Oxidation of 2,3,6-trimethylphenol with potassium peroxymonosulfate catalyzed by iron and cobalt phthalocyanine tetrasulfonates in a methanol–water mixture

Oxidation of 2,3,6-trimethylphenol (TMP) with potassium peroxymonosulfate (KHSO5) catalyzed by iron phthalocyanine tetrasulfonate ([FePcTS]) in an 8-to-1 methanol–water mixture resulted in 43.2–100.0% conversion of TMP and 60.5–100.0% selectivity of trimethyl-1,4-benzoquinone (TMQ) after 5 min at ambient temperature when the oxidant/substrate molar ratio was changed from 1 to 4 at a constant substrate/catalyst molar ratio of 300. Higher conversion of TMP and selectivity of TMQ were obtained when the reaction time was extended to 30 min. A minor product, 2,2′,3,3′,5,5′-hexamethyl-4,4′-biphenol (BP), was formed in reactions carried out with an oxidant/substrate molar ratio of 3 or lower. When cobalt phthalocyanine tetrasulfonate ([CoPcTS]) was employed as a catalyst instead of [FePcTS], a slower reaction rate for the oxidation of TMP was observed and the product composition was about the same as that observed in the [FePcTS] catalysis. Oxone, which is a solid consisting of a 2:1:1 mixture of KHSO5, KHSO4, and K2SO4, was used to introduce KHSO5 into the reaction mixture.

Graphical abstractOxidation of 2,3,6-trimethylphenol (TMP) with potassium peroxymonosulfate (KHSO5) was efficiently catalyzed by iron phthalocyanine tetrasulfonate ([FePcTS]) in a 8-to-1 methanol–water mixture. When cobalt phthalocyanine tetrasulfonate ([CoPcTS]) was used as catalyst instead of [FePcTS], slower reaction rate for the oxidation was observed. Figure optionsDownload full-size imageDownload as PowerPoint slide