THE EFFECTS OF RING MODIFICATION ON THE MASS-SPECTROMETRIC FRAGMENTATION OF SOME 2,3-DIARYL-1,3-THIAZOLIDIN-4-ONES UNDER ELECTRON-IMPACT

The effects of ring modification on the mass spectral fragmentations o f 2,3-diaryl-1,3-thiazolidin-4-ones were established by comparing thei r spectra with those of their S-oxides and with compounds in which the aromatic groups at C(2) or N(3) had been replaced by non-aromatic sub stituents. 3-Benzyl-2-phenyl-1,3-thiazolidin-4-one and 3-butyl-2-pheny l-1,3-thiazolidin-4-one gave mass spectra which differed from those of the diaryl compounds in ways which could largely be accounted for by the absence of N-aryl p-pi overlap and by the stability of the benzyl ion formed from the former compound. 3-Phenyl-2-thioxo-1,3-thiazolidin -4-one was found to break down to give ions analogous to those formed in the spectra of the diaryl compounds and by loss of ketene or of a h ydrogen atom from the molecular ion. Generally, the loss of oxygen fro m the molecular ions of the sulphoxides was not important in their mas s spectra. Instead, their fragmentation was found to occur mainly by f ormation of the protonated form of the Schiff base and by cleavage of the N-aryl bond to give an aryl ion. The sulphone phenyl)-3-phenyl-1,3 -thiazolidin-4-one-1,1-dioxide appeared to be less stable than the cor responding sulphoxide and was found to lose sulphur dioxide from its m olecular ion.