Search results for " Catalysis"

Synthesis, characterization and catalytic behavior of AlTf/UVM-7 as new green catalysts for the glycols etherification reactions

2010

Abstract Bimodal porous Al–UVM-7 system materials with different Si-to-Al ratios were prepared using the Atrane route. These were converted in strong acid heterogeneous AlTf-based catalysts after the treatment with methanolic solutions of triflic acid. The materials so obtained were used as catalysts for the conversion of ethylene glycol (EG) and propylene glycol (PG) with octanol under solvent-free conditions. The process is selective to short ethoxylated structures resulting in the corresponding monoethers. While the conversion of EG and PG was very high (>94%) irrespective of the support characteristics, 1-octanol was transformed only in low degree (3–35%), and its conversion depends on …

Heterogeneously catalyzed Suzuki-Miyaura conversion of broad scope

2012

The reaction tolerates a broad range of functional groups in the coupling partners and is usually performed in solution under homogeneous conditions at T ¢ 60 uC using 2–3 mol% catalytic amounts. The catalyst is often a Pd(0) complex with triarylphosphane ligands. 2 The catalytic cycle (Scheme 2) begins with the oxidative addition of an aryl halide to a Pd(0) species formed in situ to form an arylpalladium(II) halide intermediate. 3 Chloroarenes, especially nonactivated aryl chlorides, are notoriously less reactive due to the stability of the C–Cl bond (the relative reactivity of Ar–X is correlated to the respective bond dissociation energy: Ph–Cl: 96 kcal mol 21 ,P h–Br: 81 kcal mol 21 ,P …

Iron-Catalyzed C(sp2)-C(sp3) Cross-Coupling of Alkyl Grignard Reagents with Polyaromatic Tosylates

2017

Halogen bonded supramolecular complexes and networks

2008

In spite of some controversy of the true nature of the interaction between polarized halogen atoms and neutral or charged Lewis bases, termed “halogen bonding”, as a primary interaction, it is a very useful new tool/way to construct supramolecular complexes and networks. This is especially true in solid state supramolecular chemistry where utilization of weak intermolecular interactions such as halogen bonding opens up new insights to materials design and supramolecular synthesis.

Zur protonenkatalysierten elektrophilen substitution von 2,3-dimethylindol mit arylaldehyden: C6-regioselektivität am indol-gerüst

1986

The proton catalyzed reaction of 2,3-dimethylindole (1) with several arylaldehydes 2 yields the 6,6′bisindolylarylmethanes 5 regioselectively. No mechanistic information about the predominant attack of the aldehydes on the indole nucleus is obtained, because the reaction proceeds too fast to control. The electron-rich aldehydes, 2,4,6-trimethoxybenzaldehyde and indole-3-carbaldehyde, yield exclusively the 6,6′,6″-trisin-dolylmethane 9. The constitutions of all isolated methanes were elucidated by 400 MHz 1H-nmr spectroscopy.

Synthesis of high surface area perovskite catalysts by non-conventional routes

1997

Abstract The use of rare earth-containing perovskite oxides as total oxidation catalysts faces to the difficulty of obtaining high surface area materials and the need of calcination at high temperatures for its synthesis. In this work, perovskite NdCoO3 catalysts with relatively high surface areas were synthesized at soft calcination conditions by two non-conventional routes: heteronuclear organic complexes and amorphous precursors obtained by freeze-drying of nitrates solutions. Depending on the method used, different degrees of homogeneity in the bulk distribution of the component cations, oxygen non-stoichiometry as well as surface Co/Nd atomic ratios are obtained. In this way, the synth…

The ionic liquid effect on the Boulton-Katritzky reaction: a comparison between substrates of different structure

2015

The mononuclear rearrangement of heterocycles, also called Boulton–Katritzky reaction, was studied in ionic liquid solution using N-(5-phenyl-1,2,4-oxadiazol-3-yl)-N′-(4-nitrophenyl)-formamidine as substrate. The investigation was carried out using piperidine as basic catalyst and several ionic liquids differing in both cation and anion structure. Kinetic data collected were compared with the ones previously reported using (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole to have information about the effect due to the different structure of the alkyl chain borne on the substrate. Furthermore, data were analysed on the grounds of polarity, Kamlet–Taft solvent parameters, but taking…

Structure and reactivity of a mononuclear gold(II) complex.

2017

Mononuclear gold(II) complexes are very rare labile species. Transient gold(II) species have been suggested in homogeneous catalysis and in medical applications, but their geometric and electronic structures have remained essentially unexplored: even fundamental data, such as the ionic radius of gold(II), are unknown. Now, an unprecedentedly stable neutral gold(II) complex of a porphyrin derivative has been isolated, and its structural and spectroscopic features determined. The gold atom adopts a 2+2 coordination mode in between those of gold(III) (four-coordinate square planar) and gold(I) (two-coordinate linear), owing to a second-order Jahn–Teller distortion enabled by the relativistical…

Novel prolinamide-supported polystyrene as highly stereoselective and recyclable organocatalyst for the aldol reaction

2008

A new prolinamide derivative anchored to a polystyrene support has been straightforwardly prepared and employed as heterogeneous catalyst in the direct asymmetric aldol reaction with good results in terms of yield and stereoselectivity. The optimal reaction conditions were found when a 1:2 (v/v) water/chloroform mixture was used. This mixture was the best compromise between the good swelling properties of chloroform and the formation of a concentrated organic phase due to the presence of water. Noticeably, the enantioselectivities obtained employing acetone as ketone were, to the best of our knowledge, the highest achieved with a supported proline derivative. This catalyst can be easily rec…

Polystyrene-supported proline as recyclable catalyst in the Baylis–Hillman reaction of arylaldehydes and methyl or ethyl vinyl ketone

2008

Abstract Polystyrene-supported proline has been used as co-organocatalyst (10 mol%) with imidazole (10 mol%) in the Baylis–Hillman reaction between methyl or ethyl vinyl ketone and arylaldehydes. Recycling studies showed that the proline resin can be used up to five cycles with high isolated yields. This study represents the first example of supported proline as heterogeneous catalyst in the above reaction and broaden the scope of this catalytic material.