7437-61-8Relevant articles and documents
The selective epoxidation of conjugated olefins containing allylic substituents and epoxidation of propylene in the presence of butadiene
Monnier, John R.,Peters, Kimberly T.,Hartley, Gary W.
, p. 374 - 380 (2007/10/03)
The epoxidation of isoprene (2-methyl-1,3-butadiene) and piperylene (1,3-pentadiene), both conjugated olefins containing allylic methyl groups, has been conducted using conventional, CsCl-promoted, Ag/α-Al 2O3 catalysts. Selectivities to the allylic olefin epoxide isomers are over 20% and are much higher than expected due to the presence of the conjugated olefin structure. The epoxidation of propylene over the same catalyst under the same conditions is only 2.5%. The epoxidation of propylene in the presence of butadiene also yields PO in much higher selectivities. The presence of as little as 1% C4H6 in the reaction feedstream increases the selectivity to PO from 2.5% to over 40% at the expense of overall activity for C3H6 conversion. The upper limit of selectivity to PO in the presence of C4H6 appears to be approximately 50%, suggesting an upper limit for the effectiveness of this methodology. Epoxidation of C4H6 alone on similar Ag catalysts indicates that the consecutive reaction of EpB to CO 2/H2O is strongly limited by the presence of excess C 4H6 in the feedstream. In addition, the selectivity to EpB is directly proportional to the amount of C4H6 in the reaction feed stream. Selectivities >90% are obtained only when there is sufficient C4H6 in the reaction feedstream to control the concentration of the reactive Ag-O surface. For C4H6 epoxidation, all CO2/H2O is formed by a consecutive reaction pathway from EpB; there is no parallel pathway for the direct formation of CO2/H2O from C4H6. Using the selective epoxidation of C4H6 as the model for understanding the enhancement in selectivity for allylic olefin epoxide formation, the most likely reason for improved selectivities is that strongly adsorbed C4H6 (or other conjugated olefins) limits the ensemble size of contiguous Ag-O surface sites. These ensembles are too small for PO combustion, but not too small for PO formation.
Gas-phase reaction of NO3 radicals with isoprene: A kinetic and mechanistic study
Berndt, Torsten,Boege, Olaf
, p. 755 - 765 (2007/10/03)
The gas-phase reaction of NO3 radicals with isoprene was investigated under flow conditions at 298 K in the pressure range 6.8 3 radicals toward isoprene was determined to be (6.86 ± 2.60) × 10-13 cm3 molecule-1 s-1. The formation of the possible oxiranes, 2-methyl-2-vinyl-oxirane and 2-(1-methyl-vinyl)-oxirane, was observed in dependence on total pressure. In the presence of O2 in the carrier gas, the product distribution was found to be strongly dependent on the reaction pathways of formed peroxy radicals, If the peroxy radicals mainly reacted in a self-reaction, the formation of organic nitrates was detected and 4-nitroxy-3-methyl-but-2-enal was identified as a main product. On the other hand, when NO was added to the gas mixture and the peroxy radicals were converted via RO2 + NO → RO + NO2, the formation of methyl vinyl ketone as the main product as well as 3-methylfuran and methacrolein was observed. From the ratio of the product yields if NO was added to the gas mixture it was concluded that the attack of NO3 radicals predominantly takes place in the 1-position. A reaction mechanism is proposed and the application of these results to the troposphere are discussed.
Regio- and enantio-selective catalytic epoxidation of conjugated dienes
Rasmussen, Kaare G.,Thomsen, Dorte S.,Joergensen, Karl Anker
, p. 2009 - 2018 (2007/10/02)
The regio-and enantio-selective catalytic epoxidation of conjugated aliphatic dienes have been studied using a variety of achiral and chiral manganese salen complexes and sodum hypochlorite or iodosylbenzene as the terminal oxidant.The catalysts show a preference for the less substituted alkene in most of the dienes studied, and in some cases a regioselectivity of 100percent is found.The regioselectivity is dependent on the terminal oxidant applied.The enantiomeric excess (ee) obtained varies for the different conjugated dienes and the ee is generally highest for internal alkenes, where an ee of up to 71percent is observed, whereas 48percent is the highest observed ee for the less substituted alkenes.The ee is also dependent on the terminal oxidant applied.The regio- and enantio-selectivity have also been studied for different 1-(para-substituted phenyl)buta-1,3-dienes, but no regio- and enantio-selectivity dependence on the different subsituents are observed.A competitive epoxidation experiment with styrene and 1-phenylbuta-1,3-diene shows that the latter is the most reactive and the difference in reactivity is discussed on the basis of frontier orbitals of the two systems.The electronic structure of the oxo-manganese salen intermadiate is investigated using INDO/1 calculations and it is found that the triplet state is the most stable state of the intermediate.Based on the electronic structure of the oxo-maganese salen intermediate a mechanism of the oxygen transfer step to the conjugated diene is proposed.
Visible Light Induced Reactions of NO2 with Conjugated Dienes in a Low-Temperature Ar Matrix
Tanaka, Nobuaki,Kajii, Yoshizumi,Shibuya, Kazuhiko,Nakata, Munetaka
, p. 7048 - 7053 (2007/10/02)
Visible light induced oxygen atom transfer from NO2 to conjugated dienes has been investigated in a low-temperature Ar matrix, where the dienes are 1,3-butadiene (BD), 2-methyl-1,3-butadiene (isoprene), and 2,3-dimethyl-1,3-butadiene (DMB).In each diene/NO2/Ar system, the corresponding nitrite radical, oxirane, aldehyde, and NO were obtained as the photochemical reaction products.The reactions are initiated by the formation of undetecteable short-lived oxirane biradical and NO due to visible light induced O atom transfer from NO2 to the conjugated dienes. (1) The recombination of oxirane biradicals and neighboring NO gives the nitrite radicals as the photochemical intermediate. (2) The ring closure of the biradicals leads to the formation of oxiranes. (3) The intramolecular H atom transfer of biradicals leads to the formation of aldehydes.The visible photolysis of the nitrite radicals gives rise to oxirane, aldehyde, and NO.The reaction rates are derived by measuring the absorbance changes of the products upon the 582-nm irradiation.The methyl substituent effect on the reactivity is discussed.
Regioselective Monoepoxidation of 1,3-Dienes Catalysed by Transition-metal Complexes
Thomsen, Dorte S.,Schioett, Birgit,Jorgensen, Karl Anker
, p. 1072 - 1074 (2007/10/02)
A procedure for regioselective monoepoxidation of mainly the less substituted double bond of 1,3-dienes with sodium hypochlorite or iodosylbenzene using various metal complexes as catalysts is presented; the results obtained are different from those found when applying the usual epoxidation reagents.
Monooxygenase-like Oxidation of Hydrocarbons by H2O2 Catalyzed by Manganese Pophyrins and Imidazole: Selection of the Best Catalytic System and Nature of the Active Oxygen Species
Battioni, P.,Renaud, J. P..,Bartoli, J. F.,Reina-Artiles, M.,Fort, M.,Mansuy, D.
, p. 8462 - 8470 (2007/10/02)
Fe and Mn porphyrins alone are almost unable to catalyze cyclooctene epoxidation or cyclooctane hydroxylation by H2O2.In the presence of imidazole, Mn(III) porphyrins, and particularly Mn(TDCPP)Cl, are much better catalysts than Fe porphyrins for oxygen-atom transfer from H2O2 to hydrocarbons.From a study of various Mn porphyrin catalysts and nitrogen base cocatalysts, the most efficient system that has been selected involves Mn(TDCPP)Cl in the presence of 10 - 20 equiv of imidazole.This system leads to high yields of alkene epoxidation (90 - 100 percent in less than 1 h at room temperature).Epoxidation of 1,2-dialkylethylenes is stereospecific and corresponds to a syn addition of an oxygen atom to the double bond.This system also leads to the oxidation by H2O2 of various alkanes such as cyclohexane, cyclooctane, adamantane, ethylbenzene, or tetralin, with formation of the corresponding alcohols and ketones in yields between 40 and 80 percent.The Mn(TDCPP)Cl-imidazole-PhIO and Mn(TDCPP)Cl-imidazole-H2O2 systems exhibit the following: (i) identical stereospecificities for the epoxidation of stilbene and hex-2-ene, (ii) identical regioselectivities for the epoxidation of iosoprene and limonene as well as for the hydroxylation of n-heptane, and (iii) almost identical chemoselectivities for the oxidation of cyclohexene and of mixtures of cyclooctane and cyclooctene.This indicates that very similar, if not identical, high-valent Mn-oxo intermediates are the active oxygenating species in both systems.Thus, thanks to the presence of imidazole, it is possible to perform efficient biomimetic monooxygenations of hydrocarbons by using the Mn(TDCPP)Cl catalyst and H2O2 instead of PhIO as the oxygen-atom donor.
NaOCl OLEFIN EPOXIDATIONS CATALYZED BY Mn-PORPHYRINS UNDER TWO-PHASE CONDITIONS. INFLUENCE OF STRUCTURAL FACTORS ON THE STABILITY, CATALYTIC ACTIVITY AND SELECTIVITY OF PORPHYRINS
Banfi, Stefano,Montanari, Fernando,Penso, Michele,Sosnovskikh, Viecheslav,Vigano, Patrizia
, p. 689 - 694 (2007/10/02)
The progressive deactivation of a series of Mn-tetraarylporphyrins (TPP, TMP, TAP, TPFPP, TDClPP), which are very efficient catalysts for olefin epoxidations, has been measured under the reaction conditions.Reactions are carried out at 0 deg C in CH2Cl2-H2O, with NaOCl aqueous solution at pH 9.5, in the presence of N-hexyl imidazole as an axial ligand and, generally, of a phase-transfer catalyst.All porphyrins are more or less rapidly deactivated, the only exception being Mn-TDClPP which can be almost quantitatively recovered.Both steric and electronic effects seem therefore to be essential for the chemical stability of metallo-porphyrins.In the presence of 0.005 molar equivalents of Mn-TDClPP, α-olefins and sterically unhindered internal olefins are epoxidized in high yields at 0 deg C and very short reaction times.Highly regio- and stereo-selective oxidations can be also achieved.
