Search results for "Reaction"
showing 10 items of 6134 documents
New aromatic diamines containing a multiring flexible skeleton for the synthesis of thermally stable polyimides
2000
Abstract Multi-ring aromatic diamines bearing a long alkyl chain (C 6 , C 8 or C 16 ) were obtained from the corresponding dinitro compounds synthesized by a Friedel–Crafts alkylation of substituted mesitylenes by paranitrobenzyl chloride. The bismaleimide synthesized from the diamine bearing a C 16 chain formed a thermostable polyimide.
Polymeric nitrones, 1. Synthesis and modification of polymeric nitrones derived from polymerizable aldehydes
1999
The model compound N,C-diphenylnitrone[N-(benzylidene)aniline-N-oxide] (3) was prepared by condensation of benzaldehyde with phenylhydroxylamine to study its thermal stability. X-ray diffraction analysis of a single crystal established the conformation of the nitrone group. A new monomer 4-(methacryloyloxy)benzaldehyde-phenylnitrone (8) was also prepared and could not be polymerized with 2,2′-azobisisobutyronitrile (AIBN) as initiator at 70°C. Under these conditions the nitrone reacted exclusively in an intermolecular 1,3-dipolar cycloaddition to give oligomeric tetrahydro-1,2-oxazoline derivates. The kinetics of the cycloaddition was investigated. Additionally, different (meth)acryl- and s…
Molecular Parameters of Hyperbranched Copolymers Obtained by Self-Condensing Vinyl Copolymerization, 2. Non-Equal Rate Constants
2001
The kinetics, molecular weight averages, and the average degree of branching, DB, are calculated for the self-condensing vinyl copolymerization (SCVCP) of a vinyl monomer M with an "inimer" AB* in the case of different reactivities of active species. Emphasis is given to two limiting cases: formation of "macroinimers" occurs if the monomer M is more reactive than the vinyl groups of inimers or polymer, and "hyperstars" are formed in the opposite case. It is shown that the kinetics, the molecular weight averages, and the average degree of branching strongly depend on the relative reactivities of monomer and inimer. Comparison with experimental data shows that consistent fits of the reactivit…
Hyperbranched methacrylates by self-condensing group transfer polymerization
1997
The synthesis of hyperbranched methacrylates was achieved by self-condensing group transfer polymerization of 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate (1). “Back-biting” is shown to be the predominant side reaction. In spite of this, the compact nature of the hyperbranched molecules was demonstrated through SEC-viscosity measurements and comparison with a linear analogue. The degree of branching can be controlled by copolymerization with conventional monomers, e.g. MMA, and the living polymers can be used as macroinitiators for star-shaped polymers.
Phenothiazine-based dyes with bilateral extension of π-conjugation for efficient dye-sensitized solar cells
2013
Four novel organic photo-sensitizers based on phenothiazine were designed, synthesized and characterized for efficient dye-sensitized solar cells. Anisole, octyloxybenzene and dodecyloxybenzene were incorporated into the phenothiazine by an Ullmann reaction. An additional octyloxybenzene was incorporated into one dye unit through a Suzuki coupling reaction. The modified phenothiazine moiety acts as an electron donor and cyanoacrylic acid acts as an electron acceptor and anchoring unit. The photophysical, electrochemical and sensitizing characteristics of the new dyes were evaluated. The bis(octyloxybenzene) substituted dye delivered the best performance with its sensitized solar cell displa…
Fluorogenic Enzyme-Triggered Domino Reactions Producing Quinoxalin-2(1H)-one-based Heterocycles
2020
International audience; A simple and effective biocompatible domino reaction triggered by a model protease and leading to formation of strongly fluorescent quinoxalin-2(1H)-one N-heterocycles is described. Some positive attributes including versatility and ability to provide outstanding fluorescence "OFF-ON" responses were revealed by this work. They open the way for practical applications of this novel type of "covalent-assembly" based fluorescent probes in the fields of sensing and bioimaging. Among the myriad of synthetic transformations and catalysts currently available for concise and efficient synthesis of organic molecules, bioinspired approaches based on the use of enzymes often int…
Photooxidations of Alkenes in Fluorinated Constrained Media: Fluoro-organically Modified NaY as Improved Reactors for Singlet Oxygen “Ene” Reactions
2007
Creating a stationary fluorinated environment inside the zeolite cavity can increase the reactivity observed for intrazeolite photooxidation of alkenes. Exchanging the zeolite with fluorinated organic cations is a much more effective strategy than simply using a fluorinated solvent for slurry irradiations. Use of cations containing C-F bonds is also more efficient than use of deuterated cations for creation of a singlet oxygen friendly environment where the quenching processes are slowed down. Doping the zeolite with fluoro-organic cation 4 resulted in an increase in the singlet oxygen lifetime to 12 micros.
Antimicrobial activity of methylene blue and toluidine blue O covalently bound to a modified silicone polymer surface
2009
Methylene Blue or Toluidine Blue O were covalently bound to an activated silicone polymer by means of an amide condensation reaction. UV-visible absorption spectra confirmed that the dye was surface bound. The new polymers with covalently attached dye display significant bactericidal activity against Escherichia coli and Staphylococcus epidermidis with a 99.999% reduction in viable bacteria after four minutes exposure to a low power laser.
Diastereodivergent Synthesis of Fluorinated Cyclic β(3)-Amino Acid Derivatives.
2015
The ability of 2-p-tolylbenzyl carbanions to behave as a source of chiral benzylic nucleophiles has been shown in its reaction with fluorinated imines. The process takes place with high levels of stereocontrol, rendering the corresponding amines as single diastereoisomers. Subsequent cross-metathesis followed by intramolecular aza-Michael reaction makes the synthesis of fluorinated homoproline derivatives bearing three stereogenic centers possible. Furthermore, the selectivity of the cyclization process can easily be tuned up in a diastereodivergent manner simply by changing the reaction conditions.
Efficient alkali iodide promoted 18F-fluoroethylations with 2-[18F]fluoroethyl tosylate and 1-bromo-2-[18F]fluoroethane
2003
Abstract Radiochemical 18 F-fluorination yields of several compounds using the secondary labelling precursors 2-[ 18 F]fluoroethyl tosylate ([ 18 F]FETos) and 1-bromo-2-[ 18 F]fluoroethane ([ 18 F]BFE) could be considerably enhanced by the addition of an alkali iodide. The radiochemical yield of [ 18 F]fluoroethyl choline for example could be doubled with [ 18 F]BFE and increased from 13% to ≈80% with [ 18 F]FETos. By addition of alkali iodide to the precursor, the 18 F-fluoroethylation yields of established radiopharmaceuticals, especially in the case of automated syntheses, could be significantly increased without major changes of the reaction conditions.