Identification of Two Positional Isomers between Ortho-Vanillin and Para-Vanillin by their Inhibitory Effects on a Briggs- Rauscher Oscillator

摘要

A suitable method by means of Briggs-Rauscher (BR) oscillating system as an analytical technique to identify the two positional isomers between ortho-vanillin (OV) and (para-)vanillin (PV) by their different perturbation effects has been proposed in this article. In BR system the macrocyclic Ni- complex, [NiL](ClO4)2 was used as catalyst, in which ligand L is 5,7,7,12,14,14-hexamethyl-1,4,8,11- tetraazacyclotetradeca-4,11-diene. The experimental data has proven that putting equal amount of same concentrations of these isomers (OV and PV) separately into the active BR system could cause the inhibition time (tin). But the tin initiated by OV is higher as compared to the tin produced by PV. Our predication for such different inhibitory effects caused by these isomers may be due to their different existing strength of intermolecular hydrogen-bonding. Furthermore, by plotting tin against the concentration of OV or PV, two linear regression curves were achieved for these two isomers in their concentrations range 2.5 × 10-6 mol L-1 to 4 × 10-5 mol L-1 with correlation coefficients of 0.98, which obviously illustrated the different behaviors of isomers. The perturbation reaction mechanism, involving hydroperoxyl radical (HOO?) on the basis of FCA has been proposed. The description of the proposed mechanism is that these isomers react with hydroperoxyl radical to form a dimeric product (divanillin).