13987-01-4Relevant academic research and scientific papers
Definitive Proof for the Operation of Isotopically Sensitive Branching ('Metabolic Switching') in FeI-Mediated C-H Bond Activation in the Gas Phase
Seemeyer, Katrin,Pruesse, Tilmann,Schwarz, Helmut
, p. 1632 - 1635 (1993)
Rigorous regio- and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of 'isotopically sensitive branching' in FeI-mediated C-H bond activation.For the hexane-1,6-diol/Fe(1+)-complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D,L- and meso--isotopomers 1e and 1f demonstrates that dehydrogenation proceeds via two competing pathways (i.e. 'anti'-vs. 'syn'-route).The contribution of these routes to the product formation is-due to a kinetic isotope effect-controlled by the relative configuration at the labeled positions C(3)/C(4).For the D,L-form 1e, we estimate a ratio of 49:1 in favor of the 'anti'-route; due to an isotope effect, this ratio drops to 4.3:1 for the meso-form 1f.
Reaction of Allylic and Benzylic Methyl Ethers with Sodium and Trimethylchlorosilane. Evidence for the Intermediacy of Allylic Radicals and Anions
Tzeng, Dongjaw,Weber, William P.
, p. 265 - 267 (1981)
Allyl methyl ether and benzyl methyl ether react with sodium and trimethylchlorosilane to yield, respectively, allyltrimethylsilane and benzyltrimethylsilane. α,α-Dimethylallyl methyl ether and γ,γ-dimethylallyl methyl ether react with sodium and trimethylchlorosilane to yield γ,γ-dimethylallyltrimethylsilane. α-Methylallyl methyl ether and trans-γ-methylallyl methyl ether react with trimethylchlorosilane and sodium to yield similar product mixtures of α-methylallyltrimethylsilane and cis- and trans-γ-methylallyltrimethylsilane.These results are discussed in ter ms of a mechanism involving electron transfer to yield allylic radicals and allylic anion intermediates.
Highly stable boron-modified hierarchical nanocrystalline ZSM-5 zeolite for the methanol to propylene reaction
Hu, Zhijie,Zhang, Hongbin,Wang, Lei,Zhang, Hongxia,Zhang, Yahong,Xu, Hualong,Shen, Wei,Tang, Yi
, p. 2891 - 2895 (2014)
A highly stable MTP (methanol to propylene) catalyst, boron-modified hierarchical nanocrystalline ZSM-5 zeolite, has been constructed by a facile salt-aided seed-induced route. The cooperative effect of its hierarchical structure and modified acidity gives rise to a significantly stable activity (725 h) even at a high WHSV (weight hourly space velocity) of 4.0 h -1. the Partner Organisations 2014.
Infrared Spectroscopic Studies of the Reactions of Alcohols over Group IVB Metal Oxide Catalysts. Part 1.-Propan-2-ol over TiO2, ZrO2 and HfO2
Hussein, Gamal A.M.,Sheppard, Norman,Zaki, Mohamed I.,Fahim, Radamis B.
, p. 1723 - 1742 (1989)
Infrared spectroscopy has been used to analyse the gas-phase reaction products and the related adsorbed species obtained between room temperature and 400 deg C from the dehydrogenation/dehydration reactions of propan-2-ol over a series of differently calcined catalysts of TiO2, ZrO2, and HfO2.The ZrO2 and HfO2 results were independent of the calcination pretreatment, and the surfaces of these oxides, like that from a TiO2 sample calcined at 800 deg C, were dehydroxylated.Different results were obtained from a TiO2 sample calcined at 300 deg C, which had a hydroxylated surface.The acidic sites and reactivities of the surfaces of TiO2(300 deg C) and TiO2(800 deg C) were explored by pyridine adsorption and infrared spectroscopy.Only Lewis-acid sites were detected by pyridine.On raising the reaction temperature, in all cases the dehydrogenation reaction to give acetone occured either before or simoltaneously to the onset of the dehydration reaction to give propene.Acetone production was most pronounced over ZrO2 and HfO2 but also occurred more with TiO2(800 degC) than with TiO2(300 deg C).The dehydrogenation reaction was largely quenched by pre-adsorbed pyridine on both TiO2 samples.The TiO2 (300 deg C) catalyst showed the presence of adsorbed propan-2-ol and 2-propoxide groups at room temperature.The dehydroxylated ZrO2, HfO2 and TiO2(800 deg C) samples only showed appreciable amounts of 2-propoxide groups.In each case the 2-propoxide ions occurred in two different forms, presumably formed by adsorption on different types of sites.Both the acetone and propene products appeared as absorptions from 2-propoxide surface species decreased in intensity, so the latter are clearly reactive species.Gas-phase acetone production was followed by the chemisorption of acetone at a higher temperature.This subsequently decomposed to give surface acetate species, and finally at 400 deg C to give CO2 and methane in the gas phase.Propene did not give rise to adsorbed species, or to further products in the gas phase.At the higher temperatures, above 300 deg C, the reaction was always selective in favour of the dehydration reaction.However, each of the dehydroxylated catalysts showed some selectivity in favour of the dehydrogenation reaction over the earliest temperature range for alcohol decomposition, between 200 and 250 deg C.A discussion is given of possible mechanistic pathways for the production of surface 2-propoxide species and the two types of products, based on the infrared-supported assumption that the different adsorbed forms of 2-propoxide are reactive intermediates.
Omium Ylide Chemistry. 1. Bifunctional Acid-Base-Catalyzed Conversion of Heterosubstituted Methanes into Ethylene and Derived Hydrocarbons. The Onium Ylide Mechanism of the C1 -> C2 Conversion
Olah, George A.,Doggweiler, Hans,Felberg, Jeff D.,Frohlich, Stephan,Grdina, Mary Jo,et al.
, p. 2143 - 2149 (1984)
The conversion of heterosubstituted methanes, such as methyl alcohol, dimethyl ether, methyl mercaptan, dimethyl sulfide, methylamines, and methyl halides, to ethylene and hydrocarbons derived thereof takes place over bifunctional acidic-basic-supported transition-metal oxide or oxyhalide catalysts, such as tungsten oxide supported on alumina, between 300 and 350 deg C.The conversion of methyl alcohol starts with bimolecular dehydration to dimethyl ether followed by acid-catalyzed transmethylation giving trimethyloxonium ion (or related catalyst-bound methyloxonium ion).The trimethyloxonium ion then undergoes base-induced deprotonation forming a catalyst surface-bound methylenedimethyloxonium ylide.Intermolecular methylation of the ylide, indicated by experiments using singly 13C-labeled dimethyl ether, gives methylethyloxonium ion thus providing the crucial first C-C bond.No intramolecular Steven's-type rearrangement takes place, and methyl ethyl ether is not a significant intermediate as also shown in experiments comparing the products formed from reacting CD3OCH2CH3 under similar conditions.The ethyloxonium ion readily undergoes β-elimination forming ethylene.Initially formed ethylene subsequently can undergo further reaction with the ylide giving via cyclopropane propylene or it can undergo more complex alkylation/oligomerization/cracking reactions giving a mixture of alkenes, alkanes and via cyclization-dehydrogenation aromatics.The complexity of these processes was shown by reacting ethylene itself, as well as 13CH3OH and ethylene, under conditions of the condensation reaction.It is also necessary to differentiate initally formed ethylene via direct C1 -> C2 conversion from that formed in secondary processes together with higher condensation products.The conversion of methyl mercaptan (dimethyl sulfide), methyl halides, and methylamines to ethylene follows similar onium ylide pathways.
Intriguing structural chemistry of neutral and anionic layered monoalkylphosphates: Single-source precursors for high-yield ceramic phosphates
Bhat, Gulzar A.,Kalita, Alok Ch.,Murugavel, Ramaswamy
, p. 5390 - 5401 (2017)
Building up on an available synthetic methodology, phosphate monoesters ROPO3H2 have been synthesized in good yields. The synthetic procedure employed features acetic anhydride mediated activation of phosphoric acid in the presence of alcohols, leading to the formation of phosphate monoesters. The products have been isolated as their cyclohexyl amine salts, [CyNH3]2[(MeO)PO3]·3H2O (1) and [CyNH3][(RO)PO3H] (Cy = cyclohexyl; R = Et (2), iPr (3), or tBu (4)). Neutralization of 1-4 by readily available inexpensive ion exchange resin Amberlite produces monoalkylphosphates (RO)P(O)(OH)2 (R = Me (5), Et (6), iPr (7), or tBu (8)). Thermally labile 1-4 and 7 have been structurally characterized by single crystal X-ray diffraction studies. Due to their intrinsic thermal instability due to β-H elimination, these compounds can be used as ligands for the preparation of single-source precursors for ceramic phosphates by reacting them with suitable metals ions. It is also possible to isolate co-crystals of the anionic and neutral forms of these phosphates as it has been demonstrated in the isolation and structural characterization of [(iPrO)PO3H2]·{[CyNH3][(iPrO)PO3H]} (9). To demonstrate the utility of these monoalkylphosphates in the low-temperature synthesis of metal phosphate bioceramics, isopropyl phosphate 7 has been employed to prepare calcium phosphate [{Ca((iPrO)PO3)(OH2)}·H2O]n (10), which undergoes neat thermal decomposition in two stages to lose water and propene to yield β-Ca2P2O7 at low temperatures (280 °C).
Mesoporogen-Free Synthesis of Hierarchical SAPO-34 with Low Template Consumption and Excellent Methanol-to-Olefin Conversion
Sun, Qiming,Wang, Ning,Bai, Risheng,Chen, Guangrui,Shi, Zhiqiang,Zou, Yongcun,Yu, Jihong
, p. 3812 - 3820 (2018)
Significant interest has emerged in the development of nanometer-sized and hierarchical silicoaluminophosphate zeolites (SAPO-34) because of their enhanced accessibility and improved catalytic activity for methanol-to-olefin (MTO) conversion. A series of nanometer-sized SAPO-34 catalysts with tunable hierarchical structures was synthesized in a Al2O3/H3PO4/SiO2/triethylamine(TEA)/H2O system by using a mesoporogen-free nanoseed-assisted method. The nanometer-sized hierarchical SH-3.0 catalyst (TEA/Al2O3=3.0) possessed the highest crystallinity, highest abundance of intracrystalline meso-/macropores, and the most suitable acidity among all obtained catalysts, showing the highest ethylene and propylene selectivity of 85.4 %. This is the highest reported selectivity for MTO reactions under similar conditions. Detailed analysis of the coke produced during the reaction revealed that the small-sized methyl-substituted benzene and bulky methyl-substituted pyrene were mainly located inside the crystals instead of on the surface of the crystals, which provided further insight into understanding the deactivation of the SAPO-34 catalyst during MTO reaction. Significantly, the simple and cost-effective synthetic process and superb catalytic performance of the nanometer-sized hierarchical SAPO-34 is promising for their practical large-scale application for MTO conversion.
The Role of Zinc Cations in the Conversion of Isobutane into Aromatics over Mechanical Mixtures of ZnO and H-ZSM-5
Osako, Kazuaki,Nakashiro, Katusmi,Ono, Yoshio
, p. 755 - 759 (1993)
Mechanical mixtures of ZnO and H-ZSM-5 show high activities and selectivities for the aromatization of isobutane.The temperature-programmed desorption spectra of ammonia and the infrared spectra of adsorbed pyridene revealed that a solid-solid-ion-exchange occurs between ZnO and H-ZSM-5.The presence of Zn cations in the zeolite channels not only enhances the dehydrogenation, but also the C-C bond cleavage of isobutane.A mechanism for the activation of isobutane is proposed.
Enhanced (photo)catalytic activity of Wells-Dawson (H6P2W18O62) in comparison to Keggin (H3PW12O40) heteropolyacids for 2-propanol dehydration in gas-solid regime
Marcì, Giuseppe,García-López, Elisa I.,Pomilla, Francesca Rita,Liotta, Leonarda F.,Palmisano, Leonardo
, p. 113 - 122 (2016)
Catalytic and photocatalytic 2-propanol dehydration to propene at atmospheric pressure and a temperature range of 60–120?°C were carried out in gas-solid regime by using bare and supported Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O62 (P2W18) heteropolyacids (HPAs). Binary materials were prepared by impregnation of the HPAs on commercial SiO2 and TiO2. The Wells-Dawson was in any case more active than the Keggin heteropolyacid and the differences were enhanced when the supported samples were used. In particular, Wells-Dawson HPA supported on TiO2 and under irradiation showed the highest activity. The HPA species played the key role both in the catalytic and photo-assisted reactions. The acidity of the cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction. The estimated apparent activation energy resulted always lower for the photocatalytic process than for the catalytic one.
A kinetic study of the reactions of 2-propyl radicals in the liquid phase in the presence and absence of oxygen
Costello, Andrew R.,Lindsay Smith, John R.,Waddington, David J.
, p. 201 - 215 (1996)
2-Propyl radicals have been generated from the photolysis of solutions of 2,2-azopropane and 2,4-dimethyl-3-pentanone in decane in a glass and a metal cell. The time course of their reactions in the presence and absence of oxygen has been monitored between 323 and 373 K. The primary process involves the formation of solvent-caged radical pairs, two 2-propyl radicals and a 2-propyl and a 2-methylpropanoyl radical from the azo and ketone precursors, respectively. Subsequently these radicals are partitioned between cage escape and dimerization and disproportionation within the cage. In oxygenated solution the free 2-propyl radicals are effectively trapped as 2-propylperoxyl radicals. However, oxygen does not react with the solvent-caged radicals. This leads to a major difference in the hydrocarbon products from the two precursors. 2,2′-Azopropane gives propane, propene, and 2,3-dimethylbutane from the start of the reaction whereas the ketone only gives propene. Following the depletion of oxygen, or in the absence of oxygen, both precursors behave analogously and give all three hydrocarbons. The 2-propylperoxyl radicals undergo self-reaction and hydrogen abstraction from the solvent to give 2-propanol, propanone, and 2-propyl hydroperoxide and, under conditions of low oxygen concentration, by reaction with 2-propyl radicals they give 2,2′-dipropylperoxide. Although the two cells lead to different overall rates of reaction, the relative rates and product distributions are unaffected by the cell design. A unified mechanism is described and the known and best estimates of rate constants for the individual steps are used to simulate the time dependence of the product yields from the photolysis of both precursors.
