- The kinetics and mechanism of the homogeneous, unimolecular gas-phase elimination of 2-(4-substituted-phenoxy)tetrahydro-2H-pyranes
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The gas-phase elimination kinetics of tetrahydropyranyl phenoxy ethers: 2-phenoxytetrahydro-2H-pyran, 2-(4-methoxyphenoxy)tetrahydro-2H-pyran, and 2-(4-tert-butylphenoxy)tetrahydro-2H-pyran were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor toluene. The working temperature and pressure were 330 to 390°C and 25 to 89?Torr, respectively. The reactions yielded DHP and the corresponding 4-substituted phenol. The eliminations are homogeneous, unimolecular, and satisfy a first-order rate law. The Arrhenius equations for decompositions were found as follows: 2-phenoxytetrahydro-2H-pyran log k1 (s?1)?=?(14.18?±?0.21)???(211.6?±?0.4)?kJ?mol?1 (2.303 RT)?1 2-(4-methoxyphenoxy)tetrahydro-2H-pyran log k1 (s?1)?=?(14.11?±?0.18)???(203.6?±?0.3)?kJ?mol?1 (2.303 RT)?1 2-(4-tert-butylphenoxy)tetrahydro-2H-pyran log k1 (s?1)?=?(14.08?±?0.08)???(205.9?±?1.0)?kJ?mol?1 (2.303 RT)?1. The analysis of kinetic and thermodynamic parameters for thermal elimination of 2-(4-substituted-phenoxy)tetrahydro-2H-pyranes suggests that the reaction proceeds via 4-member cyclic transition state. The results obtained confirm a slight increase of rate constant with increasing electron donating ability groups in the phenoxy ring. The pyran hydrogen abstraction by the oxygen of the phenoxy group appears to be the determinant factor in the reaction rate.
- Alvarez-Aular, Alvaro,Cartaya, Loriett,Maldonado, Alexis,Coll, David Santiago,Chuchani, Gabriel
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- Heterogeneous acidic catalysts for the tetrahydropyranylation of alcohols and phenols in green ethereal solvents
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The application of heterogeneous catalysis and green solvents to the set up of widely employed reactions is a challenge in contemporary organic chemistry. We applied such an approach to the synthesis and further conversion of tetrahydropyranyl ethers, an important class of compounds widely employed in multistep syntheses. Several alcohols and phenols were almost quantitatively converted into the corresponding tetrahydropyranyl ethers in cyclopentyl methyl ether or 2-methyltetrahydrofuran employing NH4HSO4 supported on SiO2 as a recyclable acidic catalyst. Easy work up of the reaction mixtures and the versatility of the solvents allowed further conversion of the reaction products under one-pot reaction conditions.
- Azzena, Ugo,Carraro, Massimo,Modugno, Gloria,Pisano, Luisa,Urtis, Luigi
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supporting information
p. 1655 - 1659
(2018/07/25)
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- Syntheses of symmetric and unsymmetric 2,6-bis(phosphino)phenols
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Compounds bearing the structural motif of 2,6-bis(phosphino)phenol have been synthesized via two general methods. Double lithium-halogen exchange occurred in low-temperature reactions of O-protected (by methyl- or tetrahydropyranyl groups) 2,6-dibromo-4-m
- Beganskiene, Aldona,Nikishkin, Nicolai I.,Luck, Rudy L.,Urnezius, Eugenijus
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p. 656 - 663
(2007/10/03)
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- Zirconium sulfophenyl phosphonate as a heterogeneous catalyst in tetrahydropyranylation of alcohols and phenols
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Zirconium Sulfophenyl Phosphonate Zr(O3PCH3)(1.2)(O3PC6- InSO3H)(0.8) was found to be an efficient heterogeneous catalyst for the tetrahydropyranylation of alcohols and phenols.
- Curini, Massimo,Epifano, Francesco,Marcotullio, Maria Carla,Rosati, Ornelio,Costantino, Umberto
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p. 8159 - 8162
(2007/10/03)
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- Solvent free tetrahydropyranylation of phenols and alcohols over zeolites HSZ as reusable catalysts
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Phenols and alcohols are tetrahydropyranylated in the presence of zeolites HSZ in good to excellent yields and selectivities. Addition of methanol performs the complete deprotection.
- Ballini, Roberto,Bigi, Franca,Carloni, Silvia,Maggi, Raimondo,Sartori, Giovanni
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p. 4169 - 4172
(2007/10/03)
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- MIXED AROMATIC-ALIPHATIC ACETALS; THEIR PREPARATION, (1)H AND (13)C-NMR SPECTRA AND HYDROGENOLYSIS BY ETHEREAL SOLUTION OF CHLOROALANE
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The corresponding p-X-phenylisobutyl acetals of acetaldehyde (I), 2-(p-X-phenoxy)tetrahydropyrans (II), 2-(p-X-phenoxy)tetrahydrofurans (III), and cyclohexyl(p-X-phenyl)acetals of acetaldehyde (IV) were prepared by addition of p-X-substituted phenols to isobutyl vinyl ether, 2,3-dihydro-4H-pyran, 2,3-dihydrofuran, and cyclohexyl vinyl ether, respectively.The structures of acetals I-IV were confirmed by their (1)H and (13)C-NMR spectra.Diastereotopic protons of the methylene and geminal methyl groups are anisochronous in the (1)H-NMR spectra of acetals I. (13)C-NMR spectra of acetals IV demonstrate anisochronous behaviour of cyclohexane ring diastereotopic carbon atoms.The constants ?p+ for several groups calculated using (13)C-NMR spectra are: 1-isobutoxy-1-ethoxy- (-0.58), 2-tetrahydrofuryloxy- (-0.59), and 1-cyclohexyloxy-(1-ethoxy) (-0.57).Experimental relative rate constants of hydrogenolysis of acetals I and II by ethereal solution of chloroalane yield best correlations with ?p+ constants of the substituent X, providing the values ρ= -1.09 for compounds of the series I and II, respectively.The importance of these results for finding the rate determining step of the studied reaction is discussed.
- Dusek, Jiri,Sklenar, Vladimir,Jonas, Jaroslav
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p. 2912 - 2923
(2007/10/02)
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