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All total 269 Articles be found
All total 269 Articles be foundCommercial Ion Exchange Resins as Catalysts in Solid-Solid-Liquid Reactions
Arrad, Onn,Sasson, Yoel
, p. 4993 - 4998 (1989)
Nucleophilic substitutions, base-catalyzed alkylations, and oxidation of a secondary alcohol have been carried out in a nonpolar solvent with inorganic solid reagents using polymer-bound quarternary ammonium or phosphonium catalysts.The products could be isolated simply by filtration and evaporation of the solvent.Some commercial ion exchange resins, which are known to be inactive in liquid-liquid systems, were found to have a similar or even superior activity in comparison with the usual "triphase catalysts".The resins were chemically stable under the reaction conditions, but their mechanical breakdown could be reduced only by application of unconventional means of agitation.
Solid state S-methylation of thiols and O-methylation of phenols and naphthols with dimethyl sulfate under microwave irradiation
Heravi, Majid M.,Ahari, Neda Zamani,Oskooie, Hossein A.,Ghassemzadeh, Mitra
, p. 1701 - 1712 (2005)
Mild and efficient S-methylation of thiols and o-methylation of phenols and naphthals occurs with dimethyl sulfate (DMS) supported on basic alumina under microwave irradiation in solventless system. Copyright Taylor & Francis Inc.
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Hodgson,Heyworth,Ward
, p. 1512 (1948)
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Hecht,Kozarich
, p. 1397,1398 (1973)
Manganese-Catalyzed One-Pot Conversion of Nitroarenes into N-Methylarylamines Using Methanol
Mast, Nicolas,Morrill, Louis C.,Reed-Berendt, Benjamin G.
, (2020)
A manganese-catalyzed one-pot conversion of nitroarenes into N-methylarylamines has been developed. This transfer hydrogenation method employs a well-defined bench stable Mn PN3P pincer precatalyst in combination with methanol as both the reductant and the C1 source. A selection of commercially available nitroarenes was converted into N-methylarylamines in synthetically useful yields.
Electrophilic nitration of aromatics in ionic liquid solvents
Laali,Gettwert
, p. 35 - 40 (2001)
Potential utility of a series of 1-ethyl-3-methylimidazolium salts [emim][X] with X = OTf-, CF3COO-, and NO3- as well as [HNEtPri2][CF3COO] (protonated Huenig's base) ionic liquids were explored as solvent for electrophilic nitration of aromatics using a variety of nitrating systems, namely NH4NO3/TFAA, isoamyl nitrate/BF3·Et2O, isoamyl nitrate/TfOH, Cu(NO3)/TFAA, and AgNO3/Tf2O. Among these, NH4NO3/TFAA (with [emim][CF3COO], [emim][NO3]) and isoamyl nitrate/BF3·Et2O, isoamyl nitrate/TfOH (with [emim][OTf]) provided the best overall systems both in terms of nitration efficiency and recycling/reuse of the ionic liquids. For [NO2][BF4] nitration, the commonly used ionic liquids [emim][AlCl4] and [emim][Al2Cl7] are unsuitable, as counterion exchange and arene nitration compete. [Emim][BF4] is ring nitrated with [NO2][BF4] producing [NO2-emim][BF4] salt, which is of limited utility due to its increased viscosity. Nitration in ionic liquids is surveyed using a host of aromatic substrates with varied reactivities. The preparative scope of the ionic liquids was also extended. Counterion dependency of the NMR spectra of the [emim][X] liquids can be used to gauge counterion exchange (metathesis) during nitration. Ionic liquid nitration is a useful alternative to classical nitration routes due to easier product isolation and recovery of the ionic liquid solvent, and because it avoids problems associated with neutralization of large quantities of strong acid.
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Pailer,Bergthaller
, p. 103 (1968)
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Sustainable heck-matsuda reaction with catalytic amounts of diazonium salts: An experimental and theoretical study
Susperregui, Nicolas,Miqueu, Karinne,Sotiropoulos, Jean-Marc,Lecallonnec, Francois,Fouquet, Eric,Felpin, Francois-Xavier
, p. 7210 - 7218 (2012)
The palladium-catalyzed Heck-Matsuda reaction with a catalytic amount of an in-situ-generated diazonium salt proceeded under mild and sustainable conditions. The reaction proceeded at room temperature, under base-free conditions, and only generated tBuOH, H2O, and N2 as by-products. Ortho-substituted diazonium salts were more-efficiently coupled to methyl acrylate than their corresponding paraisomers, which required the addition of anisole as an additive. In support of these experimental data, we carried out theoretical studies to gain a deeper understanding of these reaction outcomes.
The synthesis and assay of radiolabelled benzene derivatives
Hales, Neil J.,Heaney, Harry,Hollinshead, John H.,Ley, Steven V.
, p. 7741 - 7754 (1995)
Several new syntheses of 1- and 4-[14C]anisole have been investigated and routes from [14C]cyanide and from 2-[14C]acetone are described which are better than those previously reported. The key step in one of the syntheses was catalytic dehydrogenation of 1-[14C]cyclohexanone to 1-[14C]phenol. Degradation of 5,6,7,8-tetrachloro-3,4-dihydro-1,4-etheno-[14C]naphthalen-2-(1H)-on e (10) prepared from [14C]anisole and tetrachlorobenzene has shown that the key step had proceeded without scrambling of the label.
Anion Activation in the Synthesis of Ethers from Oxygen Anions and 1-Chloro-4-nitrobenzene
Paradisi, Cristina,Quintily, Ugo,Scorrano, Gianfranco
, p. 3022 - 3026 (1983)
Reactions of 1-chloro-4-nitrobenzene (1) with alkoxide ions in the parent alcohols do not afford satisfactory yields of the expected alkyl 4-nitroaryl ether except in the case of the short-chain primary alcohols.We report that in the model reaction of 1 with KOH in 2-propanol good yields of 1-isopropoxy-4-nitrobenzene (2) are obtained provided Bu4NBr or alkali ion complexing agents such as 18-crown-6, Carbowax 20M, MPEG 5000, and Triton X-100 are present.Low molecular weight ethers, like glyme-5, are less effective, with ethylene glycol dimethyl ether having no effect at all.Work at temperatures below the solution boiling point is recommended to avoid competitive reduction of the NO2 group.The preparative value of Bu4NBr additions in analogous reactions of 1 to give 4-O2NC6H4OR ethers (3) is also very significant when R is primary, secondary, and aryl (1-octyl, sec-butyl, phenyl).The reaction fails when R = tert-butyl and 4-O2NC6H4.
Photoinduced Iron-Catalyzed ipso-Nitration of Aryl Halides via Single-Electron Transfer
Wu, Cunluo,Bian, Qilong,Ding, Tao,Tang, Mingming,Zhang, Wenkai,Xu, Yuanqing,Liu, Baoying,Xu, Hao,Li, Hai-Bei,Fu, Hua
, p. 9561 - 9568 (2021)
A photoinduced iron-catalyzed ipso-nitration of aryl halides with KNO2 has been developed, in which aryl iodides, bromides, and some of aryl chlorides are feasible. The mechanism investigations show that the in situ formed iron complex by FeSO4, KNO2, and 1,10-phenanthroline acts as the light-harvesting photocatalyst with a longer lifetime of the excited state, and the reaction undergoes a photoinduced single-electron transfer (SET) process. This work represents an example for the photoinduced iron-catalyzed Ullmann-type couplings.
Microwave-assisted methylation of carboxylic acids and phenolic compounds with dimethyl-carbonate under solvent-free condition
Rajabi, Fatemeh,Saidi, Mohammad R.
, p. 4179 - 4188 (2004)
Phenolic compounds and carboxylic acids are methylated with dimethyl carbonate in the presence of a catalytic amount of BF3· OEt2, DBU, or KOH, in good to excellent yields under microwave irradiation and solvent-free conditions.
An unconventional cobalt-catalyzed aerobic oxidation of tertiary nitrogen compounds to N-oxides
Jain, Suman L.,Sain, Bir
, p. 1265 - 1267 (2003)
A simple system, simple workup, and excellent yields make the new method for the oxidation of tertiary nitrogen compounds described in Equation (1) an attractive, environmentally acceptable synthetic tool. Molecular oxygen serves as the oxygen source and no sacrificial agents are required.
Selective O-methylation of phenols and benzyl alcohols in simple pyridinium based ionic liquids
Das, Pranab Jyoti,Das, Jupitara
, p. 94 - 98 (2015)
Synthesis of pyridinium based ionic liquids were reported and applied as catalyst for the selective O-methylation of phenols and benzyl alcohols. The reactions were carried out by using dimethylcarbonate (DMC) as the methylating agent. High selectivity, high yield and recyclability of the ionic liquids are important features of the reactions.
Mitsunobu reaction modifications allowing product isolation without chromatography: Application to a small parallel library
Pelletier, Jeffrey C.,Kincaid, Scott
, p. 797 - 800 (2000)
Readily available reagents, triphenylphosphine resin and di-t- butylazodicarboxylate, were used in Mitsunobu reactions and the byproducts were removed without chromatography. The new modification was utilized to prepare a small, parallel, solution phase library. (C) 2000 Elsevier Science Ltd.
Perfluorocarbon soluble crown ethers as phase transfer catalysts
Pozzi, Gianluca,Quici, Silvio,Fish, Richard H.
, p. 2425 - 2436 (2008)
Fluorous derivatives of dibenzo-18-crown-6 ether were readily prepared by means of metal-catalyzed cross-coupling reactions, and then successfully applied as catalysts in representative solid-liquid phase transfer catalysis (PTC) reactions, which were performed in standard organic solvents, such as chlorobenzene and toluene, and also in fluorous solvents, such as perfluoro-1,3-dimethylcyclohexane (PFDMC). It was clearly shown that properly designed fluoroponytailed crown ethers can promote the disintegration of the crystal lattice of alkali salts and transfer anions from the solid surface into an apolar, non-coordinating perfluorocarbon phase. Far from beinga simple chemical curiosity, this unprecedented observation has relevant implications in the design of PTC scenarios of wide applicability. This new paradigm represents an advance in crown ether chemistry, and their use as recyclable phase transfer catalysts.
Behavior of 3,5-bis(4-methoxyphenyl)-1,2-oxathiolan-2-oxide under nitrosation conditions
Saginova,Grigor'ev
, p. 246 - 247 (1999)
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Miller et al.
, p. 466 (1978)
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A new protocol for O-methylation of phenolic compounds with trimethyl phosphite or trimethyl phosphate under solvent-free condition and microwave irradiation
Saidi, Mohammad R.,Rajabi, Fatemeh
, p. 2343 - 2348 (2003)
A simple method for the preparation of industrially important alkyl aryl ethers is reported. Several phenolic compounds such as phenols, naphthols, and hydroxy coumarins were O-methylated with trimethyl phosphite or trimethyl phosphate under microwave irradiation and solvent-free condition in almost quantitative yields. Reaction of 2-naphthol with trimethyl phosphate gave mixture of 2-methoxynaphthalene and 1-methyl-2-methoxynaphthalene while the reaction with trimethyl phosphite gave mostly 2-methoxynaphthalene. This method is highly efficient for the methylating of phenolic compounds with very easy experimental procedure and environmental friendly conditions.
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Baudet,Calin
, p. 398 (1968)
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Bonner,Hancock
, p. 780 (1967)
Ion-dipole SN2 reaction in acetone - Water mixtures. Electrostatic and specific solute - Solvent interactions
Humeres,Nunes,Machado,Gasques,Machado
, p. 1163 - 1170 (2001)
The rate constants of the SN2 reaction of sodium 4-nitrophenoxide (1) and iodomethane were determined by UV - visible spectrophotometry in acetone - water mixtures at 25, 30, and 35 °C. The rate - Xwater (mole fraction of water) profile shows that the reaction depends strongly on the medium. The fastest rate constant was obtained in pure acetone, and a minimum occurred at Xwater = 0.4, whereas the observed second-order rate constants k′2 increases again in the water-rich region. In pure acetone, in the presence of dicyclohexano-[18]-crown-6, k′2 increases linearly with the concentration of the crown ether as a result of the complexation of the sodium ion (KS = 104.8 M) of the ion-pair and the increase in the effective concentration of free 4-nitrophenoxide ion, which was assumed to be the only reactive species. Ion-pairing was also detected at Xwater = 0.65 with a dissociation constant Kd = 7.82 × 10-4 M-1. The solvatochromic behaviors of 2,6-diphenyl-4-(2,4,6triphenyl-1-pyridinio)-1-phenoxide(2),4- [(1-methyl-4(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (3), and 1-methyl-8-oxy-quinolinium betaine (4) were investigated in the entire range of acetone - water mixtures. The dyes presented an increasing order of hydrophilicity compatible with their chemical structure, i.e., 2 T values of the dyes show a linear correlation of the polarity in the region of Xwater = 1.0-0.40 for 3 and 4, and it was observed that the more hydrophilic the dye the better the correlation coefficient, because of the structural similarity with 1. The activation parameter - Xwater profile shows extrema at Xwater + and 4-nitrophenoxide that extends even to water-rich mixtures. A model, based on the assumption that the free-energy terms involved in the second-order rate constant and the dissociation constant of the ion-pair have two components, is invoked to explain the kinetic data. One of the components depends on electrostatic interactions for which the main variable is the dielectric constant of the solvent mixture, and the other depends on the specific solute - solvent interactions, expressed by the activity coefficients of transfer of the species involved. The model indicates that in the range of Xwater = 1.0-0.40 the interactions are exclusively electrostatic, while for the rest of the acetone-rich region they are specific with a large contribution of the 4-nitrophenoxide ion.
ALKOXYCARBONYLATION AND AMIDATION OF ARYL IODIDES CATALYZED BY PALLADIUM COMPLEXES
Bumagin, N. A.,Gulevich, Yu. V.,Beletskaya, I. P.
, p. 1498 - 1504 (1986)
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Kinetic and spectroscopic studies of aerobic copper(II)-catalyzed methoxylation of arylboronic esters and insights into aryl transmetalation to copper(II)
King, Amanda E.,Ryland, Bradford L.,Brunold, Thomas C.,Stahl, Shannon S.
, p. 7948 - 7957 (2012)
We previously reported a preliminary mechanistic study of aerobic Cu(OAc)2-catalyzed methoxylation of 4-tolylboronic ester (King et al. J. Am. Chem. Soc., 2009, 131, 5044-5045), which revealed that aryl transmetalation from the boronic ester to CuII is the turnover-limiting step. In the present study, more thorough kinetic and spectroscopic studies provide additional insights into the transmetalation pathway and identity of the CuII catalyst resting state(s). EPR spectroscopic studies show that at least two copper(II) species are present under catalytic conditions, and their relative populations vary as a function of reaction time and acidity of the arylboronic ester and are influenced by addition of acetic acid or acetate to the reaction mixture. Analysis of kinetic data and 11B NMR and EPR spectra under diverse reaction conditions suggests that aryl transmetalation occurs from a tetracoordinate, anionic boronate to a cationic CuII species, mediated by a methoxide bridge.
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Antener
, p. 812,813 (1938)
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Exploiting a silver-bismuth hybrid material as heterogeneous noble metal catalyst for decarboxylations and decarboxylative deuterations of carboxylic acids under batch and continuous flow conditions
?tv?s, Sándor B.,Fül?p, Ferenc,Kónya, Zoltán,Kukovecz, ákos,Márton, András,Mészáros, Rebeka,Pálinkó, István,Szabados, Márton,Varga, Gábor
, p. 4685 - 4696 (2021/07/12)
Herein, we report novel catalytic methodologies for protodecarboxylations and decarboxylative deuterations of carboxylic acids utilizing a silver-containing hybrid material as a heterogeneous noble metal catalyst. After an initial batch method development, a chemically intensified continuous flow process was established in a simple packed-bed system which enabled gram-scale protodecarboxlyations without detectable structural degradation of the catalyst. The scope and applicability of the batch and flow processes were demonstrated through decarboxylations of a diverse set of aromatic carboxylic acids. Catalytic decarboxylative deuterations were achieved on the basis of the reaction conditions developed for the protodecarboxylations using D2O as a readily available deuterium source.
Crystallography-guided discovery of carbazole-based retinoic acid-related orphan receptor gamma-t (RORγt) modulators: insights into different protein behaviors with “short” and “long” inverse agonists
Yu, Ming-cheng,Yang, Feng,Ding, Xiao-yu,Sun, Nan-nan,Jiang, Zheng-yuan,Huang, Ya-fei,Yan, Yu-rong,Zhu, Chen,Xie, Qiong,Chen, Zhi-feng,Guo, Si-qi,Jiang, Hua-liang,Chen, Kai-xian,Luo, Cheng,Luo, Xiao-min,Chen, Shi-jie,Wang, Yong-hui
, p. 1524 - 1534 (2020/12/01)
A series of 6-substituted carbazole-based retinoic acid-related orphan receptor gamma-t (RORγt) modulators were discovered through 6-position modification guided by insights from the crystallographic profiles of the “short” inverse agonist 6. With the increase in the size of the 6-position substituents, the “short” inverse agonist 6 first reversed its function to agonists and then to “long” inverse agonists. The cocrystal structures of RORγt complexed with the representative “short” inverse agonist 6 (PDB: 6LOB), the agonist 7d (PDB: 6LOA) and the “long” inverse agonist 7h (PDB: 6LO9) were revealed by X-ray analysis. However, minor differences were found in the binding modes of “short” inverse agonist 6 and “long” inverse agonist 7h. To further reveal the molecular mechanisms of different RORγt inverse agonists, we performed molecular dynamics simulations and found that “short” or “long” inverse agonists led to different behaviors of helixes H11, H11’, and H12 of RORγt. The “short” inverse agonist 6 destabilizes H11’ and dislocates H12, while the “long” inverse agonist 7h separates H11 and unwinds H12. The results indicate that the two types of inverse agonists may behave differently in downstream signaling, which may help identify novel inverse agonists with different regulatory mechanisms.
