Study of methylation of nitrogen-containing compounds in the gas phase.

The methyl migration between the protonated N,N-dimethylisopropylamine and other neutral aliphatic amines in the gas phase has been investigated by a hybrid external chemical ionization source ion trap mass spectrometer. Similar reactions have been found in the aqueous solution by Callahan and Wolfenden (J. Am. Chem. Soc. 2003; 125: 310). At the same time, density functional theory (DFT) calculations show that in contrast with the neutral N,N-dimethylisopropylamine, protonated N,N-dimethylisopropylamine is a better methyl donor. These results indicate that protonation promotes the methyl migration between aliphatic amines both in the gas phase and in the aqueous solution. In addition, methyl transfer also exists between the protonated N,N-dimethylisopropylamine and some other nitrogen-containing compounds.