The oxidation of 2,6-di-tert-butylphenol (DTBP) with tert-butylhydroperoxide (Bu'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(2)DPQ) 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'OOH, and [CoPcTS](4-) in millimoles were 0.300, 1.52, and 3.0 x 10(-3), respectively. The yield of DPQ was 56 % in 3 h and 73 % in 8 h whereas that of H(2)DPQ was about 14 % in 3 and 8 h. H(2)DPQ 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'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. (c) 2005 Elsevier B.V. All rights reserved.