Oxidation of 2,6-di- tert-butylphenol with tert-butylhydroperoxide catalyzed by cobalt(II) phthalocyanine tetrasulfonate in a methanol–water mixture and formation of an unusual product 4,4′-dihydroxy-3,3′,5,5′-tetra- tert-butylbiphenyl

Abstract

The oxidation of 2,6-di- tert-butylphenol (DTBP) with tert-butylhydroperoxide (Bu t OOH) catalyzed by cobalt(II) phthalocyanine tetrasulfonate ([CoPcTS] 4−) in a 4:1 methanol–water mixture gave predominantly the coupled products 3,3′,5,5′-tetra- tert-butyl-4,4′-diphenoquinone (DPQ) and 4,4′-dihydroxy-3,3′,5,5′-tetra- tert-butylbiphenyl (H 2DPQ) when the oxidant/substrate ratio was less than 10. The conversion of DTBP was 70% in 3 h and 86% in 8 h when the amounts of DTBP, Bu t OOH, and [CoPcTS] 4− in millimoles were 0.300, 1.52, and 3.0 × 10 −3, respectively. The yield of DPQ was 56% in 3 h and 73% in 8 h whereas that of H 2DPQ was about 14% in 3 and 8 h. H 2DPQ is not commonly encountered the oxidation product of DTBP and is considered unstable. When the oxidant/substrate ratio was over 10, 2,6-di- tert-butylbenzoquinone was also formed. The degradation of [CoPcTS] 4− by Bu t OOH also occurred during the oxidation of DTBP. About three-fourths of the catalyst was degraded in the first hour and about 2% of the catalyst remained after 8 h.