Oxidation of 2,6-di-tert-butylphenols to Diphenoquinones Catalysed by Schiff Base-Cu(II) Systems Immobilized on Polymer Support

Abstract

Benzoquinone, diphenoquinones and its derivatives are important intermediates for industrial synthesis of a wide variety of special chemicals, such as pharmaceuticals, dyes and agricultural chemicals. The useful catalyst were obtained by aminolysis of vinylbenzyl chloride/divinylbenzene copolymer with ethylenediamine (1) or urotropine (2) and then modification by salicylaldehyde (1A, 2A) or picolinaldehyde (1B, 2B). The catalytic activity of Cu(II) complexes with Schiff base immobilized on the synthesized supports were tested in the oxidation reaction of 2,6-di-tert-butylphenol (DTBP) to diphenoquinone (PQ) with tertbutylhydroperoxide. The best oxidation degree of DTBP (60-70%) and the selectivity towards PQ (80%) is revealed by Cu(II) complexes with long Schiff base ligands derived from salicylaldimine (1A), which have CuL structure (EPR measurement).

Polymer anchored Schiff base complexes of transition metal ions and their catalytic activities in oxidation of phenol

“…The polymer supported metal complexes found to be more catalytic in selective epoxidation of dienes [28], oligomerization of ethylene [29], decomposition of hydrogen peroxide [30], oxidation of alcohol [31,32] and selective oxidation of aliphatic and aromatic hydrocarbons [31,33] in comparison to homogeneous metal complexes. The length of Schiff base ligands and their types has influenced the loading of metal ions [34] as well as the catalytic activity of metal complexes on polymer supports [35]. The most commonly used ligands on polymer supports are aminomethylpyridine [3,36], phosphines [37,38], diketones [39], multidentate amines [20], salen [40] and hydrazine [41].…”

Synthesis and Structural Studies of Nickel Complex Supported by-ONNO-Tetra Dentate Schiff-Base Ligand: Efficient Catalysts for Oxidation of Phenol

“…[19][20] the activity of catalysts also showed dependence on properties of polymer supports and amount of loaded catalysts. Thermal stability of catalysts is required to be high, if these catalysts have to be applied in high temperature reactions.…”

“…[8] But the recovery of physically linked catalysts has been found to be low in comparison to covalently bound catalysts due to the leaching of catalysts. The oxidation of phenol using unsupported Schiff base complexes of metal ions is reported, [18] but the oxidation of phenol using polymer-supported transition metal complexes was found to be high [19] in the presence of tert-butyl hydroperoxide (t-BHP). In these investigations, the homogeneous cobalt salen complexes have shown poor catalytic activity in comparison to polymer bound cobalt (II) salen complexes.…”

Aspects of Immobilisation of Catalysts on Polymeric Supports

“…Cu(II)L 2 complexes could only be obtained with an excess of ligand. [80] The solid was active in the oxidation with tert-butyl hydroperoxide of 2,6-di tertbutylphenol into diphenoquinone. In a similar way FeA C H T U N G T R E N N U N G (III)L 2 complexes were immobilised on PS with chlorotolyl as pendant groups (Scheme 23, 21).…”