PHOTOCATALYTIC AND PHOTOCHEMICAL REACTIONS OF NATURALLY OCCURRING PHENOLIC COMPOUNDS OF LIGNIN ORIGIN by MORGAN ZIELINSKI A thesis submitted to the Graduate School- Camden Rutgers, The State University of New Jersey in partial fulfillment of the requirements for the degree of Master of Science Graduate Program in Chemistry written under the direction of Dr. Alexander Samokhvalov and approved by ______________________________________________________ Dr. Alexander Samokhvalov ______________________________________________________ Dr. Alex J. Roche ______________________________________________________ Dr. Georgia Arbuckle-Keil Camden, New Jersey May 2013 i ABSTRACT OF THE THESIS Photocatalytic and Photochemical Reactions of Naturally Occurring Phenolic Compounds of Lignin Origin By: MORGAN ZIELINSKI Thesis Director: Dr. Alexander Samokhvalov 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 ii 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”. iii Dedications I would like to dedicate this thesis to my entire family for their unconditional love, support and encouragement throughout my academic career: my husband Mark Zielinski, my parents Karen Genoese and Michael Goldberg and their significant others, Dominic Genoese and Lisa Passione, as well as my brothers Brad and Brian Goldberg and my sister-in-law Crystal Goldberg. Each of you is very special to me. I am very lucky to have such a wonderful family. iv Acknowledgements To Dr. Samokhvalov, I would like to express my gratitude and appreciation for your leadership and support which has guided me through this project. You have had such dedication, patience, and enthusiasm for this project and my success. Thank you for helping me to develop my research skills and for truly enriching my learning experience. To Dr. Roche, I am very grateful for all of your moral and academic support throughout my undergraduate and graduate studies here at Rutgers. You have been a great leader and mentor to me in countless ways. You have taught me so many unforgettable lessons that I know I will apply in my future endeavors. To Dr. Arbuckle-Keil, I would like to thank you for continued encouragement and guidance throughout my graduate studies. You certainly helped me to stay on track as I pursued my degree and you always pushed me to do my best. To Dr. Burke, I would like to thank you for developing my chemistry foundation. You have taught me so much from undergraduate chemical principles to graduate level advanced organic chemistry. Thank you for always challenging me and supporting me throughout my academic career. To Mrs. Craig, I would like to express how grateful I am for your unconditional support and for keeping me levelheaded as I rode the emotional, mental, and physical roller- coaster of this research-based master’s degree with a teaching assistantship. At times I questioned my judgment of taking on such a load, but you were always encouraging and motivating when I needed it the most. The lessons you have taught me about teaching and life are unforgettable. v Table of Contents Abstract of Thesis ii Dedications iv Acknowledgements v Table of Contents vi List of Tables viii List of Figures ix Chapter 1: Introduction 1.1 Biomass 1 1.2 Biorefineries and Lignin 2 1.3 Platform Molecules 3 1.4 Photocatalysis and Photochemistry 5 1.4.1 Photocatalytic Oxidation 6 1.4.2 Photochemical Oxidation 8 Chapter 2: Experimental 2.1 Safety Precautions 9 2.2 Organic Molecules 9 2.3 Solvent Selection 11 2.4 Photocatalyst 12 2.5 Apparatus 12 2.6 Photoreaction procedures 13 2.7 Product Analysis 14 Chapter 3: Photocatalytic Oxidation Reactions 3.1 Screening of Phenolic Compounds 18 3.2 Chemical reactions involving the C=C bond 19 vi 3.2.1 Isoeugenol 20 3.2.2 Eugenol 31 3.2.3 Origin of reactivity of the radical intermediate 32 3.3 Chemical reactions involving the C=O bond 34 Chapter 4: Solvent Dependence for Photooxidation of Isoeugenol 4.1 Effect of Dipole Moment of the Solvent 35 4.2 Effect of Oxygen Solubility of the Solvent 41 Chapter 5: Photochemical Oxidation Reactions 5.1 Chemical reactions involving the C=O bond 44 5.2 Dependence of Reaction upon Pressure of Oxygen 45 Chapter 6: Conclusion 53 Chapter 7: Future Plans 55 List of Presentations 56 References 57 vii List of Tables Table 1. The TLC Rf values and assignments of photocatalytic oxidation 22 products from silica gel plates. Table 2. The concentration of dehydrodiisoeugenol (DHDIE) produced from 39 each solvent tested under photocatalytic oxidation (λ ≥ 355 nm). Table 3. The concentration of dehydrodiisoeugenol (DHDIE) produced from 40 each solvent tested under photochemical oxidation (λ ≥ 355 nm). viii List of Figures Figure 1. Typical fragments of lignin molecules with multiple functional groups 2 (5). Figure 2. Energy-band diagram of the photocatalyst, titanium dioxide (TiO2) 6 (22). Figure 3. An illustration of how photocatalysis works to form hole-pairs and 7 radicals where ads stands for “adsorbed on the surface of the photocatalyst” (19). Figure 4. A general example of a photochemical reaction (22). 8 Figure 5. Selected phenolic compounds commonly found in bio-oil. 10 Figure 6. Optical spectrum of light that penetrates the Pyrex reaction vessel 18 (top) and the quartz vessel (bottom). Figure 7. TLC plate of phenolic compounds that do not react under 19 photocatalytic oxidation. Figure 8. Isoeugenol with an internal carbon-carbon double bond. 20 Figure 9. TLC silica gel plate of vanillin and isoeugenol photoreaction products 21 from both Pyrex and quartz reaction vessels. Figure 10. UV-Vis absorption spectra of isoeugenol in acetonitrile. Before 23 reaction (A); after reaction (B). Figure 11. Chromatogram of isoeugenol stock solution (optical absorption at 24 275 nm). X axis: retention time, min. Y axis: optical absorbance at 275 nm, a.u. Figure 12. Reaction of isoeugenol to form vanillin under photocatalytic 25 oxidation. Figure 13. Reaction of isoeugenol to form dehydrodiisoeugenol under 26 photocatalytic oxidation. Figure 14. Chromatogram of the isoeugenol product in the Quartz vessel (λ ≥ 27 254 nm) after photocatalytic oxidation. X axis: retention time, min. Y axis: optical absorbance at 275 nm, a.u. ix Figure 15. Chromatogram of the isoeugenol product in the Pyrex vessel (λ ≥ 28 355 nm) after photocatalytic oxidation. X axis: retention time, min. Y axis: optical absorbance at 275 nm, a.u. Figure 16. Chromatogram of the synthesized dehydrodiisoeugenol in 29 acetonitrile. X axis: retention time, min. Y axis: optical absorbance at 275 nm, a.u. Figure 17. The mass spectrum of DHDIE 29 Figure 18. Calibration curve of DHDIE stock solution. 31 Figure 19. Eugenol with a terminal carbon-carbon double bond. 32 Figure 20. Resonance structures which illustrate the delocalization of the likely 33 radical intermediate of isoeugenol. Figure 21. Chromatogram of “butyl substituted” DHDIE formed in dibutyl ether 36 at a retention time of 10.56 minutes. Figure 22. The concentration of DHDIE (mM) compared to the dipole moment 39 of each solvent under photocatalytic oxidation (λ ≥ 355 nm). Figure 23. The concentration of DHDIE (mM) versus dipole moment of each 40 solvent used under photochemical oxidation (λ ≥ 355 nm). Figure 24. The concentration of DHDIE