- Controlling the Lewis Acidity and Polymerizing Effectively Prevent Frustrated Lewis Pairs from Deactivation in the Hydrogenation of Terminal Alkynes
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Two strategies were reported to prevent the deactivation of Frustrated Lewis pairs (FLPs) in the hydrogenation of terminal alkynes: reducing the Lewis acidity and polymerizing the Lewis acid. A polymeric Lewis acid (P-BPh3) with high stability was designed and synthesized. Excellent conversion (up to 99%) and selectivity can be achieved in the hydrogenation of terminal alkynes catalyzed by P-BPh3. This catalytic system works quite well for different substrates. In addition, the P-BPh3 can be easily recycled.
- Geng, Jiao,Hu, Xingbang,Liu, Qiang,Wu, Youting,Yang, Liu,Yao, Chenfei
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p. 3685 - 3690
(2021/05/31)
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- Chemoselective Hydrogenation of Olefins Using a Nanostructured Nickel Catalyst
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The selective hydrogenation of functionalized olefins is of great importance in the chemical and pharmaceutical industry. Here, we report on a nanostructured nickel catalyst that enables the selective hydrogenation of purely aliphatic and functionalized olefins under mild conditions. The earth-abundant metal catalyst allows the selective hydrogenation of sterically protected olefins and further tolerates functional groups such as carbonyls, esters, ethers and nitriles. The characterization of our catalyst revealed the formation of surface oxidized metallic nickel nanoparticles stabilized by a N-doped carbon layer on the active carbon support.
- Klarner, Mara,Bieger, Sandra,Drechsler, Markus,Kempe, Rhett
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supporting information
p. 2157 - 2161
(2021/05/21)
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- Novel CoNi-metal-organic framework crystal-derived CoNi?C: Synthesis and effective cascade catalysis
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Evaluating the catalytic influence of metal sites on derivates obtained from the calcination of metal-organic frameworks (MOFs) is very important for the rational construction of novel MOFs. Based on this catalytic functional guidance, two new Co-MOF and CoNi-MOF crystals were designed and synthesized, and further pyrolyzed to obtain corresponding porous carbon-based catalysts. Interestingly, the derivates exhibited better catalytic performance toward the tandem reaction of dehydrogenation of NH3BH3 and subsequent hydrogenation reduction of nitro/olefin compounds than those of the CoNi-ZIF (a star MOF)-derived CoNi?carbon and most metal catalysts. Significantly, the CoNi?C maintained excellent activity, even after 30 cycles, demonstrating its great longevity and durability, which are especially important for the practical application of metal catalysts in industrial catalysis.
- Chen, Yu-Zhen,Li, Chenchen,Sun, Jia-Lu,Wang, Guo-Ming,Wang, Lin,Zhang, Jian-Wei
-
supporting information
p. 10567 - 10573
(2020/09/18)
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- Hydrogenation of Alkenes Catalyzed by a Non-pincer Mn Complex
-
Hydrogenation of substituted styrenes and unactivated aliphatic alkenes by molecular hydrogen has been achieved using a Mn catalyst with a non-pincer, picolylphosphine ligand. This is the second reported example of alkene hydrogenation catalyzed by a Mn complex. Mechanistic studies showed that a Mn hydride formed by H2 activation in the presence of a base is the catalytically active species. Based on experimental and DFT studies, H2 splitting is proposed to occur via a metal-ligand cooperative pathway involving deprotonation of the CH2 arm of the ligand, leading to pyridine dearomatization.
- Rahaman, S. M. Wahidur,Pandey, Dilip K.,Rivada-Wheelaghan, Orestes,Dubey, Abhishek,Fayzullin, Robert R.,Khusnutdinova, Julia R.
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p. 5912 - 5918
(2020/10/30)
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- Transition metal complexes of a bis(carbene) ligand featuring 1,2,4-triazolin-5-ylidene donors: structural diversity and catalytic applications
-
Dialkylation of the 1,3-bis(1,2,4-triazol-1-yl)benzene with ethyl bromide results in the formation of [L-H2]Br2which, upon salt metathesis with NH4PF6, readily yields the bis(triazolium) salt [L-H2](PF6)2with non-coordinating counterions. [L-H2](PF6)2and Ag2O react in a 1?:?1 ratio to yield a binuclear AgI-tetracarbene complex of the composition [(L)2Ag2](PF6)2which undergoes a facile transmetalation reaction with [Cu(SMe2)Br] to deliver the corresponding CuI-NHC complex [(L)2Cu2](PF6)2. In contrast, the [L-H2]Br2reacts with [Ir(Cp*)Cl2]2to generate a doubly C-H activated IrIII-NHC complex5. Similarly, the triazolinylidene donor supported diorthometalated RuII-complex6is also obtained. Complexes5and6represent the first examples of a stable diorthometalated binuclear IrIII/RuII-complex supported by 1,2,4-triazolin-5-ylidene donors. The synthesized IrIII-NHC complex5is found to be more effective than its RuII-analogue (6) for the reduction of a range of alkenes/alkynesviathe transfer hydrogenation strategy. Conversely, RuII-complex6is identified as an efficient catalyst (0.01 mol% loading) for the β-alkylation of a wide range of secondary alcohols using primary alcohols as alkylating partnersviaa borrowing hydrogen strategy.
- Donthireddy, S. N. R.,Illam, Praseetha Mathoor,Rit, Arnab,Singh, Vivek Kumar
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p. 11958 - 11970
(2020/09/21)
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- COBALT COMPLEXES, PROCESS FOR PREPARATION AND USE THEREOF
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The present invention discloses a cobalt compound of formula (I), a process for the preparation and use thereof. The present invention further relates to a pharmaceutical composition and a method inhibition of Tau Aggregation in a subject in need thereof using compound of formula (I).
- -
-
Page/Page column 17; 18
(2019/01/06)
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- Microwave assisted hydrogenation of olefins by Pd NPs@polystyrene resin using a gas addition kit: A robust and sustainable protocol
-
Polystyrene (PS) resin bead supported palladium nanoparticles (Pd NPs@PS resin) were prepared and their catalytic activity for the hydrogenation of olefins was investigated under microwave heating. The hydrogenation of styrene was effectively carried out in EtOH/H2O, in the presence of 0.00035 mmol of the catalyst to afford the corresponding ethylbenzene in high yield within 20 min under microwave heating. The catalyst efficiency measured in terms of turn over number (TON) and turn over frequency (TOF) was found to be 2829 and 8573 (h-1), respectively. The encapsulated palladium nanoparticles were easily recovered by a simple filtration method and reused several times without significant loss in their catalytic activity. Further, the method showed a wide substrate scope under mild reaction conditions, making it a green versatile and highly sustainable protocol.
- Sharma, Anuj S.,Kaur, Harjinder
-
supporting information
p. 18935 - 18941
(2018/11/27)
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- Visible Light-Induced Oxidative Chlorination of Alkyl sp3 C-H Bonds with NaCl/Oxone at Room Temperature
-
A visible light-induced monochlorination of cyclohexane with sodium chloride (5:1) has been successfully accomplished to afford chlorocyclohexane in excellent yield by using Oxone as the oxidant in H2O/CF3CH2OH at room temperature. Other secondary and primary alkyl sp3 C-H bonds of cycloalkanes and functional branch/linear alkanes can also be chlorinated, respectively, under similar conditions. The selection of a suitable organic solvent is crucial in these efficient radical chlorinations of alkanes in two-phase solutions. It is studied further by the achievement of high chemoselectivity in the chlorination of the benzyl sp3 C-H bond or the aryl sp2 C-H bond of toluene.
- Zhao, Mengdi,Lu, Wenjun
-
supporting information
p. 4560 - 4563
(2017/09/11)
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- Enantioselective hydroformylation of 2- and 4-substituted styrenes with PtCl2[(R)-BINAP] + SnCl2‘in situ’ catalyst
-
Two sets of styrenes possessing various substituents either in ortho or para position were hydroformylated in the presence of ‘in situ’ catalyst formed from PtCl2[(R)-BINAP] and tin(II) chloride. The reversal of the absolute configuration of the preferred enantiomers was observed using both sets of substrates by the variation of the reaction temperature in the range of 40–100 °C. In case of the 4-substituted styrenes, the reversal temperature of the enantioselectivity shows correlation with the Hammett substituent constants, i.e., with the electron donor or electron acceptor properties of the para-substituents. This phenomenon was explained by the reversible formation of the Pt-branched alkyl intermediates, leading to the corresponding (R)- and (S)-enantiomers of 2-arylpropanals. Strong substituent effect on the regioselectivity was observed in the hydroformylation of 2-substituted styrenes: the presence of substituents characterised by larger steric parameter resulted in the highly favoured formation of the linear aldehyde. For instance, regioselectivities of 45%, 22% and 7% towards branched aldehyde were obtained with styrene, 2-fluoro- and 2-bromostyrene, respectively, at 80 °C reaction temperature. In addition to the characteristic change of regioselectivity, the reversal of absolute configuration as a function of reaction temperature was also observed.
- Pongrácz, Péter,Kollár, László
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p. 118 - 123
(2016/10/25)
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- Cu(II)/Cu(0)@UiO-66-NH2: Base metal@MOFs as heterogeneous catalysts for olefin oxidation and reduction
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Two copper-loaded MOF materials, namely Cu(ii)@Ui-O-66-NH2 (1) and Cu(0)@UiO-66-NH2 (2), are reported. They can, respectively, serve as highly efficient heterogeneous catalysts for olefin oxidation and hydrogenation under mild conditions. Complete styrene hydrogenation occurs in 15 min at ambient temperature with quantitative yield.
- Wang, Jian-Cheng,Hu, Yu-Hong,Chen, Gong-Jun,Dong, Yu-Bin
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p. 13116 - 13119
(2016/11/09)
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- Iron-catalyzed olefin hydrogenation at 1 bar H2 with a FeCl3-LiAlH4 catalyst
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The scope and mechanism of a practical protocol for the iron-catalyzed hydrogenation of alkenes and alkynes at 1 bar H2 pressure were studied. The catalyst is formed from cheap chemicals (5 mol% FeCl3-LiAlH4, THF). A homogeneous mechanism operates at early stages of the reaction while active nanoparticles form upon ageing of the catalyst solution. This journal is
- Gieshoff, Tim N.,Villa, Matteo,Welther, Alice,Plois, Markus,Chakraborty, Uttam,Wolf, Robert,Jacobi Von Wangelin, Axel
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supporting information
p. 1408 - 1413
(2015/03/18)
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- Regioselective hydroaminomethylation of vinylarenes by a sol-gel immobilized rhodium catalyst
-
In the course of our studies toward the development of new heterogeneous conditions for better controlling regioselectivity in organic reactions, we investigated the application of sol-gel immobilized organometallic catalyst for regioselective hydroaminomethylation of vinylarenes with aniline or nitroarene derivatives in an aqueous microemulsion. By immobilization of 6 mol % [Rh(cod)Cl]2 within a hydrophobic silica sol-gel matrix we were able to perform efficient hydroaminomethylation under mild conditions and isolate 2-arylpropylamines with high regioselectivity. The regioselectivity of the reaction was found to be mainly dependent on the hydrophobicity of the catalyst support. It is also significantly affected by the electronic nature of the substrates, by the reaction temperature, and by syngas pressure. The heterogenized catalyst can be reused for several times.
- Nairoukh, Zackaria,Blum, Jochanan
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p. 2397 - 2403
(2014/04/17)
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- Rhenium-mediated dehydrogenative silylation and highly regioselective hydrosilylation of nitrile substituted olefins
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The rhenium (I) complex [Re(CH3CN)3Br 2(NO)] catalyzes the homogeneous hydrosilylation of a variety of substituted acrylonitriles, which were converted into the corresponding silyl-substituted alkanes with high regioselectivity of up to 94%. The products were analyzed by 1H NMR and GC-MS. A rhenium specific mechanism is proposed for the hydrosilylation of olefins.
- Dong, Hailin,Jiang, Yanfeng,Berke, Heinz
-
-
- Ligand-metal cooperating PC(sp3)P pincer complexes as catalysts in olefin hydroformylation
-
Ligand-metal cooperation: A new ligand-metal cooperating catalyst for the hydroformylation of olefins is described (see scheme). The mechanism of the H2 activation and C-H bond formation of the catalyst involves an intramolecular cooperation between the structurally remote functionality and the metal center and proceeds without change of the oxidation state of the metal.
- Musa, Sanaa,Filippov, Oleg A.,Belkova, Natalia V.,Shubina, Elena S.,Silantyev, Gleb A.,Ackermann, Lutz,Gelman, Dmitri
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supporting information
p. 16906 - 16909
(2014/01/06)
-
- Efficient palladium-catalyzed C-O hydrogenolysis of benzylic alcohols and aromatic ketones with polymethylhydrosiloxane
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A simple method has been developed for the reductive deoxygenation of aromatic ketones and benzylic alcohols in the presence of polymethylhydrosiloxane (PMHS). The reductive deoxygenation of aromatic ketones and benzylic alcohols, including secondary alcohols, to the corresponding methylene hydrocarbons has been achieved in good to excellent yields using palladium chloride (PdCl2) as catalyst and PMHS as hydride source. Such deoxygenations were successfully with aryl alkyl ketones and diaryl ketones, as exemplified by the reductive deoxygenation of acetophenone and benzopheneone, respectively. The corresponding benzylic alcohols and secondary alcohol analogues could also be converted into their respective methylene hydrocarbons by the PdCl2/PMHS system.
- Wang, Hu,Li, Li,Bai, Xing-Feng,Shang, Jun-Yan,Yang, Ke-Fang,Xu, Li-Wen
-
supporting information
p. 341 - 347
(2013/05/08)
-
- Highly efficient iron(0) nanoparticle-catalyzed hydrogenation in water in flow
-
Highly efficient catalytic hydrogenations are achieved by using amphiphilic polymer-stabilized Fe(0) nanoparticle (Fe NP) catalysts in ethanol or water in a flow reactor. Alkenes, alkynes, aromatic imines and aldehydes were hydrogenated nearly quantitatively in most cases. Aliphatic amines and aldehydes, ketone, ester, arene, nitro, and aryl halide functionalities are not affected, which provides an interesting chemoselectivity. The Fe NPs used in this system are stabilized and protected by an amphiphilic polymer resin, providing a unique system that combines long-term stability and high activity. The NPs were characterized by TEM of microtomed resin, which established that iron remains in the zero-valent form despite exposure to water and oxygen. The amphiphilic resin-supported Fe(0) nanoparticles in water and in flow provide a novel, robust, cheap and environmentally benign catalyst system for chemoselective hydrogenations.
- Hudson, Reuben,Hamasaka, Go,Osako, Takao,Yamada, Yoichi M. A.,Li, Chao-Jun,Uozumi, Yasuhiro,Moores, Audrey
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p. 2141 - 2148
(2013/09/24)
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- Iron-catalysed alkene hydrogenation and reductive cross-coupling using a bench-stable iron(II) pre-catalyst
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Operationally simple, iron-catalysed hydrogenation and reductive cross-coupling protocols have been developed using a bench-stable iron(ii) pre-catalyst. The hydrogenation of 18 alkenes (50-99%) and reductive cross-coupling of vinyl halides with aryl- and alkyl Grignard reagents (8 examples, 18-99%) is reported using 3 mol% pre-catalyst and hydrogen as stoichiometric reductant (1-50 bar).
- Frank, Dominik J.,Guiet, Lea,Kaeslin, Alexander,Murphy, Elliot,Thomas, Stephen P.
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p. 25698 - 25701
(2013/12/04)
-
- Metal and H2O2 free aerobic oxidative aromatic halogenation with [RNH3+] [NO3-]/HX and [BMIM(SO3H)][NO3)x(X)y] (X = Br, Cl) as multifunctional ionic liquids
-
Novel multifunctional ionic liquids (ILs) are generated by addition of HBr or HCl to alkylammonium nitrates ([RNH3+] [NO 3-]) and to 3-methyl-1-(butyl-4-sulfonyl)imidazolium nitrate ([BMIM(SO3H)][NO3]). The resulting [RNH 3+] [NO3-]/HX and mono (3-methyl-1-(butyl-4-sulfonyl)imidazolium) monohalogenide mononitrate ([BMIM(SO3H)][NO3)x(X)y] (X = Br, Cl)) systems act as solvent and promoter for aerobic oxidative halogenation of arenes under mild conditions in high yields that can be repeated over several cycles.
- Prebil, Rok,Laali, Kenneth K.,Stavber, Stojan
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supporting information
p. 2108 - 2111
(2013/06/05)
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- Aromatic substitution in ball mills: Formation of aryl chlorides and bromides using potassium peroxomonosulfate and NaX
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Aryl chlorides and bromides are formed from arenes in a ball mill using KHSO5 and NaX (X = Cl, Br) as oxidant and halogen source, respectively. Investigation of the reaction parameters identified operating frequency, milling time, and the number of milling balls as the main influencing variables, as these determine the amount of energy provided to the reaction system. Assessment of liquid-assisted grinding conditions revealed, that the addition of solvents has no advantageous effect in this special case. Preferably activated arenes are halogenated, whereby bromination afforded higher product yields than chlorination. Most often reactions are regio- and chemoselective, since p-substitution was preferred and concurring side-chain oxidation of alkylated arenes by KHSO5 was not observed. The Royal Society of Chemistry.
- Schmidt, Robert,Stolle, Achim,Ondruschka, Bernd
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p. 1673 - 1679
(2013/02/22)
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- A mild and efficient rhenium-catalyzed transfer hydrogenation of terminal olefins using alcoholysis of amine-borane adducts as a reducing system
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[ReBr2(NO)(CH3CN)(PTA)2] (PTA = 1, 3, 5-triaza-7-phosphaadamantane) catalyzes the alcoholysis of ammonia-borane and amine-boranes and the catalytic transfer hydrogenations of various terminal olefins. Excellent yields were achieved at 70 °C in isopropanol using tBuOK as a co-catalyst affording TOF values up to 396 h-1.
- Dong, Hailin,Berke, Heinz
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experimental part
p. 1803 - 1808
(2011/06/19)
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- Chlorination of aromatics with trichloroisocyanuric acid (TCICA) in bronsted-acidic imidazolium ionic liquid [BMIM(SO3H)][OTf]: An economical, green protocol for the synthesis of chloroarenes
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A survey study on electrophilic chlorination of aromatics with trichloroisocyanuric acid (TCICA) in Bronsted-acidic imidazolium ionic liquid [BMIM(SO3H)][OTf] is reported. The reactions are performed under very mild conditions (at ~50°C) and give good to excellent yields, depending on the substrates. Chemoselectivity for mono- v. dichlorination can be tuned by changing the arene-to-TCICA ratio and the reaction time. The survey study and competitive experiments suggest that triprotonated/protosolvated TCICA is a selective/moderately reactive transfer-chlorination electrophile. Density functional theory was used as guide to obtain further insight into the nature of the chlorination electrophile and the transfer-chlorination step. CSIRO 2007.
- Hubbard, Abigail,Okazaki, Takao,Laali, Kenneth K.
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p. 923 - 927
(2008/03/17)
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- Aromatic chlorination of ω-phenylalkylamines and ω- phenylalkylamides in carbon tetrachloride and α,α,α- trifluorotoluene
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The aromatic halogenation of simple alkylbenzenes with chlorine proceeds smoothly in acetic acid but is much less efficient in less polar solvents. By contrast chlorination of ω-phenylalkylamines, such as 3-phenylpropylamine, occurs readily in either acetic acid, carbon tetrachloride or α,α,α-trifluorotoluene, and in the latter solvents gives high proportions of ortho-chlorinated products. These effects are attributable to the involvement of N-chloroamines as reaction intermediates, with intramolecular delivery of the chlorine electrophile. ω-Phenylalkylamides, such as 3-phenylpropionamide, also easily undergo aromatic chlorination in carbon tetrachloride and α,α,α-trifluorotoluene. These reactions generally show a first-order dependence on the substrate concentration, but not on the amount of chlorine. With carbon tetrachloride, very similar reaction rates are observed with chlorine concentrations ranging from 0.1-1.5 M. In α,α,α-trifluorotoluene, the rates reach a plateau at a chlorine concentration of approximately 0.2 M. These features indicate that the reactions proceed via the formation of intermediates which evidence suggests may be the corresponding O-chloroimidates. Irrespective of the mechanistic details, the reactions are remarkably rapid, being faster than analogous reactions in acetic acid and three to four orders of magnitude more rapid than reactions of simple alkylbenzenes in carbon tetrachloride. Therefore, chlorination of the amines and amides may be accomplished without the need for highly polar solvents, added catalysts or large excesses of chlorine, which are often employed for electrophilic aromatic substitutions. Although the use of carbon tetrachloride is becoming increasingly impractical due to environmental concerns, the trifluorotoluene is a suitable alternative. The Royal Society of Chemistry 2006.
- O'Connell, Jenny L.,Simpson, Jamie S.,Dumanski, Paul G.,Simpson, Gregory W.,Easton, Christopher J.
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p. 2716 - 2723
(2008/02/08)
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- Halogenation of Aromatic Compounds by N-chloro-, N-bromo-, and N-iodosuccinimide
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An efficient and mild method for the halogenation of aromatic compounds using N-chloro-, N-bromo-, and N-iodosuccinimide in the presence of NH 4NO3 or FeCl3 in acetonitrile was developed.
- Tanemura, Kiyoshi,Suzuki, Tsuneo,Nishida, Yoko,Satsumabayashi, Koko,Horaguchi, Takaaki
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p. 932 - 933
(2007/10/03)
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- Electrophilic aromatic chlorination and haloperoxidation of chloride catalyzed by polyfluorinated alcohols: A new manifestation of template catalysis
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We have demonstrated that a polyfluorinated alcohol, 2,2,2-trifluoroethanol, solvent enables haloperoxidase type activity and the oxychlorination of arenes (benzene and its alkylated derivatives) without a metal catalyst. The polyfluorinated alcohol has a dual function; it catalyzes electrophilic chlorination of less reactive arenes by several orders of magnitude and oxidation of chloride at lower H+ concentrations. DFT calculations show that a complementary charge template in the transition state explains the catalysis of the electrophilic chlorination. Copyright
- Ben-Daniel, Revital,De Visser, Samuel P.,Shaik, Sason,Neumann, Ronny
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p. 12116 - 12117
(2007/10/03)
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- Highly efficient, para-selective oxychlorination of aromatic compounds using potassium chloride and Oxone
-
A highly efficient, regioselective method for oxychlorination of aromatic compounds is possible through electrophilic substitution of chlorine generated in situ from KCl as a chlorine source and Oxone as an oxidant for the first time.
- Narender,Srinivasu,Kulkarni,Raghavan
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p. 279 - 286
(2007/10/03)
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- Reaction of Aromatic and Unsaturated Compounds with the Potassium Permanganate/HCI (HBr) Acetonitrile Reagent
-
Addition of hydrochloric or hydrobromic acid to a solution of potassium permanganate in acetonitrile produced a homogeneous mixture, which is suitable for laboratory chlorination or bromination, respectively. Aromatic compounds more reactive than alkylbenzenes can be chlorinated or brominated without additional catalyst. Alkenes and alkynes give the corresponding vicinal dihaloalkanes and vinyl halides. All reactions complete within two hours under mild condition (25-60 °C) with excellent to moderate yields.
- Liu, Lilian Kao,Lin, Ching-Shan
-
-
- Direct Formation of (Haloaryl)copper Nucleophiles from Haloiodobenzenes and Active Copper
-
(o-Halophenyl)-, (m-halophenyl)-, and (p-halophenyl)copper reagents have been formed in moderate to high yields at room temperature from active copper and the corresponding haloiodobenzenes.These reagents have been cross-coupled with a variety of alkyl and acyl halides to produce the respective haloarenes and haloaryl ketones.Remarkably, (o-fluorophenyl)- and (o-chlorophenyl)copper are produced in good yields by this procedure without undergoing elimination to form benzyne making this approach a convenient method for generating o-halophenyl nucleophiles.
- Ebert, Greg W.,Pfennig, Deborah R.,Suchan, Scott D.,Donovan, Thomas A.,Aouad, Emmanuel,et al.
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p. 2361 - 2364
(2007/10/02)
-
- Facile Hydrodehalogenation with H2 and Pd/C Catalyst under Multiphase Conditions. 2. Selectivity and Kinetics
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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.
- Marques, Carlos Alberto,Selva, Maurizio,Tundo, Pietro
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p. 3830 - 3837
(2007/10/02)
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- Remarkably stable ortho-halophenylcopper reagents
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We wish to report the generation of remarkably stable o-halophenlycopper reagents at room temperature by the direct oxidative addition of activated copper to o-flouro-and o-choloriodobenzene. The reagents will undergo substitution reactions with suitable organic halides at 25°C.
- Ebert, Greg W.,Pfennig, Deborah R.,Suchan, Scott D.,Donovan Jr., Thomas A.
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p. 2279 - 2282
(2007/10/02)
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- Effect of an ortho-Substituent on the Decomposition of Crown Ether Complexed Arenediazonium Ions in 1,2-Dichloroethane
-
The effect of an o-substituent (CH3, C2H5 and COCH3) on the complexation and the kinetics of thermal decomposition of arenediazonium tetrafluoroborates in the presence of crown ethers (15-crown-5, 18-crown-6 and 21-crown-7) and the effect of temperature on the decomposition of the complexed ions were studied by UV spectrophotometry in 1,2-dichloroethane.Solid 1:1 complexes were prepared and analyzed (by IR spectroscopy and by decomposition temperature).In the solid state, none of the arenediazonium ions is stabilized by complexation with crown ethers.In solution they form at most very weak charge-transfer complexes with 15-crown-5 but stronger insertion-type complexes with the larger 18-crown-6 and 21-crown-7 molecules (except for the o-acetyl-substituted ion, which is destabilized with increasing and ).The values of the complexation equilibrium constant K and the stabilization ability of the complexation are largest for 21-crown-7, and are much smaller than the corresponding values for the complexation of p- or m-substituted arenediazonium ions with the same complexing agents: e.i. there are clear ortho-effects due to the steric hindrance for the complexation.The values of the activation parameters ΔH and ΔS for the thermal decomposition of the complexed ions are large and positive (largest for 21-crown-7) and suggest an isokinetic relationship for each ion.The complexation in solution causes a hypsochromic shift in the UV spectrum of the arenediazonium ion which is proportional to the strength of the complexation.
- Kuokkanen, Toivo,Slotte, Thomas,Virtanen, Vesa
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p. 674 - 680
(2007/10/02)
-
- Selective Mono-Alkylation and Arylation of Dichlorobenzenes by Palladium-Catalyzed Grignard Cross-Coupling
-
Palladium(II)-phosphine complexes, especially PdCl2(dppf) where dppf stands for 1,1'-Bis(diphenylphosphino)ferrocene, are effective catalysts for the cross-coupling of Grignard reagents with dichlorobenzenes to produce selectively mono-alkylated and arylated benzenes.The addition of ligands is also effective for the cross-coupling of Grignard reagents containing a β-hydrogen(s).
- Katayama, Tatsuo,Umeno, Masayuki
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p. 2073 - 2076
(2007/10/02)
-
- Versatility of Zeolites as Catalysts for Ring or Side-Chain Aromatic Chlorinations by Sulfuryl Chloride
-
Zeolites catalyze chlorination of aromatics by sulfuryl chloride SO2Cl2.It is possible by an appropriate choice of the catalyst to effect at will, with very high selectivity, either the ring or the side-chain chlorination.Zeolite ZF520 is the choice catalyst for the former, because of its high Broensted acidity.Zeolite NaX (13X) is a fine catalyst for the latter, free-radical chlorination; the reaction is best effected in the presence of a light source; the catalyst can be reused many times with no loss in activity.Both reaction modes, the ionic (ring chlorination)and the radical (side-chain substitution), are likely to occur outside of the channel network in the microporous solid.The effects of various experimental factors - such as the nature of the solvent, the reaction time and temperature, the Broensted acidity of the solid support, the presence of radical inhibitors, and the quantity of catalysts - were investigated.The procedures resulting from this study are very easy to implement in practice and are quite effective.
- Delaude, Lionel,Laszlo, Pierre
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p. 5260 - 5269
(2007/10/02)
-
- Selective Aromatic Chlorination and Bromination with N-Halogeno Amines in Acidic Solution
-
1,2-Dimethoxybenzene and 3,4-dimethoxytoluene are efficiently chlorinated by N-chlorodialkylamines in sulphuric acid.The reaction has a very marked selectivity for monochlorination of the para-position.The chlorination and bromination of monoalkylbenzenes (toluene, ethyl-, and isopropyl-benzenes) under the same conditions is much less selective, but the para/ortho ratio can be reversed going from unsubstituted alkyl groups in the N-halogeno amines to alkyl groups substituted at the β-position by electron-withdrawing groups . m-Xylene is chlorinated with high selectivity at the 4-position.The nature of the chlorinating species is discussed.
- Minisci, Francesco,Vismara, Eelena,Fontana, Francesca,Platone, Eduardo,Faraci, Giovanni
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p. 123 - 126
(2007/10/02)
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- New Reagent Systems for Electrophilic Chlorination of Aromatic Compounds: Organic Chlorine-Containing Compounds in the Presence of Silica
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In the presence of silica, a number of chlorine-containing organic compounds, such as N,N-dichlorourethane, dichloramine-T, and t-butyl hypochlorite, become active electrophilic reagents capable of controlled monochlorination of aromatic compounds under mild conditions; for example, t-butyl hypochlorite/silica chlorinates alkylbenzenes, naphthalene, and anisole readily at 25 deg C; N,N-dichlorourethane/silica chlorinates benzene within 2 days 50 deg C.
- Smith, Keith,Butters, Michael,Paget, Walter E.,Nay, Barry
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p. 1155 - 1156
(2007/10/02)
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- Highly para-Selective Mono-Chlorination of Aromatic Compounds Under Mild Conditions by t-Butyl Hypochlorite in the Presence of Zeolites
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t-Butyl hypochlorite supported on H(1+), Na(1+) faujasite X (zeolite X) produces para-selective monochlorination of alkyl-, phenyl-, and halobenzenes under mild conditions; for example, chlorobenzene in acetonitrile (at 40 deg C) is chlorinated in high yield of isolated product (92percent) to give dichlorobenzene with an isomer ratio 97percent para/3percent ortho.
- Smith, Keith,Butters, Michael,Nay, Barry
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p. 1157 - 1158
(2007/10/02)
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- Alkylation of Arenes with Ethylene over H-ZSM-5 and Modernite-H Catalysis
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Attempts were made to alkylate acetophenone, benzene, benzonitrile, bromobenzene, chlorobenzene, ethylbenzene, fluorobenzene, iodobenzene, methoxybenzene, nitrobenzene, toluene and α,α,α-trifluorotoluene with ethylene over H-ZSM-5 and mordenite-H catalysts at 400 and 250 deg C, respectively.Over H-ZSM-5 benzene, bromobenzene, chlorobenzene, ethylbenzene and toluene gave monoethylarenes as the major product (95-100percent) with the para product as the dominant isomer (87-95percent).Over mordenite-H benzene, bromobenzene, chlorobenzene and toluene reacted.The monoethylarenes were again the major product (85-95percent) but the isomer distributions were close to the thermodynamically controlled ones due to isomerization of the initially formed products.Over H-ZSM-5 the results indicated the reaction to be of a Friedel-Crafts type.It was proposed that the product composition was determined by the chemical reaction, not by the rate of diffusion of the products.
- Akervold, Idar,Bakke, Jan M.,Steinsvik, Eirik
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p. 437 - 444
(2007/10/02)
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- REGIOSELECTIVE PARA-CHLORINATION OF ALKYLBENZENES ON CHEMICALLY-MODIFIED SILICA SURFACES
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Chlorination of alkylbenzenes was carried out with chlorine in carbon tetrachloride in the presence of chemically-modified silica catalysts.The para/ortho ratios were remarkably higher than those obtained in the FeCl3-catalyzed chlorination. t-Butylbenzene was chlorinated at para-position almost exclusively.The catalyst could be reused several times.
- Konishi, Hisatoshi,Yokota, Kiyoshi,Ichihashi, Yuji,Okano, Tamon,Kiji, Jitsuo
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p. 1423 - 1426
(2007/10/02)
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