 °C) but high pressure (> 100 bar). In this case, the bimolecular reactions are favoured (radical addition, hydrogen abstraction). Thus, an equimolar distribution ofn-alkanes and 1-alkenes is obtained. 

In their original paper, Ayscough and Steacie42 claimed that the photolysis was very simple and that only carbon monoxide and hexa-fluoroethane were formed as a result of a reaction of type B. Subsequent work has thrown some doubt on this simple interpretation, nevertheless, the ratio of the quantum yields of carbon monoxide and hexafluoro-ethane was close to unity for a temperature range of 25-300°C. (above which temperature, thermal decompositions become important) and at wavelengths of 3130 A. and 2537 A. No trace of perfluorobiacetyl was found, nor any other product which could arise from the reactions of the trifluoroacetyl radical. 

Thermal decomposition of 1-butene provides a more complex product spectrum than is obtained from either cis- or trans-2-butenes. Between 550° and 760°C in a flow system with nitrogen dilution (3), methane, propylene, butadiene, and ethylene were major products as well as hydrogen, ethane, 1-pentene, 2-pentene, 3-methyl-1-butene, and 1,5-hexa-diene. In studies in a static system (4), cyclohexadienes, benzene, cyclopentene, cyclopentadiene, toluene, orthoxylene, and cyclohexene were observed among the liquid products of the reaction over the temperature range 490°-560°C. 

The thermal decomposition of vinyl thiol, CH2=CHSH, appears to proceed by a molecular mechanism, similar to that of ethane thiol. This conclusion was derived indirectly from the thermal decomposition of ethylene sulfide at 1000 °C vide infra), in a fast flow system in which the major products are C2H4, C2H2 and H2S, the latter two compounds formed in equal quantities if the reaction products are quickly trapped out of the effluent stream, vinyl thiol can be detected. Preliminary results suggest the following steps... 

For such a second-order reaction, a plot of Ijc against t is linear (Fig. 18.7). The factor 2 multiplying kt in this expression arises from the stoichiometric coefficient 2 for NO2 in the balanced equation for the specific example reaction. For other second-order reactions with different stoichiometric coefficients for the reactant (see the thermal decomposition of ethane described on page 755), we must modify the integrated rate law accordingly. 

As observed with the monohydroperoxides (Section D), thermal decomposition of the hydroperoxy bicyclo-endoperoxides from methyl linolenate produced more complex mixtures of volatile compounds than acid decomposition with acidic methanol. The thermal decomposition products included methyl 9-oxononanoate, propanal, 2,4-heptadienal, methyl octanoate, methyl 13-0X0-9,11-tridecadienoate and ethane (Figure 4.25X The acid decomposition products, analysed as the di- and tetramethyl acetals, comprised only propanal, methyl 9-oxononaoate, and malonaldehyde. As with the monohydroperoxides, by thermal decomposition the bicyclo-endoperoxides are cleaved on either side of the hydroperoxide group, whereas by acid decomposition they are cleaved only between the hydroperoxide group and the... 

HD was obtained directly from a one-ton storage container from the U.S. Army Aberdeen Proving Ground chemical stockpile where it had been stored for approximately 40 years. It was determined to be 89.2 area % pure by gas chromatography/mass spectrometry (GC/MS). The major impurity (4.7%) was l,2-bis(2-chloro-ethylthio)ethane, also known as compound Q or sesquimustard. The next in prominence was 1,2-dichloroethane (2.4%), which is probably formed by thermal decomposition of the HD dimer. C6H12CI2S isomers comprised a total of 2.0 area % of the material. These isomers are believed to be sulfonium ion thermal decomposition products [2]. The HD was used as received for all hydrolysis and biodegradation studies. 

Dehydrogenation equilibrium constants for the thermal decomposition of ethane, propane, and butane are given in Fig. 19-4, and the percentage of dehydrogenation that takes place at various temperatures can be estimated from Table 20-18. 

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