De-t-butylation of Phenols Catalysed by Bulk and Supported Heteropoly Acid
Journal of Molecular Catalysis (Continued after 1994 as Journal of Molecular Catalysis A: Chemical and Journal of Molecular Catalysis B: Enzymatic)
Kinetics and mechanism of the liquid-phase reaction, 2,6-di-t-butyl-4-methylphenol (DBMP) + ArH → 2-t-butyl-4-methylphenol + ArBut, in the presence of bulk and SiO2-supported heteropoly acid H3PW12O40 (PW) as a heterogeneous catalyst have been studied (ArH = PhH, PhMe, PhBut, o-xylene, m-xylene, [DBMP]/[ArH] = 122 mol mol−1, 5–25 °C). Under these conditions no isobutene is formed. The reaction was found to be first order with respect to both DBMP and the catalyst. The rate depends on the nature of ArH in a way that is typical of electrophilic aromatic substitution. The activation energies are 29 ± 3 and 19 ± 2 kcal mol−1 for bulk PW and 25% PW/SiO2, respectively. The activity of the surface protons of PW/SiO2 (turnover number) increases monotonically as their acid strength increases with increasing total PW loading, reaching a maximum for the bulk PW. The mechanism of the reaction is discussed.