Search results for "Reaction"
showing 10 items of 6134 documents
Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran
1997
The anionic polymerization of methyl methacrylate using tetraphenylphosphonium triphenylmethanide as an initiator proceeds in a living manner even at room temperature. The rate constants of propagation were measured between -20 and +20 °C using a flow tube reactor. At 0 °C the reaction half-lives range from 0.3 to 1 s. The polymerization follows first-order kinetics with respect to monomer conversion (with a short induction period) and shows a linear dependence of the number-average degree of polymerization on conversion with high initiator efficiencies and narrow molecular weight distributions (M w /M n < 1.1). The dependence of the measured rate constants on the active center concentratio…
Bis(N-substituted oxamate)palladate(ii) complexes as effective catalysts for sustainable Heck carbon–carbon coupling reactions in n-Bu4NBr as the sol…
2015
Five bis(oxamato)palladate(II) complexes of the formulae (n-Bu4N)2[Pd(4-Fpma)2] (1), (n-Bu4N)2[Pd(4-Clpma)2] (2), (n-Bu4N)2[Pd(4-Brpma)2] (3), (n-Bu4N)2[Pd(4-Brpma)2]·H2O (3a), (n-Bu4N)2[Pd(4-MeOpma)2] (4) and (n-Bu4N)2[Pd(4-Isopma)2] (5) (n-Bu4N+ = tetra-n-butylammonium, 4-Fpma = N-4-fluorophenyloxamate, 4-Clpma = N-4-chlorophenyloxamate, 4-Brpma = N-4-bromophenyloxamate, 4-MeOpma = N-4-methoxyphenyloxamate and 4-isopma = N-4-isopropylphenyloxamate) have been easily prepared and characterized by spectroscopic methods and the crystal structures of two of them (3a and 4) have been determined by single crystal X-ray diffraction. Each palladium(II) ion in 3a and 4 is four-coordinate with two o…
Sustainable carbon–carbon bond formation catalyzed by new oxamate-containing palladium(II) complexes in ionic liquids
2013
Abstract New and versatile bis(oxamato)palladate(II) complexes of formula ( n -Bu 4 N) 2 [Pd(2-Mepma) 2 ]·4H 2 O ( 1a ) and ( n -Bu 4 N) 2 [Pd(4-Mepma) 2 ]·2H 2 O·MeCN ( 1b ) ( n -Bu 4 N + = tetra- n -buthylammonium, 2-Mepma = N -2-methylphenyloxamate and 4-Mepma = N -4-methylphenyloxamate) have been synthesized and characterized by spectroscopic methods and single crystal X-ray diffraction. Each palladium(II) ion in 1a and 1b is four-coordinate with two oxygen and two nitrogen atoms from two fully deprotonated oxamate ligands building a centrosymmetric square planar surrounding. Their catalytic role has been investigated for both Heck and Suzuki coupling reactions using a series of aryl…
FORMATION OF ALIPHATIC CARBOXYLIC ACIDS DURING ALKALINE PULPING OF MULI BAMBOO
2002
ABSTRACT A study on the formation of aliphatic carboxylic acids, i.e., formic and acetic acids and various hydroxy monocarboxylic and dicarboxylic acids, during soda-AQ, kraft, and kraft-AQ pulping of muli bamboo (Melocanna baccifera) was carried out. Detailed gas chromatographic analyses revealed that the most abundant hydroxy carboxylic acids were 2-hydroxybutanoic, lactic, glucoisosaccharinic, glycolic, xyloisosaccharinic, 3,4-dideoxypentonic, and 3-deoxypentonic acids. The presence of AQ depressed the formation of 2-hydroxybutanoic, xyloisosaccharinic, and glucoisosaccharinic acids, and accelerated the formation of glycolic and 3-deoxypentonic acids as well as 3-deoxytetronic acid but h…
ChemInform Abstract: Ring Expansion of 1,2,3,4-Tetrahydroisoquinolines to Dibenzo[c,f]azonines. An Unexpected [1,4]-Sigmatropic Rearrangement of Nitr…
2014
When the products of a Strecker reaction of 1,2,3,4-tetrahydroisoquinolines with aromatic aldehydes are quaternized with alkyl triflates and subsequently treated with base, a ring expansion to 6,7,8,13-tetrahydro-5H-dibenzo[c,f]azonine-5-carbonitriles takes place. The nine-membered cyclic products can be obtained in good yields (78–89%) in a process involving the [1,4]-sigmatropic rearrangement of a nitrile-stabilized ammonium ylide. The reaction sequence provides a new, simple, and efficient method for the synthesis of these unusual N-heterocycles.
Green conditions for the Suzuki reaction using microwave irradiation and a new HNT-supported ionic liquid-like phase (HNT-SILLP) catalyst
2014
A new catalytic system based on modified halloysite nanotubes was employed in the Suzuki reaction under microwave irradiation. A set of solvents, times and bases was screened and the best experimental conditions were obtained when the reactions were carried out for 10 min in water–ethanol at 120 °C in presence of K2CO3 as base. Good recyclability was observed. The new catalytic system was employed using either 1 mol% or 0.1 mol%. The palladium catalyst displayed good activity, allowing the synthesis of several biphenyl compounds in high yield working with only 0.1 mol% palladium loading. The application of microwave irradiation decreased the reaction time and also improved conversion with r…
Evidence of a 1,4-dipole intermediate in the reaction of 1-phenyl-4-vinylpyrazole with ptad
1985
Abstract 1-Phenyl-4-vinylpyrazole reacts with 1-phenyl-1,2,4-triazoline-3,5-dione in methylene chloride to form an unstable azetidine (4). An intermediate 1,4-dipole is probably involved since, when the reaction is conducted in acetone, a 1:1:1 adduct (3) is isolated.
Proteolytic cleavage of soybean Bowman-Birk inhibitor monitored by means of high-performance capillary electrophoresis. Implications for the mechanis…
1996
The hydrolysis of the soybean Bowman-Birk inhibitor in the presence of catalytic amounts of bovine trypsin and the formation of the non-covalent enzyme-inhibitor complex with an equimolar amount of enzyme are monitored by means of high-performance capillary electrophoresis (HPCE). The inhibitor is cleaved in the trypsin-reactive and more slowly in the chymotrypsin-reactive subdomain. HPCE proves itself as the only reliable analytical tool to monitor these reactions in clear contrast to classical electrophoretic, chromatographic and enzymatic methods. The most efficient separation of the intact and the two active site cleaved forms of the inhibitor was achieved in borate buffer at pH 10.0. T…
Crystal structure of the chalcone (E)-3-(furan-2-yl)-1-phenylprop-2-en-1-one
2015
The crystal packing of the compound is described by an intermolecular arrangement with the molecules as interlaced layers in a zigzag fashion, denoting interacting self-complementary dimers mainly by the localization of weak hydrogen bonds in a head-to-tail arrangement.
Outstandingly robust anodic dehydrogenative aniline coupling reaction
2020
Abstract Oxidative treatment of anilines usually leads to the formation of black polymers, often referred to as “aniline black”. This over-oxidation is hardly controllable and also a challenging task in the anodic conversion of anilines. Here, a quick and efficient access to valuable building blocks by anodic cross- and homo-coupling of aniline and benzidine derivatives is reported. This electrosynthesis is easily performed in a simple undivided cell using constant current conditions. The key to the observed outstanding performance and robustness of this system is attributed to the used solvent 1,1,1,3,3,3-hexafluoroisopropanol. The extraordinary performance over a broad range of current de…