- Directing the Rate-Enhancement for Hydronium Ion Catalyzed Dehydration via Organization of Alkanols in Nanoscopic Confinements
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Alkanol dehydration rates catalyzed by hydronium ions are enhanced by the dimensions of steric confinements of zeolite pores as well as by intraporous intermolecular interactions with other alkanols. The higher rates with zeolite MFI having pores smaller than those of zeolite BEA for dehydration of secondary alkanols, 3-heptanol and 2-methyl-3-hexanol, is caused by the lower activation enthalpy in the tighter confinements of MFI that offsets a less positive activation entropy. The higher activity in BEA than in MFI for dehydration of a tertiary alkanol, 2-methyl-2-hexanol, is primarily attributed to the reduction of the activation enthalpy by stabilizing intraporous interactions of the Cβ-H transition state with surrounding alcohol molecules. Overall, we show that the positive impact of zeolite confinements results from the stabilization of transition state provided by the confinement and intermolecular interaction of alkanols with the transition state, which is impacted by both the size of confinements and the structure of alkanols in the E1 pathway of dehydration.
- Shetty, Manish,Wang, Huamin,Chen, Feng,Jaegers, Nicholas,Liu, Yue,Camaioni, Donald M.,Gutiérrez, Oliver Y.,Lercher, Johannes A.
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supporting information
p. 2304 - 2311
(2020/12/01)
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- Ligand exchange processes in zirconocene dichloride-trimethylaluminum bimetallic systems and their catalytic properties in reaction with alkenes
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Ligand exchange processes in the systems L2ZrCl2-AlMe3 (L2ZrCl2: Cp2ZrCl2, (CpMe)2ZrCl2, (C5Me5)2ZrCl2, Me2SiCp2ZrCl2, Me2Si(C5Me4)2ZrCl2, rac-Me2C(2-Me-4-But-Cp)2ZrCl2, meso-Me2C(2-Me-4-But-Cp)2ZrCl2, rac-Me2C(3-But-Cp)2ZrCl2, Ind2ZrCl2, rac-H2C(Ind)2ZrCl2, rac-Me2C(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2, rac-C2H4(Ind)2ZrCl2, rac-C2H4(THInd)2ZrCl2, rac-Me2Si(THInd)2ZrCl2) and Cp2ZrMeCl2-n-AlMe3 (n = 1, 2) were studied by NMR spectroscopy with the goal to establish the structures and dynamic features of probable intermediates in the zirconocene-catalyzed reactions of alkenes with AlMe3. The effect of solvent, the organoaluminum compound concentration and the addition of (ClAlMe2)2 on the activation parameters of the alkyl exchange in the trimethylaluminum dimer was studied as well. The constants and activation parameters of the methyl group exchange in the monoalkyl-substituted ansa-complexes L2ZrMeCl (L2 = rac-Me2C(2-Me-4-But-Cp)2, rac-Me2C(3-But-Cp)2, rac-H2CInd2, rac-Me2CInd2, rac-Me2SiInd2, rac-H4C2Ind2) were established for the first time. The catalytic activity and chemoselectivity of zirconocenes in the reaction of alkenes with AlMe3 were evaluated and compared with the exchange and equilibrium constants of ligand exchange processes. A mechanism of the reaction was proposed.
- Parfenova, Lyudmila V.,Kovyazin, Pavel V.,Gabdrakhmanov, Vener Z.,Istomina, Galina P.,Ivchenko, Pavel V.,Nifant'Ev, Ilya E.,Khalilov, Leonard M.,Dzhemilev, Usein M.
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p. 16918 - 16937
(2019/01/03)
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- Graphite oxide activated zeolite NaY: Applications in alcohol dehydration
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A mixture of graphite oxide (GO) and the zeolite NaY (Si/Al = 5.1) was used to dehydrate various alcohols to their respective olefinic products. Using conditions optimized for 4-heptanol (15 wt% GO-NaY (1 : 1 wt/wt), 150°C, 30 min), a series of secondary and tertiary aliphatic alcohols were cleanly dehydrated in moderate to excellent conversions (27.5-97.2%). Several primary alcohols were also dehydrated, although higher catalyst loadings (200 wt% GO-NaY (1 : 1) and longer reaction times (3 h) were required. The enhanced dehydration activity was attributed to the ability of GO to convert NaY to an acidic form and without the need for ammonium cation exchange and/or high temperature calcination. The Royal Society of Chemistry 2013.
- Todd, Alexander D.,Bielawski, Christopher W.
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p. 135 - 139
(2013/03/29)
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- Enantioselectivity of chiral zirconocenes as catalysts in alkene hydro-, carbo- and cycloalumination reactions
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The enantioselectivity of chiral Zr catalysts L1L2ZrCl2 [L1 = L2 = 1-neomenthylindenyl (Ind*), 1; L1 = Cp, L2 = Ind* 2; L1 = Cp, L2 = 1-neomenthylindenyl-4,5,6,7-tetrahydroindenyl (Cp*) 3] in the hydro-, carbo- and cycloalumination of alkenes by organoaluminium compounds (OAC) (AlMe3, AlEt3, HAlBu2i) has been studied. It was found that OAC exhibit the most effect on the reaction chemo- and enantioselectivity. The reaction chemo- and enantioselectivity depend on the catalyst structure and reaction conditions (solvent type, catalyst concentration, temperature) as well. It is shown that the lack of asymmetric induction in the reaction of α-methylstyrene hydroalumination by HAlBu2i, catalyzed with complexes 1 or 3, is the result of the formation of Zr hydride complexes of different structures as reaction intermediates. MTPA was used as a derivatization reagent for the enantiomeric excess estimation and absolute configuration assignment of β-chiral alcohols obtained after the oxidation and hydrolysis of the reaction products. The applicability of MTPA for the assignment of the absolute configuration of the stereogenic centre in β-ethyl substituted primary alcohols and β-alkyl-1,4-butanediols is shown.
- Parfenova, Lyudmila V.,Berestova, Tatyana V.,Tyumkina, Tatyana V.,Kovyazin, Pavel V.,Khalilov, Leonard M.,Whitby, Richard J.,Dzhemilev, Usein M.
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experimental part
p. 299 - 310
(2010/06/14)
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- On study of chemoselectivity of reaction of trialkylalanes with alkenes, catalyzed with Zr π-complexes
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The influence of the organoaluminium compound nature, Zr π-ligand environment, solvent type and reagent ratio on the chemoselectivity of reactions of trialkylalanes (AlMe3, AlEt3) with alkenes, catalyzed with L2ZrCl2
- Parfenova, Lyudmila V.,Gabdrakhmanov, Vener Z.,Khalilov, Leonard M.,Dzhemilev, Usein M.
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scheme or table
p. 3725 - 3731
(2009/12/31)
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- Selective, catalytic carbon-carbon bond activation and functionalization promoted by late transition metal catalysts
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The selective catalytic activation and functionalization of carbon-carbon bonds in a series of substituted cyclopropane substrates has been developed using commercially available transition metal catalysts. Catalytic hydrogenation and olefination procedures, tolerant of a range of functional groups, have been discovered. Introduction of a chelate-assisting substituent such as [PPh2] is effective in altering the kinetic selectivity and lowering the activation barrier for the catalytic processes. Copyright
- Bart, Suzanne C.,Chirik, Paul J.
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p. 886 - 887
(2007/10/03)
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- 1,1,2,2-Tetrafluoroethyl-N,N-dimethylamine: A new selective fluorinating agent
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The title compound has been prepared in 96-98% yield by the reaction of tetrafluoroethylene and dimethylamine. 1,1,2,2-Tetrafluoroethyl-N,N-dimethylamine (1) is found to be an effective reagent for the conversion of alcohols into alkyl fluorides. Reaction of 1 and primary alcohols proceeds with high yield formation of the corresponding alkyl fluorides at elevated temperature. However, the reaction of secondary and tertiary alcohols rapidly takes place at 0-10°C, producing corresponding alkyl fluorides as major product along with some olefins.
- Petrov,Swearingen,Hong,Chris Petersen
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- Organic reactions catalyzed by methylrhenium trioxide: Dehydration, amination, and disproportionation of alcohols
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Methylrhenium trioxide (MTO) is the first transition metal complex in trace quantity to catalyze the direct formation of ethers from alcohols. The reactions are independent of the solvents used: benzene, toluene, dichloromethane, chloroform, acetone, and in the alcohols themselves. Aromatic alcohols gave better yields than aliphatic. Reactions between two different alcohols could also be used to prepare unsymmetric ethers, the best yields being obtained when one of the alcohols is aromatic. MTO also catalyzes the dehydration of alcohols to form olefins at room temperature, aromatic alcohols proceeding in better yield. When primary (secondary) amines were used as the limiting reagent, direct amination of alcohols catalyzed by MTO gave good yields of the expected secondary (tertiary) amines at room temperature. Disproportionation of alcohols to alkanes and carbonyl compounds was also observed for aromatic alcohols in the presence of MTO. On the basis of the results of this investigation and a comparison with the interaction between MTO and water, a concerted process and a mechanism involving carbocation intermediates have been suggested.
- Zhu, Zuolin,Espenson, James H.
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p. 324 - 328
(2007/10/03)
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- Competitive intramolecular Ti-C versus Al-C alkene insertions: examining the role of Lewis acid cocatalysts in Ziegler-Natta alkene insertion and chain transfer reactions
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Mechanistic aspects of Ziegler-Natta olefin insertion, which include catalyst/cocatalyst interactions, chain propagation, and chain termination, have been examined for systems which model the Cp2Ti(Cl)R/RAlCl2 and Cp2Ti(Cl)R/MgX2 catalyst complexes.The reaction of (2-butyl-6-hepten-1-yl)titanocene chloride with (2-propyl-6-hepten-1-yl)aluminum dichloride:diethyl etherate produced 78percent cyclization of the titanocene ligand, while less than 2percent of the ligand originating on aluminum cyclized.In a complementary experiment, the reaction of (2-propyl-6-hepten-1-yl)titanocene chloride and (2-butyl-6-hepten-1-yl)aluminum dichloride:diethyl etherate again produced only intramolecular insertion of the titanium ligand (58percent).Based on these results, equilibretion of ligands through transmetallation between titanium and aluminum did not occur under these reaction conditions, and selective insertion into the titanium-carbon bond was confirmed for this process.Similarly, ligand cyclization with Cp2Ti(Cl)R/MgX2 also occurred through insertion into the titanium-carbon bond.The product distribution generated by the MgX2 was highly solvent dependent.Cyclization in CH2Cl2 was very efficient, while reaction in toluene generated numerous products.Included in the toluene reaction mixture were compounds that resulted from ligand transposition/chain transfer of the titanium ligand. Keywords: Titanium; Aluminium; Magnesium; Olefin insertion; Ziegler-Natta catalysts; Chain transfer
- Barta, Nancy S.,Kirk, Brian A.,Stille, John R.
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- Organomolybdenum and Organotungsten Reagents, III. Selective, Nonbasic Carbonylmethylenation Reagents from MoOCl3(THF)2 and MoOCl4: Formation, Thermolability, Structure
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From the family of more than 20 carbonylolefinating μ-methylene molybdenum and tungsten complexes the reagent "3", obtained in solution by treatment of MoOCl3(THF)2 with two equivalents of methyllithium, is probably the most favorable one for chemoselective carbonylolefination reactions.As judged by the 13C- and 1H-NMR spectra the reagent is not a single species, but a mixture of either isomeric 1,3-dioxo-1,3-dimolybda(V)cyclobutane complexes 3, differing in the position of the ligands Cl, O, and THF at the molybdenum atoms, or of oligomers of 3. - Treatment of MoOCl4 with two equivalents of methyllithium gave a carbonylolefinating reagent "4" which, according to NMR data, consists of isomeric or oligomeric 1,3-dioxo-1,3-dimolybda(VI)cyclobutane complexes 4.Both reagents are labile at room temperature, but differ from the classical carbonylolefinating reagents by an acidic rather than a basic character, resistance to hydroxy groups, and high selectivity. Key Words: Carbonylolefination / μ-Methylene complexes / Molybdenum reagent
- Kauffmann, Thomas,Fiegenbaum, Petra,Papenberg, Michael,Wieschollek, Raphael,Wingbermuehle, Dorothea
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- Stereoselective synthesis of gem-disubstituted cyclopropanes from gem-dibromocyclopropanes
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The title reaction is realized by utilizing an intramolecular alkylation reaction of zincate carbenoids followed by a Pd (0)-catalyzed coupling reaction with acyl, aryl, and alkenyl halides.
- Harada,Katsuhira,Hattori,Oku
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p. 6039 - 6040
(2007/10/02)
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- ACTIVATION OF REDUCING AGENTS. SODIUM HYDRIDE CONTAINING COMPLEX REDUCING AGENTS 24. BENEFICIAL EFFECT OF Me3SiCl ON THE REDUCING PROPERTIES OF NiCRA
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Reduction of carbon-carbon double bonds can be achieved with either NiCRA or NiCRASi (nickel containing Complex Reducing Agent activated by Me3SiCl).Selective reduction of polyunsaturated hydrocarbons or unsaturated ketones are easily performed with both reagents.
- Fort, Y,Vanderesse, R,Caubere, P
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p. 5487 - 5490
(2007/10/02)
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- Correlation of Alkyl and Polar Substituents at the Alcoholic Side of Tertiary Acetates with the Rate of Pyrolyses in the Gas Phase
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The rate coefficients for the gas-phase pyrolysis of several tertiary acetates have been measured in a static system over the temperature range of 220-340 deg C and pressure range of 40-186 torr.In seasoned vessels the reactions are homogeneous, follow a first-order rate law, and are unimolecular.The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3,3,3-trichloro-2-methyl-2-propyl acetate, log k1 (s-1) = (13.86 +/- 0.35) - (188.8 +/- 3.8) kJ mol-1 (2.303 RT)-1; for methyl α-acetoxyisobutyrate, log k1 (s-1) = (12.42 +/- 0.28) - (174.6 +/- 3.2) kJ mol-1 (2.303 RT)-1; for 2-methyl-2-hexyl acetate, log k1 (s-1) = (13.35 +/- 0.33) - (166.1 +/- 3.4) kJ mol-1 (2.303 RT)-1; for 2,4-dimethyl-2-pentyl acetate, log k1 (s-1) = (12.42 +/- 0.19) - (154.1 +/- 1.9) kJ mol-1 (2.303 RT)-1; for 2-methyl-2-acetoxy-4-phenylbutane, log k1 (s-1) = (11.97 +/- 0.55) - (151.5 +/-5.6) kJ mol-1 (2.303 RT)-1.The effectof substituents in the gas-phase elimination of 2-substituted 2-propyl acetates may be either electronic or steric in nature.The linear correlations for electron-releasing groups and for electron-withdrawing groups are presented and discussed.The results of the present work together with those reported in the literature lead to the establishment of a possible generalization on the influence of substituents at the alcohols side of primary, secondary, and tertiary acetates pyrolyses in the gas phase.
- Gonzalez, Neil,Martin, Ignacio,Chuchani, Gabriel
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p. 1314 - 1318
(2007/10/02)
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- CATALYTIC ACID DEHYDROCHLORINATION OF TERTIARY AND BENZYLIC CHLORIDES
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For the case of a series of tertiary and bezylic chlorides it was shown that elimination by the acid-catalyzed generation of cationoid intermediates is no less effective for the production of olefins than the widely employed alkaline dehydrochlorination.
- Arakelyan, A. S.,Dvoryanchikov, A. I.,Gevorkyan, A. A.
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p. 1193 - 1196
(2007/10/02)
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- Deoxygenation of allylic alcohols to terminal olefins via stannylation/destannylation
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Deoxygenation of allylic alcohols to terminal olefins was performed via three steps; 1) [3,3]-sigmatropic rearrangement of O-allylxanthates, 2) the successive stannolysis with tributyltin hydride yielding allylic stannanes, and 3) final protolysis of allylic stannanes to terminal olefins.
- Ueno, Yoshio,Sano, Hiroshi,Okawara, Makoto
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p. 1767 - 1770
(2007/10/02)
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