Investigation of Reaction Steps for the Hydrodechlorination of Chlorine-Containing Organic Compounds on Pd Catalysts

Reaction steps for the reaction of hydrodechlorination on Pd were investigated by means of isotope-exchange experiments. The reversibility of bond scission for the two C–Cl bonds in CF3CFCl2 was investigated by following 37Cl enrichment in the reactant and products. No enrichment of 37Cl was observed in the reactant CF3CFCl2 but the product CF3CHFCl was enriched. Thus, the scission of the first C–Cl bond is irreversible; once the reactant loses the first chlorine it desorbs only as a product. However, after the first C–Cl bond is broken, the second chlorine may be exchanged with the pool of surface chlorine. Isotope exchange experiments between D2 and HCl during hydrodechlorination of CF3CFCl2 showed that the forward rate and reverse rate for the overall reaction H2+2Cl*=2HCl+2* were nearly 400 times faster than the overall hydrodechlorination reaction rate. Thus, this experiment confirms that this step is in quasi-equilibrium.