Alkylation of phenol with tert-butyl alcohol (TBA) over Hb zeolite was studied using ONIOM approach with two proposed reaction paths: stepwise and concerted mechanisms. The computational results obtained by the ONIOM (B3LYP/6-31G(d,p):UFF) method revealed that the reaction preferentially occurs through a concerted mechanism rather than via the stepwise mechanism. The reactivity difference between the 2- and 4-tert-butylation became more apparent in the concerted mechanism where the 2-tert-butylation proceeded faster. The reaction activation energies of the 2- and 4-tert-butylation were predicted to be 110.7 and 121.9kJ/mol, respectively. In the stepwise mechanism, the formation of the tert-butyl carbenium species was the rate-limiting step. In the subsequent tert-butylation process, phenol tert-butylation was faster than the tert-butyl carbenium formation, with the activation energies of 94.3 and 99.3 kJ/mol for the 2- and 4-tert-butylation, respectively. It was found that 2-tert-butyl phenol was a kinetically favored product, whereas 4-tert-butyl phenol was the thermodynamically most preferred product.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)