PYROLYSIS OF 1-FUROYL-3-PHENYLTHIOUREAS IN MASS-SPECTROMETRY

Substituent effects on decomposition products of phenyl-substituted 1- furoyl-3-phenylthioureas were investigated, using a mass spectrometer with an indirect sample inlet system. It was demonstrated by means of correlational analysis, using Hammett sigma constants, that the produc t formation (mainly furoyl isothiocyanate, aniline, furamide and pheny l isothiocyanate) is not influenced exclusively by the experimental co nditions (pressure, temperature) but by an intrinsic factor such as th e substituent in the molecule. A good correlation is observed between the ratio of furamide and furoyl isothiocyanate intensities compared w ith the non-substituted compound. The intercept is close to zero and t he slope (b = 0.305) shows that the electron-withdrawing substituents favor the proton migration of the most adjacent NH group to the benzen e ring, very probably through a four-member cyclic transition-state me chanism.