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Suitable Precursors (suitable + precursor)
Selected AbstractsPorosity and surface characteristics of activated carbons produced from waste tyre rubberJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2002Guillermo San Miguel Abstract Waste tyre rubber has proven to be a suitable precursor for the production of high quality activated carbons. The performance of these carbons in commercial applications such as water treatment or gas purification is highly dependent on their surface characteristics. This paper presents an in-depth investigation on how production conditions may affect the yield and characteristics of activated carbons produced from tyre rubber. For this purpose, three tyre rubbers of different particle sizes were consecutively pyrolysed and then activated in a steam atmosphere at 925,°C using a laboratory-scale rotary furnace. Activation was conducted at different intervals over 80,640,min to achieve different degrees of carbon burn-off. The resulting carbons were analysed for their elemental composition, ash content and nitrogen gas adsorption characteristics. The BET and t -plot models were used to investigate various aspects of their porosity and surface area characteristics. SEM analyses were also conducted for visual examination of the carbon surface. Results show that pyrolytic chars, essentially mesoporous materials, developed a very narrow microporosity during the initial stages of the activation process (up to 15,25,wt% burn-off). Further activation resulted in the progressive enlargement of the average micropore width and a gradual development of the mesoporous structure. Total micropore volumes and BET surface areas increased continuously with the degree of activation to reach values up to 0.498,cm3g,1 and 1070,m2g,1 respectively, while external surface areas developed more rapidly at degrees of activation above 45,wt% burn-off. Results presented in this work also illustrate that carbons produced from powdered rubber developed a narrower and more extensive porosity, both in the micropore and mesopore range, than those produced from rubber of a larger particle size. © 2001 Society of Chemical Industry [source] Synthesis of L -Furanomycin and Its Analogues via Furoisoxazolines,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2005Peter J. Zimmermann Abstract The 1,3-dipolar cycloaddition of nitrile oxides and 2-methylfuran has provided suitable precursors for ,-amino acids such as L -furanomycin (1) that contain a dihydrofuran ring. By using a chiral nitrile oxide derived from D -glyceraldehyde, the enantiomerically pure furoisoxazolines 9 and 10 were obtained. Owing to the bicyclic, bowl-shaped structure of furoisoxazoline 9 highly stereoselective additions were feasible, in particular, the epoxidation of 9 with dimethyldioxirane provided the required (5'S) configuration in 1 after epoxide reduction. Hydroboration of 9 led to the (5'R) epimer 2 and nucleophilic addition of a methyl Grignard reagent to epoxyfuroisoxazoline 11 gave rise to 5'-methylfuranomycin (3). Further, catalytic hydrogenation of the dihydrofuran intermediate 22, derived from 11, afforded the tetrahydrofuranyl derivative 31 from which dihydrofuranomycin (4) was obtained in enantiomerically pure form. The biological activities of these ,-amino acids showed an extremely narrow structure,activity profile, the natural product being the only compound of this series with high activities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Positive Temperature Coefficient of Resistivity in Donor-Doped BaTiO3 Ceramics derived from Nanocrystals synthesized at Low Temperature,ADVANCED MATERIALS, Issue 5 2008L. Brutchey Small, donor-doped Ba1- xLaxTiO3nanocrystals are successfully prepared for the first time. These nanocrystals are suitable precursors for small-grain Ba1- xLaxTiO3 ceramics with a sizeable positive temperature coefficient of resistivity (PTCR) that is comparable to that of traditional large-grain ceramics derived from solid-state routes. [source] Phase-Transfer-Catalyzed Enantioselective Mannich Reaction of Malonates with ,-Amido SulfonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 15 2006Francesco Fini Abstract The highly enantioselective reaction between in situ generated, Cbz-protected azomethines and malonates in the presence of 150 mol,% of potassium carbonate (50,% w/w) and 1 mol,% of quinine-derived quaternary ammonium bromides as phase-transfer organocatalysts has been developed. This study reports a novel approach for the asymmetric Mannich-type reaction and a wide range of azomethines, including those derived from enolizable aldehydes, is tolerated by the present system. The adducts, obtained in excellent yields with ee up to 98,%, are suitable precursors of optically pure ,-amino acids. [source] | ||||||||||