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

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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.

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