25068-26-2Relevant articles and documents
Fast propene dimerization using upper rim-diphosphinated calix[4]arenes as chelators
Lejeune, Manuel,Semeril, David,Jeunesse, Catherine,Matt, Dominique,Lutz, Pierre,Toupet, Loic
, p. 881 - 886 (2006)
The complexes [NiBr2·1] and [NiBr2· 2], containing the upper rim-diphosphinated calixarenes 5,17-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene (1) and 5,17-dibromo-11,23-bis(diphe-nylphosphino)-25,26,27,28-tetrapropoxycalix[4] arene (2) were assessed as propene dimerization catalysts. Combined with methylaluminoxane, both complexes result in highly efficient dimerization catalysts displaying C6 selectivities in the range 80-97% and activities that compare with the best reported systems, the latter using PCy3 as ligand. The origin of the remarkable activities of the calixarene derivatives may be the ability of the diphosphine to undergo a periodic bite angle increase that incidentally favors the insertion step. Calixarenes such as 1 or 2, which each incorporate two "stable" Ph2PAr moieties, constitute interesting alternatives to the use PCy3 in propene dimerization.
Acid-base properties and catalytic activity of nanophase ceria-zirconia catalysts for 4-methylpentan-2-ol dehydration
Cutrufello,Ferino,Solinas,Primavera,Trovarelli,Auroux,Picciau
, p. 3369 - 3375 (1999)
The room-temperature high energy ball-milling technique was used to prepare nanophase Ce(1-x)Zr(x)O2 (x = 0; 0.2; 0.5; 0.8; 1) catalysts. The acid-base properties of these catalysts were investigated by means of adsorption microcalorimetry, using NH3 and CO2 as probe molecules. The catalytic activity for 4-methylpentan-2-ol dehydration was tested at atmospheric pressure in a fixed-bed flow microreactor. The inclusion of increasingly high contents of zirconium into the ceria lattice has a complex influence on the acidity and basicity of the pure parent oxide, in terms of both number and strength of the sites. A maximum in 1-alkene selectivity is observed for the ceria-rich catalyst and a minimum for the zirconia-rich sample. Catalytic results are correlated with the acid-base properties and can be interpreted in the light of the mechanism formerly proposed for zirconia, ceria and lanthania. Surface conditioning of the zirconia-rich catalyst occurs during the run, resulting in a remarkable variation of selectivity.
Dispersion of nanosized ceria-terbia solid solutions over silica surface: Evaluation of structural characteristics and catalytic activity
Miah, Abu Taleb,Saikia, Pranjal
, p. 96 - 104 (2018)
In this work, we investigated the dispersion effects of nanosized ceria-terbia solid solutions over silica surface in terms of structural characteristics and catalytic activity. The dispersion process was carried out via a soft chemical route using colloidal silica precursor and nitrate precursors of cerium and terbium. The structural features were elucidated by means of analytical techniques namely TGA, BET surface area, XRD, Raman Spectroscopy, UV-vis DRS, TEM, XPS, and TPR-TPO. The catalyst samples were subjected to thermal treatments at different temperatures ranging from 773 to 1073 K to understand the influence of silica support on dispersion, textural properties, and thermal stability. Catalytic activity was evaluated for selective dehydration of 4-methylpentan-2-ol to 4-methylpent-1-ene in the vapor phase at atmospheric pressure. The silica supported ceria-terbia catalyst exhibited better dehydration activity as well as selectivity in comparison to the unsupported catalyst. The catalytic properties were found to be dependent on structural features of the prepared catalyst samples.
4-BROMO-3,3-DIMETHYL-1-BUTENE: A NEW PROBE FOR RADICAL INTERMEDIATES IN REACTIONS IN STRONGLY BASIC MEDIA
Newcomb, Martin,Williams, William G.,Crumpacker, Elizabeth L.
, p. 1183 - 1184 (1985)
The preparation, isolation and purification of the title bromide (1) are described, and the application of 1 as a mechanistic probe is demonstrated in the metal-halogen interchange reaction with tert-butyllithium.
KINETIC STUDY THE 2,2-DIMETHYL-3-BUTEN-1-YL TO 2-METHYL-4-PENTEN-2-YL RADICAL REARRANGEMENT IN THE TEMPERATURE RANGE 37-74 deg C
Newcomb, Martin,Williams, William G.
, p. 1179 - 1182 (1985)
The tin hydride method was used to determine the rates of the title rearrangement over the temperature range 37-74 deg C; the data was combined with the previously reported low temperature kinetic studies to give a new temperature dependent function: at 25 deg C the calculated rate constant is 5E6 sec-1.
Rate Constants and Arrhenius Functions for Rearrangements of the 2,3-Dimethyl-3-butenyl and (2,2-Dimethylcyclopropyl)methyl Radicals
Newcomb, Martin,Glenn, Anne G.,Williams, William G.
, p. 2675 - 2681 (1989)
Rate constants for the rearangement of the 2,2-dimethyl-3-butenyl radical (1) to the 1,1-dimethyl-3-butenyl radical (3) via the intermediate (2,2-dimethylcyclopropyl)methyl radical (2) were measured over the temperature range 74 to -78 deg C by the competition method using the reaction of radical 1 with Bu3SnH as the basis reaction.Rate constants for ring opening of radical 2 to both 1 and 3 were measured over the temperature range 50 to -78 deg C by competition against reaction of 2 with PhSH.Arrhenius functions for the 1 to 3, 1 to 2, 2 to 1, and 2 to 3 conversions were calculated; at 25 deg C, the rate constants for these conversions are 4.8*106, 5.6*106, 1.2*108, and 7.7*108 s-1, respectively.At room temperature, cyclization of gem-dimethyl-substituted radical 1 is accelerated by about 3 orders of magnitude over its parent, 3-butenyl radical.Ring opening of 2 is about 1 order of magnitude faster than ring opening of its parent, cyclopropylcarbinyl radical.For the 1 to 2 conversion, K12 varies from 0.05 at 25 deg C to 0.02 at -78 deg C, ΔH12 is 1.0 kcal/mol, ΔS12 is -2.7 eu, and ΔG12 at 25 deg C is 1.8 kcal/mol.
Synthesis of 2,3-Dimethylbutenes by Dimerization of Propene Using Highly Active Nickel-Phosphine Catalysts in the Presence of Sulfonic Acids and/or Dialkyl Sulfates
Nomura, Kotohiro,Ishino, Masaru,Suzukamo, Gohfu
, p. 2671 - 2676 (1997)
A nickel-phosphine catalyst system consisting of nickel naphthenate, P(cyclo-C6H11)3, AlEt3, and 2,4,6-trichlorophenol (TCP) in the presence of sulfonic acids (CF3SO3H and MeSO3H) or dialkyl sulfates (Me2SO4 and Et2SO2) exhibits remarkable catalytic activity for the dimerization of propene. The catalytic activity (turnover number (TON) for the formation of C6, olefins or 2,3-dimethylbutenes) was enhanced when the catalyst was combined with effective additives, such as Et2SO4 and MeSO3H. The reaction products consisted of 2,3-dimethyl-1-butene (DMB-1) and/or 2,3-dimethyl-2-butene (DMB-2) in high yields (selectivity of dimers based on the reacted propene = 70-80%: selectivity of 2,3-dimethylbutenes in C6 olefins = 78-80%). The ratio of DMB-1/DMB-2 could be controlled by varying the molar ratios of the catalyst ingredients without decreasing in the turnover numbers. Although CF2SO3H was found to be the best additive as far as the catalytic activity and the selectivity of dimers (94-99%) are concerned, the selectivity of 2,3-dimethylbutenes in C6 olefins decreased. The addition of a small amount of water was also effective to enhance the catalytic activity: The turnover number for the formation of 2,3-dimethylbutenes was raised from 7050 to 30360.
N-Hydroxypyridine-2-thione Esters as Radical Precusors in Kinetic Studies. Measurements of Rate Constants for Hydrogen Atom Abstraction Reactions
Newcomb, Martin,Un Park, Seung
, p. 4132 - 4134 (1986)
N-hydroxypyridine-2-thione esters were employed as radical precursors in kinetic studies.Radical chain reactions of the precursor esters gave 2,2-dimethyl-3-butenyl and 5-hexenyl.These radicals either were trapped by H-atom donors or rearranged, and the rate constants for trapping were determined from the known rate constants for rearrangement and measured product yields.For hydrogen atom donors that reacted too slowly to trap radicals before rearrangement, an estimate of the rate constants for hydrogen atom transfer was made from the yields of rearranged hydrocarbon and alkyl pyridyl sulfide (formed by scavenging of the alkyl radical by the precursor ester).The methods work for a variety of H-atom donors, including thiols, stannanes, phosphines, silanes, and reactive hydrocarbons.The rate constants determined for reduction of alkyl radicals by dicyclohexylphosphine, 1,4-cyclohexadiene, and THF are important for mechanistic studies of potential electron-transfer processes in ractions of nukleophiles with alkyl halides.
Merging Halogen-Atom Transfer (XAT) and Cobalt Catalysis to Override E2-Selectivity in the Elimination of Alkyl Halides: A Mild Route towardcontra-Thermodynamic Olefins
Zhao, Huaibo,McMillan, Alastair J.,Constantin, Timothée,Mykura, Rory C.,Juliá, Fabio,Leonori, Daniele
supporting information, p. 14806 - 14813 (2021/09/18)
We report here a mechanistically distinct tactic to carry E2-type eliminations on alkyl halides. This strategy exploits the interplay of α-aminoalkyl radical-mediated halogen-atom transfer (XAT) with desaturative cobalt catalysis. The methodology is high-yielding, tolerates many functionalities, and was used to access industrially relevant materials. In contrast to thermal E2 eliminations where unsymmetrical substrates give regioisomeric mixtures, this approach enables, by fine-tuning of the electronic and steric properties of the cobalt catalyst, to obtain high olefin positional selectivity. This unprecedented mechanistic feature has allowed access tocontra-thermodynamic olefins, elusive by E2 eliminations.
METHOD OF PRODUCING TERMINAL DOUBLE BOND-CONTAINING COMPOUND
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Paragraph 0044-0048, (2020/10/09)
SOLUTION: A method of producing a terminal double bond-containing compound includes: reacting a compound represented by the following general formula (I) under a pressure of 0 MPa-G or lower in the presence of a metal oxide catalyst to produce a terminal double bond-containing compound represented by the following general formula (II). In formula (I) and formula (II), R1 and R2 represent hydrocarbon groups, and R1 and R2 may bond each other to form a ring together with carbon atoms by which R1 and R2 bond. EFFECT: According to the present invention, a terminal double bond-containing compound can be safely and easily produced with high selectivity. SELECTED DRAWING: None COPYRIGHT: (C)2020,JPOandINPIT
