- The Inhibiting Effects of Tetraalkylammonium Cations on Simple Heterogeneous Electron Transfer Reactions in Polar Aprotic Solvents
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Kinetic data for the electroreduction of nitromesitylene at mercury in propylene carbonate have been determined in the presence of tetraalkylammonium salts of varying chain length, both as a function of electrode potential and temperature.Although the standard rate constant decreases with increase in cation size, the experimental activation enthalpy is independent of the cation for variation in this ion from tetraethylammonium to tetraoctylammonium.These results indicate that the tetraalkylammonium ions are adsorbed on the electrode forming a blocking layer whose thickness increases with alkyl chain length.Electron transfer to the redox center takes place by tunneling through this film.Theoretical estimates of the activation enthalpy support this conclusion and suggest that the redox reaction occurs in a region where solvent reorganization determines the largest portion of its magnitude.
- Fawcett, W. Ronald,Fedurco, Milan,Opallo, Marcin
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Read Online
- Determination of the [15N]-nitrate/[14N]-nitrate ratio in plant feeding studies by GC–MS
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Feeding experiments with stable isotopes are helpful tools for investigation of metabolic fluxes and biochemical pathways. For assessing nitrogen metabolism, the heavier nitrogen isotope, [15N], has been frequently used. In plants, it is usually applied in form of [15N]-nitrate, which is assimilated mainly in leaves. Thus, methods for quantification of the [15N]-nitrate/[14N]-nitrate ratio in leaves are useful for the planning and evaluation of feeding and pulse–chase experiments. Here we describe a simple and sensitive method for determining the [15N]-nitrate to [14N]-nitrate ratio in leaves. Leaf discs (8 mm diameter, approximately 10 mg fresh weight) were sufficient for analysis, allowing a single leaf to be sampled multiple times. Nitrate was extracted with hot water and derivatized with mesitylene in the presence of sulfuric acid to nitromesitylene. The derivatization product was analyzed by gas chromatography–mass spectrometry with electron ionization. Separation of the derivatized samples required only 6 min. The method shows excellent repeatability with intraday and interday standard deviations of less than 0.9 mol%. Using the method, we show that [15N]-nitrate declines in leaves of hydroponically grown Crassocephalum crepidioides, an African orphan crop, with a biological half-life of 4.5 days after transfer to medium containing [14N]-nitrate as the sole nitrogen source.
- Schramm, Sebastian,Boco, Maria Fe Angela Comia,Manzer, Sarah,K?nig, Oliver,Zhang, Tong,Mony, Fatima Tuz Zohora,Adedeji-Badmus, Adebimpe Nafisat,Poppenberger, Brigitte,Rozhon, Wilfried
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Read Online
- Selective Mild Oxidation of Anilines into Nitroarenes by Catalytic Activation of Mesoporous Frameworks Linked with Gold-Loaded Mn3O4 Nanoparticles
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This work reports the synthesis and catalytic application of mesoporous Au-loaded Mn3O4 nanoparticle assemblies (MNAs) with different Au contents, i. e., 0.2, 0.5 and 1 wt %, towards the selective oxidation of anilines into the corresponding nitroarenes. Among common oxidants, as well as several supported gold nanoparticle platforms, Au/Mn3O4 MNAs containing 0.5 wt % Au with an average particle size of 3–4 nm show the best catalytic performance in the presence of tert-butyl hydroperoxide (TBHP) as a mild oxidant. In all cases, the corresponding nitroarenes were isolated in high to excellent yields (85–97 %) and selectivity (>98 %) from acetonitrile or greener solvents, such as ethyl acetate, after simple flash chromatography purification. The 0.5 % Au/Mn3O4 catalyst can be isolated and reused four times without a significant loss of its activity and can be applied successfully to a lab-scale reaction of p-toluidine (1 mmol) leading to the p-nitrotulene in 83 % yield. The presence of AuNPs on the Mn3O4 surface enhances the catalytic activity for the formation of the desired nitroarene. A reasonable mechanism was proposed including the plausible formation of two intermediates, the corresponding N-aryl hydroxylamine and the nitrosoarene.
- Armatas, Gerasimos S.,Daikopoulou, Vassiliki,Koutsouroubi, Eirini D.,Lykakis, Ioannis N.,Skliri, Euaggelia
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- Method and device for preparing methylnitro-benzene by channelization
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The invention discloses a method and a device for preparing methylnitro-benzene by channelization. The device comprises a storage tank, a nitrogen dioxide cylinder, an ozone generator, a flow pump, agas flowmeter, a reaction pipeline filled with a catalyst, a mixing pipeline, two T-shaped mixed joints, a cooling system, a heating system, a back pressure valve and a receiving tank. The method specifically comprises the following steps: opening the cooling system and the heating system; opening the ozone generator; arranging the flow pump and the gas flowmeter; and mixing raw materials liquid methyl benzene and nitrogen dioxide through the first T-shaped mixing joint and feeding the mixture into the mixing pipeline, then mixing the mixture with ozone in the second T-shaped mixing joint, feeding the mixture into the reaction pipeline filled with the catalyst for a nitrifying reaction, and post-treating a reaction liquid to obtain methylnitro-benzene. The method is controlled precisely and automatically, and is simple to operate, mild in reaction condition, simple in post treatment, quick to transfer mass and heat, high in safety and good in economical benefit.
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Paragraph 0056; 0057; 0058
(2019/02/04)
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- HNO3/HFIP: A Nitrating System for Arenes with Direct Observation of π-Complex Intermediates
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This report describes an efficient nitrating system for the nitration of arenes at room temperature by using an equivalent of nitric acid in HFIP (1,1,1,3,3,3-hexafluoroisopropanol). The π-complex intermediate of an arene with a nitronium ion stabilized by HFIP can be directly observed by UV-vis spectra and is supported by theoretical calculations.
- Lu, Le,Liu, Huixin,Hua, Ruimao
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supporting information
p. 3197 - 3201
(2018/06/11)
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- POLYCYCLIC AMINES AS OPIOID RECEPTOR MODULATORS
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The present invention provides a genus of polycyclic amines that are useful as opioid receptor modulators. The compounds of the invention are useful in both therapeutic and diagnostic methods, including for treating pain, neurological disorders, cardiac disorders, bowel disorders, drug and alcohol addiction, drug overdose, urinary disorders, respiratory disorders, sexual dysfunction, psoriasis, graft rejection or cancer.
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Paragraph 0288
(2018/10/11)
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- Highly efficient protocol for the aromatic compounds nitration catalyzed by magnetically recyclable core/shell nanocomposite
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An efficient protocol for the nitration of aromatic compounds in the presence of a catalytic amount of sulfuric acid-functionalized silica-based magnetic core/shell nanocomposite was reported. The designed products were obtained in high yields in relatively short reaction times at room temperature under solvent-free conditions. The nanocatalyst was simply recovered from the reaction mixture by using an external magnet and efficiently reused for several times. The characterization of particle size, morphology and elemental analysis of the nanocatalyst were provided by scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses, respectively.
- Maleki, Ali,Aghaei, Morteza,Paydar, Reza
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p. 485 - 490
(2017/01/10)
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- NH4I/tert-butyl hydroperoxide-promoted oxidative C–N cleavage of tertiary amines leading to nitroaromatic compounds
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A NH4I/tert-butyl hydroperoxide-promoted oxidation of tertiary N-aryl-N,N-dialkylamines in DMSO has been developed to access nitroaromatic compounds. This methodology involves sequential N-dealkylation reactions in one-pot and a radical pathway is proposed.
- Shao, Ying,Zheng, Hao,Wu, Zhuhong,Huang, Lei,Tong, Jingjing,Wu, Ming,Sun, Xiaoqiang
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p. 504 - 508
(2017/10/03)
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- One-Pot C?H Functionalization of Arenes by Diaryliodonium Salts
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A transition-metal-free, mild, and highly regioselective synthesis of nitroarenes from arenes has been developed. The products are obtained in a sequential one-pot reaction by nitration of iodine(III) reagents with two carbon ligands, which are formed in situ from iodine(I). This novel concept has been extended to formation of aryl azides, and constitutes an important step towards catalytic reactions with these hypervalent iodine reagents. An efficient nitration of isolated diaryliodonium salts has also been developed, and the mechanism is proposed to proceed by a [2,2] ligand coupling pathway.
- Reitti, Marcus,Villo, Piret,Olofsson, Berit
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supporting information
p. 8928 - 8932
(2016/07/26)
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- Chemoselective reduction and self-immolation based FRET probes for detecting hydrogen sulfide in solution and in cells
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Hydrogen sulfide (H2S) has been regarded as the third gaseous transmitter. Based on the mechanism of chemoselective azido reduction and self-immolation, five fluorescence resonance energy transfer (FRET) probes for the detection of H2S were designed and synthesized. The effect of functional substitution of the self-immolative moiety on azido reduction and quinone-methide rearrangement were investigated. Their fluorescence responses and chemoselectivity for H2S detection were evaluated in solutions and in cells. This strategy may provide a general route for designing H 2S probes with many commercially available FRET pairs. the Partner Organisations 2014.
- Chen, Bifeng,Wang, Peng,Jin, Qingqing,Tang, Xinjing
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supporting information
p. 5629 - 5633
(2014/07/22)
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- Oxidation of aromatic amines into nitroarenes with m-CPBA
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A versatile and highly efficient approach for the synthesis of nitroarenes from aromatic amine using m-CPBA has been developed. This oxidation reaction was operationally straightforward and proceeded to afford products in good isolated yields.
- Liu, Jia,Li, Jue,Ren, Jiangmeng,Zeng, Bu-Bing
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p. 1581 - 1584
(2014/03/21)
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- Bis(tridentate) ruthenium-terpyridine complexes featuring microsecond excited-state lifetimes
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A series of heteroleptic bis(tridentate) ruthenium(II) complexes, each bearing a substituted 2,2′:6′,2″-terpyridine (terpy) ligand, is characterized by room temperature microsecond excited-state lifetimes. This observation is a consequence of the strongly σ-donating and weakly π-accepting tridentate carbene ligand, 2′,6′-bis(1-mesityl-3- methyl-1,2,3-triazol-4-yl-5-idene)pyridine (C^N^C), adjacent to the terpy maintaining a large separation between the ligand field and metal-to-ligand charge transfer (MLCT) states while also preserving a large 3MLCT energy. The observed lifetimes are the highest documented lifetimes for unimolecular ruthenium(II) complexes and are four orders in magnitude higher than that associated with [Ru(terpy)2]2+.
- Brown, Douglas G.,Sanguantrakun, Nawaporn,Schulze, Benjamin,Schubert, Ulrich S.,Berlinguette, Curtis P.
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supporting information; scheme or table
p. 12354 - 12357
(2012/09/05)
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- Aromatic nitration with bismuth nitrate in ionic liquids and in molecular solvents: A comparative study of Bi(NO3)3·5H 2O/[bmim][PF6] and Bi(NO3)3· 5H2O/1,2-DCE systems
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A suspension of bismuth nitrate pentahydrate (BN) in [bmim][PF6] or [bmim][BF4] imidazolium ionic liquid (IL) is an effective reagent for ring nitration of activated aromatics under mild conditions without the need for external promoters. Nitration can also be effected in 1,2-DCE, MeCN, or MeNO2 without additives. Nitration of activated arenes (anisole, toluene, ethylbenzene, cumene, p-xylene, mesitylene, durene, and 1,3-dimethoxybenzene) is considerably faster (time to completion) in BN/[bmim][PF6] relative to BN/1,2-DCE and there are also differences in isomer distributions (for anisole, toluene, and ethylbenzene). With introduction of strongly deactivating substituents (-CHO; -MeCO; -NO 2) the BN/IL system is no longer active but reactions still proceed with BN/1,2-DCE in reasonable yields. The ready availability and low cost of BN, simple operation, and absence of promoters, coupled to recycling and reuse of the IL, provide an attractive alternative to classical nitration methods for activated arenes. Switching from Bi(NO3)3·5H 2O/[bmim][PF6] to Bi(NO3)3· 5H2O/1,2-DCE increases the scope of the substrates that can be nitrated.
- Jacoway, Jonathan,Kumar, G. G. K. S. Narayana,Laali, Kenneth K.
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p. 6782 - 6785,4
(2012/12/12)
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- Ethylammonium nitrate (EAN)/Tf2O and EAN/TFAA: Ionic liquid based systems for aromatic nitration
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Acting as in situ sources of triflyl nitrate (TfONO2) and trifluoroacetyl nitrate (CF3COONO2), the EAN/Tf 2O and EAN/TFAA systems, generated via metathesis in the readily available ethylammonium nitrate (EAN) ionic liquid as solvent, are powerful electrophilic nitrating reagents for a wide variety of aromatic and heteroaromatic compounds. Comparative nitration experiments indicate that EAN/Tf2O is superior to EAN/TFAA for nitration of strongly deactivated systems. Both systems exhibit low substrate selectivity (K T/KB = 5-10) in (Figure presented) between values reported for covalent nitrates and preformed nitronium salts.
- Aridoss, Gopalakrishnan,Laali, Kenneth K.
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experimental part
p. 8088 - 8094
(2011/11/13)
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- Effect of the ortho modification of azobenzene on the photoregulatory efficiency of DNA hybridization and the thermal stability of its eis form
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We synthesized various azobenzenes methylated at their ortho positions with respect to the azo bond for more effective photoregulation of DNA hybridization. Photoregulatory efficiency, evaluated from the change of T m (ΔTm) induced by trans-cis isomerization, was significantly improved for all ortho-modified azobenzenes compared with non-modified azobenzene due to the more stabilized trans form and the more destabilized cis form. Among the synthesized azobenzenes, 4-carboxy-2',6'- dimethylazobenzene (2',6'-Me-Azo), in which two ortho positions of the distal benzene ring with respect to carboxyl group were methylated, exhibited the largest ΔTm, whereas the newly synthesized 2,6-Me-Azo (4-carboxy-2,6- dimethylazobenzene), which possesses two methyl groups on the two ortho positions of the other benzene ring, showed moderate improvement of ΔTm. Both NMR spectroscopic analysis and computer modeling revealed that the two methyl groups on 2',6'-Me-Azo were located near the imino protons of adjacent base pairs; these stabilized the DNA duplex by stacking interactions in the trans form and destabilized the DNA duplex by steric hindrance in the cis form. In addition, the thermal stability of cis-2',6'-Me-Azo was also greatly improved, but not that of cis2,6-Me-Azo. Solvent effects on the half-life of the cis form demonstrated that cis-to-trans isomerization of all the modified azobenzenes proceeded through an inversion route. Improved thermal stability of 2',6'-Me-Azo but not 2,6-Me-Azo in the eis form was attributed to the retardation of the inversion process due to steric hindrance between lone pair electrons of the π orbital of the nitrogen atom and the methyl group on the distal benzene ring.
- Nishioka, Hidenori,Liang, Xingguo,Asanuma, Hiroyuki
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supporting information; experimental part
p. 2054 - 2062
(2010/07/05)
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- Acetyl nitrate nitrations in [bmpy][N(Tf)2] and [bmpy][OTf], and the recycling of ionic liquids
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In this work we have examined the nitration by acetyl nitrate of a range of activated and deactivated aromatic substrates in two ionic liquids and compared the results to the same reaction in dichloromethane. Both ionic liquids are stable to the reaction conditions, and in both ionic liquids the yields of reaction are higher after unit time than the same reactions in dichloromethane, although the regioselectivity is little affected by solvent choice. This result gives further support to the suggestion that in the ionic liquid, acetyl nitrate dissociates to give the nitronium ion, and that this is the effective nitrating agent here. However, it is shown that [bmpy][N(Tf)2] is a better solvent for aromatic nitration than [bmpy][OTf]. This is due to the ease of formation of nitronium ion in the former ionic liquid, and is consistent with the fact that [bmpy][N(Tf)2] is a weaker hydrogen bond acceptor solvent than [bmpy][OTf]. Finally, a method by which [bmpy][N(Tf)2] may be recovered and reused for aromatic nitration has been demonstrated.
- Dal, Emilie,Lancaster, N. Llewellyn
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p. 682 - 686
(2007/10/03)
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- Supported tetramethylamonium nitrate/silicasulfuric acid as a useful reagent for nitration aromatic compounds under solvent-free conditions
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A variety of aromatic compounds are nitrated to the parent nitro aromatic compounds under solvent-free conditions using supported tetramethylammonium nitrate/silicasulfuric acid as a useful reagent. This methodology is useful for nitration of activated and deactivated aromatic rings. Copyright Taylor & Francis, Inc.
- Hajipour, Abdol R.,Zarei, Amin,Khazdooz, Leila,Ruoho
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p. 2237 - 2241
(2007/10/03)
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- Nitric acid in the presence of P2O5 supported on silica gel - A useful reagent for nitration of aromatic compounds under solvent-free conditions
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A variety of aromatic compounds are nitrated to parent nitro aromatic compounds under solvent-free conditions using 65% nitric acid in the presence of P2O5 supported on silica gel is described. This methodology is useful for nitration of activated and deactivated aromatic rings.
- Hajipour, Abdol Reza,Ruoho, Arnold E.
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p. 8307 - 8310
(2007/10/03)
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- Oxidative dearomatization of phenols and anilines via λ3 - and λ5-iodane-mediated phenylation and oxygenation
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Treatment of 2-methylphenols with chloro(diphenyl)-λ3- iodane led to their regioselective dearomatizing 2-phenylation into cyclohexa-2,4-dienone derivatives via a proposed ligand coupling reaction. In the same vein of investigation, treatment of 2-methylanilines with the λ5-iodane 2-iodoxybenzoic acid IBX reagent led to their regioselective dearomatization into previously undescribed ortho-quinol imines.
- Quideau, Stephane,Pouysegu, Laurent,Ozanne, Aurelie,Gagnepain, Julien
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p. 201 - 216
(2007/10/03)
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- A fast and mild method for nitration of aromatic rings
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The use of benzyltriphenylphosphonium nitrate (PhCH2Ph 3P+NO3-) (BTPPN) as a useful reagent for nitration aromatic compounds in the presence of methanesulfonic anhydride under solvent-free conditions is described. This methodology is useful for nitration of activated aromatic rings.
- Hajipour, Abdol R.,Ruoho, Arnold E.
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p. 221 - 226
(2007/10/03)
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- Selective nitration of aromatic compounds with bismuth subnitrate and thionyl chloride
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Bismuth subnitrate/thionyl chloride have been found to be an efficient combination of reagents for nitration of a wide range of aromatic compounds in dichloromethane. Phenols, in particular, were easily mononitrated and dinitrated with the reagents by controlling the stoichiometry.
- Muathen, Hussni A.
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p. 593 - 598
(2007/10/03)
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- Aromatic nitrations in ionic liquids: The importance of cation choice
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Aromatic substrates can be nitrated in high yields and with efficient use of the nitrating agent in ionic liquids, although a suitably inert ionic liquid cation must be used.
- Lancaster, N. Llewellyn,Llopis-Mestre, Veronica
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p. 2812 - 2813
(2007/10/03)
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- SUBSTITUTED NITROBENZENE DERIVATIVES AS MEDICINES AND OTHER USEFUL USES THEREOF
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The present invention relates to a use of substituted nitrobenzene derivatives of general Formula I in medicine and health food, the pharmaceutical compositions comprising substituted nitrobenzene derivatives of general Formula I and the methods thereof for the prophylaxis and treatment of diseases.
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- Synthesis and binding studies of bowl-shaped hosts for quaternary ammoniums
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Two bowl-shaped hosts for quaternary ammonium salts were synthesized and their binding properties, along with the anion effect, were systematically examined and compared in CDCl3.
- Jeong, Kyu-Sung,Shin, Kwang Hoon,Kim, Soong-Hyun
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p. 1166 - 1167
(2007/10/03)
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- Scandium(III) trifluoromethanesulfonate catalyzed aromatic nitration with inorganic nitrates and acetic anhydride
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The rare earth metal(III) trifluoromethanesulfonate (rare earth metal(III) triflate, RE(OTf)3) was found to be an efficient catalyst for aromatic nitration with carboxylic anhydride-inorganic nitrate as the nitrating agent. In the presence of a catalytic amount of RE(OTf)3, the nitration of substituted benzenes proceeded to afford the corresponding nitrobenzenes. Especially, scandium(III) trifluoromethanesulfonate (scandium(III) triflate, Sc(OTf)3) is the most active catalyst among our tested Lewis acids. It was also found that acetic anhydride-Al(NO 3) · 9H2O is the most active nitrating agent in this system.
- Kawada, Atsushi,Takeda, Shigemitsu,Yamashita, Kazumi,Abe, Hitoshi,Harayama, Takashi
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p. 1060 - 1065
(2007/10/03)
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- An efficient nitration of light alkanes and the alkyl side-chain of aromatic compounds with nitrogen dioxide and nitric acid catalyzed by N-hydroxyphthalimide
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Nitration of light alkanes and the alkyl side-chain of aromatic compounds with NO2 and HNO3 was successfully achieved by the use of N-hydroxyphthalimide (NHPI) as a catalyst under relatively mild conditions. For example, the nitration of propane with NO2 catalyzed by NHPI at 100 °C for 14 h gave 2-nitropropane in good yield without formation of 1-nitropropane and cleaved products such as nitroethane and nitromethane. Various aliphatic nitroalkanes, which are difficult to prepare by conventional methods, could be selectively obtained by means of the present methodology by using NHPI as the key catalyst. In addition, the side-chain nitration of alkylbenzenes such as toluene was selectively carried out to lead to α-nitrotoluene without the ring nitration. The present reaction provides an efficient selective method for the nitration of light alkanes and alkylbenzenes, which has been very difficult to carry out so far.
- Nishiwaki, Yoshiki,Sakaguchi, Satoshi,Ishii, Yasutaka
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p. 5663 - 5668
(2007/10/03)
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- Electrophilic nitration of aromatics in ionic liquid solvents
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Potential utility of a series of 1-ethyl-3-methylimidazolium salts [emim][X] with X = OTf-, CF3COO-, and NO3- as well as [HNEtPri2][CF3COO] (protonated Huenig's base) ionic liquids were explored as solvent for electrophilic nitration of aromatics using a variety of nitrating systems, namely NH4NO3/TFAA, isoamyl nitrate/BF3·Et2O, isoamyl nitrate/TfOH, Cu(NO3)/TFAA, and AgNO3/Tf2O. Among these, NH4NO3/TFAA (with [emim][CF3COO], [emim][NO3]) and isoamyl nitrate/BF3·Et2O, isoamyl nitrate/TfOH (with [emim][OTf]) provided the best overall systems both in terms of nitration efficiency and recycling/reuse of the ionic liquids. For [NO2][BF4] nitration, the commonly used ionic liquids [emim][AlCl4] and [emim][Al2Cl7] are unsuitable, as counterion exchange and arene nitration compete. [Emim][BF4] is ring nitrated with [NO2][BF4] producing [NO2-emim][BF4] salt, which is of limited utility due to its increased viscosity. Nitration in ionic liquids is surveyed using a host of aromatic substrates with varied reactivities. The preparative scope of the ionic liquids was also extended. Counterion dependency of the NMR spectra of the [emim][X] liquids can be used to gauge counterion exchange (metathesis) during nitration. Ionic liquid nitration is a useful alternative to classical nitration routes due to easier product isolation and recovery of the ionic liquid solvent, and because it avoids problems associated with neutralization of large quantities of strong acid.
- Laali,Gettwert
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- Sulfuric acid on silica-gel: An inexpensive catalyst for aromatic nitration
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Solid acidic catalysts made of sulfuric acid supported on silica-gel and their application to the nitration of aromatics with nitric acid and isopropyl nitrate are described. Substrates with very different levels of activation were investigated. Methods to overcome the poisoning produced by water and to tune the catalysts activity according to the reactivity of the substrate are outlined.
- Riego, Juan M.,Sedin, Zeno,Zaldivar, Jose M.,Marziano, Nunziata C.,Tortato, Claudio
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p. 513 - 516
(2007/10/02)
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- Cobalt schiff base complex-catalyzed oxidation of anilines with tert-butyl hydroperoxide
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Cobalt Schiff base complexes [Co(SB)] catalyze the oxidation of anilines (1) with tert-butyl hydroperoxide to give nitrobenzenes 2 and 4-(tert-butylperoxy)-2,5-cyclohexadien-1-imine derivatives 3 in yield distributions depending on the substitution mode of the substrate. 4-Alkyl- and 4-aryl-2,6-di-tert-butylanilines gave mixtures of 2 and 3, where the higher the bulkiness of the 4-substituent, the higher the yield of 2. With 2,4,6-trimethylaniline, the ratio of oxidations of the nitrogen and C-4 atoms was almost the same; but a hydrolyzed product 5 of the imine was obtained. 2,4,6-Triphenylaniline gave only 2. Nitrobenzene derivatives were also obtained from 2,6-dialkylanilines and 4-substituted anilines. The catalytic activity of Co(SB) depended on the nature of the SB ligand: the formal potential E° and steric factors seem to affect the reaction rate. Kinetic studies showed that the key step may involve hydrogen abstraction from the aniline, presumably by t-BuO? generated from homolytic decomposition of initially formed CoIII(SB)(OO-t-Bu). A precursor of 2 was found to be the nitrosobenzene derivative.
- Foerster, Stefan,Rieker, Anton,Maruyama, Kazushige,Murata, Kunihiko,Nishinaga, Akira
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p. 3320 - 3326
(2007/10/03)
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- Phase-Transfer Catalysis in Electrophilic Substitution Reactions. IV. Reactivity in Nitration under Conditions of Phase-Transfer Catalysis
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Phase-transfer nitration catalyzed by tetra(perfluorophenyl)borates have been performed with a series of mono- and polycyclic arenes.The unexpectedly low reactivity of monocyclic hydrocarbons is explained in terms of correlation between the substrate selectivity and ionization potentials.The regioselectivity of nitration of alternant hydrocarbons is qualitatively consistent with the density of frontier electrons in the ground state of the substrate molecule.
- Kachurin, O. I.,Velichko, L. I.,Zaraiskii, A. P.
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p. 651 - 656
(2007/10/03)
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- Thermal and Photochemical Nitration of Aromatic Hydrocarbons with Nitrogen Dioxide
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Aromatic hydrocarbons (ArH) are readily nitrated by nitrogen dioxide (NO2) in dichloromethane at room temperature and below (in the dark).The red colors, transiently observed, arise from the metastable precursor complex NO3(1-), which is formed in the prior disproportionation of nitrogen dioxide induced by the aromatic donor (eq 7).The deliberate irradiation of the diagnostic (red) charge-transfer absorption band (hνCT) of NO3(1-) at low temperatures results directly in aromatic nitration, even at -78 deg C, where the thermal nitration is too slow to complete.The mechanism of the photochemical (charge-transfer) nitration is established by time-resolved laser spectroscopy to proceed via the aromatic cation radical (ArH.+) formed spontaneously upon the charge-transfer excitation of NO3(1-) in Scheme 1.The related thermal activation of NO3(1-) derives from the adiabatic electron transfer that produces the same radical pair as the reactive intermediate in Scheme 3.The close relationship between the thermal/photochemical nitrations with nitrogen dioxide and those conventionally carried out with nitric acid (in the presence of nitrous acid) is delineated by Scheme 4.
- Bosch, E.,Kochi, J. K.
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p. 3314 - 3325
(2007/10/02)
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- Electron Affinities of Naphthalene, Anthracene and Substituted Naphthalenes and Anthracenes
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The determination of electron transfer equilibria A(1-) + B = A + B(1-) in the gas phase, with a pulsed-electron high-pressure mass spectrometer, leads to ΔG10, ΔH10, and ΔS10 values.These can be converted into the free energy, enthalpy and entropy changes, ΔGa0(B), ΔHa0(B) and ΔSa0(B), for the reaction e + B = B(1-), since the corresponding values for the reference compounds A are known.Results were obtained for 18 substituted naphthalenes, anthracene and substituted anthracenes.The results are compared with some theoretical predictions and the corresponding reduction potentials in solution.Rate constants for 13 exoergic electron-transfer reactions were also measured.These were found to be close to the ADO collision rates.
- Heinis, Thomas,Chowdhury, Swapan,Kebarle, Paul
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p. 358 - 365
(2007/10/02)
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- Ozone-mediated Nitration of Alkylbenzenes and Related Compounds with Nitrogen Dioxide
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In the presence of ozone, nitrogen dioxide exhibits a strong nitrating ability for alkylbenzenes at low temperatures, converting them into the corresponding nitro derivatives in high yield.The addition of a protonic acid as catalyst enhances considerably the ability of this nitrating system and leads to a good yield of polynitro compounds.The reaction is clean and proceeds rapidly without any accompanying side-chain substitution or aryl-aryl coupling.It shows no kinetic dependence on the concentration of substrates and, as far as can be judged from relative reactivities and isomer distributions of products, it gives the appearance of being an electrophilic aromatic process.A possible role for nitrogen trioxide has been suggested as the initial electrophilic agent for the nitration of alkylbenzenes.
- Suzuki, Hitomi,Murashima, Takashi,Kozai, Iku,Mori, Tadashi
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p. 1591 - 1598
(2007/10/02)
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- Aromatic nitration with electrophilic N-nitropyridinium cations. Transitory charge-transfer complexes as key intermediates
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Electrophilic aromatic nitration of various arenes (ArH) is shown to be critically dependent on labile charge-transfer complexes derived from N-nitropyridinium cations. The electrophiles XPyNO2+, with X = CN, CO2CH3, Cl, H, CH3, and OCH3, form a highly graded series of electron acceptors that produce divers [ArH,XPyNO2+] complexes, with charge-transfer excitation energies (hvCT) spanning a range of almost 50 kcal mol-1. The latter underlie an equally broad spectrum of aromatic substrate selectivities from the different nitrating agents (XPyNO2+), but they all yield an isomeric product distribution from toluene that is singularly insensitive to the X substituent. The strong correlation of the nitration rates with the HOMO-LUMO gap in the [ArH,XPyNO2+] complex is presented (Scheme III) in the context of a stepwise process in which the charge-transfer activation process is cleanly decoupled from the product-determining step-as earlier defined by Olah's requirement of several discrete intermediates. This charge-transfer formulation thus provides a readily visualized as well as a unifying mechanistic basis for the striking comparison of XPyNO2+ with other nitrating agents, including the coordinatively unsaturated nitronium cation (NO2+BF4-), despite their highly differentiated reactivities.
- Kim,Lee,Kochi
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p. 1756 - 1770
(2007/10/02)
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- Co(salen) catalyzed oxidation of 2,4,6-trisubstituted anilines with tert-butylhydroperoxide
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Co(salen) catalyzed oxidation of 2,4,6-trisubstituted (preferentially 2,6-di-tert-butylated) anilines with tert-butylhydroperoxide gives 4-tert-butylperoxy-2,5-cyclohexadien-1-imine and nitrobenzene derivatives. The relative ratio of the products depends on the nature of the substituents in the substrate.
- Nishinaga,Forster,Eichhorn,Speiser,Rieker
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p. 4425 - 4428
(2007/10/02)
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- 15N Nuclear Polarisation in Nitration and Related Reactions. Part 5. The Borderline between the Classical and the Electron Transfer Mechanisms in Nitration by the Nitronium Ion
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The nitration of p-xylene, mesitylene, naphthalene, 2H8>naphthalene, durene and some related compounds has been followed by 15N NMR spectroscopy in a mixture of trifluoroacetic acid and nitromethane containing sufficient sodium azide to inhibit nitrous acid catalysed nitration.Significant 15N nuclear polarisation occurs with durene and the naphthalenes and has been analysed by comparison with theoretical curves leading to the calculation of enhancement coefficients.The results indicate that a small part of the reaction of naphthalene with nitronium ions under these conditions involves direct electron transfer between the reactants before the formation of the Wheland intermediate.The extent of this electron transfer is much greater than expected from Marcus theory calculations based on an outer-sphere electron transfer (ET) reaction: the discrepancy is discussed in terms of the initial interaction between the reactants and the solvent effects on the equilibrium constant for the electron transfer.
- Johnston, James F.,Ridd, John H.,Sandall, John P. B.
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p. 623 - 628
(2007/10/02)
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- Direct Observation of the Kinetic Acidities of Transient Aromatic Cation Radicals. The Mechanism of Electrophilic Side-Chain Nitration of the Methylbenzenes
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The transient cation radicals ArCH3(.+) are spontaneously generated by the 532-nm excitation of the charge-transfer complexes with a 10-ns laser pulse.The decay kinetics of the spectral transients in the presence of added base establish the kinetic acidities (kH) for various methylarene cation radicals with different pyridines and trinitromethide.Such a proton transfer from ArCH3(.+) proceeds with a deuterium kinetic isotope effect of kH/kD ca. 3.Side-chain nitration of hexamethylbenzene (HMB) is shown to proceed in high yields via the intimate triad of reactive fragments II, , that is produced upon the charge-transfer excitation.The subsequent annihilation of the reactive triad II occurs via a rapid succession of bimolecular steps involving either (i) the initial ion-pair collapse of by proton transfer, as shown in Scheme VI, or (ii) the alternative sequence with the initial ion-radical collapse of by homolytic coupling, as shown in Scheme VII.The marked variations of kH/kD with solvent polarity and added innocuous salt (Bu4N(+)ClO4(-)), as reflected in ion-pair separation and the "special" salt effect, serve to effectively distinguish these pathways.The direct bearing of Schemes VI and VII on the mechanism of the thermal (adiabatic) nitration of methylarene side chains with nitric acid is delineated.
- Masnovi, J. M.,Sankararaman, S.,Kochi, J. K.
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p. 2263 - 2276
(2007/10/02)
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- Oxidative Aromatic Nitration with Charge-Transfer Complexes of Arenes and Nitrosonium Salts
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Brightly colored solutions are obtained immediately upon the exposure of various arenes (ArH) to nitrosonium (NO+) salts.The colors arise from the charge-transfer transitions of 1:1 complexes +> that are reversibly formed as persistent intermediates.However the yellow-red charge-transfer (CT) colors are readily bleached by dioxygen, and the corresponding nitroarenes (ArNO2) can be isolated in excellent yields from acetonitrile solutions.Such an oxidative aromatic nitration of aromatic donors proceeds via the initial autooxidation of the charge-transfer complex.The collapse of the resulting radical ion pair .+,NO2> to the ?-adduct, followed by the loss of proton, affords ArNO2.Direct evidence for electron transfer in the initial step when anthracene is treated with NO+PF6- stems for the isolation of (a) the anthracene ion radical salt .+PF6-> along with nitric oxide in dichloromethane solution and (b) the formation of 9-nitroanthracene (admixed with anthraquinone) in the more polar acetonitrile.The aromatic products (and isomer distribution) from oxidative aromatic nitration are highly reminiscent of those from electrophilic aromatic nitration.The possibility of common reactive intermediates in these two distinctive pathways for aromatic nitration is discussed.
- Kim, E. K.,Kochi, J. K.
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p. 1692 - 1702
(2007/10/02)
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- Substituent and Ring Size Dependence of the 4J(Me-C-C-H) Coupling Constant
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The magnitude of the 4J proton-proton coupling constant across the fragment CH3-C-C-H (a probe of the bond order between the central sp2-sp2 hybridized carbon atoms) has been found to be essentially independent of substitution on a toluene fragment and the size of the ring containing the ortho-allylic fragment.The coupling constant is sensitive to direct substitution on the ortho-allilyc fragment, especially where the substituent is placed α to methyl group.KEY WORDS - 4J proton-proton coupling constant ortho-benzylic coupling constant ring size dependence substituent dependence
- Collins, M. J.,Hatton, P. M.,Sternbell, S.,Tansey, C. W.
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p. 824 - 828
(2007/10/02)
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- Electron Affinities of Di- and Tetracyanoethylene and Cyanobenzenes Based on Measurements of Gas-Phase Electron-Transfer Equilibria
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The electron affinities of tetracyanoethylene, trans-1,2-dicyanoethylene, and eleven substituted benzonitriles as well as two naphthonitriles were determined by measurement of the electron-transfer equilibria A-+B=A+B- with a pulsed electron high ion source pressure mass spectrometer.Rate constants for exothermic electron transfer involving the cyano compounds were found to be near unit collision efficiency.The EA (tetracyanoethylene)=3.17 eV obtained in the present work is considerably higher than the 2.3 eV photodetachment value of Palmer and Lyons.The electron affinities of benzene and benzonitrile substituted by CN, CHO, and NO2 increase in the given order, while the order for nitrobenzene is CHO, CN, NO2.This reversal of order is explained on the basis of a larger attenuation of the ?-withdrawing effect relative to the field effect of substituents when the electron density in the ?* single-electron orbital is decreased.
- Chowdhury, Swapan,Kebarle, Paul
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p. 5453 - 5459
(2007/10/02)
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- 15N NUCLEAR POLARISATION IN NITRATION AND RELATED REACTIONS. PART 1. MESITYLENE
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The nitration of mesitylene by nitric acid in trifluoroacetic acid has been followed by 1H and 15N n.m.r. spectroscopy using H(15)NO3 (95-99percent 15N).With concentrations of mesitylene > 0.5 mol dm3, the direct nitration by the nitronium ion is accompanied by an autocatalytic reaction involving nitrous acid.The nitrous acid-catalysed process is inhibited by azide ions and can be made to predominate by the addition of nitrous acid.Nitration by the nitronium ion gives no nuclear polarisation in the product but the nitrous acid-catalysed reaction gives marked 15N nuclear polarisation: the 15N n.m.r. spectrum of nitromesitylene during reaction then appears in emission with a degree of enhancement that can exceed a factor of 200.This nuclear polarisation is attributed to the formation of a radical pair ArH+.NO2. by the diffusion together of the components.The side-products formed in the nitrous acid-catalysed process are consistent with reactions through ArH+..The direct nitration of mesytilene by the nitronium ion does not appear to involve this cation radical.
- Clemens, Anthony H.,Ridd, John H.,Sandall, John P. B.
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p. 1659 - 1666
(2007/10/02)
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- Reactions of Cerium(IV) Ammonium Nitrate with Aromatic Compounds in Acetonitrile. Part 2. Nitration; Comparison with Reactions of Nitric acid
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The nitration of benzene and a number of alkylbenzenes by cerium(IV) ammonium nitrate in acetonitrile shows the same intra- and inter-molecular selectivity as nitration with nitric acid under the same conditions but the extent of the other products formed in the two sets of reactions is very different.Nitration by cerium(IV) ammonium nitrate (but not side-chain substitution) is suppressed by the addition of water.The results suggest that these nitration reactions by cerium(IV) ammonium nitrate occur through the intermediate formation of a nitronium ion from the cerium(IV) complex but the order with recpect to the aromatic compound shows that this nitronium ion must then be formed in the presence of the aromatic substrate as a 'spectator'.The relative reactivities with respect to benzene in the nitration of anisole and naphthalene are much greater than those observed in nitration by nitric acid and, with both, the isomer proportions are also anomalous.
- Dinctuerk, Suphi,Ridd, John H.
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p. 965 - 970
(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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- Aromatic Substitution. 45. Transfer Nitration of Aromatic with N-Nitropyridinium and Quinolinium Ions
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The transfer nitration of aromatics with various N-nitropyridinium and quinolinium salts (PF6- or BF4-) was studied.The nitroanions were found to take place via a nicleophilic displacement pathway, involving the N-nitropyridinium ions themselves and not free nitronium ion.Steric factors were, however, shown to play an insignificant role in determining the positional selectivity of nitration.Positional and substrate selectivities were found to be independent of one another and are suggested to be determined in two separate steps.
- Olah, George A.,Narang, Subhash C.,Olah, Judith A.,Pearson, Ronald L.,Cupas, Chris A.
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p. 3507 - 3510
(2007/10/02)
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