A Shock Tube Study of the Decomposition Mechanism of Chloroform in the Presence of Deuterium or Methane

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Abstract
Chloroform was pyrolyzed in the absence and in the presence of one of three additives—D2, CH4, and CD4, over the temperature range of 1000–1200 K in a single-pulse shock tube. The main products of the decomposition of chloroform by itself were tetrachloroethylene and hydrogen chloride. On the other hand, tetrachloroethylene, trichloroethylene, dichloromethane, and hydrogen chloride were the major products in the presence of D2, while in the chloroform–methane systems they were tetrachloroethylene, trichloroethylene, 1,1-dichloroethylene, vinyl chloride, ethane, and hydrogen chloride. From the deuterium distribution of the products, as determined by mass spectrometry, it is found that the hydrogen atoms of trichloroethylene and 1,1-dichloroethylene mainly came from chloroform and methane respectively, while the hydrogen atoms of vinyl chloride came from both chloroform and methane. The change in the product distribution resulting from the addition of deuterium or methane and the hydrogen isotopic distribution suggest that the mechanism is composed of Cl atom elimination in the initiation step and successive reactions involving “hot” molecule reactions. The hydrogen isotopic distribution of vinyl chloride may indicate that the three-centered hydrogen elimination (αα) process competes with the four-centered (αβ) process in the decomposition of “hot” 1,1-dichloroethane.

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