104809-90-7Relevant articles and documents
Facile Hydrodehalogenation with H2 and Pd/C Catalyst under Multiphase Conditions. 2. Selectivity and Kinetics
Marques, Carlos Alberto,Selva, Maurizio,Tundo, Pietro
, p. 3830 - 3837 (1994)
Hydrodehalogenation of polyhalogenated aromatics with Pd/C catalyst carried out in the presence of a quaternary onium salt follows zero-order kinetics in the substrate and first-order kinetics in the Pd/C catalyst; the related rate constants were determined for o-, m- and p-bromotoluenes, o-, m- and p-chloroalkylbenzenes (methyl, ethyl, and propyl derivatives), and other aryl halides.Reaction rates, depending on the aromatic to be reduced, may be strongly enhanced by the presence of quaternary onium salts: the isomeric chloroethylbenzenes were reduced 50 times faster when operating in the presence of Aliquat 336 (1).Also the hindered 2-chloro-m-xylene easily yielded m-xylene.The cocatalyst onium salts operate by being adsorbed on the Pd/C surface, as shown when kinetic constants are reported by varying the onium salt amount: classical Langmuir adsorption isotherms are observed.The presence of the onium salt may also influence selectivity in the reduction of isomeric aryl halides: when 1 is present, p-dichlorobenzene reacts in diethyl ether at 20 deg C, 5-fold slower than the ortho isomer; whereas the reduction rates of the two compounds are almost the same in its absence.
Fine Control of the Pore-Opening Size of Zeolite ZSM-5 by Chemical Vapor Deposition of Silicon Methoxide
Niwa, Miki,Kato, Masaaki,Hattori, Tadashi,Murakami, Yuichi
, p. 6233 - 6237 (1986)
The pore-opening size of ZSM-5 was finely controlled by the chemical vapor deposition (CVD) of silicon methoxide.The silicon compound vapor was deposited, and the deposited material was calcined by oxygen, finally forming a silica-coated zeolite (SiHZSM-5).This was characterized by temperature-programmed desorption of ammonia and adsorption experiments using various molecules.It was found that the silica was deposited only on the external surface and narrowed the pore-opening size effectively with the internal structure unaltered.The fine control of the pore-opening size was tested, exemplified by the conversion of methanol.Hydrocarbon product distribution shifted to smaller molecules over the SiHZSM-5: the formation of smaller olefins such as ethylene and propylene increased in place of the complementary decrease of large aromatics.Enhancement of the preoduct shape selectivity was remarkable in xylene isomers and larger aromatics, which indicated the fine controls of the pore-opening size according to the deposition extent.Structures of the CVD zeolite and the enhanced shape selectivity in the methanol conversion were discussed.
CO2 atmosphere-enhanced methanol aromatization over the NiO-HZSM-5 catalyst
Li, Junhui,Hu, Chao,Tong, Kai,Xiang, Hao,Zhu, Zhirong,Hu, Zhonghua
, p. 44377 - 44385 (2014)
The aromatization of methanol over parent HZSM-5 and the modified NiO-HZSM-5 in a fixed-bed reactor was investigated under CO2 and N2 flow. The as-prepared catalysts were characterized by H2-TPR, XRD, BET, NH3-TPD, CO2-TPD and probe-molecule reaction. Compared with parent HZSM-5 in CO2 or N2 flow and with NiO-HZSM-5 in N2 flow, NiO-HZSM-5 showed greatly improved aromatization activity and BTX (benzene, toluene and xylene) yield in CO2 atmosphere. This is attributed to the cooperation of acid sites with the activated CO2 (over NiO species), which not only can effectively promote dehydrogenation of alkanes to form olefin intermediates, but also can accelerate dehydrogenation in the conversion of olefin intermediates to aromatics. In particular, an optimized NiO-HZSM-5 with 2.0 wt% NiO loading showed 50.1% total aromatic yield and 35.5% BTX yield in CO2 atmosphere. It also showed high catalytic stability resulting from the restriction of coking due to its acidity, carbonaceous elimination by the activated CO2-reacting deposited coke, and the suppressed reduction of highly active NiO species by activated CO2.
Transient puffs of trace organic emissions from a batch-fed waste propellant incinerator
Hart, John R.
, p. 559 - 569 (2001)
Emissions data have been obtained from a waste propellant incinerator. The incinerator is a dual fixed hearth, controlled air incinerator equipped with acid gas and particulate scrubbing. Puffing has been evident in this waste propellant incinerator by spikes in the CO concentration. Transient puffs of organics may travel down the combustion chambers and lead to stack emissions. The major conclusions from this study are that (1) transient puffs are formed due to the semi-batch feed nature of the combustion process (causing a local oxygen deficiency) and high water content of the desensitized propellant; (2) in batch-fed combustors, puffs can contribute to most of the organic emissions (which are relatively low) measured with US EPA sampling and analytical methods; (3) it is estimated that batch-fed combustion contributes up to 7-18 times more emissions than steady-state combustion will generate; (4) by applying dispersion analyses to determine the amount of oxygen deficiency in the flame zone, the combustion zone concentration of CO during batch-fed operation could be as high as 160,000 ppm, compared to a measured peak stack concentration of 1200 ppm CO; and (5) an organic sample is collected and averaged over at least a 2-h period that smooths out the transient peaks of organics emissions during batch-fed operation. For emissions that are associated with long-term potential health impacts, this is an appropriate sampling method. However, if a compound has a short-term potential health impact, it may be important to measure the time-resolved emissions of the compound.
-
Pines et al.
, p. 6226 (1953)
-
Structural and catalytic characterization of solid acids based on zirconia modified by tungsten oxide
Barton, David G.,Soled, Stuart L.,Meitzner, George D.,Fuentes, Gustavo A.,Iglesia, Enrique
, p. 57 - 72 (1999)
Tungsten oxide species form strong acid sites on ZrO2 supports and inhibit ZrO2 crystallite sintering and tetragonal to monoclinic structural transformations. W-LI X-ray absorption near-edge spectra suggest that the W centers are in a distorted octahedral oxygen environment, even after dehydration at 673 K, in all WOx-ZrO2 samples (2-21 wt.% W) oxidized at 1073 K. Maximum o-xylene isomerization turnover rates (per W atom) on WOx-ZrO2 solids occur at WOx surface densities (10 W nm-2) that exceed the theoretical monolayer capacity of ZrO2. Similar turnover rates are obtained on WOx-ZrO2 samples with similar WOx surface densities (W nm-2) over a large range of oxidation temperatures (773-1223 K) and WOx concentrations (5-21 wt.% W). UV-visible spectra suggest an increase in WOx domain size with increasing surface density. High isomerization turnover rates appear to require the presence of WOx domains of intermediate size on ZrO2 surfaces. WOx domains of intermediate size appear to provide a compromise between reducibility and accessibility of WOx centers. These domains are necessary to delocalize a temporary charge imbalance that forms Bronsted acid sites in the presence of H2 and stabilizes carbocation intermediates. The presence of H2 during o-xylene isomerization increases turnover rates and prevents rapid deactivation. Slow D2/o-xylene exchange reactions indicate that H atoms from H2 are not frequently involved in the activation or desorption of xylenes. H2 is required, however, in order to reverse the occasional desorption of H atoms during o-xylene isomerization reactions. These desorption processes lead to the destruction of Bronsted acid sites by the formation of strongly adsorbed unsaturated species in the absence of H2. After promotion with Pt (0.3 wt.%), WOx-ZrO2 solids catalyze n-heptane isomerization in the presence of H2 at 400-500 K with much higher selectivity than sulfated oxides or zeolitic acids at similar turnover rates. On Pt/WOx-ZrO2, efficient hydrogen transfer steps prevent extensive cracking of adsorbed carbocations by limiting their surface lifetimes.
Simple two-step ipso substitution of aromatic carboxylic acids by alkyl halides
Vorndran, Katja,Linker, Torsten
, p. 2489 - 2491 (2003)
Methyl-substituted arenes can be synthesized with high regioselectivity in only two steps through formal exchange of an aromatic carboxylic acid function with an alkyl substituent. The results obtained with toluic acid illustrate that good to very good yields can be obtained from inexpensive reagents (see scheme).
Surface-Passivated Hierarchically Structured ZSM5 Zeolites: High-Performance Shape-Selective Catalysts for para-Xylene Production
Lv, Jian,Hua, Zile,Zhou, Jian,Liu, Zhicheng,Guo, Hangle,Shi, Jianlin
, p. 2278 - 2284 (2018)
Hierarchically structured ZSM-5 zeolites (HSZ) were synthesized and used as high-performance catalysts for para-xylene (p-X) production by tuning their pore structures and external surface acidity, which was achieved by two independent passivation approaches: dealumination in oxalic acid solution and chemical liquid deposition of tetra-ethoxysilane (CLD of TEOS). The mesoporous structures of HSZ were well-preserved after dealumination or CLD of TEOS, and the external surfaces of HSZ were passivated significantly. Compared to dealumination, CLD is more efficient because not only the external surface could be passivated, but also the pore-openings of HSZ had been effectively narrowed, which both favored the enhancement of product p-X selectivity in ortho-xylene (o-X) isomerization. The constraint index (CI) of as-synthesized catalysts derived from the competitive reactions of ethylbenzene (EB) dealkylation and meta-xylene (m-X) isomerization and gravimetric adsorption measurements were introduced to investigate the extent of pore-narrowing by CLD of TEOS. Benefitting from the auxiliary mesopores and surface-passivation treatments, the optimized catalyst HSZ(Si0.5) showed remarkably enhanced catalytic activity over the microporous ZSM-5 counterpart in the model reaction of o-X isomerization.
-
Hopper,Shigemura
, p. 1025,1031 (1973)
-
On the mechanism of palladium-catalyzed coupling of haloaryls to biaryls in water with zinc
Mukhopadhyay, Sudip,Rothenberg, Gadi,Gitis, Diana,Sasson, Yoel
, p. 211 - 214 (2000)
(matrix presented) Kinetics and process parameters of coupling and hydro-dehalogenation reactions of chloroaryls are studied in the presence of zinc, water, and catalytic Pd/C. Good yields are obtained for the coupling of chlorobenzene, 4-chlorotoluene, and 4-chloro-1,1,1-trifluorotoluene. It is shown that water is actually one of the reagents, reacting with zinc in the presence of palladium to give zinc oxide and hydrogen gas, which then regenerates the Pd0 catalyst for the coupling reaction.
Gas-Phase Cationic Methylation of Biphenyl and Methylbiphenyls. A Mass Spectrometric and Radiolytic Study
Cacace, Fulvio,Petris, Giulia de,Fornarini, Simonetta,Giacomello, Pierluigi
, p. 7495 - 7501 (1986)
Alkylation of biphenyl and methylbiphenyls by Me2F+ and Me2Cl+ ions has been studied in the gas phase by a combination of radiolytic and mass spectrometric techniques, including chemical ionization and collisionally induced dissociation spectrometry.The results, in particular, the disproportionately high extent of ortho substitution, conform to a mechanistic model envisaging, in addition to direct substitution, the preliminary formation of an electrostatically bound adduct between the symmetric, bidentate electrophile and both rings of the substrate.Formation of the adduct increases the local concentration of the electrophile, hence the rate of alkylation at the ortho positions of biphenyl.
Isopropylation of xylenes catalyzed by ultrastable zeolite Y (USY) and some other solid acid catalysts
Patra, Chitta Ranjan,Kumar, Rajiv
, p. 216 - 224 (2002)
The isopropylation of all three xylene isomers was carried out over ultrastable zeolite Y (USY) catalyst to give corresponding dimethyl (1-methylethyl) benzenes, or in other words dimethyl cumenes (DMCs), using isopropanol as alkylating agent. The effect of reaction temperature, space velocity, substrate-to-alkylating-agent molar ratio, and time-on-stream on conversion of xylene isomers and selectivity to dimethyl cumene was studied. Isopropylation of xylenes over USY gives quite high (80 to 95%) DMC selectivity among the dimethyl cumenes, along with a 70-90% yield of DMCs in total products with respect to limiting reagents, i.e., isopropylating agents at relatively low reaction temperatures (423 ± 10 K) and at quite high xylene conversions (85-97% of theoretical maximum value). The solid acid catalysts zeolites H-Y, H-beta, H-mordenite, as well as silica-alumina and sulfated zirconia, were included for comparative studies in the isopropylation of m-xylene.
Rearrangement pathways of the tricyclo[4.1.0.01,3]heptyl skeleton
Dombrowski, Gary W.,Gassman, Paul G.,Kass, Steven R.
, p. 7819 - 7822 (1997)
Syn- and anti-1-methyltricyclo[4.1.0.04,6]heptan-2-ol derivatives (4a and 4b) have been prepared. Their buffered solvolyses in anhydrous 2,2,2- trifluoroethanol were studied. Anti dinitrobenzoate 4a solvolyzes to give mainly m-xylene and two trifluoroethyl ethers (5 and 6). Solvolysis of the syn mesylate 4b gives 6-methyl-1-(2,2,2- trifluoroethoxy)tricyclo[4.1.0.03,5]heptane (7), the product of a solvent trapped cyclopropyl cation.
-
Carbonaro et al.
, p. 5129 (1968)
-
Mechanistic Study of the Role of Substrate Steric Effects and Aniline Inhibition on the Bis(trineopentylphosphine)palladium(0)-Catalyzed Arylation of Aniline Derivatives
Hu, Huaiyuan,Qu, Fengrui,Gerlach, Deidra L.,Shaughnessy, Kevin H.
, p. 2516 - 2527 (2017)
The mechanism of the bis(trineopentylphosphine)palladium(0) (Pd(PNp3)2)-catalyzed coupling of aryl halides and aniline derivatives was studied in an effort to understand the role of substrate steric effects on the reaction. Prior studies had shown that the rate of Pd/PNp3-catalyzed coupling of aryl bromides and aniline derivatives was largely unaffected by substrate steric demand. The oxidative addition of aryl bromides to Pd(PNp3)2 is found to follow first-order kinetics with a rate that is independent of both ligand and aryl halide concentration. Thus, the rate limiting step for oxidative addition of aryl bromides is irreversible ligand dissociation. In the case of aryl chlorides, the oxidative addition rate has a first-order dependence on [ArCl] and an inverse dependence on [PNp3], indicating a mechanism involving reversible dissociation of the ligand followed by rate limiting oxidative addition. This difference in aryl halide effect was also found for the catalytic coupling reaction. Aryl bromide steric demand does not affect the coupling rate with hindered anilines, whereas the coupling rate of aryl chlorides is negatively affected by substrate steric demand. These results suggest that oxidative addition is rate limiting in the catalytic reaction for aryl chlorides but that oxidative addition is not rate limiting for aryl bromides. Aniline was found to give coupling rates significantly slower than those of 2,6-diisopropylaniline for both aryl bromides and chlorides. Aniline promotes the decomposition of the [(PNp3)Pd(Ar)(μ-X)]2 catalytic intermediate to a catalytically inactive palladacycle ([(κ2-P,C-Np2PCH2C(Me2)CH2)Pd(μ-X)]2) through C-H activation of a neopentyl group and elimination of arene. These studies show that the ability of the Pd/PNp3 catalyst system to tolerate steric demand in aryl bromides stems from the fact that the rate limiting step of the catalytic cycle is independent of the concentration and steric demand of aryl bromides. A catalyst deactivation pathway involving ligand metalation was identified that is promoted by unhindered aniline derivatives.
Evidence of single electron transfer from the enolate anion of an: N, N ′-dialkyldiketopiperazine additive in BHAS coupling reactions
Emery, Katie J.,Tuttle, Tell,Murphy, John A.
, p. 8810 - 8819 (2017)
A designed N,N′-dialkyldiketopiperazine (DKP) provides evidence for the role of DKP additives as initiators that act by electron transfer in base-induced homolytic aromatic substitution reactions, involving coupling of haloarenes to arenes.
-
Yashima et al.
, p. 273,276 (1970)
-
SEQUENCE OF STAGES IN THE AROMATIZATION OF ETHYLENE ON HIGH-SILICON ZEOLITES
Romannikov, V. N.,Ione, K. G.
, p. 1352 - 1356 (1986)
-
Catalytic conversion of isophorone to jet-fuel range aromatic hydrocarbons over a MoOx/SiO2 catalyst
Chen, Fang,Li, Ning,Wang, Wentao,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
, p. 11876 - 11879 (2015)
For the first time, jet fuel range C8-C9 aromatic hydrocarbons were synthesized in high carbon yield (～80%) by the catalytic conversion of isophorone over MoOx/SiO2 at atmospheric pressure. A possible reaction pathway was proposed according to the control experiments and the intermediates generated during the reaction.
Interconversion equilibrium of para-meta isomerization of alkylbenzenes
Nesterov,Nesterova,Roshchupkina
, p. 444 - 453 (2008)
The equilibrium of the reaction of para-meta isomerization of alkylbenzenes in the liquid phase was studied. The thermodynamic characteristics of the reaction were determined and interpreted. It was shown that the enthalpic term of the interaction between substituents in the case of their meta arrangement in the molecule depends on the effective size of the substituents. An approach to the prediction of the equilibrium constants of para-meta isomerization is proposed.
A new catalytic process for the synthesis of para-xylene through benzene methylation with CH3Br
Zhang, Ying-Ying,Li, Yue-Fang,Chen, Lang,Au, Chak-Tong,Yin, Shuang-Feng
, p. 6 - 10 (2014)
A new process for the generation of para-xylene (p-xylene) through benzene alkylation with CH3Br has been proposed for the first time. CH 3Br is prepared by the catalytic bromination of methane (the main component of natural gas), and benzene can be prepared from methane dehydroaromatization. Over the optimized P2O5-ZnO/HZSM-5 catalyst, benzene conversion is 43.6% and p-xylene selectivity is 91.2% at 475 °C, and the molar ratio of p-xylene in the liquid product is 28.7%. The relationship between the acidity and the catalytic efficiency of the modified H-ZSM-5 samples was investigated. It is found that isomerization of p-xylene occurs on the strong acid sites rather than on the weak acid sites, and benzene conversion is subject to the influence of strong acid sites.
-
Kohlrausch,Pongratz
, p. 427,437 (1933)
-
Carbon-Halogen Bond Activation with Powerful Heavy Alkaline Earth Metal Hydrides
Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Mai, Jonathan,R?sch, Bastian,Wiesinger, Michael
, p. 3731 - 3741 (2021)
Reaction of [(DIPePBDI)SrH]2 with C6H5X (X=Cl, Br, I) led to hydride-halogenide exchange (DIPePBDI=HC[(Me)CN-2,6-(3-pentyl)phenyl]2). Conversion rates increase with increasing halogen size (FDIPePBDI)SrH]2 with C6H5F was slow and ill-defined but addition of C6H4F2 gave smooth hydride-fluoride exchange. After addition of THF the full range of Sr halogenides was structurally characterized: [(DIPePBDI)SrX ? THF]2 (X=F, Cl, Br, I). Mixtures of AeN“2 and PhSiH3 in situ formed less defined but more robust Ae metal hydride clusters (AexN”yHz, Ae=Ca, Sr, Ba and N“=N(SiMe3)2) which are able to hydrodefluorinate C6H5F. Conversion rates increase with increasing metal size (Ca2/PhSiH3 mixtures also converted SF6 at room temperature to give undefined decomposition products. Addition of Me6Tren to a SrN“2/PhSiH3 led to crystallization of [Sr6N”2H9 ? (Me6Tren)3+][SrN“3?]; Me6Tren=tris[2-(dimethylamino)ethyl]amine). After hydrodefluorination, Sr6N”4F8 ? (Me6Tren)2 was formed and structurally characterized. Dissolution in THF led to cluster growth and the larger cluster Sr16N“8F24 ? (THF)12 is structurally characterized. DFT calculations support that hydrodehalogenation of halobenzenes follows a concerted nucleophilic aromatic substitution mechanism (cSNAr).
-
Schriesheim
, p. 3530 (1961)
-
Fabrication of a core-shell MFI?TON material and its enhanced catalytic performance for toluene alkylation
Chen, Huimin,Chen, Zhiqiang,Li, Yong-Wang,Liu, Suyao,Ren, Jie,Wen, Xiaodong,Yang, Yong,Zhang, Huaike,Zhang, Liwei
, p. 1281 - 1291 (2020)
Core-shell MFI?TON composites were designed and synthesized as a highly shape-selective catalyst for toluene alkylation with methanol by passivating the nonselective acid sites and tuning the diffusion behavior. The synthesis parameters were comprehensively investigated, indicating the importance of the Si/Al ratio compatibility of the ZSM-5 and ZSM-22 components on the formation of a core-shell structure. The synthesis process was systemically traced, which allowed the formulation of a crystallization mechanism involving the oriented crystal growth and selective fusion steps during the secondary crystallization. As a result, the MFI zeolites as the core were fully covered by the TON zeolites as the shell, yielding spherical morphology. When applied to toluene alkylation with methanol, the core-shell MFI?TON composite exhibited significantly improved para-xylene selectivity in comparison with the original, unattached, and physically mixed catalysts. The enhanced catalytic behaviors of the core-shell MFI?TON composite could be ascribed to the effective suppression of para-xylene isomerization as a result of the passivated acid sites on the external surface and the improved diffusion time and distance for the intermediates inside the channels due to the unique structure. The synthesis method for the MFI?TON composite described herein may provide a generic platform for the design of core-shell zeolites with potentially broader applicability to other porous materials with advanced applications.
Photochemical and electrochemical C-N borylation of arylhydrazines
Du, Linlin,Sun, Li,Zhang, Hua
supporting information, p. 1716 - 1719 (2022/02/21)
The C-N borylation of arylhydrazine hydrochlorides with bis(pinacolato)diboron was achieved under photochemical and electrochemical conditions, respectively. This novel and scalable transformation provides two efficient and mild transition-metal-free synt
Protodesilylation of Arylsilanes by Visible-Light Photocatalysis
García Manche?o, Olga,Kuhlmann, Jan H.,Uygur, Mustafa
supporting information, p. 1689 - 1694 (2022/03/14)
The first visible-light-mediated photocatalytic, metal- and base-free protodesilylation of arylsilanes is presented. The C(sp2)-Si bond cleavage process is catalyzed by a 5 mol % loading of a commercially available acridinium salt upon blue-light irradiation. Two simple approaches have been identified employing either aerobic or hydrogen atom transfer cocatalytic conditions, which enable the efficient and selective desilylation of a broad variety of simple and complex arylsilanes under mild conditions.
One-Pass Conversion of Benzene and Syngas to Alkylbenzenes by Cu–ZnO–Al2O3 and ZSM-5 Relay
Dong, Jinxiang,Ge, Hui,Han, Tengfei,Li, Xuekuan,Liu, Jianchao,Xu, Hong,Zhou, Ligong
, (2021/05/21)
Alkylbenzenes have a wide range of uses and are the most demanded aromatic chemicals. The finite petroleum resources compels the development of production of alkylbenzenes by non-petroleum routes. One-pass selective conversion of benzene and syngas to alkylbenzenes is a promising alternative coal chemical engineering route, yet it still faces challenge to industrialized applications owing to low conversion of benzene and syngas. Here we presented a Cu–ZnO–Al2O3/ZSM-5 bifunctional catalyst which realizes one-pass conversion of benzene and syngas to alkylbenzenes with high efficiency. This bifunctional catalyst exhibited high benzene conversion (benzene conversion of 50.7%), CO conversion (CO conversion of 55.0%) and C7&C8 aromatics total yield (C7&C8 total yield of 45.0%). Characterizations and catalytic performance evaluations revealed that ZSM-5 with well-regulated acidity, as a vital part of this Cu–ZnO–Al2O3/ZSM-5 bifunctional catalyst, substantially contributed to its performance for the alkylbenzenes one-pass synthesis from benzene and syngas due to depress methanol-to-olefins (MTO) reaction. Furthermore, matching of the mass ratio of two active components in the dual-function catalyst and the temperature of methanol synthesis with benzene alkylation reactions can effectively depress the formation of unwanted by-products and guarantee the high performance of tandem reactions. Graphic Abstract: [Figure not available: see fulltext.]
