Collisionally-induced dissociation mass spectra of organic sulfate anions

Abstract

The collisionally-induced dissociation mass spectra of a variety of organic sulfate ester anions are described and mechanistically rationalized. A cyclic syn-elimination pathway, analogous to that of the Cope elimination, is postulated for the commonly observed formation of bisulfate anion (HSO₄⁻, m/z 97). Deuterium labeling experiments confirm that the proton transferred to oxygen during bisulfate elimination normally originates from the C-2 position, although examination of the spectra of polyfunctional steroids reveals that the proton abstracted may originate from more distant sites as well. Adamantyl, phenyl, and vinyl sulfate anions, which do not readily lend themselves to a cyclic syn-elimination, do not give rise to an m/z 97 ion. Instead, these sulfates undergo both heterolytic and homolytic S–O bond cleavages to yield an m/z M − 80 anion, resulting from loss of neutral SO₃, as well as an ion at m/z 80, corresponding to SO₃⁻˙, respectively. Sulfates that can give rise to a resonance stabilized radical by homolytic C–O bond fission, as exemplified by benzyl and linalyl sulfates, can be recognized by the formation of an m/z 96 (SO₄⁻˙) ion.