The Reaction of Atomic Hydrogen with an Imine: Direct Kinetic Measurements and Computational Studies.

Imines are of interest in the combustion modeling of nitrogen-based fuels such as ammonia, as intermediates in atmospheric oxidation of amines, and may offer a new class of environmentally benign substitutes for perhalogenated reagents. Elementary gas-phase rate constants for the consumption of H atoms by 1,1,1,3,3,3-hexafluoro-2-propanimine were measured over 294-736 K using the laser flash photolysis/atomic resonance fluorescence technique. The results are summarized as 3.0 × 10-11 exp(-14.5 kJ mol-1/RT) cm3 molecule-1 s-1 with a confidence interval of ±13%. These are the first temperature-dependent kinetic experiments on an imine of the form R2C═NH and thereby provide the only validation of transition-state modeling for such systems. Several pathways are feasible; comparison of theory and experiment suggests the dominant channel is addition of H atoms to the nitrogen atom. On this basis, the observations are rationalized quantitatively. Computations also yield the thermochemistry of (CF3)2CNH, with ΔfH298 = -1232 kJ mol-1.