A study of the catalytic dehydrochlorination of 2-chloropropane in oxidizing conditions

The conversion of 2-chloropropane (2-CP) in the presence of oxygen has been investigated over a number of catalysts including alumina and alumina-supported copper chloride, manganese tungstate, mixed manganese - aluminum oxide, silica - alumina, and ZSM5 zeolite. Dehydrochlorination to propene + HCl is predominant, but other reactions such as oxychlorination to deeper chlorided compounds, cracking, oligomerization, and aromatization can occur. On silica - alumina, a selectivity to propene approaching 100% is found and very high conversion can be obtained above 400 K. Over this catalyst the reaction kinetics is found to be zero order in 2-CP with an activation energy near 14.5 kcal/mol. 2-CP converts definitely faster than 1-chloropropane. FT-IR spectroscopy shows that the molecular adsorption of 2-CP is fast and reversible at low temperature, while a nucleophilic substitution occurs to give strongly adsorbed 2-propoxide species starting from near 373 K. The elimination reaction of 2-propoxide to gas-phase propene occurs slowly just near 400 K. The desorption of HCl is also observed to be quite fast in this low-temperature range. FT-IR and kinetic data suggest that the rate - determining step is associated with the elimination reaction from 2-propoxides to propene occurring via an E1-type mechanism through a secondary carbenium ion.