- Mechanistic insights into the rhenium-catalyzed alcohol-to-olefin dehydration reaction
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Rhenium-based complexes are powerful catalysts for the dehydration of various alcohols to the corresponding olefins. Here, we report on both experimental and theoretical (DFT) studies into the mechanism of the rhenium-catalyzed dehydration of alcohols to olefins in general, and the methyltrioxorhenium-catalyzed dehydration of 1-phenylethanol to styrene in particular. The experimental and theoretical studies are in good agreement, both showing the involvement of several proton transfers, and of a carbenium ion intermediate in the catalytic cycle. Ionic or concerted? Rhenium-based complexes are powerful catalysts for the dehydration of various alcohols to the corresponding olefins. Experimental and DFT studies into the mechanism of the rhenium-catalyzed dehydration of alcohols to olefins are reported. The experimental and theoretical studies are in good agreement, both showing the involvement of a carbenium ion intermediate in the catalytic cycle (see figure). Copyright
- Korstanje, Ties J.,Jastrzebski, Johann T. B. H.,Kleingebbink, Robertus J. M.
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p. 13224 - 13234
(2013/10/01)
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- Novel route to a fruitful mixture of terpene fragrances in particular phellandrene starting from natural feedstock geraniol using weak acidic boron based catalyst
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Myrcene, ocimene and in particular phellandrene were selectively generated as products by dehydration of the natural feedstock geraniol over a weak acidic boron pentasil zeolite catalyst in a gas phase reaction. Additionally linalool was formed by rearrangement reaction. The total selectivity of these 4 terpenes is up to 99%.
- Eisenacher, Matthias,Beschnitt, Stefan,H?lderich, Wolfgang
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experimental part
p. 214 - 217
(2012/09/08)
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- Cyclization of citronellal in a supercritical solvent in a flow reactor in the presence of Al2O3
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The reactivity of citronellal under supercritical solvent conditions in a flow reactor in the presence of Al2O3 is examined. It is shown that at 160°C, the main transformation product of citronellal is isopulegol, and when the temperature is increased to 190°C, they are monoterpenes with a para-menthane framework and myrcene. Pleiades Publishing, Ltd., 2012.
- Anikeev,Il'Ina,Volcho,Salakhutdinov
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p. 1917 - 1919
(2013/01/15)
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- Hydrolysis od Bismetallic Complexes of Linalyldiphosphate and their Participation in the Biosynthesis of Cyclic Monoterpenes
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The allylic diphosphate ester linalyldiphosphate forms mono- and bis-metallic complexes with Mg(2+) and Mn(2+).Complexes of the trianion of the ligand are 50 to 100 times more stable than those of the dianion.Mg(2+) and Mn(2+) are bound in the monometallic complex 1E3 and 1E4 times more strongly than in the bismetallic species.The rate constant of the uncatalysed hydrolysis of linalyldiphosphate at pH 7.0 is 1.2 x E4 s-1, which is higher than reported values for the primary diphosphates.Mg(2+) and Mn(2+) affect its rate of hydrolysis and it is shown that the rate enhancement observed is a function of the concentration of the bismetallic complexes.The rate of cyclic terpene hydrocarbon biosynthesis catalysed by carbocyclase from Citrus limonum also correlates with the concentration of the bismetallic complexes.Linalyl monophosphate, which is not a substrate for carbocyclase hydrolyses at a rate proportional to the concentration of the monometallic complex of Mn(2+).The neutral charge of this complex, as opposed to the positively charged bismetallic complex of linalyl diphosphate may be an explanation of the absence of utilization of this complex as a substrate.It appears from the data presented and from previous evidence that bismetallic complexes of allylic diphosphates are the most reactive species in their hydrolysis and the only reactive species in the enzymic cyclizaton of these precursors of monoterpenes.
- Portilla, Gloria,Rojas, M. Cecilia,Chiong, Evaristo,Cori, Osvaldo
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p. 1479 - 1484
(2007/10/02)
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- Preparation of 1-Alkenes by the Palladium-Catalyzed Hydrogenolysis of Terminal Allylic Carbonates and Acetates with Formic Acid-Triethylamine
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A useful method for the preparation of 1-alkenes from terminal allylic carbonates and acetates by the palladium-catalyzed reaction with formates is described.Formic acid-triethylamine is a suitable reductant.As catalyst, Pd2(dba)3CHCl3-P(n-Bu)3 gave the best result, 0.05-0.2 molpercent being sufficient (turnover 500-2000).Using this method, various 1-alkenes were prepared in good yields with high selectivity.
- Tsuji, Jiro,Minami, Ichiro,Shimizu, Isao
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p. 623 - 627
(2007/10/02)
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- α-HALOALKANESULFONYL BROMIDES IN ORGANIC SYNTHESIS. 4. REGIOSELECTIVE γ-DEPROTONATION OF α,β-UNSATURATED SULFONES. A SIMPLE SYNTHESIS OF 2-ALKYL-1,3-BUITADIENES
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A simple method for converting 2-methyl-1-alkenes into 2-alkyl-1,3-butadienes is described.Evidence for complexation of lithium cations by sulfonyl groups in the course of reactions of α,β-unsaturated sulfones with LiOt-Bu is presented.
- Block, Eric,Eswarakrishnan, Venkatachalam,Gebreyes, Kassu
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p. 5469 - 5472
(2007/10/02)
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- MOLYBDENUM CATALYZED ELIMINATIONS OF ALLYLIC ACETATES. NEW DIENE SYNTHESIS
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Allyl acetates smoothly eliminate the elements of acetic acid in the presence of O,N-bis(trimethylsilyl)acetamide and molybdenum hexacarbonyl; a simple sequence permits elaboration of saturated aldehydes into α,β,γ,δ-dienoates which resulted in a four step synthesis of trichonine.
- Trost, Barry M.,Lautens, Mark,Peterson, Brian
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p. 4525 - 4528
(2007/10/02)
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- PHOTOCHEMISTRY OF AZOLES, PART VII. PHOTOSOLVOLYSIS OF ALKYLMERCAPTOAZOLES. AN APPLICATION TO SOME ACYCLIC MONOTERPENE DERIVATIVES
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Salts derived from 2-alkylmercapto-1-methylimidazoles 1b-e and 3-alkylmercapto-4-methyl-1,2,4-triazoles 2b-d have been found to undergo photochemical heterolytic fission of the S-alkyl bond in aqueous or methanolic solution to give solvolysis-type products.
- Iwasaki, Shigeo
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p. 125 - 138
(2007/10/02)
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- ENHANCEMENT OF THE HYDROLYSIS OF GERANYL PYROPHOSPHATE BY BIVALENT METAL IONS. A MODEL FOR ENZYMIC BIOSYNTHESIS OF CYCLIC MONOTERPENES
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Hydrolysis of geranyl pyrophosphate is catalyzed by salts of Mn2+ and involves C-O bond cleavage.The first order rate constants reach limiting values with 2+> 10E-2 M, and the most reactive species is GPP (Mn2+)2 at the optimum pH of 6.5-7.The products are similar to those from acid hydrolysis except that more cyclic hydrocarbons are formed in the presence of metal ions.Hydrolysis of geranyl phosphate is inhibited, and that of citronellyl pyrophosphate is weakly catalyzed by Mn2+.Other divalent metal cations catalyze the hydrolysis of geranyl pyrophosphate and the sequence of effectiveness is Cu2+>Mn2+>Co2+>Mg2+ Ca2+.
- Vial, M. V.,Rojas, C.,Portilla, G.,Chayet, L.,Perez,L. M.,et al.
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p. 2351 - 2358
(2007/10/02)
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