Identification of Two Aliphatic Position Isomers between alpha- and beta-Ketoglutaric Acid by Using a Briggs-Rauscher Oscillating System

摘要

This paper reports a novel method for identification of two aliphatic position isomers between alpha-ketoglutaric acid (alpha-KA) and beta-ketoglutaric acid (beta-KA) by their different perturbation effects on a Briggs-Rauscher oscillating system, in which tetraaza-macrocyclic complex [NiL](ClO4)(2) is used as the catalyst. The ligand L in the complex is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacydotetradeca-4,11-diene. The experimental results have shown that addition of alpha-KA into the system does not affect the oscillating patterns, while the presence of beta-KA in a dynamic system influences the oscillatory amplitude. A more interesting feature is that, in the presence of a higher concentration of beta-KA, there are damped oscillations after the initial spike, followed by quenching (more exactly: very small oscillations) of the oscillations before the subsequent regeneration of oscillations. A qualitative approach was thus established by employing a Briggs-Rauscher system for identification of these two isomers. The concentrations of these two isomers that can be distinguished lie over the range between 5.0 X 10(-6) and 2.5 X 10(-3) mol/L. A reaction mechanism based on the FCA model has been proposed. An explanation is that beta-KA reacts with HOO center dot radicals to form acetone, whereas the alpha-KA does not.