Homogeneous catalysis by Pt(II)–Sn(II) chloride complex. Part 1.—Kinetics and mechanisms of the hydrogenations of acetylene and ethylene

Abstract

Detailed kinetics of the hydrogenation of acetylene and ethylene catalyzed by methanolic solutions of Pt(II)–Sn(II) chloride complexes have been studied within a temperature range 0 to 20°C and at pressures up to 100 Torr. Initial rates of hydrogenation exhibit maxima in terms of Sn to Pt atomic ratio or catalyst concentration, expressed by ν=kK_hcP_hcP_h/(1 +K_hcP_hc) for fixed Sn/Pt = 10, where P_h and P_hc are pressures of hydrogen and hydrocarbon respectively, and k and K_hc are constants. Acetylene is consecutively hydrogenated to ethane via ethylene as an intermediate. In the reaction of C₂H₂ or C₂H₄ with D₂ in CH₃OH, hydrogen atoms in the hydrocarbon are hardly substituted with deuterium, and C₂H₄ or C₂H₆ is produced predominantly. Acetylene-d₂ also hardly exchanges its D-atoms in the reaction with H₂ in CH₃OH and cis-C₂H₂D₂ is formed preferentially, while the exchange proceeds to a considerable extent in the case of C₂D₄.

These results are interpreted in terms of heterolytic splitting of hydrogen, competitive coordination of acetylene and ethylene, and successive reactions with hydride and protonic hydrogens.