Unimolecular Fragmentation of CH 3 NH 2 : Towards a Mechanistic Description of HCN Formation

The mechanism of the consecutive fragmentation of methylamine, CH 3 NH 2 , is studied by means of neutralization‐reionization mass spectrometry (NRMS), labeling experiments, and calculations employing density functional theory. It is shown that under the conditions of NRMS the fragmentations proceed by a radical mechanism that involves four distinct X–H bond cleavages (X = C, N). In the first step, a hydrogen atom is eliminated from the methyl group; next, homolytic cleavage of an N–H bond occurs. The so‐formed CH 2 NH intermediate then, in competition, releases a hydrogen atom either from the nitrogen or the carbon part, resulting in the formation of the radicals H 2 CN · and HCNH · , respectively. The reaction sequence is terminated by yet another homolytic bond cleavage to produce HCN. An alternative pathway proceeding by an initial 1,1‐elimination of H 2 from the methyl group of CH 3 NH 2 , followed by a 1,1‐elimination of H 2 from the amino function, is also considered, but found to be more energy‐demanding. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)