- Kinetic understanding using NMR reaction profiling
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The combination of kinetic understanding and reaction modeling has been successfully applied to the development of processes from laboratory to manufacturing plant. Although extensively used in bulk chemistry, polymers, and the oil industry [ Bayer Technology Services, http://www.bayertechnology.cn/ uploads/media/0707-e-300dpi.pdf, July 2011; Lawrence Livermore National Laboratory, http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit-review-2011/ fuel-technologies/ft010-pitz-2 011-o.pdf,July 2011; Shin, S. B.; Han, S. P.; Lee, W. J.; Chae, J. H.; Lee, D. I.; Lee, W. H.; Urban, Z.Hydrocarbon Process. 2007, April) 83; Baumer, C.; Urban, Z.Hydrocarbon Process. 2007, June) 71 ], it has not been exploited to its full potential in the pharmaceutical industry. We present a fast and efficient methodology for kinetic modeling of chemical reactions using 1H NMR reaction monitoring that can be used for the process understanding and development of active pharmaceutical ingredients. The parameters that are important for the development of a good, reliable model for the prediction and optimization of reaction conditions are discussed. The hydrolysis of acetic anhydride was chosen to illustrate the methodology because it is mechanistically and kinetically well established.
- Susanne, Flavien,Smith, David S.,Codina, Anna
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Read Online
- Efficient generation of an oxidopyrylium ylide using a Pd catalyst and its [5+2] cycloadditions with several dipolarophiles
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An efficient method for the generation of an oxidopyrylium ylide from 6-acetoxy-6-acetoxymethyl-2H-pyran-3(6H)-one using a Pd catalyst and [5+2] cycloadditions of the resulting ylide are described. Among substituted styrene derivatives as dipolarophiles, electron-rich styrenes showed higher yield (up to 80%). The [5+2] cycloaddition reactions can also be applied to exo-methylene cyclic compounds, and an improved method for the synthesis of polygalolide intermediate has been demonstrated.
- Suga, Hiroyuki,Iwai, Taichi,Shimizu, Masahiro,Takahashi, Kie,Toda, Yasunori
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Read Online
- One-pot synthesis of microporous and mesoporous (NH4) 3PW12O40 by reaction of in-situ generated PW12O403- with NH4+ in a strongly acidic solution
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A simple synthesis of microporous and micro/meso bimodal porous (NH 4)3PW12O40 by reaction of in-situ generated [PW12O40]3- with NH4 + in a strongly acidic
- Sahiro, Koichi,Ide, Yusuke,Sano, Tsuneji,Sadakane, Masahiro
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Read Online
- Late-Stage β-C(sp3)-H Deuteration of Carboxylic Acids
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Carboxylic acids are highly abundant in bioactive molecules. In this study, we describe the late-stage β-C(sp3)-H deuteration of free carboxylic acids. On the basis of the finding that C-H activation with our catalysts is reversible, the de-deuteration process was first optimized. The resulting method uses ethylenediamine-based ligands and can be used to achieve the desired deuteration when using a deuterated solvent. The reported method allows for the functionalization of a wide range of free carboxylic acids with diverse substitution patterns, as well as the late-stage deuteration of bioactive molecules and related frameworks and enables the functionalization of nonactivated methylene β-C(sp3)-H bonds for the first time.
- Mal, Sourjya,Uttry, Alexander,Van Gemmeren, Manuel
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supporting information
p. 10895 - 10901
(2021/08/03)
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- Stepwise Iodide-Free Methanol Carbonylation via Methyl Acetate Activation by Pincer Iridium Complexes
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Iodide is an essential promoter in the industrial production of acetic acid via methanol carbonylation, but it also contributes to reactor corrosion and catalyst deactivation. Here we report that iridium pincer complexes mediate the individual steps of methanol carbonylation to methyl acetate in the absence of methyl iodide or iodide salts. Iodide-free methylation is achieved under mild conditions by an aminophenylphosphinite pincer iridium(I) dinitrogen complex through net C-O oxidative addition of methyl acetate to produce an isolable methyliridium(III) acetate complex. Experimental and computational studies provide evidence for methylation via initial C-H bond activation followed by acetate migration, facilitated by amine hemilability. Subsequent CO insertion and reductive elimination in methanol solution produced methyl acetate and acetic acid. The net reaction is methanol carbonylation to acetic acid using methyl acetate as a promoter alongside conversion of an iridium dinitrogen complex to an iridium carbonyl complex. Kinetic studies of migratory insertion and reductive elimination reveal essential roles of the solvent methanol and distinct features of acetate and iodide anions that are relevant to the design of future catalysts for iodide-free carbonylation.
- Yoo, Changho,Miller, Alexander J. M.
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supporting information
p. 12633 - 12643
(2021/08/23)
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- Highly efficient visible-light photocatalytic ethane oxidation into ethyl hydroperoxide as a radical reservoir
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Photocatalytic ethane conversion into value-added chemicals is a great challenge especially under visible light irradiation. The production of ethyl hydroperoxide (CH3CH2OOH), which is a promising radical reservoir for regulating the oxidative stress in cells, is even more challenging due to its facile decomposition. Here, we demonstrated a design of a highly efficient visible-light-responsive photocatalyst, Au/WO3, for ethane oxidation into CH3CH2OOH, achieving an impressive yield of 1887 μmol gcat?1in two hours under visible light irradiation at room temperature for the first time. Furthermore, thermal energy was introduced into the photocatalytic system to increase the driving force for ethane oxidation, enhancing CH3CH2OOH production by six times to 11?233 μmol gcat?1at 100 °C and achieving a significant apparent quantum efficiency of 17.9% at 450 nm. In addition, trapping active species and isotope-labeling reactants revealed the reaction pathway. These findings pave the way for scalable ethane conversion into CH3CH2OOH as a potential anticancer drug.
- Zhu, Yao,Fang, Siyuan,Chen, Shaoqin,Tong, Youjie,Wang, Chunling,Hu, Yun Hang
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p. 5825 - 5833
(2021/05/07)
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- Production of Pure Aqueous13C-Hyperpolarized Acetate by Heterogeneous Parahydrogen-Induced Polarization
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A supported metal catalyst was designed, characterized, and tested for aqueous phase heterogeneous hydrogenation of vinyl acetate with parahydrogen to produce13C-hyperpolarized ethyl acetate for potential biomedical applications. The Rh/TiO2catalyst with a metal loading of 23.2 wt % produced strongly hyperpolarized13C-enriched ethyl acetate-1-13C detected at 9.4 T. An approximately 14-fold13C signal enhancement was detected using circa 50 % parahydrogen gas without taking into account relaxation losses before and after polarization transfer by magnetic field cycling from nascent parahydrogen-derived protons to13C nuclei. This first observation of13C PHIP-hyperpolarized products over a supported metal catalyst in an aqueous medium opens up new possibilities for production of catalyst-free aqueous solutions of nontoxic hyperpolarized contrast agents for a wide range of biomolecules amenable to the parahydrogen induced polarization by side arm hydrogenation (PHIP-SAH) approach.
- Kovtunov, Kirill V.,Barskiy, Danila A.,Shchepin, Roman V.,Salnikov, Oleg G.,Prosvirin, Igor P.,Bukhtiyarov, Andrey V.,Kovtunova, Larisa M.,Bukhtiyarov, Valerii I.,Koptyug, Igor V.,Chekmenev, Eduard Y.
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supporting information
p. 16446 - 16449
(2016/11/09)
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- Degradation of 2,5-dihydroxy-1,4-benzoquinone by hydrogen peroxide: A combined kinetic and theoretical study
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2,5-Dihydroxy-1,4-benzoquinone (DHBQ) is one of the key chromophores formed upon aging in cellulosic materials. This study addresses the degradation mechanism of DHBQ by hydrogen peroxide to provide a solid knowledge base for optimization of bleaching sequences aiming at DHBQ removal. Kinetic analysis provided an activation energy (Ea) of 20.4 kcal/mol. Product analyses indicated the product mixture to contain malonic acid, acetic acid, and carbon dioxide. DFT(B3LYP) computation presented a plausible mechanism for the formation of these products from DHBQ. DHBQ forms intermediate I2k, having an intramolecular O-O bridge between C-2 and C-5 of the 1,4-cyclohexadione structure. This O-O bond is homolytically cleaved, and the subsequent β-fragmentation of the resulting radical forms ketene and oxaloacetic acid. While ketene yields acetic acid, oxaloacetic acid then gives malonic acid and carbon dioxide through further attack of hydrogen peroxide via an intermediate that is oxidatively decarboxylated. The calculated Ea value (23.3 kcal/mol) in the rate-determining step, i.e., the homolysis of I2k, agreed well with the experimental value. There is also a minor pathway in which the spin state changes to triplet during the homolysis of I2k; in this way two malonyl radicals are formed that are converted to two molecules of malonic acid.
- Hosoya, Takashi,Rosenau, Thomas
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p. 3176 - 3182
(2013/07/04)
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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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- Kinetics and mechanism of oxidation of aliphatic aldehydes by morpholinium chlorochromate
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Oxidation of six aliphatic aldehydes by morpholinium chlorochromate (MCC) in dimethyl sulfoxide (DMSO) leads to the formation of corresponding carboxylic acids. The reaction is first order each in MCC and the aldehyde. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form : k ods = a + b[H+]. The oxidation of deuteriated acetaldehyde, MeCDO, exhibited a substantial primary kinetic isotope effect (kH/kD = 5.95 at 298 K). The oxidation of acetaldehyde has been studied in 19 different organic solvents. The solvent effect has been analysed using Taft's and Swain's multiparametric equations. The rate constants correlate well with Taft's σ* values and reaction constants are negative. A mechanism involving transfer of hydride ion has been suggested.
- Soni, Neelam,Tiwari, Vandana,Kumbhani,Shastri,Sharma, Vinita
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experimental part
p. 857 - 861
(2009/12/01)
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- The kinetics and mechanism of oxidation of aliphatic aldehydes by benzyltriethylammonium chlorochromate
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The oxidation of six aliphatic aldehydes by benzyltriethylammonium chlorochromate (BTEACC) in dimethyl sulfoxide (DMSO) leads to the formation of corresponding carboxylic acids. The reaction is first order each in BTEACC and the aldehyde. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: kobs = a + 6[H+]. The oxidation of deuteriated acetaldehyde, MeCDO, exhibited a substantial primary kinetic isotope effect (kH/ kD = 5.89 at 298 K). The oxidation of acetaldehyde has been studied in 19 different organic solvents. The solvent effect has been analysed using Taft's and Swain's multiparametric equations. The rate constants correlate well with Taft's σ* values; reaction constants being negative. A mechanism involving transfer of hydride ion has been suggested.
- Chouhan, Kavita,Rao, P.T.S.R.K. Prasad,Sharma, Pradeep K.
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p. 191 - 194
(2007/10/03)
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- Low-temperature NMR spectra of fluoride-acetic acid hydrogen-bonded complexes in aprotic polar environment
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Using low-temperature NMR (1H, 19F) technique in the slow exchange regime, the solutions containing tetrabutylammonium (TBA) acetate and HF have been studied in an aprotic freon mixture, CDF3/CDF 2Cl, exhibiting a dielectric permittivity, which increases strongly by lowering the temperature. Two different hydrogen bonded anionic clusters, a 1:1 cluster of the type AcOδ-?H?F -1+δ+ ([AcOHF]-) and a 2:1 cluster of the type AcOH?F-?HOAc ([(AcOH)2F]-) have been detected in equilibrium with each other, both forming ion pairs with the TBA countercation. [AcOHF]- exhibits an extremely strong hydrogen bond, with a proton shared between partially negatively charged oxygen and fluorine atoms. The NMR chemical shifts and scalar spin-spin coupling constants, 1J(FH), have been measured in the temperature range between 110 and 160 K, where separate NMR signals are observed for both species. In addition, H/D isotope effects on the 19F NMR chemical shielding have been measured for both clusters. In contrast to the related complexes [(FH) nF]- (n=1-4) studied previously, the NMR parameters of [AcOHF]- and of [(AcOH)2F]- depend strongly on temperature. This effect is associated with the increasing polarity of the solvent with decreasing temperatures, established earlier, which displaces the proton from fluorine to oxygen. As a motive power of this conversion, preferential solvation of the compact fluoride ion as compared to acetate is proposed.
- Golubev, Nikolai S.,Tolstoy, Peter M.,Smirnov, Sergei N.,Denisov, Gleb S.,Limbach, Hans-Heinrich
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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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- Thermolysis of methanolic solutions of acetyl propionyl peroxide
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Kinetic measurements by 1H NMR spectroscopy and chemically induced dynamic nuclear polarization (CIDNP) effects were used to study thermolysis of solutions of acetyl propionyl peroxide in methanol-d4. It is found that the thermolysis may occur both by radical and by nonradical mechanisms. A scheme of the thermolysis is proposed. Parameters of the Arrhenius equation for the rate constants of the decomposition of the peroxide and the decarboxylation of acyloxyl radicals are obtained.
- Skakovskii,Stankevich,Lamotkin,Tychinskaya,Rykov
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p. 614 - 622
(2007/10/03)
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- Analysis of the Mechanism of Photolysis of Methanol-d4 Solutions of Acetylpropionyl Peroxide With the Use of Chemically Induced Dynamic Nuclear Polarization
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On the basis of the effects of chemically induced dynamic nuclear polarization of 1H and 13C and the yields of reaction products, the photolysis of methanol-d4 solutions of acetylpropionyl peroxide is investigated within the. temperature interval 193-333
- Skakovskii, E. D.,Stankevich, A. I.,Lamotkin, S. A.,Tychinskaya, L. Yu.,Avrinskii, G. S.,Rykov, S. V.
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p. 770 - 777
(2007/10/03)
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- Kinetics and mechanism of oxidation of aliphatic aldehydes by 2,2′-bipyridinium chlorochromate
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Oxidation of six aliphatic aldehydes by 2,2′-bipyridinium chlorochromate (BPCC) in dimethyl sulphoxide (DMSO) leads to the formation of corresponding carboxylic acids. The reaction is first order each in BPCC and the aldehyde. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: kobs = a + b[H+]. The oxidation of deuteriated acetaldehyde, MeCDO, exhibits a substantial primary kinetic isotope effect (kH/kD = 5.90 at 298K). The oxidation of acetaldehyde has been studied in nineteen different organic solvents. The solvent effect has been analysed using Taft's and Swain's multiparametric equations. The rate constants correlate well with Taft's σ* values; reaction constants being negative. A mechanism involving transfer of hydride ion has been suggested.
- Kumbhat,Sharma,Banerji
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p. 1169 - 1173
(2007/10/03)
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- Kinetic and Mechanism of the Oxidation of Aliphatic Aldehydes by Benzyltrimethylammonium Chlorobromate
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The oxidation of six aliphatic aldehydes by benzyltrimethylammonium chlorobromate (BTMACB) in acetic acid, resulted in the formation of corresponding carboxylic acids. The reaction is first order with respect to BTMACB and the aldehyde. The oxidation of deuteriated acetaldehyde (MeCDO) showed the presence of a substantial kinetic isotope effect (kH/kD = 6.14 at 298 K). Addition of benzyltrimethylammonium chloride or bromide ion has no effect on the reaction rate. The rates constant correlate well with Taft's ?' constants: the reaction constant being negative. A mechanism involving a hydride-ion transfer from the aldehyde hydrate to the oxidant in the rate-determining step has been suggested.
- Bohra, Anupama,Sharma, P. K.,Banerji, Kalyan K.
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p. 1343 - 1356
(2007/10/03)
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- Hydrogen isotope fractionation factors for N,N-dimethylbenzyl-ammonium ion and some related species: An unusually strong preference for deuterium over protium
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Deuterium fractionation factors were determined by the 1H and 13C NMR methods in aqueous solution for PhCH2NLMe2+ (φ = 1.47 ± 0.05), PhCH2OL (φ = 1.04 ± 0.06), PhCO2L (φ = 1.04 ± 0.08), and CH3CO2L (φ = 0.99 ± 0.02). The medium effect for transferring PhCH2NMe2 from H2O to D2O, Φ = 1.025 ± 0.003, was also determined by partitioning this substance between water and immiscible organic solvents, and a UV spectroscopic method was used to measure the solvent isotope effect on the acid ionization of PhCH2NLMe2+, (Qa)H/(Qa)D = 4.88 ± 0.16. This solvent isotope effect agrees well with the value predicted using the relevant fractionation factors, (Qa)H/(Qa)D = 4.38 ± 0.28. The unusually large value of φ for PhCH2NLMe2+ is attributed to stiffened bending vibrations of its N-L bond imposed by the tetrahedral structure of the ion and the bulk of its methyl groups.
- Guo, Hong-Xun,Kresge, A. Jerry
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p. 295 - 298
(2007/10/03)
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- Photolysis of methanolic solutions of benzyl acetate
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Photolysis of solutions of benzyl acetate in CD3OD has been studied.As has been established based on the effects of CIDNP and the yields of products, decomposition of the starting compound occurs from both excited singlet and triplet electronic states.The contributions of homolysis and solvolysis to the overall photochemical process have been measured, and the lifetimes of the acetoxy radicals formed have been evaluated.Toluene-d has been shown to be formed mostly by disproportionation of benzyl radicals with hydroxymethyl radicals derived from the solvent molecules.Key words: benzyl acetate; methanol; photolysis; homolysis; solvolysis; CIDNP effects.
- Skakovskii, E. D.,Rykov, S. V.,Tychinskaya, L. Yu,Murashko, V. L.,Ogorodnikova, M. M.,et al.
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p. 647 - 650
(2007/10/02)
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- A Novel Hybrid System for the Direct Oxidation of Ethane to Acetic and Glycolic Acids in Aqueous Medium
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A combination of platinum(II) ion and metallic platinum is found to oxidise ethane to a mixture of acetic and glycolic acids in aqueous medium in the presence of oxygen; the platinum(II) ion is responsible for the initial C-H activation step leading eventually to the formation of ethanol and ethylene glycol, while metallic platinum catalyses the subsequent air oxidation of the alcohols to the corresponding acids.
- Sen, Ayusman,Lin, Minren
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p. 508 - 510
(2007/10/02)
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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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p. 892 - 893
(2007/10/02)
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- C-H activation in aqueous medium. The diverse roles of platinum(II) and metallic platinum in the catalytic and stoichiometric oxidative functionalization of organic substrates including alkanes
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The oxidation of ethers, alcohols, esters, and light alkanes (ethane, propane) by K2PtCl4 and Pt/O2 in aqueous medium has been studied. Results appear to indicate that unactivated C-H bonds were attacked and oxidized by Pt(II) whereas C-H bonds a to an oxygen were activated and catalytically oxidized by metallic Pt in the presence of O2. For example, Pt(II) was found to oxidize ethane selectively to the alcohols, ethanol, and ethylene glycol. In the presence of metallic Pt and O2, further oxidation of the alcohol functionality occurred to generate the corresponding carboxylic acids. Thus, with proper choice of the C-H activating system, it was possible to oxidize substrates with a fairly high degree of selectivity with respect to the oxidation level, as well as the particular C-H bond that was functionalized. With respect to the latter, because of the "chelate effect", the selective activation and oxidation by Pt(II) of C-H bonds suitably distant from a coordinating oxygen was achieved. For ethers, the order of reactivity was α-C-H β-C-H γ-C-H.
- Sen, Ayusman,Lin, Minren,Kao, Lien-Chung,Hutson, Alan C.
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p. 6385 - 6392
(2007/10/02)
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- STEREOCHEMISTRY AND MECHANISM OF CYCLOPROPENE RING OPENING IN REACTIONS OF CYCLOPROPENE COMPOUNDS WITH ELECTROPHILES. STEREOCHEMISTRY OF ADDITION OF 2,4-DINITROBENZENESULFENYL CHLORIDE TO 1-METHYLCYCLOPROPENE
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Cyclopropene ring opening in reactions of 1-methylcyclopropene with electrophilic reagents can be proceed with high stereoselectivity.The configuration of the products depends on the nature of the electrophile.Reaction with deuterium chloride gave products with the Z-configuration.In the reaction of 1-methylcyclopropene with reagents that tend to form cyclic intermediates (sulfenyl halides, N-bromosuccinimide, tert-butyl hypochlorite), the cyclopropene ring opened E-stereoselectively.Reaction with bromide gave a mixture of E- and Z- isomers in the ratio 3 : 1.It was established by X-ray structure analysis that 1-methylcyclopropene reacts with 2,4-dinitrobenzenesulfenyl chloride by a Markovnikov trans-addition scheme.Mechanism for the reaction of cyclopropene compounds with electrophiles are proposed and discussed.
- Kartashov, V. R.,Skorobogatova, E. V.,Afanas'ev, P. S.,Chertkov, V. A.,Sergeev, N. M.,et al.
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p. 1639 - 1648
(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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- Electrophilic Cleavage of Cyclopropanes. Acetolysis of Alkylcyclopropanes
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The solvent kinetic hydrogen isotope effect showed that proton transfer is at least partially rate determining for the acetolysis of cyclopropanes which span a range of 1010 in reactivity.The energies and structures of protonated cyclobutanes were calculated and provide an explanation for the large difference in reactivity between cyclopropanes and cyclobutanes despite their similarity in enthalpies of reaction.The rates and products of acetolysis of a series of alkyl-substituted cyclopropanes were examined.The data, along with the results of ab initio calculations, indicate that for alkyl-substituted cyclopropanes, the protonated species is highly unsymmetrical.Cleavage of the cyclopropane ring always occurs so that the nucleophile becomes attached to the most substituted carbon, but the proton may attack either of the remaining carbons.Proton attack may lead to either retention or inversion of configuration depending on the orientation of the attacking proton with respect to the ring.
- Wiberg, Kenneth B.,Kass, Steven R.
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p. 988 - 995
(2007/10/02)
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- ADDITION OF ACETIC ACID TO 5-METHYLENE- AND 5-METHYL-6-METHYLENEBICYCLOHEPT-2-ENE
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The reaction of acetic acid with 5-methylene- and 5-methyl-6-methylenebicyclohept-2-ene takes place through protonation of the semicyclic double bond with the intermediate formation of a homoallylic ion.When the reaction was realized under kinetically controlled conditions, the tertiary acetates of endo-5-methyl- and endo,endo-5,6-dimethylbicyclohept-2-en-exo-5-ol were obtained; the final products were only the esters of 1-methyl- and 1,7-dimethyltricyclo2,6>heptan-3-ol.The rate of the reaction of 5-methyl-6-methylenebicyclohept-2-ene with acetic acid was determined.The reactions are proposed as methods for the production of esters and also of alcohols, ketones, and hydrocarbons with the tricyclo2,6> heptane structure.
- Bobyleva, A. A.,Dubitskaya, N. F.,Pekhk, T. I.,Belikova, N. A.
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p. 921 - 927
(2007/10/02)
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- Mecanisme d'acetolyse d'esters d'enol styreniques
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We have studied the reaction of enol esters in acidic media: wherein Z = H, CH3, CH2Cl, CHCl2 and CCl3.The raction is first order.Log kex = α H'0 + β (H'0 = acidity function of Hammett) with α-1.A general acid catalysis is observed.Following a discussion of possible SN, AAC2 and ASE2 mechanisms, we propose an ASE2 mechanism for this reaction.
- Montheard, Jean-Pierre,Camps, Marcel,Chatzopoulos, Michel,Benzaid, Ahmed
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p. 109 - 116
(2007/10/02)
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- Phosphoric-Carboxylic Imides. 2. Solvolytic Cleavage of the Nitrogen-Carbonyl and Nitrogen-Phosphoryl Bonds
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The neutral and acid-catalyzed solvolysis (hydrolysis and alcoholysis) of mixed phosphoric-carboxylic imides (1), X2P(O)-NR-C(O)R'(X = EtO, MeO, CH2O, Et; R = H, Me; R'= Me, Ph) has been studied and compared with the solvolytic behavior of parent phosphoric and carboxylic amides and symmetrical imides.The neutral cleavage of the P-N bond is believed to involve an oxyphosphorane intermediate.The ionization of 1 follows the amide acidity function, with half-protonation at the carbonyl oxygen atom occuring at ca. 70percent D2SO4.The remarkable stability of the P-N bond in acidic solutions, together with the susceptibility of the N-C(O)solvolysis toward acid catalysis, is consistent with the exclusion of the N-protonation of 1 and is in accordance with carbonyl oxygen protonation and the significant electron-withdrawing effect of the N-phosphinyl substituent.The hydration parameter treatment was applied to the acid-catalyzed N-C(O) hydrolysis of 1d (1, X = EtO; R = R'= Me), and the results are compared with those obtained for the acid-catalyzed hydrolysis of N-methylacetamide.The acidic solvolysis of 1, with respect to both the P(O)-N and N-C(O) cleavage, lies between the extremes characterized by the respective parent amides and symmetrical imides.
- Mizrahi, V.,Modro, T. A.
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p. 3030 - 3037
(2007/10/02)
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- A Comparison between the Stereoselective Thermal-Induced and Ionization-Induced Elimination of Acetic Acid from 2-Butyl Acetate
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Photoelectron photoion coincidence spectrometry shows that the ionized acetate ester of sec-butyl alcohol eliminates acetic acid just above the ionization potential but cleaves to form C2H3O+ at energies greater than 2 eV above this point.Experiments with the C-3 deiterium-labeled diastereomers of 2-butyl acetate show the elimination reaction to be stereoselective at all energies 0.1 eV greater than the ionization potential.These measurements were made by threshold photoelectron photoion coincidence spectrometry (TPEPICO).The TPEPICO stereoselective channel ratios were fit well by RRKM calculations in which the threshold energy dif ference for the stereoisomeric pathways was 600-800 cal/ mol.These numbers may be minimum values if a C-3 epimerization, i.e., stereochemical scrambling, mechanism intervenes in these ions.Such a process is probably responsible for the absence of stereoselection in the metastable ions formed in an electron-impact mass spectrometer.Published data on the thermal decomposition of 2-butyl acetate imply a difference in threshold energy for the stereochemical paths of 690-830 cal/mol.Existing mechanistic proposals for the loss of acetic acid from the ion (McLafferty rearrangement) and from the neutral suggest similar threshold energy differences for the stereoselective pathways.Integration of the microscopic stereoselective channel ratios over PEPICO-derived energy distribution function of those molecular ions which undergo elimination of acetic acid predicts the photoionization source temperature dependence of the stereoselectivity should be less than that experimentally observed in an electron-impact mass spectrometer.
- Green, Mark M.,McCluskey, Richard J.,Vogt, Juergen
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p. 2262 - 2269
(2007/10/02)
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- The stereochemistry of the enzymic decarboxylation of L-arginine and L-ornithine
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The decarboxylation of L-ornithine to yield putrescine, catalyzed by the L-ornithine decarboxylase (EC 4.1.1.17) of E. coli, and the decarboxylation of L-arginine to yield agmatine, catalyzed by the L-arginine decarboxylase (EC 4.1.1.19) of E. coli, take place with retention of configuration.
- Richards, James C.,Spenser, Ian D.
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p. 2810 - 2820
(2007/10/02)
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- Acyl Substituent Effects on Rates of Acyl Transfer to Thiolate, Hydroxide, and Oxy Dianions
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The rates of transfer of a series of polar aliphatic acyl groups (-0.3 (*) (*) (*) 1.05) from p-nitrophenol to hydroxide, to the thiol anion of N-acetyl-L-cysteine, and to a series of phosphonate dianions have been determined in aqueous solution.The rate constants for the alkaline hydrolysis of ten p-nitrophenyl esters can be correlated reasonably well (r = 0.981) to the single-parameter Hammett-Taft equation based on the polar substituent constant.The reaction constant for the alkaline hydrolysis is (*) = 2.9 with an interval estimator (90percent confidence) of +/-0.3.The (*) value for the thiolysis reaction is only slightly larger (16 +/- 13percent) than the corresponding value for the alkaline hydrolysis reaction.These kinetic (*) values are essentially identical with the equlibrium (*) for hydroxide or thiolate addition to aldehydes (Kanchuger and Byers).To the extent that gem diolate and thiohemiacetalate formation are appropriate model reactions for the formation of the anionic tetrahedral intermediates in the corresponding acyl transfer reactions, the magnitude of the kinetic (*) values suggests that the transition states for the alkaline hydrolysis and for the thiolysis reactions are similar, in geometry and charge distribution, to the intermediates.Acyl transfer from p-nitrophenol to phosphonate dianions involves an uncatalyzed nucleophilic displacement by the oxy dianion.The (*) value for the reaction of (chloromethyl)phosphonate with the p-nitrophenyl esters is 2.4 (+/-0.3).The second-order rate constants for the reactions between the phosphonates and p-nitrophenyl acetate, p-nitrophenyl chloroacetate, and p-nitrothiophenyl acetate show a small sensitivity to the basicity (pKa2) of the nucleophile (βnuc ca. 0.3).An explanation of the magnitudes of the (*) and βnuc values, and of the anomalously low reaction rates (relative to oxy monoanions and amines of comparable basicities) for acyl transfer to the phosphonates, is that electrostatic interactions and desolvation of the oxy dianion make substantial contributions to the activation energy barrier for nucleophilic attack.
- Shames, Spencer L.,Byers, Larry D.
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p. 6170 - 6177
(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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- Deamination via Nitrogen Derivatives of Sulfonic Acids: N-Alkyl-N-nitroso-4-toluenesulfonamides, N-Alkyl-N-nitro-4-toluenesulfonamides, and N-Alkyl-N'-(4-toluenesulfonyloxy)diimide N-Oxides
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The thermal decomposition of several N-alkyl-N-nitroso-4-toluenesulfonamides, N-alkyl-N-nitro-4-toluenesulfonamides, and N-alkyl-N'-(4-toluenesulfonyloxy)diimide N-oxides was undertaken to determine whether the basicity of the negatively charged counterion in deamination reactions was a reaction variable.The nitrososulfonamides decompose following first-order kinetics to give the corresponding esters with retention of configuration.The reaction characteristics are very similar to those of the N-nitrosocarboxamides, and the reaction mechanisms are presumably very similar also.The N-nitrosulfonamides required high temperatures for decomposition, and they gave an anomalous set of products: amide (by denitration) and olefins, but no nitrous oxide or toluenesulfonate esters.The N'-toluenesulfonoxydiimide N-oxides, isomeric to the nitrosulfonamides, proved to be surprisingly stable compounds; they decompose by first-order kinetics to yield the corresponding esters and nitrous oxide.
- White, Emil H.,Lewis, Charles P.,Ribi, Max A.,Ryan, Thomas J.
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p. 552 - 558
(2007/10/02)
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- Stereochemistry and Regiochemistry of Electron Impact Thermally and Photolytically Induced Eliminations from 2-Decalyl Acetates
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Deuterium-labeled compounds are used to define the stereochemistry and regiochemistry of the electron impact induced elimination of acetic acid from trans,trans-2-decalyl acetate and trans,cis-2-decalyl acetate.Both compounds fragment with very predominant abstraction of equatorial hydrogen atoms.Since the trans equatorial hydrogens of the trans,trans acetate cannot be approached within the requisite 1.8 Angstroem by the acetate carbonyl in any boatlike conformer, this result demonstrates that hydrogen abstraction largely occurs from the chair conformer of the cyclohexyl ring.Both compounds fragment with predominant elimination toward C-1 rather than C-3.The regiochemistry of the pyrolysis of the acetates and the photolysis of the corresponding phenylacetates is compared with that of the mass spectral elimination.
- Rej, R. N.,Taylor, C.,Eadon, G.
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p. 126 - 130
(2007/10/02)
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