P-Cresol polymerization

The simplest p-alkylphenol is p-cresol (35), which has a methyl substituent. One of the first detailed studies of the HRP-catalyzed oxidation of p-cresol was reported in 1976 [51]. Recently, a detailed in situ NMR analysis revealed details of the coupling mechanism of the p-cresol polymerization. NMR and H- H gCOSY 2D NMR analysis suggested that ortho-ortho coupling (43) is the dominant coupling mechanism at the initial stage of the polymerization. The consumption of dimer accelerated only after the complete conversion of the monomer in the reaction mixture. After a reaction time of about 75 min, the formation of Pummerer s ketone (44) was observed. These ketonic species are formed from ortho-para-coupled dimers by intramolecular Michael addition. They are probably not able to participate in the further polymerization process and remain as side products (Scheme 9) [76]. Experiments with 4-propylphenol have revealed that the formation of Pummerer s ketone may be suppressed at lower temperatures [112]. 

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