Fast atom bombardment induced ring rupture of silatranes

During a comparison study of the fast atom bombardment (FAB) and electron impact mass spectra of 1-organyl-2,9,10-trioxa-6-aza-1-silatricyclo4.3.3.0^1,6]dodecanes, an unusual ion peak at m/z 164 was noticed in the FAB spectra. Accurate mass measurement indicated that m/z 164 corresponds to protonated 1-N,N-bis(2-hydroxyethyl)amino]-1-propanol (BHAP), which is produced by a ring-rupture reaction. Further experiment showed that the intensity of the BHAP + H]⁺ ion peak increased markedly as the 7keV Ar⁰ bombardment proceeded, suggesting a FAB-induced reaction. The possible mechanism is also discussed.