- Evidence for Generation of the Unsaturated Sila-acetate Species Me(O-)Si=O by Dissociation of the Silanediolate Dianion m-ClC6H4CH2SiMe(O-)2
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Kinetic studies indicate that in the cleavage of m-ClC6H4CH2SiMe(OH)2 by NaOH in Me2SO-H2O there is a major contribution by unimolecular dissociation of the dianion m-ClC6H4CH2SiMe(O-)2 to give the acetate ion analogue Me(O-)Si=O.
- Chmielecka, Jadwiga,Chojnowski, Julian,Eaborn, Colin,Stancyzk, Wlodimierz A.
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- Thermodynamic Analysis of Isomerization Equilibria of Chlorotoluenes and Dichlorobenzenes in a Biphasic Reaction Systems Containing Highly Acidic Chloroaluminate Melts
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Thermodynamics and kinetics of the isomerization of chlorotoluenes and dichlorobenzene to the technically desired meta-isomers have been studied in the presence of highly acidic chloroaluminate melts with alkali metal and organic imidazolium cations. Enthalpies of four isomerization processes in reacting systems of chlorotoluenes and dichlorobenzene were obtained from temperature dependencies of the corresponding equilibrium constants in the liquid phase. Experimental reaction enthalpies, enthalpies of vaporization, and absolute vapor pressures of chlorotoluenes and dichlorobenzene have been used for the validation of quantum-chemical methods to predict thermodynamic functions of the four reactions under study successfully. Values of the standard Gibbs energies of formation, standard enthalpies and entropies of formation of chlorotoluenes and dichlorobenzenes in the liquid and in the gas phase have been derived. These values allow optimization of liquid-liquid biphasic manufacturing technologies for halogen-substituted benzenes.
- Verevkin, Sergey P.,Messner, Julia,Emel'Yanenko, Vladimir N.,Gantman, Mikhail G.,Schulz, Peter S.,Wasserscheid, Peter
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- Chemistry of superacids: 35. * NO2Cl-3MXN systems: Superelectrophilic aprotic nitrating agents for deactivated aromatics
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Superelectrophilic nitration of deactivated aromatics with NO2Cl-3MXn complexes in aprotic nonpolar solvents such as CH2Cl2 makes it possible to obtain the corresponding nitro derivatives in good to almost quantitative yields under mild conditions.
- Olah,Orlinkov,Ramaiah,Oxyzoglou,Prakash
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Read Online
- Two efficient methods for the preparation of 2-chloro-6-methylbenzoic acid
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Two efficient methods for the preparation of 2-chloro-6-methylbenzoic acid were developed: one based on nucleophilic aromatic substitution and the other based on carbonylation. In the first approach, 2-chloro-6-fluorobenzaldehyde was converted to its n-butylimine, then treated with 2 equiv of methylmagnesium chloride in THF to give, after hydrolysis, 2-chloro-6-methylbenzaldehyde. Subsequent oxidation of this compound gave the title compound in 85% overall yield. In the second approach, 3-chloro-2-iodotoluene was efficiently carbonylated in methanol to give methyl 2-chloro-6-methylbenzoate, which after hydrolysis afforded the title compound in 94% yield (84% yield after recrystallization). The carbomethoxylation proceeded smoothly even at a high substrate-to-Pd ratio of 10 000. Both methods do not require isolation of intermediates and are suitable for the preparation of kilogram quantities of 2-chloro-6-methylbenzoic acid.
- Daniewski, Andrzej R.,Liu, Wen,Puentener, Kurt,Scalone, Michelangelo
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Read Online
- Deep compositional understanding of TBA: AlCl3 ionic liquid for its applications
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Chloroaluminate ionic liquids (ILs) have been immensely used as homogeneous catalyst in Friedel-Crafts reaction. We have recently synthesized chloroaluminate ILs by reacting aluminium chloride with a hydrophobic neutral ligand i.e. tributylamine (TBA:AlCl3). The current study elaborates on the investigations of the composition of the ionic liquids at various stages of their formation. The ionic liquids were synthesized using various mole ratios of tributyl amine and aluminium chloride in range of 1:1 to 1:2.3, in presence of an aromatic solvent in a one pot reaction. Various characterization techniques like Mass spectrometry, 27Al Nuclear Magnetic Resonance, 31P Nuclear Magnetic Resonance and Fourier Transform Infrared spectroscopy were used to elucidate the formation of various moieties of the TBA:AlCl3 Ionic Liquid. This study also elaborates on the investigations of the cationic and anionic moieties and their structure-property relationship for various applications. Various Friedel-Crafts reaction of industrial importance were performed using the ionic liquid having (Al2Cl7)?moiety to assess its performance and compared with conventional processes. The synthesized products were characterised by sophisticated analytical techniques like 1H NMR, 13C NMR, FTIR, GC–MS, GC-FID, to name a few. This class of ionic liquids also have importance in various electrochemical applications like aluminium deposition and aluminium batteries.
- Bhakthavatsalam, Vishnupriya,Chandra, Sudeshna,Choudhury, Rudra Prosad,Lande, Sharad V.,Pradhan, Jeevan,Sakhalkar, Mangesh
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- Catalytic Reductions Without External Hydrogen Gas: Broad Scope Hydrogenations with Tetrahydroxydiboron and a Tertiary Amine
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Facile reduction of aryl halides with a combination of 5% Pd/C, B2(OH)4, and 4-methylmorpholine is reported. Aryl bromides, iodides, and chlorides were efficiently reduced. Aryl dihalides containing two different halogen atoms underwent selective reduction: I over Br and Cl, and Br over Cl. Beyond these, aryl triflates were efficiently reduced. This combination was broadly general, effectuating reductions of benzylic halides and ethers, alkenes, alkynes, aldehydes, and azides, as well as for N-Cbz deprotection. A cyano group was unaffected, but a nitro group and a ketone underwent reduction to a low extent. When B2(OD)4 was used for aryl halide reduction, a significant amount of deuteriation occurred. However, H atom incorporation competed and increased in slower reactions. 4-Methylmorpholine was identified as a possible source of H atoms in this, but a combination of only 4-methylmorpholine and Pd/C did not result in reduction. Hydrogen gas has been observed to form with this reagent combination. Experiments aimed at understanding the chemistry led to the proposal of a plausible mechanism and to the identification of N,N-bis(methyl-d3)pyridin-4-amine (DMAP-d6) and B2(OD)4 as an effective combination for full aromatic deuteriation. (Figure presented.).
- Korvinson, Kirill A.,Akula, Hari K.,Malinchak, Casina T.,Sebastian, Dellamol,Wei, Wei,Khandaker, Tashrique A.,Andrzejewska, Magdalena R.,Zajc, Barbara,Lakshman, Mahesh K.
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supporting information
p. 166 - 176
(2020/01/02)
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- Generation of Phosphoranyl Radicals via Photoredox Catalysis Enables Voltage-Independent Activation of Strong C-O Bonds
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Despite the prevalence of alcohols and carboxylic acids as functional groups in organic molecules and the potential to serve as radical precursors, C-O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen-centered nucleophile. We show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H atom trapping to afford the deoxygenated products. Using the same method, we demonstrate access to synthetically versatile acyl radicals, which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radical cyclizations to forge C-O, C-N, and C-C bonds in a single step.
- Stache, Erin E.,Ertel, Alyssa B.,Rovis, Tomislav,Doyle, Abigail G.
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p. 11134 - 11139
(2018/11/21)
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- A process for preparing O-toluene
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The present invention provides a process for preparing dichloro toluene, relates to the field of preparation of organic intermediates. The invention relates to 2, 3 - dichloro toluene, 2, 4 - dichloro toluene and 2, 5 - dichloro toluene in more than one type of raw materials, supported palladium as the catalyst, a fixed bed continuous reaction preparation of O-toluene. This invention uses the industrial by-product 2, 3 - dichloro toluene, 2, 4 - dichloro toluene and 2, 5 - dichloro toluene as the raw materials, supported palladium catalyst good selectivity, long-time use, O-chlorotoluene high yield.
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Paragraph 0015-0018
(2018/10/11)
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- Decarbonylation of Aromatic Aldehydes and Dehalogenation of Aryl Halides Using Maghemite-Supported Palladium Catalyst
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A facile decarbonylation reaction of a variety of aromatic and heteroaromatic aldehydes using maghemite-supported palladium catalyst has been developed. The magnetic properties of catalyst facilitated an easy and efficient recovery of the catalyst from the reaction mixture using an external magnet. It was found that the catalyst could be reused up to four consecutive catalytic runs without a significant change in activity. In addition, the catalyst was also very effective in the dehalogenation of aryl halides. This is the first report on efficient utilization of directly immobilized Pd on maghemite in decarbonylation and dehalogenation reactions.
- Ajda?i?, Vladimir,Nikoli?, Andrea,Simi?, Stefan,Manojlovi?, Dragan,Stojanovi?, Zoran,Nikodinovic-Runic, Jasmina,Opsenica, Igor M.
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p. 119 - 126
(2017/12/27)
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- Substd. photoisomerization arom. compd. method
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Isomerizing substituted aromatic compounds (I), comprises carrying out isomerization in the presence of a salt melt, which contains a metal compound (II) and at least one metal compound (III). Isomerizing substituted aromatic compounds of formula (Ar1-R n) (I) or their mixtures, comprises carrying out isomerization in the presence of a salt melt, which contains a metal compound of formula ([M1][X1] m 1) (II) and at least one metal compound of formula ([M2][X2] m 2) (III). Ar1 : n-valent aryl radical; R : halo, alkyl, fluoroalkyl, aryl, alkyl-aryl or amino; M1 : Al, Ga, In, Cu, Fe, Co or Ni; X1, X2 : halo, preferably Cl or Br; M2, m2 : alkaline earth metal or alkali metal, where M2 is preferably Li, Na, or K; m1 : Al, Ga, In, Fe(III), Co, Ni or Cu(II); and n : >= 2, preferably 2.
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Paragraph 0065
(2017/01/02)
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- The ortho-substituent effect on the Ag-Catalysed decarboxylation of benzoic acids
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A combined experimental and computational investigation on the Ag-catalysed decarboxylation of benzoic acids is reported herein. The present study demonstrates that a substituent at the ortho position exerts dual effects in the decarboxylation event. On one hand, ortho-substituted benzoic acids are inherently destabilised starting materials compared to their meta- And para-substituted counterparts. On the other hand, the presence of an ortho-electron-withdrawing group results in an additional stabilisation of the transition state. The combination of both effects results in an overall reduction of the activation energy barrier associated with the decarboxylation event. Furthermore, the Fujita- Nishioka linear free energy relationship model indicates that steric bulk of the substituent can also exert a negative effect by destabilising the transition state of decarboxylation.
- Grainger, Rachel,Cornella, Josep,Blakemore, David C.,Larrosa, Igor,Campanera, Josep M.
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supporting information
p. 16680 - 16687
(2015/03/05)
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- Cu(I)/cu(II)/TMEDA, new effective available catalyst of sandmeyer reaction
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The system Cu(I)/Cu(II)/N,N,N',N'-tetramethylethylenediamine is a highly effi cient and accessible catalyst of Sandmeyer reaction. The reaction of aryldiazonium salts with chlorides, bromides cyanides, and thiocyanates of alkaline metals in the presence of this catalytic system leads to the formation of the corresponding aryl halides, nitriles, and thiocyanates in high yields.
- Sigeev, A. S.,Beletskaya, I. P.,Petrovskii, P. V.,Peregudov, A. S.
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p. 1055 - 1058,4
(2020/10/15)
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- IMPROVED METHOD FOR THE PREPARATION OF ENANTIOMERICALLY ENRICHED SECONDARY ALCOHOLS BY THE ADDITION OF ORGANOALUMINIUM REAGENTS TO CARBONYL COMPOUNDS
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A process for converting a carbonyl group within a substrate to a chiral alcohol moiety comprising reacting the carbonyl containing substrate with an organoaluminium reagent in the presence of a Group 5-12 transition metal based catalyst which is complexed with a chiral ligand; novel chiral ligands and organoluminium reagents, a chiral ligand or organoaluminium reagent for use in the process.
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Page/Page column 24-25
(2008/06/13)
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- PROCESS FOR HALOGENATION OF BENZENE AND BENZENE DERIVATIVES
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In a process of halogenation of benzene or benzene derivatives, di-substituted halobenzene derivatives having para-aromatic compounds or tri-substituted halobenzene derivatives having 1,2,4-substituted aromatic compounds are selectively produced. In halogenation of benzene or benzene derivatives, a fluorine-containing zeolite catalyst such as L-type zeolite, or a zeolite catalyst having the crystal size of at most 100 nm is used. The reaction is preferably effected in the presence of a solvent, and the solvent is preferably a halogenated compound.
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Page/Page column 17; 18
(2008/06/13)
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- pH effects on ethanolysis of some arenediazonium ions: Evidence for homolytic dediazoniation proceeding through formation of transient diazo ethers
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The effects of pH on the observed rate constants (kobsd.) and on the solvolytic dediazoniation product distributions of ethanolysis of 2-, 3-, and 4-methylbenzenediazonium ions (2MBD, 3MBD, and 4MBD, respectively) were determined by a combination of spectrophotometric (UV/Vis) and Chromatographic (HPLC) techniques. The variation of both kobsd. and product yields with pH follow S-shaped curves with inflection points at pH ≈ 3.6, depending on solvent composition. With increasing pH, kobsd. values increase by factors of up to about 4 (2MBD), about 3 (3MBD), and about 50 (4MBD) with respect to the kobsd. values at low pH. HPLC analyses of the reaction mixtures show that only heterolytic products are obtained at low pH, indicating that solvolytic dediazoniation takes place through an ionic mechanism, but an increase in pH favors homolytic dediazoniation, with quantitative conversion into the reduction product toluene being obtained at pH ≥ 6 (4MBD), indicating that a turnover from the heterolytic to the homolytic mechanisms is taking place under experimental conditions under which insignificant amounts of EtO- or OH- should be present in solution. The obtained S-shaped profiles suggest that the initiation process of the homolytic pathway is the result of the formation of a highly unstable transient diazo ether complex and not by direct electron transfer from the solvent (EtOH) to the arenediazonium ions as is currently believed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Pazo-Llorente, Roman,Bravo-Diaz, Carlos,Gonzalez-Romero, Elisa
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p. 3221 - 3226
(2007/10/03)
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- Electroreduction of Organic Compounds, 34 [1]. Cathodic Dehalogenation of Chloroarenes with Electron-Donating Substituents
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The electrochemical reduction of chlorinated arenes with electron-donating substituents, i.e. chlorotoluenes, -anisoles and -phenols, is studied. Preparative electrolyses are run in various solvent-supporting electrolytes under potentiostatic and galvanostatic conditions at lead or carbon cathodes. A partial and mostly regioselective hydrodechlorination of compounds with two or more chloro substituents is possible under suitable conditions. The replacement of one single chloro substituent, in particular in a para-position, is difficult. Highly toxic and persistent oligochloro derivatives are thus transformed into less problematic compounds with a low degree of chlorination. The chlorine content of real-life materials such as extracts of soil contaminated with chlorinated phenols and Nitrofen can also be significantly decreased by electroreduction.
- Kranz, Olaf,Voss, Jürgen
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p. 1187 - 1200
(2007/10/03)
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- Solvolysis of some arenediazonium salts in binary EtOH/H2O mixtures under acidic conditions
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We have determined the product distribution, the rate constants for dediazoniation product formation, and the solvolytic rate constants for 2-, 3-, and 4-methylbenzenediazonium ions (2-, 3-, and 4-MBD, respectively) loss in acidic ethanol/water mixtures over the whole composition range by a combination of spectrophotometric (UV/Vis) and high performance liquid chromatography (HPLC) measurements. The observed rate constants (kobs) for substrate loss are equal to those for product formation, and they remain essentially constant (2-MBD) with changing solvent composition but increase by a factor of ≈2 (4MBD) on going from water to 100% EtOH. Up to four dediazoniation products - cresols (ArOH), chlorotoluene (ArCl), methylphenetole (ArOEt), and toluene (ArH) - were detected, depending on the solvent composition; the major dediazoniation products were the ArOH and ArOEt derivatives. The product selectivity (S) of the reaction towards nucleophiles is low and essentially constant with changing solvent composition, and good linear correlations between log kobs and Yc1 (solvent ionizing power) were observed for the three ArN2+ ions. All data are consistent with the rate-determining formation of an aryl cation, which reacts immediately with available nucleophiles. The data suggest that the distribution of neutral and anionic nucleophiles in the neighborhood of the ground state arenediazonium ion remains essentially unchanged upon dediazoniation, the observed product distribution reflecting the concentrations of nucleophiles in their immediate environment (i.e., in the first solvation shells of the arenediazonium ions). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Pazo-Llorente, Roman,Bravo-Diaz, Carlos,Gonzalez-Romero, Elisa
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p. 3421 - 3428
(2007/10/03)
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- Continuous-flow generation of anhydrous diazonium species: Monolithic microfluidic reactors for the chemistry of unstable intermediates
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Monolithic microfluidic reactors for the safe, expedient, and continuous synthesis of products involving unstable intermediates were fabricated and assessed. The formation of diazonium salts in anhydrous conditions and their subsequent in situ chlorination within microfiuidic channels under hydrodynamic pumping regimes is presented. Significant enhancements in yield were observed due to enhanced heat and mass transfer in microfluidic systems. Analysis performed using off-line GC and GC-MS was compared with on-line, on-chip Raman spectroscopy for the direct determination of analytes.
- Fortt, Robin,Wootton, Robert C. R.,De Mello, Andrew J.
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p. 762 - 768
(2013/09/05)
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- Induced thermolysis of tert-butyl phenylperacetates by thiophenol: Simultaneous occurrence of homolysis and single electron transfer
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Thermolysis of tert-butyl phenylperacetates in the presence of thiophenol takes place via dual mechanism. The two-bond homolysis indicates ρH+ = -1.16, testifying to polar transition states. The single electron transfer yields a radical anion intermediate which undergoes fragmentation with ρET = 1.01.
- Sung Soo Kim,Tuchkin,Chun Soo Kim
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p. 7738 - 7740
(2007/10/03)
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- Formation and decomposition of chloroaromatic compounds in chlorine-containing benzene/oxygen flames
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Premixed chlorine-containing, fuel-rich, low-pressure benzene/oxygen flames were analysed for the formation of (oxygenated) chloroaromatic compounds and their radicals by means of the condensation/radical-scavenging method (Hausmann, M., Homann, K.-H., 1995. Ber. Busenges. Phys. Chem. 99, 853-862). Several chlorinated organic compounds (methyl chloride, t-butyl chloride, chlorobenzene, chloroform) were used as additives within a maximum concentration of 10% of total fuel. Product identification and quantification were performed by GC/MS. The extent of formation of chloroaromatic compounds in these flames was largest in the cases of chlorobenzene and chloroform as additives. For chlorobenzene, 12 different chloroaromatics could be analysed in between C7H7Cl and C12H9Cl. Their formation is mainly due to conversion of initial chlorobenzene into substituted or oxidised derivatives, or growth products. Additional chlorination of aromatics is shown to be of minor importance in chlorobenzene-containing flames. Three isomeric (o/m/p) scavenging products could be identified for the chlorophenyl radical. In the chloroform case, 15 chloroaromatics could be analysed in between C6H5Cl and C14H9Cl. The weak C-Cl bond in chloroform is responsible for the high extent of chloroaromatics formation, either by Cl abstraction from the additive or by chlorination reactions via Cl radicals. Additionally, specific pathways to (di)chloroaromatics and chlorinated fulvene-type structures are outlined via CHCl2 and CCl2 radicals.
- Burfeindt,Homann
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p. 439 - 447
(2007/10/03)
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- Competitive homolytic and heterolytic dediazoniation mechanisms: Rate constants and product distribution of methoxy-, hydroxy-, and hydro-dediazoniation of 3- and 4-methylbenzenediazonium salts in acidic MeOH/H2O mixtures
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The rates and product distribution for methoxy-, hydroxy- and hydro-dediazoniation and the rate constants for disappearance of 3- and 4-methylbenzenediazonium tetrafluoroborate in acidic MeOH/H2O mixtures, in the presence and absence of electrolytes like HCl, NaCl, and CuCl2, are reported. Data were obtained by using a combination of VIS-UV and HPLC techniques. The kinetics and product distributions are completely consistent with competitive homolytic and heterolytic mechanisms, the heterolytic one being predominant at any solvent composition. Heterolytic data are in agreement with the predictions of a DN+AN mechanism; that is, rate determining formation of an aryl cation that reacts immediately with available nucleophiles. Selectivity values, determined from product yields, are low and independent of solvent composition. Product formation is discussed in terms of a preassociation step between aryl cations and the nucleophile, which does not account for much of the trapping, and a nucleophilic attack on a `free' arenediazonium cation. Activation parameters were also determined at 99.5% MeOH: enthalpies of activation are high and entropies of activation are positive, and they are similar to those reported for pure water.
- Pazo-Llorente, Roman,Gonzalez-Romero, Elisa,Bravo-Diaz, Carlos
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p. 210 - 220
(2007/10/03)
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- Halodediazoniations of dry arenediazonium o-benzenedisulfonimides in the presence or absence of an electron transfer catalyst. Easy general procedures to prepare aryl chlorides, bromides, and iodides
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The paper reports the results of a wide study aimed at preparing aryl chlorides 3 (19 examples), bromides 4 (19 examples), and iodides 5 (9 examples) by halodediazoniation of dry arenediazonium o-benzenedisulfonimides 1 with tetraalkylammonium halides 2. The reactions were carried out in anhydrous acetonitrile at room temperature (~20 °C) in the presence of copper powder and at 60 °C or room temperature without the catalyst. In optimal conditions the yields were from good to excellent (60 reactions, 61- 94% yield), with only a few exceptions (8 reactions, 51-55% yield). A good amount of the o-benzenedisulfonimide (7) was always recovered from the reactions and could then be reused to prepare salts 1. An interesting aspect of this research is the surprising role of the anion of o- benzenedisulfonimide (9) as an electron transfer agent.
- Barbero,Degani,Dughera,Fochi
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p. 3448 - 3453
(2007/10/03)
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- Hydroxy- and chloro-dediazoniation of 2- and 3-methylbenzenediazonium tetrafluoroborate in aqueous solution
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We have measured the rates and product yields of dediazoniation of 2- and 3-methylbenzenediazonium tetrafluoroborate in the presence and absence of electrolytes like HCl, NaCl, and CuCl2 using a recently reported methodology that allows simultaneous determination of product concentrations and rates of product formation and, indirectly, loss of starting material. Activation parameters were also obtained: enthalpies of activation are high, and entropies of activation are positive. All results are consistent with a heterolytic mechanism involving the fragmentation of the arenediazonium ion into a very reactive phenyl cation.
- Pazo-Llorente, Roman,Sarabia-Rodriguez, Maria Jose,Bravo-Diaz, Carlos,Gonzalez-Romero, Elisa
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- Benzopyridazinone and pyridopyridazinone compounds
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Benzo or pyridopyridazinones and pyridazinthiones of the formula STR1 wherein: X and Y are nitrogen or carbon, provided that at least one is carbon, and Z is oxygen or sulfur; R1 is hydrogen, lower alkyl, aryl, aralkyl, heterocyclo, heterocyclo lower-alkyl, heteroaryl, or heteroaralkyl; R2, R3, R4, R5 and R6 are independently selected from hydrogen, lower alkyl, halo, carboxy, alkoxycarbonyl, carbamoyl, lower-alkyl carbonyl, halocarbonyl, thiomethyl, trifluoromethyl, cyano or nitro; or a pharmaceutically acceptable ester, ether or salt thereof, have been found to be useful as an anti-inflammatory, antasthmatic, immunosuppressive, anti-allograft rejection, anti-graft-vs-host rejection, autoimmune disease or analgetic agent(s).
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- Arenediazonium tetrachlorocuprates(ii). Modification of the meerwein and sandmeyer reactions
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In the copper-catalysed reactions of arenediazonium chlorides with unsaturated compounds arenediazonium tetrachlorocuprates(II) are formed as intermediates. A general method of preparation of these complexed diazonium salts is described. In polar solvents these salts undergo chlorinative dediazoniation to give chloroarenes in high yield. The reaction of an arenediazonium tetrachlorocuprate(II) with an activated alkene results in the same products as the Meerwein reaction. A radical cation mechanism for this reaction is proposed.
- Obushak, Mykola D.,Lyakhovych, Mykhaylo B.,Ganushchak, Mykola I.
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p. 9567 - 9570
(2007/10/03)
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- Mechanism of the Solution-Phase Reaction of Alkyl Sulfides Atomic Hydrogen. Reduction via a 9-S-3 Radical Intermediate
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The low selectivity of benzyl alkyl sulfide fragmentation subsequent to its reaction with atomic hydrogen is indicative of a reaction that proceeds via an early transition state. The competitive reduction of a series of substituted-benzyl alkyl sulfides was insensitive to the substituent on the aromatic ring (ρ = -0.13, r = 0.99). The relative rates of fragmentation of a series of the substituted-benzyl alkyl sulfides gave a V-shaped Hammett plot. Both electron-donating and electron-withdrawing groups destabilized the transition state (ρ = +0.99, r = 0.999; ρ = -0.82, r = 0.992). Since the relative rates of disappearance of the alkyl benzyl sulfides are not substituent dependent, but the relative rates of fragmentation are, a 9-S-3 intermediate is preferred as the structure leading to products.
- Tanner, Dennis D.,Koppula, Sudha,Kandanarachchi, Pramod
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p. 4210 - 4215
(2007/10/03)
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- Direct Formation of (Haloaryl)copper Nucleophiles from Haloiodobenzenes and Active Copper
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(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)
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- Base Cleavage of the Benzyl-Silicon Bonds in m-ClC6H4CH2SiMe(OH)2 and m-ClC6H4CH2Si(OH)3. Proposed Formation of Metasilicate Intermediates
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A kinetic study of the base-catalysed cleavage of the diol RSiMe(OH)2 (R = m-ClC6H4CH2) in Me2SO-H2O or MeOH-H2O has indicated that at high base concentrations the main process is the unimolecular dissociation of the dianion RSiMe(O-)2 into R- and Me(O-)Si=O (an analogue of acetate ion), both of which then react rapidly with the solvent.Likewise for the triol RSi(OH)3 in Me2SO-H2O the main process appears to be the formation of R- and the metasilicate ion HO(O-)Si=O from the dianion R(OH)Si(O-)2.Base cleavage of the silanols RSiMe2OH (R = PhCH2 or m-ClC6H4CH2) in Me2SO-H2O probably involves a contribution from the unimolecular dissociation of the anion RSiMe2O- to give R- and Me2Si=O.
- Chmielecka, Jadwiga,Chojnowski, Julian,Stanczyk, Wlogdzimierz A.,Eaborn, Colin
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p. 865 - 872
(2007/10/02)
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- Silylative Decarbonylation: A New Route to Arylsilanes
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A new synthetic procedure for the preparation of aromatic chlorosilanes via the palladium-catalyzed reaction of methylchlorodisilanes and aromatic acid chloride is described.The silylative decarbonylation process is solventless, can utilize low metal catalyst loadings (500-1000 ppm Pd), is carried out under moderate conditions (145 deg C), and selectively gives aromatic chlorosilanes in good yield, generally 60-85percent.The procedure is tolerant of a variety of aromatic substituents, for example, alkyl, halo, nitro, cyano, imide, acid anhydride, etc., and the synthesis ofseveral new substituted aromatic chlorosilanes containing benzoyl chloride and phthalic anhydride moieties is described.Chloromethyldisilane starting reagents are available from the direct reaction of methyl chloride and silicon, making this methodology an attractive synthetic route to functionalized aromatic chlorosilanes.
- Rich, Jonathan D.
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p. 5886 - 5893
(2007/10/02)
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- Decomposition of Dibenzyl Ether Over Alumina
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Dibenzyl ether decomposes over alumina at 340 deg C to yield mainly benzaldehyde and toluene.Evidence for the dissociative adsorption of the ether and disproportionation of two neighbouring benzyl oxide species by intermolecular hydride transfer is presented.
- Ananthan, S.,Ganesan, K.,Pillai, C. N.
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p. 512 - 513
(2007/10/02)
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- Vapor-Phase Isomerization of o-Chlorotoluene over H-Mordenite Treated with CF3Cl
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Vapor-phase isomerization of o-chlorotoluene was somewhat promoted by H-mordenite (HM).The catalytic activity was appreciably enhanced by treatment with CF3Cl and other chlorofluorocarbons such as CF2ClCF2Cl and CF2ClCF3.In particular, maintenance of the HM catalyst activity was remarkably improved by CF3Cl treatment.The CF3Cl-treated HM also promoted vapor phase isomerization of p- and m-chlorotoluene.The catalytic activity was relatively long-lasting for the isomerization of p-chlorotoluene.Enlargement of the HM pore size on treatment with CF3Cl and other chlorofluorocarbons may contribute to increasing the catalytic activity and then maintaing it.
- Okazaki, Susumu,Jouhouji, Hirofumi
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p. 1931 - 1936
(2007/10/02)
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- ALKYLATION OF CHLOROBENZENE WITH CH3OH OVER H-MORDENITE TREATED WITH CHLOROFLUOROBENZENE
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The vapor phase alkylation of chlorobenzene was promoted by H-mordenite treated with chlorofluoromethane.Ortho alkylation was preferentially promoted in the catalyticreaction after process times of 1 h.
- Horie, Osamu,Okazaki, Susumu
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p. 1089 - 1090
(2007/10/02)
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- Reaction of Diazonium Salts with Transition Metals. 8. Palladium-Catalyzed Carbon-Carbon Coupling of Arenediazonium Salts with Organotin Compounds
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Arenediazonium salts are effectively functionalized with a methyl or vinyl group by palladium-catalyzed coupling with organotin compounds in acetonitrile at room temperature.Fairly good yields were obtained irrespective of the nature of a substituent on the aromatic ring, including a nitro group.Transformation of the diazonium group can proceed chemoselectively even in the presence of halogen substituents.
- Kikukawa, Kiyoshi,Kono, Kiyoshi,Wada, Fumio,Matsuda, Tsutomu
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p. 1333 - 1336
(2007/10/02)
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- REACTION OF 1,3-ALKADIENES WITH ARENEDIAZONIUM CHLORIDES IN THE PRESENCE OF IRON(II) CHLORIDE
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The reaction of arenediazonium chlorides with 1,3-alkadienes in the presence of iron(II) chloride was investigated.It was established that the reaction takes place with the formation of products from chloroarylation of the dienes, telomerization, and additive dimerization.A method is proposed for the synthesis of diaryloctatetraenes containing substituents in the aromatic rings and in the aliphatic chain.
- Ganushchak, N. I.,Obushak, N. D.,Polishchuk, O. P.
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p. 633 - 639
(2007/10/02)
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- EFFECTS OF VARYING THE MEDIA FOR BASE CLEAVAGE OF SOME BENZYL-SILICON AND-TIN COMPOUNDS IN ALCOHOLS
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The effects on the rates of cleavage of 3-ClC6H4CH2MMe3 and 3,5-Cl2C6H3CH2MMe3 compounds with M = Si and Sn have been examined for (a) various concentrations of NaOMe-MeOH; (b) various concentrations of H2O in NaOH-H2O-MeOH; and (c) variation of R from Me to Et, i-Pr and t-Bu for metal alkoxide-ROH mixtures.Rates have also been measured for cleavages in NaOCH2CF3HOCH2CF3-Me2SO.In all cases there are differences in behaviour between the silicon and tin compounds which are consistent with the postulated difference in the mechanisms of their reactions.
- Eaborn, Colin,Mahmoud, Foad M.S.
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- Reactivities of Several Nucleophiles toward 4-Methylbenzyne in Very Hot Water
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By means of competition experiments, the relative rates of reaction of several nucleophiles with 4-methylbenzyne in aqueous solution at temperatures up to 318 deg C have been determined.The relative nucleophilicities vs. chloride ion are as follows: PhS-, 46; I-, 6.2; piperidine, 3.0; Br-, 1.7; aniline, 1.3; Cl-, (1.0); PhO-, 1.0; ammonia, 0.55; F-, 0.20.For all but PhS-, piperidine, and iodide, the p/m product ratio is 0.83+/-0.02.In the cases of PhS- and piperidine a competing mechanism of ipso substitution, probably involving catalysis by copper ions, caused the observed p/m ratios to be high and variable.Our experimental design precluded determination of the p/m ratio for iodide ion.Because of chemical complications, only rough estimates could be made of the nucleophilicities of nitrite and benzenesulfinate ions.
- Zoratti, Mario,Bunnett, J. F
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p. 1776 - 1782
(2007/10/02)
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- Polar Radicals. 14. On the Mechanism of Trialkylstannane Reductions. Positive ρ Values for the Tri-n-butylstannane Reduction of Benzyl Halides. A Correlation with ?-
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The relative reactivities towards reduction by tri-n-butylstannane of a series of substituted benzyl halides have been determined.The order of reactivity was shown to be I > Br > Cl, the same as that reported for alkyl halide reductions.Under the reaction conditions (90 deg C, benzene as solvent, benzoyl peroxide initiation), both aralkyl and alkyl fluorides were shown to be completely unreactive.Activation energies were estimated for the direct abstraction of halogen by tri-n-butyl radicals, and on the basis of these estimates all of the halogens would be predicted to readily undergo abstraction.To explain the non-reactivity of the fluorides several other mechanisms were considered: reversible tin radical addition to the halogen to form an intermediate with an expanded octet, and a free radical chain mechanism involving an electron-transfer reaction between the trialkyltin radical and the benzyl halide. The benzyl halide reductions showed excellent Hammett correlations with positive ρ values; all of these correlations were obtained using ?- substituent constants.The demonstration (the first ever reported) that ?- substituent constants correlate with the relative reactivities for reduction infers that bond breaking takes place in the transition state for the reaction.The magnitudes of the ρ values were not found, as were expected, to be in the inverse order of the relative reactivities: ρ for the iodides (+0.81), for the bromides (+0.17), and for the chlorides (+0.34).To explain the anomalously high value of ρ found for the iodide reduction, it was suggested that the benzyl iodides underwent reduction by a different mechanism than the chlorides and the bromides.The relative rates of reduction of the benzyl iodides in a more polar solvent than benzene, acetonitrile, showed decreased sensitivity to substituents, whereas the reduction of the bromides and chlorides was relatively insensitive to solvent effects.
- Blackburn, Edward V.,Tanner, Dennis D.
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p. 692 - 697
(2007/10/02)
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- Indenylacetic acid compounds
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4, 5, 6 or 7 Aryl substituted indenyl acetic acids and pharmaceutically acceptable salts, amides and esters thereof. The 4, 5, 6 or 7 aryl substituted indenyl acetic acids have anti-inflammatory, anti-pyretic and analgesic activity. The invention also includes methods for the preparation of these compounds, pharmaceutical compositions and methods of treating inflammation by administering these particular compounds to patients.
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