RESUMO
Sugars are abundant in waste biomass, making them sustainable chiral building blocks for organic synthesis. The demand for chiral saturated heterocyclic rings for pharmaceutical applications is increasing as they provide well-defined three-dimensional frameworks that show increased metabolic resistance. A range of sugar thioacetals can be dehydrated selectively at C-2 under mild basic conditions, and the resulting ketene thioacetals can be applied to the production of useful chiral building blocks via further selective dehydration reactions.
Assuntos
Acetais/química , Carboidratos/química , Etilenos/síntese química , Cetonas/síntese química , Compostos de Sulfidrila/química , Técnicas de Química Sintética/métodos , Desidratação , Etilenos/química , Cetonas/química , Estrutura Molecular , EstereoisomerismoRESUMO
Nucleosidic and oligonucleotidic diarylethenes (DAEs) are an emerging class of photochromes with high application potential. However, their further development is hampered by the poor understanding of how the chemical structure modulates the photochromic properties. Here we synthesized 26 systematically varied deoxyuridine- and deoxycytidine-derived DAEs and analyzed reaction quantum yields, composition of the photostationary states, thermal and photochemical stability, and reversibility. This analysis identified two high-performance photoswitches with near-quantitative, fully reversible back-and-forth switching and no detectable thermal or photochemical deterioration. When incorporated into an oligonucleotide with the sequence of a promotor, the nucleotides maintained their photochromism and allowed the modulation of the transcription activity of T7 RNA polymerase with an up to 2.4-fold turn-off factor, demonstrating the potential for optochemical control of biological processes.
Assuntos
RNA Polimerases Dirigidas por DNA/antagonistas & inibidores , Desenvolvimento de Medicamentos , Inibidores Enzimáticos/farmacologia , Etilenos/farmacologia , Oligonucleotídeos/farmacologia , Nucleosídeos de Pirimidina/farmacologia , Proteínas Virais/antagonistas & inibidores , Bacteriófago T7/enzimologia , RNA Polimerases Dirigidas por DNA/genética , RNA Polimerases Dirigidas por DNA/metabolismo , Inibidores Enzimáticos/síntese química , Inibidores Enzimáticos/química , Etilenos/síntese química , Etilenos/química , Oligonucleotídeos/síntese química , Oligonucleotídeos/química , Processos Fotoquímicos , Nucleosídeos de Pirimidina/síntese química , Nucleosídeos de Pirimidina/química , Proteínas Virais/genética , Proteínas Virais/metabolismoRESUMO
Two-photon fluorescence imaging technology has the advantages of high light stability, little light damage, and high spatiotemporal resolution, which make it a powerful biological analysis method. However, due to the high concentration or aggregation state of traditional organic light-emitting molecules, the fluorescence intensity is easily reduced or disappears completely, and is not conducive to optimal application. The concept of aggregation-induced emission (AIE) provides a solution to the problem of aggregation-induced luminescence quenching (ACQ), and realizes the high fluorescence quantum yield of luminescent molecules in the aggregation state. In addition, two-photon absorption properties can readily be improved just by increasing the loading content of AIE fluorogen (AIEgen). Therefore, the design and preparation of two-photon fluorescence probes based on AIEgen to achieve high-efficiency fluorescence imaging inâ vitro/inâ vivo has become a major research hotspot. This review aims to summarize representative two-photon AIEgens based on triphenylamine, tetraphenylethene, quinoline, naphthalene and other new structures from the past five years, and discuss their great potential in bioimaging applications.
Assuntos
Corantes Fluorescentes/química , Imagem Óptica , Fótons , Compostos de Anilina/síntese química , Compostos de Anilina/química , Etilenos/síntese química , Etilenos/química , Corantes Fluorescentes/síntese química , Naftalenos/síntese química , Naftalenos/química , Quinolinas/síntese química , Quinolinas/químicaRESUMO
AIM AND OBJECTIVE: The research focuses on recent progress in the production of light olefins. Hence, as the common catalyst of the reaction (SAPO-34) deactivates quickly because of coke formation, we reorganized the mechanism combining SAPO-34 with a natural zeolite in order to delay the deactivation time. MATERIALS AND METHODS: The synthesis of nanocomposite catalyst was conducted hydrothermally using experimental design. Firstly, Clinoptilolite was modified using nitric acid in order to achieve nano-scaled material. Then, the initial gel of the SAPO-34 was prepared using DEA, aluminum isopropoxide, phosphoric acid and TEOS as the organic template, sources of Aluminum, Phosphor, and Silicate, respectively. Finally, the modified zeolite was combined with SAPO-34's gel. RESULTS: 20 different catalysts due to D-Optimal design were synthesized and the nanocomposite with 50 weight percent of SAPO-34, 4 hours Crystallization and early Clinoptilolite precipitation showed the highest relative crystallinity, partly high BET surface area and hierarchical structure. CONCLUSION: Different analyses illustrated the existence of both components. The most important property alteration of nanocomposite was the increment of pore mean diameters and reduction in pore volumes in comparison with free SAPO-34. Due to the low price of Clinoptilolite, the new catalyst renders the process as economical. Using this composite, according to the formation of multi-sized pores located hierarchically on the surface of the catalyst and increased surface area, significant amounts of Ethylene and Propylene, in comparison with free SAPO-34, were produced, as well as the deactivation time was improved.
Assuntos
Alcenos/síntese química , Etilenos/síntese química , Metanol/química , Nanocompostos/química , Zeolitas/química , Catálise , Cristalização , Ácido Nítrico/química , Porosidade , Relação Estrutura-Atividade , Propriedades de SuperfícieRESUMO
BACKGROUND: Ethylene, propylene, and butylene as light olefins are the most important intermediates in the petrochemical industry worldwide. Methanol to olefins (MTO) process is a new technology based on catalytic cracking to produce ethylene and propylene from methanol. AIMS AND OBJECTIVE: This study aims to simulate the process of producing ethylene from methanol by using Aspen HYSYS software from the initial design to the improved design. METHODS: Ethylene is produced in a two-step reaction. In an equilibrium reactor, the methanol is converted to dimethyl ether by an equilibrium reaction. The conversion of the produced dimethyl ether to ethylene is done in a conversion reactor. Changes have been made to improve the conditions and get closer to the actual process design carried out in the industry. The plug flow reactor has been replaced by the equilibrium reactor, and the distillation column was employed to separate the dimethyl ether produced from the reactor. RESULT: The effect of the various parameters on the ethylene production was investigated. Eventually, ethylene is produced with a purity of 95.5 % in the improved design, and thermal integration was performed to minimize energy consumption. CONCLUSION: It was finally found according to the exothermic reaction of the dimethyl ether production, thermal integration in the process reduces the energy consumption in the heater and cooler.
Assuntos
Alcenos/síntese química , Etilenos/síntese química , Metanol/química , Catálise , Simulação por Computador , Desidratação , Temperatura Alta , Cinética , Éteres Metílicos/química , Modelos QuímicosRESUMO
AIM AND OBJECTIVE: The effect of two different modification methods for introducing Ni into the ZSM-5 framework was investigated under high-temperature synthesis conditions. The nickel was successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance. MATERIALS AND METHODS: A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM- 5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BETBJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPD-NH3) were applied to investigate the physicochemical properties. RESULTS: Although all the catalysts showed pure silica MFI-type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced the more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH3 analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm3/gcat.h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores. CONCLUSION: The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.
Assuntos
Alcenos/síntese química , Etilenos/síntese química , Metanol/química , Nanocompostos/química , Níquel/química , Zeolitas/química , Adsorção , Amônia/química , Catálise , Temperatura Alta , Porosidade , Propriedades de SuperfícieRESUMO
OBJECTIVES: A four-lump dynamic kinetic model on the hierarchical SAPO-34 catalyst in the methanol to light olefins (MTO) process has been presented using the power law models. Since decreased catalyst activity in the MTO process is common, for the applicability of the proposed model, the function of catalyst activity was computed as a function of the coke percentage deposited on the catalyst. MATERIALS AND METHODS: The reactant and products were divided into four lumps, including methanol and dimethyl ether (DME), light olefins (ethylene and propylene), light paraffin (methane, ethane, and propane) and heavier hydrocarbons from C4. The one-dimensional ideal plug reactor was used for the simulation of the MTO reactor. The kinetic parameters and the catalyst activity function were predicted using the particle swarm optimization (PSO) algorithm. RESULTS: The comparison of product distribution in the experimental model and the results of the kinetic model indicated the high accuracy of the presented model. The effect of operational parameters such as temperature and weight hourly space velocity (WHSV) on the mole percent of light olefins was investigated using the proposed kinetic model. The optimized value of temperature and WHSV to reach the maximum yield of light olefins was respectively 460 ËC and 4.2 h-1. CONCLUSION: The passive kinetic coefficients were estimated in the reaction rate constant and catalyst activity function with the help of the PSO optimization algorithm. The mole fraction of different products and the reactant arising from modeling at the reactor outlet was compared with experimental results, which indicated the high accuracy of the presented kinetic model. The results also revealed that the selection of high and low temperatures and WHSV decreases the yield of light olefins and the lifetime of the catalyst.
Assuntos
Alcenos/síntese química , Etilenos/síntese química , Metanol/química , Zeolitas/química , Algoritmos , Catálise , Temperatura Alta , Cinética , Modelos QuímicosRESUMO
AIMS AND OBJECTIVE: In this work, the performance of a sodalite membrane reactor (MR) in the conversion of methanol to olefins (MTO process) was evaluated for ethylene and propylene production with in situ steam removal using 3-dimensional CFD (computational fluid dynamic) technique. METHODS: Numerical simulation was performed using the commercial CFD package COMSOL Multiphysics 5.3. The finite element method was used to solve the governing equations in the 3- dimensional CFD model for the present work. In the sodalite MR model, a commercial SAPO-34 catalyst in the reaction zone was considered. The influence of key operation parameters, including pressure and temperature on methanol conversion, water recovery, and yields of ethylene, propylene, and water was studied to evaluate the performance of sodalite MR. RESULTS: The local information of component concentration for methanol, ethylene, propylene, and water was obtained by the proposed CFD model. Literature data were applied to validate model results, and a good agreement was attained between the experimental data and predicted results using CFD model. Permeation flux through the sodalite membrane was increased by an increase of reaction temperature, which led to the enhancement of water stream recovered in the permeate side. CONCLUSION: The CFD modeling results showed that the sodalite MR in the MTO process had higher performance in methanol conversion compared to the fixed-bed reactor (methanol conversion of 97% and 89% at 733 K for sodalite MR and fixed-bed reactor, respectively).
Assuntos
Alcenos/síntese química , Etilenos/síntese química , Metanol/química , Zeolitas/química , Catálise , Simulação por Computador , Temperatura Alta , Membranas Artificiais , Modelos Químicos , Vapor , Propriedades de SuperfícieRESUMO
The deoxygenation reaction of m-benzenediol (resorcinol), an important lignin model compound, was studied in a hot microreactor. We revealed three decomposition channels by detecting elusive and reactive intermediates and product isomers selectively and found that resorcinol, similarly to catechol (o-benzenediol) and hydroquinone (p-benzenediol), (i) gets decarbonylated to yield hydroxycyclopentadiene. Additionally, (ii) decarboxylation (CO2 loss) yields C5H6 species in a retro-Diels-Alder reaction from a lactone species. Only acyclic products are detected at lower reactor temperatures and the most stable C5H6 isomer, cyclopentadiene (c-C5H6), is only observed at higher temperatures. Finally, (iii) two reactive ketene species, ethenone and buta-1,3-dienal, were observed in a third reaction channel. Both decarboxylation and ketene formation channels are unique among benzenediols for the meta-isomer, resorcinol. We have explored the resorcinol potential energy surface to rationalize the observed reactions. These findings may help to understand the source of ketenes in catalytic lignin depolymerization and give new insight into isomer-specific deoxygenation processes.
Assuntos
Dióxido de Carbono/síntese química , Etilenos/síntese química , Cetonas/síntese química , Resorcinóis/química , Reação de Cicloadição , Isomerismo , Oxigênio/química , TemperaturaRESUMO
A rhodium-catalyzed direct insertion of ethylene into a relatively unstrained carbon-carbon bond in 1-indanones is reported, which provides a two-carbon ring expansion strategy for preparing seven-membered cyclic ketones. As many 1-indanones are commercially available and ethylene is inexpensive, this strategy simplifies synthesis of benzocycloheptenones that are valuable synthetic intermediates for bioactive compounds but challenging to prepare otherwise. In addition, the reaction is byproduct-free, redox neutral, and tolerant of a wide range of functional groups, which may have implications on unconventional strategic bond disconnections for preparing complex cyclic molecules.
Assuntos
Benzocicloeptenos/síntese química , Etilenos/química , Indanos/química , Benzocicloeptenos/química , Carbono/química , Catálise , Cicloeptanos/síntese química , Cicloeptanos/química , Etilenos/síntese química , Indanos/síntese química , Ródio/químicaRESUMO
A series of (hetero)arylethenesulfonyl fluorides (1-58) were synthesized and screened for their in vitro antioxidant (DPPH, ABTS and DMPD methods) and anti-inflammatory activities. The results revealed that compounds 4, 15, 16, 24, 25, 26, 38, 39, 40, and 54 exhibited excellent antioxidant activity using all the three performed antioxidant methods, which were superior to the standard antioxidants ascorbic acid and gallic acid. Compounds 6-9, 11, 18, 19, 21, 22, 30, 39, 40, 44, 45, 48-50, 54, 55 and 57 displayed promising anti-inflammatory activity, which were better than the reference drug indomethacin. Preliminary structure-activity relationship (SAR) revealed that compounds containing electron donating (OH and OCH3) groups on the phenyl ring possessed excellent antioxidant properties while compounds containing electron-withdrawing (Cl, NO2, F and Br) groups on the phenyl ring were found to be most potent anti-inflammatory agents. The presence of SO2F group played a crucial role in increases both antioxidant and anti-inflammatory activities.
Assuntos
Anti-Inflamatórios não Esteroides/farmacologia , Etilenos/farmacologia , Sequestradores de Radicais Livres/farmacologia , Ácidos Sulfínicos/farmacologia , Anti-Inflamatórios não Esteroides/síntese química , Anti-Inflamatórios não Esteroides/química , Benzotiazóis/antagonistas & inibidores , Compostos de Bifenilo/antagonistas & inibidores , Relação Dose-Resposta a Droga , Eritrócitos/efeitos dos fármacos , Etilenos/síntese química , Etilenos/química , Sequestradores de Radicais Livres/síntese química , Sequestradores de Radicais Livres/química , Humanos , Estrutura Molecular , Fenilenodiaminas/antagonistas & inibidores , Picratos/antagonistas & inibidores , Relação Estrutura-Atividade , Ácidos Sulfínicos/síntese química , Ácidos Sulfínicos/química , Ácidos Sulfônicos/antagonistas & inibidoresRESUMO
In this work, a novel probe D-HBT-NBD (1O) based on diarylethene to detect biothiols (including Cys, Hcy and GSH) was synthesized and the relative colorimetric and fluorescent properties were tested. The probe exhibited excellent photochromic properties and showed apparent colorimetric and fluorescent signals for Cys, Hcy and GSH. The probe can selectively detect Cys, Hcy and GSH by naked eyes for its open-ring isomer 1O and can discriminate Cys from Hcy/GSH by apparent color change from light orange to dark pink at the closed-ring state under the irradiation of UV light. At the excitation wavelength of 465â¯nm, the probe could be used to discriminate GSH from Cys/Hcy with no fluorescent emission at 570â¯nm. Taking advantage of the photochromic property of the diarylethene moiety and the different fluorescent properties of NBD derivatives of GSH and Cys/Hcy, 1O could be used as a novel probe to discriminate Cys, Hcy and GSH from each other simultaneously. Meanwhile, a logic gate was constructed based on the colorimetric and fluorescent properties of 1O.
Assuntos
Cisteína/análise , Etilenos/química , Corantes Fluorescentes/química , Glutationa/análise , Homocisteína/análise , Técnicas de Química Sintética , Colorimetria/métodos , Etilenos/síntese química , Corantes Fluorescentes/síntese química , Espectrometria de Fluorescência/métodosRESUMO
This study aims to investigate the production of ethylene and diethyl ether from ethanol via catalytic dehydration using Si- and Al-based catalysts with Pd modification. First, six catalysts including H-beta zeolite (HBZ), mixed phases of γ-χ-Al2O3 (M-Al) and γ-Al2O3 (G-Al) with and without Pd modification (0.5 wt%) were prepared. The catalytic dehydration of vaporized ethanol at temperature ranging from 200 to 400°C was performed over the catalysts. For ethylene production, the most promising catalyst is HBZ (giving ethylene yield of ca. 99% at 400°C), whereas Pd modification has no significant effect on ethylene production. Considering the production of diethyl ether, it is produced at lower temperature (ca. 250°C) than that of ethylene. The most active catalyst to produce diethyl ether is HBZ with Pd modification (giving diethyl ether yield of ca. 48% at 250°C). Thus, increased diethyl ether yield can be achieved with Pd modification at low temperature for the HBZ catalyst. Other catalysts such as M-Al and G-Al can also produce significant amounts of ethylene. To elucidate the effect of Pd modification on these catalysts, different characterization techniques such as nitrogen physisorption (BET and BJH methods), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and ammonia temperature-programmed desorption were performed and further discussed in more detail.
Assuntos
Compostos de Alumínio/química , Etanol/química , Éter/síntese química , Etilenos/síntese química , Paládio/química , Compostos de Silício/química , Catálise , Química Orgânica/métodos , Dessecação , Temperatura , VolatilizaçãoRESUMO
Four new α-glucosidase inhibitors have been synthesised through 5-8 synthetic steps from a common synthetic intermediate obtained through a recently developed carbocyclisation. The compounds were designed as hybrids of the known glucosidase inhibitors valienamine, voglibose and miglitol. All four compounds showed activity against rat intestinal sucrase with the most potent inhibitor acting at low micromolar concentration. The newly synthesised compounds were not as potent as miglitol against sucrase but showed greater selectivity towards the tested glycosidases. The most potent inhibitors were docked into a homology model built for this study of rat intestinal sucrase explaining the difference in potency between two diastereoisomers with varying orientation of a secondary amine.
Assuntos
Etilenos/química , Etilenos/farmacologia , Inibidores de Glicosídeo Hidrolases/química , Inibidores de Glicosídeo Hidrolases/farmacologia , alfa-Glucosidases/metabolismo , Técnicas de Química Sintética , Ciclização , Etilenos/síntese química , Etilenos/metabolismo , Inibidores de Glicosídeo Hidrolases/síntese química , Inibidores de Glicosídeo Hidrolases/metabolismo , Simulação de Acoplamento Molecular , Conformação Proteica , alfa-Glucosidases/químicaRESUMO
The beneficial use of computer simulations to track the microstructural evolution of individual species is highlighted in view of macromolecular engineering and design, considering two case studies on catalytic polymerization, and both "low" (<100) and "high" (>100) chain lengths, that is, i) atom transfer radical copolymerization of n-butyl acrylate and styrene aiming at the synthesis of functional macrospecies of "identical' chain length; and ii) chain shuttling polymerization of ethylene and 1-octene toward the production of segmented block copolymers with "soft" and "hard" segments. Model parameters are validated and/or tuned based on literature data. The modeling strategy supports the future identification of chemical structure-polymer property relationships and is based on the combination of principles from polymer reaction engineering, chemistry, and physics.
Assuntos
Catálise , Substâncias Macromoleculares/química , Polímeros/química , Acrilatos/síntese química , Acrilatos/química , Alcenos/síntese química , Alcenos/química , Simulação por Computador , Etilenos/síntese química , Etilenos/química , Cinética , Substâncias Macromoleculares/síntese química , Polimerização , Polímeros/síntese química , Estireno/síntese química , Estireno/químicaRESUMO
Diarylethene derivatives, the biological activity of which can be reversibly changed by irradiation with light of different wavelengths, have shown promise as scientific tools and as candidates for photocontrollable drugs. However, examples demonstrating efficient photocontrol of their biological activity are still relatively rare. This concept article discusses the possible reasons for this situation and presents a critical analysis of existing data and hypotheses in this field, in order to extract the design principles enabling the construction of efficient photocontrollable diarylethene-based molecules. Papers addressing biologically relevant interactions between diarylethenes and biomolecules are analyzed; however, in most published cases, the efficiency of photocontrol in living systems remains to be demonstrated. We hope that this article will encourage further discussion of design principles, primarily among pharmacologists, synthetic and medicinal chemists.
Assuntos
Etilenos/efeitos da radiação , Animais , Compostos Azo/química , Compostos Azo/efeitos da radiação , Etilenos/síntese química , Inibidores de Histona Desacetilases/química , Inibidores de Histona Desacetilases/efeitos da radiação , Luz , Bicamadas Lipídicas/química , Bicamadas Lipídicas/efeitos da radiação , Modelos Moleculares , Estrutura Molecular , Processos Fotoquímicos , Inibidores de Proteínas Quinases/química , Inibidores de Proteínas Quinases/efeitos da radiação , EstereoisomerismoRESUMO
Substantial natural gas liquids recovery from tight shale formations has produced a significant boon for the US chemical industry. As fracking technology improves, shale liquids may represent the same for other geographies. As with any major industry disruption, the advent of shale resources permits both the chemical industry and the community an excellent opportunity to have open, foundational discussions on how both public and private institutions should research, develop, and utilize these resources most sustainably. This review summarizes current chemical industry processes that use ethane and propane from shale gas liquids to produce the two primary chemical olefins of the industry: ethylene and propylene. It also discusses simplified techno-economics related to olefins production from an industry perspective, attempting to provide a mutually beneficial context in which to discuss the next generation of sustainable olefin process development.
Assuntos
Alcenos/química , Etilenos/química , Gás Natural , Alcenos/síntese química , Alcenos/economia , Indústria Química , Metabolismo Energético , Etilenos/síntese química , Etilenos/economia , Gás Natural/economia , Oxidantes/química , TermodinâmicaRESUMO
The present work deals with the catalytic performance of SBA-15 supported catalysts in the gas phase catalytic dehydration of ethanol in the temperature range of 200 to 400°C. The SBA-15 support was incorporated on a zirconium (Zr) and bimetal of zirconium and lanthanum (Zr-La) prepared by sol-gel (SG) and hydrothermal (HT) methods. The catalysts were characterized by means of N2 physisorption, SEM/EDX, and NH3-TPD. The experimental results demonstrated that the Zr-La/SBA-15-HT exhibited the highest catalytic activity. Ethanol conversion and ethylene selectivity were found to increase with increased reaction temperature. The best catalytic results were achieved for Zr-La/SBA-15-HT indicating values of ethanol conversion and ethylene yield of ca. 84% and 80%, respectively at 400°C. The most important parameter influencing their catalytic properties appears to be the interaction between metal and support depending on different methods. The metal dispersion inside the siliceous matrix of SBA-15 has a direct influence on their surface acidity. Meanwhile, the performance of these SBA-15 supported catalysts in ethanol dehydration is also related with the alteration of surface acidity caused by the introduction of Zr and Zr-La.
Assuntos
Química Orgânica/métodos , Etanol/química , Etilenos/síntese química , Dióxido de Silício/química , Catálise , Dessecação , Lantânio/química , Temperatura , Zircônio/químicaRESUMO
The study is aimed to investigate the combination of nanocrystalline γ- and χ- alumina that displays the attractive chemical and physical properties for the catalytic dehydration of ethanol. The correlation between the acid density and ethanol conversion was observed. The high acid density apparently results in high catalytic activity, especially for the equally mixed γ- and χ- phase alumina (G50C50). In order to obtain a better understanding on how different catalysts would affect the ethylene yield, one of the most powerful techniques such as X-ray photoelectron spectroscopy (XPS) was performed. Hence, the different O 1s surface atoms can be identified and divided into three types including lattice oxygen (O, 530.7 eV), surface hydroxyl (OH, 532.1 eV) and lattice water (H2O, 532.9 eV). It was remarkably found that the large amount of O 1s surface atoms in lattice water can result in increased ethylene yield. In summary, the appearance of metastable χ-alumina structure exhibited better catalytic activity and ethylene yield than γ- alumina. Thus, the introduction of metastable χ- alumina structure into γ- alumina enhanced catalytic activity and ethylene yield. As the result, it was found that the G50C50 catalyst exhibits the ethylene yield (80%) at the lowest reaction temperature ca. 250°C among other catalysts.
Assuntos
Óxido de Alumínio/química , Etanol/química , Etilenos/síntese química , Nanopartículas/química , Catálise , Desidratação , Hidróxidos , Oxigênio , Espectroscopia Fotoeletrônica , Temperatura , ÁguaRESUMO
Carvone is a sustainable and readily available starting material for organic synthesis. Herein, we present the syntheses of various natural product scaffolds that rely on a novel benzannulation involving the α-methyl group (C-10) of carvone to afford a versatile tetralin. The utility of our synthetic approach is highlighted by its application to a short synthesis of the ent-3,4-seco-atisane diterpenoid (-)-crotogoudin. The 13-step enantiospecific synthesis features a regioselective double oxidative dearomatization, a Diels-Alder cycloaddition with ethylene gas (to construct the bicyclo[2.2.2]octane framework), and a final acid-mediated lactonization. The versatility of this benzannulation strategy is demonstrated by its utility in the preparation of the carbon skeleton of ent-3,4-seco-abietane diterpenoids using an intramolecular oxidative dearomatization.