Chemical oxidation of aniline and N-methylaniline: a kinetic study by Raman spectroscopy.

For the first time, chemical oxidation of aniline and N-methylaniline with dichromate as oxidant has been studied by Raman spectroscopy with 785 nm laser beam excitation, and the suitability of this technique for kinetic study of this process was demonstrated. For both monomers used, a sigmoidal growth of the intensities for most prominent Raman bands was observed, showing a self-accelerating character of this reaction. Self-acceleration appears most clearly expressed for aniline, and for the low oxidant-to-monomer molar ratio used. After reaching their maximum values, the intensities of Raman bands drop almost to zero, most probably due to increase in opacity and optical absorbance of reaction mixture. The kinetics of an increase, and the next following decrease of band intensities depend on the monomer used, and oxidant-to-monomer molar ratio.