Acetylene catalytic hydrochlorination over mechanically pre-activated K2PdCl4 salt: A study of the reaction mechanism

Mechanical pre-grinding of solid K2PdCl4 in a vibratory micromill under acetylene or propylene atmosphere leads to the formation of catalyst for acetylene hydrochlorination by gaseous HCl. The active sites of the heterogeneous catalyst are Pd(II) chloro complexes with a coordination vacancy, capable reversibly form π-acetylene complexes. The HCl molecules participate in two steps of the reaction: acetylene chloropalladation (rate-limiting step) forming intermediate σ-chlorovinyl Pd(II) derivative and protonolysis of the last one.

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► Pre-grinding of K2PdCl4 under acetylene forms acetylene hydrochlorination catalyst.
► The active sites of catalyst are complexes with a coordination vacancy, [PdCl3]−.
► Participation of HCl in chloropalladation and protodepalladation steps was proved.
► The limiting step is ethyne chloropalladation forming vinyl palladium(II) derivative.