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Suk Bong Hong - One of the best experts on this subject based on the ideXlab platform.
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reaction intermediates and mechanism of the zeolite catalyzed transalkylation of 1 2 4 trimethylbenzene with toluene
Journal of Catalysis, 2018Co-Authors: Seung Hyeok Cha, Suk Bong HongAbstract:Abstract We report the catalytic properties of a series of large-pore (H-Y, H-beta, H-mordenite, and H-UZM-35) and medium-pore (H-NU-87, H-TNU-9, and H-ZSM-5) zeolites with different framework structures for the transalkylation of 1,2,4-trimethylbenzene (1,2,4-TMB) with toluene. H-NU-87 with intersecting 10- and 12-ring channels, but in which access to the inner part of the crystal can only occur through the 10-ring pores, was found to show a significantly higher xylene yield (40% vs. 23% at 673 K and 10 h on stream) and catalyst stability (31% vs. 17% 1,2,4-TMB conversion after 30 h on stream at 673 K) than the cage-based large-pore zeolite H-Y, the current commercial transalkylation catalyst. GC–MS analyses of organic species occluded in used zeolite catalysts reveal that the type of Diphenylmethane derivatives serving as key reaction intermediates of 1,2,4-TMB-toluene transalkylation is strongly influenced by the pore architecture of the zeolite catalyst. A bimolecular Diphenylmethane-mediated reaction mechanism for this transalkylation is proposed and discussed based on both experimental and theoretical results.
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1 2 4 trimethylbenzene disproportionation over large pore zeolites an experimental and theoretical study
Journal of Catalysis, 2015Co-Authors: Seung Hyeok Cha, Youngchul Byun, Hyungki Min, Suk Bong HongAbstract:While 1,2,4-trimethylbenzene (TMB) disproportionation is one of the potential technologies for p-xylene production, its reaction intermediates have been neither experimentally observed nor identified yet. Here we present GC–MS evidence that not only pentamethylated Diphenylmethane (5mDPM) derivatives but also hexamethylated Diphenylmethane (6mDPM) ones are serving as key reaction intermediates of 1,2,4-TMB disproportionation over large-pore zeolites. We also propose a new bimolecular Diphenylmethane-mediated reaction pathway for the formation of tetramethylbenzenes (TeMBs) and xylenes over large-pore zeolites based on the GC–MS results obtained. Comparison with the GC–MS results from LaNa-Y after transalkylation reactions of three different TeMB isomers with three xylene and three TMB isomers, respectively, allows us to rationally identify most of the seven 5mDPM and three 6mDPM derivatives at their isomer level. A combination of GC–MS and DFT calculation results demonstrates that the bimolecular 1,2,4-TMB disproportionation over LaNa-mordenite, a practically one-dimensional 12-ring zeolite with regard to this reaction, is a new example of transition state shape selectivity in zeolite catalysis.
Rujong Jeng - One of the best experts on this subject based on the ideXlab platform.
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poly urethane malonamide dendritic structures featuring blocked deblocked isocyanate units
Polymer Chemistry, 2011Co-Authors: Yungchung Chen, Tzongyuan Juang, Shenghong A Dai, Yingling Liu, Rongho Lee, Rujong JengAbstract:We have used 4-isocyanato-4′-(3,3-dimethyl-2,4-dioxoazetidino)Diphenylmethane and diethylenetriamine as building blocks to synthesize novel poly(urethane/malonamide) dendrons possessing terminal methyl ethyl ketoxime (MEKO) units (blocked isocyanate groups). Heating the MEKO-containing dendrons regenerated the terminal isocyanate groups. Subsequently, the regenerated isocyanate groups would react with any compound with active hydrogens. In one example, the dendrons with the deblocked isocyanates further reacted with stearyl alcohol (C18-OH) to form the corresponding dendrons presenting C18 moieties. This deblocking strategy allows replacement of reactive exterior groups with desired functionality for the construction of dendritic macromolecules.
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facile approach to polyurea malonamide dendrons via a selective ring opening addition reaction of azetidine 2 4 dione
Journal of Polymer Science Part A, 2005Co-Authors: Chih-ping Chen, Shenghong A Dai, Huey-ling Chang, Rujong JengAbstract:A bifunctional compound [(4-isocyanato-4′(3,3-dimethyl -2,4-dioxo-acetidino)Diphenylmethane] (MIA) has been used as a building block for the synthesis of novel polyurea/malonamide dendrons. This is based on selectively sequential addition reactions of amines to isocyanato-azetidine-2,4-diones. After incorporation of the MIA onto the growing dendrons, rapid entry into polyurea/malonamide dendrons was achieved via a convergent route with the processing advantages of easy purification, high yield, and rapid synthesis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 682–688, 2005
Zhipei Zhang - One of the best experts on this subject based on the ideXlab platform.
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bismuth triflate catalyzed vinylogous nucleophilic 1 6 conjugate addition of para quinone methides with 3 propenyl 2 silyloxyindoles
Organic Letters, 2017Co-Authors: Kaixue Xie, Zhipei ZhangAbstract:A highly diastereoselective vinylogous nucleophilic 1,6-conjugate addition reaction of para-quinone methides with 3-propenyl-2-silyloxyindoles by a bismuth triflate catalyst has been developed. A number of Diphenylmethane type compounds functionalized with oxindole motifs was obtained with excellent yields (up to 99%) and very good diastereoselectivities (up to Z/E > 99:1).
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Bismuth Triflate-Catalyzed Vinylogous Nucleophilic 1,6-Conjugate Addition of para-Quinone Methides with 3‑Propenyl-2-silyloxyindoles
2017Co-Authors: Kaixue Xie, Zhipei ZhangAbstract:A highly diastereoselective vinylogous nucleophilic 1,6-conjugate addition reaction of para-quinone methides with 3-propenyl-2-silyloxyindoles by a bismuth triflate catalyst has been developed. A number of Diphenylmethane type compounds functionalized with oxindole motifs was obtained with excellent yields (up to 99%) and very good diastereoselectivities (up to Z/E > 99:1)
Seung Hyeok Cha - One of the best experts on this subject based on the ideXlab platform.
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reaction intermediates and mechanism of the zeolite catalyzed transalkylation of 1 2 4 trimethylbenzene with toluene
Journal of Catalysis, 2018Co-Authors: Seung Hyeok Cha, Suk Bong HongAbstract:Abstract We report the catalytic properties of a series of large-pore (H-Y, H-beta, H-mordenite, and H-UZM-35) and medium-pore (H-NU-87, H-TNU-9, and H-ZSM-5) zeolites with different framework structures for the transalkylation of 1,2,4-trimethylbenzene (1,2,4-TMB) with toluene. H-NU-87 with intersecting 10- and 12-ring channels, but in which access to the inner part of the crystal can only occur through the 10-ring pores, was found to show a significantly higher xylene yield (40% vs. 23% at 673 K and 10 h on stream) and catalyst stability (31% vs. 17% 1,2,4-TMB conversion after 30 h on stream at 673 K) than the cage-based large-pore zeolite H-Y, the current commercial transalkylation catalyst. GC–MS analyses of organic species occluded in used zeolite catalysts reveal that the type of Diphenylmethane derivatives serving as key reaction intermediates of 1,2,4-TMB-toluene transalkylation is strongly influenced by the pore architecture of the zeolite catalyst. A bimolecular Diphenylmethane-mediated reaction mechanism for this transalkylation is proposed and discussed based on both experimental and theoretical results.
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1 2 4 trimethylbenzene disproportionation over large pore zeolites an experimental and theoretical study
Journal of Catalysis, 2015Co-Authors: Seung Hyeok Cha, Youngchul Byun, Hyungki Min, Suk Bong HongAbstract:While 1,2,4-trimethylbenzene (TMB) disproportionation is one of the potential technologies for p-xylene production, its reaction intermediates have been neither experimentally observed nor identified yet. Here we present GC–MS evidence that not only pentamethylated Diphenylmethane (5mDPM) derivatives but also hexamethylated Diphenylmethane (6mDPM) ones are serving as key reaction intermediates of 1,2,4-TMB disproportionation over large-pore zeolites. We also propose a new bimolecular Diphenylmethane-mediated reaction pathway for the formation of tetramethylbenzenes (TeMBs) and xylenes over large-pore zeolites based on the GC–MS results obtained. Comparison with the GC–MS results from LaNa-Y after transalkylation reactions of three different TeMB isomers with three xylene and three TMB isomers, respectively, allows us to rationally identify most of the seven 5mDPM and three 6mDPM derivatives at their isomer level. A combination of GC–MS and DFT calculation results demonstrates that the bimolecular 1,2,4-TMB disproportionation over LaNa-mordenite, a practically one-dimensional 12-ring zeolite with regard to this reaction, is a new example of transition state shape selectivity in zeolite catalysis.
Michael R Wasielewski - One of the best experts on this subject based on the ideXlab platform.
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controlling electron transfer in donor bridge acceptor molecules using cross conjugated bridges
Journal of the American Chemical Society, 2010Co-Authors: Annie Butler Ricks, Gemma C Solomon, Michael T Colvin, Amy M Scott, Kun Chen, Mark A Ratner, Michael R WasielewskiAbstract:Photoinitiated charge separation (CS) and recombination (CR) in a series of donor−bridge−acceptor (D−B−A) molecules with cross-conjugated, linearly conjugated, and saturated bridges have been compared and contrasted using time-resolved spectroscopy. The photoexcited charge transfer state of 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ−An) is the donor, and naphthalene-1,8:4,5-bis(dicarboximide) (NI) is the acceptor in all cases, along with 1,1-diphenylethene, trans-stilbene, Diphenylmethane, and xanthone bridges. Photoinitiated CS through the cross-conjugated 1,1-diphenylethene bridge is about 30 times slower than through its linearly conjugated trans-stilbene counterpart and is comparable to that observed through the Diphenylmethane bridge. This result implies that cross-conjugation strongly decreases the π orbital contribution to the donor−acceptor electronic coupling so that electron transfer most likely uses the bridge σ system as its primary CS pathway. In contrast, the CS rate through the cross-con...
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controlling electron transfer in donor bridge acceptor molecules using cross conjugated bridges
Journal of the American Chemical Society, 2010Co-Authors: Annie Butler Ricks, Gemma C Solomon, Michael T Colvin, Amy M Scott, Kun Chen, Mark A Ratner, Michael R WasielewskiAbstract:Photoinitiated charge separation (CS) and recombination (CR) in a series of donor-bridge-acceptor (D-B-A) molecules with cross-conjugated, linearly conjugated, and saturated bridges have been compared and contrasted using time-resolved spectroscopy. The photoexcited charge transfer state of 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An) is the donor, and naphthalene-1,8:4,5-bis(dicarboximide) (NI) is the acceptor in all cases, along with 1,1-diphenylethene, trans-stilbene, Diphenylmethane, and xanthone bridges. Photoinitiated CS through the cross-conjugated 1,1-diphenylethene bridge is about 30 times slower than through its linearly conjugated trans-stilbene counterpart and is comparable to that observed through the Diphenylmethane bridge. This result implies that cross-conjugation strongly decreases the π orbital contribution to the donor-acceptor electronic coupling so that electron transfer most likely uses the bridge σ system as its primary CS pathway. In contrast, the CS rate through the cross-conjugated xanthone bridge is comparable to that observed through the linearly conjugated trans-stilbene bridge. Molecular conductance calculations on these bridges show that cross-conjugation results in quantum interference effects that greatly alter the through-bridge donor-acceptor electronic coupling as a function of charge injection energy. These calculations display trends that agree well with the observed trends in the electron transfer rates.
