Synthesis and Oxidizing Ability of p-Chloranil Dimer

A p-chloranil dimer (pCh2) has been synthesized. The first reduction potential of pCh2 shifted to a more positive value than that observed for the p-chloranil monomer (pCh1) and was more negative than that for 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). As expected, pCh2 oxidized 9,10-dihydroanthracene and α-tetralol to give anthracene and α-tetralone, respectively, more efficiently than pCh1 did. The advantages of pCh2 were observed in oxidations of 2,4-di-tert-butylphenol and 2,6-di-tert-butyl-4-methylphenol. Although further oxidation took place in DDQ oxidations and no reaction occurred in pCh1 oxidations, initial oxidation products were solely obtained in pCh2 oxidation because of its moderate oxidizing ability.