Pyrolysis of diallyl oxalate vapour. Part 1.—Kinetics of the unsensitized decomposition

Abstract

The unsensitized thermal decomposition of the vapour of diallyl oxalate has been studied in a fused quartz cell between 130 and 190°C. The products are consistent with the formation of allyl radicals in the primary dissociation: (COOC₃H₅)₂→ 2CO₂+ 2C₃H₅·; k₁= 10^{14 ± 1} exp(–40 ± 3) 10³/RT sec^–1 This system is well suited to the study of the reactions of the allyl radical as its rate of generation is equal to the rate of formation of carbon dioxide and no other radical is present in significant amount. The ratio of mutual disproportionation to mutual combination of allyl radicals is given by the corresponding ratio of rate constants : k₃/k₂= 0.008. Arrhenius parameters were estimated for the slow metathesis between the allyl radical and diallyl oxalate. Decomposition of pure liquid diallyl oxalate was detected at 120°, and was accompanied at 160° by the slow formation of an insoluble polymer. Cyclohexadiene-1,4 acts as a scavenger of allyl radicals in the vapour and liquid phases.