- Olefin oligomerization via new and efficient Br?nsted acidic ionic liquid catalyst systems
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Olefin oligomerization reaction catalyzed by new catalyst systems (a Br?nsted-acidic ionic liquid as the main catalyst and tricaprylylmethylammonium chloride as the co-catalyst) has been investigated. The synthesized Br?nsted acidic ionic liquids were characterized by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV), 1H nuclear magnetic resonance (NMR), and 13C NMR to analyze their structures and acidities. The influence of different ionic liquids, ionic liquid loading, different co-catalysts, catalyst ratios (mole ratio of ionic liquid to co-catalyst), reaction time, pressure, temperature, solvent, source of reactants, and the recycling of catalyst systems was studied. Among the synthesized ionic liquids, 1-(4-sulfonic acid)butyl-3-hexylimidazolium hydrogen sulfate ([HIMBs]HSO4) exhibited the best catalytic activity under the tested reaction conditions. The conversion of isobutene and selectivity of trimers were 83.21% and 35.80%, respectively, at the optimum reaction conditions. Furthermore, the catalyst system can be easily separated and reused; a feasible reaction mechanism is proposed on the basis of the distribution of experimental products.
- Wang, Guoqin,Song, Heyuan,Li, Ruiyun,Li, Zhen,Chen, Jing
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p. 1110 - 1120
(2018/05/28)
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- Highly efficient trimerization of isobutene over silica supported chloroaluminate ionic liquid using C4 feed
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A series of silica, glass and molecular sieves supported chloroaluminate ionic liquids (ILs) were prepared and their catalytic performance on the trimerization of isobutene based on C4 mixture was investigated. Interestingly, it was found that the carrier played a key role in the reaction route. Among these supported catalysts, silica supported chloroaluminate ionic liquid was highly efficient for the trimerization of isobutene. X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) characterizations suggested that the synergy between Al2Cl7- anion and silica induced the catalytic activity for isobutene oligomerization due to the strong interaction between ILs and silanol group. The reaction conditions including loading amount, temperature, reactant concentration, and space velocity for the isobutene oligomerization were optimized. Ultimately, complete conversion of isobutene and 91.4% selectivity of trimers were obtained over the IL/silica (30 wt.%) catalyst at mild conditions. Moreover, catalyst stability and deactivation were preliminarily studied.
- Liu, Shimin,Shang, Jianpeng,Zhang, Shiguo,Yang, Benqun,Deng, Youquan
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- Tandem cyclopropanation with dibromomethane under Grignard conditions
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(Chemical Equation Presented) Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnesium and CH 2Br2 under Barbier conditions at higher temperatures. The reaction rates depend on the substitution pattern of the (homo)allylic alcoholates and on the counterion with lithium giving best results. Good to excellent syn-selectivities are obtained from α-substituted substrates, which are in accord with a staggered Houk model. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl carboxylates or vinyloxiranes. Using this methodology, numerous fragrance ingredients and their precursors were efficiently converted to the corresponding cyclopropyl carbinols.
- Brunner, Gerhard,Eberhard, Laura,Oetiker, Juerg,Schroeder, Fridtjof
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p. 7543 - 7554
(2008/12/22)
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- The Grunwald-Winstein relationship in the solvolysis of crowded tertiary alkyl chlorides. Hindered hydration and hydrophobic effect
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Various highly crowded tertiary alkyl chlorides having a neopentyl or a (1-adamantyl)methyl substituent on the reaction center were subjected to solvolysis rate studies, and the Grunwald-Winstein (GW) type relationship with respect to the YCl scale was examined. Analyses of the plots showed that these bulky substituents efficiently preclude the nucleophilic solvent participation from the rear side and that the data points for non-aqueous protic solvents give linear GW type plots. On the other hand, increased crowding causes considerable downward dispersions of the data points in aqueous mixtures of ethanol, acetone and 1-propanol. The magnitude of the downward dispersion increases in this order, giving a curvature with a downward bulge in the GW type relationship. Aqueous mixtures of the smallest alcohol, methanol, on the other hand, give only slight downward dispersions of the data points, which constitute a linear GW type plot. These results can be explained in terms of two causes. First, structural crowding makes the transition state of ionization less susceptible to the Bronsted base-type hydration to the β-hydrogens than 1-chloroadamantane as the standard of the YCl scale. Second, with highly hydrophobic substrates the first solvation shell in aqueous ethanol is expected to become more ethanol rich than the bulk phase, causing less easy ionization of the substrate. The rate data can be semiquantitatively analyzed by using Hansch's hydrophobicity parameters. The present anomalies found in solvolysis reactions are regarded as a kinetic version of Wepster's observations of the solvent effects on the magnitude of Hammett σ constants of bulky alkyl groups. Copyright
- Takeuchi, Ken'ichi,Takasuka, Masaaki,Shiba, Eiji,Tokunaga, Hironobu,Endo, Tadasuke,Ushino, Takuhiro,Tokunaga, Kazuhiko,Okazaki, Takao,Kinoshita, Tomomi,Ohga, Yasushi
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p. 229 - 238
(2007/10/03)
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- C-N, Si-N and P-N Bond Cleavage in Reactions of Phosphorus Pentafluoride with a Fluorophosphine and a Fluorophosphorane, Containing the N-Trimethylsilyl-N-tert-butyl Group
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PF5 reacts with Me3Si(But)NPF2(E) (E = lone electron pair or OC(CF3)2C(CF3)2O) to give products whose formation can be rationalised in terms of assuming the decomposition of the intermediates F4PN(But)PF2(E) into ButF and F3P=N-PF2(E).But, in the presence of PF5, trimerises to give a 1:1 mixture of tri-iso-butene isomers.During this reaction HF is formed, giving rise to additional Si-N and P-N bond cleavage reactions in which the compounds ButNHPF2, F3P(E), ButNH3(+)PF6(-) and NH4(+)PF6(-) are formed. - Key words: N-trimethylsilyl-N-tert-butylaminodifluorophosphine, 2,2-Difluoro-2(N-trimethylsilyl-N-tert-butylamino)-4,4,5,5-tetrakis(trifluoromethyl)-1,3,2λ5-dioxaphospholane, 1:1 Mixture of Tri-isobutene Isomers
- Roeschenthaler, Gerd-Volker,Storzer, Werner,Schmutzler, Reinhard
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p. 1125 - 1129
(2007/10/02)
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