ISOTOPIC EXCHANGE-REACTIONS OF AMINES .2. AMINO-AMIDE PROTON-EXCHANGE IN THE POTASSIUM METHYLAMIDE-METHYLAMINE SYSTEM

The kinetics of the methylamine-potassium methylamide amino proton exchange reaction were studied by 1H NMR as a function of temperature and catalyst concentration. Rates were determined by analysis of the line shapes of both the amino and methyl peaks. The exchange kinetics cannot be described by a single bimolecular rate constant based on solvent and stoichiometric amide concentration. By using published data for the dissociation constant of potassium methylamide in methylamine, we calculated bimolecular rate constants for two catalytically active species in solution: free methylamide ions and potassium methylamide ion pairs. These are at 25°C as follows: k2(free ion) = 1.42 × 109 L·mol-1·s-1, k2(ion pair) = 1.04 × 108 L·mol-1·s-1, with activation parameters ΔH‡ = 12.8 and 10.3 kJ·mol-1 and ΔS‡ = -27 and -57 J·mol-1·K-1, respectively. The NMR spectrum of anhydrous methylamine was recorded as a function of temperature over the range -82 to +75°C. Values of 46.7 and 7.04 Hz, respectively, were found for the 14N-H and H-N-C-H spin coupling constants in methylamine. In addition the spin lifetimes of the methylamine 14N yielded an activation energy for quadrupole relaxation, a parameter characterizing rotational diffusion in the liquid phase, of 8.7 kJ·mol-1. © 1979 American Chemical Society.