The mechanism and kinetics of the (CH3)6Al2 + O2 reaction and some associated reactions were studied at the CCSD(T)//B3LYP/6–311++(3df,2p) level of theory as well as VTST and RRKM Master Equation calculations. The predicted potential energy surface reveals that the reaction of O2 with TMA dimer has two pathways: one proceeds via a tight transition state with the energy barrier of 27.1 kcal.mol−1 and the other occurs via a loose transition state above the reactants by 9.5 kcal.mol−1, resulting in the formation of the major products, (CH3)2AlOAl(CH3)2OCH3 + CH3. The former, larger radical product was found to be unstable under the ambient condition; it readily fragments to give (CH3)2AlOAl(CH3)OCH3 + CH3 barrierlessly with a small endothermicity, 3.3 kcal.mol−1. (CH3)2AlOAl(CH3)OCH3 was, however, found to be quite stable; its most favorable reaction path taking place by a four-member ring transition state producing CH3-cyc-Al(O)(CH2)Al-CH3 and CH3OH has an energy barrier of 48 kcal.mol−1. The equilibrium constants for the (TMA)2 ⇌ 2TMA reaction at temperatures 100.3, 115, and 155.7 °C were predicted to be 33.3, 92.2, and 1023.7 atm, respectively, agreeing satisfactorily with experimental values, 28.3, 76.7, and 931 atm, respectively, measured by Laubengayer et al. (J. Am. Chem. Soc. 1941, 63, 477). The temperature-dependent rate constants for three investigated reactions have been computed in the range of 300–2000 K and 760 Torr N2. A least-squares analysis of the result for the (TMA)2 + O2 reaction, presented with the modified Arrhenius form, can be written by the expression: k(T) = 2.64 × 10-21T3.08 exp(-9.50 kcal.mol−1/RT) cm3 molecule-1 s−1; T = 300 – 2000 K.
- (CH)Al + O
- Hypergolic phenomenon