- Specific features of solvation effects in monomolecular and bimolecular solvolysis
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A method was suggested for distinguishing monomolecular and bimolecular solvolysis on the basis of reaction kinetics in water, MeOH, EtOH, i-PrOH, cyclohexanol, and t-BuOH. In solvolysis of n-PrBr, CH2=CHCH2Br, PhCOCl, and MeOClO3 (SN2 reactions), a linear correlation is observed between log k and the solvent ionizing power Z, whereas in solvolysis of t-BuBr, t-BuCl, and 1-AdI (SN1, E1 reactions) this correlation is nonlinear. Deviations from linearity are due to steric hindrance decreasing the negative effect of nucleophilic solvation.
- Ponomarev,Michkov,Dvorko
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- Controlling the Lewis Acidity and Polymerizing Effectively Prevent Frustrated Lewis Pairs from Deactivation in the Hydrogenation of Terminal Alkynes
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Two strategies were reported to prevent the deactivation of Frustrated Lewis pairs (FLPs) in the hydrogenation of terminal alkynes: reducing the Lewis acidity and polymerizing the Lewis acid. A polymeric Lewis acid (P-BPh3) with high stability was designed and synthesized. Excellent conversion (up to 99%) and selectivity can be achieved in the hydrogenation of terminal alkynes catalyzed by P-BPh3. This catalytic system works quite well for different substrates. In addition, the P-BPh3 can be easily recycled.
- Geng, Jiao,Hu, Xingbang,Liu, Qiang,Wu, Youting,Yang, Liu,Yao, Chenfei
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p. 3685 - 3690
(2021/05/31)
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- Tailoring Interfacial Lewis Acid-Basic Pair on ZnO/4Mg1ZrOx Allows Dehydrogenative α-Methylenation of Alcohols with Methanol to Allylic Alcohols
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Allylic alcohols are the essential building blocks widely used in diverse streams of organic inventions for pharmaceuticals, fragrances, agrochemicals and polymers. Currently, allylic alcohols are industrially produced from petroleum-based feedstocks via atom uneconomic processes. More sustainable synthesis route for allylic alcohols is limited. Herein, a methodology for the direct and highly selective production of allylic alcohols has been accomplished by controlled dehydrogenative α-methylenation of alcohols with methanol. This transformation is enabled by interfacial Lewis acid-basic pair on tailor-made ZnO/4Mg1ZrOx mixed oxide. High selectivity (83~92%) of allylic alcohols is the consequence of alcohols acceptorless dehydrogenation to liberation of H2 and Meerwein-Ponndorf-Verley type hydrogen transfer onto C = O bonds of unsaturated aldehydes. Furthermore, the prepared ZnO/4Mg1ZrOx mixed oxide shows good stability after 200 h time on stream test. These observations could additionally allow us to design multifunctional solid acid-basic catalysts for the transformations of renewable oxygenates into value-added chemicals.
- Fu, Aixiao,Jiang, Shifeng,Liu, Qiang,Liu, Xiaoran,Liu, Xiuyun,Mu, Xindong,Sun, Mengqing,Wang, Xicheng,Xu, Guoqiang,Zhao, Lingling
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- Iron-Catalyzed Ring-Closing C?O/C?O Metathesis of Aliphatic Ethers
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Among all metathesis reactions known to date in organic chemistry, the metathesis of multiple bonds such as alkenes and alkynes has evolved into one of the most powerful methods to construct molecular complexity. In contrast, metathesis reactions involving single bonds are scarce and far less developed, particularly in the context of synthetically valuable ring-closing reactions. Herein, we report an iron-catalyzed ring-closing metathesis of aliphatic ethers for the synthesis of substituted tetrahydropyrans and tetrahydrofurans, as well as morpholines and polycyclic ethers. This transformation is enabled by a simple iron catalyst and likely proceeds via cyclic oxonium intermediates.
- Biberger, Tobias,Makai, Szabolcs,Lian, Zhong,Morandi, Bill
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supporting information
p. 6940 - 6944
(2018/05/14)
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- On the miscibility of ethers and perfluorocarbons. An experimental and theoretical study
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Despite their significant polar character, some organic ethers such as diethyl ether were found to be miscible with perfluorocarbon solvents. Solubilities of various ethers in perfluorocarbons and miscibility temperatures were determined. These properties were found to be greatly dependent on the polarity but also size and shape of the ether molecule. Theoretical calculations of the miscibility temperatures of organic solvents and perfluorocarbons using COSMO-RS method were correlated with experimental data. Considering the difficulties in the accurate description of the macroscopic properties, such as miscibility temperatures, from the first principles, the agreement between experimental and theoretical data is reasonable.
- Babiak, Peter,Němcová, Adriana,Rulí?ek, Lubomír,Beier, Petr
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p. 397 - 401
(2008/12/21)
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- METHOD FOR THE PRODUCTION OF ISOPROPENYL ETHERS
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The invention relates to a method for the production of isopropenyl ethers of formula (A), wherein R represents an aliphatic, cycloaliphatic, aralyphatic, aromatic or heterocyclic radical which can include other substituents which do not react with acetylenes or allens, by reacting a gaseous flow (I), containing MAPD which is obtained from an olefin system and which is used to separate C3-sections, with at least one gaseous flow selected from a gaseous flow (II) containing an acetone ketal of formula (B), wherein R has the above-mentioned meaning, and a gaseous flow (III) containing a monohydroxyalcohol ROH, wherein R has the above-mentioned meaning, in the presence of a heterogeneous catalyst.
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Page/Page column 14
(2010/02/13)
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- Reaction network of aldehyde hydrogenation over sulfided Ni-Mo/Al 2O3 catalysts
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A reaction network of aldehyde hydrogenation over NiMoS/Al 2O3 catalysts was studied with aldehydes with straight and branched carbon chains and different chain lengths as feed materials. The reactions in the gas phase and the liquid phase were compared. The main reaction in the aldehyde hydrogenation process is the hydrogenation of the CO double bond, which takes place over the coordinatively unsaturated sites. The major side reactions are self-condensation of aldehydes and condensation of aldehydes with alcohols. Both reactions involve α-hydrogen and are primarily catalyzed by acid-base bifunctional sites over the exposed Al2O 3 surfaces.
- Wang, Xueqin,Saleh, Ramzi Y.,Ozkan, Umit S.
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- Trends in alkyl substituent effects on nucleophilic reactions of carbonyl compounds: Gas phase reactions between ammonia and R1R2COCH3+ oxonium ions
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The reactivity of carbonyl substituted methyl oxonium ions (R1R2COCH3-) towards ammonia has been investigated using an FT-ICR mass spectrometer and ab initio calculations. The monosubstituted ions (R1=H: R2 = H, CH3, C2H5 and i-C3H7) show different reaction patterns with variable degree of: (1) nucleophilic substitution, (2) addition elimination and (3) proton transfer, when reacted with ammonia. In all cases addition-elimination dominates over nucleophilic substitution, and the observed reactions are slow. The trends in reactivity are consistent with the alkyl group's electronic properties, as expressed by a single parameter linear or slightly non-linear model.
- Bache-Andreassen, Lihn,Uggerud, Einar
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p. 705 - 713
(2007/10/03)
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- Transformation of vinyloxirane on Pt-SiO2 and Pd-SiO2
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The transformation of vinyloxirane and ethyloxirane were studied on Pt-SiO2 and Pd-SiO2 catalysts at 273 and 301 K in a recirculation reactor, in the presence of hydrogen or deuterium. There are significant differences, not only in reaction rates, but also in reaction routes, depending upon the nature of the metal. The main reaction routes are: deoxygenation and hydrogen or deuterium addition on Pt-SiO2; isomerization and hydrogenolysis on Pd-SiO2. The reaction routes leading to the formation of the individual products are interpreted on the basis of the experimental results. In the case of the hydrogenolysis of oxiranes, Pd was shown to exhibit a special reactivity, unlike earlier observations described in the literature.
- Bartok, Mihaly,Fasi, Andras,Notheisz, Ferenc
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- Hydrolysis and Alcoholysis of Esters of o-Nitrobenzenesulfonic Acid
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The rate of solvolysis of esters of o-nitrobenzenesulfonic acid with water and C1-C4 alcohols is satisfactorily described by two-parametric Hammett-Taft equation with predominating effect of the electronic factor σ*. The effect of the structure of the hydrocarbon rest in the sulfonic ester group does not fit to this relationship.
- Sendega,Makitra,Pirig
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p. 1438 - 1446
(2007/10/03)
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- A Gas-Phase E2 Reaction: Methoxide Ion and Bromopropane
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We describe a procedure for studying gas-phase ion-molecule chemistry in which the reaction pathway is elucidated by direct detection of the neutral products.Our experiment uses a flowing afterglow device configured with a novel cold finger trap coupled to a GC/MS.Material collected by the trap is separated by capillary gas chromatography and the individual components identified by their retention times and electron impact mass spectra.We have used this device to study the reaction of methoxide ion with 1-bromopropane.CH3O(-) + CH3CH2CH2Br --> Br(-) + CH3OH + CH3CH=CH2 (a) Br(-) + CH3CH2CH2OCH3 (b) We find that the reaction produces only products resulting from elimination a; there is no evidence for the species resulting from displacement b.The E2 product, propylene, is detected while the SN2 product, 1-methoxypropane, is not.Our gas-phase results contrast sharply with solution studies, which show an overwhelming preference for the displacement channel b.
- Jones, Mark E.,Ellison, G. Barney
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p. 1645 - 1654
(2007/10/02)
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- Gas-Phase Addition of the Vinyl Cation to Hydrogen and Methane. A Nuclear Decay Study
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A nuclear technique based on the spontaneous decay of multitritiated precursors that allows the generation of free carbenium ions of exactly the same nature in different enviroments has been employed for generating the labeled vinyl cation (C2X3(1+), X = H,T) from multitritiated ethylene and for investigating its reactivity toward hydrogen and methane at pressures ranging from 60 to 720 Torr.Kinetic data for the addition of C2X3(1+) to H2 and CH4 and the ensuing product distributions are obtained by intercepting the ionic species with different gaseous nucleophiles, i.e., 1,4-dibromobutane, benzene, and methanol, and by isolating the corr esponding neutral end products.The results are consistent with the intermediacy of the vinyl cation, formed by the β(1-) transition with a limited excess of vibrational energy, which insert into the ?-bonds of H2 and CH4 yielding respectively C2H5(1+) and sC3H7(1+) ions.The experiments provide no evidence for the occurrence of alternative C3H7(1+) structures, i.e., protonated cyclopropane, from the C2X3(1+) attack on CH4.At CH4 pressures below 200 Torr, a fraction of the C3H7(1+) adducts fragments diretly into allyl cations and H2.A definition of the C2X3(1+) + H2(or CH4) addittion and fragmentation mechanism is obtained by comparison of the present data with those arisisng from previous experimental studies based on different approaches (i.e., radiolysis, ICR, SIFT, HMPS, etc.) and with those of ab initio calculations.
- Fornarini, Simonetta,Speranza, Maurizio
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p. 2154 - 2160
(2007/10/02)
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- Chemistry of Carbenes: Part III - Reaction of Methylene with Ethyl n-Propyl Ether
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The bond reactivities for ethyl n-propyl ether, based on unity for the primary bonds of ethyl group, again prove the discriminate attack of methylene.All secondary bonds are attacked faster than the primary bonds of ethyl, the 2 C-H of ethyl itself being attacked 1.83 times, which is higher than the attack on secondary αC-H (1.74) and βC-H (1.29) bonds.The descending order of reactivities of C-H bonds in propyl is α > β > γ.Additional evidence of the electrophilic effect of ethereal oxygen on the insertion reactions as also on the displacement reaction where methylene gives a methyl alkyl ether and displaces an olefin has been obtained.Similarly, the predicted formation of aldehydes resulting from the abstraction reactions of methylene has been observed.These results obtained in gas phase contrasted with the liquid phase work of Doering et al who found the attack to be indiscriminate.This work further confirms the difference between the two phases.
- Mehta, R. K. S.
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- Onium Ylide Chemistry. 2. Methylenedialkyloxonium Ylides
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We report evidence for the long sought after methylenedialkyloxonium ylides from methyloxonium ions by two independent routes, proving their intermediate formation through derived product analysis.Reaction of trimethyloxonium salts with sodium hydride results in competing proton abstraction besides methane formation (hydride methylation).Subsequent methylation of the formed methylenedimethyloxonium ylide by excess trimethyloxonum ion is resulting in C1 --> C2 conversion and formation of dimethylethyloxonium ion which with sodium hydride gives ethane (and methane) or by β-elimination ethylene.Besides expected fluoride alkylation products, i.e., alkyl fluorides and fluorosilanes, fluoride-induced desylilation of dimethyl((trimethylsilyl)methyl)oxonium tetrafluoroborate also results in the formation of methylenedimethyloxonium ylide giving via subsequent methylation and cleavage methyl ethyl ether and ethyl fluoride.
- Olah, George A.,Doggweiler, Hans,Felberg, Jeff D.
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p. 2112 - 2116
(2007/10/02)
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- Kinetics and Mechanisms of Nucleophilic Displacement with Heterocycles as Leaving Groups. 17. Solvolysis of 14-(Primary alkyl)-5,6,8,9-tetrahydro-7-phenyldibenzoacridiniums: Rates, Identification of Products, Activation Parameters, and a General Discussion of Mechanism
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Solvolysis rate are reported for the Me, Et, n-Pr, n-Pent, n-Oct, i-Bu, neo-Pent, PhCH2CH2, and MeOCH2CH2 title compounds in MeOH, EtPH, PentOH, CH3CO2H, and CF3CO2H.Rate variations with alkyl group structure are far less than the corresponding rate variations for the tosylate solvolysis, and afford no evidence for rate-enhancing participation by β-phenyl or β-methoxy groups in the acridinium solvolyses.The n-propyl, n-pentyl, and n-octyl title compounds solvolyze in CH3OD and CH3CO2D to give mixtures of normal and rearranged products, none of which contain deuterium and which are therefore not formed via olefin intermediates.Methanolysis of the isobutyl title compounds occurs via olefin, but the acetolysis also involves an important nonolefinic pathway yielding isobutyl and sec-butyl acetates.Methanolysis products from the neopentyl derivative are heavily deuterated, but acetolysis yields undeuterated neopentyl acetate as well as deuterated tert-pentyl acetate.Product proportions calculated using GC/MS were used to deduce the fractions of reactions by various mechanistic pathways.Individual rates are calculated for solvolysis to the various unrearranged and rearranged products.They indicate that normal substitution in MeOH occurs by a classical SN2 reaction, but that such substitution in AcOH involves ion-pair intermediates.It is concluded that such ion pairs under go Me and H migration after the rate-determining stage, in competition with substitution.Activation parameters provide further evidence for the mechanistic paths proposed which are discussed in relation to literature data available for the corresponding tosylate.
- Katritzky, Alan R.,Dega-Szafran, Zofia,Lopez-Rodriguez, Maria L.,King, Roy W.
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p. 5577 - 5585
(2007/10/02)
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- Onium Ylide Chemistry. 3. Evidence for Competing Oxonium Ylide Formation with C-H Insertion in Meerwein's Reaction of Methylene and Methylene-d2 with Dialkyl Ethers
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Meerwein's reaction of singlet methylene, produced by photolysis of diazomethane, with dialkyl ethers has been reinvestigated on the basis of reactions using CD2N2.In competition with methylene insertion into the various C-H bonds, about 10percent of methyl alkyl ether and small amounts of dimethyl ether formation are also observed.This indicates evidence for competing attack of methylene on oxygen leading to the corresponding intermediate methylenedialkyloxonium ylides which are immediately protonated by methyl alkohol (or water)impurity present in the reaction medium togive the corresponding methyldialkyloxonium ions.Dealkylative cleavage of the latter gives the observed methyl alkyl ethers.By the use of deuterium-labeled diazomethane CD2N2 it has been shown that ethylene and propylene formed under the reaction conditions are coming predominantly from diazomethane itself and not via intramolecular β-elimination of the oxonium ylides.
- Olah, George A.,Doggweiler, Hans,Felberg, Jeff D.
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p. 2116 - 2120
(2007/10/02)
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- Acid-induced 13C Nuclear Magnetic Resonance Chemical Shift Changes of Ether and Ester Carbon Atoms
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13C N.m.r. chemical shifts of ehters dissolved in tetrachloromethane are displaced on addition of trifluoroacetic acid.The displacements result from independent interactions of the acid with the substrate oxygen atoms and alkyl residues.The structure-dependent and stereoselective shift changes are useful for signal assignments, structure determination, conformational analysis, assessment of the distribution of rapidly interconverting conformers of esters, and estimation of the relative basicity of ethers.
- Begtrup, Mikael
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p. 1609 - 1618
(2007/10/02)
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- HOMOGENEOUS CATALYTIC HYDROGENATION OF DIOLEFINS AND ALKYNES IN THE PRESENCE OF PALLADIUM(II) COMPLEXES
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Palladium(II)chloride in dimethylformamide catalyzes the hydrogenation of conjugated diolefins and alkynes in homogeneous solution.Monoolefins are formed selectively.
- Sisak, A.,Jablonkai, I.,Ungvary, F.
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