Electron Ionization Mass Spectrometric study of 5-Benzylidene Rhodanines Differentially Substituted in the Phenyl Ring and 3-Phrnyl Rhodanine

The electron ionization behaviour of 5-benzylidene rhodanines (1-10) and 3-phenyl rhodanine (11) was studied. For each of the 1-10 an efficient loss of mass 87, namely the loss of HNCS and CO molecules, was observed. The compounds containing a hydroxy group at the ortho position to the rhodanine moiety showed also an abundant fragment ion formed by the loss of HNCS. The other phenyl ring substituents did not affect this fragmentation pathway. On the other hand, decomposition of the [M-87]+ _ fragment ion strongly depends on the phenyl ring substitution, e.g. for 5 having a methoxy group at the meta position to the rhodanine moiety, in contrast to its ortho and para correspondents 4 and 6, the loss of the fragments HCO. and H2CO proceeded. 3-Phenyl rhodanine lost the ketene molecule yielding the fragment ion of m/z 167. On the grounds of its decomposition and comparison with reference compound decomposition it was deduced that this ion had the structure of 2-mercaptobenzothiazole.