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1.
The catalytic properties of MCM-22 and NU-87 were investigated for the disproportionation of toluene to produce benzene and
xylene, and the results were compared with those obtained over mordenite, beta and ZSM-5. It turns out that dealumination
of MCM-22 removes selectively the acid sites from the external surface and thus suppresses the secondary isomerization of
p-xylene, enhancing the para-selectivity. This indicates that the dealuminated MCM-22 is a promising catalyst for the selective formation of p-xylene from toluene disproportionation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
S. B. Agaeva B. A. Dadashev D. B. Tagiev S. I. Abasov 《Russian Journal of Applied Chemistry》2005,78(11):1854-1858
The possibility of increasing the yield of target products and para-selectivity of toluene disproportionation on modified zeolites by optimization of their microporous structure was studied. 相似文献
3.
Daniel B. Larsen Dr. Allan R. Petersen Dr. Johannes R. Dethlefsen Dr. Ayele Teshome Dr. Peter Fristrup 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16621-16631
The molybdate‐catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by oxidation of the solvent isopropyl alcohol to acetone has been investigated by using a combination of experimental and computational methods. A Hammett study that compared the relative rates for the transfer HDO of five para‐substituted benzylic alcohols was carried out. Density‐functional theory (DFT) calculations suggest a transition state with significant loss of aromaticity contributes to the lack of linearity observed in the Hammett study. The transfer HDO could also be carried out in neat PhCH2OH at 175 °C. Under these conditions, PhCH2OH underwent disproportionation to yield benzaldehyde, toluene, and significant amounts of bibenzyl. Isotopic‐labelling experiments (using PhCH2OD and PhCD2OH) showed that incorporation of deuterium into the resultant toluene originated from the α position of benzyl alcohol, which is in line with the mechanism suggested by the DFT study. 相似文献
4.
Manh Hoang Joseph F. Mathews Kerry C. Pratt 《Reaction Kinetics and Catalysis Letters》1997,61(1):21-26
Para-selectivity of ZSM-5 zeolites with similar bulk Si/Al ratio, but different particle size and surface Al concentration has
been investigated in toluene disproportionation. Results showed that enhancedpara-selectivity is a consequence not only of the particle size but also of the external surface aluminium concentration in the
particles. 相似文献
5.
The reaction of 1,2,3-trimethylbenzene (1,2,3-TMB) over HY zeolite was investigated in a fixed-bed flow reactor at 200-300 °C under atmospheric pressure. The reaction products include toluene, pentamethylbenzene and isomers of xylene, 1,2,3-TMB and tetramethylbenzene. Based on the time-on-stream theory, the types and initial selectivities of these products were determined from plots of product selectivity. 1,2,4-TMB is initially produced from 1,2,3-TMB via isomerization whereas o-xylene, m-xylene, 1,2,3,4- and 1,2,3,5-tetramethylbenzene were primarily formed by disproportionation of 1,2,3-TMB. Isomerization and disproportionation obeyed first- and second-order kinetics, respectively; both reactions proceeded via a carbonium ion mechanism with the former occurring by methyl transfer on the benzene ring whereas the latter proceeded through the diphenylmethane transition state. The activation energies are 31.6 and 37.2 kJ mol?1 for isomerizaion and disproportionation, respectively. 相似文献
6.
Charge‐Transfer Complex Formation in Gelation: The Role of Solvent Molecules with Different Electron‐Donating Capacities
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Shibaji Basak Sumantra Bhattacharya Dr. Ayan Datta Prof. Arindam Banerjee 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5721-5726
A naphthalenediimide (NDI)‐based synthetic peptide molecule forms gels in a particular solvent mixture (chloroform/aromatic hydrocarbon, 4:1) through charge‐transfer (CT) complex formation; this is evident from the corresponding absorbance and fluorescence spectra at room temperature. Various aromatic hydrocarbon based solvents, including benzene, toluene, xylene (ortho, meta and para) and mesitylene, have been used for the formation of the CT complex. The role of different solvent molecules with varying electron‐donation capacities in the formation of CT complexes has been established through spectroscopic and computational studies. 相似文献
7.
Theoretical study of molecular and electronic structure of 2‐Se‐(2‐methyl‐2‐propenyl)‐1‐benzoic acid
Ali Jameel Hameed Abraham F. Jalbout Bartosz Trzaskowski 《International journal of quantum chemistry》2007,107(1):152-158
A theoretical study of 2‐Se‐(2‐methyl‐2‐propenyl)‐1‐benzoic acid was carried out to investigate the molecular and electronic structure of this molecule, using the B3LYP density functional theory (DFT) method with the 6‐311+G** basis set. The optimized geometry of the molecule was obtained for the ortho, meta, and para isomers of the complex. In addition, the theoretical vibrational spectrum is presented, and thermal corrections in the limit of 100–1,000 K are discussed using the Shomate thermodynamic equations. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
8.
I. P. Pozdnyakov Yu. A. Sosedova V. F. Plyusnin V. P. Grivin D. Yu. Vorob’ev N. M. Bazhin 《Russian Chemical Bulletin》2004,53(12):2715-2722
The nature, optical spectra, and kinetic characteristics were determined for intermediate radicals formed upon the photolysis of aqueous solutions of a FeOHaq
2+ complex with phenol additives. The primary radical ·OH reacts with phenol to form ortho- and para-isomers of the Ph(OH)2
· radical. The Ph(OH)2
· radical eliminates a water molecule to form a phenoxyl radical PhO·. The latter disappears in the reactions with FeIII complexes, recombination, and disproportionation. The final products of photochemical transformations were determined. Among them, o-quinone and diphenoquinones were identified.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2605–2612, December, 2004. 相似文献
9.
Richard Hildner Dr. Laura Winterling Ulrich Lemmer Prof. Dr. Ullrich Scherf Prof. Dr. Jürgen Köhler Prof. Dr. 《Chemphyschem》2009,10(14):2524-2534
We employ low‐temperature single‐molecule spectroscopy combined with pattern recognition techniques for data analysis on a methyl‐substituted ladder‐type poly(para‐phenylene) (MeLPPP) to investigate the electron–phonon coupling to low‐energy vibrational modes as well as the origin of the strong spectral diffusion processes observed for this conjugated polymer. The results indicate weak electron–phonon coupling to low‐frequency vibrations of the surrounding matrix of the chromophores, and that low‐energy intrachain vibrations of the conjugated backbone do not couple to the electronic transitions of MeLPPP at low temperatures. Furthermore, these findings suggest that the main line‐broadening mechanism of the zero‐phonon lines of MeLPPP is fast, unresolved spectral diffusion, which arises from conformational fluctuations of the side groups attached to the MeLPPP backbone as well as of the surrounding host material. 相似文献
10.
Mustapha Aitali Larbi El Firdoussi Abdellah Karim Alejandro F. Barrero Miguel Quirs 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(9):1088-1089
The title compound, [(S)‐2‐(anilinomethyl)pyrrolidine‐N,N′]‐chloro(η6‐para‐cymene)ruthenium(II) chloride, [RuCl‐(C10H14)(C11H16N2)]Cl, has been synthesized by the reaction of [RuCl2(p‐cymene)]2 (p‐cymene is para‐isopropyltoluene) with (S)‐2‐(anilinomethyl)pyrrolidine in triethylamine/2‐propanol. The Ru atom is in a pseudo‐tetrahedral environment coordinated by a chloride ligand, the aromatic hydrocarbon is linked in a η6 manner and the amine is linked via its two N atoms. The chloride anion is involved in hydrogen bonding with the diamine moieties through N—H?Cl interactions, with N?Cl distances of 3.273 (4) and 3.352 (4) Å. 相似文献
11.
Ajit Kumar Chaudhuri Santi R. Palit 《Journal of polymer science. Part A, Polymer chemistry》1968,6(8):2187-2196
The mode of termination in the vinyl acetate–isobutyl methacrylate (VA–IBMA) and methyl methacrylate–methyl acrylate (MMA–MA) copolymerization systems has been investigated at 60°C. by using the dye-interaction technique for functional endgroup estimation. The results show that pairs of poly(vinyl acetate) radicals interact almost exclusively through a disproportionation mechanism. In the homopolymerization of methyl methacrylate and methyl acrylate, about 1.16 and 1.22 carboxyl-containing endgroups per polymer molecule have been estimated, which shows the predominance of disproportionation over combination in these termination reactions. In poly(isobutyl methacrylate) about 1.55 tagged initiator fragments per chain indicate that 29% of the total radicals terminate through the disproportionation mechanism. Cross termination in the (VA–IBMA) copolymerization system occurs almost entirely through combination for monomer feeds richer in isobutyl methacrylate content while for the MMA–MA system, combination is more important at intermediate monomer feed ratios. These results have been discussed in the light of different explanations for the reaction mechanism. 相似文献
12.
Glen B. Deacon Ewan E. Delbridge Craig M. Forsyth 《Angewandte Chemie (International ed. in English)》1999,38(12):1766-1767
A linear supramoleculecular array of anions and cations is present in the solvent-free potassium salt of the homoleptic erbium pyrazolate complex [K{Er(η2-tBu2pz)4}n] ( 1 ). Treatment of 1 with [18]crown-6 in toluene/dimethoxyethane leads to formation of a charge-separated salt [Eq. (a)] in which the methyl group of a toluene molecule interacts with the potassium ion. tBu2pz=3,5-di-tert-butylpyrazolate. 相似文献
13.
Kirill V. Tretyakov Nino G. Todua Roman S. Borisov Vladimir G. Zaikin Stephen E. Stein Anzor I. Mikaia 《Rapid communications in mass spectrometry : RCM》2010,24(17):2529-2532
A new kind of ‘para‐effect’ under electron ionization (EI) conditions has been discovered for a series of bis(perfluoroacyl) derivatives of o‐, m‐ and p‐phenylenediamines, ‐hydroxybenzeneamines and ‐mercaptobenzeneamines of a common structure RCOX–C6H4–NHCOR (X = NH, S, O; R = CF3, C2F5, C3F7). Only the para‐isomers showed successive loss of a radical RCO? and a molecule RCN, leading to very intense peaks in the EI spectra. The composition and the origin of the [M–COR–NCR]+ ions were confirmed by exact mass measurements and linked scan experiments. The proposed mechanism of their formation takes into account likely para‐quinoid structures of the precursor ions. A similar rearrangement has not been observed for para‐isomers in the series of bis(perfluoroacyl) derivatives of benzenediols, mercaptophenols and dimercaptobenzenes. Published in 2010 by John Wiley & Sons, Ltd. 相似文献
14.
Dicopper(II) Metallacyclophanes with Electroswitchable Polymethyl‐Substituted para‐Phenylene Spacers
Dr. Jesús Ferrando‐Soria María Castellano Dr. Rafael Ruiz‐García Dr. Joan Cano Prof. Dr. Miguel Julve Prof. Dr. Francesc Lloret Prof. Dr. Catalina Ruiz‐Pérez Dr. Jorge Pasán Dr. Laura Cañadillas‐Delgado Dr. Donatella Armentano Dr. Yves Journaux Dr. Emilio Pardo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(36):12124-12137
15.
Mervyn A. Long John K. Saunders Philip G. Williams Allan L. Odell R. Wayne Martin 《Magnetic resonance in chemistry : MRC》1984,22(10):665-667
Chemical shifts for the aromatic tritons of toluene decrease in the order meta>para>ortho for pure toluene, but in the order meta>ortho>para for dilute solutions of toluene in carbon tetrachloride, chloroform, cyclohexane and dimethyl sulphoxide; m-xylene shifts are 5>4,6>2 in the pure state and 5>2>4,6 in carbon tetrachloride and dimethyl sulphoxide; o-xylene shifts are 4,5>3,6 in the pure state and reversed in carbon tetrachloride. 相似文献
16.
Chemical shifts for tritons in ortho, meta and para positions in toluene have been determined using a 64 MHz tritium NMR spectrometer. The order of shift is meta>para>ortho, whereas the calculated shift order for protons is meta>ortho>para. 相似文献
17.
Brian Maurice Lynch 《Magnetic resonance in chemistry : MRC》1974,6(3):190-192
The methyl 1H NMR shifts for series of para-substituted N,N-dimethylanilines as their conjugate acids in trifluoroacetic acid, and series of para-substituted N,N,N-trimethylphenyl-ammonium iodides in acetonitrile and in deuterium oxide, and the methylene shifts for series of para-substituted N,N-diethylanilines as their conjugate acids in deuteriosulfuric acid, are shown to be linearly related to the Hammett σp+ parameter. It is proposed that this dependence reflects a response of the chemical shift of the proton of the probe moiety to the electron density at the point of attachment of the probe to the aromatic ring and that this response is determined by the electric field effect of the charge at the point of attachment. Literature data are cited to indicate that Hammett σp+–1H NMR shift relationships may be general for probe moieties lacking a through-resonance mechanism for interaction between the probe and the aromatic ring. 相似文献
18.
Shogo Okumura Takuya Komine Erika Shigeki Prof. Dr. Kazuhiko Semba Prof. Dr. Yoshiaki Nakao 《Angewandte Chemie (International ed. in English)》2018,57(4):929-932
We report meta‐ and para‐selective linear alkylation reactions of anilides with alkenes by nickel/N‐heterocyclic carbene (NHC) and aluminum catalysis. With a less bulky NHC, the alkylation reaction of N‐methyl‐N‐phenylcyclohexanecarboxamides proceeded mainly at the meta position. In contrast, a bulky NHC ligand led to the para‐selective alkylation of N‐sec‐alkyl anilides. 相似文献
19.
Dr. Jamie Hicks Dr. Petra Vasko Andreas Heilmann Prof. Jose M. Goicoechea Prof. Simon Aldridge 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20556-20560
The reactivity of the electron-rich anionic AlI aluminyl compound K2[(NON)Al]2 (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C−H activation chemistry with n-butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical SNAr chemistry, which implies the destabilisation of transition states featuring electron-donating groups in either ortho or para positions. In the cases of toluene and the three isomers of xylene, benzylic C−H activation is also possible, with the product(s) formed reflecting the feasibility (or otherwise) of competing arene C−H activation at a site which is neither ortho nor para to a methyl substituent. 相似文献
20.
Complementary Diastereoselective Cobalt Methylations of the Vitamin-B12 Derivative Cobester Treatment of heptamethyl cob(I)yrinate ( 2 ) in toluene/tetrahydrofurane (ca. 4:1) with methyl p-toluenesulfonate under exclusion of O2 and with protection from light leads to the selective formation of the heptamethyl Coβ-methylcob(III)yrinate (perchlorate 1b ) in 75% yield. In contrast, methylation of 2 with methyl iodide under the same conditons results in the isomeric heptamethyl Coα-methyulcob(III)yrinate (perchlorate 1a ) in 73% yield, besides 7% of 1b . This complementary diastereoface-selectivity of the methylation at the Co-center results from alkylation under kinetic control and apparently involves two mechanistically distinct alkylation processes. A radical mechanism is considered to account for the stereochemically unusual outcome of the reaction with methyl iodide. 相似文献