- Metal Nanoparticles Catalyzed Selective Carbon-Carbon Bond Activation in the Liquid Phase
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Understanding the C-C bond activation mechanism is essential for developing the selective production of hydrocarbons in the petroleum industry and for selective polymer decomposition. In this work, ring-opening reactions of cyclopropane derivatives under hydrogen catalyzed by metal nanoparticles (NPs) in the liquid phase were studied. 40-atom rhodium (Rh) NPs, encapsulated by dendrimer molecules and supported in mesoporous silica, catalyzed the ring opening of cyclopropylbenzene at room temperature under hydrogen in benzene, and the turnover frequency (TOF) was higher than other metals or the Rh homogeneous catalyst counterparts. Comparison of reactants with various substitution groups showed that electron donation on the three-membered ring boosted the TOF of ring opening. The linear products formed with 100% selectivity for ring opening of all reactants catalyzed by the Rh NP. Surface Rh(0) acted as the active site in the NP. The capping agent played an important role in the ring-opening reaction kinetics. Larger particle size tended to show higher TOF and smaller reaction activation energy for Rh NPs encapsulated in either dendrimer or poly(vinylpyrrolidone). The generation/size of dendrimer and surface group also affected the reaction rate and activation energy.
- Ye, Rong,Yuan, Bing,Zhao, Jie,Ralston, Walter T.,Wu, Chung-Yeh,Unel Barin, Ebru,Toste, F. Dean,Somorjai, Gabor A.
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- Ipso-nitration of arylboronic acids with copper nitrate and trifluoroace-tic acid
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An efficient and novel nitrating reagent has been developed for ipso-nitration of arylboronic acids. By using inexpensive and commercially available Cu(NO3)2/CF3COOH as nitrating reagent, various nitroarenes are produced in moderate to excellent yields (51-96%). Advantages of this procedure are the operational simplicity and no need of extra catalyst.
- Wang, Zhu-Qing,Guo, Meng-Ping,Wen, Yong-Ju,Shen, Xiu-Li,Lv, Mei-Yun,Zhou, Xiu-Ling
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p. 891 - 894
(2018/11/06)
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- Poly(4-vinylpyridine)-nitrating mixture complex (PVP-NM): Solid nitrating mixture equivalent for safe and efficient aromatic nitration
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Friedel-Crafts type aromatic nitration has served as an indispensable reaction within both industrial and academic applications. However, growing concern over the use of copious amounts of strong acids has prompted the search for more environmentally friendly alternatives. Polymer-bound Bronsted acids, on the other hand, have been shown useful as convenient alternatives to liquid acids. Nitric acid and sulfuric acids have, therefore, been combined, both individually and as a mixture, with poly(4-vinylpyridine). The new solid acid systems have been used to nitrate both activated and deactivated arenes under mild conditions and proved to be effective nitrating agent.
- Surya Prakash,Gurung, Laxman,Glinton, Kevin E.,Belligund, Kavita,Mathew, Thomas,Olah, George A.
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supporting information
p. 3446 - 3451
(2015/06/25)
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- Regioselective dinitration of simple aromatics over zeolite Hβ/nitric acid/acid anhydride systems
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Various nitration systems comprising nitric acid, acid anhydride and zeolite H£] in the absence of solvent are described. Direct double nitration of toluene with a nitric acid, propanoic anhydride and zeolite Hβ system has been developed to give 2,4-dinitrotoluene in 98% yield, with a 2,4-:2,6-dinitrotoluene ratio of 123:1. This system also nitrates activated mono-substituted benzenes (anisole and phenetole) and moderately activated mono-substituted benzenes (ethylbenzene and propylbenzene) to give mainly 2,4-dinitro derivatives. The zeolite can be recovered, regenerated and reused to give almost the same yield as that given when fresh zeolite is used. ARKAT-USA, Inc.
- Smith, Keith,Alotaibi, Mohammad Hayal,El-Hiti, Gamal A.
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p. 107 - 123
(2014/04/17)
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- Highly regioselective dinitration of toluene over reusable zeolite Hβ
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A nitration system comprising nitric acid, propanoic anhydride, and zeolite Hβ has been developed for dinitration of toluene to give 2,4-dinitrotoluene in 98% yield, with a 2,4-:2,6-dinitrotoluene ratio of over 120. This represents the most selective quantitative method for 2,4-dinitration of toluene; the catalyst is reusable, solvent is not needed, and an aqueous work-up is not required.
- Smith, Keith,Alotaibi, Mohammad Hayal,El-Hiti, Gamal A.
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p. 244 - 247
(2013/02/22)
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- Design and synthesis of boronic acid inhibitors of endothelial lipase
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Endothelial lipase (EL) and lipoprotein lipase (LPL) are homologous lipases that act on plasma lipoproteins. EL is predominantly a phospholipase and appears to be a key regulator of plasma HDL-C. LPL is mainly a triglyceride lipase regulating (V)LDL levels. The existing biological data indicate that inhibitors selective for EL over LPL should have anti-atherogenic activity, mainly through increasing plasma HDL-C levels. We report here the synthesis of alkyl, aryl, or acyl-substituted phenylboronic acids that inhibit EL. Many of the inhibitors evaluated proved to be nearly equally potent against both EL and LPL, but several exhibited moderate to good selectivity for EL.
- O'Connell, Daniel P.,Leblanc, Daniel F.,Cromley, Debra,Billheimer, Jeffrey,Rader, Daniel J.,Bachovchin, William W.
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scheme or table
p. 1397 - 1401
(2012/03/26)
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- Clay supported ammonium nitrate "clayan": A new reagent for selective nitration of arenes
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The nitration of activated, deactivated and highly functionalized arenes is described using clay-supported ammonium nitrate in the presence of perchloric acid.
- Meshram,Ganesh,Madhavi,Eshwaraiah,Yadav,Gunasekar
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p. 2497 - 2503
(2007/10/03)
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- Nitration of Alkylbenzenes in Trifluoroacetic Acid
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The substrate selectivity of alkylbenzene nitration with nitric acid in trifluoroacetic acid is controlled either by electronic or by steric effects of the substituents, depending the medium composition and temperature. The positional selectivity of this reaction is sterically controlled, even under electronic control of substrate selectivity.
- Krylov,Gvozdareva
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p. 1618 - 1623
(2007/10/03)
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- PARA-SELECTIVE MONONITRATION OF ALKYLBENZENES UNDER MILD CONDITIONS BY USE OF BENZOYL NITRATE IN THE PRESENCE OF A ZEOLITE CATALYST
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Toluene and other alkylbenzenes are mononitrated in essentially quantitative yield at ambient temperature by benzoyl nitrate in the presence of aluminium/proton exchanged large port mordenite; the reaction is highly para-selective.
- Smith, Keith,Fry, Karl,Butters, Michael,Nay, Barry
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p. 5333 - 5336
(2007/10/02)
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- REGIOSELECTIVE NITRATION OF AROMATIC HYDROCARBONS BY METALLIC NITRATES ON THE K10 MONTMORILLONITE UNDER MENKE CONDITIONS
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Aromatic hydrocarbons are nitrated with good regioselectivities by clay-supported cupric nitrate in the presence of acetic anhydride.The procedure commends itself by its simplicity and gives useful yields (75-98percent).In each case, the predominant product can be predicted by consideration of the Hueckel HOMO for the aromatic ring.
- Laszlo, Pierre,Vandormael, Joseph
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p. 1843 - 1846
(2007/10/02)
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- Electrophilic Aromatic Nitration in the Gas Phase
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Aromatic nitration by MeO+(H)NO2, in essence nitronium ion solvated by one methanol molecule, has been studied in the gas phase by using an integrated approach, based on the coordinate application of ICR, Cl, and CID mass spetrometric methods with a highly complementary radiolytic technique.The latter can be used in gases at atmospheric pressure and allows direct evaluation of key mechanistic features, in particular of substrate and positional selectivity.The results resolve early discrepancies between gas-phase and liquid-phase studies, characterizing the reaction as a typical, well-behaved electrophilic substitution of moderate selectivity.The date from the gas-phase nitration of ten monosubstituted benzenes fit a Hammett's type linear plot, characterized by a ρ value of -3.87.The correlation does not extend to highly activated substrates, such as anisole and mesitylene, since the nitration rate tends to a limiting value that cannot be increased by further enhancing the activation of the substrate, exactly as in "encounter-rate" nitrations occurring in solution.The mechanism and the energetics of the gas-phase nitration have been investigated, and the relative stability of the charged intermediates involved, in particular of the isomeric protonated nitrobenzenes, has been estimated by theoretical approaches at two different levels, using STO-3G minimal basis and 4-31G split-valence basis sets.
- Attina, Marina,Cacace, Fulvio,Yanez, Manuel
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p. 5092 - 5097
(2007/10/02)
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- Relative Conjugative Abilities of Three-Membered Ring Heterocycles with Benzene Based on 13C and 15N NMR
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The conjugative ability of various three-membered rings with benzene was investigated by observing the sensitivity of β-carbon 13C chemical shifts to para substituents.These Hammett ρ values were 2.0, 1.5, 1.0, and 0.9 ppm for arylcyclopropanes, N-methyl-2-arylaziridines, phenyloxiranes, and N,N-dimethyl-2-arylaziridinium fluorosulfonates, respectively.These values were intermediate to ones for para-substituted styrenes (6.5 ppm) and ethylbenzenes (-0.9 ppm), model compounds which were taken to represent extremes of conjugative ability.Similar results were found for 15N chemical shifts of trans-3-aryl-oxaziridines, which had a slope of 2.1 ppm, intermediate to those for benzylimines (20.2 ppm) and benzylamines (-1.3 ppm).The order of conjugative ability, which decreases with increasing electronegativity of the hetero group, could not be explained by hybridization changes based on comparing open chain analoques with the above compounds or by conformational factors.The trend can, however, be interpreted qualitatively by perturbation theory which shows that more electronegative hetero groups decrease the extent of interaction between aryl-? and cyclopropane orbitals as well as cross ring conjugation.
- Crist, DeLanson R.,Jordan, Guy J.,Moore, Donald W.,Hashmall, Joseph A.,Borsetti, Arnold P.,Turujman, Saleh A.
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p. 4136 - 4142
(2007/10/02)
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- Arylhydroxamic acid N,O-acyltransferase substrates. Acetyl transfer and electrophile generating activity of N-hydroxy-N-(4-alkenyl-, and 4-cyclohexylphenyl)acetamides
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Arylhydroxamic acid N,O-acyltransferase (AHAT) is an enzyme system that is capable of converting many N-arylhydroxamic acids into reactive electrophilic species. As part of an investigation into the influence of the structure of the aryl group upon the ability of N-arylhydroxamic acids to serve as substrates for AHAT, a series of N-hydroxy-N-(4-alkyl-, 4-alkenyl-, and 4-cyclohexylphenyl) acetamides was prepared and evaluated in vitro with partially purified rat and hamster hepatic AHAT. The nature of the 4-substituent markedly influenced the ability of the hydroxamic acids to serve as acetyl donors in the AHAT-catalyzed transacetylation of 4-aminoazobenzene (AAB). As the length of the 4-substituent was increased from methyl to pentyl, the compounds became increasingly more effective substrates. The compounds containing vinyl, propenyl, and 2-methylpropenyl 4-substituents were more effective acetyl donors than the corresponding compounds containing saturated 4-substituents. The three most effective AHAT substrates in the AAB transacetylation assay were N-hydroxy-N-(4-pentylphenyl)- (7), N-hydroxy-N-(4-propenylphenyl)- (10), and N-hydroxy-N-[4-(2-methylpropenyl)phenyl]acetamide (11), each of which was approximately as active as the standard compound, N-hydroxy-4-acetamidobiphenyl (1), with rat hepatic AHAT and approximately 60% as active as 1 with hamster hepatic AHAT. Both 1 and N-hydroxyl-N-(4-cyclohexylphenyl)acetamide (8) were activated by hamster hepatic AHAT to yield electrophilic intermediates that formed adducts with 2-mercaptoethanol. The 2-mercaptoethanol adducts were characterized by mass spectrometry and were identified as 4-phenyl-2-[(2-hydroxyethyl)thio]aniline (22) and 4-cyclohexyl-2-[(2-hydroxyethyl)thio]aniline (21). The structure of compounds 21 and 22 were confirmed by an unambiguous chemical synthesis. Both compounds 1 and 8 irreversibly inactivated hamster hepatic AHAT by a time-dependent process. The results of the inactivation experiments confirmed that 1 inactivates AHAT primarily via a suicide substrate mechanism and revealed that 8 inactivates the enzyme by a process consisting primarily of a pathway in which electrophiles are released into the medium and subsequently react with nucleophiles present on AHAT.
- Mangold,Hanna
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p. 630 - 638
(2007/10/02)
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- Aromatic Substitution. 471. Acid-Catalyzed Transfer Nitration of Aromatics with N-Nitropyrazole, a Convenient New Nitrating Agent
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N-Nitropyrazole in the presence of Lewis or Bronsted acid catalysts was found to be an effective transfer nitrating agent for aromatic substrates.The nature of the acid catalyst both substrate and positional selectivies of the nitration of alkylbenzenes.No relationship was found between substrate and positional selectivities, which are considered to be determined in two separate steps.
- Olah, George A.,Narang, Subhash C.,Fung, Alexander P.
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p. 2706 - 2709
(2007/10/02)
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- Aromatic Substitution. 48. Boron Trifluoride Catalyzed Nitration of Aromatics with Silver Nitrate in Acetonitrile Solution
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Benzene, alkylbenzenes, halobenzenes, and anisole were nitrated with silver nitrate/boron trifluoride in acetonitrile solution.Correlation of competitive rates with ?- and ?-complex stabilities indicated that the transition state of highest energy lies relatively early on the reaction coordinate.Data indicate that nitrations occur via a polarized complex of the nitrating agent, with the catalyst undergoing nucleophilic displacement by the aromatic substrate.
- Olah, George A.,Fung, Alexander P.,Narang, Subhash C.,Olah, Judith A.
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p. 3533 - 3537
(2007/10/02)
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