Experimental and mechanistic investigation of an iodomalonic acid-based Briggs-Rauscher oscillator and its perturbations by resorcinol.

Classic Briggs-Rauscher oscillators use malonic acid (MA) as a substrate. The first organic product is iodomalonic acid. Iodomalonic acid (IMA) can serve as a substrate also; thus, the first product in that case is diiodomalonic acid (I(2)MA). Nonoscillating iodination kinetics can be followed by absorbance at 462 nm in acidic KIO(3) so long as IMA is in substantial excess over [I(2)]. At 25 °C, simulations lead to the two most important rate laws, and related rate constant estimates are reported. I(2)MA eventually decomposes by unknown processes, but I(2), O(2), H(2)O(2), and Mn(2+) speed up that decomposition, liberating most of the iodine back to the solution. Resorcinol is an effective inhibitor of oscillations both in MA oscillators and in IMA oscillators. Response of an IMA oscillator to varying amounts of resorcinol is shown herein and is similar to that for MA-based oscillators. The inhibitory effect of resorcinol is diminished by addition of IMA to a MA-based oscillator. The iodination reaction between IMA and resorcinol is too slow (0.043 M(-1) s(-1)) to account for the decreased inhibitory effectiveness of resorcinol. Rather, the decomposition of I(2)MA is responsible for the inhibition decrease.