Unraveling the Kinetics and Mechanism of Ethane Chlorination in the Gas Phase

The selective chlorination of ethane to 1,2-dichloroethane offers a promising route for upgrading ethane, yet its efficiency remains constrained by limited mechanistic insights into gas-phase chlorine-radical-mediated pathways, which govern target product selectivity and competing dehydrochlorination side reactions. This work systematically decouples the kinetics of ethane chlorination and chloroethane functionalization under varying Cl₂ concentrations, revealing that chlorine radicals govern product distribution through thermodynamically favored pathways. This results in an interesting phenomenon whereby the product ratio between 1,1-C₂H₄Cl₂ and 1,2-C₂H₄Cl₂ maintains a constant 2:1 stoichiometry regardless of Cl₂ concentration variation. A critical observation is that the rate of all chlorination steps remains independent of alkane concentrations, highlighting the dominant role of chlorine radicals in rate-determining steps. Furthermore, ethylene byproducts are demonstrated to originate from the dechlorination of chlorine-radical-induced 2-chloroethyl radicals derived from chloroethane, rather than the direct dehydrochlorination of chloroethane itself. These insights into the dual role of chlorine radicals-mediating both the chlorination and dehydrochlorination pathways-establish a foundational framework for integrating gas-phase radical chemistry with catalytic engineering strategies to suppress undesired side reactions and enable scalable, selective ethane chlorination.