Reactions of C₃H₃Cl with H₂, C₃H₄, C₂H₂ and C₂H₄ Behind Reflected Shock Waves

Abstract

Mixtures of propargyl chloride diluted in neon have been studied by dynamic sampling of the reflected shock zone by time-of-flight mass spectrometry. For the C₃H₃Cl system, benzene is detected only in trace amounts as an expected product of reactions involving C₃H₃ radicals; only C₂H₂, C₄H₂ and HCl appear as major products. However, in mixtures of C₃H₃Cl containing H₂, benzene is readily observed. Experiments on a 3% C₃H₃Cl - 5% D₂ mixture reveal a constant temporal HCl/DCl product ratio that is approximately equal to 5. It is proposed that the major channel for C₃H₃Cl dissociation yields HCl and c-C₃H₂ (singlet cyclopropenylidene). In the presence of H₂, c-C₃H₂ reacts exothermically to form the thermally excited adduct C₃H₄* which readily isomerizes to either allene or propyne as predicted by a bimolecular-QRRK calculation. The calculations reveal that formation of allene and propyne account for 89% of the product distribution in the reaction of c-C₃H₂ with H₂. Benzene production is also recorded in mixtures of C₃H₃Cl + allene, C₃H₃CI + propyne, C₃H₃Cl + C₂H₂ and C₃H₃CI + C₂H₄. The products observed in these mixtures over the range 1350 - 1700 K are C₂H₂, C₄H₂, HCl, benzene and trace amounts of C₆H₂. The model utilizes a 36 step mechanism and yields satisfactory agreement between the calculated and experimental results.