Tuning alkylation reactions with temperature in near‐critical water

Quantitative kinetics for the alkylation reactions of phenol and p‐cresol with tert‐butyl alcohol in near‐critical water as a function of temperature are reported. The reaction products of the alkylation reactions were ortho‐ and para‐substituted phenols, which are used extensively as antioxidants in numerous polymer systems. A new experimental reaction apparatus was designed, constructed, and successfully operated to allow pressure control and sampling of the reaction systems, which provided rate constants in the temperature range 250–300°C. Additionally, activation energies and heats of formation were calculated from the temperature dependence of the rate constants, and ortho‐substitution was found to be exothermic whereas para‐substitution was found to be endothermic. These results demonstrate that product distribution of the alkylation reactions could be tuned with temperature to produce specific products.