Thermolysis of vinyl chloride in nitrogen; rates and products between 601‐681°C

Abstract

AbstractIn a 10‐15‐fold excess of nitrogen, at normal pressure and with τ ca. 3 s, decomposition of vinyl chloride (VC) sets in at about 550°C. At 680°C about 35% decomposition takes place. Major products in this region are HCl, acetylene, 2‐chlorobutadiene and vinylacetylene (1‐buten‐3‐yne). At higher temperatures formation of tar and soot becomes increasingly important. A reaction mechanism in accord with the experimental facts is proposed and analyzed via thermo‐chemical kinetics. Free‐radical chain processes play a major part, with Cl· atoms as important carriers. H abstraction from VC by Cl· leads to ·CH = CHCl and CH2=CCl radicals, respectively. Their relative rate of formation on a per‐H basis is ca. 1/5 around 620°C. The former lose Cl· to give acetylene. The latter add to VC which leads to 2‐chlorobutadiene irrespective of the site of addition (Scheme 1). Various routes to vinylacetylene are discussed. The formation of other (minor) products such as ethylene and methyl chloride is also rationalized. Added HCl is seen to increase the acetylene/2‐chlorobutadiene product ratio with little effect on the rate of conversion of VC. This is due to reversal of the reaction leading to CH2=CCl radicals, through H‐atom transfer from HCl.