Kinetics and Mechanism of Catalytic Acetylene Hydrochlorination with Gaseous HCl on the Surface of Mechanically Activated K2PdCl4

The catalyst for acetylene hydrochlorination with gaseous HCl at room temperature is prepared by mechanical pretreatment of K2PdCl4 in an acetylene atmosphere. The rate-determining step of the reaction is the chloropalladation of pi-coordinated acetylene involving an HCl molecule. As a consequence, the replacement of HCl with DCl brings about a kinetic isotope effect of 2.8 +/- 0.4, which differs substantially from that observed in the protodemetalation of the intermediate palladium(II) chlorovinyl derivative yielding vinyl chloride (6.8 +/- 0.6).