No description available.

A STUDY OF LIGNIN DEPOLYMERIZATION BY SELECTIVE CLEAVAGE OF THE Cα-Cβ LINKAGES IN LIGNIN MODEL COMPOUNDS VIA BAEYER-VILLIGER OXIDATION Lignin is amorphous aromatic polymer derived from plants and is a potential source of fuels and bulk chemicals. Herein, we present a survey of reagents for selective stepwise oxidation of lignin model compounds. Specifically, we have targeted the oxidative cleavage of Cα-Cβ bonds as a means to depolymerize lignin and obtain useful aromatic compounds. In this work, we prepared several lignin model compounds that possess structures, characteristic reactivity, and linkages closely related to the parent lignin polymer. We observed that selective oxidation of benzylic hydroxyl groups using TEMPO/O2, followed by Baeyer-Villiger oxidation of the resulting ketones using H2O2, successfully cleaves the Cα-Cβ linkage in the model compounds. This process was also applied to depolymerization of Organosolv lignin. The deconstructed lignin was analyzed by a number of techniques, including ATR-IR, GPC, and 31P NMR of suitably derivatized samples. AN INVESTIGATION OF THE CHANNELING REACTION IN NITROGEN-DOPED MULTIWALLED CARBON NANOTUBES (N-MWCNTS) The reduction of nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) with Li/NH3 results in deep longitudinal cuts in the nanotubes structure. As the N-MWCNTs are anisotropic, we were able to investigate whether the unzipping process proceeds with equal efficiency from the tip end or from the root (catalyst) end of the N-MWCNT structure. To accomplish this we prepared polymer filled aligned arrays of N-MWCNTs, then exposed one or the other end. Through this approach we were able to shield the sidewalls and either end of the nanotubes from the Li/NH3 solution We have found that when the top end of the N-MWCNTs array was exposed to the reaction mixture, very few nanotubes suffered significant ‘unzipping’. However, when the root (substrate) side of the array is exposed to the reaction mixture, we observe the features characteristic of nanotubes with longitudinal cuts. Our finding provides some insight into the mechanism of the unzipping process, and provides evidence that the unzipping process has a directional preference-unzipping from the root end towards the tip end. And may provide a method for selective functionalization of the interior of tubes and create a new form of nanotube- based porous membrane.

Woody plants are the most abundant renewable resources on the earth. From the paper we consume to the house we live in, our daily lives rely heavily on woody plants. Over the past decades, enormous efforts have been expended to improve the utilization of fiber and wood. For example, much research has been conducted to develop environmentally benign, and economically feasible techniques for pulp and papermaking. The economical conversion of wood to useful sugars and alcohol has also been the subject of intensive research. Investigations aimed at the genetic manipulation of wood growth to better meet our needs are also underway. Nonetheless, harsh pulping and bleaching conditions are still required in the pulp and paper industry, and the bioconversion of polysaccharides in biomass to alcohol is still too expensive. An argument could be put forth that a major reason for this is the lack of basic knowledge concerning the structural and biochemical characteristics of the plant cell wall. The three major polymeric components of plant cell walls, cellulose, hemicellulose and lignin, are intimately associated with one another. Cellulose is associated with hemicellulose via non-covalent linkages, whereas lignin is theorized to be associated with cellulose and hemicellulose via both covalent and non-covalent linkages. The nature of associations between wood polymers is still poorly understood. However, it is these intimate associations that make delignification difficult, and make the bioconversion of polysaccharides to alcohol inefficient. It is also believed that the linkages between lignin and polysaccharides are responsible for the reduced digestibility of grasses by ruminants. Besides cellulose, hemicellulose and lignin, there are many secondary metabolites such as lignans, neolignans, tannins and terpenoids. The structures of lignans and neolignans are analogous to the interunits of lignin. Lignin is considered an optically inactive polymer, whereas lignans and neolignans are optically active small molecules. Although it has been proposed that the biosynthesis of lignin, lignans and neolignans are via the same oxidative coupling mechanism, it is still unclear that how the plant cell wall differentiates the formation of lignans, neolignans and lignin. How and why plant cell wall generates so many lignans and neolignans having broad structural variation is also unknown. As a matter of fact, it is still uncertain which enzymes are actually involved in the biosynthesis of lignin. A better understanding of biosynthetic pathways of lignin, lignans and neolignans is a prerequisite for the genetic manipulation of plant growth. Investigations described in this dissertation were an effort to better understand the fundamental aspects of covalent linkages between lignin and hemicellulose in wood. Enantiomeric synthesis of neolignans provides a tool for investigating the optically active nature of neolignans, and may be helpful to study the biosynthetic pathways of neolignans. Chapter | describes chemical structures of wood components and the biosynthesis of lignin, lignans and neolignans. The mechanisms of lignin-carbohydrate bond formation are also discussed, and a concise review of lignin-carbohydrate linkages proposed in the literature concludes Chapter 1. Chapter 2 presents the methods used in investigating covalent linkages in wood, which include methods of isolating lignin-carbohydrate complexes, chemical cleavage methods, DDQ oxidation and model compound/NMR methods. The synthesis of plant cell wall model compounds and neolignans are reviewed in Chapter 3. The experimental work performed for the completion of this thesis is described in Chapters 4-8. A method which provides β-𝘖-4 lignin model dimers with complete threo stereospecificity is described in Chapter 4. This method is complementary to the current method for the preparation of erythro lignin model dimers. Chapter 5 presents a practical synthesis of methyl 4-𝘖-methy] α-D-glucopyranosiduronic acid. Methyl 4-𝘖-methyl-α-D-glucopyranosiduronic acid was prepared from methyl α-D-glucopyranoside in 4 steps (74% overall yield). Previous preparations of this compound were much lengthier, and had very low overall yields. Chapter 6 deals with the synthesis and rearrangement reactions of ester-linked lignin-carbohydrate model compounds. A series of ester-linked lignin-carbohydrate model compounds were synthesized, and migration of the uronosy] group between the primary (γ) and benzyl (α) position of lignin side chain is discussed. Several approaches to synthetic neolignans are described in Chapter 7. Chapter 8 presents a novel approach for the preparation of chiral aryl alkylethers. The successful application of this novel approach to synthesis of several optically active 8-𝘖-4 neolignans and a 1,4- benzodioxane neolignan is described, as is the introduction of an alkyl] aryl ether bond in carbohydrate molecules. Some of the material of this dissertation has been reported in the following papers: 1. Li, K. and Helm, R. F. Approaches to Synthetic Neolignans. J. Chem. Soc. Perkin Trans 1. Accepted. 6. Li, K. and Helm, R. F. Use of Carbohydrates as Building Blocks to Synthesize Neolignans. 211th ACS National ACS Meeting, New Orleans, March 24-28, 1996. CELL-079. 2. Li, K. and Helm, R. F. A Practical Synthesis of Methyl 4-𝘖-Methylα-D-Glucopyranosiduronic Acid. Carbohydr. Res. 273(1995), 249-253. 3. Li, K. and Helm, R. F. Synthesis and Rearrangement Reactions of Ester-Linked Lignin-Carbohydrate Model Compounds. J. Agric. Food Chem. 48(1995), 2098-2103. 4. Helm, R. F. and Li, K. Complete threo Stereospecificity for the Preparation of β-𝘖-4 Lignin Model Dimers. Holzforschung. 49(1995), 533-536. 5. Helm, R. F. and Li, K. Synthesis and Rearrangement Reactions of Lignin-uronic Acid Model Compounds Related to Hardwood Cell Wall Structure. The 8th International Symposium on Wood and Pulping Chemistry. Helsinki, Finland, June 1995, vol. 1, pp107-114. 7. Li, K. and Helm, R. F. Approaches to Synthetic Neolignans, 34th National Organic Symposium, Williamsburg, VA. June 11-15, 1995. Poster 281. / Ph. D.

The oxidation of lignin model compounds was studied in conventional solvents in parallel with oxidations in ionic liquid solvents. Catalyst systems were investigated in ionic liquid solvents to determine how reaction rates and the selectivity for benzylic carbon oxidation were affected. Oxidation rates were often lower in ionic liquids than in conventional solvents ‒ as indicated by lower conversion in a standard reaction time ‒ likely due, at least in part, to the higher viscosity of ionic liquids. Mechano chemical treatment of Indulin AT kraft lignin by ball milling with KOH and toluene produced significant carbonyl functionality, among other changes. The chemical reactivity of the lignin was increased, resulting in greater lignin degradation from porphyrin oxidation followed by Baeyer-Villiger oxidation. The mechanochemical treatment produced a level of lignin oxidation that was similar to that produced by porphyrin-catalyzed oxidation. Combining mechanochemical treatment with porphyrin oxidation produced a synergistic positive effect on the depolymerization of lignin, as demonstrated by a significantly higher yield of monomers. The methyl ester of vanillic acid was obtained as the main monomeric product (after methylation), along with a small amount of methyl 5-carbomethoxyvanillate.

Lignin, the second most abundant biopolymer on earth, is potentially a replaceable source for bulky fuels and chemical feedstocks. There have been numerous reports on methods for the oxidative cleavage of β-O-4 linkages but relatively few reports of how those methods affect other linkages that are present in lignin. We investigated how the β-1 and β-5 linkages respond under oxidative conditions proposed for lignin deconstruction based on their effect on β-O-4 linkages. Mechanochemical treatment of lignin can greatly improve the yield of monomer products and we applied a mechanochemical approach, using powerful ring-and-puck milling to promote lignin degradation. Along with similar production of monomers in a much shorter period than what we observed in previous ball-milling process, much more unexpected reactions were taking place during the current mechanochemical process. Lignin is a promising feedstock for epoxy resins since lignin-derived aromatic monomers usually bear hydroxyl and carboxyl groups. We are working on utilizing these mono-aromatic compounds and highly-functionalized-lignin as precursors for preparation of epoxy thermosets. We are interested in investigating the properties of thermosets by utilizing the actual isolated monomer streams from raw lignin. We expect to observe attractive thermal and mechanical properties from these lignin-derived epoxy thermosets compare to that of the commercialized but currently limited-used BPA-based epoxy resins.

No description available.

The effect of HZSM-5 catalyst and NaOH pretreatment on the product distribution and bio oil properties from pyrolysis of cellulose, hemicellulose and lignin model compounds was investigated at 450 °C. NaOH pretreated and untreated cellulose was pyrolyzed on sand and the HZSM-5 catalysts; VPISU001 HZSM-5, BASF HZSM-5, and Sud-Chemie HZSM-5. The pyrolysis of cellulose on BASF and Sud-Chemie HZSM-5 catalysts increased the yields of the organic liquid fraction, total liquid and char while decreasing the gas yields. However the catalyst decreased the organic and char yields while increasing the water yields but there was no change in gas yields. The NaOH treatment caused a decrease in the organic and total oil yields relative to the control but the char yield increased. The change in gas yields was not significant. The characterization of the oils using FTIR and ¹³C−nmr showed that, the VPISU001 HZSM-5 with and without NaOH pretreatment caused elimination of the levoglucosan fraction while increasing the aromatic fraction. The NaOH pretreated cellulose pyrolyzed on sand reduced the levoglucosan groups while increasing the aromatic fraction of the bio oil. In the hemicellulose studies, birchwood xylan and NaOH treated xylan samples were pyrolyzed on sand and VPISU001 HZSM-5 catalyst. The organic liquid yields were very low and ranged from 3.3 wt% to 7.2 wt%, the water yields ranged from 17.8-25.7 wt%, the char yield were 17.8-25 wt% and gas yield were 40.9-49.6 wt%. The HZSM-5 catalysts increased the water and gas yields and produced the lowest char yield. NaOH pretreatment produced the lowest water yield while the char yield was the highest. The combined effect of NaOH pretreatment and HZSM-5 produced the lowest organic yield and highest char yield. The FTIR and ¹³C-nmr analyses of the organic liquids showed that the HZSM-5 catalyst promoted the formation of aromatic products, while the NaOH pretreatment promoted the formation of aliphatic hydrocarbons. The combined effect of NaOH pretreatment and HZSM-5 catalyst seem to promote the formation of anhydrosugars. The main gases evolved were CO, CO₂ and low molecular weight hydrocarbons. The HZSM-5 catalyst promoted CO formation while NaOH pretreatment promoted CO₂. The HZSM-5 catalyst produced the highest yield of low molecular weight hydrocarbon gases. The lignin and model compounds studies involved using low molecular weight kraft lignin, guaiacol, and syringol which were pyrolyzed on sand and VPISU001 HZSM-5 catalyst at 450 °C. The kraft lignin pyrolysis produced low liquid and gas yields and high char yields. The HZSM-5 catalysts increased the water yield and decreased the organic liquid yield. NaOH pretreatment increased the char yield and decreased the liquid products. NaOH and the HZSM-5 catalyst together decreased the char and increased the gas yields. The ¹³C-nmr and FTIR analysis showed that NaOH pretreatment promoted the formation of mainly guaiacol while the HZSM-5 catalyst formed different aromatic components. NaOH pretreatment promoted the formation of more CO₂ than CO whilst HZSM-5 catalyst promoted the formation of more CO than CO₂. Methane formation was enhanced by NaOH pretreatment. Other hydrocarbon gases were however enhanced by the HZSM-5 catalysts. Pyrolysis of the model compounds on the HSZM-5 catalyst showed an increase in pyrolytic water. The HZSM-5 catalyst promoted demethylation in syringol pyrolysis as compared to guaiacol. / Master of Science

La pyrolyse rapide est une des voies de conversion thermochimique qui permet la transformation de biomasse lignocellulosique en bio-huiles. Ces bio-huiles, différentes des coupes lourdes du pétrole ne peuvent pas être directement mélangés dans les procédés de valorisation. En effet, en raison de leur forte teneur en oxygène, les bio-huiles nécessitent une étape de pré-raffinage, telle que l’hydrotraitement, pour éliminer ces composants.L’objectif de ce travail est de comprendre la structure, la composition et la réactivité de la bio-huile grâce à la modélisation de données expérimentales. Pour comprendre leur structure et leur composition, des techniques de reconstruction moléculaire basées sur des données analytiques, ont été appliquées, générant un mélange synthétique, dont les propriétés correspondent à celles du mélange. Pour comprendre leur réactivité, l'hydrotraitement de molécules modèles a été étudié: gaïacol et furfural. Pour cela, un modèle déterministe et stochastique a été créé pour chacun d’eux. L’approche déterministe visait à récupérer une gamme de paramètres cinétiques, qui ont ensuite été affinés par l’approche stochastique créant un nouveau modèle. Cette approche a permis de générer un réseau de réactions en définissant et en utilisant un nombre limité de familles et règles des réactions. Finalement, le mélange synthétique a été utilisé dans la simulation stochastique de l’hydrotraitement de la bio-huile, étayée par la cinétique des molécules modèles.En conclusion, ce travail a permis de recréer la fraction légère de la bio-huile et de simuler leur l'hydrotraitement, via les paramètres cinétiques des composés modèles, qui prédisent de manière raisonnable les effluents de l'hydrotraitement de celles-ci, mais sont inadéquat pour le bio-huile / Fast pyrolysis is one of the thermochemical conversion routes that enable the transformation of solid lignocellulosic biomass into liquid bio-oils. These complex mixtures are different from oil fractions and cannot be directly integrated into existing petroleum upgrading facilities. Indeed, because of their high levels of oxygen compounds, bio-oils require a dedicated pre-refining step, such as hydrotreating, to remove these components.The aim of the present work is to understand the structure, composition and reactivity of bio-oil compounds through modeling of experimental data. To understand the structure and composition, molecular reconstruction techniques, based on analytical data, were applied generating a synthetic mixture, whose properties are consistent with the mixture properties. To understand the reactivity, the hydrotreating of two model molecules was studied: Guaiacol and Furfural. A deterministic and stochastic model were created for each compounds. The deterministic approach intended to retrieve a range of kinetic parameters, later on refined by the stochastic simulation approach into a new model. This approach generates an reaction network by defining and using a limited number of reaction classes and reaction rules. To consolidate the work, the synthetic mixture was used in the stochastic simulation of the hydrotreating of bio-oils, supported by the kinetics of the model compounds.In sum, the present work was able to recreate the light fraction of bio-oil and simulate the hydrotreating of bio-oils, via the kinetic parameters of model compounds, which can reasonably predict the effluents of the hydrotreating of these, but are unsuitable for bio-oil.Fast pyrolysis is one of the thermochemical conversion routes that enable the transformation of solid lignocellulosic biomass into liquid bio-oils. These complex mixtures are different from oil fractions and cannot be directly integrated into existing petroleum upgrading facilities. Indeed, because of their high levels of oxygen compounds, bio-oils require a dedicated pre-refining step, such as hydrotreating, to remove these components.The aim of the present work is to understand the structure, composition and reactivity of bio-oil compounds through modeling of experimental data. To understand the structure and composition, molecular reconstruction techniques, based on analytical data, were applied generating a synthetic mixture, whose properties are consistent with the mixture properties. To understand the reactivity, the hydrotreating of two model molecules was studied: Guaiacol and Furfural. A deterministic and stochastic model were created for each compounds. The deterministic approach intended to retrieve a range of kinetic parameters, later on refined by the stochastic simulation approach into a new model. This approach generates an reaction network by defining and using a limited number of reaction classes and reaction rules. To consolidate the work, the synthetic mixture was used in the stochastic simulation of the hydrotreating of bio-oils, supported by the kinetics of the model compounds.In sum, the present work was able to recreate the light fraction of bio-oil and simulate the hydrotreating of bio-oils, via the kinetic parameters of model compounds, which can reasonably predict the effluents of the hydrotreating of these, but are unsuitable for bio-oil

In der vorliegenden Arbeit werden unter Verwendung von Hydrotris(pyrazolyl)-boraten (Tp) als tripodale Zuschauerliganden Modellsysteme für unterschiedliche Nicht-Häm-Eisenenzyme entwickelt und untersucht. Dabei steht im ersten Schritt die Syntheseoptimierung und Implementierung der noch nicht für biomimetische Studien verwendeten TpMes und TpMes* Liganden im Vordergrund. Darauffolgend werden geeignete Metall-Chloro-Vorläuferkomplexe [TpMesMCl] synthetisiert. Das Koordinationsverhalten des TpMes*-Liganden gegenüber zweiwertigen Übergangsmetallionen wird systematisch untersucht und eine Reihe von heteroleptischen [TpMes*MCl] und homoleptischen [(TpMes*)2M] Komplexen synthetisiert und charakterisiert. Die Modellverbindungen [TpMesFeCysOEt] und [TpMesFeCysAm], welche Cysteinatethylester und Cysteaminat als Substratliganden tragen, dienen jeweils als strukturelles sowie funktionelles Modell für die Cystein- und die Cysteamindioxygenase. Die Mesitylreste des TpMes-Liganden bilden eine schützende, becherartige Struktur um das Eisenzentrum. Die Reaktionsprodukte können so unter anderem erstmalig kristallografisch charakterisiert werden. Zudem wird ein Intermediat in der Reaktion von [TpMes*FeCysAm] mit O2 beobachtet und eingehend untersucht. Die Eisen(II)komplexe [TpMesFeOBzR], die neben dem Tp-Liganden unterschiedlich substituierte Benzoate tragen, zeigen bemerkenswerte Ähnlichkeit zum Ruhezustand von Lipoxygenasen. Mit tert-Butylhydroperoxid (tBuOOH) können temperaturempfindliche Spezies beobachtet werden, die den mononuklearen [TpMesFe(OOtBu)(OBzR)] Alkylperoxiden zugeordnet werden. Im letzten Teil dieser Arbeit wird [TpMesFeACC] als Modell für die 1-Aminocyclopropansäureoxidase dargestellt. Es ist möglich, reaktive Spezies mit tBuOOH und meta-Chlorperbenzoesäure (mCPBA) zu beobachten. Zudem liefert die elektrochemische in-situ-Aktivierung von Sauerstoff in Folge Hinweise auf (Hydro-)-peroxidkomplexe bei der Reaktion von [TpMesFeACC] mit dem Superoxidradikalanion. / In the present work model systems for different non-heme iron enzymes are developed and investigated with the help of hydrotris(pyrazolyl) borates (Tp) as tripodal spectator ligands. The first part focusses on the optimization of the synthesis and implementation of the TpMes and TpMes* ligands for biomimetic studies. Following this, suitable precursor complexes [TpMesMCl] are prepared. The coordination behavior of the so far rarely used TpMes* ligand towards divalent transition metal ions is systematically investigated and several heteroleptic [TpMes*MCl] and homoleptic [(TpMes*)2M] complexes are synthesized and characterized. The model complexes [TpMesFeCysOEt] and [TpMesFeCysAm], which carry cysteinate ethylester and cysteaminate as substrate ligands, serve as structural and functional models for the cysteine and cysteamine dioxygenase, respectively. The mesityl residues of the TpMes ligand form a protective, cup-like structure around the iron center. The reaction products could be characterized crystallographically for the first time. An intermediate in the reaction of [TpMes*FeCysAm] with O2 is intensively studied. The iron(II) complexes [TpMesFeOBzR], which in addition to the Tp ligand carry substituted benzoates, show remarkable similarities to the resting state of lipoxygenases. With tert-butyl hydroperoxide (tBuOOH) temperature-sensitive species are observed, which are assigned to the mononuclear [TpMesFe(OOtBu)(OBzR)] alkylperoxides. In the last part of this work, [TpMesFeACC] is presented as a model for 1-aminocyclopropan-1-carboxylic acid oxidase. It is possible to observe reactive species with tBuOOH and meta-chloroperbenzoic acid (mCPBA). In addition, the electrochemical in-situ activation of oxygen provides evidence for (hydro-)peroxide complexes in the reaction of [TpMesFeACC] with the superoxide radical anion.

No description available.