Spectrophotometric determination of the formation constants of the cupric halogen complexes with 1,3-propanediamine and 1,4-butanediamine in methanol solution and their activity on the oxidative coupling of the 2,6-di-tert-butylphenol

Abstract

In order to understand the effect that diamine ligands induce in the cupric complexes used as catalyst in the oxidative coupling of 2,6-di-tert-butylphenol, a spectrophotometric study of the speciation of copper(II) with 1,3-propanediamine and 1,4-butanediamine both with Cl− or Br− in methanol solution, was carried out at 303K. The formation constants and the individual calculated electronic spectra of each species in methanol solution were obtained. The obtained formation constants for the copper(II)–1,3-propanediamine system are: log β110=6.70±0.06, log β120=11.59±0.09, while for the ternary-chloro or -bromo complexes are log β111=10.23±0.06 and log β111=10.39±0.02, respectively. On the other hand, for the copper(II)–1,4-butanediamine system are log β110=7.44±0.04, log β210=11.07±0.04, log β120=11.86±0.05, log β230=22.53±0.09, though for the ternary systems copper(II)–1,4-butanediamine–chloro or –bromo, the formation constants cannot be determined.A comparative study of the kinetics for the oxidation reaction of 2,6-di-tert-butylphenol, catalyzed using the different cupric complexes with 1,3-propanediamine or 1,4-butanediamine and –chloro or –bromo, has been carried out. The catalytic activity of each complex on the oxidation of 2,6-di-tert-butylphenol was monitored in methanol solution, following the corresponding quinone formation, at 418nm (ε=3.95×104Lmol−1cm−1 at 303K). These kinetic studies indicate that all the copper(II)–1,4-butanediamine complexes, show a remarkable high activity, while the complexes with 1,3-propanediamine are less active although much more active than 1,2-ethylenediamine complexes.