Fragmentations of organic negative ions. Mercapto acids and esters. A reinvestigation

Abstract

Thioglycollates and β-thiopropionates with SH and/or CO₂H groups yield pronounced (M-H)^- ions in their negative ion spectra, not molecular negative ions as we previously reported. Compounds containing R¹-S-CH₂- functionality (R¹ = alkyl or aryl) undergo α cleavage to S to yield R¹S- and -S-CH₂-ions. Hydrogen rearrangements are rare but thioglycollates R₁SCH₂CO₂H characteristically eliminate R¹SH to yield CH₂CO₂-. Fragment negative ions generally do not contain enough excess energy to allow decomposition, so we have studied their collision induced dissociations. Simple cleavage reactions are usual: for example BuSCH₂CO₂- decomposes to yield both BuS- and BuSCH₂-. Group migration to sulfur is also observed; for example, ions ^-SCH₂CO₂R² (R² = alkyl or aryl) eliminate carbon dioxide to produce R²SCH₂- as the major product.