Photocatalytic and photochemical reactions of naturally occurring phenolic compounds of lignin origin

This research focuses on photocatalytic and photochemical reactions of naturally occurring phenolic compounds of lignin origin in non-water solvents. The purpose of this research is to determine platform molecules from lignin that can make usable products via photoreactions. The specific goals of the research are to determine molecular reaction networks of organic phenolic compounds from lignin (isoeugenol, eugenol and vanillin) in solution, under: 1) heterogeneous photocatalytic oxidation; 2) photochemical oxidation. Other specific goals are to study the dependence of the yield of photochemical oxidation upon the pressure of oxygen, and upon the non-water solvent used. Photocatalytic oxidation reactions were tested using UV-Vis light, oxygen, and titanium dioxide as the heterogeneous photocatalyst, whereas photochemical oxidation reactions utilized UV-Vis light and oxygen only. In order to monitor the progress of reactions, chemical analysis such as thin layer chromatography (TLC), ultraviolet-visible spectroscopy (UV-Vis) and Fourier transform infrared spectroscopy (FTIR) were used. To identify molecular products, high-performance liquid chromatography (HPLC) with ultraviolet detection (HPLC-UV) and with mass-spectrometric detection (HPLC-MS) was used. It was determined that under heterogeneous photocatalytic oxidation, the typical phenolic compound from lignin, isoeugenol with an internal C=C bond is much more reactive than its isomer eugenol with a terminal C=C bond. With oxygen from air, in solution under UV and visible light (λ ≥ 254 nm) in the presence of TiO2 Degussa P25 photocatalyst, isoeugenol yields two major photooxidation products: vanillin and dehydrodiisoeugenol (DHDIE). Under the same conditions, but under near-UV and visible light (λ ≥ 355 nm), the yields of these products were lower. Under photochemical oxidation in several non-water solvents, isoeugenol produces different yields of DHDIE, as compared to photocatalytic oxidation. Specifically, with oxygen from air and in non-water solution under near-UV and visible light (λ ≥ 355 nm), isoeugenol produced the highest yield of DHDIE when dimethyl sulfoxide is used as solvent. A typical phenolic compound from lignin with a C=O group, vanillin undergoes photochemical oxidative polymerization in a non-water solvent, using near-UV and visible light (λ ≥ 355 nm), at approximately 100 psi oxygen to produce a solid powder of “polyvanillin”.M.S.Includes bibliographical referencesby Morgan Zielinsk