Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Thermal and Photodehydrogenation Reactions of Terpenes Over Zeolites(Izmir Institute of Technology, 2003) Tuzcuoğlu, Esra; Artok, LeventIn this thesis study, catalytic activity of cation exchanged (Na+, Li+, Ca2+, K+, Cs+) zeolite Y, especially NaY, and various microporous and mesoporous (Na exchanged, Beta, Mordenite, and NaX, CsNaX, MCM-41, Montmorillonite KSF and amorphous Silica) catalysts was investigated in the dehydrogenation reaction of terpenes to p-cymene.The results suggested that, there are two types of acid sites are present in cation exchanged zeolites from NH4Y, which are Br Bronsted and Lewis sites. a-terpinene, disproportionated by Br Bronsted acid catalysis into 3-p-menthene and p-cymene, and pcymene was also formed by direct dehydrogenation of a-terpinene can possibly occur with the participation of Lewis acid sites in cation exchanged zeolite Y. Best conversion to p-cymene were observed in the NaHY, LiHY and CaHY exchange from NH4Y that have relatively small cations, which more acidic than the larger ones.With the catalysts that have Bronsted acid sites except ion-exchanged zeolite Y, no conversion or only acid catalyzed isomerization reactions occur that shows the Bronsted acidity was not enough to catalyze the dehydrogenation of a-terpinene. Also Lewis acidic character and the structure morphology are the most important factors affecting the conversion. Lewis acidity is influenced from the cation and zeolite type.Master Thesis Short-Time Suzuki Reactions of Arly Halides Catalyzed by Palladium-Loaded Nay Zeolite Under Aerobic Conditions(Izmir Institute of Technology, 2006) Durgun, Gülay; Artok, LeventThe palladium-catalyzed Suzuki cross-coupling reaction is a powerful methods used in the synthesis of biaryl compounds.In this study, the Suzuki reactions of aryl bromides and chlorides with arylboronic acid were carried out over a Pd(NH3)42+-loaded NaY type zeolite. On the basis of our results, the Pd(NH3)42+-loaded NaY zeolite was found to be highly active for the Suzuki reactions of wide range of aryl bromides and electron poor aryl chlorides at low Pd concentrations (0.1-0.001mol %Pd), in air and at short times (5-45 minutes). The presence of relatively large amount of zeolite (1-4 g) was crucial for the success of the reactions with aryl chlorides. It was determined that there was a synergistic effect of the water- zeolite pair on the reaction rate.It was found that reactions were catalyzed dissolved palladium species. However,the palladium was largely recovered and only traces of palladium remained within the solution at the end of reaction (<0.8 ppm).Master Thesis Silica Supported N-Heterocyclic Carbenes: Active and Reusable Heterogeneous Catalysts for Mizoroki-Heck Reactions(Izmir Institute of Technology, 2004) Açıkel, Müge; Artok, LeventCarbon-carbon bond formation reactions are among the most important processes in chemistry, as they represent key steps in the synthesis of more complex molecules from simple precursors. This thesis describes mainly the development of novel applications of the mild and versatile palladium-catalyzed carbon-carbon coupling method, commonly known as the Heck reaction. Most of the reactions performed in homogeneous media bearing the difficulty of separation from the reaction mixture. For this reason, N-heterocarbenes (NHCs) that gains scientific interest due to their high catalytic activity and stability were used to combine the practical advantage of a heterogeneous catalyst with the efficiency of a homogeneous system Immobilized Pd(NHC) complex 64 (A) and its modified derivatives (B and C),either with trimethylchlorosilane or with imidazolidinium salt 63, were synthesized. Characterization of the novel materials were performed using elemental analysis, AAS, NMR, DRIFTS and BET analysis. On the basis of the results, catalyst C showed higher activity among the others.The results also verified that the predominant activity of C could be ascribed to direct beneficial effect of imidazolidinium salt by being on the silica surface, in the vicinity of the anchored Pd-NHC complex 64. The catalyst showed high activity and reusability towards the Mizoroki-Heck reactions iodoanisole and bromoarenes (activated, nonactivated and deactivated) with styrene, when reactions at 140 °C in the presence of 1.5 molar equivalent NaOAc.3H2O base and 0.5 % Pd with respect to the aryl halide. The catalyst preserved its original activity for 4-iodoanisole, 4-bromoacetophenone, 4- bromotoluene and even for highly deactivated 4-bromoanisole reagent at least 7 uses.Although the addition of immobilized salt to the catalyst C increased the activity,addition of commonly used Bu4NBr showed no gradual increase in the activity. The catalyst C was also active for 4-chloroacetophenone albeit at higher temperature (170°C). The AAS analysis indicated that the reaction was truly heterogeneous.Master Thesis The Activity of Silica Immobilized Palladium N-Heterocyclic Carbene Complexes Toward Mizoro-Heck Reaction and Their Characterization(Izmir Institute of Technology, 2005) Aksın, Özge; Artok, LeventC-C bond formation reactions are among the important processes in chemistry.A palladium-catalyzed reaction, commonly known as the Mizoroki-Heck (M-H) reaction, is a powerful method in construction of C-C coupling of olefins with aryl and vinyl halides.This thesis describes, mainly development and applications of novel silica anchored saturated molecular Pd-N-heterocyclic carbene (Pd-NHC) catalysts toward the M-H reactions of aryl halides.Characterization of the novel Pd-NHC complexes were performed using elemental analysis, NMR and X-ray crystallography techniques. The synthesized complexes were anchored over an amorphous silica surface through their triethoxy silane groups.On the basis of the results, the silica supported saturated Pd-NHCs were found to be highly active catalyst precursors for Mizoroki-Heck reactions of iodo- and bromoarenes with styrene and butyl acrylate olefins, when reactions were performed at 140 C in the presence of 1.5 molar equivalent Na2CO3 base. The catalyst preserved its original activity for 4-iodoanisole, 4-bromoacetophenone, 4-iodoacetophenone, iodobenzene and 4-iodotoluene reagents at least for 8 uses when Pd concentration, with respect to the aryl halide, was 0.5% in the reaction medium.The higher turnover frequencies were realized at the lower Pd concentrations. The AAS analyses revealed the presence of dissolved Pd species within the reaction medium at the early stages of reaction. Along with this finding, determination of Pd agglomerates onto silica surface by TEM examination indicates that the catalyst acted as a Pd reservoir and reactions were catalyzed homogeneously. In the course of reaction, Pd is liberalized to the solution involved with the reaction cycle and deposited onto silica surface to lead to form less active Pd agglomerates. That no trace of dissolved Pd was detected at the end of reaction by AAS is a positive finding for the purity of product.