Protonation of Polymethylphenols

Abstract

The protonation of a series of polymethylphenols in fluorosulfonic acid at −50° has been studied. For those phenols with no substituent at C-4, protonaton occurs exclusively at that position. Isomeric ions were obtained for all phenols with a methyl substituent at C-4. 4-Methylphenol and 2,4-dimethylphenol each gave three ions, one from O-protonation and two from protonation at C-2 and C-4, whereas 2,4-dimethylphenol, 2,3,4-, 2,4,5-, and 3,4,5-trimethylphenol, and 2,3,4,5-tetramethylphenol gave only the C-protonated species. These studies establish that although electronic factors are important, steric factors play a predominant role in determining the relative proportions of the various species.