Vapor-phase Beckmann rearrangement of oxime molecules over H-Faujasite zeolite.

The Beckmann rearrangement (BR) plays an important role in a variety of industries. The mechanism of this reaction rearrangement of oximes with different molecular sizes, specifically, the oximes of formaldehyde (H₂C?NOH), Z‐acetaldehyde (CH₃HC?NOH), E‐acetaldehyde (CH₃HC?NOH) and acetone (CH₃)₂C?NOH, catalyzed by the Faujasite zeolite is investigated by both the quantum cluster and embedded cluster approaches at the B3LYP level of theory using the 6‐31G (d,p) basis set. To enhance the energetic properties, single point calculations are undertaken at MP2/6‐311G(d,p). The rearrangement step, using the bare cluster model, is the rate determining step of the entire reaction of these oxime molecules of which the energy barrier is between 50–70 kcal mol^?1. The more accurate embedded cluster model, in which the effect of the zeolitic framework is included, yields as the rate determining step, the formaldehyde oxime reaction rearrangement with an energy barrier of 50.4 kcal mol^?1. With the inclusion of the methyl substitution at the carbon‐end of formaldehyde oxime, the rate determining step of the reaction becomes the 1,2 H‐shift step for Z‐acetaldehyde oxime (30.5 kcal mol^?1) and acetone oxime (31.2 kcal mol^?1), while, in the E‐acetaldehyde oxime, the rate determining step is either the 1,2 H‐shift (26.2 kcal mol^?1) or the rearrangement step (26.6 kcal mol^?1). These results signify the important role that the effect of the zeolite framework plays in lowering the activation energy by stabilizing all of the ionic species in the process. It should, however, be noted that the sizeable turnover of a reaction catalyzed by the Brønsted acid site might be delayed by the quantitatively high desorption energy of the product and readsorption of the reactant at the active center.     

磺酸树脂在樟脑肟贝克曼裂解反应中的催化作用

我们发现以磺酸树脂作为固体酸催化樟脑肟贝克曼裂解反应可以生成α-龙脑烯腈.考察了溶剂、催化剂用量、反应温度和反应时间等对反应的影响.在优化条件下樟脑肟可以完全转化,α-龙脑烯腈选择性高达90.5%.动力学研究表明,樟脑肟在磺酸树脂催化下的贝克曼裂解反应服从准一级动力学模型,经过最小二乘法求得反应的表观活化能为64.6kJ/mol.     

The Catalysis of Vapor-Phase Beckmann Rearrangement for the Production of ε-Caprolactam

Recently, Sumitomo Chemical Co., Ltd. developed the vapor-phase Beckmann rearrangement process for the production of -caprolactam. In the process, cyclohexanone oxime is rearranged into -caprolactam using a zeolite as a catalyst instead of sulfuric acid. EniChem in Italy developed the ammoximation process that involves the direct production of cyclohexanone oxime without producing any ammonium sulfate. Sumitomo Chemical Co., Ltd. has commercialized the combined process of vapor-phase Beckmann rearrangement and ammoximation in 2003.In this paper, the authors focus on some aspects of the vapor-phase Beckmann rearrangement catalysis. A solid catalyst that is mainly composed of a high-silica MFI zeolite (Silicalite-1) has been developed for the vapor-phase Beckmann rearrangement. This catalyst does not possess acidity that can be detected by ammonia TPD. Methanol fed into the reactor with cyclohexanone oxime improves the yield of caprolactam. Methanol reacts with terminal silanols on the zeolite surface and converts them to methoxyl groups. The modification of the catalyst by methanol has an important role for the Beckmann rearrangement reaction.Nest silanols located just inside the pore mouth of the MFI zeolite are supposed to be the active sites of the catalyst. We propose that the coordination between the NOH group of cyclohexanone oxime molecule and the nest silanols through hydrogen bonding is responsible for the reaction. The reaction mechanism of Beckmann rearrangement under vapor-phase conditions is the same as in the liquid phase, namely, the alkyl group in anti-position against the hydroxyl group of the oxime migrates to the nitrogen atom's position.     

Beckmann rearrangement of cyclotriveratrylene (CTV) oxime: tandem Beckmann-electrophilic aromatic addition

The Beckmann rearrangement has been performed on the oxime of cyclotriveratrylene (CTV) with thionyl chloride affording the ring-expanded 10-membered ring amide exclusively in high yield. Modified conditions afford a helical pentacycle derived from an unusual tandem Beckmann rearrangement and electrophilic aromatic addition followed by demethylation and tautomerization.     

Quantum chemical investigation of the adsorption of methanol on a cluster model of faujasite

The adsorption of methanol in zeolites of the faujasite type with sodium and calcium counter ions is studied with quantum chemical methods. The zeolite is represented with a cluster model allowing calculations at the Møller-Plesset as well as the DFT level of theory. An adsorption energy of −62.4 kJ/mol is calculated at the MP2/TZVP//BP86/TZVP level of theory for one methanol molecule at one site II sodium cation. Insight into the adsorption process is obtained with a three-body decomposition which reveals a strong destabilisation of the adsorption strength by large, positive three-body terms, which is important for force field development.     

Theoretical study of the adsorption of ethylene on alkali‐exchanged zeolites

The structures of alkali‐exchanged faujasite (X–FAU, X = Li⁺ or Na⁺ ion) and ZSM‐5 (Li–ZSM‐5) zeolites and their interactions with ethylene have been investigated by means of quantum cluster and embedded cluster approaches at the B3LYP/6‐31G(d, p) level of theory. Inclusion of the Madelung potential from the zeolite framework has a significant effect on the structure and interaction energies of the adsorption complexes and leads to differentiation of different types of zeolites (ZSM‐5 and FAU) that cannot be drawn from a typical quantum cluster model, H₃SiO(X)Al(OH)₂OSiH₃. The Li–ZSM‐5 zeolite is predicted to have a higher Lewis acidity and thus higher ethylene adsorption energy than the Li–FAU zeolites (16.4 vs. 14.4 kcal/mol), in good agreement with the known acidity trend of these two zeolites. On the other hand, the cluster models give virtually the same adsorption energies for both zeolite complexes (8.9 vs. 9.1 kcal/mol). For the larger cation‐exchanged Na–FAU complex, the adsorption energy (11.6 kcal/mol) is predicted to be lower than that of Li–FAU zeolites, which compares well with the experimental estimate of about 9.6 kcal/mol for ethylene adsorption on a less acidic Na–X zeolite. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 333–340, 2003     

分子筛催化cis-2-丁烯的双键异构反应机理的DFT研究

基于含有两个Si和一个Al的分子筛3T簇模型, 利用密度泛函方法(DFT)研究了分子筛催化1-丁烯双键异构为cis-2-丁烯的反应机理. 在B3LYP/6-31G(d,p)计算水平上对反应各驻点进行了全优化, 并计算了反应的活化能. 研究发现, 分子筛上的酸性OH基团首先通过物理吸附靠近1-丁烯的双键, 形成了π配位复合物后, 丁烯双键的端基C原子逐渐抽取这个质子, 同时相邻酸性位的一个O原子也抽取丁烯碳链上的一个H原子, 形成吸附态的cis-2-丁烯, 最后通过脱附形成产物, 使分子筛复原, 反应按照协同反应机理发生. 计算得到的表观活化能是55.9 kJ/mol, 与实验结果接近.     

LaC4团簇的理论研究

应用量子化学从头算方法研究了LaC4团簇，结果表明，在所提出的构型中，稀土位于碳环上最稳定，计算得到该团簇的绝热电子亲和势为81．05kJ/mol，离化能为628．88kJ/mol。该结果解决了实验中无法测定的问题，同时为合成实验提供了一定的理论指导。     

Theoretical Study of the AlEt3-Promoted Tandem Reductive Rearrangement of Epoxides

The AlEt3-promoted tandem reductive rearrangement reactions of epoxides was studied at B3LYP/6-31G(d,p) level. For the model compound σ-hydroxy epoxides, two possible reaction pathways I and II were calculated. The main difference is the order of ethylene release and six- to five-member ring rearrangement.The ring contraction rearrangement in pathway I is the first step and this step is the rate controlling step with a free energy barrier of 116.62 kJ/mol. For pathway II, the ethylene release occurs first, and is followed by a six-member ring opening reaction which is the rate controlling step, and the barrier is 251.38 kJ/mol.The reason for such high barrier is that the ethylene release results in the following reaction being moredifficult. The results show that pathway I (C-C rearrangement and then ethylene release) is more favorable,which is consistent with experimental results.     

Cyanuric chloride as a mild and active Beckmann rearrangement catalyst

The first general organocatalytic Beckmann rearrangement of ketoximes into amides has been realized by the catalytic use of cyanuric chloride. Furthermore, acids such as HCl and ZnCl2 are effective as cocatalysts with cyanuric chloride. For example, azacyclotridecan-2-one, which is synthetically useful as a starting material for nylon-12, was prepared in quantitative yield by the Beckmann rearrangement of cyclododecanone oxime (100 mmol scale) catalyzed by cyanuric chloride (0.5 mol %) and ZnCl2 (1 mol %).     

Pd-N to Pd-O rearrangement for a carbamate synthesis from carbon dioxide and methane: a density functional and ab initio molecular dynamics metadynamics study

We investigated the key step of Pd-N to Pd-O rearrangement from a model catalytic cycle for the activation of carbon dioxide and methane with static quantum chemical calculations and metadynamics simulation. Our calculations show that different bottlenecks appear in the catalytic cycle but that the investigated rearrangement of the Pd-N to Pd-O bounded complex has a barrier ΔG(#)/ΔF(#) of approximately 20 kJ mol?1 and is therefore accessible at ambient reaction conditions.     

A DFT study on secondary reaction pathways in the acid-catalysed Beckmann rearrangement of cyclohexanone oxime in aprotic solvent

In recent studies regarding acid-catalysed Beckmann rearrangement of cyclohexanone oxime in aprotic solvents it has been observed that a quite surprising hydrolysis of the starting material, i.e., cyclohexanone oxime, occurs even if the experimental conditions and the water concentration in the reaction mixture can not justify such a side-reaction. Being this apparent hydrolysis critical for catalyst selectivity and poisoning, a computational DFT study on a possible secondary reaction pathway, involving a bi-molecular reaction between two cyclohexanone oxime molecules in acid media as the primary step, is here reported to explain the experimental results.     

Novel quantum mechanical/molecular mechanical method combined with the theory of energy representation: free energy calculation for the Beckmann rearrangement promoted by proton transfers in the supercritical water

The Beckmann rearrangement of acetone oxime promoted by proton transfers in the supercritical water has been investigated by means of the hybrid quantum mechanical/molecular mechanical approach combined with the theory of energy representation (QM/MM-ER) recently developed. The transition state (TS) structures have been explored by ab initio calculations for the reaction of hydrated acetone oxime on the assumption that the reaction is catalyzed by proton transfers along the hydrogen bonds connecting the solute and the solvent water molecules. Up to two water molecules have been considered as reactants that take part in the proton transfers. As a result of the density functional theory calculations with B3LYP functional and aug-cc-pVDZ basis set, it has been found that participation of two water molecules in the reaction reduces the activation free energy by -12.3 kcal/mol. Furthermore, the QM/MM-ER simulations have revealed that the TS is more stabilized than the reactant state in the supercritical water by 2.7 kcal/mol when two water molecules are involved in the reaction. Solvation free energies of the reactant and the TS have been decomposed into terms due to the electronic polarization of the solute, electron density fluctuation, and others to elucidate the origin of the stabilization of the TS as compared with the reactant. It has been revealed that the promotion of the chemical reaction due to the hydration mainly originates from the interaction between the nonpolarized solute and the solvent water molecules at the supercritical state.     

Theoretical study of modes of adsorption of water dimer on H-ZSM-5 and H-Faujasite zeolites

Modes of adsorption of water dimer on H-ZSM-5 and H-Faujasite (H-FAU) zeolites have been investigated by a quantum embedded cluster approach, using the hybrid B3LYP density functional theory. The results indicate that there are two possible adsorption pathways, namely the stepwise process where only one water binds strongly to the (-O)3-Al-O(H) tetrahedral unit while the other weakly binds to the zeolite framework and the concerted process where both water molecules form a large ring of hydrogen-bonding network with the Br?nsted proton and an oxygen framework. With inclusion of the effects of the Madelung potential from the extended zeolite framework, for adsorption on H-ZSM-5 zeolite, both the neutral and ion-pair complexes exist with adsorption energies of -15.13 and -14.73 kcal/mol, respectively. For adsorption on the H-FAU, only the ion-pair complex exists with the adsorption energy of -14.63 kcal/mol. Our results indicate that adsorption properties depend not only on the acidity of the Br?nsted acidic site but also on the topology of the zeolite framework, such as on the spatial confinement effects which lead to very different adsorption structures for the ion-pair complexes in H-ZSM-5 and H-FAU, even though their adsorption energies are quite similar. Our calculated vibrational spectra for these ion-pair complexes support previous experimental IR interpretations.     

HZSM-5 分子筛上乙烯芳构化过程中 C4 至 C6 中间体的反应机理

 应用量子力学和分子力学联合的 ONIOM2 (B3LYP/6-31G(d,p):UFF) 方法, 采用包含分子筛孔道结构的 78T 簇模型, 对 HZSM-5 分子筛上乙烯芳构化过程中 C4 至 C6 中间体的反应历程进行了研究, 探讨了分子筛的酸催化机理和择形催化作用. 结果表明, 作为乙烯二聚产物的表面正丁基烷氧络合物 (C4) 直接与乙烯作用得到正己基烷氧络合物 (C6), 在分子筛孔穴尺寸的限制下, 很难实现碳链的折叠环化. 按照间歇反应历程, 丁基烷氧络合物先发生 C–O 键断裂, 脱质子生成 1-丁烯, 然后在酸性位上再与乙烯加成, 在分子筛表面生成 3-甲基戊基烷氧络合物. 该烷氧络合物脱除质子给分子筛, 同时环化生成甲基环戊烷, 后者再与分子筛酸性质子共同脱除氢分子, 生成不稳定的碳正离子中间体, 然后重构成环己烷正离子. 丁基烷氧络合物脱质子的活化能为 158.42 kJ/mol; 1-丁烯与乙烯加成反应的活化能为 130.71 kJ/mol; 3-甲基戊基烷氧络合物脱氢环化生成甲基环戊烷的活化能为 122.06 kJ/mol. 由于孔穴的限域作用, 五员环的甲基环戊烷是重要的中间体.     

High-Yield Method for the Preparation of 1,3,4,5-Tetrahydro-7-methoxy-2H-1-benzazepin-2-one with Excellent Regio- and Stereoselectivity

We have surveyed the effects of different acid catalysts, reaction times, and temperatures on the yield, regioselectivity, and stereoselectivity and calculated the ketoxime isomerization and activation energy of the title compound. A facile synthetic procedure with good yields and good regio- and stereoselectivity for Beckmann rearrangement of oxime sulfonate with ZnCl₂ in the presence of solvent is developed.     

Synthesis of Ti-Hβ zeolites by liquid-solid isomorphous substitution and the catalytic properties in the vapor phase Beckmann rearrangement of cyclohexanone oxime

A series of Ti-Hβ zeolites were synthesized by liquid-solid isomorphous substitution. Hβ and Ti-Hβ zeolites were characterized by BET, XPS, IR, etc., and studied in the vapor phase Beckmann rearrangement of cyclohexanone oxime. In comparison with pure Hβ, the incorporation of Ti in the Hβ framework leads to larger BET surface area and weaker Br?nsted acid sites. The incorporation of Ti in the Hβ framework increases the conversion of cyclohexanone oxime and its stability. It is inferred that for the catalysts having the structure of a β zeolite, the suitable acid sites for the vapor phase Beckman rearrangement might be the weak Br?nsted acid sites.     

Treating dispersion effects in extended systems by hybrid MP2:DFT calculations--protonation of isobutene in zeolite ferrierite

We propose use of a hybrid method to study problems that involve both bond rearrangements and van-der-Waals interactions. The method combines second-order M?ller-Plesset perturbation theory (MP2) calculations for the reaction site with density functional theory (DFT) calculations for a large system under periodic boundary conditions. Hybrid MP2:DFT structure optimisation for a cluster embedded in the periodic model is the first of three steps in a multi-level approach. The second step is extrapolation of the MP2 energy to the complete basis set limit. The third step is extrapolating the high-level (MP2) correction to the limiting case of the full periodic structure. This is done by calculating the MP2 correction for a series of cluster models of increasing size, fitting an analytic expression to these energy corrections, and applying the fitted expression to the full periodic structure. We assume that, up to a constant, the high-level correction is described by a damped dispersion expression. Combining the results of all three steps yields an estimate of the MP2 reaction energy for the full periodic system at the complete basis set level. The method is designed for a reaction between a small or medium sized substrate molecule and a very large chemical system. For adsorption of isobutene in zeolite H-ferrierite, the energies obtained for the formation of different structures, the pi-complex, the isobutoxide, the tert-butoxide, and the tert-butyl carbenium ion, are -78, -73, -48, and -21 kJ mol(-1), respectively. This corresponds to corrections of the pure DFT (PBE functional) results by -62, -70, -67, and -29 kJ mol(-1), respectively. Hence, the MP2 corrections are substantial and, perhaps more importantly, not the same for the different hydrocarbon species in the zeolite. Coupled-cluster (CCSD(T)) calculations change the MP2 energies by -4 kJ mol(-1) (tert-butyl cation) or less (below +/-1 kJ mol(-1) for the other species).     

A dielectric study of the structure of propylene glycol

The dielectric spectra of propylene glycol over the frequency and temperature ranges 10 mHz–75 GHz and 175–423 K, respectively, were analyzed using the Dissado-Hill cluster model. A correlation between relaxation processes of breaking and formation of intermolecular H-bonds in clusters was obtained. A correlation of fluctuation processes of synchronous exchange of molecules between neighboring clusters corresponded to the redistribution of H-bonds between them. The Dissado-Hill theory was used to determine the integral relaxation times, n _DH and m _DH parameters and calculate the mean dipole moments of propylene glycol clusters and the energy characteristics of processes of their rearrangement. The mean dipole moments of clusters (23617–18.65 D) were compared with those of molecules in the liquid phase (3.67–3.03 D). The apparent activation enthalpy of processes of cluster rearrangements decreased from 141.8 to 25.2 kJ/mol, the activation energy decreased from 46.03 to 18.47 kJ/mol, and the energy of orientation dipole-dipole interactions, from 3.78 to 3.45 kJ/mol as the temperature increased.     

Hierarchically structured monolithic silicalite-1 consisting of crystallized nanoparticles and its performance in the Beckmann rearrangement of cyclohexanone oxime

In this study, we present a synthetic pathway for the fabrication of self-supporting zeolite monoliths consisting of crystallized nanoparticles. A resorcinol-formaldehyde-based organic aerogel is used as a template, and silicalite-1 is used as the zeolite example. The silicalite-1 monoliths obtained consist of individual well-defined zeolite nanocrystals with sizes of 30-40 nm. The monoliths exhibit a high mechanical stability and have hierarchical porosity, with micropores within the zeolite particles, a mesopore system formed by the packing of the nanoparticles, and a macropore system on the monolith level. Such monolithic zeolites show high selectivity typically above 80% to epsilon-caprolactam combined with a high rate of reaction of 0.46 g(caprolactame)/(g(catalyst).h) in the Beckmann rearrangement of cyclohexanone oxime.