Nitrogen Protonation of N-Nitrosodimethylamine

Article abstract of DOI:10.1021/ja00230a029

Evidence for the presence of the Me2N(H)NO⁺ ion at kinetically significant concentrations in aqueous solutions of N-nitrosodimethylamine (NDMA) at pH =/<2 has been found.To obtain this evidence, the methyl group syn to the oxygen of NDMA was selectively deuteriated and the rate of Z <*> E equilibration in the resulting NDMA-d3 was measured by nuclear magnetic resonance spectroscopy as a function of pD.The reaction was first order in +>, with the plot of observed first-order rate constants versus +> having a slope of k/+> =1E-2 M^-1 s^-1 at 3 deg C and an ionic strength of 0.2 M.The observed rate date were used to estimate K_a for N-protonated NDMA as 1E12-1E13 M by assuming that the rates of rotation about the N-N bond in Me2N(H)NO⁺ and of its deprotonation are similar to those for the isoelectronic N-protonated carboxamide function.The trisubstituted nitrogen of the nitrosamine thus appears to be several orders of magnitude less basic than that of the carboxamides.