Cyclohexyl Hydroperoxide Research Articles

Infrared signature of the hydroperoxyalkyl intermediate (·QOOH) in cyclohexane oxidation: An isomer-resolved spectroscopic study.

Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010cm-1 (∼10-20kcal mol-1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products.

Epoxidation of cyclohexene with cyclohexyl hydroperoxide

Objectives. To investigate the regularities of the process of joint production of epoxycyclohexane, cyclohexanol, and cyclohexanone using the cyclohexene epoxidation reaction with cyclohexyl hydroperoxide in the presence of an ammonium paramolybdate catalyst, representing an alternative to the method of cyclohexanol and cyclohexanone synthesis by alkaline catalytic decomposition of cyclohexyl hydroperoxide.Methods. The qualitative and quantitative analysis of the obtained intermediate and target compounds was determined using modern physicochemical research methods: gas–liquid chromatography using the Chromatec-Crystal 5000.2 hardware and software complex with a flame ionization detector and infrared spectroscopy on an RX-1 infrared Fourier spectrometer. The content of hydroperoxide in the oxidation products was determined using iodometric titration, while the carboxylic acid content was determined by the titrimetric method based on the neutralization reaction.Results. The presented method for obtaining cyclohexanol and cyclohexanone together with epoxycyclohexane by the reaction of cyclohexene epoxidation with cyclohexyl hydroperoxide containing cyclohexane in the products of high-temperature liquid-phase oxidation is experimentally substantiated. The influence of various technological parameters on the process of liquid-phase oxidation of cyclohexane to hydroperoxide is described. The conditions for carrying out this reaction are determined to ensure the achievement of a content of cyclohexyl hydroperoxide of 1.5 wt % in the products of oxidation. The regularities of the epoxidation reaction of the synthesized cyclohexyl hydroperoxide with cyclohexene in the presence of an ammonium paramolybdate catalyst are analyzed.Conclusions. Epoxidation of cyclohexene with cyclohexyl hydroperoxide produced epoxycyclohexane at a yield of 80–90% and a conversion of cyclohexane hydroperoxide of 85%.

Vibrational spectroscopy and dissociation dynamics of cyclohexyl hydroperoxide.

Organic hydroperoxides (ROOH) are ubiquitous in the atmospheric oxidation of volatile organic compounds (VOCs) as well as in low-temperature oxidation of hydrocarbon fuels. The present work focuses on a prototypical cyclic hydroperoxide, cyclohexyl hydroperoxide (CHHP). The overtone OH stretch (2νOH) spectrum of jet-cooled CHHP is recorded by IR multiphoton excitation with UV laser-induced fluorescence detection of the resulting OH products. A distinctive IR feature is observed at 7012.5 cm-1. Two conformers of CHHP are predicted to have similar stabilities (within 0.2 kcal mol-1) and overtone OH stretch transitions (2νOH), yet are separated by a significant interconversion barrier. The IR power dependence indicates that absorption of three or more IR photons is required for dissociation of CHHP to cyclohexoxy (RO) and OH radical products. Accompanying high-level single- and multi-reference electronic structure calculations quantitatively support the experimental results. Calculations are extended to a range of organic hydroperoxides to examine trends in bond dissociation energies associated with RO + OH formation and compared with prior theoretical results.

“Chair”–“Boat” Conformational Transition of Cyclohexanone during the Oxidation of Cyclohexane

The B3LYP/6-311g++(d,p), G3, and CBS-QB3 methods (DFT) have been used to calculate the free energy and equilibrium constants of the “chair”–“boat” conformational transition of cyclohexanone in the temperature range 298.15–428.15 K. The equilibrium composition of the chair and boat conformers of cyclohexanone has been calculated. It has been shown that with an increase in the proportion of the boat conformation, the selectivity of the process of cyclohexane oxidation to cyclohexanone decreases. The transition states of addition reactions of cyclohexyl hydroperoxide at the carbonyl group of cyclohexanone for chair and boat conformations have been found by the QST2 method. The energy profiles of these reactions have been calculated. It has been established that the addition of hydroperoxide to the carbonyl group of the boat conformation of the ketone is accompanied by a transition to the chair conformation.

One-step highly selective catalytic oxidation of cyclohexane to KA-oil over functional CeMn0.5Co0.5Ox composite oxide: Synergistic effects between Mn and Co species with different valences and metal ion ratios

Presently, one-step highly selective oxidation of cyclohexane to KA-oil, which is a crucial organic chemical intermediate for the production of ε-caprolactam and adipic acid, is still a tremendous challenge. In this work, the functional CeMn0.5Co0.5Ox composite oxide catalysts were successfully prepared by glycine-nitrate combustion method. The results showed that 93.0% of selectivity to KA-oil with 4.6% of cyclohexane conversion was achieved over CeMn0.5Co0.5Ox under the optimal reaction conditions. The experimental and characterization results showed that the excellent catalytic performance of CeMn0.5Co0.5Ox is attributed to the synergistic effects between Mn and Co species with different valences and metal ion ratios, which efficiently promote the directional decomposition or reduction of cyclohexyl hydroperoxide (CHHP) intermediate to KA-oil. The density functional theory (DFT) calculations further confirmed the synergistic catalysis of CeMn0.5Co0.5Ox in the selective oxidation. This work affords the new insights into the design of efficient catalyst for the selective oxidation of alkanes.

Cycloalkane Oxidation Catalyzed by Copper‐based Catalysts with H2O2 under Mild Conditions

AbstractCopper‐catalyzed cycloalkane oxidation using H2O2 as an oxidant was investigated under mild conditions. The copper catalysts studied in this work ranged from commercially‐available copper(II) salts to copper(II) complexes containing polypyridyl ligands. Various factors that affected catalytic activity of copper catalysts were elucidated. It was found that geometry of the copper complex in solution and coordinated anions played important roles in catalytic activity. The copper(II) complex generated in‐situ by mixing Cu(OAc)2 and TMPA ligand (TMPA=tris(2‐pyridylmethyl)amine) adopted trigonal bipyramidal geometry and was competent to catalyze cyclohexane oxidation with higher yields, compared to those of other Cu2+ species used in this work. The optimal catalytic condition was achieved using 1.0 % mol of Cu(OAc)2/TMPA and 10 equivalents of H2O2 with respect to cyclohexane in CH3CN at 33–35 °C for 3 hours, resulting in the total product yield of 44 %. Moreover, since cyclohexyl hydroperoxide was detected as a major product, the Fenton‐like mechanism via one electron process was proposed as a plausible mechanism in this cycloalkane oxidation. In addition, our catalytic system was further demonstrated to be applicable for oxidation of various cycloalkane substrates with moderate yields and relatively short time.

Fe3O4@MOF hybrid for supercilious recovery of Au(III) and Pd(II) from e-waste and spent as catalysts for cyclohexane oxidation

Improving the economic viability of the most successful precious metal catalysts is one of the significant challenges in renewable energy production. We designed a magnetic hybrid material based on Cu-pPDA MOF and Fe3O4 nanosphere for selective recovery of Au(III) and Pd(II) from e-waste. Owing to its superior maximum adsorption capacities of 1450 and 1236 mg/g for Au (III) and Pd(II), respectively, at 45 °C with the pH of 3 and 1, the sorbed samples were converted into catalysts through an annealing process to obtain carbon supported FeAu and FePd nanoparticles catalysts (FeAu/C and FePd/C). Furthermore, these catalysts were applied for the oxidation of cyclohexane and resulted that FeAu/C catalyst exhibited higher conversion rate of cyclohexane (93.2%) than FePd/C catalyst (88.3%). Mechanistic investigations suggested that synergetic effect of Fe and Au on the supported carbon promoted better bond cleavage of the O–O bond in cyclohexyl hydroperoxide, a crucial intermediate species in the oxidation of cyclohexane. This study provides an alternate approach for the sustainable preparation of highly desired catalytic materials.

Conformational analysis of cyclohexyl hydroperoxide by rotational spectroscopy

Cyclohexyl hydroperoxide was observed in the gas phase using a supersonic expansion coupled with broadband chirped-pulse Fourier transform microwave spectroscopy. Cyclohexyl hydroperoxide is a simple but important organic peroxide due to its rather high stability in solution and because of its applications in polymer industry. Furthermore, it is one of the products of the oxidation process of cyclohexane. We detected this molecule in the spectrum of a complex non-commercial sample containing many molecular species from the oxidation of cyclohexane. The peroxy group O-O-H gives flexibility to the molecule and results in different stable conformations. Each of the conformations presents two equivalent forms due to the high symmetry of cyclohexane. From the dataset of rotational constants observed, we determined a partial effective structure for cyclohexyl hydroperoxide and compared it with other peroxides studied in the gas phase.

Hybrid Silsesquioxane/Benzoate Cu7-Complexes: Synthesis, Unique Cage Structure, and Catalytic Activity

A series of phenylsilsesquioxane-benzoate heptacopper complexes 1-3 were synthesized and characterized by X-ray crystallography. Two parallel routes of toluene spontaneous oxidation (into benzyl alcohol and benzoate) assisted the formation of the cagelike structure 1. A unique multi-ligation of copper ions (from (i) silsesquioxane, (ii) benzoate, (iii) benzyl alcohol, (iv) pyridine, (v) dimethyl-formamide and (vi) water ligands) was found in 1. Directed self-assembly using benzoic acid as a reactant afforded complexes 2-3 with the same main structural features as for 1, namely heptanuclear core coordinated by (i) two distorted pentameric cyclic silsesquioxane and (ii) four benzoate ligands, but featuring other solvate surroundings. Complex 3 was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with hydrogen peroxide and tert-butyl hydroperoxide, respectively, at 50 °C in acetonitrile. The maximum yield of cyclohexane oxidation products as high as 32% was attained. The oxidation reaction results in a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone. Upon the addition of triphenylphosphine, the cyclohexyl hydroperoxide is completely converted to cyclohexanol. The specific regio- and chemoselectivity in the oxidation of n-heptane and methylcyclohexane, respectively, indicate the involvement of of hydroxyl radicals. Complex 3 exhibits a high activity in the oxidation of alcohols.

Alkane Oxidation with H2O2 Catalyzed by Dicopper Complex with 6-hpa Ligand: Mechanistic Insights as Key Features for Methane Oxidation

Abstract Alkane oxidations with H2O2 catalyzed by copper complexes [Cu2(µ-OH)(6-hpa)]3+ (1) and [Cu(MeCN)(tpa)]2+ (2) were examined. In the oxidation of cyclohexane (CyH), cyclohexyl hydroperoxide (CyO2H) was formed as the first product and converted to cyclohexanol (CyOH) with PPh3. The turnover frequency (TOF/h) and turnover number (TON) of 1 are 150 and 1030, respectively. The kinetic studies showed that the product formation rate, d[CyO2H]/dt, is proportional to [1] and [H2O2], and partly to [Et3N] and [H2O]. Solvent kinetic isotope effect kH2O/kD2O was 2.2, showing that a H2O molecule is involved in the rate-limiting step. tert-BuO2H disturbs the formation of a di(hydroperoxo) intermediate [Cu2(O2H)2(6-hpa)]2+ to reduce the d[CyO2H]/dt. The active species [Cu2(O•)(O2•)(6-hpa)]2+ was detected by CSI MS. The inhibitory effects of a radical trap reagent DMPO and CO gas revealed that 1 suppresses the HO• formation. Methane oxidation with H2O2 catalyzed by 1, 2, and related complexes was conducted using a high-pressure reactor. Key features for the high catalytic activity of 1 in the methane oxidation are the complex-based active species [Cu2(O•)(O2•)(6-hpa)]2+ capable of cleaving the strong C-H bond of methane and the long catalyst life enabled by the suppression of the HO• formation.

Enhanced flow electrochemistry for cyclohexane Conversion: From simulation to application

To further improve the capability of flow electrochemistry, the multistage plug-flow electrochemical membrane reactor (PF-ECMR) with membrane electrode was developed for enhancing the oxidation of cyclohexane (CHA) to produce KA oil (mixture of cyclohexanol and cyclohexanone). The catalytic results demonstrated that the CHA conversion and the selectivity to KA oil were up to 95.6% and > 99%, which was the highest in comparison with most of the state-of-the-art catalytic processes reported in the previous works. The mechanism was explored by density functional theory (DFT) calculations, indicating the auxo-action effect of cyclohexanone was beneficial for the formation of cyclohexyl hydroperoxide so as to enhance the CHA conversion. The excellent performance of PF-ECMR was also attributed to the staggered electric field and the accumulative effect of the multi-electrodes. This study provided a successful case of a combination of theoretical prediction and experimental verification together for organic synthesis.

Alkane Oxidation with H2O2 Catalyzed by OsO4-carboxylate Adduct and Its Application to Heterogeneous Catalyst

Abstract Cyclohexane is selectively oxidized to cyclohexyl hydroperoxide (P) by the reaction with hydrogen peroxide (H2O2) in the presence of a catalytic amount of osmium tetroxide (OsO4). The product is converted to cyclohexanol (A) by the treatment with PPh3. The catalytic reactivity of OsO4 is enhanced by adding a coordinative anion such as benzoate anion. Encouraged by this result, we have developed an OsO4-immobilized heterogeneous catalyst using mesoporous silica (SBA-15) containing carboxylate groups on the surface.

Decomposition of Cyclohexyl Hydroperoxide Catalyzed by Core-shell Material Co3O4@SiO2

Decomposition of Cyclohexyl Hydroperoxide Catalyzed by Core-shell Material Co₃O₄@SiO₂

Vanadium(IV) Complexes with Methyl-Substituted 8-Hydroxyquinolines: Catalytic Potential in the Oxidation of Hydrocarbons and Alcohols with Peroxides and Biological Activity.

Methyl-substituted 8-hydroxyquinolines (Hquin) were successfully used to synthetize five-coordinated oxovanadium(IV) complexes: [VO(2,6-(Me)2-quin)2] (1), [VO(2,5-(Me)2-quin)2] (2) and [VO(2-Me-quin)2] (3). Complexes 1–3 demonstrated high catalytic activity in the oxidation of hydrocarbons with H2O2 in acetonitrile at 50 °C, in the presence of 2-pyrazinecarboxylic acid (PCA) as a cocatalyst. The maximum yield of cyclohexane oxidation products attained was 48%, which is high in the case of the oxidation of saturated hydrocarbons. The reaction leads to the formation of a mixture of cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone. When triphenylphosphine is added, cyclohexyl hydroperoxide is completely converted to cyclohexanol. Consideration of the regio- and bond-selectivity in the oxidation of n-heptane and methylcyclohexane, respectively, indicates that the oxidation proceeds with the participation of free hydroxyl radicals. The complexes show moderate activity in the oxidation of alcohols. Complexes 1 and 2 reduce the viability of colorectal (HCT116) and ovarian (A2780) carcinoma cell lines and of normal dermal fibroblasts without showing a specific selectivity for cancer cell lines. Complex 3 on the other hand, shows a higher cytotoxicity in a colorectal carcinoma cell line (HCT116), a lower cytotoxicity towards normal dermal fibroblasts and no effect in an ovarian carcinoma cell line (order of magnitude HCT116 > fibroblasts > A2780).

Solvent-free partial oxidation of cyclohexane to KA oil over hydrotalcite-derived Cu-MgAlO mixed metal oxides

A highly efficient and stable hydrotalcite-derived Cu-MgAlO catalyst was developed for the partial oxidation of cyclohexane with molecular oxygen. The physical–chemical properties of Cu-MgAlO catalysts were studied, and the results indicated that the copper component had been successfully introduced into the hydrotalcite unit layer structure. The catalytic reaction results showed that copper as the active species could activate CH bond and effectively promote the decomposition of cyclohexyl hydroperoxide (CHHP) to the mixture of cyclohexanol and cyclohexanone (KA oil). 8.3% of cyclohexane conversion and 82.9% of selectivity for KA oil were obtained over 9%Cu-MgAlO catalyst at 150 °C with 0.6 MPa of oxygen pressure for 2 h. Especially, its catalytic performance was still stable after five runs.

Mononuclear iron(III) piperazine-derived complexes and application in the oxidation of cyclohexane

Oxygenated products from selective hydrocarbon oxidation have high commercial value as industrial feedstocks. One of the most important industrial processes is the cyclohexane oxidation to produce cyclohexanol and cyclohexanone. These organic substances have special importance in the Nylon manufacture as well as building blocks for a variety of commercially useful products. In this work we present the synthesis and characterization of a new mononuclear piperazine-derived series of iron(III) complexes and their catalytic activity towards cyclohexane oxidation essays. All complexes present octahedral high-spin iron(III) center according to elemental analysis, FTIR, UV-VIS and Mössbauer spectroscopy characterization. The cyclohexane oxidation resulted in cyclohexanol, cyclohexanone and cyclohexyl hydroperoxide as products, with yields up to 39 %. The best results were obtained with the complex (NH4)[Fe(BPPZ)Cl2] (BPPZ: lithium 1,4-bis-(propanoate) piperazine) and with hydrogen peroxide as oxidant. The reactions were carried out at room temperature and atmospheric pressure, which incomes a great advantage over the current industrial process of cyclohexane production.

Cobalt oxide encapsulated hydrophilic hierarchical Silicalite-1 for highly efficient conversion of cyclohexyl hydroperoxide

Abstract CHHP is the main product of the cyclohexane oxidation process, the rational design and preparation of solid catalysts are vital important for the development of an environmental benign CHHP conversion process. Herein, cobalt oxide encapsulated hydrophilic hierarchical Silicalite-1 was developed for CHHP conversion. In the presence of an organosilane, the encapsulation of cobalt oxide, creation of intracrystalline secondary porosity, and introduction of surface silanols were simultaneously achieved via hydrothermal synthesis. The particle size of the encapsulated cobalt oxide was about 4.7–6.3 nm, while the SBET, VT and VME are 527 m2/g, 0.417 cm3/g and 0.3 cm3/g, respectively. Moreover, the SBET further increases to 692 m2/g when the silanization process was intensified by surfactants, and the hydrophilic substrates could more easily be adsorbed by the catalyst for the abundant terminal silanols. Then, the dilute CHHP could selectively be adsorbed and activated by the catalyst, and a CHHP conversion of more than 99% could be achieved in 20min. More importantly, the catalyst exhibits outstanding activity in both the CHHP decomposition reactions and cyclohexane oxidation reaction with CHHP as the oxidant, the oxygen utilization efficiency (60%) and KA oil selectivity (120%) were notably improved. The stability of the catalyst is excellent, the activity retained after recycling for 20 times. This strategy is general, which could further be applied for the development of heterogeneous catalysts for more environmental benign chemical processes.

Enhanced catalytic performance of porphyrin cobalt(II) in the solvent-free oxidation of cycloalkanes (C5~C8) with molecular oxygen promoted by porphyrin zinc(II)

Dual-metalloporphyrins catalytic system based on T(p-Cl)PPCo and T(p-Cl)PPZn was presented to enhance the oxidation of cycloalkanes, especially for cyclohexane, the selectivity towards KA oil increasing from 90.7% to nearly 100.0%, meanwhile the conversion increasing from 3.42% to 4.29%. Enhancement on conversion and selectivity was realized simultaneously. In the dual-metalloporphyrins system, T(p-Cl)PPCo served the role to activate molecular oxygen and promote the decomposition of cyclohexyl hydroperoxide, and T(p-Cl)PPZn catalyzed the decomposition of cyclohexyl hydroperoxide to avoid unselective thermal decomposition. This protocol is also very applicable to other cycloalkanes and will provide a applicable strategy to enhance the oxidation of alkanes.

A Comparative Study of the Catalytic Behaviour of Alkoxy-1,3,5-Triazapentadiene Copper(II) Complexes in Cyclohexane Oxidation

The mononuclear copper complexes [Cu{NH=C(OR)NC(OR)=NH}2] with alkoxy-1,3,5-triazapentadiene ligands that have different substituents (R = Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) were prepared, characterized (including the single crystal X-ray analysis of 3) and studied as catalysts in the mild oxidation of alkanes with H2O2 as an oxidant, pyridine as a promoting agent and cyclohexane as a main model substrate. The complex 4 showed the highest activity with a yield of products up to 18.5% and turnover frequency (TOF) up to 41 h−1. Cyclohexyl hydroperoxide was the main reaction product in all cases. Selectivity parameters in the oxidation of substituted cyclohexanes and adamantane disclosed a dominant free radical reaction mechanism with hydroxyl radicals as C–H-attacking species. The main overoxidation product was 6-hydroxyhexanoic acid, suggesting the presence of a secondary reaction mechanism of a different type. All complexes undergo gradual alteration of their structures in acetonitrile solutions to produce catalytically-active intermediates, as evidenced by UV/Vis spectroscopy and kinetic studies. Complex 4, having tertiary C–H bonds in its iPr substituents, showed the fastest alteration rate, which can be significantly suppressed by using the CD3CN solvent instead of CH3CN one. The observed process was associated to an autocatalytic oxidation of the alkoxy-1,3,5-triazapentadiene ligand. The deuterated complex 4-d32 was prepared and showed higher stability under the same conditions. The complexes 1 and 4 showed different reactivity in the formation of H218O from 18O2 in acetonitrile solutions.

Organic Acid Anions Modified α-Co(OH)2 with Enhanced Activity for the Decomposition of Cyclohexyl Hydroperoxide

α-Co(OH)2 nanoplatelets with tunable wettability (hydrophilicity/hydrophobicity) and interlayer spacing were designed to catalyze cyclohexyl hydroperoxide (CHHP) decomposition in alkali-free medium...