- Germanium(II) hydride mediated reduction of carbon dioxide to formic acid and methanol with ammonia borane as the hydrogen source
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LGeOC(O)H (3) (L = CH{(CMe)(2,6-iPr2C6H 3N)}2), from the straightforward conversion of LGeH (2) with CO2, reacts with LiH2NBH3 giving 2 and LiOC(O)H (4), while the corresponding reaction of 3 with H3NBH 3 after aqueous workup releases 2 and CH3OH (5). This opens the possibility to use hydride 2 as a mediator in the reduction of carbon dioxide to formic acid and methanol.
- Jana, Anukul,Tavcar, Gasper,Roesky, Herbert W.,John, Michael
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- Functionalization of RhIII-Me Bonds: Use of capping Arene Ligands to Facilitate Me-X Reductive Elimination
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We show how to improve the yield of MeX from CH4 activation catalysts from 12% to 90% through the use of capping arene ligands. Four (FP)RhIII(Me)(TFA)2 {FP = capping arene ligands, including 8,8′-(1,2-phenylene)diquinoline (6-FP), 8,8′-(1,2-naphthalene)diquinoline (6-NPFP), 1,2-bis(N-7-azaindolyl)benzene (5-FP), and 1,2-bis(N-7-azaindolyl)naphthalene (5-NPFP)} complexes. These complexes and (dpe)RhIII(Me)(TFA)2 (dpe = 1,2-di-2-pyridylethane) were synthesized and tested for their performance in reductive elimination of MeX (X = TFA or halide). The FP ligands were used with the goal of blocking a coordination site to destabilize the RhIII complexes and facilitate MeX reductive elimination. On the basis of single-crystal X-ray diffraction studies, the 6-FP and 6-NPFP ligated Rh complexes have Rh-arene distances shorter than those of the 5-FP and 5-NPFP Rh complexes; thus, it is expected that the Rh-arene interactions are weaker for the 5-FP complexes than for the 6-FP complexes. Consistent with our hypothesis, the 5-FP and 5-NPFP RhIII complexes demonstrate improved performance (from 12% to ~60% yield) in the reductive elimination of MeX. The reductive elimination of MeX from (FP)RhIII(Me)(TFA)2 can be further improved by the use of chemical oxidants. For example, the addition of 2 equiv of AgOTf leads to 87(2)% yield of MeTFA and can be achieved in CD3CN at 90 °C using (5-FP)Rh(Me)(TFA)2.
- Gu, Shunyan,Chen, Junqi,Musgrave, Charles B.,Gehman, Zo? M.,Habgood, Laurel G.,Jia, Xiaofan,Dickie, Diane A.,Goddard, William A.,Gunnoe, T. Brent
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- Ion-molecule association of H3O+ and C2H2: Interstellar CH3CHO
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The C2H2 · H3O+ product of the ion-molecule association reaction between H3O+ and C2H2 is found to consist of a ca. 50 : 50 mixture of two isomeric ions. These two isomeric ions are identified in a selected ion flow tube, by their different proton transfer behaviour with the neutral reagents C2H5Br, 4-fluorotoluene, CH3OH and benzene, as protonated vinyl alcohol, CH2CHOH2+ and either protonated acetaldehyde, CH3CHOH+ or the electrostatic complex H3O+ · C2H2. These conclusions are supported by Gaussian G2 level calculations based on ab initio molecular orbital theory, which are applied to calculate the proton affinities of CH3CHO, CH2CHOH, oxirane and acyclic CH2OCH2. Reaction rate coefficients and product ratios are also reported for the reactions of specific C2H5O+ isomers, viz: CH3CHOH+, CH3OCH2+ and CH2OHCH2+ with CH3OH, 4-fluorotoluene and C6H6. The implications of the current results to the interstellar synthesis of CH3CHO are discussed briefly.
- Fairley, David A.,Scott, Graham B. I.,Freeman, Colin G.,Maclagan, Robert G. A. R.,McEwan, Murray J.
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- The Methyldiazonium Ion in Water: Competition Between Hydrolysis and Proton Exchange
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The methyldiazonium ion, generated from four different precursors, was found to undergo proton exchange with deuteriated phosphate buffer solutions.
- Smith, Richard H.,Koepke, Steven R.,Tondeur, Yves,Denlinger, Cheryl L.,Michejda, Christopher J.
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- Formation of HCOH + H2 through the Reaction CH3 + OH. Experimental Evidence for a Hitherto Undetected Product Channel
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In an extension of our earlier studies at lower temperatures the title reaction was measured directly in a flow reactor at temperatures of 600 and 700 K.The pressure of 0.65 mb was chosen that low in order to reduce the contribution of the stabilization channel.OH was used in an excess over CH3.Both reactants along with the reaction products were monitored by mass spectrometry.CH3 profiles served as the major observable quantity for the extraction of rate data.This had to be done by using computer simulation since it was impossible to work under pseudo-first-order conditions.The obtained total rate coefficients were divided into channel rate coefficients by means of branching ratios as determined by the mass spectrometric measurement of the reaction products.For CH3 + OH, this led to a rate coefficient, k1a into the stabilization channel, and another one, k1e+f referring to the sum of two H2-eliminating channels yielding the biradical HCOH and to a minor extent H2CO.These latter channels have not been measured before.In order to distinguish between them we switched over from OH to OD to get (1'e) CH3 + OD -> HCOD + H2, (1'f) -> H2CO + HD so that the biradical and/or aldehyde channels could be determined by their by-products H2 and HD, respectively.The use of OD makes it also possible to measure the channel (1'd) CH3 + OD -> 1CH2 + HDO through its by-product, HDO.A comparison of the rate coefficients of both systems, i.e., CH3 + OH and CH3 + OD, indicates that within our error limits no significant isotope effect takes place.For the rate coefficient into the HCHO channel, we arrive at a preliminary Arrhenius expression in units of cm, molec, and s: k1e = 9.1*10-11 exp(-1500/T).The H2CO channel could not be detected at our lower temperature rendering us with a rate coefficient at 700 K: k1f(700 K) = 1.7*10-12.Since simulation is needed for the deduction of the total rate coefficients as well as of the branching ratios, an uncertainty factor of 1.5 has to be attributed to these numbers.
- Humpfer, Robert,Oser, Harry,Grotheer, Horst-Henning
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- Decomposition of 1,3-Dialkyltriazenes in Aqueous Buffers: Kinetic and Mechanistic Studies
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1,3-Dialkyltriazenes, prepared by the reaction of alkyl azides with alkyllithiums, are stable as pure liquids or in aprotic solutions.The kinetics of decomposition of 1,3-dimethyltriazene (DMT) were investigated in buffered, aqueous solutions over the pH range of 9-12.The reaction is acid-catalyzed since the rate is inversely proportional to pH.The invariance of the rate with (cyclohexylamino)propanesulfonic acid (CAPS) buffer concentration at pH 9.5 and the finding of an inverse solvent isotope effect of 0.35 suggest that the reaction follows simple specific acid catalysis in that buffer.Decomposition of DMT in phosphate and carbonate buffers, however, indicated dependence of rate on buffer concentration, although the solvent isotope effects were still less than 1.These data suggested that the reaction in those buffers is catalyzed by specific acid, followed by general base.The kinetics of decomposition of 1,3-diethyltriazene (DET) and 1,3-diisopropyltriazene (DIT) were also studied.DET decomposed slightly more rapidly than DMT in phosphate and carbonate buffers but showed a similar dependence of the rate on the buffer concentration.This triazene also exhibited an inverse solvent isotope effect.DIT, on the other hand, showed a rate that was invariant with phosphate buffer concentration and exhibited a biphasic profile of rate vs. carbonate buffer concentration.The rate of decomposition of DIT was also invariant with the pKa of various buffers and showed an inverse solvent isotope effect.Decomposition of DMT in buffered deuterium oxide resulted in incorporation of deuterium into the product methanol, which indicated that an intermediate product of the reaction was the methyldiazonium ion.The dependence of the rate of decomposition on buffer concentration of DMT and DET is explained in terms of nucleophilic attack of buffer anions on N-2 of the protonated triazenes.The proponated DIT, on the other hand, is seen as dissociating directly to the isopropyl carbonium ion in phosphate buffer and in low concentrations of carbonate buffer.
- Smith, Richard H.,Denlinger, Cheryl L.,Kupper, Robert,Mehl, Andrew F.,Michejda, Christopher J.
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- CO2 and CO/H2 Conversion to Methoxide by a Uranium(IV) Hydride
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Here we show that a scaffold combining siloxide ligands and a bridging oxide allows the synthesis and characterization of the stable dinuclear uranium(IV) hydride complex [K2{[U(OSi(OtBu)3)3]2(μ-O)(μ-H)2}], 2, which displays high reductive reactivity. The dinuclear bis-hydride 2 effects the reductive coupling of acetonitrile by hydride transfer to yield [K2{[U(OSi(OtBu)3)3]2(μ-O)(μ-κ2-NC(CH3)NCH2CH3)}], 3. Under ambient conditions, the reaction of 2 with CO affords the oxomethylene2- reduction product [K2{[U(OSi(OtBu)3)3]2(μ-CH2O)(μ-O)}], 4, that can further add H2 to afford the methoxide hydride complex [K2{[U(OSi(OtBu)3)3]2(μ-OCH3)(μ-O)(μ-H)}], 5, from which methanol is released in water. Complex 2 also effects the direct reduction of CO2 to the methoxide complex 5, which is unprecedented in f element chemistry. From the reaction of 2 with excess CO2, crystals of the bis-formate carbonate complex [K2{[U(OSi(OtBu)3)3]2(μ-CO3)(μ-HCOO)2}], 6, could also be isolated. All the reaction products were characterized by X-ray crystallography and NMR spectroscopy.
- Falcone, Marta,Scopelliti, Rosario,Mazzanti, Marinella
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- Deuterium-Protium Separation Factor between Hydrogen and Liquid Methanols
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The overall deuterium-protium isotope separation factor, α, between hydrogen and the hydroxyl group of liquid methanols containing both CH3 and CD3 substituents has been measured directly between -30 and +64 deg C.The temperature dependence of the respective separation factors is given by the equations ln α(CH3) = -0.4641 + (540.4/T) + (9849.5/T2) and ln α(CD3) = -0.8183 + (708.4/T) - (15263/T2) where T is the absolute temperature.The α values are about 12percent larger than that for liquid water.The equilibrium constants, K1 and K2, for isotopic exchange between hydrogen and the isotopically substituted methanol vapors were calculated from the α values and the corresponding liquid-vapor separation factors αv.At 25 deg C the experimental values of K1 and K2 differ by 7percent, indicating that methyl deuteration exerts a significant secondary isotope effect on deuterium-protium fractionation between methanol vapor and hydrogen.A comparison of equilibrium constants is made with theoretical values calculated from the ratios of partition functions of molecular hydrogen and those derived from the available spectroscopic data of the isotopically substituted methanols.
- Rolston, J.H.,Gale, K.L.
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- Transition state modeling and catalyst design for hydrogen bond-stabilized enolate formation
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A catalyst for enolate formation was designed that incorporates an amine base along with a thiourea to bind to the oxygen atom of the substrate and enolate through hydrogen bonding. A computational model of the transition state was developed in which the thiourea (modeled initially as a urea) and amine were separate molecules. This model and models incorporating one or two methanol molecules in place of the urea showed an out-of-plane hydrogen bond, apparently to the carbonyl π-bond, in addition to an in-plane hydrogen bond to an unshared electron pair. In contrast, optimized complexes of the ketone and the fully formed enolate showed only in-plane hydrogen bonding. The transition state model with the urea and amine was used to define a database search with the computer program CAVEAT to identify structures suitable for linking the amine and urea/thiourea moieties in the transition state. On the basis of a group of structures identified from this search, a flexible but conformationally biased linker was designed to connect the two catalytic moieties. The molecule having the amine and thiourea moieties connected by this linker was synthesized and was shown to catalyze proton exchange between methanol and deuterated acetone. The catalyst was about 5-fold more efficient than the amine and thiourea as separate molecules and relative to a similar but less conformationally biased catalyst.
- Zhu, Yimin,Drueckhammer, Dale G.
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- Reactions of 1,2-Oxaphospholene 2-Oxides. 6. Free-Radical and Nucleophilic Substitution at C5: Anomalous Proton-Transfer Behavior of Cyclic Ketals
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The free-radical bromination of 3,5-di-tert-butyl-2-hydroxy-1,2-oxaphosphol-3-ene 2-oxide (1b) with N-bromosuccinimide (NBS) gave the corresponding 5-bromo-3,5-di-tert-butyl-2-hydroxy-1,2-oxaphosphol-3-ene 2-oxide (3) in good yield.Bromide 3 was extremely labile and could not be purified rigorously, but it readily underwent methanolysis to give 3,5-di-tert-butyl-2-hydroxy-5-methoxy-1,2-oxaphosphol-3-ene 2-oxide (7) or hydrolysis to 3,5-di-tert-butyl-2,5-dihydroxy-1,2-oxaphosphol-3-ene 2-oxide (8), both crystalline compounds.Compounds 7 and 8, though somewhat less reactive than 3, were readily interconverted.Treatment of 8 with diazomethane led to dimethyl (Z)-2,2,6,6-tetramethyl-3-oxohept-4-en-5-ylphosphonate (10), indicating that 8 is in equilibrium with its open phosphonic acid isomer.Ketal 7 underwent methoxy exchange at 35.5 deg C with a first-order rate constant of 0.075 m-1, and the rate was only slightly increased by a large excess of trifluoroacetic acid.The conjugate base of 7 did not undergo exchange.By contrast, 3,5-di-tert-butyl-2,5-dimethoxy-1,2-oxaphosphol-3-ene 2-oxide (11), the methyl ester of 7, was totally inert toward methoxy exchange except in the presence of excess HBr at high temperature for extended periods.The contrasting solvolytic behavior of 7 and 11 under acidic conditions has been interpreted as evidence for an intramolecular proton transfer from an oxygen on phosphorus to the nucleofuge.Ketal-ester 11 underwent slow ring opening in base, which was immediately reversed upon neutralization.The methyl ester (1c) of 1b, the 4-bromo derivative (1d) of 1b, and its methyl ester (1e) all undergo similar reactions with NBS.However, 4,5-dibromide 20 was anomalously unreactive toward nucleophilic substitution.
- Rardon, Daniel,Macomber, Roger S.
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- Oxidation and Oxidative Carbonylation of Methane and Ethane by Hexaoxo-μ-peroxodisulfate(2-) Ion in Aqueous Medium. A Model for Alkane Oxidation through the Hydrogen-atom Abstraction Pathway
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In aqueous medium, at 105-115 deg C, SO4 radical-anion (generated from S2O82-) was found to abstract a hydrogen atom from methane and ethane to form the corresponding alkyl radicals which could be trapped efficiently by carbon monoxide, the resultant acyl radicals being ultimately converted into the homologous carboxylic acids.
- Lin, Minren,Sen, Ayusman
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- Comparison of ΔG°Acid (gas phase) and kinetic acidities measured in methanolic sodium methoxide
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Hydron exchange rates, kexc (M-1s-1), using methanolic sodium methoxide were compared with ΔG°Acid, (kcal mol-1) (gas phase) for 9-phenylfluorene, C6H5CH(CF3)2, m-CF3C6H4CH(CF3)2, p-CF3C6H4CHClCF3, m-CF3C6H4CHClCF3, 3,5-(CF3)2C6H3CHClCF3, fluorene and C6F5H. There is a good linear correlation for p-CF3C6H2CHClCF3, m-CF3C6H4CHClCF3 and 3,5-(CF3)2C6H3CHClCF3, with the others falling off the line. The fluorinated benzyl compounds and pentafluorobenzene have near-unity isotope effects and therefore differ from the fluorenyl compounds. Although the acidity and the exchange rates for three of the compounds [9-phenylfluorene, C6H5CH(CF3)2 and p-CF3C6H4CHClCF3] are similar, the important proton-transfer step to form a hydrogen-bonded carbanion intermediate and the subsequent breaking of that weak bond to form a free carbanion in methanol differ significantly for the fluoernyl compound compared with the two fluorinated benzylic compounds.
- Koch, Heinz F.,Biffinger, Justin C.,Mishima, Masaaki,Mustanir,Lodder, Gerrit
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- Hydride-transfer domino rearrangement of glycine-containing dioxa-azawurtzitane
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The novel synthetic method for dioxa-azawurtzitanes to selectively cap amino groups in amino acids or peptides is described. Mixing the CH3CN solution of cis,cis-1,3,5-triformyl-1,3,5-trimethylcyclohexane (2) with the aqueous solution of the eq
- Izumi, Hiroshi,Futamura, Shigeru
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- Cobalt catalysed reduction of CO2via hydroboration
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We report an operationally convenient reduction of CO2 to methanol via cobalt catalysed hydroboration which occurs under mild reaction conditions. Addition of NaHBEt3 to Co(acac)3 generates an active hydroboration catalyst, which is proposed to be a “Co-H” species on the basis of infrared spectroscopy. The reduction of CO2 in the presence of various boranes showed that BH3·SMe2 afforded near quantitative conversion (98% NMR yield) to methanol upon hydrolysis.
- Tamang, Sem Raj,Findlater, Michael
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p. 8199 - 8203
(2018/07/10)
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- Synthesis of ethanol via a reaction of dimethyl ether with CO2 and H2
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Ethanol is currently produced via the catalytic hydration of ethylene or fermentation of foods. The synthesis of ethanol from cheap and renewable CO2 is of great importance, but the state of the art routes encounter difficulties, especially in reaction selectivity and activity. Here we show a strategy of ethanol synthesis from CO2, dimethyl ether (DME) and H2. The reaction can be effectively promoted with a Ru-Co bimetallic catalyst using LiI as a promoter in 1,3-dimethyl-2-imidazolidinone (DMI) solvent. The predominant product of this reaction was ethanol and the selectivity of ethanol in total products could reach 71.7 C-mol%. The selectivity of ethanol in the liquid product could reach 94.1%, which was higher than the reported routes using CO2/CO. To the best of our knowledge, this is the first work on ethanol synthesis from DME, CO2 and H2. The reaction mechanism is discussed based on a series of control experiments.
- Qian, Qingli,Cui, Meng,Zhang, Jingjing,Xiang, Junfeng,Song, Jinliang,Yang, Guanying,Han, Buxing
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supporting information
p. 206 - 213
(2018/01/12)
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- Aqueous phase hydrodeoxygenation of polyols over Pd/WO3-ZrO2: Role of Pd-WO3 interaction and hydrodeoxygenation pathway
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Aqueous phase processing of biomass derived sugar alcohols is one of the promising routes to convert biomass into fuels and chemicals. Bifunctional catalysts are critical in the aqueous phase hydrodeoxygenation of sugar alcohol. Understanding the interaction between metal and acidic metal oxides as well as the hydrodeoxygenation pathways will help develop more efficient bifunctional catalysts. Here, tungstated zirconia supported palladium catalysts were prepared and further characterized using nitrogen sorption, X-ray diffraction, FT-IR analysis of adsorbed pyridine, CO chemisorption and diffuse reflectance UV-vis. Strong interaction between palladium and WO3 in addition to a synergetic effect of the acidic and metallic sites were found to promote the aqueous phase hydrodeoxygenation of ethylene glycol. H-D exchange experiments using 13C{1H} NMR spectroscopy confirmed that the aqueous phase hydrodeoxygenation follows a dehydration-hydrogenation pathway. The hydrogenation of the dehydration products shifts the dehydration-hydration equilibrium toward the dehydration pathway and leads to highly selective C-O cleavage.
- Liu, Changjun,Sun, Junming,Brown, Heather M.,Marin-Flores, Oscar G.,Bays, J. Timothy,Karim, Ayman M.,Wang, Yong
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p. 103 - 109
(2016/05/11)
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- Aromaticity as stabilizing element in the bidentate activation for the catalytic reduction of carbon dioxide
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A new transition-metal-free mode for the catalytic reduction of carbon dioxide via bidentate interaction has been developed. In the presence of Li2[1,2-C6H4(BH3)2], CO2 can be selectively transformed to either methane or methanol, depending on the reducing agent. The bidentate nature of binding is supported by X-ray analysis of an intermediate analogue, which experiences special stabilization due to aromatic character in the bidentate interaction. Kinetic studies revealed a first-order reaction rate. The transformation can be conducted without any solvent.
- Lu, Zhenpin,Hausmann, Heike,Becker, Sabine,Wegner, Hermann A.
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p. 5332 - 5335
(2015/05/13)
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- Mechanistic studies of CO2 reduction to methanol mediated by an N-heterocyclic germylene hydride
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The labile germylene hydride LCyGeH is capable of activating CO2 affording the corresponding formate LCyGeOCH(O) (2) (LCy = cyclo-C6H8-1-NAr-2-C(Ph)NAr, Ar = 2,6-iPr2C6H3). Compound 2 and the previously reported LGeOCH(O) (L = CH(MeCNAr)2, Ar = 2,6-iPr2C 6H3) (2′) could be further converted to methanol with the AlH3·NMe3 alane-amine adduct as a hydrogen source upon workup with water. A plausible mechanism for the conversion of the formate complexes to methanol is proposed based on additional results from the conversion of 2′ with the milder hydride delivery agent LAlH2. This journal is the Partner Organisations 2014.
- Tan, Gengwen,Wang, Wenyuan,Blom, Burgert,Driess, Matthias
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p. 6006 - 6011
(2014/04/17)
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- Synthesis, reactivity and catalytic properties of the allenylidene [Ru(C=C=CPh2)Cp(PTA)(PPh3)](CF3SO3) (PTA = 1,3,5-triaza-7-phosphaadamantane)
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The reactivity of [RuCpCl(PTA)(PPh3)] with HC≡CPh and HC≡CC(OH)PPh2 has been studied. The reaction with the phenylacetylene did not provide the desired vinylidene ruthenium complex but as a collateral result the complex [RuCp(DMSO-κS)(PTA)(PPh 3)](CF3SO3) (1) was obtained by reaction of [RuCpCl(PTA)(PPh3)] with Ag(CF3SO3) in DMSO. Reaction of [RuCpCl(PTA)(PPh3)] with HC≡CC(OH)PPh2 provided the Ruthenium(II) diphenyl-allenylidene complex [Ru(C=C=CPh 2)Cp(PTA)(PPh3)](CF3SO3) (2) that was characterized by NMR, IR spectroscopy and elemental analysis. The chemistry of the new diphenyl-allenylidene ruthenium complex has been studied towards a variety of small molecules such as water, O2, n-propylamine, cyclohexylamine and ethanethiol. From the reaction of 2 with the amines and thiol, two isomers are obtained respectively but only one of them could be isolated and characterized. The allenylidene complex was found to be a useful catalyst for the trans-etherification of 1,4-butanedioldivinyl-ether, ethoxyethene and 1-methoxycyclohexa-1,3-diene
- Serrano-Ruiz, Manuel,Lidrissi, Chaker,Ma?as, Sonia,Peruzzini, Maurizio,Romerosa, Antonio
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p. 654 - 661
(2014/03/21)
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- A new, higher yielding synthetic route towards dodecaphenyl cage silsesquioxanes: Synthesis and mechanistic insights
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Cage dodecaphenylsilsesquioxane (T12-Phenyl) was synthesized in a one batch, mildly basic aqueous solution under room temperature conditions using a trialkoxysilane precursor. Significant improvements in synthetic yield (>95%) were observed compared with previous reports. Kinetic studies of the hydrolysis of phenyltrimethoxysilane were conducted and the condensation was monitored by 29Si NMR which revealed the presence of a transient, intermediary T1 species as the pathway to dodecaphenylsilsesquioxane spherulites, and the tendency for T12 structures over T8, T10, and other substructures was explained through MM2 simulations.
- Lee, Albert S.,Choi, Seung-Sock,Lee, He Seung,Baek, Kyung-Youl,Hwang, Seung Sang
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p. 10585 - 10588
(2013/01/14)
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- Oxidative functionalization of methane in the presence of a homogeneous rhodium-copper-chloride catalytic system: Transformation of acetic and propionic acids as solvent components
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The oxidative functionalization of methane (O2, CO, 95°C, Rh III/CuI, II/Cl- catalytic system) was studied in an aqueous acetic or propionic acid medium. It was shown that oxidative decarbonylation of carboxylic acids takes place along with methanol and methyl carboxylate formation.
- Chepaikin,Bezruchenko,Menchikova,Moiseeva,Gekhman,Moiseev
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scheme or table
p. 133 - 142
(2012/01/13)
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- Room temperature reduction of CO2 to methanol by Al-based frustrated Lewis pairs and ammonia borane
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(Formula Presented) AlX3 (X = Cl or Br) and PMes3 (Mes = 2,4,6-C6H2Me3) react to form weak Lewis adducts but also react with CO2 to give Mes3P(CO 2)(AlX3)s
- Menard, Gabriel,Stephan, Douglas W.
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supporting information; experimental part
p. 1796 - 1797
(2010/04/25)
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- CATALYTIC OXY-FUNCTIONALIZATION OF METAL-CARBON BONDS
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The development of compatible functionalization reactions with methyl rhenium(I) species, for integration with the CH activation reaction of hydrocarbons by transition metal alkoxo complexes is described. The invention is applicable to the design of rapid, stable CH activation systems integrated with an oxy-functionalization reaction for selective, low temperature hydrocarbon oxidation catalysts.
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Page/Page column 16
(2009/08/16)
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- Efficient synthesis of the A-ring phosphine oxide building block useful for 1α,25-dihydroxy vitamin D3 and analogues
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The 1α-hydroxy A-ring phosphine oxide 1, a useful building block for vitamin D analogues, was synthesized from (S)-carvone in nine synthetic operations and a single chromatographic purification in 25% overall yield. The synthesis features two novel efficient synthetic transformations: the Criegee rearrangement of α-methoxy hydroperoxyacetate 10 in methanol to obtain directly the desired secondary 3β-alcohol 11 and the highly chemo- and stereoselective isomerization of dieneoxide ester (E)-7 to the 1α-allylic alcohol with an exocyclic double bond (E)-8. Further insight into the selectivity control of the latter rearrangement was obtained from the reactions of (Z)epimeric substrates. The new synthetic approach leading to the 1α-hydroxy epimers complements our previously reported synthesis of the corresponding 1β-epimers, thus producing all stereoisomers of these versatile building blocks efficiently from carvone.
- Daniewski, Andrzej R.,Garofalo, Lisa M.,Hutchings, Stanley D.,Kabat, Marek M.,Liu, Wen,Okabe, Masami,Radinov, Roumen,Yiannikouros, George P.
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p. 1580 - 1587
(2007/10/03)
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- Catalysis of transesterification reactions by lanthanides - Unprecedented acceleration of methanolysis of aryl and alkyl esters promoted by La(OTf)3 at neutral sspH and ambient temperatures
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La3+ catalysis of the methanolysis of the esters p-nitrophenyl, 2,4-dinitrophenyl, and phenyl acetate (1-3), phenyl benzoate (4), and ethyl, i-propyl, cyclohexyl, and tert-butyl acetate (5, 6a, 6b, 7) was studied at 25°C as a function of sspH and [La(OTf)3]. The active form of the catalyst is attributed to a dimethoxy-bridged dimer of stoichiometry (La3+)2(-OCH3)2, having maximum activity atsspH 8 to 9. For preparative reactions, the active catalyst can be made in situ simply by adding 0.01 equiv of La(OTf)3, and 0.01 equiv of NaOCH3 to a methanol solution containing the ester (1 M). Strong catalysis of methanolysis of both aryl and alkyl esters was observed, although tert-butyl acetate was inert. At sspH 8.5, where the catalyst is maximally active, the transesterification reactions are accelerated by 40 000-fold to 18 000 000-fold in the presence of as little as 5 mM catalyst relative to the background reaction depending on the ester structure. A mechanism for catalysis of transesterification is presented wherein the reactive species is generated by breaking a single La-OCH3 bond of the dimethoxy-bridged dimer to reveal a nucleophilic metal-bound methoxide - Lewis acid La3+ electrophilic pair.
- Neverov, Alexei A.,McDonald, Todd,Gibson, Graham,Brown
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p. 1704 - 1710
(2007/10/03)
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- NMR study of hydrothermal reactions of dichloromethane with and without alkali
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Hydrothermal reactions of considerably concentrated (ca. 1 M; M = mol dm-3) dichloromethane, CH2Cl2, were investigated with and without alkali in the temperature range of 150 - 300 °C by using batch reactors, such as an autoclave and sealed glass tubes. 1H, 2H, and 13C NMR spectra were taken at room temperature as a function of reaction time to analyze the quenched reactants, intermediates, and products. In the presence of NaOH at 2 M, the complete dechlorination was achieved in 270 min at 250 °C and in 60 min at 300 °C. Such gaseous by-products as CO, CO2, and H2 were generated by the decomposition of the disproportionation product, HCOO-. Without alkali, CH2(OH)2 could be detected by 1H and 13C NMR as an intermediate in the hydrolysis of CH2Cl2, before such Cannizzaro products as methanol and formate ion were formed. The mechanism of the hydrothermal reactions of CH2Cl2 is discussed in terms of the hydrolysis intermediate, CH2(OH)2.
- Yamasaki, Yuki,Enomoto, Heiji,Yamasaki, Nakamichi,Nakahara, Masaru
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p. 2687 - 2693
(2007/10/03)
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- Study of the mechanism for the hydrolysis of alkoxy(aryl)(phenyl)-λ6- sulfanenitriles, ArPhS(OR)(?N)
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The hydrolysis of alkoxy(aryl)(phenyl)-λ6-sulfanenitriles in several buffer solutions was found to follow a good pseudo-first-order kinetic equation, giving the corresponding sulfoximides and alcohols (for the case of the hydrolysis of neopentyloxy-λ6-sulfanenitrile, giving a rearranged product, 2-methyl-2-butanol). The dependence of the rate of hydrolysis on the structure of the alkyl group showed the opposite trend to the usual S(N)2 character, i.e. Me +] at pH more than 6.08, and trends to saturate at low pH. According to these kinetic results, a two-step reaction mechanism was proposed which involves a pre-equilibrium protonation on the nitrogen atom of the alkoxy-λ6- sulfanenitriles, followed by a rate-determining C-O bond cleavage via an S(N)2 or S(N)1 mechanism on the alkyl carbon atom depending on the structure of the alkyl group. From a double-reciprocal plot of 1/k(obs) vs. 1/[H+], the pK(a) value and the rate constant of the second reaction of neopentyloxy(diphenyl)-λ6-sulfanenitrile were estimated to be 5.02 and 7.02x10-3 s-1, respectively. The substituent effects on the phenyl group of neopentyloxy(diphenyl)-λ6-sulfanenitrile afforded a large negative p- value (-1.88) for pK(a) and positive one (+1.66) for the second reaction at 25.2 °C. The small negative p-values observed at pH 6.27 for diphenyl(propoxy)-λ6-sulfanenitrile (-0.42) and neopentyloxy(diphenyl)- λ6-sulfanenitrile (-0.26) were found to be the results of a cancellation of those for the opposite trend of the reactions of the pre-equilibrium and the second step. The activation parameters for both the pre-equilibrium and the subsequent reactions were also estimated based on the parameters for the hydrolysis of neopentyloxy(diphenyl)-λ6-sulfanenitrile at pH 6.22 and 2.99. The buffer effect is due to a nucleophilic attack of the buffer base to the alkyl carbon atom of the protonated alkoxy-λ6-sulfanenitriles. The sulfoximide moiety in the protonated λ6-sulfanenitrile is revealed to be a very good leaving group.
- Yoshimura, Toshiaki,Dong, Tiaoling,Fujii, Takayoshi,Ohkubo, Masanori,Sakuta, Mikiko,Wakai, Youko,Ono, Shin,Morita, Hiroyuki,Shimasaki, Choichiro
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p. 957 - 965
(2007/10/03)
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- Controlled formation of tetramethylammonium mono- and diylide
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The reaction of tetramethylammonium bromide with n -butyllithium can selectively yield either trimethylammonium methylide or lithium dimethylammonium dimethylide, depending on the reaction conditions, as shown by 13C-NMR analysis of the deuterium-labelled species resulting from acidic trapping with DCl. So a simple synthesis of mono- or twice-functionalised methylammonium salts is allowed from a very usual starting material.
- Cristau, Henri-Jean,Plenat, Francoise,Bayssade, Sylvie
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- Decomposition of the Antitumour Drug Temozolomide in Deuteriated Phosphate Buffer: Methyl Group Transfer is accompanied by Deuterium Exchange
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The antitumour prodrug temozolomide 1 undergoes ring-opening in deuteriated phosphate buffer; deuterium incorporation into the methyl group transferred from the reactive species 5-(3-methyltriazen-1-yl)imidazole-4-carboxamide (MTIC) 2 has been monitored by observing D-H and P-H couplings in the NMR spectra of the products.
- Wheelhouse, Richard T.,Stevens, Malcolm F. G.
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p. 1177 - 1178
(2007/10/02)
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- Structure and Catalytic Activity of Alumina-Supported Pt-Co Bimetallic Catalysts. 2. Chemisorption and Catalytic Reactions
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A series od Pt1-xCox/Al2O3 bimetallic catalysts have been characterized by temperature-programmed reduction (TPR), chemisorption of hydrogen and CO, deuterium exchange using both methanol and methane, and activity for the CO/H2 reaction.A Pt-assisted reduction mechanism over the entire range of composition was established by the TPR studies as well as by the chemisorption results.An enhanced metallic dispersion for the Pt-rich catalyst and formation of bimetallic particles on the Co-rich side was also indicated.In the CO hydrogenation over the Pt-rich catalysts the predominant products are methanol and dimethyl ether whereas on the Co-rich samples hydrocarbons and higher alcohols are produced.The mechanisms of deuterium exchange with methane and methanol are significantly different, the former being catalyzed solely by metallic sites while the latter utilizes both oxide and metallic sites for stepwise and multiple exchange, respectively.On the basis of the XPS data (preceding article) as well as the chemisorption results reported here, a surface model is introduced for interpretation of the catalytic results.
- Guczi, Lazlo,Hoffer, Tamas,Zsoldos, Zoltan,Zyade, Souad,Maire, Gilbert,Garin, Francois
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p. 802 - 808
(2007/10/02)
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- Hydrogen-deuterium-exchange reactions of methoxide-methanol clusters
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The tandem flowing afterglow-selected ion flow tube has been employed to measure rate coefficients for a series of 12 bimolecular isotope-exchange reactions of methoxide-methanol clusters. From these kinetic measurements the dissociation energies of several hydrogen-bonded dimers were determined: CH3O-·DOCH3 (28.3 ± 0.1 kcal/mol), CH3O-·HOCD3 (28.5 ± 0.1 kcal/mol), CH3O-·DOCD3 (28.1 ± 0.1 kcal/mol) CD3O-·HOCD3 (28.9 ± 0.1 kcal/mol), and CD3O-·DOCD3 (28.5 ± 0.1 kcal/mol). Differences in the bond strengths of these cluster ions can be understood in terms of the acidity of the neutral molecule and the basicity of the anion involved in the cluster; a given ion makes a stronger bond with a stronger acid while a given neutral molecule makes a stronger bond with a stronger base. By use of literature values of the electron affinity of the methoxy radicals along with the known RO-H and RO-D bond strengths, the gas-phase acidities (ΔH° acid) of CD3OD (383.9 ± 0.7 kcal/mol), CH3OD (383.5 ± 0.7 kcal/mol), and CD3OH (382.0 ± 0.7 kcal/mol) were calculated. A simple model is employed to predict reaction efficiencies and branching ratios for these isotope-exchange reactions.
- Barlow,Dang, Thuy Thanh,Bierbaum, Veronica M.
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p. 6832 - 6838
(2007/10/02)
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- Gas-phase SN2 and E2 reactions of alkyl halides
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Rate coefficients have been measured for the gas-phase reactions of methyl, ethyl, n-propyl, isopropyl, tert-butyl, and neopentyl chlorides and bromides with the following set of nucleophiles, listed in order of decreasing basicity: HO-, CH3O-, F-, HO- (H2O), CF3CH2O-, H2NS-, C2F5CH2O-, HS-, and Cl-. For methyl chloride the reaction efficiency first falls significantly below unity with HO- (H2O) as the nucleophile and for methyl bromide with HS- as the nucleophile; in both cases the overall reaction exothermicity is about 30 kcal mol-1. Earlier conclusions that these halides react slowly with stronger bases are shown to be in error. In the region where the rates are slow oxygen anions react with the alkyl chlorides and bromides by elimination while sulfur anions of the same basicity react by substitution. This difference is due to a slowing down of elimination with the sulfur bases; sulfur anions show no increased nucleophilicity as compared to oxy anions of the same basicity. Rate coefficients have also been measured for reaction of methyl fluoride with HO- and CH3O- and ethylene oxide with HO-, CH3O-, and F-. All of these rates are slow but measurable; combining the results of these experiments with those of the alkyl chlorides and bromides suggests that the gas-phase barrier to the symmetrical SN2 reaction of F- with methyl fluoride is lower than previous estimates. We have also measured rates for reaction of allyl chloride with F-, H2NS-, and HS-, chloromethyl ether with H2NS- and HS-, chloroacetonitrile with F-, H2NS-, HS-, and 37Cl-, bromoacetonitrile with Cl- and 81Br-, and α-chloroacetone with H2NS-, HS-, and 37Cl-. Our results also imply that the gas-phase SN2 barrier for Br- reacting with methyl bromide is nearly equal to the ion-dipole attraction energy of the reactants, in agreement with previous estimates.
- DePuy, Charles H.,Gronert, Scott,Mullin, Amy,Bierbaum, Veronica M.
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p. 8650 - 8655
(2007/10/02)
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- Study of Reactions Leading to Sulfine Formation. 3. Competition of Reaction Pathways in the Reaction of Methoxide Ion with Methyl 1-Naphthylmethanesulfinates
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In CD3O1-/CD3OD methyl 1-naphthylmethanesulfinates, NpCH2S(O)OCH3 (2), undergo both exchange of CH3O by CD3O by substitution at the sulfinyl group and elimination to form the sulfine, NpCH=S=O.With use of methyl (2-methoxy-1-naphthyl)methanesulfinate (2a) it has been shown that formation of the sulfine takes place by an (E1cB)irrev mechanism.The rates of substitution (ks) and elimination (ke) of a series of 2 have been determined in CD3O1-/CD3OD by 1H NMR spectroscopy, and the effect of several reaction variables on the competition between substitution and elimination has been examined.Salient results are as follows: (1) the rate of elimination is markedly increased by the presence of electron-withdrawing substituents on the aromatic ring, but the rate of substitution is increased only modestly by the same substituents; (2) substituents at the 2-position of the naphthyl group cause a large decrease in ks (steric hindrance to substitution at S=O) but have little effect on ke (elimination rate not sensitive to steric requirements of ortho substituents); (3) the activation energy for elimination is almost 9 kcal/mol greater than the activation energy for substitution.This large difference in activation energy contrasts with the 1-2 kcal/mol difference for elimination vs substitution found14 with alkyl halides.
- Kice, John L.,Lotey, Harvinder
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p. 3596 - 3602
(2007/10/02)
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- Bis(dimethoxymethyl) peroxide and bis(1,1-dimethoxyethyl) peroxide
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The title compounds 1 and 2, the first examples of peroxides polysubstituted at the α and α' positions by alkoxy groups, are formed by benzophenone sensitized photooxygenation of trimethoxymethane and 1,1,1-trimethoxyethane, respectively.No peroxide was formed from tetramethoxymethane.Allowing 98percent hydrogen peroxide and trimethylmethane to stand results in an 80percent yield of 1, so that 1 and 2 are probably formed by such a disproportionation reaction during photooxygenation.Compound 1 is converted quantitatively to methanol, methyl formate, and dimethyl carbonate in pyridine solution at 60 deg C.In acidic methanol both 1 and 2 undergo solvolysis rapidly with exclusive cleavage of the carbon - peroxy oxygen bond.Signals for the ether and peroxy oxygens of 1 appear at 34 and 263 ppm and those of 2 appear at 40 and 264 ppm in the 17O nuclear magnetic resonance spectrum.Luminescence results when 1 and 2 are heated to 150 deg C.
- Kopeczky, Karl R.,Molina, Jose
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p. 2350 - 2355
(2007/10/02)
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- Phosphoric Amides. Part 8. The Effect of the Ethyleneimine Substituent on the Solvolytic Reactivity of Phosphate and Phosphoramidate Bonds
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Rates and products of the base-catalysed hydrolysis of some amidoesters of phosphoric acid have been determined in the N,N-dimethyl derivative, the P-N bond is resistant, and the P-O bond deactivated towards hydrolysis, while in the N-methyl substrate, the reactivity of the ester link is similar to that in trimethyl phosphate.In the N-ethylene compound, both P-O and P-N bonds are strongly activated.The N-(β-chloroethyl) substrate reacts via fast, base-catalysed cyclization to the N-ethylene amidate.
- Davidowitz, Bette,Modro, Tomasz A.
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p. 303 - 306
(2007/10/02)
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- Gas-Phase Hydrogen-Deuterium Exchange Reactions of Anions: Kinetics and Detailed Mechanism
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Rate coefficients and branching ratios for anionic hydrogen-deuterium exchange reactions between isotopically labeled hydroxide, amide, hydrogen sulfide, and methoxide ions and their corresponding neutral compounds have been measured in the gas phase by using the selected ion flow tube (SIFT) technique.The kinetic data for the methoxide-methanol systems lead to a determination of the relative base strength of CD3O(1-) and CH3O(1-).The reaction efficiencies and branching ratios of hydroxide-water, amide-ammonia, and amide-water systems are discussed in terms of the mechanism by which exchange occours; the multiply labeled systems reveal that more proton transfer occur than one might expect upon initial inspection of the data.The product distributions are discussed in terms of relative ion-molecule complex lifetimes and dissociation of the complex is competition with scrambling.Efficient H/D exchange was also observed to occur between compounds containing second-row elements and the implications of this are discussed.
- Grabowski, Joseph J.,DePuy, Charles H.,Doren, Jane M.Van,Bierbaum, Veronica, M.
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p. 7384 - 7389
(2007/10/02)
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- A New Method for Obtaining Isotopic Fractionation Data at Multiple Sites in Rapidly Exchanging Systems
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A new method for rapidly and conveniently obtaining isotopic fractionation factors in dilute aqueous solutions of compounds containing rapidly exchanging OH, NH, and SH groups is described.Shifts in the positions of NMR peaks for spectroscopically observable nuclei induced by isotopic substitution are the basis of this procedure which has the unique capability of separately measuring the isotopic exchange constants simultaneously for several different groups in the same molecule.The results for a series of alcohols, amines, thiols, phenols, acids, and amides with use of 13C NMR spectroscopy are reported.Atypically low values of Kfrac are observed in several cases, indicating that there are strong internal hydrogen bonds in competition with those to water, yielding conformational information.
- Jarret, Ronald M.,Saunders, Martin
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p. 2648 - 2654
(2007/10/02)
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- Thermoneutral Isotope Exchange Reactions of Cations in the Gas Phase
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Rate constants have been measured for reactions of the type AD2+ + MH --> MD + ADH+, where AD2+ is CD3CND+, CD3CDOD+, (CD3COCD3)D+, or (C2D5)2OD+ and the MH molecules are alcohols, acids, mercaptanes, H2S, AsH3, PH3, or aromatic molecules.Rate constants are also presented for the reactions ArHD+ + D2O --> ArDD+ + HDO, where ArHD+ is a deuteronated aromatic molecule and ArDD+ is the same species with a D atom incorporated on the ring.In all but two cases, the competing deuteron transfer is sufficiently endothermic that it cannot be observed under the conditions of the ICR experiments at 320 - 420 K.The efficiencies of the isotope exchange reactions are interpreted in terms of estimated potential surface cross sections for the reactions AD2+ + MH --> 2+*MH> --> +> --> +*MD> --> ADH+ + MD.When the formation of the +> complex is estimated to be thermoneutral or slightly endothermic, the isotope exchange process is inefficient (probability of a reactive collision 2+*MH> --> +> is exothermic.For most of the systems, trends in reaction efficiency appear to be related to factors such as dipole moments of reactant species (or for aromatic compounds, the electron-donating or -withdrawing properties of ring substituents) which influence the relative orientation of the two reactant species in the complex.
- Ausloos, P.,Lias, S. G.
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p. 3641 - 3647
(2007/10/02)
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- Solvolysis of a cyclic phosphonate with retention of the ring caused by orientation and steric effects
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Methanolysis and hydrolysis of 2-methoxy-5,5-dimethyl-2-oxo-1,2-oxaphosphol-3-ene(1) are fast in comparison with the acyclic phosphonate (2) and proceed predominantly by exocyclic alkyl cleavage.
- Aken, D. van,Castelijns, A. M. C. F.,Buck, H. M.
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p. 322 - 323
(2007/10/02)
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- Vapour Pressure Study of the Deuterium Exchange Reaction in Methanol-Ethanol Systems: Equilibrium Constant Determination
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The equilibrium constant of the reaction: CH3OH(l) + C2H5OD(l) --> CH3OD(l) + C2H5OH(l) is obtained from vapour pressure measurements on methanol+ethanol systems.The value obtained, 1.03 +/- 0.01 at 298 K, is in good agreement with that calculated independently from previously reported vapour pressure studies of water+methanol systems and water+ethanol systems.Vapour pressures at 298.15 K are reported for the systems CH3OH+C2H5OH, CH3OH+C2H5OD, CH3OD+C2H5OH and CH3OD+C2H5OD.Molar excess Gibbs functions are obtained from these vapour pressures.
- Kooner, Zorawar S.,Fenby, David V.
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p. 1943 - 1946
(2007/10/02)
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- PHOSPHORORGANISCHE VERBINDUNGEN 93 Zur Chemie optisch aktiver Phosphinigsaereamide
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Optically active ethyl-phenyl-phosphinous acid diethylamide 1 was treated with HCl, HBF4, alcohols, thiols, carboxylic acids, esters, anhydrides, acid chloride, compounds with the structure element P-Cl and secondary phosphines to give in each case a racemic mixture of the corresponding, previously described, reaction products.Reaction of optically active 1 with para-cresol, para-cresyltrifluoro-acetate or 2,2,2-trifluoro-ethyl-trifluoro-acetate gives the corresponding optically active ester of ethyl phenyl phosphinous acid under retention of configuration.
- Horner, Leopold,Jordan, Manfred
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p. 235 - 242
(2007/10/02)
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