The mass spectra of some 2,1,3-benzothiadiazoline and 2,1,3-benzothiadiazine 2,2-dioxides

Although the behaviour of 1H, 2H-2,1,3-benzothiadiazoline 2,2-dioxide is similar to that of sulphoxides in the mass spectrometer in losing a molecule of SO₂, the 1,3-dimethyl derivative loses the radical SO₂H. In addition the radical CH₃SO₂ is lost in a one step process that must involve a methyl migration. The radical SO₂H is also lost from 2,1,3-benzothiadiazine 2,2-dioxides methylated in the 3-position and the hydrogen involved is shown to originate from this methyl group by deuterium labelling. The mass spectra of other 2,1,3-benzothiadiazine 2,2-dioxides are also discussed.