- 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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- 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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- 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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- 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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- The Kinetics and Mechanism of Ring Opening of Radicals containing the Cyclobutylcarbinyl System
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The kinetic parameters of β-fission of radicals containing the cyclobutylcarbinyl system have been determined by analysis of the mixtures obtained when suitable chloro-compounds are treated with tributylstannane.Under these conditions ring opening is irreversible and in the rigid bicyclic system (4) is under stereoelectronic control.For ring opening of cyclobutylcarbinyl radical (8) kf = 4.3 x 103 s-1 at 60 deg C, and the best values of the activation parameters appear to be ΔH(excit.) = 12.2 kcal mol-1 and ΔS(excit.) = -7.4 cal mol-1 K-1.Monocyclic systems undergo preferential fission of the more substituted βγ-bond.Methyl substituents at the α-, β-, or δ-positions have little effect but γ-substitution strongly enhances the rate of ring opening.The transition state is reactant-like and has a similar disposition of centres to that (1) for homolytic addition.
- Beckwith, Athelstan L. J.,Moad, Graeme
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p. 1083 - 1092
(2007/10/02)
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