Beckmann Rearrangement Research Articles

Controllable Synthesis and Structure-Performance Relationship of Silicalite-1 Nanosheets in Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime

Bulky silicalite-1 shows high catalytic activity for vapor phase Beckmann rearrangement of cyclohexanone oxime. However, it often deactivates rapidly and the structure-performance relationship is unclear. Here, a series of well-crystallized silicalite-1 catalysts from three-dimensional micron particles (n < 10) to two-dimensional nanosheets (10 ≤ n ≤ 18) were controllably synthesized using diquaternary ammoniums [CnH2n+1-N+(CH3)2-C6H12-N+(CH3)2-C6H13](Br−)2 (n = 6–18) as the structure directing agent. The influence of morphology of catalysts on active sites distribution and the pore confinement effect on caprolactam selectivity and the catalytic stability were studied by XRD, SEM, TEM, In situ vacuum IR, 29Si MAS NMR and N2 adsorption/desorption isotherms. The silicalite-1 nanosheets with relatively high crystallinity exhibited superior catalytic activity to almost 100% and remarkably high caprolactam selectivity (92%). The catalytic lifetime of silicalite-1 nanosheets could be increased by 28 times in comparison to bulky silicalite-1 zeolite. The external surface area and mesopore volume of the synthesized catalyst dramatically increase with increasing the tail length of surfactant from C6 to C18, leading to high active sites and coke tolerance capacity. It was found the lifetime of the catalysts is almost linearly related to the product of area of silanol nest and volume of mesopore (Asilanol·nest*Vmeso) with correlation coefficient of 0.97, which strongly supports the excellent performance of nanosheets results from the synergetic effect of its high active sites and high coke tolerance capacity. This provides a theoretic guide for designing new catalysts with high catalytic activity. Silicalite-1 nanosheets were controllable synthesized through adjusting alkyl tail length of diquaternary ammoniums, resulting in large mesoporous volume and external surface area, which effectively improve high coke tolerance capacity and active sites of catalysts and exhibit much longer catalytic lifetime and high selectivity.

Probing the Design Rationale of a High-Performing Faujasitic Zeotype Engineered to have Hierarchical Porosity and Moderated Acidity.

Porosity and acidity are influential properties in the rational design of solid‐acid catalysts. Probing the physicochemical characteristics of an acidic zeotype framework at the molecular level can provide valuable insights in understanding intrinsic reaction pathways, for affording structure–activity relationships. Herein, we employ a variety of probe‐based techniques (including positron annihilation lifetime spectroscopy (PALS), FTIR and solid‐state NMR spectroscopy) to demonstrate how a hierarchical design strategy for a faujasitic (FAU) zeotype (synthesized for the first time, via a soft‐templating approach, with high phase‐purity) can be used to simultaneously modify the porosity and modulate the acidity for an industrially significant catalytic process (Beckmann rearrangement). Detailed characterization of hierarchically porous (HP) SAPO‐37 reveals enhanced mass‐transport characteristics and moderated acidity, which leads to superior catalytic performance and increased resistance to deactivation by coking, compared to its microporous counterpart, further vindicating the interplay between porosity and moderated acidity.

Probing the Design Rationale of a High‐Performing Faujasitic Zeotype Engineered to have Hierarchical Porosity and Moderated Acidity

AbstractPorosity and acidity are influential properties in the rational design of solid‐acid catalysts. Probing the physicochemical characteristics of an acidic zeotype framework at the molecular level can provide valuable insights in understanding intrinsic reaction pathways, for affording structure–activity relationships. Herein, we employ a variety of probe‐based techniques (including positron annihilation lifetime spectroscopy (PALS), FTIR and solid‐state NMR spectroscopy) to demonstrate how a hierarchical design strategy for a faujasitic (FAU) zeotype (synthesized for the first time, via a soft‐templating approach, with high phase‐purity) can be used to simultaneously modify the porosity and modulate the acidity for an industrially significant catalytic process (Beckmann rearrangement). Detailed characterization of hierarchically porous (HP) SAPO‐37 reveals enhanced mass‐transport characteristics and moderated acidity, which leads to superior catalytic performance and increased resistance to deactivation by coking, compared to its microporous counterpart, further vindicating the interplay between porosity and moderated acidity.

An Electrochemical Beckmann Rearrangement: Traditional Reaction via Modern Radical Mechanism.

Electrosynthesis as a potential means of introducing heteroatoms into the carbon framework is rarely studied. Herein, the electrochemical Beckmann rearrangement, i. e. the direct electrolysis of ketoximes to amides, is presented for the first time. Using a constant current as the driving force, the reaction can be easily carried out under neutral conditions at room temperature. Based on a series of mechanistic studies, a novel radical Beckmann rearrangement mechanism is proposed. This electrochemical Beckmann rearrangement does not follow the trans-migration rule of the classical Beckmann rearrangement.

Diversification of Nucleophile-Intercepted Beckmann Fragmentation Products and Related Density Functional Theory Studies.

The nucleophile-intercepted Beckmann fragmentation (NuBFr) has the potential to be broadly applicable to the synthesis of indoline alkaloid-based natural products. However, the reaction has not been widely adopted, in part, because of limitations associated with the availability of appropriate promoter-Nu reagents. We have devised a stereospecific Ag(I)-promoted reaction for functionalizing NuBFr products to give novel compositions of matter that may be useful in synthesis and medicinal chemistry. With unhindered amine nucleophiles, structurally unique [2.2.2]-bicycloamidines are generated. We also disclose for the first time detailed density functional theory studies, which shed light on the mechanism of the NuBFr and Ag-promoted substitution reaction that supports an unusual aziridinium ion as a key intermediate.

Visible-Light-Induced Beckmann Rearrangement by Organic Photoredox Catalysis.

A facile and general strategy for efficient direct conversion of oximes to amides using an inexpensive organic photocatalyst and visible light is described. This radical Beckmann rearrangement can be performed under mild conditions. Various alkyl aryl ketoximes and diaryl ketoximes can be effectively converted into the corresponding amides in excellent yields.

Synthesis of mesoporous silicalite-1 zeolite for the vapor phase Beckmann rearrangement of cyclohexanone oxime

Abstract Mesoporous silicalite-1 zeolites with large mesopore volume have been synthesized with the assisting of CO2 solvent. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images show that mesoporous silicalite-1 zeolites have good crystallinity. N2 sorption isotherm and transmission electron microscopy (TEM) images indicate the mesoporous silicalite-1 zeolites have mesopores. Catalytic tests for the vapor phase Beckmann rearrangement of cyclohexanone oxime show that mesoporous silicalite-1 zeolites have high conversion of cyclohexanone oxime and selectivity of e-caprolactam compared with conventional silicalite-1 zeolites.

Sulfuryl Fluoride Mediated Synthesis of Amides and Amidines from Ketoximes via Beckmann Rearrangement.

A metal-free and redox-neutral method for Beckmann rearrangement employing inexpensive and readily available SO2 F2 gas is described. The reported transformation proceeds at ambient temperature and is compatible with a wide range of sterically and electronically diverse aromatic, heteroaromatic, aliphatic and lignin-like oximes providing amides in good to excellent yields. The reaction proceeds through the formation of an imidoyl fluoride intermediate that can also be used for the synthesis of amidines.

Hierarchical zeolites comprising orthogonally stacked bundles of zeolite nanosheets for catalytic and adsorption applications

The synthesis of hierarchical MFI zeolites comprising orthogonally stacked bundles of zeolite nanosheets using a new type of triblock structure-directing agents (SDAs) was reported. The textural properties, including the degree of nanosheet branching and the spacing between adjacent nanosheets, could be controlled by changing the length of the linkers in the triblock SDAs. The hierarchical pure-silica silicalite-1 materials exhibited high and stable catalytic activity for the vapor-phase Beckmann rearrangement of cyclohexanone oxime with high selectivity of ε-caprolactam. On the other hand, the hierarchical ZSM-5 materials showed high adsorption capacity of Pb2+ ion following a Langmuir-type adsorption behavior. After being deposited with Pd nanoparticles, the hierarchical Pd/ZSM-5 nanocomposites exhibited high activity in the aqueous-phase hydrogenation of phenol to cyclohexanone at room temperature. The results show promise of the disclosed hierarchical zeolites for catalytic and adsorption applications.

Zinc(II)-Catalyzed Synthesis of Secondary Amides from Ketones via Beckmann Rearrangement Using Hydroxylamine-O-sulfonic Acid in Aqueous Media

A zinc(II)-catalyzed single-step protocol for the Beckmann rearrangement using hydroxylamine-O-sulfonic acid (HOSA) as the nitrogen source in water was developed. This direct method efficiently produces secondary amides under open atmosphere in a pure form after basic aqueous workup. It is environmentally benign and operationally simple.

Design, synthesis, brine shrimp lethality and cytotoxicity of some novel 17a-aza-D-homo-androster-17-one derivatives

In this work, twenty-eight novel 17a-aza-D-homo-androster-17-one derivatives, which divided into two categories, were synthesized with commercial available starting material (dehydroepiandrosterone) via oximation reaction, Beckmann rearrangement, hydroxyl protection, N-alkylation and deprotection. All compounds were characterized by 1H NMR, 13C NMR and HRMS. The structure of 14 g was also identified by X-ray single crystal diffraction. The bioactivities, brine shrimp toxicity and cytotoxicity, of all derivatives were tested. The results indicated that compounds 11 h, 11i, 11 m, 11 s, 14 b and 14 g exhibited excellent toxicity against brine shrimp with LC50 values ranging from 5.34 to 16.89 μg/mL, and compounds 11 s and 14 g displayed significant cytotoxicity against HT29 cells and A549 cells with IC50 values of 9.70 μM and 8.85 μM, respectively. Structure-activity relationships are discussed based on the results obtained from our research, and some important determinants for further modification of steroids towards the development of novel drug candidates are identified.

Beckmann rearrangement: Thiamine hydrochloride as a remarkable catalyst for one-pot synthesis of amides from ketones

Thiamine hydrochloride catalyzed synthesis of amides from ketones including 3-acetyl coumarin via Beckmann rearrangement has been reported. The reaction is believed to involve oxime formation, cleavage of CC bond followed by CN bond formation in one-pot. Thiamine hydrochloride is stable, cheap, easy to handle and environmentally friendly.

Direct synthesis of secondary amides from ketones through Beckmann rearrangement using O-(mesitylsulfonyl)hydroxylamine

The Beckmann rearrangement is a versatile method for the preparation of secondary amides from ketones via oxime intermediates and has been widely used in the synthesis of bioactive natural products and pharmaceuticals. Herein, we have developed a highly efficient direct method for the preparation of secondary amides and lactams from ketones using O-(mesitylsulfonyl)hydroxylamine (MSH). The reactions proceed rapidly at room temperature under mild condition without requiring any additive, and tolerate multiple functional groups. A simple aqueous work-up often furnished the products in excellent yield with high purity.

Weakly acidic zeolites: A review on uses and relationship between nature of the active sites and catalytic behaviour

Abstract Weakly acidic zeolites play a role in catalytic reactions, especially for transformation of biomass-derived products, where the control of the selectivity plays a crucial role. This review discusses this topic, having received limited attention in literature, to remark how represent both a scientific and applicative valuable area. The review offers clues for understanding how weak acid sites in zeolites could be an opportunity in some specific cases, but the aim is not to provide a systematic state-of-the-art. Rather, after introducing considerable examples and cases where mild acidity could be important (etherification, esterification, epoxidation and Beckmann rearrangement) and a discussion of the nature of weak acid sites, related to defects, present in Silicalite and how to control their nature/amount, the discussion is centred on a more in-depth analysis of three case examples: i) the effect of introduction of T3+ atoms in Silicalite-1, ii) the creation of mesoporosity in Fe-MFI and iii) catalysis by ammonium zeolite forms. HMF (5-hydroxymethyl furfural) etherification reaction is a main reaction discussed.

Characterization of chemical profiles of pH-sensitive cleavable D-gluconhydroximo-1, 5-lactam hydrolysates by LC–MS: A potential agent for promoting tumor-targeted drug delivery

Currently, controllable linker cleavage at the target site will facilitate the clinical treatment of cancer. Dual-functional prodrugs in combination of carbohydrate as targeting group and pH-sensitive cleavable linker are desired in clinical development. Here, a qualified structure of N-phenylcarbamate-d-gluconhydroximo-1,5-lactam was employed and proved to be a potential candidate prodrug in the drug design. To proof this concept, the possible mechanism of Beckmann rearrangement and the degraded products were confirmed by HPLC and LC–MS under the acid condition mimic lysosome. Hence, the strategy of d-gluconhydroximo-1,5-lactam as a prodrug carrier fabricated with interested drugs will provide a great potential approach for chemotherapy.

Synthesis of new fused dipyrroloazepinones via a two-step tandem reaction: Comparison of the Schmidt and Beckmann pathways

A new set of polyheterocyclic compounds (4,7,7-trimethyl-5-aryl-7a,8,9,10-tetrahydrodipyrrolo[3,2-c;2′,1′-g]azepin-2-ones) was synthesized via a tandem process involving a Beckmann rearrangement followed by a cyclization between the nitrogen atom and primary halide fragment. Ring expansion from 6 to 7 members and the fusion of the resulting ring with a five-membered ring took place in just one process.

In situ sulfonic acid-functionalized MIL-101(Cr) catalyzed liquid-phase Beckmann rearrangement of cyclohexanone oxime

Abstract We prepared in situ sulfonic-acid-functionalized MIL-101(Cr) catalysts using different chromium sources and mineralizers. We characterized these catalysts by X-ray diffraction, N2-physical adsorption, Fourier-transform infrared, scanning electron microscopy, X-ray photoelectron spectroscopy, NH3 temperature-programmed desorption, and inductively coupled plasma measurements. We subsequently used the solid acid catalysts to catalyze the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam for the first time. The results showed that when the reaction was carried out at 130 °C for 4 h with benzonitrile as the solvent, the MIL-101(Cr)-S1, prepared using chromium trioxide (CrO3) as the chromium source and hydrochloric acid as the mineralizer, showed the highest conversion of 35.1% and selectivity of 65.9%. This was better than that of MIL-101(Cr)-S2, which was prepared using chromium (III) nitrate nonahydrate [Cr(NO3)3·9H2O] as the chromium source and hydrofluoric acid as the mineralizer. This occurred because the MIL-101(Cr)-S1 had a higher acid content and strength than those of the MIL-101(Cr)-S2. Additionally, the MIL-101(Cr)-S1 could be reused three times in succession without loss of its catalytic activity.

Chlorotropylium Promoted Conversions of Oximes to Amides and Nitriles

Chlorotropylium chloride as a catalyst for the transformations of oximes, ketones, and aldehydes to their corresponding amides and nitriles in excellent yields (up to 99 %) and in short reaction times (mostly 10–15 min). Oximes were electrophilically attacked on the hydroxyl oxygen by chlorotropylium. The produced tropylium oxime ethers were the key intermediates, of which the ketoxime ether led to amide through Beckmann rearrangement, and the aldoxime ether led to nitrile by nitrogen base DBU assisted formal dehydration. This chlorotropylium activation protocol offered general, mild, and efficient avenues bifurcately from oximes to both amides and nitriles by one organocatalyst.

Total Synthesis of Galanthamine and Lycoramine Featuring an Early-Stage C-C and a Late-Stage Dehydrogenation via C-H Activation.

Herein, we report a novel strategy toward galanthamine and lycoramine. The concise synthesis was enabled by a Rh-catalyzed gram-scale C-C activation for the tetracyclic carbon framework and a regioselective Pd-catalyzed C-H activation for double-bond introduction. An aqueous-phase Beckmann rearrangement was performed for nitrogen atom insertion. Galanthamine and lycoramine were completed in 11 and 10 steps, respectively.

Hypervalent iodine reagent-mediated reactions involving rearrangement processes.

Hypervalent iodine reagents have been extensively employed in various types of oxidative organic reactions including oxidative coupling/cyclization, bifunctionalization of olefins and cyclopropane, C-H functionalization, and oxidative rearrangement reactions. In this review, the developments of the exclusive hypervalent iodine-mediated reactions involving oxidative rearrangement processes, including [1,2]-migration, Hofmann rearrangement, Beckmann rearrangement, ring contraction, ring expansion, [3,3]-sigmatropic/iodonium-Claisen rearrangement and some miscellaneous rearrangements, have been summarized.