Computational Investigations Of Oxygen-Containing Donor-Acceptor Complexes Involving Sulfur Dioxide Or Sulfur Trioxide

George A. Van Den Driessche, Illinois State University

Imported from ProQuest VanDenDriessche_ilstu_0092N_10552.pdf

Abstract

Sulfur dioxide (SO2) and sulfur trioxide (SO3) are components in the formation of atmospheric sulfuric acid (acid rain). Sulfur dioxide is a common byproduct of combustion reactions that is released into the atmosphere. Recently, experimental results have shown that amine-functionalized polyethylene glycols (PEGs) have demonstrated efficient SO2 capture (see for example, Yang, D.; Hou, M.; Ning, H.; Zhang, J.; Ma, J.; Han, B. Phys. Chem. Chem. Phys., 2013, 15, 18123-18127). Both SO2 and SO3 are known to form donor-acceptor complexes with a variety of electron-pair-donating molecules such as water and ammonia. While a multitude of studies, both experimental and computational, have focused on complexes formed between amines and SO2 or SO3, fewer have investigated the interaction between ethers and SO2 or SO3. In this work, the properties of ether-SO2 and ether-SO3 complexes have been explored at the B3LYP level of theory using correlation-consistent basis sets in the gas phase and in solution phase with the Polarizable Continuum Model and a dielectric constant corresponding to water. A variety of ethers have been investigated, ranging from dimethyl ether to 1,3,5-trioxane.

Optimized geometries and other properties, including binding energies, dipole moments, and charge transfer, have been obtained for the ether-SO2 and ether-SO3 complexes. For example, in the gas phase ether-SO3 complexes have a binding energy range of 5-12 kcal/mol, while the ether-SO2 complexes have a range of 2-6 kcal/mol (in both cases the binding energies show strong correlations with charge transfer and dipole moments). In addition, the ether-SO2 and ether-SO3 complexes exhibit significant gas vs. solution phase differences in properties. For example, the average difference between gas phase and solution phase bond distance, Sâ??Oether, for ether-SO2 complexes is 0.12 Ã?, while for ether-SO3 complexes the difference is 0.17 Ã?. Additional computational studies have been performed to explore complexation of SO2 with model PEGs. Both physical and chemical absorption of SO2 at the amino-ethanol site of the model PEGs has been modeled, and binding energies of about 5 kcal/mol were observed for physical absorption, while binding energies of either approximately 2 kcal/mol or 5 kcal/mol were determined for chemical absorption. Finally, the reaction path for conversion between the physically absorbed and chemically absorbed SO2 was investigated for diethyl-amino- ethanol.