Theoretical Computational Study Of Reaction Mechanisms For Br(?)nsted Acid-Catalyzed Alkylation Of Aromatic Compounds By Zeolite And Ionic Liquid

With the recent advances of computer science and software technique, theoretical computational simulation has become an important method for research into the microscopic mechanisms of chemical reactions. It has brought about major changes and progresses in the whole chemistry field. Theoretical calculation has shown some advantages in the study of catalytic reactions, thus becoming a complementary tool for experimental catalysis research.In this thesis, the ONIOM and DFT theoretical calculation methods were employed to study the reaction mechanisms for Bronsted acid (B-acid)-catalyzed alkylation of aromatic compounds with alcohols using zeolite and ionic liquid. By examining molecular geometry, electronic structure, adsorption behavior, and reaction potential energy surface, the microscopic nature for formation of the reaction intermediate and transition state were clarified. The relationship between reaction mechanisms and molecular structure of reactants, molecular size of alcohols as alkylation reagents for zeolite-type B-acid-catalyzed alkylation of benzene, phenol and 2-methylnaphthalene were demonstrated including the impact of water on the reaction. Through a comparative study on ionic liquid B-acid-catalyzed tert-butyaltion of phenol, o-cresol and catechol, the relationship between reaction kinetics, ether regioselectivity and the molecular structure of phenol reactants, molecular size of alcohols as alkylation reagents was uncovered including the influence of solvent on the reaction. Furthermore, the catalytic mechanisms and impact factors on the product selectivity for a same organic reaction by zeolite and ionic liquid catalysis were discussed.By discussion of H-ZSM-5 B-acid-catalyzed alkylation of benzene with ethanol, H-βB-acid-catalyzed alkylation of phenol with tert-butanol, and H-ZSM-5 B-acid-catalyzed alkylation of 2-methylnaphthalene with methanol, it was found that the molecular structure of aromatic compounds does not have a significant impact on alkylation mechanism. The reaction mechanism mainly depends on the molecular size and structure of alcohol reagents. The calculation results on molecular structure, stability of the reaction intermediate, transition state, and reaction barrier indicate that benzene alkylation with ethanol,2-methylnaphthalene alkylation with methanol both show stepwise mechanism as the kinetically dominant path. But for phenol alkylation with tert-butanol, it demonstrates concerted mechanism as the kinetically favored path. The in-situ formed byproduct water strongly adsorbs on the B-acid site of zeolite, and would inhibit the further adsorption and reaction of the aromatic reactants and alcohol reagents.The comparative study of ionic liquid B-acid-catalyzed tert-butyaltion of phenol, o-cresol and catechol shows that the molecular size of alcohol reagents does not have a significant influence on the regioselectivity to ether product. The reaction kinetics and ether regioselectivity depond on the molecular strcture of phenol reactants. The particular molecular structure of catechol makes its reaction kinetics unique. The addition of solvent with high dielectric-constant would retard catechol tert-butylation.Through discussion of H-βzeolite and ionic liquid catalyzed tert-butylation of phenol, it demonstrates that the kinetically dominant reaction mechanism does not change with the changing of B-acid catalyst which is both the concerted mechanism. The shape-selectivity fromβzeolite pore structure has a significant impact on the selectivity of tert-butylation products.