Transient Chemical Oscillations in the 4-(N,N-Dimethylamino) Benzoic Acid-Bromate Reaction

The bromination and oxidation of 4-(N,N-dimethylamino) benzoic acid (DMABA) by acidic bromate was investigated in a batch reactor through following their redox potential and UV/vis absorption spectra, in which transient oscillations with a long induction time were observed. Different from most of the bromate-aromatic compound oscillators reported earlier, the addition of metal catalysts such as manganese, cerium, and ferroin does not significantly affect the nonlinear phenomena, but the induction time could be greatly shortened by adding bromide ions as a starting reagent. The reaction between bromine and DMABA was identified through H-1 NMR spectroscopy to form 3-bromo-4-(N,N-dimethylamino) benzoic acid. The compound 3-bromo-DMABA was also found to occur relatively early during the bromate-DMABA reaction and was determined to be a major component prior to the onset of oscillations. Periodic evolution of 3-bromo-4-(N,N-dimethylamino) benzoic acid has been detected with a UV/vis spectrophotometer.