Me3AlNH3 Formation and Pyrolytic Methane Loss: Thermodynamics, Kinetics and Mechanism
Abstract
The thermodynamics, kinetics, and mechanism of the reactions Me3Al + Ammonia yields Me3AlNH3 yields 1/3 (ME2AlNH2)3 + Methane in homogeneous solution were investigated by solution calorimetry, DSC, and 1H NMR rate measurements. The enthalpy for complex formation from NH3 and monomeric Me3Al in benzene was - 93kJ/mole. The observed Delta H for methane loss from the complex was -82.2 kJ/ mole. Methane loss from Me3AlNH3 was catalyzed by excess Me3Al monomer or monomeric Me2AlNH2 in equilibrium with (Me2AlNH2)2 and (Me2AlNH2)3. A mechanism for the Me2AlNH2 catalyzed reaction involving formation of the methyl-bridged intermediate (mu-Me) (Me2AlNH2) (Me2AlNH3), and subsequent loss of CH4 by proton transfer was proposed. The enthalpy of activation for the autocatalytic reaction was 92.8 kJ/mole. A deuterium isotope effect of 8.8 was measured for this reaction. A similar mechanism was proposed for the Me3Al catalyzed reaction, involving formation of an analogous methyl-bridged species (mu-Me)(Me3Al) (Me2AlNH3) which apparently loses CH4 and closes to metastable (mu-NH2)(mu-Me) Al2Me4. This slowly disproportionates to (Me3Al)2 and Me2AlNH2)3; the autocatalytic path is thus slowed. Delta H for the Me3Al-catalyzed pathway was 113 kJ/mole. The deuterium isotope effect was 5.5. (aw)
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 15, 1990
- Accession Number
- ADA218713
Entities
People
- Frederick C. Sauls
- Leonard V. Interrante
- Zhiping Jiang
Organizations
- Rensselaer Polytechnic Institute