Chlorine-catalysed pyrolysis of 1,2-dichloroethane. Part 1.—Experimental results and proposed mechanism
- 1 January 1982
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 78 (3) , 657-676
- https://doi.org/10.1039/f19827800657
Abstract
Experimental studies of the pyrolysis and chlorination of 1,2-C2H4Cl2 in the presence of small proportions of chlorine, or of chlorine plus nitric oxide, confirm that the main propagating steps between 520 and 620 K are Ċl + C2H4Cl2(DCE) [graphic omitted] Ċ2H3Cl2(R)+ HCl, Ċ2H3Cl2 [graphic omitted] C2H3Cl(VC)+Ċl, Cl2+Ċ2H3Cl2 [graphic omitted] C2H3Cl3(TCE)+Ċl. The initial rates (d[VC]/dt)0 and (d[TCE]/dt)0 decrease together as the vessels age, but k2/k3=γ remains constant at constant pDCE˙γ increases as pDCE is increased, or if inert gases are added, as expected from unimolecular behaviour of k2, and the Arrhenius parameters of γ increase together as pDCE is increased. γ(p) is evaluated for several ranges of pDCE at five temperatures to allow study of k(p) 2 by unimolecular theory in Part 2. The addition of VC lowers (d[VC]/dt)0 through reaction (– 2), and the results are used to evaluate k–2/k1;k–2 is also pressure-dependent. In vessels with fresh surfaces, d[VC]/dt is proportional to pDCE×p0.5 Cl2 for low pCl2 and is independent of added inert gases; in aged vessels, the order in pDCE becomes 0.62, very close to the dependence of γ(p) on pDCE. Calculations of [R]0 and [Ċ]0 from the observed rates and rate constants point to an initiation step Cl2 S → CIS +Ċl and termination by the reverse reaction in fresh-surfaced vessels, where S is a surface site; with aged surfaces, the results point to the same initiation step combined with termination by R + SCl → C2H3Cl3+ S especially at lower temperatures.Keywords
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