Reactions of group III metalalkyls in the gas phase. Part 4.—Kinetics of the homogeneous dimerization of ethylene to 1-butene, catalyzed by gaseous triethylaluminium

Abstract

The kinetics of the homogeneous dimerization of ethylene into but-1-ene, catalyzed by triethyl-aluminium (Alet₃) in the gas phase was studied in Teflon coated reactors for temperatures ranging between 160 and 233°C. The only significant side reaction is the isomerization of but-1-ene to but-2-ene. The reaction is second order in ethylene pressure and the catalyst Alet₃, can practically quantitatively be recovered from the product mixture. Consistent second order rate constants have been obtained despite large variations in the individual reaction parameters, yielding the Arrhenius relationship log k₁(l. mol^–1 s^–1)=(6.15 ± 0.68)–(16.3±1.5)/θ where θ equals 4.58 × 10^–3T in kcal mol^–1 or log k(l. mol^–1 s^–1=(6.15 ± 0.68)–(6.82 ± 0.63)/θ where θ equals 1.914 × 10^–3T in kJ mol^–1). The rate controlling step is the addition of ethylene to Alet₃ to form n-butyl-diethyl-aluminium and the detailed reaction mechanism involves the establishment of a pre-equilibrium between Alet₃ and ethylene to form a Alet₃· C₂H₄π-complex prior to the formation of the four-centre cyclic transition state.