Dissertationen zum Thema „Hydroxylation reactions“

The diploma thesis deals with post-polymerization hydroxylation of polypropylene in solid state. Regarding the literature review, polypropylene was hydroxylated by radical grafting in aqueous solution of potassium persulfate at 100 °C, under nitrogen atmosphere for 60 minutes. Hydroxylation of polypropylene was performed at different concentrations of potassium persulfate (1; 5; 10 mol. %) and two different water/potassium persulfate molar ratios. The effects of reaction system composition and reaction conditions on reaction efficiency, extent of side reactions, thermal and rheological properties of hydroxylated polypropylene were evaluated. The presence and concentration of hydroxyl groups on polypropylene surface was determined by structural analysis (FTIR, XPS), while the highest efficiency was achieved in the presence of nonionic wetting agents, using 10 mol. % potassium persulfate and at lower water/potassium persulfate molar ratio. Based on changes in polypropylene structure, the modification took place mainly in the amorphous phase of the polymer. In addition to hydroxylation, concurrent side reactions have been reported, in particular the oxidation of wetting agents and polypropylene, which has resulted in chain cleavage, reducing the average molecular weight of the polypropylene.

Les catalyseurs chimiques sont utilisés dans différents procédés de synthèse. Cependant, la pollution qu'ils causent sur l'environnement n’est pas prise en considération. Les procédés de synthèse chimique nécessitent généralement un grand volume de solvants organiques, produisant d’énormes quantités de déchets chimiques, souvent toxiques et non dégradables. Le remplacement des catalyseurs chimiques par des biocatalyseurs (enzymes) pourrait donc bénéficier de leur nature écologique et de leur grande sélectivité envers les produits désirés. Néanmoins, la faible activité et stabilité des enzymes ainsi que leurs coûts élevés sont des obstacles majeurs au développement des systèmes enzymatiques. Par conséquent, des études axées sur le développement de systèmes biocatalytiques plus actifs, stables et rentables, pouvant ouvrir les portes vers un environnement plus vert, sont très souhaitables. Parmi les enzymes qui catalysent des réactions d’importance dans de nombreux procédés de synthèse, le cytochrome P450 BM3 issu de Bacillus megaterium fait l'objet de cette thèse. L'enzyme est capable d’hydroxyler les liaisons C–H des acides gras (C₁₂-C₂) à température ambiante et pH physiologique. Pour cette réaction, BM3 n'a besoin que d’oxygène et de deux électrons habituellement obtenus de son cofacteur naturel, le NADPH. Cependant, pour engager cette enzyme dans les réactions d'hydroxylation, quelques obstacles importants doivent être surmontés : (i) le cofacteur coûteux (NADPH), devrait être remplacé par une source d'électrons moins chère ou régénérée, (ii) la stabilité enzymatique devrait être améliorée et (iii) l'enzyme devrait être facilement récupérable du milieu de réaction pour être réutilisée. Dans ce contexte, cette étude propose pour la première fois l'immobilisation d'un BM3 sur des nanoparticules magnétiques (NMP) d’oxyde de fer. Ce système enzymatique bénéficie (i) de la préférence de l'enzyme pour les cofacteurs NADH et BNAH (moins chers que le NADPH), (ii) de la réutilisation facile du biocatalyseur et (iii) d’une stabilité significative de l’enzyme lors du stockage. Les NMP synthétisées ont été fonctionnalisées pour permettre l’immobilisation de l'enzyme par adsorption ou liaison covalente. Par conséquent, les BM3-NMP adsorbées / réticulées ou liées de façon covalente ont été obtenues en immobilisant P450 BM3 (R966D / W1046S) sur Ni²⁺-PMIDA-NMP ou sur des NMP activés par glutaraldéhyde, respectivement.
L'activité de l’enzyme immobilisée a été comparée avec celle de l’enzyme libre dans la réaction d'hydroxylation du 10-pNCA comme substrat modèle. L'acide myristique a également été utilisé comme substrat modèle pour confirmer la capacité d’hydroxylation sélective de l’enzyme sur les atomes de carbone ω-1, -2 ou -3. Pour les mêmes conditions opératoires, le BM3 adsorbé / réticulé a montré plus de 85% de l'activité de l’enzyme libre, alors que pour les BM3-NMP liées de manière covalente cela représente 60%. La séparation facile des NMP du milieu réactionnel à l’aide d’un aimant a permis de réutiliser le système enzymatique cinq fois consécutives. Après 5 cycles de réaction, l'enzyme réticulée a conservé 100% de son activité initiale. Compte tenu que le recyclage de l’enzyme libre n’est pas faisable, ce résultat est d’une importance considérable dans les applications pratiques. De plus, la stabilité de l’enzyme pendant un mois de stockage à 4 ºC a été évaluée pour chaque système de BM3. Les résultats ont montré que l’enzyme libre n’était plus active après seulement une semaine de stockage dans ces conditions. L'enzyme réticulée n'a montré qu'une activité relative de 41% après un mois de stockage, mais pour le BM3 fixée de façon covalente, la valeur correspondante a été de 80%. La cinétique de l'hydroxylation du 10-pNCA en présence de l’enzyme libre ou immobilisée a été également étudiée. Sur la base des données expérimentales, un modèle de Hill (coefficient de Hill égal à 2) a été obtenu pour l'enzyme libre. Il a été démontré que les mêmes paramètres cinétiques sont capables de prédire le comportement du système BM3-adsorbé et BM3-réticulé dans la réaction d’hydroxylation, étant donné sa similarité avec celui de l’enzyme libre. En conclusion, les résultats de cette thèse ont montré qu'un système enzymatique actif, stable et rentable peut être obtenu en immobilisant le BM3 sur des NMP fonctionnalisées. Il bénéficie autant des avantages de l'enzyme que du support. Ainsi, l'immobilisation sur des NMP d’une enzyme spécialement conçue pour remplacer le couteux NADPH par des cofacteurs moins chers mais efficaces (NADH et BNAH) offre en même temps une amélioration significative de sa stabilité et facilite son recyclage.
MNPs have been synthesized and surface functionalized to attach the enzyme via two different methods, adsorption and covalent binding. Moreover, glutaraldehyde was used to treat the adsorbed enzyme molecules on MNPs (crosslinking-adsorption). Therefore, adsorbed, crosslinked-adsorbed, or covalently bound BM3-MNPs were obtained by immobilizing P450 BM3 on synthesized Ni²⁺-functionalized MNPs or glutaraldehyde pre-activated MNPs, respectively. The immobilized enzyme activity was compared to its free counterpart in hydroxylation reaction of 10-pNCA (10-(4-Nitrophenoxy) decanoic acid) as a substrate model. Myristic acid was also used as a substrate model to confirm the enzyme selective hydroxylation at ω-1, -2, or -3 carbon positions. The effect of cofactor (NADH and its analogue, BNAH) on the enzyme activity was also investigated. The adsorbed/crosslinked-adsorbed BM3 showed more than 85% of the free enzyme activity while the covalently bound BM3-MNPs presented 60% of the free enzyme activity under the same reaction conditions. An important feature of BM3-MNPs system is the possibility of recycling the biocatalyst. Facile separation of the magnetic nanoparticles from the reaction medium by applying a magnet provided the opportunity of reusing the enzymatic system for five times. After 5 cycles of reaction, the crosslinked-adsorbed enzyme retained 100% of its initial activity. Although the covalently bound enzyme showed, only half of the crosslinked-adsorbed enzyme activity, its storage stability was more significant. Taking into account that the enzyme reuse is an essential concern in many large-scale applications and the free BM3 cannot be recovered and reused, this result is noteworthy. Storage stability tests revealed that the free enzyme became inactive after one-week while the crosslinked-adsorbed enzyme and the covalently attached BM3 on MNPs showed 41% and 80% relative activity after one month, respectively. Finally, the steady-state kinetics of 10-pNCA hydroxylation by free and immobilized BM3 was investigated. Based on the experimental data, a non-Michaelis-Menten, Hill model (Hill coefficient of 2) was obtained for the free enzyme which could also predict the adsorbed and crosslinked-adsorbed BM3-MNPs system performance. This sigmoidal behavior was found to be independent of enzyme concentration and type of cofactor. However, since the enzyme activity was only 60% of the free enzyme for covalently bound BM3, further studies are necessary for a better understanding of this system. In summary, the results of this thesis show that an active, stable, and cost-effective BM3-MNPs system can be obtained by immobilizing an engineered BM3 on functionalized MNPs. Such systems benefit from the advantages of both enzyme and support. An engineered enzyme can fulfill the desired targets including the replacement of costly NADPH by less-expensive, yet effective cofactors namely NADH and BNAH. Furthermore, immobilization of this enzyme on MNPs improves its stability and facilitates the recycling process.
Chemical catalysts are used in different synthetic processes from lab to industrial scales. High reaction yields usually achieved by this type of processes favor their application in many industries without considering the pollution they cause to the environment. Chemical synthesis processes usually require a high volume of organic solvents and produce tons of chemical wastes which are often toxic and not degradable. Replacing conventional catalysts by biocatalysts (enzymes) can benefit from their environmentally friendly nature and high selectivity toward the desired products. Although the advantages of biocatalysts over chemical catalysts have been proven, the application of enzymes in an industrial level is still not considerable. The enzyme low activity, stability, and high cost are the main concerns in developing large-scale enzymatic systems. Therefore, in the context of a greener environment, studies focusing on the development of more active, stable, and cost-effective enzymatic systems are in great demand. Among several enzymes that can catalyze essential synthesis reactions, cytochrome P450 BM3 from Bacillus megaterium is the subject of this thesis. This enzyme hydroxylates the saturated and unsaturated C–H bonds of medium to long chain fatty acids at room temperature and physiological pH. For this reaction, BM3 only needs molecular oxygen and two electrons usually obtained from its natural cofactor, NADPH. However, to engage this enzyme in hydroxylation reactions, some important obstacles should be overcome: (i) the costly cofactor (NADPH) should be replaced by a cheaper source of electrons or regenerated, (ii) the enzyme stability should be improved, and (iii) the enzyme should be easily recovered from the reaction medium to be reused. In this context, this study proposes for the first time the immobilization of an optimized BM3 mutant on functionalized iron oxide magnetic nanoparticles (MNPs). This enzymatic system benefits from (i) the enzyme preference towards cofactors like the reasonably priced NADH and the very cheap BNAH, (ii) facile recovery and reuse of the biocatalyst (enzyme-MNPs), and (iii) the enzyme significant storage stability.

Since the rediscovery of carbon nanotubes (CNTs) due to the publication of Sumio Iijima's article Helical microtubules of graphitic carbon in the magazine Nature in 1991 the interest in carbon nanotubes has rapidly increased. This bachelor thesis also deals with this popular material with the aim to functionalize CNTs for further uses in the microelectronic industry. A promising approach is the functionalization of the CNTs with metal nanoparticles or metal films. To achieve this, one can perform an atomic layer deposition (ALD) on CNTs. In the present work the Trimethylaluminum (TMA) ALD is the chosen process for the functionalization of the CNTs, which will be studied here. Since the available knowledge on the CNT-functionalization by gas phase reactions is very limited, a theoretical study of possible reaction pathways is necessary. Those studies are carried out with two modern quantumchemical programs, Turbomole and DMol³, which are described together with an introduction into Density Functional Theory, as well as an introduction of CNTs and the ALD process. A basic model of a CNT with a Single Vacancy defect, which had been selected according to the demands of the studies, is introduced. Because the TMA ALD process requires hydroxyl groups as its starting point, not only is the performance of a TMA ALD cycle on a CNT studied, but also reactions which result in the CNTs owning of hydroxyl groups. Consequently, this bachelor thesis will focus on two di erent aspects: The performance of one TMA ALD cycle and the study of possible educts for the TMA ALD process. This study of the educts includes possible structures which can be formed when a CNT comes into contact with air.

L'électrochimie est apparue comme un puissant outil de synthèse durable en chimie organique, qui évite l'utilisation d'un oxydant stoechiométrique externe et permet le développement de méthodes de difonctionnalisation très efficaces et sélectives des indoles dans des conditions douces. L'utilisation de médiateurs redox pour réaliser l'électrolyse indirecte a gagné en importance ces dernières année, ce qui offre de nombreux avantages par rapport à l'électrolyse directe. Les réactions de désaromatisation des hétéroarènes achiraux, et en particulier des indoles, donnent des structures tridimensionnelles d’un grand intérêt pour la synthèse totale ou la découverte de médicaments, via la génération de deux centres stéréogéniques contigus. Ainsi des efforts de synthèse intensifs ont été consacrés à la difonctionnalisation désaromatisante d’indoles. Dans ce contexte, le développement de réactions de désaromatisation des indoles a été étudié au cours de cette thèse. Dans la première partie de la thèse, une diallylation désaromatisante de N-acylindoles médiée par FeCl₃ a été développée pour obtenir des indolines tridimensionnelles sélectives possédant deux centres stéréogéniques contigus. Dans ce procédé, deux groupes allyle ont été introduits sur des N-acylindoles avec de l'allyltriméthylsilane en présence de FeCl₃, conduisant à la formation de deux liaisons carbone-carbone et de deux centres stéréogéniques contigus. La stéréosélectivité de cette transformation est contrôlée par la substitution du noyau indole. Des applications synthétiques ont permis d'obtenir des squelettes trans-tétrahydrocarbazoles et aza[4.4.3]propellanes par RCM. L'hydratation sélective de l'un des groupes allyliques a également été réalisée. Dans la deuxième partie de la thèse, une désomatisation oxydante directe des indoles a été réalisée par électrochimie, conduisant à des 2,3-dialcoxy ou des 2,3-diazido indolines avec une cellule non divisée à courant constant. Cette difonctionnalisation électrochimique des indoles évite l'utilisation d'un oxydant externe et présente une excellente compatibilité de groupes fonctionnels, ce qui devrait inspirer le développement d'autres réactions de désaromatisation afin d'accéder à des architectures à haute valeur ajoutée à partir de matériaux de départ facilement disponibles. Sur la base de l'étude mécanistique, nous pensons que la formation des deux liaisons C-O ou C-N résulte de l'oxydation des indoles en un intermédiaire radical cation. Dans la troisième partie de la thèse, une désaromatisation oxydante par électrolyse indirecte des indoles a été conçue en utilisant MgBr₂ comme médiateur redox pour éviter l'oxydation directe du noyau indole à l'anode. L’oxydation de l’indole en un ion bromonium induite par la génération d’un réactif électrophile bromé à partir de MgBr₂, conduit à des réactions de dihydroxylation, d’hydroxycyclisation et de bromocyclisation d’indoles. Aucun sous-produit organique n'est généré avec ce protocole qui ne nécessite aucun électrolyte supplémentaire. L’intérêt de cette transformation est démontré par les applications synthétiques
Electrochemistry emerged as a powerful sustainable synthetic tool in organic chemistry, which avoids the use of an external stoichiometric oxidant and enables the development of methods for the highly efficient and selective difunctionalization of indoles in mild conditions. The use of redox mediators to achieve indirect electrolysis is attaining increased significance, which offers many advantages compared to direct electrolysis. Dearomatization reactions of achiral heteroarenes and in particular of indoles, afford three-dimensional structures of high interest for total synthesis or drug discovery, through the generation of two contiguous stereogenic centers. Intensive synthetic efforts have been devoted to dearomative difunctionalization of indoles. In this context, the development of dearomatization reactions of indoles has been studied in this thesis. In the first part of the thesis, a dearomative diallylation of N-acylindoles mediated by FeCl₃ was developed to obtain selectively three-dimensional indolines possessing two contiguous-stereogenic centers. In this process, two allyl groups were introduced to N-acylindoles with allyltrimethylsilane in the presence of FeCl₃, leading to the formation of two carbon-carbon bonds and two contiguous-stereogenic centers. The stereoselectivity of this transformation is controlled by the substitution of the indole nucleus. Synthetic application allowed to obtain trans-tetrahydrocarbazoles and aza[4.4.3]propellane scaffolds by RCM. Selective hydration of one of the allyl group was achieved. In the second part of the thesis, a direct oxidative dearomatization of indoles was performed with electrochemistry, leading to 2,3-dialkoxy or 2,3-diazido indolines under undivided cell conditions at a constant current. This general difunctionalization of indoles avoids the use of an external oxidant and displays excellent functional group compatibility, which should inspire the development of other dearomatization reactions to access high added-value architectures from readily available starting materials. Based on the mechanistic study, the formation of the two C-O or C-N bonds is believed to arise from the oxidation of the indoles into radical cation intermediates. In the third part of the thesis, an indirect oxidative dearomatization of indoles was devised by using MgBr₂ as the redox mediator to avoid the direct oxidation of the indole nucleus at the anode. The oxidation of the indole into a bromonium ion induced by the generation of an electrophilic bromine reagent from MgBr₂, and lead to dihydroxylation, hydroxycyclization and bromocyclization reactions of indoles. No organic byproducts are generated with this protocol which requires no additional electrolyte. The potential of this transformation is demonstrated by synthetic applications

In the first part of this thesis is related to the regioselectivity in ene reaction of singlet oxygen with cyclic alkenes. The photooxygenation of 1-methyl-, 2,3-dimethyl-, 1,4-dimethylcyclohexa-1,4-dienes, 1,2,3,4,5,8-hexahydronaphthalene (16) and 2,3,4,7-tetrahydro-1H-indene (17) which are readily available through Birch reduction, yielded the ene products. The formed endocyclic dienes were trapped by the addition of singlet oxygen to give corresponding bicyclic endoperoxy-hydroperoxides. In the case of 1-methylcyclohexa-1,4-diene (13) and 1,4-dimethyl-cyclohexa-1,4-diene (15), cis-effect determined the product distribution. Photooxygenation of 2,3-dimethylcyclohexa-1,4-dienes (14) gave mainly exocyclic olefin, which was attributed to the lowered rotational barrier of the methyl group and increased reactivity of the methyl groups. Photooxygeneation of 1,2,3,4,5,8-hexahydronaphthalene (16) and 2,3,4,7-tetrahydro-1H-indene (17) shows importance of the geometry of the allylic hydrogen in the ground state. In the second part of this thesis is related to the stereoselective synthesis of carbaheptopyranose derivatives. Two new carbaheptopyranoses, 5a-carba-6-deoxy-&alpha
-DL-galacto-heptopyranose (184) and 5a-carba-6-deoxy-&alpha
-DL-gulo-heptopyranose (185) have been prepared starting from cyclohexa-1,4-diene. The addition of dichloroketene to cyclohexa-1,4-diene followed by subsequent reductive elimination and Baeyer-Villiger oxidation formed the bicyclic lactone 188. Reduction of the lactone moiety followed by acetylation gave the diacetate 182b with cis-configuration. Introduction of additional acetate functionality into the molecule was achieved by singlet oxygen ene-reaction. The formed hydroperoxide 189 was reduced and then acetylated. The double bond in triacetate was further functionalized either by direct cis-hydroxylation using OsO4 or epoxidation followed by ring-opening reaction to give the hepto-pyranose derivatives 184 and 185.

La réaction de désaromatisation hydroxylante de phénols (HPD) est un outil puissant pour accéder de façon biomimétique, en une seule étape à partir de 2-alkylphénols, aux ortho-quinols, c’est-à-dire les 6-alkyl-6-hydroxycyclohexa-2,4-diénones. Ces synthons peuvent être présentés tels quels par de nombreux produits naturels mais peuvent aussi servir d’intermédiaires hautement fonctionnalisés pour la construction rapide d’architectures structurales complexes. L’acide o-iodoxybenzoïque (IBX), un réactif de type iodane-?5, et sa formulation stabilisée non-explosible (SIBX) se sont révélés particulièrement efficaces pour promouvoir des réactions HPD de manière ortho-sélective. Ces travaux de thèse concernent l’application de cette réaction à l’élaboration d’un intermédiaire ortho-quinolique clé hautement fonctionnalisé pour la synthèse d’un antibiotique de type angucycline, la (+)-aquayamycine, ainsi qu’à la première synthèse totale d’un ortho-quinol naturel non dimérisant, la (+)-wasabidiénone B1. Enfin, le développement d’une version asymétrique de cette réaction a été entrepris. La génération in situ de iodanes à partir de iodoarènes chiraux et de m-CPBA comme co-oxydant permet de préparer soit des ortho-quinols de façon non racémique lorsque des quantités stoechiométriques des deux réactifs sont utilisées, soit des ortho-quinols régio- et diastéréosélectivement époxydés lorsqu’une quantité catalytique de iodoarène chiral est employée. Un suivi de ces réactions par spectrométrie de masse a conduit à la détection d’espèces de type iodanyl-?3 et/ou -?5, et à la proposition d’un mécanisme pour ces réactions de désaromatisation hydroxylante asymétrique
The hydroxylative phenol dearomatization (HPD) reaction is a powerful tool to access, in one biomimetic step from various 2-alkylphenols, ortho-quinols, i.e., 6-alkyl-6-hydroxycyclohexa-2,4-dienones. These dearomatized moieties can be found as such in few natural products or can be used as highly functionalized intermediates. The ?5-iodane 2-iodoxybenzoic acid (IBX) and its stabilized nonexplosive formulation (SIBX) have proved particularly useful and efficient in mediating HPD reactions in a strictly ortho-selective manner. This PhD work describes the application of our SIBX-mediated HPD reaction to the elaboration of a key ortho-quinolic advanced intermediate for the synthesis of the angucycline-type antibiotic (+)-aquayamycin, and to the first total synthesis of the natural non-dimerizing ortho-quinol (+)-wasabidienone B1. An asymmetric version of this HPD reaction has been also developed. In situ generation of iodanes from chiral iodoarenes and m-CPBA as co-oxidant enables the preparation of either ortho-quinols in a non racemic form when using stoechiometric amounts of both reagents, or regio- and diastereoselectively epoxidized ortho-quinols when a catalytic amount of the chiral iodoarene is used. Monitoring of these reactions by mass spectrometry allowed the detection of ?3- and/or ?5-iodanyl-type species, and the proposition of a mechanism for these asymmetric hydroxylative dearomatization reactions

La transformation de la cfarvone en quatre diastereoisomeres precurseurs du cycle a des dihydrovitamines et dihydrotachysterols est decrite dans la premiere partie. Par couplage d'un acetylure derive des cycles c/d de la vitamine d::(3) avec la cetone precurseur du cycle a, puis sa formation du systeme dienique a l'aide de titane a basse valence nous avons obtenu des dihydrotachysterols majoritairement. D'un autre cote, l'utilisation de sulfoxydes optiquement actifs dans l'intention de creer des centres hydroxyles chiraux et son application a la synthese du fragment polyhydroxyle de l'amphotericine b et du l-arabinitol est decrite dans la deuxieme partie. Les trois etapes-cles de cette methodologie sont: reduction stereospecifique d'un beta-cetosulfoxyde; condensation stereospecifique; cis-hydroxylation d'un beta-hydroxysulfoxyde

Notre travail s'inscrit dans le cadre de la recherche de complexes modeles de sites actifs binucleaires d'enzymes a fer non heminique et plus particulierement de l'hemerythrine et de la methane monooxygenase. Pour cela, nous avons synthetise des composes dans lesquels le centre binucleaire est dissymetrique, c'est a dire que les deux ions metalliques sont dans des environnements differents. Ainsi lors de la synthese de complexes a valence mixte, fe#i#i#ife#i#i, l'ion ferrique est dans un environnement n#3o#3 alors que l'ion ferreux se trouve dans un environnement n#2o#3x, un ligand exogene completant sa sphere de coordination. Notre projet s'articule ensuite principalement autour de deux axes : - l'etude de la structure electronique du centre a fer suivant les conditions de solvatation et d'hydratation du milieu, donc suivant la nature du ligand x. On montre par ces experiences que les proprietes spectroscopiques et electrochimiques des complexes varient suivant si x est une molecule d'acetonitrile ou une molecule d'eau et, de plus, lors de l'oxydation de la forme fe#i#i#ife#i#i-oh#2 il se produit une deprotonation spontanee pour conduire a une espece fe#i#i#ife#i#i#i-oh. - la capacite des complexes a catalyser des reactions d'hydroxylation de substrats, en presence de donneurs d'oxygene. Les resultats obtenus indiquent que les complexes possedent une activite monooxygenase et, de plus, en presence de toluene, il se produit une hydroxylation en position ortho pour donner comme produit d'oxydation l'ortho-cresol, ce qui modelise la reactivite de la toluene-2-monooxygenase. Enfin, dans une derniere partie, nous presentons la structure d'un nouveau complexe possedant une entite fe#i#i#i#2(-oh)#2.

La synthèse d'une pophyrine de fer à "anses de panier" chirale comportant des aminoacidés de configuration déterminée est décrite. On a étudié sa pureté optique et sa conformation en solution. Dans une deuxième partie on décrit un nouveau système oxydant catalytique utilisant l'eau oxygénée en présence d'une porphyrine de manganèse et d'imidazole permettant la conversion quantitative d'alcènes en époxydes et d'alcanes en alcools et cétones.

Polyurethanes are valuable polymers with a wide variety of applications. They are normally produced from polyol feedstocks derived from petroleum. As petroleum is a non-renewable resource, an alternative source of feedstock is sought. A potential source is rice bran oil. However, far too little attention has been paid to the utilization of rice bran oil as a potential raw material to produce polyol as it contains unsaturated fatty acids that can be converted to polyol and is the by product of rice milling process and available at very low cost. There are two sequential processes to produce polyol from rice bran oil, namely the epoxidation and hydroxylation reactions. In this work, the optimal conditions in the epoxidation reaction were investigated using acetic acid and formic acid as oxygen carriers in terms of reaction time and temperature. Furthermore, the reaction kinetics were also determined using formic acid as an oxygen carrier in the epoxidation step. Finally, the influence of reaction time and temperature in the hydroxylation step were also investigated in this study. In order to determine the optimal condition, the epoxidation reaction was performed in a three neck flask with the use of acetic and formic acid as oxygen carriers. Result shows that the conversion of iodine value increased with reaction time and temperature when acetic acid was used as an oxygen carrier (peroxyacetic acid). Interestingly, the oxirane content increased with reaction time and temperature then declined after having achieved the optimal point. The optimal condition was achieved at a reaction time of 4.3 h and a temperature of 63.8°C by performing response surface methodology. The conversion of iodine value also displayed similar behaviour during the epoxidation reaction when formic acid was used as an oxygen carrier (peroxyformic acid), namely the conversion increased with reaction time and temperature. The measured rate constants were 0.172h⁻ ¹ (40°C), 0.304h⁻ ¹(50°C), 0.374h⁻ ¹(60°C), 0.425h⁻ ¹(70°C) and 0.492h⁻ ¹(80°C). The activation energy was 22.6 kJ/mol and the epoxidation reaction was pseudo-first order with respect to the concentration of double bonds in the oil. Interestingly, peroxyformic acid shows improved performance as indicated by higher content of maximal oxirane content 3.26% compared to peroxyacetic acid which is only 2.62%. The optimal condition with the use of formic acid as an oxygen carrier was obtained at reaction time of 4 h and temperature of 60°C. In the hydroxylation step, results indicate that the hydroxyl value of polyol was a quadratic function of reaction time and temperature and the optimal condition was achieved at a reaction time of 125.5 min and temperature of 49°C, with maximal hydroxyl value 161.5 mg KOH/g oil by performing response surface methodology. The viscosity of polyol increased with reaction time and temperature and resulted in polyol with viscosity in the range 29.9 – 95.3 cP. Temperature was found to have the most significant effect on the viscosity of polyol. The results of this study confirm the potential of rice bran oil as a feedstock for synthesis of polyol and show that the optimal conditions in the epoxidation and hydroxylation reactions are a key control variable to obtain a high quality of polyol.
Thesis (M.Eng.Sc.) -- University of Adelaide, School of Chemical Engineering, 2010

碩士
國立清華大學
化學系
92
Abstract Various deuterated propanes and butanes have been synthesized to serve as mechanistic probes to explore the C-H hydroxylation occurring at the hydrophobic pocket within the particulate methane monooxygenase (pMMO) from M. capsulatus (Bath). The enantiomeric excess (ee) of the oxidation products for [1,1,1-2H3]butane and [1,1,1,4,4,4-2H6]butane was determined to be 94% and 86%, respectively, in favor of the formation of the 2R-alcohol. According to our previous experiment, in the case of [2,2-2H2]butane, the insertion of the CH3CD2- end was more favorable than the CH3CH2- end due to the tightness of the hydrophobic pocket. The van der Waal radius of the C-D bond is about 0.01 Å shorter than that of C-H bond. Therefore, the different ee value between [1,1,1-2H3]butane and [1,1,1,4,4,4-2H6]butane may simply reflect the higher steric hinderance of 4-CH3- end of [1,1,1-2H3]butane adjacent to the edge of the hydrophobic pocket. This steric effect may control the stereochemistry in order to bias the hydroxylation toward the R-alcohol at the 4-CD3- end. From GC-MS analysis of m/z 141 and 144 ratio of the correponding trifluoroacetic ester derivatives of [1,1,1-2H3]butan-2-ol products we measured, we obtained kCH3-/kCD3-= 0.73(0.01), indicating that the insertion is in preference for the CD3CH2- end relative to CH3CH2- end. In the case of [2-2H1]propane, we measured a modest kinetic isotope effect (KIE) of hydrogen vs. deuterium of 5.79(0.04), in full agreement with KIE value previously determined for cryptically chiral ethane and d.l-chiral butane (5.5). These data provide further support for the concerted oxene insertion instead of radical rebound mechanism in the hydroxylation reaction of propane molecule mediated by pMMO. Finally, we conducted experiments on the oxidation of the trans-2-butene by pMMO. The enantiomeric excess of the products trans-2,3-epoxybutane was determined to be 10.2% in favor of (2S,3S)-products. The epoxidation of vinylic carbon mediated by pMMO does not give rise to the same high chiral selectivity in comparison with the hydroxylation of the aliphatic compound. This result indicates that the sp3 carbon center encounters a stronger stereoelectronic orientation relative to the sp2 carbon center at the active site.

Since the rediscovery of carbon nanotubes (CNTs) due to the publication of Sumio Iijima's article Helical microtubules of graphitic carbon in the magazine Nature in 1991 the interest in carbon nanotubes has rapidly increased. This bachelor thesis also deals with this popular material with the aim to functionalize CNTs for further uses in the microelectronic industry. A promising approach is the functionalization of the CNTs with metal nanoparticles or metal films. To achieve this, one can perform an atomic layer deposition (ALD) on CNTs. In the present work the Trimethylaluminum (TMA) ALD is the chosen process for the functionalization of the CNTs, which will be studied here. Since the available knowledge on the CNT-functionalization by gas phase reactions is very limited, a theoretical study of possible reaction pathways is necessary. Those studies are carried out with two modern quantumchemical programs, Turbomole and DMol³, which are described together with an introduction into Density Functional Theory, as well as an introduction of CNTs and the ALD process. A basic model of a CNT with a Single Vacancy defect, which had been selected according to the demands of the studies, is introduced. Because the TMA ALD process requires hydroxyl groups as its starting point, not only is the performance of a TMA ALD cycle on a CNT studied, but also reactions which result in the CNTs owning of hydroxyl groups. Consequently, this bachelor thesis will focus on two di erent aspects: The performance of one TMA ALD cycle and the study of possible educts for the TMA ALD process. This study of the educts includes possible structures which can be formed when a CNT comes into contact with air.:Abstract 1. Introduction 2. Carbon Nanotubes and the Atomic Layer Deposition 2.1. Carbon Nanotubes 2.1.1. Graphene and Its Relation to Carbon Nanotubes 2.1.2. Classi cations 2.1.3. Defects 2.2. Atomic Layer Deposition 2.2.1. Introduction to Atomic Layer Deposition 2.2.2. Trimethylaluminum Atomic Layer Deposition 3. Theoretical Background 3.1. The Schrödinger Equation and the Variational Principle 3.2. Electron Density 3.2.1. The Wave Function 3.2.2. The Electron Density 3.3. The Hohenberg-Kohn Theorems 3.3.1. The First Hohenberg-Kohn Theorem 3.3.2. The Second Hohenberg-Kohn Theorem 3.4. The Kohn-Sham Approach 4. Computational Details and the Model System 4.1. Model System 4.1.1. The Basic (5; 5)-CNT 4.1.2. Further Adjustments to the Basic (5; 5)-CNT 4.2. Computational Details 4.2.1. Materials Studio/Dmol³ 4.2.2. Turbomole 5. Results and Discussion 5.1. Educt Formation Reactions 5.1.1. Educts with Two Oxygen Atoms 5.1.2. Educts with Two Hydroxyl Groups and One Oxygen Atom 5.1.3. Educts with Two Hydroxyl Groups and Two Hydrogen Atoms 5.1.4. Educts with Four Hydroxyl Groups 5.1.5. Educts with Peroxy Groups 5.1.6. Summary - Educts 5.2. Performance of the First Trimethylaluminum Atomic Layer Deposition Cycle 5.2.1. The First Trimethylaluminum Atomic Layer Deposition Half Cycle 5.2.2. The Second Trimethylaluminum Atomic Layer Deposition Half Cycle 6. Summary and Outlook A. Appendix A.1. Note on the Multiplicity A.2. Note on the Computation Time A.3. Comparison between Dmol³ and Turbomole A.4. Tables of Energies for the Studied Educts in 5.1 A.5. Tables of Energies for the Study of the Trimethylaluminum Atomic Layer Deposition Cycle in 5.2 Bibliography Acknowledgment