- Hydride Ion Transfer Reactions in the Gas Phase. Pressure Dependence of Reaction Efficiency as a Criterion for the Recognition of Anchimeric Assistance
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The efficiency (kobs/kcoll) of the gas phase hydride ion transfer from 2,2-dimethylbutane to tert-butyl cation displays a pronounced positive pressure dependence, which suggests significant anchimeric assistance of the methyl groups of 2,2-dimethylbutane adjacent to the departing CH2 hydride in the transition state.
- Crestoni, Maria Elisa,Fornarini, Simonetta,Lentini, Massimo,Speranza, Maurizio
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Read Online
- METHOXYCARBONYLATION WITH FORMIC ACID AS CO SOURCE
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Process for methoxycarbonylation with formic acid as the CO source.
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Paragraph 0045-0047
(2019/02/24)
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- Palladium-catalyzed selective generation of CO from formic acid for carbonylation of alkenes
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A general and selective palladium-catalyzed alkoxycarbonylation of all kinds of alkenes with formic acid (HCOOH, FA) is described. Terminal, di-, tri-, and tetra-substituted including functionalized olefins are converted into linear esters with high yields and regioselectivity. Key-to-success is the use of specific palladium catalysts containing ligands with built-in base, e.g., L5. Comparison experiments demonstrate that the active catalyst system not only facilitates isomerization and carbonylation of alkenes but also promotes the selective decomposition of HCOOH to CO under mild conditions.
- Sang, Rui,Kucmierczyk, Peter,Dong, Kaiwu,Franke, Robert,Neumann, Helfried,Jackstell, Ralf,Beller, Matthias
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supporting information
p. 5217 - 5223
(2018/04/24)
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- Development of efficient palladium catalysts for alkoxycarbonylation of alkenes
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Herein, we report a general and efficient Pd-catalysed alkoxycarbonylation of sterically hindered and demanding olefins including a variety of tri-, tetra-substituted and 1,1-disubstituted alkenes. In the presence of 1,3-bis(tert-butyl(pyridin-2-yl)phosphanyl)propane L3 or 1,4-bis(tert-butyl(pyridin-2-yl)phosphanyl)butane L4 the desired esters are obtained in good yields and selectivities. Similar transformation is obtained using tertiary ether as showcased in the carbonylation of MTBE to the corresponding linear ester in high yield and selectivity.
- Liu, Jiawang,Dong, Kaiwu,Franke, Robert,Neumann, Helfried,Jackstell, Ralf,Beller, Matthias
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supporting information
p. 12238 - 12241
(2018/11/21)
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- Isomerizing Methoxycarbonylation of Alkenes to Esters Using a Bis(phosphorinone)xylene Palladium Catalyst
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The synthesis and characterization of bulky diphosphine 1,2-bis(4-phosphorinone)xylene, BPX, and its palladium complexes [(BPX)PdCl2] and [(BPX)Pd(O2CCF3)2] are described. BPX was evaluated as a ligand in Pd-catalyzed isomerizing methoxycarbonylation. A broad range of alkenes, including terminal, internal, branched, and functionalized alkenes, can be converted to esters with activities and selectivities matching or surpassing the performance of the state-of-the-art palladium bis(di(tert-butyl)phosphino-o-xylene (Pd-DTBPX) catalyst. A molecular structure of the precatalyst [(BPX)Pd(O2CCF3)2] was obtained showing a square planar geometry and a bite angle of 100.11(3)°. Rhodium carbonyl complexes [(BPX)Rh(CO)Cl] and [(DTBPX)Rh(CO)Cl] were synthesized to compare the relative electronic parameters, revealing a ν(C≡O) of 1956.8 and 1948.3 cm-1, respectively, suggesting a reduced ability of BPX to donate electron density to the metal relative to DTBPX. Competitive protonation experiments between BPX and DTBPX in the presence of CH3SO3H exclusively produce [DTBPX(H)2]2+, providing additional evidence that BPX is a much weaker base than DTBPX. This could be due to either the effect of the electron-withdrawing ketone group in the phosphorinone ring or the compression of the C-P-C bond angle induced by the ring structure. The 31P NMR (CDCl3) chemical shift of BPX is 5.6 ppm, upfield of DTBPX at 27.6 ppm. This anomalous result is attributed to a strong gamma substituent effect of C=O in the BPX ligand. The improved activity of Pd-BPX, relative to Pd-DTBPX, could be attributed to a more electrophilic PdII center, which could accelerate the rate-determining methanolysis step.
- Nobbs, James D.,Low, Choon Heng,Stubbs, Ludger P.,Wang, Cun,Drent, Eite,Van Meurs, Martin
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p. 391 - 398
(2017/04/26)
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- Benzene-based diphosphine ligands for alkoxycarbonylation
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The invention relates to benzene-based diphosphine ligands for alkoxycarbonylation. Specifically, the invention relates to compounds of formula (I), where m and n are each independently 0 or 1; R1, R2, R3, R4 are each independently selected from -(C1-C12)-alkyl, -(C3-C12)-cycloalkyl, -(C3-C12)-heterocycloalkyl, -(C6-C20)-aryl, -(C3-C20)-heteroaryl; at least one of the R1, R2, R3, R4 radicals is a -(C3-C20)-heteroaryl radical; and to the use thereof as ligands in alkoxycarbonylation.
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Paragraph 0161; 0163
(2017/02/28)
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- Silica-supported sulfated zirconia: A new effective acid solid for etherification
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Silica-supported sulfated zirconia exhibits a comparable and even higher ether production than a reference acid resin (Amberlyst 15) giving an ether yield of 30% at 50% conversion.
- Wang,Guin
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p. 2499 - 2500
(2007/10/03)
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- Synthesis of 2,3-Dimethyl-2-methoxybutane and 2-Methyl-2-methoxypentane from Methanol and Propylene Dimers Produced by the Dimerization of Propylene on Complex Nickel Catalysts
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A study has been made of the addition of methanol under the action of acid catalysts to propylene dimers 2,3-dimethylbut-1-ene, 2,3-dimethylbut-2-ene, 2-methyl-1-pentene and 2-methyl-2-pentene with the formation of 2,3-dimethyl-2-methoxybutane and 2-methyl-2-methoxypentane respectively.
- Zakharkin, L. I.,Zhigareva, G. G.
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p. 416 - 420
(2007/10/03)
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- Solvomercuration-Demercuration. 12. The Solvomercuration-Demercuration of Olefins in Alcohol Solvents with Mercuric Trifluoroacetate--An Ether Synthesis of Wide Generality
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Studies on the solvomercuration-demercuration (SM-DM) of olefins in methyl, ethyl, isopropyl, and tert-butyl alcohols with mercuric trifluoroacetate have been extended. 1-Dodecene undergoes the SM-DM sequence with typical results for a monosubstituted olefin.Cyclopentene similarly exhibited behavior characteristic of a 1,2-disubstituted olefin in methanol, ethanol, and 2-propanol, giving high yields, >90percent of the corresponding ethers.However, in tert-butyl alcohol, the yields of ether were lower than normal and decreased somewhat with time. 2-Methyl-1-butene gives >90percent yields of the Markovnikov methyl ether.On the other hand, the yields of ethyl, isopropyl, and tert-butyl ethers are lower and decrease with time.Major improvements in yields, however, are possible by lowering the reaction temperature from room temperature to 0 deg C.Cyclooctene, surprisingly, behaves more like a tri-, tetra-, or isosubstituted olefin than a 1,2-disubstituted olefin.The yields of cyclooctyl methyl ether are >90percent and do not decrease with time.However, yields of the ethyl, isopropyl, and tert-butyl ethers are lower and drop with time.Again, lowering the reaction temperature from room temperature to 0 deg C markedly improves the yields of the cyclooctyl ethers.These results, coupled with those of a previous study, clearly reveal the exceptional superiority of mercuric trifluoroacetate for the SM-DM of olefins in alcohol solvents.
- Brown, Herbert C.,Kurek, Joseph T.,Rei, Min-Hon,Thompson, Kerry L.
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p. 1171 - 1174
(2007/10/02)
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- Solvomercuration-Demercuration. 11. Alkoxymercuration-Demercuration of Representative Alkenes in Alcohol Solvents with the Mercuric Salts Acetate, Trifluoroacetate, Nitrate, and Methanesulfonate
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The alkoxymercuration-demercuration of seven representative olefins with the mercuric salts acetate, trifluoroacetate, nitrate, and methanesulfonate, in methyl, ethyl, isopropyl, and tert-butyl alcohols was examined.Mercuric acetate was effective only in methanol and ethanol.On the other hand, mercuric trifluoroacetate was effective in all four solvents, giving in most cases high yields of the corresponding ethers.Both mercuric nitrate and mercuric methanesulfonate were effective in methanol, ethanol, and 2-propanol.However, in several cases poor selectivity for the ether was observed, as evidenced by the formation of significant amounts of side products.Both electronic and steric effects are important factors in the reaction.Moreover, the structure of the olefin has a pronounced effect, both on the types of oxymercurials formed and on their stability to the reaction conditions.
- Brown, Herbert C.,Kurek, Joseph T.,Rei, Min-Hon,Thompson, Kerry L.
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p. 2551 - 2557
(2007/10/02)
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- Acid-induced 13C Nuclear Magnetic Resonance Chemical Shift Changes of Ether and Ester Carbon Atoms
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13C N.m.r. chemical shifts of ehters dissolved in tetrachloromethane are displaced on addition of trifluoroacetic acid.The displacements result from independent interactions of the acid with the substrate oxygen atoms and alkyl residues.The structure-dependent and stereoselective shift changes are useful for signal assignments, structure determination, conformational analysis, assessment of the distribution of rapidly interconverting conformers of esters, and estimation of the relative basicity of ethers.
- Begtrup, Mikael
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p. 1609 - 1618
(2007/10/02)
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- EXCIPLEX AND RADICAL ION INTERMEDIATES IN THE PHOTOCHEMICAL REACTION OF 9-CYANOPHENANTHRENE WITH 2,3-DIMETHYL-2-BUTENE
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The photochemical reaction of 9-cyanophenanthrene and 2,3-dimethyl-2-butene, first reported by Mizuno, Pac and Sakurai, has been reinvestigated.The formation of a -cycloadduct via a singlet exciplex is the exclusive reaction in the nonpolar solvents benzene and ethyl acetate.Photochemical behavior in polar solvents is far more complicated than previously reported.Mechanisms consistent with the effects of solvent polarity, methanol concentration, methanol deuteration, and light intensity upon product yields are proposed.Formation of a 9-cyanophenanthrene anion radical and 2,3-dimethyl-2-butene cation radical is the primary photoinitiated process in polar solvent.The cation radical can undergo deprotonation to yield an allyl radical or nucleophilic attack by methanol to yield a methoxyalkyl radical.Covalent bonding of these radicals and the 9-cyanophenanthrene anion radical gives rise to the acyclic adducts obtained in polar solvents.The anion radical can also be protonated, leading ultimately to the formation of 9,10-dihydro-9-cyanophenanthrene.
- Lewis, Frederick D.,DeVoe, Robert J.
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p. 1069 - 1078
(2007/10/02)
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