Catalytic activity of Cu ion-exchanged Na center dot MCM-41 in the liquid-phase oxidation of 2,6-di-tert-butylphenol

The liquid-phase catalytic oxidation of 2,6-di-tert-butylphenol (BOH) was p erformed under mild reaction conditions using a Cu ion-exchanged Na . MCM-4 1 (Cu-Na . MCM-41) catalyst. 4,4'-Dihydroxy-3,3',5,5-tetra-tert-butylbiphen yl (H(2)DPQ) and 3,3',5,5'-tetra-tert-butyl-4, 4'-diphenoquinone (DPQ) were obtained as the oxidation products. The addition of an inorganic base such as KOH onto the Cu-Na . MCM-41 catalyst or to the reaction solution was fo und to cause the increase in the oxidation activity. The oxidation activity of BOH in the presence of KOH in the reaction solution was greater than wh en using the K added Cu-Na . MCM-41 catalyst. The reaction scheme for the B OH oxidation was proposed, in which scheme the DPQ formation involves both a consecutive pathway via H(2)DPQ intermediate and an oxidative dehydrogena tion of a dimer formed by the C-C coupling of the corresponding phenoxy rad icals, without H(2)DPQ intermediate. To study the influence of the mesopore of the Na . MCM-41 on the oxidation of BOH, a comparably bulky molecule, C u ion-exchanged NaZSM-5 (Cu-NaZSM-5) zeolite, whose pens are micro range in size, was attempted as a catalyst for the bulky phenol oxidation. The oxid ation activity of the Cu-NaZSM-5 zeolite was found to be considerably lower than that of the Cu-Na . MCM-41 catalyst. The preference of the mesopore e nvironment for the 2, 6-di-tert-butylphenol oxidation against the micropore counterpart was thus confirmed. (C) 2000 Elsevier Science B.V. All rights reserved.