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Centrifugation-free and high yield synthesis of nanosized H-ZSM-5 and its structure-guided aromatization of methanol to 1,2,4-trimethylbenzene
Nanosized H-ZSM-5 has been proven to be an efficient way to improve mass transport properties with shape selectivity in many catalytic reactions. Generally, the synthesis of very fine nanosized H-ZSM-5 always suffers from low product yield and requires a complicated centrifugal separation process, both of which severely hinder its large-scale preparation and industrial applications. Herein, we report a centrifugation-free and high yield synthesis route for hierarchically nanosized ZSM-5 with a wide Si/Al ratio range by a combination of pre-aging process and steam-assisted conversion method using alkalis-free powder as the ZSM-5 precursor. This facile route not only avoids the energy-intensive centrifugal separation and ion-exchange process, but also significantly increases the crystallization efficiency along with a high yield. The obtained nanosized ZSM-5 possesses an ultrafine uniform size, high surface area, high total pore volumes, tunable Si/Al molar ratio, and high crystallinity. As a result, the nanosized ZSM-5 shows excellent catalytic performance when used in the catalytic conversion of methanol to aromatics. Notably, the nanosized ZSM-5 with a Si/Alth of 60 (NZS-60) shows an almost 25-fold longer catalytic lifetime, as well as up to 16% higher total aromatic selectivity when compared with conventional ZSM-5. Furthermore, the selectivity of 1,2,4-trimethylbenzene over this catalyst can be up to 44% in all products and 64% in aromatics products. Characterization results of the spent samples reveal that the most-improved catalytic performance and high selectivity of 1,2,4-trimethylbenzene over the nanosized ZSM-5 could be attributed to its small crystal size and hierarchical structure, which not only prevents the deposition of polyaromatic hydrocarbon in the microspores, but also sharply increases the reaction efficiency of bulky intermediate products on the surface of the catalyst.
Shen, Kui,Qian, Weizhong,Wang, Ning,Su, Chang,Wei, Fei
p. 19797 - 19808
(2014)
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Highly effective and chemoselective hydrodeoxygenation of aromatic alcohols
Effective hydrodeoxygenation (HDO) of aromatic alcohols is very attractive in both conventional organic synthesis and upgrading of biomass-derived molecules, but the selectivity of this reaction is usually low because of the competitive hydrogenation of the unsaturated aromatic ring and the hydroxyl group. The high activity of noble metal-based catalysts often leads to undesired side reactions (e.g., saturation of the aromatic ring) and excessive hydrogen consumption. Non-noble metal-based catalysts suffer from unsatisfied activity and selectivity and often require harsh reaction conditions. Herein, for the first time, we report chemoselective HDO of various aromatic alcohols with excellent selectivity, using porous carbon-nitrogen hybrid material-supported Co catalysts. The C-OH bonds were selectively cleaved while leaving the aromatic moiety intact, and in most cases the yields of targeted compounds reached above 99% and the catalyst could be readily recycled. Nitrogen doping on the carbon skeleton of the catalyst support (C-N matrix) significantly improved the yield of the targeted product. The presence of large pores and a high surface area also improved the catalyst efficiency. This work opens the way for efficient and selective HDO reactions of aromatic alcohols using non-noble metal catalysts.
Han, Buxing,He, Mingyuan,Mei, Xuelei,Wu, Haihong,Wu, Wei,Xu, Caiyun,Zhai, Jianxin,Zhang, Kaili,Zhang, Zhanrong,Zheng, Bingxiao
p. 1629 - 1635
(2022/02/21)

Probing the pore structure of hierarchical EU-1 zeolites by adsorption of large molecules and through catalytic reaction
The adsorption of toluene and 1,3,5-trimethylbenzene and the catalytic transformation of 1,3,5-trimethylbenzene are applied as probing approaches to characterize the pore system of hierarchical EU-1 zeolites prepared using organofunctionalized fumed silica as the silicon source. The adsorption and diffusion of toluene and 1,3,5-trimethylbenzene are significantly improved in the hierarchical EU-1 zeolites compared with the conventional microporous EU-1 zeolite. The adsorption kinetics of toluene and 1,3,5-trimethylbenzene suggested that introducing mesopores significantly increases the rate of adsorption and improved the diffusion of large molecules. In the catalytic transformation of 1,3,5-trimethylbenzene, the conversion of 1,3,5-trimethylbenzene on the hierarchical EU-1 zeolites is doubled compared with the conventional microporous EU-1 zeolite, due to the improved diffusion of bulky molecules and enhanced accessibility of active sites in the hierarchical EU-1 structure. Although isomerization is the main reaction, differences are observed in the product ratios of isomerization to disproportionation between the hierarchical EU-1 zeolites and the microporous counterpart with different times on stream. The transformation of 1,3,5-trimethylbenzene over the hierarchical EU-1 zeolites has a higher isomerization to disproportionation ratio than that over the microporous EU-1 zeolite; this is due to the increased mesoporosity.
Guo, Zaibin,Hao, Wenming,Ma, Jinghong,Li, Ruifeng
p. 187 - 193
(2020/07/04)

Selective production of bio-based: Para -xylene over an FeOx -modified Pd/Al2O3catalyst
para-Xylene (PX) is a basic building block of polyethylene terephthalate, which is currently produced from petroleum resources. Developing a renewable route to PX is highly desirable to address both economic and environmental concerns. Several attempts used noble metal catalysts, e.g. Pd/Al2O3, to synthesize PX from biomass-derived 4-methyl-3-cyclohexene-1-carboxaldehyde (4-MCHCA), but suffered from a severe decarbonylation reaction, resulting in toluene as the main product. In this paper, we report an FeOx modification strategy to suppress the decarbonylation reaction on a Pd/Al2O3 catalyst, leading to a drastic shift in selectivity towards PX with a yield up to 81percent via a cascade dehydroaromatization-hydrodeoxygenation (DHA-HDO) pathway. Characterization and control experiments revealed that the electron density of Pd sites decreased in an FeOx-modified Pd/Al2O3 catalyst compared to Pd/Al2O3, thus tuning the preferential adsorption mode of the substrate from η2-(C,O), the key transition state of the decarbonylation reaction, to the η1-(O) mode that favors the hydrodeoxygenation process. Notably, this designed catalyst is highly stable and is readily applicable in the selective synthesis of a broad range of desired aromatic chemicals via the same DHA-HDO pathway from cyclohex-3-enecarbaldehyde derivatives. Overall, this work develops a controllable catalyst modification strategy that tailors an efficient catalyst for petroleum-independent bio-PX synthesis.
Fu, Zaihui,Li, Changzhi,Meng, Qingwei,Pan, Xiaoli,Xiao, Yuxue,Zhang, Chao
p. 4341 - 4349
(2020/07/14)

PROCESS FOR CO-PRODUCTION OF MIXED XYLENES AND HIGH OCTANE C9+ AROMATICS
Disclosed is a process for producing mixed xylenes and C9+ hydrocarbons in which an aromatic hydrocarbon feedstock comprising benzene and/or toluene is contacted with an alkylating agent comprising methanol and/or dimethyl ether under alkylation conditions in the presence of an alkylation catalyst to produce an alkylated aromatic product stream comprising the mixed xylenes and C9+ hydrocarbons. The mixed xylenes are subsequently converted to para-xylene, and the C9+ hydrocarbons and its components may be supplied as motor fuels blending components. The alkylation catalyst comprises a molecular sieve having a Constraint Index in the range from greater than zero up to about 3. The molar ratio of aromatic hydrocarbon to alkylating agent is in the range of greater than 1:1 to less than 4:1.
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Paragraph 0067-0072

(2019/10/23)

Methods for preparing benzene-ring-containing compounds from pinacol
The invention relates to methods for preparing durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from pinacol. Durene, 1,2,3-trimethylbenzene and o-xylene are prepared through three steps of reaction, and pyromellitic acid and trimellitic acid are prepared through four steps of reaction. A catalytic system used in the invention is green and environment-friendly, andcan be recycled. The raw materials of method, i.e., pinacol, crotonaldehyde, acrolein and crotonate can all be derived from biomass, and are cheap and easily available. All the reaction processes aresimple and are high in activity and selectivity in the dehydration of pinacol and the dehydrogenation, decarbonylation and oxidation of D-A products. The invention provides novel methods for preparingfine chemicals including durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from lignocellulose-based platform chemicals.
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Paragraph 0057; 0058; 0059; 0061

(2018/08/04)

Selective Production of Renewable para-Xylene by Tungsten Carbide Catalyzed Atom-Economic Cascade Reactions
Tungsten carbide was employed as the catalyst in an atom-economic and renewable synthesis of para-xylene with excellent selectivity and yield from 4-methyl-3-cyclohexene-1-carbonylaldehyde (4-MCHCA). This intermediate is the product of the Diels–Alder reaction between the two readily available bio-based building blocks acrolein and isoprene. Our results suggest that 4-MCHCA undergoes a novel dehydroaromatization–hydrodeoxygenation cascade process by intramolecular hydrogen transfer that does not involve an external hydrogen source, and that the hydrodeoxygenation occurs through the direct dissociation of the C=O bond on the W2C surface. Notably, this process is readily applicable to the synthesis of various (multi)methylated arenes from bio-based building blocks, thus potentially providing a petroleum-independent solution to valuable aromatic compounds.
Dai, Tao,Li, Changzhi,Li, Lin,Zhao, Zongbao Kent,Zhang, Bo,Cong, Yu,Wang, Aiqin
supporting information
p. 1808 - 1812
(2018/02/10)

Pushing the Limits on Metal-Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation
Acid-catalyzed skeletal C-C bond isomerizations are important benchmark reactions for the petrochemical industries. Among those, o-xylene isomerization/disproportionation is a probe reaction for strong Br?nsted acid catalysis, and it is also sensitive to the local acid site density and pore topology. Here, we report on the use of phosphotungstic acid (PTA) encapsulated within NU-1000, a Zr-based metal-organic framework (MOF), as a catalyst for o-xylene isomerization at 523 K. Extended X-ray absorption fine structure (EXAFS), 31P NMR, N2 physisorption, and X-ray diffraction (XRD) show that the catalyst is structurally stable with time-on-stream and that WOx clusters are necessary for detectable rates, consistent with conventional catalysts for the reaction. PTA and framework stability under these aggressive conditions requires maximal loading of PTA within the NU-1000 framework; materials with lower PTA loading lost structural integrity under the reaction conditions. Initial reaction rates over the NU-1000-supported catalyst were comparable to a control WOx-ZrO2, but the NU-1000 composite material was unusually active toward the transmethylation pathway that requires two adjacent active sites in a confined pore, as created when PTA is confined in NU-1000. This work shows the promise of metal-organic framework topologies in giving access to unique reactivity, even for aggressive reactions such as hydrocarbon isomerization.
Ahn, Sol,Nauert, Scott L.,Buru, Cassandra T.,Rimoldi, Martino,Choi, Hyeju,Schweitzer, Neil M.,Hupp, Joseph T.,Farha, Omar K.,Notestein, Justin M.
supporting information
p. 8535 - 8543
(2018/06/25)

Standard and rapid scan infrared spectroscopic studies of: O -xylene transformations in terms of pore arrangement of 10-ring zeolites-2D COS analysis
This study attempts to offer an insight into o-xylene isomerization process in terms of steric constraints of 10-ring zeolites. The zeolites under investigation, i.e. ZSM-5, IM-5 and TNU-9, have purely microporous structures and crystals with the same shape and offer comparable protonic functionality, both in manner of amount and strength of Si(OH)Al groups. Under these conditions, micropore topology is recognised to deliver differentiated catalytic performance of each zeolitic structure. Moreover, 10-ring zeolites of reduced dimensionality, i.e. TNU-10 and ZSM-22, are chosen as reference materials. The 2D COS analysis of IR spectra reveal that interaction and catalytic activity in o-xylene isomerization process are strongly influenced by diffusion of reagents in rigid microporous environment and the formation of intermediate species is characterised by IR bands at 1485 and 1455 cm-1. With a prolonged time of the reaction (15 min), the formation of the latter species is observed for zeolite IM-5 characterised by limited 3-dimensionality. Rapid scan experiments show that in a shorter reaction time (4 min), these intermediate moieties are present for all the structure studied. The intermediate species are believed to originate from arenium ions such as methylbenzenium CH3-C6H5+-CH3 and/or methyl-substituted cycloheptatrienyl ions CH3-C7H7+. Their amount is strictly related to the rigidity of the microporous system: the most spacious environment for o-xylene transformation, e.g. TNU-9, is characterised by the lowest population of intermediates, whereas structures offering sufficiently tight geometry, e.g. TNU-10, can accommodate intermediate species in higher quantities, finally leading to the production of p-xylene with high selectivity.
Go?bek, Kinga,Tarach, Karolina A.,Góra-Marek, Kinga
p. 9934 - 9950
(2017/08/10)

Sustainable Production of o-Xylene from Biomass-Derived Pinacol and Acrolein
o-Xylene (OX) is a large-volume commodity chemical that is conventionally produced from fossil fuels. In this study, an efficient and sustainable two-step route is used to produce OX from biomass-derived pinacol and acrolein. In the first step, the phosphotungstic acid (HPW)-catalyzed pinacol dehydration in 1-ethyl-3-methylimidazolium chloride ([emim]Cl) selectively affords 2,3-dimethylbutadiene. The high selectivity of this reaction can be ascribed to the H-bonding interaction between Cl? and the hydroxy group of pinacol. The stabilization of the carbocation intermediate by the surrounding anion Cl? may be another reason for the high selectivity. Notably, the good reusability of the HPW/[emim]Cl system can reduce the waste output and production cost. In the second step, OX is selectively produced by a Diels–Alder reaction of 2,3-dimethylbutadiene and acrolein, followed by a Pd/C-catalyzed decarbonylation/aromatization cascade in a one-pot fashion. The sustainable two-step process efficiently produces renewable OX in 79 % overall yield. Analogously, biomass-derived crotonaldehyde and pinacol can also serve as the feedstocks for the production of 1,2,4-trimethylbenzene.
Hu, Yancheng,Li, Ning,Li, Guangyi,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
p. 2880 - 2885
(2017/07/25)

One-Pot Defunctionalization of Lignin-Derived Compounds by Dual-Functional Pd50Ag50/Fe3O4/N-rGO Catalyst
Generation of hydrogen from renewable sources and its safe utilization for efficient one-pot upgrading of renewable biofuels are a challenge. Bimetallic PdAg catalyst supported on Fe3O4/nitrogen-doped reduced graphene oxide (N-rGO) were synthesized for hydrogen generation from formic acid with high TOF (497 h-1 at 50 °C), and the hydrogen was subsequently utilized in situ for selective defunctionalization of lignin-derived chemicals with preserved aromatic nature at ambient pressure. Hydrodeoxygenation of aromatic aldehydes and ketones gave excellent yields (99% at 130 °C) with no use of additives. Furthermore, hydrogenolysis of β-O-4 and α-O-4 C-O model compounds produced only two products with high selectivity at 120 °C, which is an efficient and versatile one-pot platform for valorization of lignin biomass.
Singh, Ajay K.,Jang, Seungwook,Kim, Jae Yul,Sharma, Siddharth,Basavaraju,Kim, Min-Gyu,Kim, Kyung-Rok,Lee, Jae Sung,Lee, Hong H.,Kim, Dong-Pyo
p. 6964 - 6972
(2015/11/18)

Methylbenzene hydrocarbon pool in methanol-to-olefins conversion over zeolite H-ZSM-5
The formation and reactivity of a methylbenzenes (MBs) hydrocarbon pool in the induction period of the methanol-to-olefins (MTO) reaction over zeolite H-ZSM-5 was investigated and the mechanistic link of MBs to ethene and propene was revealed. Time evolution analysis of the formed MBs and 12C/13C methanol-switching experiments indicate that in the induction period bulkier compounds such as tetraMB and pentaMB have higher reactivity than their lighter counterparts such as p/m-diMB and triMB. By correlating the distribution of MBs trapped on H-ZSM-5 with ethene and propene, we found that tetraMB and pentaMB favor the formation of propene, while p/m-diMB and triMB mainly contribute to the formation of ethene. On the basis of this relationship, the olefin (ethene and propene) selectivity can be controlled by regulating the distribution of trapped MBs by varying the silicon-to-aluminum ratio of ZSM-5, reaction temperature, and space velocity. The reactivity of MBs and the correlation of MBs with olefins were also verified under steady-state conditions. By observation of key cyclopentenyl and pentamethylbenzenium cation intermediates using in situ solid-state NMR spectroscopy, a paring mechanism was proposed to link MBs with ethene and propene. P/M-diMB and triMB produce ethylcyclopentenyl cations followed by splitting off of ethene, while tetraMB and pentaMB generate propyl-attached intermediates, which eventually produce propene. This work provides new insight into the MBs hydrocarbon pool in MTO chemistry.
Wang, Chao,Xu, Jun,Qi, Guodong,Gong, Yanjun,Wang, Weiyu,Gao, Pan,Wang, Qiang,Feng, Ningdong,Liu, Xiaolong,Deng, Feng
p. 127 - 137
(2015/11/09)

Catalytic conversion of isophorone to jet-fuel range aromatic hydrocarbons over a MoOx/SiO2 catalyst
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.
Chen, Fang,Li, Ning,Wang, Wentao,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
supporting information
p. 11876 - 11879
(2015/07/15)

K-promoted Mo/Co- and Mo/Ni-catalyzed Fischer-Tropsch synthesis of aromatic hydrocarbons with and without a Cu water gas shift catalyst
The catalyst systems Mo/Co/K/ZSM-5 and Mo/Ni/K/ZSM-5, alone and with the added copper-based water gas shift catalyst, were used for the conversion of two CO/H2 ratios in a batch reactor. GC analysis of the gas phase was used to determine CO conversion while GCMS and NMR studies were used to characterize the liquid products formed and liquid product selectivities. The liquids were hydrocarbons consisting mainly of alkyl substituted benzenes. Methyl substitution in the alkyl benzenes in the product liquid ranged from an average of 1.3 to 4.5 methyls per ring depending on reaction conditions and reactant gas mole ratios. The additional presence of the WGS catalyst significantly increased CO conversion in the reactions taking place at 280 °C from ～25% to ～90% while increasing selectivity toward higher average methyl substitution. Similar conversions and selectivities were observed with both a bio-syngas and a 50/50 mixture of H2 and CO.
Wijayapala, Rangana,Yu, Fei,Pittman Jr., Charles U.,Mlsna, Todd E.
p. 93 - 99
(2014/06/09)

Kinetics and mechanism of benzene, toluene, and xylene methylation over H-MFI
The methylation of benzene, toluene, para-xylene, and ortho-xylene over MFI structured H-ZSM-5 and mesoporous self-pillared pentasil (H-SPP) with dimethyl ether (DME) at low conversions (30:1) showed linear rate dependencies on aromatic pressure and zero dependence on DME pressure for benzene and toluene. These results are consistent with studies performed for olefin methylation, and are indicative of a zeolite surface covered in DME-derived species reacting with benzene or toluene in the rate-determining step. Saturation in the reaction rate was observed in xylene pressure dependence experiments (at 473 K, H/kD = 1.25-1.35) and extents of d0, d 3, and d6 DME formation in the effluent because of isotopic scrambling between unlabeled and d6 DME when co-fed with aromatics over H-ZSM-5. Post-reaction titration of surface species with water after desorption of physisorbed intermediates showed a 1:1 evolution of methanol to Al present in the catalyst, indicating the presence and involvement of surface methoxides during steady-state methylation of aromatics species.
Hill, Ian,Malek, Andre,Bhan, Aditya
p. 1992 - 2001
(2013/09/24)

ZEOLITIC CATALYTIC CONVERSION OF ALCOHOLS TO HYDROCARBONS
A method for converting an alcohol to a hydrocarbon, the method comprising contacting said alcohol with a metal-loaded zeolite catalyst at a temperature of at least 100°C and up to 550°C, wherein said alcohol can be produced by a fermentation process, said metal is a positively-charged metal ion, and said metal-loaded zeolite catalyst is catalytically active for converting said alcohol to said hydrocarbon.
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Page/Page column 19

(2013/02/28)

Stoichiometric and catalytic reactions of thermally stable nickel(0) NHC complexes
Although there are many organic reactions that are catalyzed by either Ni0 or Pd0 complexes, in comparison with the case for Pd0 there has been significantly less work studying coordinatively unsaturated Ni0 complexes. Here, we develop a simple synthetic route for preparing a number of thermally stable NHC-supported Ni0 hexadiene complexes in good yield. We examine the stoichiometric reactivity of one of these species and demonstrate that the coordinated hexadiene moiety is labile and can be replaced with a variety of different ligands, including CO, phosphines, isonitriles, and olefins. In addition, we show that the Ni 0 hexadiene complexes are relatively rare examples of homogeneous first-row transition-metal catalysts for the hydrogenation of olefins.
Wu, Jianguo,Faller, John W.,Hazari, Nilay,Schmeier, Timothy J.
scheme or table
p. 806 - 809
(2012/05/04)

Catalytic transformation of methyl benzenes over zeolite catalysts
Catalytic transformation of three methyl benzenes (toluene, m-xylene, and 1,2,4-trimethyl benzene) has been investigated over ZSM-5, TNU-9, mordenite and SSZ-33 catalysts in a novel riser simulator at different operating conditions. Catalytic experiments were carried out in the temperature range of 300-400 °C to understand the transformation of these alkyl benzenes over large pore (mordenite and SSZ-33) in contrast to medium-pore (ZSM-5 and TNU-9) zeolite-based catalysts. The effect of reaction conditions on the isomerization to disproportionation product ratio, distribution of trimethylbenzene (TMB) isomers, and p-xylene/o-xylene ratios are reported. The sequence of reactivity of the three alkyl benzenes depends upon the pore structure of zeolites. The zeolite structure controls primarily the diffusion of reactants and products while the acidity of these zeolites is of a secondary importance. In the case of medium pore zeolites, the order of conversion was m-xylene > 1,2,4-TMB > toluene. Over large pore zeolites the order of reactivity was 1,2,4-TMB > m-xylene > toluene for SSZ-33 catalyst, and m-xylene ～ 1,2,4-TMB > toluene over mordenite. Significant effect of pore size between ZSM-5 and TNU-9 was observed; although TNU-9 is also 3D 10-ring channel system, its slightly larger pores compared with ZSM-5 provide sufficient reaction space to behave like large-pore zeolites in transformation of aromatic hydrocarbons. We have also carried out kinetic studies for these reactions and activation energies for all three reactants over all zeolite catalysts under study have been calculated.
Al-Khattaf,Akhtar,Odedairo,Aitani,Tukur,Kub?,Musilová-Pavla?ková,?ejka
experimental part
p. 176 - 190
(2012/01/06)

Vapor phase alkylation of toluene using various alcohols over H 3PO4/MCM-41 catalyst: Influence of reaction parameters on selectivity and conversion
A mesoporous MCM-41 molecular sieve material with a molar ratio of SiO 2/Al2 O3 = 70 and loaded with H3 PO4 was used as a catalyst for the alkylation of toluene, using various alcohols, namely methanol, iso-propanol, and tert-butanol, as alkylating agents. Para-alkylated toluene was the predominant product, formation of which was enhanced by moderate temperature, low amounts of the alkylating agents in the feed, and high carrier gas flow rate. Time on stream was found to exert a profound effect on the selectivity and conversion to the different products. TUeBITAK.
Abbaspourrad, Alireza,Kalbasi, Roozbeh Javad,Zamani, Farzad
experimental part
p. 875 - 885
(2011/08/06)

Aromatization of isobutene using H-ZSM-5/Oxide composite catalysts
Aromatization of isobutene was investigated using zeolite H-ZSM-5 (Si/Al = 30) as well as physical mixtures of H-ZSM-5 with metal oxides (Ga 2O3, ZnO and CuO). The study was aimed at determining the effect on the selectivity to aroma
Al-Otaibi, Naif M.,Hutching, Graham
experimental part
p. 191 - 195
(2011/01/03)

Accurate oxidation potentials of benzene and biphenyl derivatives via electron-transfer equilibria and transient kinetics
(Graph Presented) Nanosecond transient absorption methods were used to determine accurate oxidation potentials (Eox) in acetonitrile for benzene and a number of its alkyl-substituted derivatives. Eox values were obtained from a combination of equilibrium electron-transfer measurements and electron-transfer kinetics of radical cations produced from pairs of benzene and biphenyl derivatives, with one member of the pair acting as a reference. Using a redox-ladder approach, thermodynamic oxidation potentials were determined for 21 benzene and biphenyl derivatives. Of particular interest, Eox values of 2.48 ± 0.03 and 2.26 ± 0.02 V vs SCE were obtained for benzene and toluene, respectively. Because of a significant increase in solvent stabilization of the radical cations with decreasing alkyl substitution, the difference between ionization and oxidation potentials of benzene is ～0.5 eV larger than that of hexamethylbenzene. Oxidation potentials of the biphenyl derivatives show an excellent correlation with substituent σ+ values, which allows Eox predictions for other biphenyl derivatives. Significant dimer radical cation formation was observed in several cases and equilibrium constants for dimerization were determined. Methodologies are described for determining accurate electrontransfer equilibrium constants even when dimer radical cations are formed. Additional equilibrium measurements in trifluoroacetic acid, methylene chloride, and ethyl acetate demonstrated that solvation differences can substantially alter and even reverse relative Eox values.
Merkel, Paul B.,Luo, Pu,Dinnocenzo, Joseph P.,Farid, Samir
experimental part
p. 5163 - 5173
(2009/12/06)

CATALYTIC PROCESS FOR CONVERTING RENEWABLE RESOURCES INTO PARAFFINS FOR USE AS DIESEL BLENDING STOCKS
A process for converting renewable resources such as vegetable oil and animal fat into paraffins in a single step which comprises contacting a feed which is a renewable resources with hydrogen and a catalyst which comprises molybdenum, a non-precious metal and an oxide to produce a hydrocarbon product having a ratio of even-numbered hydrocarbons to odd-numbered hydrocarbons of at least 2:1.
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Page/Page column 7

(2009/01/24)

Room temperature Ni-catalyzed reduction of aryl tosylates by borane hydrides
Mild Ni-catalyzed homogeneous reductions of aryl tosylates are described for the first time. The catalytic system Ni(PPh3)2Cl2 and PCy3 is shown to be general for hydrogenolysis of a wide range of tosylates, including hindered, deactivated, heterocyclic, and bifunctional examples.
Kogan, Vladimir
p. 7515 - 7518
(2007/10/03)

Process for producing alicyclic aldehydes
In the production of an alicyclic aldehyde, a starting aromatic aldehyde is converted into an aromatic acetal for protecting the formyl group. The aromatic ring of the aromatic acetal is then hydrogenated to convert the aromatic acetal into an alicyclic acetal, which is then hydrolyzed to cleave the acetal protecting group to obtain the aimed alicyclic aldehyde.
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Page/Page column 5

(2008/06/13)

Process for the production of mesitylene and durene
A process is described for the contemporaneous preparation of mesitylene and durene, characterized in that mesitylene and durene are obtained exclusively starting from pseudo-cumene without the use of any further chemical compound, operating in continuous, at a temperature ranging from 210 to 400° C., at a pressure ranging from 1 to 50 bar, with a weight space velocity ranging from 0.1 to 20 hours?1 and in the presence of a catalyst based on crystalline metal-silicates in acid form. After the recovery of mesitylene and durene from the reaction raw product, some of the remaining components of the raw product itself are recycled and fed to the reactor together with the pseudo-cumene.
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Page 7

(2008/06/13)

Photo- and radiation-chemical production of radical cations of methylbenzenes and benzyl alcohols and their reactivity in aqueous solution
Radical cations of methylated benzenes and benzyl alcohols were generated by photoionization and by reaction SO4·- in aqueous solution. The photoionization requires two 248 nm photons. The lifetimes with the oxidant SO4 and absorption spectra of the radical cations produced were determined by time-resolved conductance and optical detection, and the reaction products were measured by GC. As expected, the radical cation lifetimes increase strongly with increasing number of additional methyl groups, and so does the ratio of deprotonation from a methyl or hydroxymethyl group vs. addition (of water) to a ring position. In the case of toluene the radical cation appears to have a chemical lifetime τ of 10-100 ps ≤ τ ≤ 20 ns, i.e., longer than it takes for an ion pair to separate into the free (solvated) ions, and it reacts predominantly by addition of water to the ring rather than by deprotonation from the methyl group. A further observation is that, as compared to methoxylated analogues, the methylated benzyl alcohol radical cations are much more reactive, such that OH-induction of side-chain fragmentation, as often required with methoxylated benzyl alcohol-type radical cations, is not necessary.
Russo-Caia, Claudia,Steenken, Steen
p. 1478 - 1485
(2007/10/03)

Electron-transfer mechanisms with photoactivated quinones. The encounter complex versus the Rehm-Weller paradigm
Photoexcited quinones (Q*) are efficiently quenched by polymethylbenzenes (ArH) via electron transfer (ET). However, the second-order rate constants (k2) exhibit Rehm-Weller (outer-sphere) dependence on the free energy (ΔGET), despite our new findings that the quenching occurs via a series of rather strong encounter complexes [Q*, ArH] with substantial (charge-transfer) bonding. The relatively high formation constants (KEC) of the encounter complexes indicate that any mechanistic interpretation of the driving-force dependence of the observed rate constants is highly ambiguous since k2 must be a composite of KEC and the intrinsic rate constant (kET) for electron transfer within the intermediate (inner-sphere) complex. As such, the reorganization energies extracted from Rehm-Weller plots lack thermodynamic significance. On the other hand, the unambiguous driving-force dependence of kET represents a unique example for the "normal" Marcus behavior of the endergonic electron transfer between the donor/acceptor pair in van der Waals contact as extant in the encounter complex.
Hubig, Stephan M.,Kochi, Jay K.
p. 1688 - 1694
(2007/10/03)

Steric control of electron transfer. Changeover from outer-sphere to inner-sphere mechanisms in arene/quinone redox pairs
The various aromatic hydrocarbons (Chart 2) constitute a sharply graded series of sterically encumbered (unhindered, partially hindered, and heavily hindered) donors in electron transfer (ET) to quinones (Chart 1). As such, steric effects provide the quantitative basis to modulate (and differentiate) outer-sphere and inner-sphere pathways provided by matched pairs of hindered and unhindered donors with otherwise identical electron-transfer properties. Thus the hindered donors are characterized by (a) bimolecular rate constants (k2) that are temperature dependent and well correlated by Marcus theory, (b) no evidence for the formation of (discrete) encounter complexes, (c) high dependency on solvent polarity, and (d) enhanced sensitivity to kinetic salt effects - all diagnostic of outer-sphere electron-transfer mechanisms. Contrastingly, the analogous unhindered donors are characterized by (a) temperature-independent rate constants (k2) that are 102 times faster and rather poorly correlated by Marcus theory, (b) weak dependency on solvent polarity, and (c) low sensitivity to kinetic salt effects - all symptomatic of inner-sphere ET mechanisms arising from the preequilibrium formation of encounter complexes with charge-transfer (inner-sphere) character. Steric encumbrances which inhibit strong electronic (charge-transfer) coupling between the benzenoid and quinonoid π systems are critical for the mechanistic changeover. Thus, the classical outer-sphere/inner-sphere distinction (historically based on coordination complexes) is retained in a modified form to provide a common terminology for inorganic as well as organic (and biochemical) redox systems.
Hubig, Stephan M.,Rathore, Rajendra,Kochi, Jay K.
p. 617 - 626
(2007/10/03)

Synthesis, characterization, and structure solution of CIT-5, a new, high-silica, extra-large-pore molecular sieve
The synthesis, structure solution, and characterization of the high-silica molecular sieve CIT-5 (California Institute of Technology Number 5) is described. CIT-5 is synthesized at hydrothermal conditions in the presence of N(16)-methylsparteinium and preferrably lithium cations. The structural solution of CIT-5 shows that it contains one-dimensional pores circumscribed by 14 tetrahedral atoms (14 MR). Rietveld refinement of the synchrotron X-ray powder data gives a symmetry and space group assignment for the structure of Pmn21 (no. 31) with refined unit cell parameters of a = 13.6738(8) ?, b = 5.0216(3) ?, and c = 25.4883(7) ? (V = 1750.1 ?3). Electron diffraction and transmission electron microscopy confirm the space group and the topology of the structure viewed along the [010] direction. Solid-state 29Si NMR spectroscopy results are consistent with the space group assignment. The thermal/hydrothermal stability of CIT-5 compares well to that of other large- and extra-large-pore, high-silica molecular sieves. The acid form of CIT-5 is able to perform hydrocarbon reactions such as cracking and alkylation and shows behaviors that are different from other zeolites.
Yoshikawa, Masahito,Wagner, Paul,Lovallo, Mark,Tsuji, Katsuyuki,Takewaki, Takahiko,Chen, Cong-Yan,Beck, Larry W.,Jones, Chris,Tsapatsis, Michael,Zones, Stacey I.,Davis, Mark E.
p. 7139 - 7147
(2007/10/03)

Acidity and catalytic properties of realuminated zeolite Y
We have compared the acidity and the catalytic properties of (i) zeolite H-Y, (ii) H-Y dealuminated by hydrothermal treatment (H-US-Y), and (iii) H-US-Y realuminated by the KOH treatment (H-Real-US-Y). Quantitative IR measurements of pyridine sorption show that the concentration of "3460 cm-1 hydroxyl groups", the Br?nsted acid sites active in many catalytic reactions, is slightly lower in sample H-Real-US-Y than in H-Y. This demonstrates that most of the 3460 cm-1 hydroxyl groups, present in the parent material and subsequently destroyed by dealumination, are restored by realumination and the K+/H+ exchange. The turnover frequency of the realuminated zeolite in m-xylene reactions is higher than in the parent sample, as a result of the higher strength of the acid sites, caused by the higher population of the most strongly acidic Si3Si-OH-AlSi3 groupings. Dealumination and realumination also alter the selectivity in the transformation of m-xylene. Disproportionation of xylenes to toluene and trimethylbenzenes, which involves bulky transition step complexes, is hindered in the dealuminated zeolite, where the channels are partly blocked by the extra-framework A1 species, but is restored in the realuminated material, in which the extra-framework species are re-inserted into the framework.
Sulikowski, Bogdan,Datka, Jerzy,Gil, Barbara,Ptaszynski, Juliusz,Klinowski, Jacek
p. 6929 - 6932
(2007/10/03)

Characterization of the extra-large-pore zeolite UTD-1
The molecular sieve UTD-1 is investigated using scanning and transmission electron microscopies (TEM), solid-state NMR spectroscopy, electron (ED) and X-ray diffraction (XRD), adsorption studies, and catalytic test reactions. The results confirm that UTD-1 is the first high-silica zeolite to contain a one;dimensional, extra-large 14-ring pore system. TEM and ED show that UTD-1 is faulted along the (002) planes. Simulations of XRD patterns of faulted structures using DIFFaX indicate that the XRD pattern of a framework containing the so-called double crankshaft chains is in better agreement with the experimental pattern than a framework with the narsarsukite chains previously reported. Thermal/hydrothermal stability studies show that UTD-1 has similar stability to other medium- and large-pore, high-silica zeolites. The ratio of isomerization to disproportionation, and the distribution of trimethylbenzene isomers in the m-xylene isomerization test reaction from UTD-1 are similar to those obtained from other large-pore zeolites (zeolites Y or L). However, UTD-1 shows a p-/o-xylene ratio of products below one.The molecular sieve UTD-1 is investigated using scanning and transmission electron microscopies (TEM), solid-state NMR spectroscopy, electron (ED) and X-ray diffraction (XRD), adsorption studies, and catalytic test reactions. The results confirm that UTD-1 is the first high-silica zeolite to contain a one-dimensional, extra-large 14-ring pore system. TEM and ED show that UTD-1 is faulted along the (002) planes. Simulations of XRD patterns of faulted structures using DIFFaX indicate that the XRD pattern of a framework containing the so-called double crankshaft chains is in better agreement with the experimental pattern than a framework with the narsarsukite chains previously reported. Thermal/hydrothermal stability studies show that UTD-1 has similar stability to other medium-and large-pore, high-silica zeolites. The ratio of isomerization to disproportionation, and the distribution of trimethylbenzene isomers in the m-xylene isomerization test reaction from UTD-1 are similar to those obtained from other large-pore zeolites (zeolites Y or L). However, UTD-1 shows a p-/o-xylene ratio of products below one.
Lobo, Raul F.,Tsapatsis, Michael,Freyhardt, Clemens C.,Khodabandeh, Shervin,Wagner, Paul,Chen, Cong-Yan,Balkus Jr., Kenneth J.,Zones, Stacey I.,Davis, Mark E.
p. 8474 - 8484
(2007/10/03)

A Superior Procedure for Generation of Substituted Benzyllithiums from the Corresponding Chlorides
The use of diethyl ether-tetrahydrofuran-light petroleum (b.p. 30-40 deg C) (4:3:1) as solvent for the reaction of substituted benzyl chlorides with lithium naphthalenide at low temperature gives useful yields of the corresponding benzyllithium compounds, which react with electrophiles such as iodomethane and water to yield the expected reaction products.
Smith, Keith,Hou, Daunjie
p. 185 - 186
(2007/10/02)

Dynamics of interconversion of contact and solvent-separated radical-ion pairs
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Arnold, Bradley R.,Noukakis, Dimitri,Farid, Samir,Goodman, Joshua L.,Gould, Ian R.
p. 4399 - 4400
(2007/10/02)

Isomerization and Disproportionation of 1,2,4-Trimethylbenzene over HY Zeolite
The conversion of 1,2,4-trimethylbenzene (1,2,4-TMB) over HY zeolite was studied at atmospheric pressure and 200-300 deg C by using a fixed-bed, integral-flow reactor.The types and initial selectivities of various products were obtained from plots of product selectivity according to the time-on-stream theory.The primarly reaction included the isomerization and the disproportionation: the former led to the simultaneous formation of 1,2,3- and 1,3,5-TMB whereas the latter produced all isomers of xylene and tetramethylbenzene.The relative initial activation energies for the primary reactions were estimated and compared with those in the reaction of 1,2,3-TMB.
Ko, An-Nan,Kuo, Ching Tung
p. 145 - 150
(2007/10/02)

Electron Transfer from Aromatic Compounds to Phenyliodinium and Diphenylsulfinium Radical Cations
Phenyliodinium (I.(+1)) and diphenylsulfinium radical cations (II.(+1)) have been generated by flash photolysis (λinc = 347 nm) of diphenyliodonium ions (I(+1)) and diphenyl(4-phenylthiophenyl)sulfonium ions (II(+1)) in acetonitrile solutions at room temperature.I.(+1) and II.(+1) were found to undergo electron-transfer reactions with benzene derivatives resulting in the formation of radical cations of the aromatic compounds.A study involving 25 compounds including various methyl- and methoxy-benzenes, biphenyl, phenol and cresols revealed that electron transfer is independent of the ionizations energy Ei provided that the rates are encounter-controlled.This applies to cases where Ei does not exceed a critical value: Ei,crit ca. 820 kJ mol-1 (I.(+1)) and 780 kJ mol-1 (II.(+1)).Bimolecular rate constants decrease with increasing Ei in the case of aromatic compounds having ionization energies exceeding the critical values.A Marcus-inverted region was not detected.
Yagci, Y.,Schnabel, W.,Wilpert, A.,Bending, J.
p. 287 - 292
(2007/10/02)

ORBITAL-CONTROLLED REACTIONS CATALYSED BY ZEOLITES: ELECTROPHILIC ALKYLATION OF AROMATICS
The role of orbital control in product selectrivity during electrophilic alkylation catalysed by zeolites was studied both theoretically and experimentally.In order to discuss this, the alkylation of toluene and m-xylene by methanol was carried out on a series of large-pore zeolites (HY).The changes in the para to ortho ratio observed on changing the framework Si/Al ratio of the zeolites were related to ab initio molecular orbital calculations of the LUMO energy of structurally alike model clusters but containing different tetrahedral cations around the active site.The observed correlation is discussed in terms of the HSAB principle by taking into account the influence of the catalyst composition on the reactivity of the electrophilic reagent.
Corma, A.,Zicovich-Wilson, C.,Viruela, P.
p. 364 - 370
(2007/10/02)

One-Electron Oxidation of Alkylbenzenes in Acetonitrile by Photochemically Produced NO3.: Evidence for an Inner-Sphere Mechanism
The reaction between NO3. and polyalkylbenzenes was studied using 308-nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the alkylbenzenes in acetonitrile solution.For all benzenes, with the exception of monoalkylbenzenes and o- and m-xylene, the reaction with NO3. was found to yield the corresponding radical cations and to proceed in an apparently straightforward bimolecular manner.For monoalkylbenzenes and o- and m-xylene, radicals were seen which are derived from the parents by formal loss of H. from the side chain of the aromatic.This reaction proceeds via a complex between the aromatic and NO3. with the decomposition of the complex being rate determining at higher concentrations of aromatic (rate constants for decomposition between 6 * 105 and 4 * 107 s-1).In the complex, electron transfer from the aromatic to NO3. is suggested to be concerted with deprotonation of the incipient radical cation.Formation of a complex between NO3. and aromatics is likely even in those cases where radical cations are observed, with the assumption that in these cases the complex decomposition rate is greater than 6 * 107 s-1.
Giacco, Tiziana Del,Baciocchi, Enrico,Steenken, Steen
p. 5451 - 5456
(2007/10/02)

Characterization and catalytic properties of USHY zeolite modified with niobium.
USHY zeolite was exchanged by niobium.Several samples were obtained with various degrees of exchange.Pore volumes and acidity were measured to characterize these exchanged zeolites.Catalytic properties were evaluated with two reaction tests: metaxylene transformation and n-heptane cracking.Key Words: USHY zeolite / niobium exchange / pore volume / acidity / catalysis
Florentino, A.,Cartraud, P.,Magnoux, P.,Guisnet, M.
p. 496 - 500
(2007/10/02)

Catalytic Isomerization of Trimethylbenzenes over a Graphite-Sulfuric Acid
The isomerization of 1,2,3- and 1,2,4-trimethylbenzene took place over a graphite-sulfuric acid to form 1,2,4- and 1,2,3-trimethylbenzene, respectively, but that of 1,3,5-trimethylbenzene was not observed.
Tsuchiya, Susumu,Fujii, Kenji,Mitsuno, Tadashi,Sakata, Yoshihisa,Imamura, Hayao
p. 1011 - 1012
(2007/10/02)

Cycloaddition of Carbon Dioxide to Propyne over Supported Rh4 and Fe2Rh4 Carbonyl Cluster-derived Catalysts
Rh4 and Fe2Rh4 carbonyl cluster-derived catalysts supported on selected metal oxides such as TiO2, Al2O3, and ZrO2 exhibit catalytic activity in the formation of 4,6-dimethyl-2-pyrone by the cycloaddition of carbon dioxide to propyne under moderate conditions.
Pillai, S. Muthukumaru,Ohnishi, Ryuichiro,Ichikawa, Masaru
p. 246 - 247
(2007/10/02)

Efficiencies of photoinduced electron-transfer reactions: Role of the Marcus inverted region in return electron transfer within geminate radical-ion pairs
In photoinduced electron-transfer processes the primary step is conversion of the electronic energy of an excited state into chemical energy retained in the form of a redox (geminate radical-ion) pair (A + D →hν A?-/D?+). In polar solvents, separation of the geminate pair occurs with formation of free radical ions in solution. The quantum yields of product formation, from reactions of either the free ions, or of the geminate pair, are often low, however, due to the return electron transfer reaction (A?-/D?+ → A + D), an energy-wasting step that competes with the useful reactions of the ion pair. The present study was undertaken to investigate the parameters controlling the rates of these return electron transfer reactions. Quantum yields of free radical ion formation were measured for ion pairs formed upon electron-transfer quenching of the first excited singlet states of cyanoanthracenes by simple aromatic hydrocarbon donors in aceonitrile at room temperature. The free-ion yields are determined by the competition between the rates of separation and return electron transfer. By assuming a constant rate of separation, the rates of the return electron transfer process are obtained. These highly exothermic return electron transfer reactions (-ΔG-et = 2-3 eV) were found to be strongly dependent on the reaction exothermicity. The electron-transfer rates showed a marked decrease (ca. 2 orders of magnitude in this ΔG-et range) with increasing exothermicity. This effect represents a clear example of the Marcus "inverted region". Semiquantum mechanical electron-transfer theories were used to analyze the data quantitatively. The electron-transfer rates were found also to depend upon the degree of charge delocalization within the ions of the pair, which is attributed to variations in the solvent reorganization energy and electronic coupling matrix element. Accordingly, mostly on the basis of redox potentials, one can vary the quantum yield of free-ion formation from a few percent to values approaching unity. Use of a strong donor with a strong acceptor to induce reactions based on electron transfer is likely to be inefficient because of the fast return electron transfer in the resulting low-energy ion pair. A system with the smallest possible driving force for the initial charge-separation reaction results in a high-energy, and therefore long-lived ion pair, which allows the desired processes to occur more efficiently. The use of an indirect path based on secondary electron transfer, a concept called "cosensitization", results in efficient radical-ion formation even when the direct path results in a very low quantum yield.
Gould, Ian R.,Ege, Deniz,Moser, Jacques E.,Farid, Samir
p. 4290 - 4301
(2007/10/02)

Solid-State NMR Studies of the Shape-Selective Catalytic Conversion of Methanol into Gasoline on Zeolite ZSM-5
13C-Magic angle spinning (MAS)-NMR of thermally treated samples of zeolite H-ZSM-5 with adsorbed methanol identifies the organic species present in the adsorbed phase, monitors their fate, and distinguishes between mobile and attached species.Only MeOH is present at room temperature; in samples treated at 150 deg C dimethyl ether (DME) is also found.At 250 deg C and above a new signal, due to CO intermediate, appears.A number of aliphatic and aromatic compounds form at 300 deg C and above, and the role of CO in this process is discussed.Neither 1,2,3- or 1,3,5-trimethylbenzene is found in the products, but both are present in the adsorbed phase, which is the first direct experimental demonstration of product selectivity.Tetramethylbenzenes have not been found in the products of the reaction at 300 deg C, but all three are present in the adsorbed phase in considerable concentrations.Their distribution (tetramethylbenzenes are not formed in the thermodynamic equilibrium distribution) reveals the presence of a new kind of shape selectivity.At 370 deg C the shape-selective action is still present but is different because of the increased effective channel diameters.MAS-NMR has a considerable potential for monitoring and prediction of the course of catalytic reactions directly at the active centers in molecular sieves and will assist the design of shape-selective solids.
Anderson, Michael W.,Klinowski, Jacek
p. 10 - 16
(2007/10/02)

INFLUENCE OF WATER ON ACTIVITY, SELECTIVITY AND DEACTIVATION OF ZEOLITES IN ACETONE TRANSFORMATION
The suppresion of the deactivation of acid forms of zeolites in acetone transormation was studied by adding water vapours to the feed.Both conversion of acetone and yield of isobutene increased remarkably.Water prevents the substitution of bridging hydroxyls for coke species and limits the aldolization steps, which are decisive for catalyst deactivation.
Cejka, Jiri,Jiru, Pavel
p. 2998 - 3002
(2007/10/02)

SELECTIVITY CHANGES OF ACETONE TRANSFORMATION OVER ZSM-5 ZEOLITES WITH DIFFERENT ACIDO-BASIC PROPERTIES
Acetone transformation catalyzed by HZSM-5 and NaZSM-5 zeolites and by zeolites modified with basic oxides was studied in an integral reactor at a temperature of 350 deg C.Modification of acido-basic properties of ZSM-5 zeolites resulted both in the total conversion changes and in the essential changes in the product composition.Isobutene was found to be the main product over HZSM-5 zeolites exhibiting low activity, while aromatics prevailed when high conversion level was attained.Classical condensation of acetone yielding mesityloxide and phorones was observedover NaZSM-5 zeolites impregnated with CaO and ZnO.
Cejka, Jiri,Kubelkova, Ludmila,Jiru, Pavel
p. 2054 - 2063
(2007/10/02)

Selektive Cyclotetramerisierung von Propargylalkohol: Ueberraschend hohe Toleranz katalytischer Nickelsysteme gegenueber "Katalysatorgiften"
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Walther, Dirk,Braun, Dagmar,Schulz, Wolfgang,Rosenthal, Uwe
p. 293 - 294
(2007/10/02)

Carbon-carbon bond formation versus hydrogen transfer in the reaction of alkynes with mono(cyclopentadienyl)zirconium(II) complexes: Regioselective dimerization, cocyclotrimerization, and catalytic cyclotrimerization. The preparation and X-ray structures of Cp(dmpe)XZr[(R)C=C(R′)C(R)=C(R′)] [R = CH3; R′ = H, CH3; X = Cl, CH3; dmpe = ...
Full title: Carbon-carbon bond formation versus hydrogen transfer in the reaction of alkynes with mono(cyclopentadienyl)zirconium(II) complexes: Regioselective dimerization, cocyclotrimerization, and catalytic cyclotrimerization. The preparation and X-ray structures of Cp(dmpe)XZr[(R)C=C(R′)C(R)=C(R′)] [R = CH3; R′ = H, CH3; X = Cl, CH3; dmpe = 1,2-bis(dimethylphosphino)ethane] and of CpZr(dmpe)Cl[C=C(t-Bu)][CH=CH(t-Bu)]. Under mild conditions, the reaction between CpZr(dmpe)2X [X = Cl (1), Me (2); dmpe = 1,2-bis(dimethylphosphino)ethane] and aliphatic alkynes yields the crystalline CpZr[(R)C=C(R′)C(R)=C(R′)]-(dmpe)X [R = R′ = Me, X = Cl (3), Me (4); R′ = H, R = Me, X = Cl (5)]. In the case of 5, the zirconacyclopentadiene ring has been formed regiospecifically via a quantitative head-to-tail dimerization reaction. Steric factors are probably the origin of the regioselectivity. The structures of the complexes have been demonstrated by X-ray analyses. Crystal data are as follows. 3: monoclinic, C2/c, a = 16.807 (1) ?, b = 9.291 (1) ?, c = 27.557 (1) ?, β = 96.906 (4)°, V = 4271.9 (5) ?3, Z = 8. 4: triclinic, P1?, a = 9.252 (1) ?, b = 9.416 (1) ?, c = 14.104 (1) ?, α = 91.822 (8)°, β = 98.948 (9)°, γ = 118.09 (1)°, V = 1063.0 (2) ?3, Z = 2. 5: monoclinic, P21/n, a = 9.699 (2) ?, b = 13.563 (5) ?, c = 15.361 (4) ?, β = 91.36 (2)°, V = 2020.1 (9) ?3, Z = 4. Hydrogen transfer between two molecules of alkyne has been observed with the bulky HC≡C(t-Bu). The structure of the resulting CpZr(dmpe)Cl[C≡C(t-Bu)][CH=CH(t-Bu)] (6) has been demonstrated by X-ray analysis. Crystal data for 6: monoclinic, P21/a, a = 11.333 (3) ?, b = 15.655 (7) ?, c = 16.051 (3) ?, β = 100.08 (2)°, V = 2804 (1) ?3, Z = 4. Stoichiometric cyclotrimerization reactions and cocyclotrimerization can be achieved by further reaction of complexes 3, 4, and 5 with small alkynes (propyne, acetylene) and acetonitrile, forming random mixtures of isomeric arenes and substituted pyridine (collidine). Catalytic cyclotrimerization has been observed in the case of acetylene (-20°C) and propyne (room temperature) with formation of benzene and a mixture of 1,3,5- and 1,2,4-mesitylene, respectively.
Wielstra, Ytsen,Gambarotta, Sandro,Meetsma, Auke,De Boer, Jan L.,Chiang, Michael Y.
p. 2696 - 2702
(2008/10/08)

Shape Selective Property of Alumina-pillared Montmorillonite with Different Lateral Distances in m-Xylene Conversion
In m-xylene conversion on alumina-pillared montmorillonite, the selectivity of disproportionation increased with increasing lateral distance, while isomerization was predominant for the small lateral distance.The observed results suggest that the shape selectivity operates in the reaction.
Mori, Toshiaki,Suzuki, Kenzi
p. 2165 - 2168
(2007/10/02)

Electron-Transfer Reactions in the Marcus Inverted Region. Charge Recombination versus Charge Shift Reactions
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Gould, Ian R.,Moser, Jacques E.,Armitage, Bruce,Farid, Samir,Goodman, Joshua L.,Herman, Michael S.
p. 1917 - 1919
(2007/10/02)

Experimental Determination of Internal Energy Barriers in the Gas-Phase Aromatic Alkylation by Dimethylchloronium Ions
The temperature and pressure dependence of the substrate selectivity of the alkylation of mesitylene (M) and p-xylene (X) by radiolytically formed CH3ClCH3+ ions have been investigated in CH3Cl gas at pressure between 50 and 760 Torr in the range 40-140 deg C.The Arrhenius plot of the empirical kM/kX ratio measured at 760 Torr is linear over the entire temperature range investigated, and its slope corresponds to a difference of 2.2 +/- 0.2 kcal mol-1 between the activation energy for the CH3ClCH3+ methylation of the p-xylene and mesitylene.A pressure-dependence study of the same competition reactions carried out at 100 deg C points to 300 Torr as the pressure limit, below which the correspondence between the phenomenological Arrhenius-plot slope and the actual activation-barrier difference is not any longer warranted.This conclusion is further corroborated by a comparison of the present results with those derived for the same reactions from reactant ion monitoring (RIM) "high-pressure" mass spectrometry at 0.5-1.2 Torr.The large discrepancy observed is interpreted as evidence that above 300 Torr the activation mechanism of the CH3ClCH3+ methylation of arenes, a typical ion-molecule process, is essentially thermal and that, below this limit, coexistence of both thermal and electrostatic activation mechanisms as well as incomplete equilibration of the internal energy of the reactants make Arrhenius plots hardly a measure of the activation barriers involved in the gas-phase aromatic alkylations.
Speranza, Maurizio,Laguzzi, Guiseppe
p. 30 - 34
(2007/10/02)

COOLIGOMERIZATION OF PROPADIENE WITH PROPYNE CATALYSED BY NICKEL(0) COMPLEXES
Cooligomerization of propadiene with propyne catalysed by bis(1,5-cyclooctadiene)nickel and tetrakis(triphenylphosphine)nickel gives a variety of products, including besides the cooligomers also the homooligomers of both monomers.The type of catalyst affects partially the product distribution due to changes in the degree of oligomerization.Cooligomerization of propadiene with 3-deuteriopropyne provided information about relative proportion of propadiene and propyne units in the oligomers.
Cermak, Jan,Blechta, Vratislav,Chvalovsky, Vaclav
p. 1274 - 1286
(2007/10/02)