- Phosphine-Catalyzed Vinylation at Low Acetylene Pressure
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The vinylation of various nucleophiles with acetylene at a maximum pressure of 1.5 bar is achieved by organocatalysis with easily accessible phosphines like tri-n-butylphosphine. A detailed mechanistic investigation by quantum-chemical and experimental methods supports a nucleophilic activation of acetylene by the phosphine catalyst. At 140 °C and typically 5 mol % catalyst loading, cyclic amides, oxazolidinones, ureas, unsaturated cyclic amines, and alcohols were successfully vinylated. Furthermore, the in situ generation of a vinyl phosphonium species can also be utilized in Wittig-type functionalization of aldehydes.
- Bienewald, Frank,Comba, Peter,Hashmi, A. Stephen K.,Menche, Maximilian,Rominger, Frank,Schafer, Ansgar,Schaub, Thomas,Sitte, Nikolai A.,Tuzina, Pavel
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p. 13041 - 13055
(2021/09/18)
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- Method for synthesizing vinyl methyl ether by using ethylene glycol dimethyl ether
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The invention discloses a method for synthesizing vinyl methyl ether by using ethylene glycol dimethyl ether. The synthesis method comprises the step of carrying out elimination reaction on ethylene glycol dimethyl ether under the catalytic action of solid alkali to obtain vinyl methyl ether and methanol, wherein the solid alkali is magnesium oxide, cerium dioxide, calcium oxide or calcium-magnesium mixed oxide, and in the calcium-magnesium mixed oxide, the molar ratio of calcium to magnesium is 0.1-4. According to the method for preparing the vinyl methyl ether by catalyzing the ethylene glycol dimethyl ether with the solid alkali, provided by the invention, the raw materials are wide in source and green; the catalyst is efficient, cheap and good in stability; the yield of the target product can reach 80%; the byproduct methanol can be recycled to prepare reaction raw materials; and the method is low in equipment requirement and small in investment, and has very important practical application value.
- -
-
Paragraph 0029-0043
(2020/11/01)
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- Thermally Stable Half-Sandwich Benzhydryl Ln(II) (Ln = Sm, Yb) Complexes Supported by Sterically Demanding Carbazolyl and Fluorenyl Ligands
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A series of new isolable and thermally stable half-sandwich Ln(II) benzhydryl complexes coordinated by the sterically demanding ligands tert-butylcarbazol-9-yl [tBu4Carb]Ln[(p-tBu-C6H4)2CH](L) (Ln = Sm, L = DME (4); Ln = Yb, L = DME (5); Ln = Yb, L = TMEDA (6)) and 2,7-di-tert-butyl-fluoren-9-trimethylsilylyl [2,7-tBu2-9-Me3Si-C13H6]Yb[(p-tBu-C6H4)2CH](DME) (7) were synthesized by the alkane elimination reaction of [(p-tBu-C6H4)2CH]2Ln(Ln) (Ln = Sm, Yb) with tBu4CarbH and 2,7-tBu2-9-Me3Si-C13H7. X-ray analysis revealed that in 4, 5, and 7 the benzhydryl ligand is coordinated to the metal ion in an ν3 coordination mode, while in 6 it is ν1-bound. The type of coordination of the benzhydryl ligands in diamagnetic 5-7 is retained in their C6D6 solutions. Complexes 4-7 demonstrated unprecedented thermal stability and do not undergo decomposition after heating their solutions in C6D6 or toluene at 100 °C for 72 h. The reactions of [tBu4Carb]Ln[(p-tBu-C6H4)2CH](DME) (Ln = Sm (4), Ln = Yb (5)) with an excess of DME led to the formation of the symmetrical bis(carbazolyl) complex products [tBu4Carb]2Ln(DME)4 (Ln = Sm (8), Yb (9)) isolated in the form of separated ion pairs.
- Selikhov, Alexander N.,Shavyrin, Andrey S.,Cherkasov, Anton V.,Fukin, Georgy K.,Trifonov, Alexander A.
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p. 4615 - 4624
(2019/12/24)
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- Influence of Boiling on the Radiolysis of Diglyme
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The radiolysis of diethylene glycol dimethyl ether (diglyme) in a boiling state has been studied for the first time. Boiling facilitates the cleavage of internal C–O bonds, weakens the cage effect and diglyme regeneration processes, and facilitates the exchange and dimerization reactions of radicals. As compared with radiolysis at room temperature, the amount of unsaturated products of diglyme fragmentation formed during irradiation in the boiling state is smaller by a factor of 4, and the disproportionation products of heavy radicals are found in negligible amounts, if any. The yield of radiolytic decomposition of diglyme under boiling conditions is ～15 molecule/100 eV, which is higher than that at room temperature by a factor of almost 1.5.
- Vlasov,Kholodkova,Ponomarev
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p. 312 - 318
(2018/08/01)
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- Chloro and alkyl rare-earth complexes supported by ansa-Bis(amidinate) ligands with a rigid o-phenylene linker. Ligand steric bulk: A means of stabilization or destabilization?
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ansa-Bis(amidinate) ligands with a rigid o-phenylene linker, C 6H4-1,2-{NC(tBu)N(2,6-R2C6H 3)H}2 (R = Me (1), iPr (2)), were successfully employed for the synthesis of rare-earth chloro and alkyl species. The reaction of dilithium derivatives of 1 and 2 with LnCl3 (Ln = Y, Lu) afforded the monomeric bis(amidinate) chloro lanthanide complexes [C6H 4-1,2-{NC(tBu)N(2,6-R2C6H3)} 2]Y(THF)(μ-Cl)2Li(THF)2 (R = Me (3), iPr (5)) and [C6H4-1,2-{NC(tBu)N(2,6-Me2C 6H3)}2]LuCl(THF)2 (4). Bis(amidinate) ligands in complexes 3 and 4 are coordinated to the metal atoms in a tetradentate fashion, while the bulkier ligand in 5 is tridentate. The alkane elimination reactions of 1 and 2 with equimolar amounts of (Me 3SiCH2)3Ln(THF)2 (Ln = Y, Lu) allowed us to obtain the monoalkyl complexes [C6H4-1,2- {NC(tBu)N(2,6-R2C6H3)}2]Ln(CH 2SiMe3)(THF)n (Ln = Y, R = Me, n = 1 (6); Ln = Lu, R = Me, n = 1 (7); Ln = Y, R = iPr, n = 2 (8)). The kinetics of thermal decomposition of complexes 6-8 were measured, and for 6 the activation energy was obtained from the temperature dependence of the rate constants (E a = 67.0 ± 1.3 kJ/mol). Complexes 6 and 7 turned out to be inert toward H2 and PhSiH3. Surprisingly, complex 8 was inert toward H2 and PhSiH3 but rapidly cleaved C-O bonds of DME. The reaction resulted in the formation of the methoxy complex {[C 6H4-1,2-{NC(tBu)N(2,6-iPr2C6H 3)}2]Y(μ2-OMe)]}2(μ 2-DME) (9) and methyl vinyl ether.
- Tolpygin, Aleksei O.,Shavyrin, Andrei S.,Cherkasov, Anton V.,Fukin, Georgy K.,Trifonov, Alexander A.
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p. 5405 - 5413
(2012/11/13)
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- Competition between reaction and intramolecular energy redistribution in solution: Observation and nature of nonstatistical dynamics in the ozonolysis of vinyl ethers
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Experimental product ratios in ozonolyses of alkyl vinyl ethers in solution do not fit with expectations based on statistical rate theories. The selectivity among cleavage pathways increases with the size of the alkyl group but to an extent that is far less than RRKM theory would predict. Trajectory studies account for the observed selectivities and support a mechanism involving a competition between cleavage of the primary ozonide and intramolecular vibrational energy redistribution. A statistical model is presented that assumes that RRKM theory holds for a molecular subset of the primary ozonides, allowing the rates of energy loss from the ozonides to be estimated from the observed product ratios.
- Quijano, Larisa Mae M.,Singleton, Daniel A.
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supporting information; body text
p. 13824 - 13827
(2011/10/12)
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- Pyrolysis of α- and β-heteroatoms substituted ethyl phenyl sulfoxides
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A study on the mechanism of the thermal decomposition of α- and β-heteroatoms substituted ethyl phenyl sulfoxides was carried out using 1-chloroethyl phenyl sulfoxide (1); two diastereomeric 1-acetoxyethyl (substituted phenyl) sulfoxides (2a) and (2b); and 2-chloroethyl phenyl, 2-bromoethyl phenyl, and 2-methoxyethyl phenyl sulfoxides (3, 4, 5). The rate of pyrolysis of 1 was 4.8 times faster at 160°C than that of ethyl phenyl sulfoxide used as a reference, while those of 2a and 2b were 107 and 155 times faster, respectively. The results indicate that the lone pair of electrons on the α-heteroatoms has a larger rate acceleration effect than the electronegativity of them. The substituent effects of the phenyl group of 2a and 2b gave positive Hammett ρ-values (ρa= 0.76 and ρb= 0.80 vs. σ). Activation parameters for 2a and 2b are as follows: 2a, ΔH?= 112 kJmol-1, ΔS?= -20 JK-1mol-1; 2b, ΔH?= 107 kJmol-1, ΔS?= -29 JK-1mol-1. Large deuterium kinetic isotope effects for 1-acetoxyethyl-2,2,2-d3 phenyl sulfoxides (2ad and 2bd) were observed (kH/kD= 3.5 ～ 4.1). These results suggest that the pyrolysis of -heteroatom substituted ethyl phenyl sulfoxides proceeds via a five-membered transition state deviated to E1-like in character. On the other hand, from the results of kinetics for the pyrolysis of 3, 4, and 5, no effect by the β-halogen atoms or some deceleration effect by the β-methoxy group was observed. Thus the reaction seems to proceed via an E1-like mechanism. Copyright Taylor & Francis Group.
- Yoshimura, Toshiaki,Sakae, Hironori,Yoshizawa, Masaki,Hasegawa, Kiyoshi,Tsukurimichi, Eiichi
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experimental part
p. 1162 - 1173
(2010/08/06)
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- CONTINUOUS METHOD FOR PRODUCING METHYL VINYL ETHER
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The invention relates to a method for continuously producing methyl vinyl ether by reacting methanol with ethyne in the liquid phase in the presence of a basic alkali metal compound or alkaline earth metal compound at a temperature ranging from 40 to 300 °C and under a pressure ranging from 0.1 to 5 MPa abs. According to the invention, the reaction is carried out in the absence of a continuous gas phase and with a methyl vinyl ether concentration in the entire liquid phase of = 30 % by weight.
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Page/Page column 13
(2008/06/13)
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- Trends in alkyl substituent effects on nucleophilic reactions of carbonyl compounds: Gas phase reactions between ammonia and R1R2COCH3+ oxonium ions
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The reactivity of carbonyl substituted methyl oxonium ions (R1R2COCH3-) towards ammonia has been investigated using an FT-ICR mass spectrometer and ab initio calculations. The monosubstituted ions (R1=H: R2 = H, CH3, C2H5 and i-C3H7) show different reaction patterns with variable degree of: (1) nucleophilic substitution, (2) addition elimination and (3) proton transfer, when reacted with ammonia. In all cases addition-elimination dominates over nucleophilic substitution, and the observed reactions are slow. The trends in reactivity are consistent with the alkyl group's electronic properties, as expressed by a single parameter linear or slightly non-linear model.
- Bache-Andreassen, Lihn,Uggerud, Einar
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p. 705 - 713
(2007/10/03)
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- Mechanism and structure-reactivity correlation in the homogeneous, unimolecular elimination kinetics of 2-substituted ethyl methylcarbonates in the gas phase
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The gas-phase elimination kinetics of 2-substituted ethyl methylcarbonates were determined in a static reaction system over the temperature range of 323-435 °C and pressure range 28.5-242 Torr. The reactions are homogeneous, unimolecular and follow a first-order rate law. The kinetic and thermodynamic parameters are reported. The 2-substituents of the ethyl methylcarbonate (CH3OCOOCH2CH2Z, Z = substituent) give an approximate linear correlation when using the Taft-Topsom method, log(k z/kH)= -(0.57 ± 0.19)σα + (1.34 ± 0.49)σR (r = 0.9256; SD = 0.16) at 400 °C. This result implies the elimination process to be sensitive to steric factors, while the electronic effect is unimportant. However, the resonance factor has the greatest influence for a favorable abstraction of the β-hydrogen of the C3- H bond by the oxygen carbonyl. Because ρα is significant, a good correlation of the alkyl substituents of carbonates with Hancock's steric parameters was obtained: log(kR/kH versus Esc for CH 3OCOOCH2CH2R at 400°C, R = alkyl, δ= -0.17 (r=0.9993, SD = 0.01). An approximate straight line was obtained on plotting these data with the reported Hancock's correlation of 2-alkyl ethylacetates. This result leads to evidence for the β-hydrogen abstraction by the oxygen carbonyl and not by the alkoxy oxygen at the opposite side of the carbonate. The carbonate decompostion is best described in terms of a concerted six-membered cyclic transition state type of mechanism. Copyright
- Chuchani, Gabriel,Marquez, Edgar,Herize, Armando,Dominguez, Rosa Maria,Tosta, Maria,Brusco, Doris
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p. 839 - 848
(2007/10/03)
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- A structure-reactivity correlation with three slopes in the elimination kinetics of 2-substituted ethyl N,N-dimethyl-carbamates in the gas phase
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The elimination kinetics of 17 2-substituted ethyl N,N-dimethylcarbamates in the gas phase were determined in the temperature range of 269.5-420.2°C and the pressure range of 24-186 Torr. The reactions in a static system and in the presence of a free radical inhibitor are homogeneous and unimolecular and follow a first-order rate law. The kinetics and thermodynamic parameters are described. The use of several structure-reactivity relationship methods meaningless results, except for Taft σ* values. Three good slopes are originated at σ*(CH3) = 0.00. Slope a: the 2-substituted alkyl groups gave a good straight line when log (k/kCH3) vs σ* values (ρ* = - 1.94 ± 0.30, r = 0.977 at 360°C) were plotted. Slope b: Polar2 substituents gave an approximate straight line with ρ* = - 0.12 ± 0.02, r = 0.936 at 360°C. Slope c:the correlation of multiple bonded and electron-withdrawing substituents interposed by a methylene group at the 2-position of ethyl N,N-dimethylcarbamate was found to give a very good straight line wirh ρ* = 0.49 ± 0.02, r = 0.991 at 360°C. Mechanisms are suggested on the basis of these relationships. The point position of the substituents phenyl (C6H5) and isopropenyl [CH2=C(CH3)] at the 2-position was found to fall far above the three slopes of the lines. These results are interpreted in terms of neighboring group participation of these substituents in the elimination process of the carbamates. However, the acidity of the benzylic and allylic Cβ-H bond for a six-membered cyclic transition state may not be ignored. Copyright
- Chuchani, Gabriel,Nunnez, Oswaldo,Marcano, Norka,Napolitano, Suvighey,Rodriguez, Henry,Dominguez, Marianella,Ascanio, Judany,Rotinov, Alexandra,Dominguez, Rosa M.,Herize, Armando
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p. 146 - 158
(2007/10/03)
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- Process for production of unsaturated ether and catalyst used for production of unsaturated ether
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The present invention provides a process for producing an unsaturated ether, which comprises subjecting a glycol ether to intramolecular dehydration in a gas phase in the presence of a catalyst to convert the glycol ether into an unsaturated ether directly in a one-step reaction. As the catalyst, an oxide containing, for example, silicon and an alkali metal is used. The process, which uses no auxiliary raw material, can produce an unsaturated ether (a vinyl ether and/or an allyl ether) simply and safely without generating any waste material derived from the auxiliary raw material.
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-
-
- Synthesis of Fischer carbene complex of iridium by C-H bond activation of methyl and cyclic ethers: Evidence for reversible α-hydrogen migration
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We report here a mild and versatile route to Fischer carbene complexes of iridium via the activation of C-H bonds of methyl and cyclic ethers, along with our preliminary studies of this rare family of carbene complexes. Theoretical studies suggest that α-hydrogen migrations can be kinetically favorable if a coordinatively unsaturated species can be accessed. Thus, the lability of the triflate ligand presumably facilitates this process. Further evidence for the rapidity, as well as reversibility, of this rearrangement was obtained by NMR analysis.
- Luecke,Arndtsen,Burger,Bergman
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p. 2517 - 2518
(2008/10/08)
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- Nucleophilic Addition to Acetylenes in Superbasic Catalytic Systems. VII. Vinylation of Lower Alcohols
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Superbasic systems KOH-DMSO and KOH-HMPA with acetylene and alcohols form highly active catalytic complexes capable of sharply increasing the rate and selectivity of nucleophilic addition of alcohols to acetylene and allowing preparation of high-purity lower alkyl vinyl ethers in high yield under acetylene pressure equal to atmospheric.
- Trofimov, B. A.,Oparina, L. A.,Lavrov, V. I.,Parshina, L. N.
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p. 597 - 600
(2007/10/03)
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- Isomerization and Decomposition of Propylene Oxide. Studies with a Single-Pulse Shock Tube
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The thermal reactions of propylene oxide (1,2-epoxypropane) were studied behind reflected shocks in a pressurized driver single-pulse shock tube over the temperature range 850-1250 K and overall densities of ca. 3E-5 mol/cm3.Four isomerization products, acetone, propanal, methyl vinyl ether, and allyl alcohol, and a large number of decomposition products were obtained under shock heating.The major decomposition products in decreasing order of abundance were CO, C2H4, C2H6, and CH4.Studies with free-radical scavengers and with isotopically labelled reactant (C3D6O) indicated that the isomerization products and ethylene retain the original skeleton of the reactant whereas all the other products involve free-radical reactions.It is believed that the free-radical reactions, as in the decomposition of ethylene oxide, are initiated by decomposition of thermally excited isomerization products prior to losing their energy by collisions.The rate constants obtained for the isomerization reactions are in very good agreement with the values extrapolated from low temperatures but are by a factor of 7-10 higher than the high-temperature rate constants obtained recently by Qin et al.A reaction scheme composed of 37 species and 68 elementary reactions accounts for the product distribution over the temperature range used in this study.First-order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of the computer simulation and the sensitivity analysis are shown.Differences and similarites between the reactions of ethylene oxide and propylene oxide are discussed.
- Lifshitz, Assa,Tamburu, Carmen
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p. 1161 - 1170
(2007/10/02)
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- Gas-Phase Thermolysis of Pyrazolines, 2. Electronic Structure and Gas-Phase Thermolysis of 4,5-Dihydro-3H-pyrazoles Studied by Photoelectron Spectroscopy, Semiempirical Quantum-Chemical Calculations, and Flash Vacuum Pyrolysis
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The PE spectra of the 4,5-dihydro-3H-pyrazoles 1, 2, of 2,5-dihydro-1,3,4-oxadiazole 3, and 2,5-dihydro-1,3,4-thiadiazole 4 have been recorded.Based on HAM/3, MNDO, AM1, and PM3 calculations, the ionization potentials have been assigned to molecular orbitals.The gas-phase thermolyses of 1-4 have been studied by PE-controlled gas analysis.Extrusion of molecular nitrogen leads to reactive species which cyclize to three-membered rings of different stability.At higher temperatures and in flash vacuum pyrolysis, consecutive reactions may lead to smaller acyclic molecules.The cyclopropanol 7, obtained by denitrogenation of 2, is thermally rather stable.Its PE spectrum has been recorded and analyzed. - Key Words: Electronic structure / PE spectroscopy / Gas-phase thermolysis / 3H-Pyrazoles, 4,5-dihydro- / 1,3,4-Oxadiazole, 2,5-dihydro- / 1,3,4-Thiadiazole, 2,5-dihydro- / Cyclopropanol, 2,2,3,3-tetramethyl-
- Kindermann, Markus Karl,Kowski, Klaus,Muchall, Heidi M.,Rademacher, Paul
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p. 2675 - 2682
(2007/10/02)
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- Hochaktive Katalysatorsysteme fur die Vinylethersynthese aus Acetylen und Alkoholen-Kaliumalkoholat/Kronenether in Kohlenwasserstoffen
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The activity of well-known alkaline-containing catalyst systems for the formation of vinyl ethers from alcohols and acetylenes can be remarkably increased by using a superbasic system: KOR-crown ether in an aprotic solvent (especially in hydrocarbons).To achieve a high catalytic activity a low concentration of alcohol in the hydrocarbon phase is essential.The results are discussed in terms of solvatation of alcoholate anion.
- Steinborn, Dirk,Mosinski, Holger,Rosenstock, Thomas
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p. C45 - C50
(2007/10/02)
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- CO2 LASER INDUCED DECOMPOSITION OF PROPYLENE OXIDE
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The continuous-wave (cw) CO2 laser induced decomposition of propylene oxide yields propanal, propanone and methyl vinyl ether as primary isomerization products.The absence of allylol and great amounts of ethene among products of ensuing fragmentation of primary products make the reaction different from conventional thermal decomposition of propylene oxide.CW CO7 laser induced decomposition of methyl vinyl ether affords propanal as isomerization product and shows thermal interconvertibility of propylene oxide and methyl vinyl ether.
- Jakoubkova, Marie,Pola, Josef
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p. 2455 - 2459
(2007/10/02)
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- Experimental and Theoretical Studies of the Gas-Phase Protonation of Vinyl Ethers, Vinyl Sulfides, and Vinyl Selenides
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A series of nine chalcogen-substituted ethylenes (chalcogen = O, S, Se) have been synthesized, and their gas-phase proton affinities (PA) were determined experimentally by measuring gas-phase basicities (GB) in an ion cyclotron resonance (ICR) spectrometer and theoretically by means of ab initio MO calculations at the STO-3G and 3-21G* levels.A satisfactory correlation (r = 0.978, slope = 1.41) has been obtained between the experimental and calculated 3-21G(*) values.In contrast with a number of previous reports, we consistently found that third- (SMe) and fourth-row (SeMe) substituents do not stabilize better the adjecent positive charge than does the second-row substituent OMe, even in the gas phase.In fact, comparison of experimental proton affinity value of ethylene with that of mono(methylchalco)ethylenes indicates that OMe, SMe, and SeMe groups stabilize the corresponding ethyl cations to very much the same extent.In 2-propyl cations the trend is O > S > Se, but the differences (δΔ in Table III) are quite small: 1.2 kcal mol-1 between O and S and 1.4 kcal mol-1 between S and Se.The superior ability of oxygen in carbenium ion stabilization appears the most clearly in the protonation of bis(methylchalco)ethylenes: dimethoxyethyl cation is more stable than the corresponding thio species by ca. 5.5 kcal mol-1, whereas dithio- and diselenocarbenium ions again have very similar stabilities.These conclusions are supported and extended by ab initio results on optimized geometries.
- Oesapay, K.,Delhalle, J.,Nsunda, K. M.,Rolli, E.,Houriet, R.,Hevesi, L.
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p. 5028 - 5036
(2007/10/02)
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- Concerning the Synthesis of Propellane
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The reaction of 1,1-dibromo-2,2-bis(chloromethyl)cyclopropane (2) with methyllithium in ether led to a solution of propellane (1) in a yield of 70percent. 1 could also be prepared free of solvent by reaction of 2 with lithium powder in triglyme/n-decane at 73 deg C. - Keywords: Cyclopropa annulation/ Propellane/ Polycycles, strained
- Belzner, Johannes,Bunz, Uwe,Semmler, Klaus,Szeimies, Guenter,Opitz, Klaus,Schlueter, Arnulf-Dieter
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p. 397 - 400
(2007/10/02)
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- Preparation of homo- and heterobimetallic μ-η2-(C,C)-ketene complexes, FpCH2COMLn, and transformation of the bridging ketene ligand into various C2 functional groups
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Eight examples of homo- and heterobimetallic μ-ketene complexes, FpCH2COMLn [3-7: Fp = (η5-C5H5)Fe(CO)2; M = Fe, Mo, Ni, Mn, Co; L = Cp, CO, PR3], are prepared by acylation of an iron-substituted acetyl chloride with various transition-metal anions. IR studies reveal the significant contribution of a π-complex Fp+[CH2=C(O-)Fp] (10) in addition to an oxycarbene structure FpCH2C(O-)=Fp+ (11) which is well-established for mononuclear acyl complexes. As a typical example, FpCH2COFp (3a) is subjected to chemical transformations relevant to catalytic CO hydrogenation. While 3a is not susceptible to carbonylation to lead to a μ-malonyl complex, decarbonylation results in quantitative liberation of ketene molecule or ligand substitution instead of formation of a μ-methylene complex. Reduction of 3a by LiAlH4 affords C3 products as major components. Reaction of 3a with electrophiles takes place at the acyl oxygen atom to give cationic binuclear oxycarbene complexes FpCH2C(OR)=Fp+TfO- (TfO = CF3SO3) (18-20) which exhibit bimodal reactivities toward both nucleophiles and electrophiles. Hard nucleophiles attack the most electrophilic carbene center, soft nucleophiles attack the alkyl side Fp group, and electrophilic reaction takes place at the methylene terminus.
- Akita, Munetaka,Kondoh, Atsuo,Kawahara, Takashi,Takagi, Takenobu,Moro-oka, Yoshihiko
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p. 366 - 374
(2008/10/08)
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- Collisionally Activated Decomposition of Poly(ethylene glycol)s: an Investigation of High-Mass Ion Abundances in the Collisional Activation Technique with Large Molecules
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The utility of the collisional activation technique in structure determination of ions is limited as parent ion mass increases.Optimum cillisionally activated dissociation yield is often obtained at parent masses of 1000-2000 u, after which daughter ion yield decreases.The apparent decrease in the efficiency of the collisional activation process has been thought of as a degree-of-freedom effect: as new rotational-vibrational modes are added to the parent ion, its lifetime with respect to dissociation increases.We have investigated this effect using an easily characterized system of several poly(ethylene glycol) homologs from the 15-mer to the 35-mer.Observed trends in the collisional activation spectra as parent mass increases support the postulated 'degree-of-freedom' effect in general.The loss of C2H4O from the - parents, a fragmentation which has a high activation barrier, however, actually becomes more favored as the parent ion becomes larger.This effect is explained in terms of statistical rate theory.
- Kiplinger, Jeffrey P.,Bursey, Maurice M.
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p. 342 - 349
(2007/10/02)
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- Gas-Phase Addition of the Vinyl Cation to Hydrogen and Methane. A Nuclear Decay Study
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A nuclear technique based on the spontaneous decay of multitritiated precursors that allows the generation of free carbenium ions of exactly the same nature in different enviroments has been employed for generating the labeled vinyl cation (C2X3(1+), X = H,T) from multitritiated ethylene and for investigating its reactivity toward hydrogen and methane at pressures ranging from 60 to 720 Torr.Kinetic data for the addition of C2X3(1+) to H2 and CH4 and the ensuing product distributions are obtained by intercepting the ionic species with different gaseous nucleophiles, i.e., 1,4-dibromobutane, benzene, and methanol, and by isolating the corr esponding neutral end products.The results are consistent with the intermediacy of the vinyl cation, formed by the β(1-) transition with a limited excess of vibrational energy, which insert into the ?-bonds of H2 and CH4 yielding respectively C2H5(1+) and sC3H7(1+) ions.The experiments provide no evidence for the occurrence of alternative C3H7(1+) structures, i.e., protonated cyclopropane, from the C2X3(1+) attack on CH4.At CH4 pressures below 200 Torr, a fraction of the C3H7(1+) adducts fragments diretly into allyl cations and H2.A definition of the C2X3(1+) + H2(or CH4) addittion and fragmentation mechanism is obtained by comparison of the present data with those arisisng from previous experimental studies based on different approaches (i.e., radiolysis, ICR, SIFT, HMPS, etc.) and with those of ab initio calculations.
- Fornarini, Simonetta,Speranza, Maurizio
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p. 2154 - 2160
(2007/10/02)
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- CONVERSION OF A DIIRON μ-KETENE COMPLEX, FpCH2COFp (Fp=(η5-C5H5)Fe(CO)2), INTO BINUCLEAR CATIONIC OXYCARBENE COMPLEXES AND THEIR BIMODAL REACTIVITIES.
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Reactions of a bimetallic μ-ketene complex, FpCH2COFp, with electrophiles take place at the acyl oxygen atom to give cationic binuclear oxycarbene complexes.Bifunctionality of their cationic enol ether structure permits subsequent transformation both with nucleophiles and electrophiles.
- Akita, Munetaka,Kondoh, Atsuo,Kawahara, Takashi,Moro-oka, Yoshihiko
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p. C43 - C46
(2007/10/02)
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- Reversal of electronic Substituent Effects in the Retro-Diels-Alder Reaction. A Charge Neutral Analogue of Oxyanion-Accelerated Cycloreversion
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The retro-Diels-Alder reaction of anthracene cycloadducts is influenced by the dienophile substituents in the following ways: (1) electron-withdrawing groups increase the rate of the reaction; (2) strongly conjugating substituents make the reaction much faster than predicted by classical electron-withdrawing or -donating ability, in the best case by a factor of 3 x 106, and (3) there is no observable steric effect, in contrast to literature statements to the contrary.
- Nanjappan, Palaniappan,Czarnik, Anthony W.
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p. 2851 - 2853
(2007/10/02)
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- Thermal Decomposition of Ions. 1. Pyrolysis of Protonated Ethers. Activation Energies and A Factors
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Unimolecular rate constants (kd) have been measured at the high-pressure limit for the thermal decomposition of protonated dimethoxyethane (glyme) and bis(2-methoxyethyl)ether (diglyme).In both cases the decomposition involves loss of CH3OH and formation of an oxycarbonium ion.The variation of kd with temperature gives log A=11.1 and Ea=21.1 kcal*mol-1 for the pyrolysis of (glyme)H+ and log A=13.7 and Ea=30.7 for (diglyme)H+.To the best of our knowledge these are first Arrhenius parameters ever determined for the decomposition of cations in the vapor phase under equilibrium conditions at the high-pressure limit.The data and thermochemistry are consistent with a transition state in which electron shifts result in the disruption of an internal hydrogen bond.
- Sieck, L. Wayne,Meot-Ner (Mautner), Michael
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p. 5324 - 5327
(2007/10/02)
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- Gaseous 1-Methyl-1-oxoniacycloalkanes as Stable Intermediates on the C3H7O+ and C4H9O+ Potential Energy Surfaces
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The nature and the isomeric distribution of the neutral products obtained from the gas-phase attack of CH5+, C2H5+, and CH3FCH3+ ions on cyclic CnH2nO (n = 2, 3, and 4) ethers provide the first experimental evidence in favour of 1-methyl-1-oxoniacyclopropane and 1-methyl-1-oxoniacyclobutane as stable intermediates on the corresponding potential energy surface.
- Angelini, Giancarlo,Speranza, Maurizio
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p. 1217 - 1219
(2007/10/02)
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- The Allopolarization Principle and its Applications, VI. The Alkylation of Enolate Anions: Polarity and Regioselectivity
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The O/C methylation ratio in the reaction of sodium enolates with dimethylsulfate depends on the polar (electronic) effect of substituents.The relative ?-charge density Px/y = lx/ly can be used as a measure for the polarity of ambifunctional anions; in case of enolate anions PO/C = lO/lC.The change of the regioselectivity Sf = log QO/QC in the alkylation of enolates is a function of a change in the polarity PO/C; ΔSf=f(ΔPx/y).The polar effect of substituents influences the charge control during the alkylation process via a change of the polarity of the enolate system: The higher the polarity of the anion, the stronger the charge control and the higher the yield of enol ether (O-alkylation). - Keywords: Alkylation, Enolate Anions
- Gompper, Rudolf,Vogt, Hans-Hubert,Wagner, Hans-Ulrich
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p. 1644 - 1652
(2007/10/02)
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- The Allopolarization Principle and its Applications, IV. Substituent Effects in the Methylation of Enolate Anions
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The ratio of O- and C-methylated products in the reaction of the sodium salts of acetophenones 1, propiophenones 3, phenylacetones 5, β-dicarbonyl compounds 12, α-cyanocarbonyl compounds 13, acetaldehyde, propionaldehyde, and diethylketone with dimethyl sulfate, methyl iodide, and trimethyl phosphate in HMPTA has been determined with regard to the effect of substituents.In some cases the influence of solvents, concentration and temperature has also been studied.
- Gompper, Rudolf,Vogt, Hans-Hubert
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p. 2866 - 2883
(2007/10/02)
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- Effects of Polar β Substituents in the Gas-Phase Pyrolysis of Ethyl Acetate Esters
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The rates of the gas phase pyrolysis of six β-substituted ethyl acetates were studied in a static system over the temperature range 319-450 deg C and the pressure range 63-207 mmHg.In seasoned vessels the reactions are homogenous, follow a first-order rate law, and are unimolecular.The temperature dependence of the rate constants is given by the following Arrhenius equations for the compounds indicated: 2-(dimethylamino)ethyl acetate, log k(s-1) = (13.90 +/- 0.30) - (220.4 +/- 3.8) kJ*mol-1 (2.303RT)-1; 2-methoxyethyl acetate, log k(s-1) = (12.04 +/- 0.24) -(203.7 +/- 2.9) kJ*mol1- (2.303RT)-1; 2-(methylthio)ethyl acetae, log k(s-1 = (11.27 +/- 0.39) - (179.0 +/- 4.6) kJ*mol-1 (2.303RT)-1; 2-chloroethyl acetate, log k(s-1) = (12.14 +/- 0.66) - (202.0 +/- 8.4)kJ*mol-1 (2.303RT)-1; 2-fluoroethyl acetate, log k(s-1) = (12.68 +/- 0.60) - (211.2 +/- 7.1) kJ*mol-1 (2.303RT)-1; 2-cyanoethylacetate, Log k(s-1) = (11.51 +/- 0.13) - (171.9 +/- 1.7) kJ*mol-1 (2.303RT)-1.The effect of substituents in the gas-phase elimination of β-substituted ethyl acetates may be grouped in three types.The linear correlation of several -I electron-withdrawing groups along strong ? bonds is presented and discussed.A small amount of anchimeric assistance is proposed in the pyrolysis of the 2-(methyltio)ethyl acetate.The experimental data are consistent with the transition state where the Cα-O bond polarization is the rate-determining process.
- Chuchani, Gabriel,Martin, Ignacio,Hernandez, Jose A. A.,Rotinov, Alexandra,Fraile, German,Bigley, David B.
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p. 944 - 948
(2007/10/02)
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