EFFECTS OF AMMONIA ON THE PYROLYTIC DECOMPOSITION OF ALKYLALUMINUM AMIDES TO ALUMINUM NITRIDE

The thermal decomposition of the organoaluminum amides, [R(2)AINH(2)]( 3), R = Et and Me, to form AIN and 2RH, have been studied by NMR, IR, TGA, DSC, and other methods. Kinetic studies of the initial stages of the decomposition of the R = Me compound, both in solution and in the condensed phase, indicate a first-order process with an activation ene rgy of 123 +/- 11 kJ/mol. The addition of ammonia is found, qualitativ ely, to markedly increase the rate of decomposition of these amides, w hile leading to more complete elimination of the hydrocarbon, RH. It a lso yields, at higher temperatures, an AW product of higher purity (lo wer carbon content) and improved crystallinity. A mechanism is propose d for the first and second stages of this decomposition in the absence of ammonia. In the first stage (amide --> imide + RH), the heterolyti c opening of the (AIN)(3) rings of the amide is postulated as the rate -determining step, which is followed by attack of the terminal nitroge n on a second (AIN)(3) ring, leading, eventually, to higher oligomeric species. It is postulated that ammonia increases the rate of decompos ition by providing a more facile pathway for ring opening (though dire ct nucleophilic attack on the Al centers); the resultant open-chain sp ecies is then stabilized by adduct formation with the NH3. In addition to increasing the rate of decomposition, the added NH3 can then serve as an additional source of H for RH elimination, thus leading to the more complete elimination of the hydrocarbon and a lower C content in the AIN final product.