Cyclohexanone Oxime Conversion Research Articles

Insight into Synergistic Brønsted and Lewis Acidic Deep Eutectic Solvent for Beckmann Rearrangement of Cyclohexanone Oxime

Abstractε‐Caprolactam (CPL) is industrially produced by Beckmann rearrangement of cyclohexanone oxime (CHO) under fuming sulfuric acid, resulting in corrosive and environmental issues. Herein, we prepared triethylamine hydrochloride (TEAHC) and ZnCl2 formed deep eutectic solvent (DES) [TEAHC:2ZnCl2] with Brønsted and Lewis acid sites for efficient liquid rearrangement, achieving 100% conversion of CHO and 95.5% yield of CPL at 80 °C for only 1 h. The results show that ZnCl2 in [TEAHC:2ZnCl2] can promote the detachment of proton, which acts as Brønsted acid site combined with another ZnCl2 molecule to synergistically catalyze the reaction. In the Brønsted acid catalyzed process, the nitrogen atom in CHO as reactive site can be readily attacked by the proton to form protonated CHO, which subsequently undergoes rearrangement. By adding ZnCl2 into TEAHC to obtain [TEAHC:2ZnCl2], the formation of ZnCl2‐CHO complex results in a significant reduction in reaction energy barrier through synergistic effect of Brønsted and Lewis acids. Particularly, the fitted reaction kinetics and low activation energy also confirm the rearrangement can occur under low reaction temperature. Thus, the DESs with efficient catalytic performances for ketoxime rearrangements provide a potential method to design active sites for Beckmann rearrangements of oximes under mild reaction conditions.

Silica Gel Supported Chlorosulfonic Acid Catalyzed Beckmann Rearrangement of Cyclohexanone Oxime in Liquid Phase

The Beckmann rearrangement of cyclohexanone oxime in the liquid phase using fuming sulfuric acid as a catalyst is a traditional method, which brings many problems, such as environmental pollution, corrosion of equipment, and difficulty in treating the by-product ammonium sulfate. This paper designs and prepares a silica gel-supported chlorosulfonic acid solid acid catalyst for the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam. The factors affecting the preparation of the catalyst and the optimal reaction conditions for Beckmann rearrangement were investigated. It was found that the best catalyst preparation conditions were as follows: mass ratio of silica gel: chlorosulfonic acid of 1:0.2, room temperature, stirring time of 3 hours, solvent dichloromethane, and silica gel mesh size of 100-200 mesh, and best Beckmann rearrangement conditions were as follows: mass ratio of cyclohexanone oxime: catalyst of 1:1, temperature of 140°C, solvent benzonitrile volume of 40 mL/g cyclohexanone oxime, reaction time of 5 hours. Under the above conditions, the conversion of cyclohexanone oxime is 74%, and the selectivity of caprolactam is 40%.

Tailoring Zn-based diacidic functionalization of Deep eutectic solvent Catalyst: Green and efficient synthesis of ε-Caprolactam under mild conditions

A novel Zn-based acidic functionalized deep eutectic solvent (DES) catalyst were prepared by a “tailoring” mixing procedure of Brønsted acidic hydrogen bond donors (HBD) and Lewis acidic hydrogen bond acceptor (HBA). It is found that the hydrogen bonded cluster with thermal stability and adjustable acidity has an excellent flexible hydrogen bond “assembly mode”, providing a suitable coordination microenvironment for Zn active center. The functionalized DESs were investigated to produce caprolactam from cyclohexanone oxime. The results showed that DES [ZnCl2][ChCl][TCA]2 had an excellent catalytic performance for the reaction with 100% cyclohexanone oxime conversion and ε-caprolactam 99.4% selectivity at 80 °C for 1.5 h, attributing to the strong complexing ability of Zn active center and the synergistic effect of BrØnsted and Lewis acid sites of DES, which also decreased the energy barriers of the intermediates and transition states, thus reducing the reaction energy (Ea = 29.22 kJ mol−1 and ΔG = –32.8 kJ mol−1). Otherwise, the recovered DES [ZnCl2][ChCl][TCA]2 was reused seven times with no significant decrease in its catalytic performance. The advantages of this method, such as high yield, short reaction time, and easy catalyst recovery, make the DES catalytic system a potential method for Beckmann rearrangement.

Novel Brønsted Acidic Ionic Liquids as High Efficiency Catalysts for Liquid-Phase Beckmann Rearrangement

Exploring environmentally friendly, efficient, cheap and recyclable catalysts are essential for the development of green, sustainable and mild processes for the liquid-phase Beckmann rearrangement. Herein, a novel caprolactam-based Brønsted acidic ionic liquid ([CPL][2MSA]) was developed for the conversion of cyclohexanone oxime (CHO) to caprolactam (CPL), not only as a catalyst, but also as a mild reaction medium. Under the reaction conditions for the reaction temperature (90 °C), reaction time (2 h) and mole ratio ([CPL][2MSA]: CHO = 3:1), [CPL][2MSA] possesses plenty of high sulfonate groups, which exhibit high conversion (100%) and selectivity (95%) without any other co-catalysts or metals. Based on the thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses, the decomposition and glass transition temperatures are gradually increased with the increase in MSA mole content, revealing the existence of hydrogen-bonded clusters. Interestingly, the occurrent route of the liquid-phase Beckmann rearrangement for CHO in [CPL][2MSA] is revealed by in situ FT-Raman. In addition, the dominating H-bond combination between CHO and [CPL][2MSA] is further confirmed by COSMO-RS model. The activation energy (Ea) of the reaction is calculated by the first-order reaction kinetics. Thus, the [CPL][2MSA] with plenty of acidic catalytic active species is an environmentally friendly and efficient candidate for the liquid-phase Beckmann rearrangement.

Vinyl Silane Modified Silica-Grafted Sulfonic Acid Based Polymeric Ionic Liquids for Efficient Catalytic Hydrolysis of Cyclohexanone Oxime

In this work, vinyl silane modified silica grafted sulfonic acid based polymeric ionic liquids (SPILs) catalysts were successfully synthesized and characterized by 13C MAS NMR, XPS, FT-IR, TG, XRD, BET, SEM, and CA. Hydroxylamine was generated by hydrolysis of cyclohexanone oxime reaction. Box–Behnken design and response surface methodology were used to further study the various reaction conditions and their interactions that affected the conversion of cyclohexanone oxime. Superior catalytic performance and more stable structure of the SPILs compared to conventional loaded ionic liquid catalysts. Furthermore, a possible reaction path was proposed for cyclohexanone oxime hydrolysis, and a series of ketoximes were also tested over the SPILs catalysts. The conversion was not less than 64.65%. Synthesis of SPILs catalysts with good properties would be very important for their applications.

Investigation of the active centers and structural modifications for TS-1 in catalyzing the Beckmann rearrangement

The Beckmann rearrangement (BR) of cyclohexanone oxime (CHO) to produce caprolactam (CPL) has been studied over various titanosilicates. TS-1 showed superior catalytic performance, compared to Ti-MWW, Ti-Beta and Ti-MOR. Based on the close relationship between Ti content and CHO conversion, and the Na+-exchange experiments, the silanol groups, adjacent to the “open” Ti sites, were proved to be the active centers for the BR reaction of CHO to produce CPL, in addition to those generated by defects including terminal silanols, hydrogen-bonded silanols and silanol nests. Moreover, monolithic TS-1 (M-TS-1) microspheres showed higher catalytic activity than the conventional TS-1. The diffusion properties of M-TS-1 were further enhanced via the chemical modifications to achieve longer lifetime for the Beckmann rearrangement under optimized reaction conditions.

High-yield and high-efficiency conversion of cyclohexanone oxime to ε-caprolactam in a green and facile reaction process over deep eutectic solvents

ε-Caprolactam (CPL) is mainly produced through Beckmann rearrangement of cyclohexanone oxime (CHO) catalyzed by oleum in industry, which suffers the problems such as serious corrosion problems. Herein, we developed a green and facile reaction process to produce CPL with deep eutectic solvents (DESs), which were investigated as catalysts and solvents in the reaction. The DFT results showed that the synergistic effect significantly decreased the energy barriers of reactants and intermediates, thus facilitating the CHO conversion to CPL. High conversion (100%) and selectivity to CPL (98.5%) were successfully obtained using [ZnCl2][Urea]2.0 (n(ZnCl2):n(Urea) = 1:2) at 130 °C for 2 h without other catalyst. The free energy (ΔG) and activation energy (Ea) of the reaction were −18.4 KJ mol−1 and 23.15 KJ mol−1, respectively. The reusability and general applicability of the DES were outstanding. The developed process provides an environmentally friendly and efficient candidate for rearrangements under mild conditions.

Application of an immobilized ionic liquid for the preparation of hydroxylamine via hydrolysis of cyclohexanone oxime

AbstractPreparation of hydroxylamine via hydrolysis of cyclohexanone oxime was studied over porous SiO2 supported acid ionic liquid catalyst. The catalyst [SPIPTES]CF3SO3@SiO2 was prepared through sol‐gel method and characterized by elemental analysis, IR and TG, etc. Various parameters such as reaction temperature and time, catalyst amount were investigated systematically. The optimized reaction conditions investigated were catalyst:cyclohexanone oxime (mass ratio) 4 : 1, conducted at 60 °C for 1 h. Since the present hydrolysis reaction is controlled by thermodynamics, the conversion of cyclohexanone oxime could not be very high. However, reasonable result was achieved under the optimized reaction conditions. Cyclohexanone oxime conversion was 38.41 % and NH2OH yield was 37.65 %. Additionally, combining experiments with density functional theory calculations, a possible catalyst structure and reaction pathway involved protonated cyclohexanone oxime mechanism was proposed for the present hydrolysis in this study.

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.

B-MCM-41 COMO CATALIZADOR NANOESTRUCTURADO PARA OPTIMIZACIÓN DE LAS CONDICIONES DE REACCIÓN DE BECKMANN

The Beckmann rearrangement of Cyclohexanone oxime at 300-380 °C and W/F = 20-60 gh/mol over a B-MCM-41 catalyst was studied at atmospheric pressure. The e-Caprolactam (precursor for nylon-6) was the major product on the whole temperature range studied and Cyclohexanone appeared as the main by-product and was generated probably due to the moderate acidity of these materials. The stability and the possibility of recycling of the catalyst were also analyzed. So, the catalyst could be used during 3600 min and then recovered and reused without significant changes in the active species. A reaction pathway was proposed in order to explain the results obtained. Finally, the better catalytic performance was observed at 320 °C and W/F = 40 gh/mol. Such conditions allowed us to achieve a Cyclohexanone oxime conversion of 54% with an e-Caprolactam selectivity of around 83%. Thus, under this soft reaction condition it could be achieved a high yield to e-Caprolactam with a low proportion of Cyclohexanone. This product mixture (e-Caprolactam and Cyclohexanone) may be separated by vacuum distillation; then the Cyclohexanone could be recycled by reaction with hydroxylamine to form again Cyclohexanone oxime (raw material for e-Caprolactam), marketed for the production of adipic acid, as adhesive in sealing PVC objects or as solvent in several industries.

Selective Synthesis of Primary Anilines from Cyclohexanone Oximes by the Concerted Catalysis of a Mg-Al Layered Double Hydroxide Supported Pd Catalyst.

Although the selective conversion of cyclohexanone oximes to primary anilines would be a good complement to the classical synthetic methods for primary anilines, which utilize arenes as the starting materials, there have been no general and efficient methods for the conversion of cyclohexanone oximes to primary anilines until now. In this study, we have successfully realized the efficient conversion of cyclohexanone oximes to primary anilines by utilizing a Mg-Al layered double hydroxide supported Pd catalyst (Pd(OH)x/LDH) under ligand-, additive-, and hydrogen-acceptor-free conditions. The substrate scope was very broad with respect to both cyclohexanone oximes and cyclohexenone oximes, which gave the corresponding primary anilines in high yields with high selectivities (17 examples, 75% to >99% yields). The reaction could be scaled up (gram-scale) with a reduced amount of the catalyst (0.2 mol %). Furthermore, the one-pot synthesis of primary anilines directly from cyclohexanones and hydroxylamine was also successful (five examples, 66-99% yields). The catalysis was intrinsically heterogeneous, and the catalyst could be reused for the conversion of cyclohexanone oxime to aniline at least five times with keeping its high catalytic performance. Kinetic studies and several control experiments showed that the high activity and selectivity of the present catalyst system were attributed to the concerted catalysis of the basic LDH support and the active Pd species on LDH. The present transformation of cyclohexanone oximes to primary anilines proceeds through a dehydration/dehydrogenation sequence, and herein the plausible reaction mechanism is proposed on the basis of several pieces of experimental evidence.

Highly stable In-SBA-15 catalyst for vapor phase Beckmann rearrangement reaction

The Indium doped SBA-15 material was prepared by sol-gel method and tested for vapor phase Beckman rearrangement reaction. Among three indium loading, In/Si ratio of 2/100 was found as an optimum composition in terms of caprolactam selectivity (100%) and cyclohexanone oxime conversion (100%). The catalysts were characterized by N2 adsorption, small-angle X-rays/neutron scattering (SAXS/SANS), XRD, FESEM, HRTEM, EDX, UV, FTIR and NH3-TPD techniques. In-situ SANS experiment was performed on the adsorption of CO2 to detect the micropores in the mesopore wall. All catalysts samples have highly ordered hexagonal structure with well dispersed indium in the silica matrix. The fine tuning of weak and strong acid sites were found in indium doped SBA-15 (In/Si = 2/100) catalyst. The same catalyst showed optimum catalytic performance, high space time yield 114.4 mol/h/gcat and high stability till 6 h of reaction without deactivation. The micro-kinetic analysis showed that there were no external and internal diffusion limitations in the SBA-15 catalyst. The reaction mechanism of Beckmann rearrangement over In-SBA-15 has been elucidated.

Caprolactam Synthesis using Ce-MCM-41Catalysts

Siliceous MCM-41 was synthesized by hydrothermal method using sodiummetasilicate as a source. Cerium ion incorporated Si-MCM-41 was synthesized by hydrothermal method using Cetyltrimethylammonium bromide as template. 2, 3 and 4 weight percentage of Ceria was loaded over MCM-41 by wet impregnation method. The synthesized catalysts were characterized using FT-IR, DRS-UV-Vis, XRD and SEM techniques. The catalytic activity of the cerium ion incorporated and ceria impregnated MCM-41 was evaluated in the synthesis of caprolactam from cyclohexanone oxime in the liquid phase condition. At high temperature all the catalyst showed high conversion. In that 4 wt.% Ce impregnated Si-MCM-41 produced high conversion (76.2%) and percentage yield (66.4%). The impregnated catalyst may contain more number of cerium present in the pores, so the lewis acid sites will be more and the conversion of cyclohexanone oxime into caprolactam will be high.

Preparation and physicochemical and catalytic properties of micro-mesoporous catalysts based on faujasite

Micro-mesoporous samples of materials based on faujasite Y (SiO2/Al2O3 = 85) have been obtained by modifying in a solution containing either a base or a base and a surfactant. The influence of the composition of the alkaline solution (NaOH, NH4OH, (CH3)4NOH) and the presence of the surfactant cetyltrimethylammonium bromide (CTAB) in the system have been studied. It has been shown that it is reasonable to prepare faujasite-based micro-mesoporous materials on by the action of the organic base tetramethylammonium hydroxide (TMAOH). It has been found that the extent of desilylation, which determines the chemical composition and share of mesopores in materials, depends on the TMAOH concentration and the presence of surfactant. In the presence of CTAB mesopores with a diameter of about 40 A are formed, the share of which can be controlled by treatment conditions. The resulting materials have been examined in the reaction of cyclohexanone oxime conversion to e-caprolactam. It has been found that materials with the combined micro-mesoporous structure show higher stability among the samples with similar acidic properties but different porosity characteristics.

NbOx/SiO2 in the gas-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam: Influence of calcination temperature, niobia loading and silylation post-treatment

NbOx/SiO2 catalyst materials prepared by the incipient wetness impregnation method were studied in the industrially relevant gas-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam. The catalytic experiments were carried out in a fixed bed reactor system at atmospheric pressure. Results have been complemented with Raman and FT-IR spectroscopy as well as N2 physisorption measurements. Optimal catalytic results were observed for a catalyst calcination temperature of 600°C and a niobia loading of 0.3wt.%. Raman spectroscopy revealed that isolated tetrahedral mono-oxo NbO4 surface species most probably play a key role in the catalytic reaction. Very positive effects were achieved by applying a catalyst silylation post-treatment. Firstly, the catalytic long-term stability increased very substantially as a consequence of a decreased coke deposition on the catalyst surface. Secondly, the harmful effect of water on catalytic performance was strongly suppressed even to such an extent that water could be added to the feed to enhance catalytic long-term stability. Cyclohexanone oxime conversion and ε-caprolactam selectivity could be maintained at constant high values >99% and around 95% respectively, for 26h time-on-stream. Finally, considering the Sumitomo gas-phase Beckmann rearrangement process as a benchmark, we made a rough comparison between the catalytic performances of our niobia/silica catalyst and the silicalite catalyst used by Sumitomo.

A simple and efficient approach for preparation of hydroxylamine sulfate from the acid-catalyzed hydrolysis reaction of cyclohexanone oxime

A simple and efficient approach for preparation of hydroxylamine sulfate from the hydrolysis reaction of cyclohexanone oxime in the presence of sulfuric acid has been developed in this work. The effects of the molar ratio of cyclohexanone oxime to sulfuric acid, the concentration of reactants, the reaction temperature, the reaction time and the extraction solvents on the hydrolysis reaction were investigated. The results indicated the conversion of cyclohexanone oxime was over 30% with excellent selectivity of cyclohexanone and hydroxylamine sulfate under the optimal reaction conditions. Furthermore, the enthalpy change, entropy change, Gibbs free energy change and thermodynamic equilibrium constant of the hydrolysis reaction were determined in present work. This reaction is an endothermic reaction and higher temperature is favorable for the synthesis of hydroxylamine sulfate. This new preparation method is simple, rapid, efficient and economical. Maybe this work can serve as a direction for preparation of other hydroxylamine salts by such hydrolysis reaction.

Bismuth supported SBA-15 catalyst for vapour phase Beckmann rearrangement reaction of cyclohexanone oxime to ɛ-caprolactam

Development of environmental benign as well as low cost metal precursor based catalyst is a challenge for chemical industry. In this work we report Bi promoted SBA-15 catalyst for vapour phase Beckmann rearrangement reaction of cyclohexanone oxime. The three different Bi loaded SBA-15 catalysts are prepared and characterized by BET surface area and porosity measurement, small angle X-ray scattering, wide angle X-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscope, ultraviolet–visible spectroscope, Fourier transform infrared spectroscopy and temperature programmed desorption techniques. Further, catalytic activity is optimized by changing reaction temperature, pre-treatment temperature and pre-treatment time so that 100% cyclohexanone oxime conversion and 100% ɛ-caprolactam selectivity has been achieved. Role of solvent, silylation and time on stream has also been examined. The TPD profiles of all three bismuth loaded samples are mainly characterized by weak acidic sites or surface silanol groups. The FTIR profile shows hydroxyl rich surface in the vicinity of bismuth at Bi-SBA-15 (Bi/Si=1/100). Based on catalyst characterization and activity data correlation, it can be suggested that protonation at oxime oxygen can be triggered by surface silanol in the vicinity of a Lewis acid centre bismuth. The high space-time-yield of caprolactum was 114.3molgcat−1h−1 was obtained.

Novel Approach for the Preparation of Hydroxylammonium Nitrate from the Acid-Catalyzed Hydrolysis of Cyclohexanone Oxime

A simple and efficient approach for the preparation of hydroxylammonium nitrate from the hydrolysis reaction of cyclohexanone oxime in the presence of nitric acid has been developed in this work. The effects of the molar ratio of cyclohexanone oxime to nitric acid, the amount of water, the reaction temperature, the reaction time, and the extraction solvent on the hydrolysis reaction were investigated. The results indicated that the conversion of cyclohexanone oxime can reach 62.6% with 96.9% selectivity to hydroxylammonium nitrate and 97.4% selectivity to cyclohexanone under the optimal reaction conditions. In addition, the possible acid-catalyzed hydrolysis reaction mechanism is discussed. This work might be very significant for establishing such a preparation method for hydroxylammonium salts from the hydrolysis reaction of oxime in the chemistry and chemical engineering fields.

Comprehensive Study for Vapor Phase Beckmann Rearrangement Reaction over Zeolite Systems

Replacement of homogeneous catalysis systems by heterogeneous catalysis systems is widely accepted throughout academia and industry due to ecological concerns, difficulty of separations, and nonrecyclability of homogeneous catalysts. Among several heterogeneous catalysts, the zeolite system has been focused extensively on vapor phase Beckmann reactions for a few decades. In this article a review of the factors affecting the cyclohexanone oxime conversion and ε-caprolactam selectivity over different zeolite systems is presented. It can be concluded that several catalyst preparation parameters such as Si/Al ratio, different metal/nonmetal loading, micropore size, and postsynthesis treatment as well as catalyst preparation parameters like temperature and solvent have crucial roles in deciding cyclohexanone oxime conversion and product selectivity over microporous zeolite catalysts. In the last section, an attempt was made to summarize the reaction mechanism for this reaction over zeolite catalyst systems. This thorough study might be useful for efficient design of a microporous zeolite system toward Beckmann rearrangement reactions.

Nature of the active sites in Al-MCM-41 nano-structured catalysts for the selective rearrangement of cyclohexanone oxime toward ɛ-caprolactam

Al-MCM-41 type nano-structured catalysts with different Al contents were prepared by direct hydrothermal synthesis. All the materials were characterized by XRD, N2 adsorption, TEM, SEM, ICP-OES, FT-IR and adsorption of pyridine coupled to FT-IR spectroscopy. The relationship between the Al contents in the synthesis gel and final solid, the degree of Al introduction in tetrahedral coordination into the framework, the formation of nest silanols and the relative density of the acidic hydroxyl sites has been exhaustively analyzed. We could corroborate that hydroxyl groups present in silanol nests are the direct responsible of the weakly acid character of our materials. Moreover, a critical concentration of framework Al seems to be necessary to generate such nests, after which the acid sites density is strongly increased, according the framework Al amount increasing. The enhancement in the density of acidic nest silanols (active sites for the selective rearrangement of cyclohexanone oxime toward ɛ-caprolactam) reached by increasing the Al content, permitted to us achieve a cyclohexanone oxime conversion about 66%. The ɛ-caprolactam selectivity was 100% for all the evaluated catalysts, indicating that the acidic strength was kept sufficiently weak to not catalyze the formation of by-products.