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Electrophilic Aromatic Alkylation by Hydroperoxides. Competition between Ionic and Radical Mechanisms with Phenols
Lucia Liguori1, Hans-René Bjørsvik, Francesca Fontana
1Dipartimento di Chimica del Politecnico di Milano, via Mancinelli 7, I-20131 Milano, Italy, Department of Chemistry, University of Bergen, Allégt 41, N-5007 Bergen, Norway, and Dipartimento di Ingegneria, Universitá di Bergamo, viale Marconi 5, 24044 Dalmine, BG Italy.
Abstract:
Tertiary hydroperoxides have been utilized for the electrophilic alkylation of activated aromatic substrates, particularly phenols and phenol ethers. Cumyl (1) and tert-butyl (2) hydroperoxides have shown a greatly different behavior as concerns the catalysis and the regioselectivity. The best catalyst for 1 is TiCl(4), which is completely inactive with 2. With the latter an effective catalyst is FeCl(3), which, however, can give rise to a combination of electrophilic and radical reactions with alkyl phenols. 2,2'-Dihydroxy-3,3'-di-tert-butyl-5,5'-dimethyldiphenyl is obtained in high yields from p-cresol.