Dokument: MICROWAVE-ASSISTED SYNTHESIS OF MONOMERIC AND POLYMERIC AMIDES:
| Titel: | MICROWAVE-ASSISTED SYNTHESIS OF MONOMERIC AND POLYMERIC AMIDES: | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=3649 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20080305-143731-9 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Iannelli, Mauro [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Dr. h.c. Ritter, Helmut [Gutachter] Prof. Dr. Staudt-Bickel, Claudia [Gutachter] | |||||||
| Stichwörter: | Microwave-assisted synthesis, (meth)acrylamides, polymer analogous reactions, sulfonimide, reaction mechanism | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 540 Chemie | |||||||
| Beschreibung: | The use of microwave irradiation has become, over the years, a well-established technique to promote and enhance chemical reactions. A proof of it is the increasing number of publications concerning the application of microwaves (MW) in all fields of the chemical sciences.
Microwaves are electromagnetic waves that can be placed between infrared radiation and radio frequencies with wavelengths ranging from 1 m to 1 mm. The corresponding frequencies range between 300 MHz and 300 GHz. Being this range extensively used for telecommunications purposes, in order to avoid interferences, almost all commercially available microwave reactors for chemical use, as well as household and industrial microwave ovens, operate at the frequency of 2.45 GHz (12.2 cm). The main advantages of MW assisted chemistry are shorter reaction times and higher selectivity compared with syntheses performed under conventional heating. Most of these enhancements can be described as thermal effects mainly due to homogeneous heating or superheating easily realized, for example, using highly polar reaction media. The possible existence of so called specific microwave effects that could rationalize specific synthetic pathways observed in microwave and not under conventional heating is still subject of debate and controversy. The chiral (R)-N-(1-phenylethyl)-methacrylamide was synthesized directly from methacrylic acid and (R)-N-1-phenylethylamine through microwave irradiation in a solvent-free medium. Kinetic comparison between reactions carried out either under MW or conventional thermal heating evidenced the higher selectivity of the MW accelerated reaction. Under the applied conditions, the desired amidation was clearly preferred to the Michael addition side-reactions. The addition of a radical initiator to the starting mixture led, in a single step, to the formation of optically active polymers containing both methacrylamide and imide moieties. The synthesis of the corresponding chiral acrylamide, prepared in MW by direct conversion of acrylic acid with (R)-N-1-phenylethylamine, without solvent or any activating reagent, was not possible to perform by conventional heating in oil-bath. In the latter case only polymeric and decomposition products were obtained. The performed kinetic measurements showed high selectivity and conversion to the amide after only a few minutes of reaction time. The irradiation of the educts mixture, in presence of AIBN, led also in this case to polymeric structures containing imide units. The applied MW power resulted to have a clear influence on yield and molecular weight distribution of the obtained optically active polymers. Acid functionalized polyethylene, containing about 10 mol % of acrylic acid units, was reacted in microwave and, as a comparison, in oil-bath with dissimilar amines to give copolymers bearing amide groups. The MW-assisted reactions showed increased conversion for most of the investigated amines. In the case of a few amines, a better conversion was obtained for the runs in oil-bath. Considering that the reactivity of the amines depends mainly on their nucleophilicity and basicity, it was attempted to correlate an experimental reactivity index (based on FT-IR analyses) with the order of basicity and nucleophilicity of the amines. For the MW runs an excellent linear correlation (R=0.97, SD=0.68) was obtained comparing basicity and reactivity. On the other hand the oil-bath reactions correlated very well (R=0.97, SD=1.13) with a nucleophilicity scale obtained by theoretical calculations. The correlation of reactivity-basicity observed in microwave has to be related to the strong microwave-absorbing capacity of ionic species (ammonium salts). Under conventional thermal heating, the amidation reaction is mainly ruled by the nucleophilicity. A reactivity behavior based on dissimilar parameters cannot be rationalized only invoking purely thermal effects. Specific microwave effects have to be considered. The synthesis of N-benzensulfonamide maleimide was performed in bulk through the microwave-assisted reaction of maleic anhydride with 4-amino-benzenesulfonamide. The product was obtained in a good yield in very short reaction time (2 min). The same reaction was also performed in oil-bath showing the superiority of the microwave-assisted approach. The monomer was polymerized under MW irradiation in N,N-dimethylformamide (DMF) solution using benzopinacol as a free radical initiator. Qualitative investigations of the pH dependent solubility of the polymer were also performed. The imide-containing diol, 2-hydroxy-N-(2-hydroxypropanoyl)-N-(1-phenylethyl)propanamide, was synthesized by microwave activation of a stoichiometric mixture of lactic acid and (R)-N-1-phenylethylamine. 20 minutes of irradiation were sufficient to reach a conversion of 90 % whereas the oil-bath reaction needed 60 minutes to provide 70 % of the desired product. Preliminary investigations of the free radical polymerization of methylmethacrylate (MMA), methacrylic acid (MA), dimethylaminoethylmethacrylate (DMAEM) and zinc methacrylate (ZMA) in tetrahydrofuran (THF) solution using AIBN as an initiator were performed in MW and in oil-bath. For MMA and ZMA no benefits could be obtained from the MW approach. In the case of the copolymer MA/DMAEM appeared the experimental evidence of a negative MW effect dependent on the applied power. A possible rationalization is proposed in terms of power influence on the acid-base equilibrium. Anyway, more detailed investigations are required to better elucidate this unexpected occurrence. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Chemie | |||||||
| Dokument erstellt am: | 01.02.2007 | |||||||
| Dateien geändert am: | 05.03.2008 | |||||||
| Promotionsantrag am: | 24.01.2007 | |||||||
| Datum der Promotion: | 24.01.2007 |
