Spectroscopic Analysis on Elementary Reactions of Oxidative Polymerization of 2, 6-Xylenol Catalyzed by Copper Complex

The catalytic cycle of the polymerization of 2,6-xylenol catalyzed by the copper-pyridine complex is divided into four elementary processes, the coordination of the substrate (k₁), the electrontransfer from the substrate to the cupric ion (k₀), the dissociation of the activated substrate (k_d) and the reoxidation of the catalyst (k₀). The rate constant of each elementary reaction was determined by means of the stopped-flow spectrophotometric study of the copper complex, and the detailed mechanism of the catalysis was discussed. From the comparison of rate constants (Table 1), the process involning. either k_e or k_d was considered to be the rate-determining step but the latter could not be measured in the present procedure. It was found that the oxygen molecule was involved in the cupric substrate complex, promoting the k_e process. The rate constants were affected by the components of the solvent. Except for a few cases where solvents having coordinating ability are used, k₁ and k₀ increased and k₀ decreased with the increasing solvent polarity.