Sequential Dehydration Research Articles

Al-MFI Nanosheets as Highly Active and Stable Catalysts for the Conversion of Propanal to Hydrocarbons

The conversion of propanal to hydrocarbons is investigated over mesoporous aluminosilicate MFI nanosheets (Al-MFI-ns) of single-unit-cell thickness and conventional aluminum MFI zeolite (Al-MFI) at 673 K and atmospheric pressure. Al-MFI-ns exhibits a fivefold in- crease in stability attributed to the shorter diffusion path lengths and open architecture of the nanosheets, which minimizes pore blocking from fouling. The overall ratio of olefin to aromatic products is similar for Al-MFI-ns and Al-MFI at all conversion levels. However, the product distribution within each group shows that the Al-MFI-ns generate a fivefold increase in selectivity to C6-8 olefins and a twofold increase in selectivity to C9-10 aromatics compared to Al-MFI. The very high selectivity to C9- aromatic trimethylbenzene supports an aromatization mechanism involving sequential aldol condensation and dehydration sequences. The very short diffusion paths in the single-unit-cell thick nanosheets allows for the C9 aromatics to diffuse out of the pores before they can be converted to lighter aromatics or olefins. Al-MFI-ns shows no indication of irreversible deactivation, fully recovering its original activity after regeneration by calcination, and retaining similar deactivation rates and product selectivities as the fresh catalyst. Al-FMI-ns improves the production of aromatics from light oxygenates at mild conditions, a key feature for bio-oil upgrading.

Formation and distribution of phases during the dehydration of large hydrargillite floccules

The phase composition and phase distribution of large floccules of hydrargillite dehydration products obtained by heat treatment at temperatures from 250 to 500°C have been studied by thermal analysis, X-ray diffraction, and IR spectroscopy. Heat treatment in the range 250–300°C leads to the formation of macrocrystalline and microcrystalline boehmite particles. The macrocrystalline boehmite is formed from large hydrargillite crystals. The microcrystalline boehmite results from the “fragmentation” of the hydrargillite crystals. The IR spectra of the samples point to an increase in the number of hydroxyls with ν(OH) = 3471 cm−1 on the lateral faces of the hydrargillite crystals. The crystallite size of the hydrargillite crystals decreases by a factor of 1.8–2.3. In the floccules, a layer of the macrocrystalline boehmite surrounds a microcrystalline boehmite core. The outer surface is covered predominantly with χ-Al2O3. Heat treatment at t ≥ 350°C leads to γ-Al2O3 formation through sequential dehydration of microcrystalline and then macrocrystalline boehmite particles.

ChemInform Abstract: Iodine‐Promoted Efficient Synthesis of Diheteroaryl Thioethers via the Integration of Iodination/Condensation/Cyclization/Dehydration Sequences.

Abstract A novel method for the construction of diheteroaryl thioethers from aromatic methyl ketones and thiourea is described. Iodine is the unique catalyst in this protocol. The transformation is free of foul-smell thiols and transition metal. In addition, this method could synthesize two thiazole rings and a sulfur bridge in one pot.

ChemInform Abstract: Four‐Component Domino Reaction for the Synthesis of 1‐(1H‐Indol‐2‐yl)‐1H‐pyrazolo[1,2‐b]phthalazine‐5,10‐diones.

Abstract Facile, efficient, four-component domino reaction of dialkylphthalates, hydrazine hydrate, indole-3-carboxaldehydes, and malononitrile/ethyl cyanoacetate leads to the formation of 1-(1H-indol-2-yl)-1H-pyrazolo [1,2-b] phthalazine-5,10-diones in the presence of InCl3 as catalyst in refluxing ethanol for 1 h in good yields. This four-component domino reaction transformation presumably proceeds via sequential addition, dehydration, condensation, and cyclization steps.

A facile synthesis of 2-aryl-4-(indol-3-yl)-4H-chromenes using amberlyst-15 as an efficient recyclable heterogeneous catalyst

Starting from 2-hydroxychalcones and indoles, a facile synthesis of 2-aryl-4-(indol-3-yl)-4H-chromenes has been achieved by use of amberlyst-15, a sulfonated polystyrene resin, as a recyclable heterogeneous catalyst. The methodology involves a domino sequence of Michael addition, cyclization, and dehydration.

Silica hydrate preserved with δ18O-rich quartz in high-temperature hydrothermal quartz in the high sulfidation copper-gold deposit at El Indio, Chile

Quartz microcrystals from the El Indio Au-Ag-Cu deposit (Chile) preserve a rare glimpse into the high-temperature evolution of silica. Here, we show for the first time that aggregates of euhedral quartz microcrystals preserve cryptocrystalline cores that contain silica hydrates “opal” and moganite. We propose that these phases are metastable remnants of progressive dehydration from a precursor silica hydrate phase. Evidence for sequential dehydration to from silica hydrate to quartz (silica hydrate⌫opal⌫moganite⌫quartz) is provided by SHRIMP 18O microanalytical data that show oscillatory isotopic zoning from 3.6‰ to 16.2‰ δ18O (±0.5‰) coupled with K and Al variations. We estimate that the precursor silica hydrate deposited between ~480–680°C and contained 32–63wt% H2O. Silica hydrate is metastable with respect to quartz and forms during rapid deposition of silica at high silica supersaturation, a consequence of rapid expansion of magmatic fluid into the fracture array that hosts the El Indio copper-gold deposit.Modern understanding of ore-forming fluids in hydrothermal ore deposits is largely underpinned by the assumption that quartz and its included fluids faithfully record depositional conditions. The discovery of silica hydrate affects the paragenetic and geochemical interpretation of quartz and included fluids. Quartz matured from silica hydrate would record “pseudo-primary” fluid inclusions such that homogenization temperatures record retrograde rather than depositional conditions while δ18O data may bias fluid provenance interpretation within sub-volcanic systems.

Four-Component Domino Reaction for the Synthesis of 1-(1H-Indol-2-yl)-1H-pyrazolo[1,2-b]phthalazine-5,10-diones

Facile, efficient, four-component domino reaction of dialkylphthalates, hydrazine hydrate, indole-3-carboxaldehydes, and malononitrile/ethyl cyanoacetate leads to the formation of 1-(1H-indol-2-yl)-1H-pyrazolo [1,2-b] phthalazine-5,10-diones in the presence of InCl3 as catalyst in refluxing ethanol for 1 h in good yields. This four-component domino reaction transformation presumably proceeds via sequential addition, dehydration, condensation, and cyclization steps.

Iodine-promoted efficient synthesis of diheteroaryl thioethers via the integration of iodination/condensation/cyclization/dehydration sequences

A novel method for the construction of diheteroaryl thioethers from aromatic methyl ketones and thiourea is described. Iodine is the unique catalyst in this protocol. The transformation is free of foul-smell thiols and transition metal. In addition, this method could synthesize two thiazole rings and a sulfur bridge in one pot.

Molecular spectroscopic identification of the water compartments in bone

Matrix bound water is a correlate of bone's fracture resistance and assessment of bound water is emerging as a novel measure of bone's mechanical integrity. Raman spectroscopy is one of the few nondestructive modalities to assess the hydration status in bone; however, it has not been used to study the OH-band in bone. A sequential dehydration protocol was developed to replace unbound (heat drying) and bound (ethanol or deuterium) water in bone. Raman spectra were collected serially to track the OH-band during dehydration. Spectra of synthetic hydroxyapatite, demineralized bone and bulk water were collected to identify mineral and collagen contributions to the OH-band. Band assignments were supported by computational simulations of the molecular vibrations of Gly-Pro-Hyp amino acid sequence. Experimentally and theoretically obtained spectra were interpreted for band-assignments. Water loss was measured gravimetrically and correlated to Raman intensities. Four peaks were identified to be sensitive to dehydration: 3220cm−1 (water), 3325cm−1 (NH and water), 3453cm−1 (hydroxyproline and water), and 3584cm−1 (mineral and water). These peaks were differentially sensitive to deuterium treatment such that some water peaks were replaced with deuterium oxide faster than the rest. Specifically, the peaks at 3325 and 3584cm−1 were more tightly bound to the matrix than the remaining bands. Comparison of dehydration in mineralized and demineralized bone revealed a volume of water that may be locked in the matrix by mineral crystals. The OH-range of bone was dominated by collagen and the water since the spectral profile of dehydrated demineralized bone was similar to that of the mineralized bone. Furthermore, water associates to bone mainly by collagen as findings of experimentally and theoretically spectra. The current work is among the first thorough analysis of the Raman OH stretch band in bone and such spectral information may be used to understand the involvement of water in the fragility of aging and in diseased bone.

A tailored catalyst for the sustainable conversion of glycerol to acrolein: mechanistic aspect of sequential dehydration.

Developing a catalyst to resolve deactivation caused from coke is a primary challenge in the dehydration of glycerol to acrolein. An open-macropore-structured and Brønsted-acidic catalyst (Marigold-like silica functionalized with sulfonic acid groups, MS-FS) was synthesized for the stable and selective production of acrolein from glycerol. A high acrolein yield of 73% was achieved and maintained for 50 h in the presence of the MS-FS catalyst. The hierarchical structure of the catalyst with macropores was found to have an important effect on the stability of the catalyst because coke polymerization and pore blocking caused by coke deposition were inhibited. In addition, the behavior of 3-hydroxypropionaldehyde (3-HPA) during the sequential dehydration was studied using density functional theory (DFT) calculations because 3-HPA conversion is one of the main causes for coke formation. We found that the easily reproducible Brønsted acid sites in MS-FS permit the selective and stable production of acrolein. This is because the reactive intermediate (3-HPA) is readily adsorbed on the regenerated acid sites, which is essential for the selective production of acrolein during the sequential dehydration. The regeneration ability of the acid sites is related not only to the selective production of acrolein but also to the retardation of catalyst deactivation by suppressing the formation of coke precursors originating from 3-HPA degradation.

The reaction mechanism of UDP-GlcNAc 5,6-dehydratase: a quantum mechanical/molecular mechanical (QM/MM) study

UDP-GlcNAc 5,6-dehydratase (TunA), a particular member of the short-chain dehydrogenase/reductase family, catalyzes the bioconversion of UDP-GlcNAc to UDP-6-deoxy-GlcNAc-5,6-ene. To elucidate the detailed mechanism of TunA, combined quantum mechanical/molecular mechanical calculations have been performed. The calculation results reveal that the TunA-catalyzed process follows a three-step sequential mechanism, including oxidation, dehydration and reduction. The oxidation step is calculated to be rate limiting and undergoes a concerted but asynchronous mechanism with an energy barrier of 21.6 kcal/mol. The dehydration step proceeds via the E1cB mechanism involving proton transfer and departure of hydroxyl group. Our calculation results show that the key residue Glu121 is ideally situated in the active site and serves as the general base and then as acid to take part in the elimination of water. The residue Cys120 is confirmed to play an important role in maintaining the active pocket arrangement. As the reverse process of the oxidation reaction, the reduction step follows the same concerted asynchronous mechanism, but the hydride transfer is prior to proton transfer.

Highly Efficient Production of Acrylic Acid by Sequential Dehydration and Oxidation of Glycerol

The selective dehydration–oxidation of glycerol to acrylic acid is a very attractive approach for glycerol utilization. In this work, we demonstrated an efficient two-bed system for this process. The dehydration catalyst was Cs2.5H0.5PW12O40 supported on Nb2O5 (CsPW-Nb), and the oxidation catalyst was vanadium–molybdenum mixed oxides supported on silicon carbide (VMo–SiC). The experimental results showed that the optimum reaction temperature and oxygen ratio for these two catalysts were very similar. This made the two-bed system simple and efficient. Compared with the single-bed system, the two-bed system with the dehydration catalyst and oxidation catalyst loaded separately was more favorable to avoid the overoxidation reaction of glycerol. A high yield of acrylic acid was achieved at optimized conditions in the two-bed system. The Bronsted acid sites on the dehydration catalysts were the active sites for acrolein formation. The byproducts produced on Lewis acid sites in the dehydration step and the wate...

Influence of charge density on rheological properties and dehydration dynamics of weakly charged poly(N-isopropylacrylamide) during phase transition

It is well-known that introduction of charged groups to poly(N-isopropylacrylamide) (PNIPAM) raises its phase transition temperature. However, the influence of charged groups on structural evolution and dehydration dynamics of weakly charged PNIPAM during phase transition still lacks systematic investigation. In the current study, armed with rheometer and two-dimensional Fourier transform infrared spectrometer (2D-FTIR), we investigated on mesoscopic and microscopic scales the phase transition of sodium poly(N-isopropylacrylamide-co-2-acrylamido-2-methylpropanesulfonate), abbreviated as poly(NIPAM-co-NaAMPS), with charge density of 1–10%. At ambient temperature, scaling exponent of poly(NIPAM-co-NaAMPS) varies from that of neutral polymer to polyelectrolytes as charge density increases. Above phase transition temperature, mesoscopic structure of poly(NIPAM-co-NaAMPS) varies from network of physical gel to viscoelastic liquid containing branched aggregates with increase of charge density, indicating increasing hindrance to intra/inter-chain association due to electrostatic repulsion. On a molecular level, poly(NIPAM-co-NaAMPS) exhibits distinctive microdynamic sequence of dehydration during phase transition, in contrast to neutral PNIPAM. In particular, sulfonate groups decouple the cooperative dehydration of alkyl and carbonyl groups, resulting in their distinctive phase transition temperature as well as temperature range. In analogy to hydration of proteins, it is proposed that the microdynamic sequence, implying the hydration stability of each group, is closely related to the density of hydration layer as well as influence of electrostatic field generated by charged groups. For poly(NIPAM-co-AMPS) with charge density of 3%, there still remains 72.3% of hydrogen bonds between carbonyl group and water at 60 °C, meanwhile a highly hydrated network forms with network strands 1–2 times as long as the copolymer chain length.

Structural characterization and comparison of the large subunits of IPM isomerase and homoaconitase fromMethanococcus jannaschii

The aconitase family of proteins includes three classes of hydro-lyase enzymes: aconitases, homoaconitases and isopropylmalate (IPM) isomerases. They have a common Fe-S cluster-binding site and catalyze the isomerization of specific substrates by sequential dehydration and hydration. The archaeon Methanococcus jannaschii contains two aconitase family proteins, IPM isomerase and homoaconitase, which have 50% sequence identity. These two enzymes are heterodimeric proteins composed of large and small subunits encoded by separate genes. Although structures have been reported for the small subunits of the two enzymes, the first structures of oxidized and reduced forms of the large subunit of IPM isomerase (ox-MJ0499 and red-MJ0499, respectively) from M.jannaschii are reported here at 1.8 and 2.7 Å resolution, respectively, together with the structure of the large subunit of homoaconitase (MJ1003) at 2.5 Å resolution. The structures of both proteins have unbound Fe-S clusters and contain a fourth cysteine in the active site. The active site of MJ1003 is homologous to that of aconitase, whereas MJ0499 has significant structural distortion at the active site compared with aconitase. In addition, significant large conformational changes were observed in the active site of red-MJ0499 when compared with ox-MJ0499. The active sites of the two proteins adopt two different states before changing to the Fe-S cluster-bound `activated' state observed in aconitase. MJ1003 has an `open' active site, which forms an active pocket for the cluster, while ox-MJ0499 has a `closed' active site, with four cysteines in disulfide bonds. These data will be helpful in understanding the biochemical mechanism of clustering of the Fe-S protein family.

Cooperativity of Brønsted and Lewis Acid Sites on Zeolite for Glycerol Dehydration

Selective dehydration of glycerol, a byproduct from the biodiesel industry, on solid acids is an important reaction in the production of the value-added chemical acrolein for economic-sustainable biorefinery. Most efforts have been made on the development of strong Brønsted acid sites (BAS) to improve the production of acrolein, because the Lewis acid sites (LAS) generally promote the generation of the byproduct acetol. However, exclusively tuning the properties of BAS or LAS did not well-promote the acrolein production from glycerol as indicated in this work. We provide a new route for efficient and selective glycerol transformation to acrolein via the cooperative dehydration between the BAS and LAS. The role of LAS (extra-framework aluminum species on zeolites) was altered from competition with BAS to generate the byproduct acetol to cooperation with the neighboring BAS. It is very beneficial for the sequential two-step dehydration of the internal and terminal hydroxyl groups of glycerol to value-added acrolein. This cooperativity of BAS and LAS significantly improved the yield of acrolein from the selective glycerol dehydration.

Copper-catalyzed one-pot synthesis of glycosylated iminocoumarins and 3-triazolyl-2-iminocoumarins

A general strategy was developed for the synthesis of glycosyl iminocoumarins (5a–x) in a one-pot, copper-catalyzed multicomponent reaction involving a domino reaction of sulfonyl azides, sugar alkynes, and salicylaldehydes via ketenimine intermediate formation. Similarly, glycosyl 3-triazolyl-2-iminocoumarin derivatives (6a–o) have also been synthesized in a one-pot, three component condensation via tandem “CuAAC-aldol-cyclization-dehydration” sequence. In this event, a copper-catalyzed cycloaddition reaction between 2-azidoacetonitrile and sugar alkynes furnished a triazole derivative in situ and activated the neighboring methylene group, inducing an aldol–cyclization–dehydration sequence in the presence of a salicylaldehyde. The yields were very good in all reactions.

The Synthesis of Some Novel 1,2‐Dihydroisoquinoline Derivatives

Treatment of methyl 2‐aryl‐1,2,3,4‐tetrahydroisoquinoline‐3‐carboxylates 5 with N‐bromosuccinimide followed by heating in the presence of an acid catalyst resulted in the formation of the corresponding methyl 2‐aryl‐1,2‐dihydroisoquinoline‐3‐carboxylates 10 via an oxidation–dehydration sequence.

Clean Synthesis of Amides over Bifunctional Catalysts of Rhodium‐Loaded Titanosilicates

AbstractRhodium‐loaded titanosilicates were prepared and employed as efficient bifunctional catalysts in the one‐pot synthesis of benzamide from benzaldehyde, hydrogen peroxide, and ammonia, which took place through a tandem reaction including ammoximation of benzaldehyde to benzaldehydeoxime and a sequential dehydration–rehydration reaction to benzamide. Various parameters that influenced the activity and product selectivity were investigated, such as crystalline topologies of the titanosilicate supports, types of transition metals, rhodium content, reaction temperature, time, solvent, and NH3/benzaldehyde molar ratio. Ti‐MWW was proved to be a suitable support for loading the Rh(OH)x species. Rh(OH)x/Ti‐MWWgave 84.9 % of benzaldehyde conversion and 86.9 % of benzamide selectivity, and it was also catalytically active for the transformation of a variety of aldehydes to the corresponding amides. The reusability of the bifunctional catalyst was also investigated. The in situ FTIR technique confirmed that the one‐pot reaction included Ti‐catalyzed ammoximation of benzaldehyde to the benzaldehyde oxime intermediate and sequential rhodium hydroxide related dehydration–rehydration reaction of oximes to amides.

Synthesis of 4-Vinylindoles Using Ruthenium-Catalyzed Ring-Closing Enyne Metathesis

The selective synthesis of substituted 4-vinylindoles by the ring-closing enyne metathesis (RCEM)/dehydration sequence is reported. In contrast with many known methods in which a pyrrole ring is constructed onto a functionalized benzene precursor, this method enables the construction of a benzene ring onto a pyrrole precursor. The RCEM/tautomerization sequence for the synthesis of 7-hydroxy-4-vinylindole is also presented as an application of this method.

Graphene oxide as a carbocatalyst: the first example of a one-pot sequential dehydration–hydrothiolation of secondary aryl alcohols

An efficient and mild one-pot graphene oxide (GO)-catalyzed sequential dehydration–hydrothiolation reaction has been developed for the first time from a mixture of secondary aryl alcohols and thiols. The resulting unsymmetrical thioethers were prepared under metal-free conditions. The catalyst can be reused for five runs with appreciable conversions.