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Knoevenagel condensation
About: Knoevenagel condensation is a research topic. Over the lifetime, 4896 publications have been published within this topic receiving 80618 citations.
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TL;DR: In this article, the scope and limitations of the two catalysts in various reaction conditions examined were described, and both HClO4−SiO2 and PPA-SiO 2 catalysts yielded only 4 as the product in aqueous medium.
Abstract: Efficient one-pot Knoevenagel condensation, Michael addition and cyclodehydration of dimedone with various aldehydes in acetonitrile and solvent free conditions using PPA–SiO2 catalyst gave 1,8-dioxo-octahydroxanthenes 3 in excellent yields; whereas in the presence of HClO4–SiO2 catalyst the reaction is limited to give only 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) 4 in very good yields. In aqueous medium both HClO4–SiO2 and PPA–SiO2 catalysts yielded only 4 as the product. The scope and limitations of the two catalysts in various reaction conditions examined were described.
235 citations
22 Nov 2013
TL;DR: In this paper, the reactivity of the Zn(+2) salt in the growth solution can also markedly affect the size and the morphology of ZIF-8 particles Small Zif-8 nanocrystals with diameters varying between ca 50 and 200 nm were obtained with reactive zinc salts.
Abstract: Metal organic frameworks (MOFs) are porous crystalline materials composed of metal ions or clusters of metal ions coordinated with organic linkers (such as terephthalic acid, 1,3,5-benzenetricarboxylic acid, or imidazoles) MOFs exhibit tunable structures, low density, ultrahigh surface area and have various potential applications in catalysis, hydrogen storage, and adsorption/separation of liquid or gaseous mixtures Among the MOFs structures, the zeolitic imidazolate frameworks (ZIFs) have recently attracted considerable attention In these materials, metal atoms such as Zn2+ are linked through N atoms by the ditopic 2-methylimidazolate ligand to form neutral frameworks ZIF-8 has a sodalite zeolite-type topology with cages of 116 A and pores of 34 A in diameter ZIF-8 are characterized by high thermal stability (550 oC in N2), large surface area (BET: 1630 m2/g) and high resistance to various solvents Concerning ZIF-8 chemical properties, these materials can successfully be used for hydrogen, carbon dioxide and iodide storage, Knoevenagel condensations, cycloadditions, oxidations, trans-esterification, and Friedel-Crafts alkylations Variations of synthetic parameters (solvent, concentration, temperature, time, molar ratio of reactants) are commonly used to manipulate the morphology and size of ZIF-8 crystals In this work, we demonstrate that the reactivity of the Zn(+2) salt in the growth solution can also markedly affect the size and the morphology of ZIF-8 particles Small ZIF-8 nanocrystals with diameters varying between ca 50 and 200 nm were obtained with reactive zinc salts like Zn(acac)2, Zn(NO3)2, ZnSO4 or Zn(ClO4)2 The use of ZnCl2, Zn(OAc)2 or ZnI2 afforded crystals with sizes varying between ca 350 and 650 nm Finally, the low reactive ZnBr2 was found to generate microsized crystals These significant changes in particle size induced distinctive changes in adsorption properties as demonstrated by BET measurements but also in the catalytic performances of ZIF-8 crystals in a Knoevenagel condensation used as model The small sized crystals produced from Zn(NO3)2 exhibit the highest surface area and the best catalytic activity
235 citations
TL;DR: A laboratory-scale continuous microwave reactor (CMR) has been developed and used to conduct organic syntheses routinely, rapidly, and safely in a range of solvents, under pressures up to 1400 kPa and at temperatures up to 200 o C as mentioned in this paper.
Abstract: A laboratory-scale continuous microwave reactor (CMR) he been developed and used to conduct organic syntheses routinely, rapidly, and safely in a range of solvents, under pressures up to 1400 kPa and at temperatures up to 200 o C. Advantages and applications of the CMR are discussed, along with the rationale for the design. Reactions carried out with the CMR included nucleophilic substitution, addition, esterification, transesterification, acetalization, amidation, base- and acid-catalyzed hydrolysis, isomerization, decarboxylation, and elimination. Name reactions included the Michael addition, Hofmann degradation, Williamson ether synthesis, and the Mannich, Finkelstein, Baylis-Hillman, and Knoevenagel reactions
232 citations
TL;DR: In this paper, a series of conjugated copolymers having oxadiazole, quinoline and quinoxaline moieties in the main chain based on fluorene were synthesized in good yields by palladium-catalyzed Suzuki coupling reaction, a new approach different from the traditional polyhydrazide precursor route.
Abstract: A novel series of conjugated copolymers having oxadiazole, quinoline, quinoxaline, and phenylenecyanovinylene moieties in the main chain based on fluorene were synthesized in good yields by palladium-catalyzed Suzuki coupling reaction, a new approach different from the traditional polyhydrazide precursor route (oxadiazole-containing polymers), acid-catalyzed Friedlander condensation reaction (polyquinolines), and Knoevenagel condensation polymerization (poly(phenylenecyanovinylene)). The thermal, electrochemical, and optical properties of these copolymers were examined. All these polymers possess excellent thermal stability with glass transition temperatures of 114−208 °C and onset decomposition temperatures of 387−415 °C. Cyclic voltammetry studies reveal that these copolymers possess low-lying LUMO energy levels ranging from −3.01 to −3.37 eV and low-lying HOMO energy levels ranging from −6.13 to −6.38 eV and may be promising candidates for electron-transporting or hole-blocking materials in light-emitt...
231 citations
230 citations