Allylic Oxidation Of Cyclohexene Research Articles

An Overview of Heterogeneous Transition Metal‐Based Catalysts for Cyclohexene Epoxidation Reaction

AbstractCyclohexane epoxide, which contains highly active epoxy groups, plays a crucial role as an intermediate in the preparation of fine chemicals. However, controlling the epoxidation pathway of cyclohexene is challenging due to issues such as the allylic oxidation of cyclohexene and the ring opening of cyclohexane epoxide during the cyclohexene epoxidation process to form cyclohexane oxide. This review focuses on the structure‐activity relationships and synthesis processes of various heterogeneous transition metal‐based catalysts used in cyclohexene epoxidation reactions, including molybdenum(Mo)‐based, tungsten(W)‐based, vanadium(V)‐based, titanium(Ti)‐based, cobalt(Co)‐based, and other catalysts. Initially, the mechanism of cyclohexene epoxidation by transition metal‐based catalysts is examined from the perspective of catalytic active centers. Subsequently, the current research of cyclohexene epoxidation catalysts is summarized based on the perspective of catalyst support. Additionally, the differences between alkyl hydroperoxide, hydrogen peroxide (H2O2), and oxygen (O2) as oxidants are analyzed. Finally, the main factors influencing catalytic performance are summarized, and reasonable suggestions for catalyst design are proposed. This work provides scientific support for the advancement of the olefin epoxidation industry.

Selective epoxidation and allylic oxidation of olefins catalyzed by BEA-Ti and porphyrin catalysts

Selective epoxidation and allylic oxidation of cyclohexene were realized in the presence of BEA-Ti and (metallo)porphyrin catalysts. The integration of BEA-Ti and porphyrin H2MTPP afforded cyclohexene oxide with excellent selectivity (cyclohexene oxide/ 2-cyclohexen-1-one=85:15). BEA-Ti and metalloporphyrin MnMTPP yielded 2-cyclohexen-1-one with high selectivity (cyclohexene oxide/ 2-cyclohexen-1-one=12:88). Resulting active species involving of (metallo)porphyrin, TiIV sites and tert-butyl hydroperoxide (TBHP) promoted the oxidation process of cyclohexene. A possible mechanism resulting in the formation cyclohexene oxide and 2-cyclohexen-1-one was proposed. The outer-sphere effect constructed by (metallo)porphyrin, TiIV sites and TBHP on the surface of BEA-Ti framework improved the epoxidation and allylic oxidation both in the conversion and selectivity.

A two-fold interpenetrating metal-organic framework based on [Co4O(COO)6] cluster: Synthesis, crystal structure and catalytic properties

One new Metal-Organic Frameworks, [Co4O(L)2]·(DMF)8·(H2O)8 (1, H3L = 4-[N,N-bis(4-methylbenzoic acid)amino]benzoic acid), had been successfully constructed under hydrothermal conditions, which firstly presents the [Co4O(COO)6] secondary-building unit similar to the typical [Zn4O(COO)6] one via single-crystal X-ray diffraction studies. All of the cobalt ions exhibit the four-coordinate environment, and possess more open metal sites. Heterogeneous catalytic experiments on allylic oxidation of cyclohexene indicate that 1 exhibits high catalytic activity by utilizing the tert-butylhydroperoxide (t-BuOOH) as the oxidant. The activation energy for the whole process of oxidation of cylcohexene had been calculated as 40.6 kJ mol−1, which indicate the important role of the special [Co4O(COO)6] cluster in the resulted heterogeneous catalyst.

Effect of Redox "Non-Innocent" Linker on the Catalytic Activity of Copper-Catecholate-Decorated Metal-Organic Frameworks.

Two new UiO-68 type of Zr-MOFs featuring redox non-innocent catechol-based linkers of different redox activities have been synthesized through a de novo mixed-linker strategy. Metalation of the MOFs with Cu(II) precursors triggers the reduction of Cu(II) by the phenyl-catechol groups to Cu(I) with the concomitant formation of semiquinone radicals as evidenced by EPR and XPS characterization. The MOF-supported catalysts are selective toward the allylic oxidation of cyclohexene and it is found that the presence of in situ-generated Cu(I) species exhibits enhanced catalytic activity as compared to a similar MOF with Cu(II) metalated naphthalenyl-dihydroxy groups. This work unveils the importance of metal-support redox interactions in the catalytic activity of MOF-supported catalysts which are not easily accessible in traditional metal oxide supports.

Synthesis and Catalytic Application of Mesoporous Titanium Silicoaluminophosphate-37 (MESO-TSAPO-37) Molecular Sieves Assembled from Microporous TSAPO-37 Precursor

Titanium containing mesoporous silicoaluminophosphate (MESO-TSAPO-37) molecular sieves were assembled from microporous titanium silicoaluminophosphate-37 (TSAPO-37) precursor possessing structural building units of SAPO-37. FT-IR studies and N2 sorption analysis supported the presence of microporosity on the walls of the mesoporous surface. The composite MESO-TSAPO-37 material showed promising catalytic activity in oxidation of cyclohexene. The catalyst showed complete conversion (100 %) of olefin with selective formation of allylic products (80 %). The catalytic activity persisted for several runs. Titanium substituted MESO-TSAPO-37 materials was assembled in presence of surfactant from microporous precursors of TSAPO-37 by a two step procedure. Thoroughly characterized MESO-TSAPO-37 was used for allylic oxidation of cyclohexene which resulted in 100 % conversion and 80 % selectivity towards allylic product.

Macrocylic Picolinamide Complexes and their Catalytic Reactivity in Allylic Oxidation

This paper describes the synthesis, characterization and catalytic activities of three closed-loop picolinamide complexes. They were prepared by Mn(II), Cu(II), Co(II) acetate and macrocylic ligand (L), which was formed by the condensation between 2,6-pyridinedicarboxylic acid chloride and 2,6-diaminopyridine. These complexes have been characterized by XRD, 1H NMR, IR, UV-vis DRS, Element analysis and TGA. Their catalytic activities in allylic oxidation of cyclohexene and isophorone with molecular oxygen as primary terminal oxidant were investigated for the first time. The influences of reaction temperature, the amount of catalyst and reaction time on the oxidation of cyclohexene by Co-L were also investigated. The results show that the Co-L can be obtained optimum catalytic efficiency, giving 58.2% conversion of cyclohexene and maximum selectivity of 83.4% for 2-cyclohexene-1-one; 15.4% conversion of isophorone and 46.2% selectivity of ketoisophorone. The heterogeneous catalysts can be easily separated for reuse at least three times without any significant change in selectivity. Keywords: Allylic oxidation, cyclohexene, macrocylic picolinamide, metal organic complexes, molecular oxygen, α-isophorone.

Allylic oxidation of cyclohexene over ruthenium-doped titanium-pillared clay

Ruthenium-doped H-Montmorillonite (H-Mont) and Ti-pillared clay (Ti-PILC) were prepared then studied for oxidation of cyclohexene, with tert-butylhydroperoxide (TBHP) as the oxygen source.

Catalytic behavior of melamine glyoxal resin towards consecutive oxidation and oxy-Michael addition

Synthesis of melamine glyoxal resin involves a catalyst-free, one pot reaction between melamine and glyoxal in DMF. The synthesized resins have a similar morphological arrangement to that of layered materials as depicted by their XRD pattern and Raman spectra. The catalytic behavior of melamine glyoxal resin (MGR) have been studied in allylic oxidation of cyclohexene and simultaneous Michael addition. The MGR/solvent/O2 oxidant system can be regarded as a metal-free, additive-free, cost-effective and environmentally benign catalytic system. The oxidative behavior of MGR is attributed to its ability to generate in situ organic peroxide species during the course of reaction. Generation of peroxide species is confirmed by the KI/starch test and further confirmed by the complete suppression effect of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) over oxidation. The activity for Michael addition can be attributed to the presence of a higher content of nitrogen atoms, which serves as the active site. In oxidation, 28.1% conversion of cyclohexene with 37.19 and 62.81% selectivities for cyclohexenol and cyclohexenone were observed, respectively. In consecutive oxidation and oxy-Michael addition, 31.5% conversion of cyclohexene was observed with selectivities of 61.6% for cyclohexenone and 38.4% for alkoxy product.

Copper metal–organic framework: Structure and activity in the allylic oxidation of cyclohexene with molecular oxygen

Cu-MOF [Cu(bpy)(H 2O) 2(BF 4) 2(bpy)] (bpy: 4,4′-bipyridine) shows promising catalytic activity and high selectivity in allylic oxidation of cyclohexene with molecular oxygen as the only oxidant. Under close to ambient conditions and in the absence of solvent the selectivity in cyclohexene hydroperoxide reached 90%. The combined catalytic, spectroscopic, thermogravimetric, and electron microscopic study indicates that the reaction occurs at the surface of the latent porous framework and both bpy and water are involved in the active complex. Removal of the structural water at 100 °C in vacuum induces a crystal-to-crystal restructuring and opens the pores but eliminates the oxidation activity. Rehydration under ambient conditions in air regenerates Cu-MOF with small structural changes and each dehydration–rehydration cycle increases the oxidation activity. Not only dehydration–rehydration but also stirring the slurry during oxidation induces remarkable changes in the shape and size of the crystallites.

Photocatalytic Aerobic Epoxidation of Alkenes under Visible Light Irradiation by an Iron(III) Porphyrin with Mg–Al Hydrotalcite Anionic Clay

Abstract In photocatalytic aerobic oxidation of cyclohexene catalyzed by 5,10,15,20-tetrakis(pentafluorophenyl)porphyriniron(III) chloride [Fe(TPFPP)Cl] under visible light irradiation, the coexistence of solid bases was found to enhance the selectivity to cyclohexene oxide drastically. In the absence of solid bases, however, only the allylic oxidation of cyclohexene was catalyzed by the porphyrin complex acting as a sensitizer. Among the various metal oxides investigated, hydrotalcite exhibited the highest conversion of cyclohexene and selectivity to cyclohexene oxide.

Allylic Oxidation of Cyclohexene with Molecular Oxygen Using Cobalt Resinate as Catalyst

Allylic oxidation of cychohexene under atmospheric pressure of molecular oxygen was carried out over cobalt resinate in the absence of solvent. It was shown that cobalt resinate exhibited promising catalytic activity for the oxidation of cyclohexene to 2-cyclohexen-1-ol and 2-cychohexen-1-one under mild condition for the first time.

Synthesis and catalysis of tungsten oxide in hexagonal mesoporous silicas (W-HMS)

Hexagonal mesoporous silicas containing tungsten complexes have been synthesized through the condensation of tetraethoxysilane templated by an amphiphilic diblock copolymers modified with tungsten isocyanide complexes under acidic conditions. Upon calcination, the tungsten complex was transformed into its oxide, which was deposited inside the channels. This material is illustrated to be a good catalyst on the allylic oxidation of cyclohexene in the presence of hydrogen peroxide under mild conditions. In addition, this catalyst could be easily recovered after the reaction and re-used without any significant loss of its activity.

Allylic oxidation of cyclohexene over silica immobilized iron tetrasulfophthalocyanine

Iron tetrasulfophthalocyanine was immobilized on silica (FePcS–SiO 2) and its activity examined on the allylic oxidation of cyclohexene using TBHP as oxidant. Under our reaction conditions, attack of the activated C–H bond was preferred instead of the epoxidation of C C bond, yielding 2-cyclohexen-1-one as the main product. μ-Oxo dimeric (d-FePcS) appears to be the active species for this reaction.

Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins

A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios. The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated up to Si/Ti = 50 successfully without forming any extra framework TiO2. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD, FTIR, UVDRS, 29SiMASNMR, BET surface area and pore size distribution techniques.

Chiral 2-pyridyl alcoholate copper complexes: crystal structures of [bis(2-pyridyl alcoholate)copper(II)] and the use of [(2-pyridyl alcoholate)copper(II)] +and [(2-pyridyl alcoholate)copper(I)] in asymmetric cyclopropanation of styene and allylic oxidation of cyclohexene

Chiral N,O pyridine alcohols HL 1– HL 6 were used to form complexes with copper(II) ions. Ligands HL 1 and HL 2 formed complexes with copper(II) ions when Cu(OAc) 2 and HL were refluxed in methanol/ethanol mixture. Ligand HL 3 formed a complex with copper(II) when deprotonated with NaH and stirred in a Cu(II) acetate THF solution. Ligands HL 4– HL 6 did not form complexes with copper(II) under similar conditions. Two complexes, [Cu( L 1) 2] and [Cu( L 2) 2], were isolated as single crystals and characterized by X-ray crystallography. These complexes showed low catalytic activities in asymmetric reactions. However, they became active when reacted with triflic acid. Copper complexes, [Cu( L)] or [Cu( L)] +, formed in situ by reacting ligands HL with copper(I) or (II) ions, respectively, were also found to be active copper catalysts for asymmetric cyclopropanation of styrene with ethyl diazoacetate and allylic oxidation of cyclohexene with t-butylperoxybenzoate. Enantioselectivities up to 56% and 38% were obtained in asymmetric cyclopropanation of styrene and asymmetric allylic oxidation of cyclohexene, respectively.

Synthesis of chiral 2,2′-dipyridylamines and their use in the copper-catalyzed asymmetric allylic oxidation of cyclohexene

Chiral dipyridylamines have been synthesized by N-arylation reactions, and the applicability of those compounds to the copper-catalyzed asymmetric allylic oxidation of cyclohexene was demonstrated.

Allylic oxidation of cyclohexene over chromium containing mesoporous molecular sieves

Allylic oxidation of cyclohexene was carried out over mesoporous (Cr)MCM-41 and (Cr)MCM-48 molecular sieve catalysts. In both the cases, 2-cyclohexen-1-one was obtained as the major product with small amounts of cyclohexene oxide and 1,2-cyclohexandiol. (Cr)MCM-48 showed higher activity than (Cr)MCM-41 owing to the high chromium content in the former. The use of polar solvents such as acetonitrile and methanol decrease the 2-cyclohexen-1-one selectivity; however, such a procedure produces double bond oxidized product, viz. cyclohexene oxide. Furthermore, unlike many other chromium-based solid catalysts, the activity over recycled as well as washed (Cr)MCM-41 and (Cr)MCM-48 remains nearly the same, indicating that the mesoporous chromosilicate materials behave truly as heterogeneous catalysts. In other words, after the initial loss of non-framework chromium ions for the first time, no leaching was noticed for the chromium-based systems.

Chiral phenanthrolines as ligands for Cu(I)-catalyzed asymmetric allylic oxidation

A number of chiral 1,10-phenanthrolines (phens) have been assessed in asymmetric Cu(I)-catalyzed allylic oxidation of cyclohexene. Very effective copper-phen catalysts are obtained only when these ligands bear at least a substituent close to the reactive site of the catalyst. Enantioselectivity up to 36% was obtained.

Selective copper-catalyzed allylic oxidations using a 1/1 ratio of cycloalkene and tert-butylperbenzoate

With Cu(MeCN) 4BF 4 as catalyst and benzotrifluoride as solvent, the allylic oxidation of cyclohexene by tert-butyl perbenzoate was performed at room temperature in 75% yield without requiring an axcess of the olefin. The benzoyloxylation of other cycloalkenes in using such a substrate/perester ratio required additives such as DBU, DBN or DMAP, and often an increase of the reaction temperature.

Photooxidation of cyclohexene and benzene with oxygen by fullerenes grafted on mesoporous FSM-16

Fullerenes (C60 and C70) are grafted on mesoporous FSM-16 (pore size 2.7 nm), and the grafted fullerenes showed high activities (TON up to 3070 in 9 h) for allylic oxidation of cyclohexene with oxygen in benzene under the irradiation of UV-vis light. In these reactions, phenol is also formed by the oxidation of benzene with cyclohexene hydroperoxide produced in the allylic oxidation of cyclohexene.