Photo‐Electrochemical C−H Bond Activation of Cyclohexane Using a WO3 Photoanode and Visible Light

The photo‐electrochemical C?H bond activation of cyclohexane to produce cyclohexanol and cyclohexanone (KA oil) with high partial oxidation selectivity (99 %) and high current utilization ratio (76 %) was achieved in air at room temperature at atmospheric pressure. The production rate of KA oil was accelerated by applying a bias. The incident photon to current efficiencies at 365 and 420 nm were 57 % and 24 %, respectively.     

Zeolite-Y entrapped bivalent transition metal complexes as hybrid nanocatalysts: density functional theory investigation and catalytic aspects

The intriguing research toward the exploitation of zeolite-Y-based hybrid nanocatalysts for catalytic oxidation reactions has been growing significantly. In the present investigation, we describe the synthesis of zeolite-Y entrapped transition metal complexes of the general formulae [M(SFCH)·xH₂O]-Y (where, M = Mn, Fe, Co, Ni (x = 3) and Cu (x = 1)); H₂SFCH = (E)-N′-(2-hydroxybenzylidene)furan-2-carbohydrazide]. These nanocatalysts have been characterized by various physicochemical techniques. Density functional theory calculations are performed to address the relaxed geometry, bond angle, bond length, dihedral angle, highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap, and electronic density of states of H₂SFCH ligand and their neat transition metal complexes. The observed HOMO–LUMO gap and the Fermi energy is higher for Cu(II) complexes, which demonstrates the better catalytic activity of this nanocatalyst. The catalytic activity was performed in liquid-phase oxidation of cyclohexane using hydrogen peroxide as oxidant to give cyclohexanone (CyONE) and cyclohexanol (CyOL). Among them, [Cu(SFCH)·H₂O]-Y catalyst has the highest selectivity toward CyONE (84.5%).     

无溶剂体系中非均相催化剂催化环己烷氧化反应研究

本文合成了苯乙烯-马来酸酐共聚物(SMA)桥联N-羟基邻苯二甲酰亚胺(NHPI)和Co/ZSM-5两种非均相催化剂, 用FT-IR、 XRD进行了结构表征. 考察了这两种非均相催化剂在无溶剂体系中对环己烷的催化氧化行为, 并对各反应因素的影响进行了研究. 结果表明: 在最佳反应条件下, 环己烷的转化率可达26.8%, 此时KA油、己二酸和环己基过氧化氢的选择性分别为71.6%、 10.9% 和2.6%. 在测试温度范围内, 反应速率常数Ka 和反应温度之间存在Arrhenius关系, 相关系数是0.9878, 数学表达式为lnKa = -3012/ T+ 1.279. 催化剂的稳定性研究显示两种非均相催化剂都具有很高的热力学稳定性, 可以重复使用五次.     

Reductive amination of cyclohexanol/cyclohexanone to cyclohexylamine using SBA-15 supported copper catalysts

Amination of cyclohexanol was investigated in vapour phase over copper catalysts supported on mesoporous SBA-15. The different products identified during reductive amination of cyclohexanol reaction were cyclohexanone, cyclohexylamine, along with small amounts of N-Cyclohexylidinecyclohexylamine and dicyclohexylamine. Among several catalysts tested for the reductive amination, 5% Cu supported on SBA-15 exhibited better catalytic performance than other catalysts with 36% selectivity towards cylclohexylamine at 80% cyclohexanol conversion. The optimum reaction conditions employed to achieve the best catalyst performance were at 250 °C, 0.1 MPa of H₂/NH₃, TOS-10h. The active Cu sites, acidity of the catalyst, and effect of reaction parameters play a pivotal role in the reductive amination reaction. The prepared catalysts were characterized by XRD, BET, SEM, H₂-TPR and NH₃-TPD. The dispersion of Cu, particle size, and metal surface area (m²/g) calculated from pulse N₂O decomposition method. TPR findings reveal the presence of substantially dispersed copper oxide species at lower loadings which is easily reducible than the bulk copper oxide species found at higher Cu loadings. The acidity measurements by NH₃-TPD analysis suggest that the maximum acidic strength was obtained at 5 wt% copper on porous SBA-15, and decreased with Cu loadings. The catalytic properties are well in agreement with the findings of catalysts characterization.     

Efficient magnetic CoFe2O4 nanocrystal catalyst for aerobic oxidation of cyclohexane prepared by sol–gel auto-combustion method: effects of catalyst preparation parameters

Six magnetic spinel-type CoFe₂O₄ samples were prepared in the form of powder by a simple sol–gel auto-combustion method from precursor solutions with different metal concentrations (0.1–0.3 mol L^?1) and pH values (<1–10). The samples were characterized by X-ray diffractometry, Fourier transform infrared spectrophotometry, transmission electron microscopy and N₂-physisorption. Their catalytic performances for oxidation of cyclohexane were evaluated using oxygen as oxidant in the absence of solvents. The results show that pH values and metal concentrations of precursor solutions play important roles in the sizes, dispersions and morphologies of the CoFe₂O₄ nanoparticles, and thus in their catalytic performances. The sample resulted from precursor solution under the conditions of pH = 7 and metal concentration = 0.1 mol L^?1 with the largest surface area, exhibited the best catalytic performance with the highest cyclohexane conversion of 13.7 % and selectivity of 93.9 % for cyclohexanol and cyclohexanone. The CoFe₂O₄ nanocrystal is also found an efficient catalyst for oxidation of aliphatic and aromatic alkenes.     

三氯化钌催化下环己烷和环己醇在离子液体中的氧化反应研究

在三氯化钌催化下,使用叔丁基过氧化氢在离子液体中可将环己烷和环己醇氧化为环己酮,结果表明环己醇的氧化具有较高的转化率和选择性．离子液体(bmim)^ PF6^-和催化剂三氯化钌均有一定的重复使用性．     

Oxidations by the system ‘hydrogen peroxide-[Mn2L2O3][PF6]2 (L=1,4,7-trimethyl-1,4,7-triazacyclononane)-carboxylic acid’. Part 10: Co-catalytic effect of different carboxylic acids in the oxidation of cyclohexane, cyclohexanol, and acetone

Hydrogen peroxide oxidation of cyclohexane in acetonitrile solution catalyzed by the dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (L=1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN) at 25 °C in the presence of a carboxylic acid affords cyclohexyl hydroperoxide as well as cyclohexanone and cyclohexanol. A kinetic study of the reactions with participation of three acids (acetic acid, oxalic acid, and pyrazine-2,3-dicarboxylic acid, 2,3-PDCA) led to the following general scheme. In the first stage, the catalyst precursor forms an adduct. The equilibrium constants K₁ calculated for acetic acid, oxalic acid, and 2,3-PDCA were 127±8, (7±2)×10⁴, and 1250±50 M⁻¹, respectively. The same kinetic scheme was applied for the cyclohexanol oxidation catalyzed by the complex in the presence of oxalic acid. The oxidation of cyclohexane in water solution using oxalic acid as a co-catalyst gave cyclohexanol and cyclohexanone, which were rapidly transformed into a mixture of over-oxidation products. In the oxidation of cyclohexanol to cyclohexanone, varying the concentrations of the reactants and the reaction time we were able to find optimal conditions and to obtain the cyclohexanone in 94% yield based on the starting cyclohexanol. Oxidation of acetone to acetic acid by the system containing oxalic acid was also studied.     

The Mechanism Study on the Catalytic Synthesis of 2,6‐Dimethylphenol from KA‐Oil and Methanol over Magnesium Oxide Catalysts

Catalytic synthesis of 2,6‐dimethylphenol from KA‐oil (a mixture of cyclohexanol and cyclohexanone) and methanol was achieved by using magnesium oxide‐supported chromium oxide catalysts in one step. At higher conversion (> 90%), dimethylphenol was formed in high yield (>60 %). The activity of Cr/MgO catalysts depended on the concentration of chromium. The yield of 2,6‐dimethylphenol was also affected by the composition of the ratio of cyclohexanol to cyclohexanone in KA‐oil. Cyclohexanol and cyclohexanone reacting with methanol under the same conditions indicated that pure cyclohexanol or cyclohexanone is less reactive than their mixture, KA‐oil. The adsorption properties of cyclohexanol and cyclohexanone on the surface of Cr/MgO determined by FT‐IR spectroscopy suggest that cyclohexanone is easily reduced to cyclohexanol by the hydrogen which formed in the reaction, and then further reacted with methanol to form 2,6‐dimethyphenol.     

Temperature dependence of catalytic cyclohexane partial oxidation in a polytetrafluoroethylene reactor

Polymer-supported Co(II) catalyst was prepared and its activity and selectivity in the partial oxidation of cyclohexane was determined at several temperatures in a polytetrafluoroethylene reactor (PTFE). The catalyst was characterized by means of SEM-EDX, FTIR, diffuse reflectance UV-Vis, N₂ sorption, and mecury porosimetry. Activation energies were determined under steady state conditions for the net production of cyclohexanone and cyclohexanol and for cyclohexane and oxygen net consumption. Some activation energies were lower than the ones reported for the uncatalyzed process, indicating that the catalyst played an important role in the initiation of the free-radical reaction. The text was submitted by the authors in English.     

Mild Oxidation of Cyclohexane Catalyzed by Cobalt(II) Acetate and Initiated by H2O2 in the Acetic Acid Medium

The homogeneous catalytic oxidation of cyclohexane by molecular oxygen and hydrogen peroxide in a solution of acetic acid (HOAc) in the presence of cobalt(II) acetate Co(OAc)₂ is studied. The high yields of cyclohexanol, cyclohexanone, and cyclohexyl hydroperoxide (0.10–0.15 mol/l) and the high rate of the process (w = 10^–5–10^–4 mol l^–1 s^–1) are explained by (1) mild conditions of oxidation in the medium of the HOAc solvent and (2) efficient initiation of the process due to the fast kinetics-controlled dissociation of H₂O₂ into radicals in the studied reaction medium under the action of cobalt cations. Quantitative relationships are found for the cyclohexane oxidation rate, the yield of target products, and the ratio of reactants participating in the process. The effect of hydrogen hydroperoxide additives on the concentrations of reduced and oxidized forms of the catalyst is studied by spectrophotometry in model mixtures. Quantum chemistry is employed to calculate the probabilities of some key elementary reactions. Calculated data agree well with the experiment.     

咪唑修饰硅胶配位固载锰(Ⅲ)卟啉对环己烷空气氧化的催化作用

应用3-氯丙基三甲氧基硅烷和咪唑成功地对硅胶表面进行了修饰,并通过咪唑基纵轴配位方式固载了四苯基锰(Ⅲ)卟啉.在无任何外加溶剂及共还原剂的条件下,应用此高分子金属卟啉作为催化剂,选择性地催化空气氧化环己烷为环己酮和环己醇.研究结果表明,与未固载金属卟啉相比,固载金属卟啉具有更高的催化活性和催化选择性,反应具有更高的酮醇比,催化剂的稳定性有了较大的提高,便于回收和重复使用.另外还探讨了载体在此催化体系中对催化性能的影响.     

Performance and pathways of electrochemical cyclohexane oxidation

Falling costs of electricity from renewable and non-renewable sources have motivated interest in electrochemical production of chemicals and fuels. Among commodity chemicals, the production of KA oil (cyclohexanol and cyclohexanone) from cyclohexane is attractive as selective alkane oxidation remains a major industrial challenge. Although this reaction has been demonstrated in the literature, its fundamental chemistry remains poorly understood. This review identifies possible pathways for the reaction mechanism, their experimental support, and remaining critical gaps in molecular understanding of electrochemical cyclohexane oxidation to KA oil.     

SYNTHESIS AND CHARACTERIZATION OF A SILICA-SUPPORTED CARBOXYMETHYLCELLULOSE PLATINUM COMPLEX AND ITS CATALYTIC BEHAVIORS FOR HYDROGENATI0N OF AR0MATICS

A silica-supported carboxymethylcellulose platinum complex (abbreviated as SiO_2-CMC-Pt) has been prepared and characterized by XPS. Its catalytic properties for hydro-genation of aromatic compounds were studied. The results showed that this catalystcould catalyze the hydrogenation of phenol, anisol, p-cresol, benzene and toluene to cyclo-hexanol, cyclohexyl methyl ether, p-methyl cyclohexanol, cyclohexane and methylcyclo-hexane, respectively in 100% yield at 30℃ and 1 atm. In the hydrogenation of phenol,COO/Pt ratio in SiO_2-CMC-Pt has much influence on the initial hydrogenation rate andthe selectivity for the intermediate product, cyclohexanone. The highest initial rate andthe highest yield of cyclohexanone both occur at COO/Pt ratio of 6. The complex is stableduring the reaction and can be used repeatedly.     

Catalytic oxidation of cyclohexane over Cu-Zn-Cr ternary spinel systems

Spinel systems with the composition of Cu_1−xZn_xCr₂O₄ [x = 0 CCr, x = 0.25 CZCr-1, x = 0.5 CZCr-2, x = 0.75 CZCr-3 and x = 1 ZCr] were prepared by homogeneous co-precipitation method and were characterized by X-ray diffraction (XRD) and FT-IR spectroscopy. Elemental analysis was done by EDX, and surface area measurements by the BET method. The redox behavior of these catalysts in cyclohexane oxidation at 243 K using TBHP as oxidant was examined. Cyclohexanone was the major product over all catalysts with some cyclohexanol. 69.2% selectivity to cyclohexanol and cyclohexanone at 23% conversion of cyclohexane was realized over zinc chromite spinels in 10 h.     

间歇电沉积法制备纳米MnOx/Ti膜电极及其催化氧化环己烷性能

高选择性氧化环己烷（CHA）制备环己酮和环己醇（KA油）具有重要的工业价值和应用前景. 本文提出采用间歇电沉积法制备纳米MnO_x催化剂负载多孔管式钛膜,构建电催化膜反应器（ECMR）催化氧化环己烷制备环己醇和环己酮. 利用场发射扫描电子显微镜（FESEM）、X射线衍射仪（XRD）和电化学工作站等表征手段对催化剂的结构与性能进行表征. 结果表明,间歇电沉积法制备的催化剂为纳米花球状γ-MnO₂. 与基体钛膜相比,MnO_x/Ti膜电极具有更优的电化学性能和传质性能. 此外,以MnO_x/Ti电催化膜为阳极,不锈钢网为阴极构建ECMR. 当环己烷初始浓度30 mmol·L^-1、反应温度30^oC、停留时间34.3 min、电流密度2.3 mA·cm^-2等条件下,ECMR环己烷转化率达25.6%,KA油总选择性高于99%. 同时,ECMR重复使用8次后表现较高催化稳定性.     

铋改性的钒磷氧化物液相催化氧化环己烷的反应机理

 制备了铋改性的钒磷氧化物(Bi-VPO)催化剂,并将其用于液相催化氧化环己烷,研究了该反应的反应机理. 结果表明,铋改性可大大提高VPO催化剂在温和条件下对环己烷液相氧化的催化性能. 无溶剂实验和四氢呋喃作溶剂的实验证明反应过程中溶剂乙腈和H2O2之间存在相互作用; 自由基捕捉实验证明环己烷氧化过程中存在自由基反应历程; 环己醇氧化实验证明环己酮并不是来自环己醇的氧化,而是由环己烷直接氧化得到的.     

A polymer-anchored cobalt(II) complex as a reusable catalyst for oxidation of benzene,ethylbenzene and cyclohexane

A polymer-supported cobalt complex of 2,6-bis(benzimidazolyl)pyridine (BBP) was synthesized by immobilization of BBP on chloromethylated polystyrene cross-linked with 6.5 % divinylbenzene, followed by complexation with CoCl₂ in methanol, and characterized by physico-chemical and spectroscopic methods. The polymer-bound Co(PS–BBP)Cl₂ was found to be more stable compared to free Co(BBP)Cl₂ as determined by TGA analyses. The catalytic activity of Co(PS–BBP)Cl₂ was investigated towards oxidation of benzene, ethylbenzene and cyclohexane using tert-butylhydroperoxide as oxidant. At optimum conditions, benzene showed 72.6 % conversion with 100 % selectivity towards phenol; ethylbenzene exhibited 97.0 % conversion with 82.5 and 17.4 % selectivity towards benzaldehyde and acetophenone, respectively, whilst conversion of cyclohexane was 60.0 with 75.8 and 24.1 % selectivity towards cyclohexanol and cyclohexanone. The unsupported complex Co(BBP)Cl₂ showed lower activities and selectivities compared to the polymer-supported complex. Co(PS–BBP)Cl₂ was found to be very active and reusable, giving high yields of the desired products. A possible reaction mechanism is proposed for these oxidation reactions.     

Efficient catalytic cycloalkane oxidation employing a "helmet" phthalocyaninato iron(III) complex

We have examined the catalytic activity of an iron(III) complex bearing the 14,28-[1,3-diiminoisoindolinato]phthalocyaninato (diiPc) ligand in oxidation reactions with three substrates (cyclohexane, cyclooctane, and indan). This modified metallophthalocyaninato complex serves as an efficient and selective catalyst for the oxidation of cyclohexane and cyclooctane, and to a far lesser extent indan. In the oxidations of cyclohexane and cyclooctane, in which hydrogen peroxide is employed as the oxidant under inert atmosphere, we have observed turnover numbers of 100.9 and 122.2 for cyclohexanol and cyclooctanol, respectively. The catalyst shows strong selectivity for alcohol (vs. ketone) formation, with alcohol to ketone (A/K) ratios of 6.7 and 21.0 for the cyclohexane and cyclooctane oxidations, respectively. Overall yields (alcohol + ketone) were 73% for cyclohexane and 92% for cyclooctane, based upon the total hydrogen peroxide added. In the catalytic oxidation of indan under similar conditions, the TON for 1-indanol was 10.1, with a yield of 12% based upon hydrogen peroxide. No 1-indanone was observed in the product mixture.     

Photooxidation of cyclohexane by (Bu4N)2Cr4O13 in acetonitrile or CH2Cl2

Upon irradiation using light with >520 nm, (Bu ₄N)₂Cr₄O₁₃ oxidizes cyclohexane to cyclohexanol as the major product and cyclohexanone in acetonitrile and to cyclohexanol as the major product, cyclohexanone, and cyclohexyl chloride in CH₂Cl₂. Carrying out this reaction in the presence of air leads to a sharp increase in the yield of cyclohexanone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 212–213, January, 1990.     

Unexpected high oxidation of cyclohexane by Fe salts and dihydrogen peroxide in acetonitrile

The reaction of cyclohexane (CyH) with 1.5 equivalent of dihydrogen peroxide (30% aqueous solution) in the presence of 1 mol% of an iron(II) or iron(III) salt (without added ligand), at 50 °C in acetonitrile, produces cyclohexanol (CyOH) and cyclohexanone (CyO) in high yields (up to 87% of CyH is converted to CyOH + CyO). Remarkably, CyH is totally converted within 2 h in the presence of Fe(ClO₄)₂ as catalyst under argon, producing 45% of CyOH and 42% of CyO. The addition of a tridentate Schiff-base ligand, namely 2,6-bis-[1-(benzylimino)ethyl]pyridine (dapb), leads to a clear increase of the selectivity towards CyOH + CyO, which are obtained with an overall yield of 93% (and even 100% selectivity to CyOH and CyO) in the case of the [Fe(ClO₄)₃/dapb] catalytic system.