Cyclohexane In Presence Research Articles

Synthesis, characterization, and performance evaluation of unsupported tetrametallic CoMoMnAl and CoMoZnAl catalysts for selective hydrodesulfurization (HDS)

New formulations of unsupported tetrametallic catalysts derived from layered double hydroxides (LDH) compounds were synthesized by a constant pH coprecipitation method, characterized, and evaluated in the selective hydrodesulfurization (HDS) of thiophene in the presence of cyclohexene. The layered double hydroxides were prepared using terephthalate (C8H8O2)2- as the interlayer anion with nominal aluminum molar fraction of 0.5, and nominal cobalt to MII (M = Zn or Mn) ratios of 0.2, 0.4 and 0.6. Molybdenum introduction in the LDH precursor was accomplished by an ion exchange process using the heptamolybdate anion. The calcined Mn samples showed a higher surface area than those obtained from Zn. The sulfidation was carried out in situ with a heating ramp up to 673 K and the catalysts were evaluated in a tubular flow reactor. The catalytic evaluation of Zn and Mn-based materials for simultaneous thiophene HDS and cyclohexene hydrogenation (HYD) was conducted at 573 K and 20 bar. The results show that the Zn-based unsupported catalysts synthesized here exhibited higher selectivity for the HDS reaction than an industrial one.

Thermal Formation of Metathesis-Active Tungsten Alkylidene Complexes from Cyclohexene.

A 7-tungstabicyclo[4.3.0]nonane complex forms slowly upon addition of cyclohexene to the ethylene complex, W(NAr)(OSiPh3)2(C2H4), at 22 °C. A single-crystal X-ray study showed its structure to be closest to a square pyramid (τ = 0.23). At 22 °C, loss of cyclohexene or ring contraction of the 7-tungstabicyclo[4.3.0]nonane complex is slow. Above ∼80 °C, cyclohexene is ejected to give W(NAr)(OSiPh3)2(C2H4), but a sufficient amount of 7-tungstabicyclo[4.3.0]nonane complex remains in the presence of cyclohexene and the ring contracts to yield methylenecyclohexane and a methylidene complex or ethylene and a cyclohexylidene complex. Other complexes that have been observed include an 8-tungstabicyclo[4.3.0]nonane complex formed from 1,7-octadiene, a 7-tungstabicyclo[4.2.0]octane complex (formed from a methylidene complex and cyclohexene), and a methylenecyclohexane complex. 13C-Labeling studies show that the exo-methylene group in methylenecyclohexane and the α positions in the 8-tungstabicyclo[4.3.0]nonane come from ethylene. An alternative ring contraction of a tungstacyclopentane made from two molecules of cyclohexene cannot be excluded when concentrations of ethylene are low. A cyclohexylidene complex could also form from two cyclohexenes via a newly proposed "alkyl/allyl" mechanism. The results reported here are the first experimental confirmations that a tungstacyclopentane can ring-contract thermally at a substituted WCα position to form a tungstacyclobutane and therefore metathesis-active alkylidenes.

Enhanced oxidative desulfurization of dibenzothiophene in the presence of cyclohexene, indole, quinoline, and p-xylene using surface-silylated titania-silica catalyst

Heterogeneously catalyzed oxidative desulfurization (ODS) offers a mild pathway to remove refractory sulfur compounds from liquid hydrocarbon fuels. However, adsorption of polar oxidation byproducts on the catalyst surface decreases desulfurization efficiency at the low ODS reaction temperature. Here, we report that high-performance surface-silylated titania-silica catalysts can be prepared by a silylation method using hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS) as the silane reagents. The bulk structure and surface properties of the catalysts before and after surface silylation were characterized by N2 adsorption–desorption, XRD, FTIR, TGA, UV–vis DRS, FESEM, EDS, and water contact angle measurement to establish the structure–function relationship. The effects of silyl groups loading, reaction temperature, type of oxidant, and inhibiting compounds on the ODS performance of the catalysts were systematically evaluated. The results revealed that TS-H-2 catalyst with the optimum loading of silyl groups was an excellent catalyst capable of ultra-fast oxidizing ∼100 % of DBT, after only 5 min, which was due to increased surface hydrophobicity and decreased accumulation of poisoning polar byproducts on the active sites. The ODS performance of TS-H-2 was better preserved compared to unmodified TS-nonsil catalyst in the presence of inhibiting compounds such as cyclohexene (CH), indole (IND), and quinoline (QU), while it increased in the presence of p-xylene (PX). The negative effects of the three former inhibiting compounds were resulted from their competition with the sulfur compound for the oxidant and poisoning of the active sites. The positive effect of PX on the ODS rate was due to solubilization of the strongly adsorbed molecules on the surface of catalyst.

Synthesis of Polyester Polyol from Cyclohexanone plant wash water

Oxidation of Cyclohexane in presence of air produces Cyclohexanone and Cyclohexanol. However, it also produces carboxylic acid by-products due to uncontrolled reactions. The by-products are washed with water to increase purity of Cyclohexanone and Cyclohexanol. The wash water is a potential source of organic acids. This manuscript describes a process for the preparation of Polyester Polyol from the wash water obtained from Gujarat State Fertilizers and Chemicals ltd. The solid mass obtained after removal of liquid mass from the wash water was reacted with diethylene glycol (DEG) to synthesize Polyester Polyol. The reaction parameters were varied to obtain Polyester Polyol without containing unreacted DEG and solid mass. The optimum reaction condition was achieved by reacting 50 g of solid mass with 42.5 g DEG in presence of catalyst at 200 degC without vacuum followed by removal of unreacted DEG and low volatiles by distillation at 200 degC and 600 mmHg vacuum.

Crystallization and Phase Transition of 1‐Butene Copolymers with Distinct Cyclic Co‐Units

Comprehensive SummaryThe dimethylpyridylamidohafnium catalyst was used to synthesize 1‐butene/cyclohexene and 1‐butene/vinylcyclohexane random copolymers, which have extra six‐membered cyclic co‐units in main chain and side chain, respectively. For the obtained copolymers of different incorporations, the crystallization from amorphous melt and the solid phase transition from tetragonal to trigonal phases were investigated with differential scanning calorimetry. Both of the incorporated cyclic co‐units decrease the crystallization kinetics, but the presence of cyclohexene keeps the melting temperature of copolymers constant. Interestingly, the strong memory effect of crystallization can appear at the elevated temperature even above the equilibrium melting temperature, as the content of co‐units was increased. The 1‐butene/vinylcyclohexane copolymer with 1.52 mol% co‐units exhibits a rather strong memory effect with the broad Domain IIa width of 43°C and the crystallization temperature raising of 24°C. Furthermore, the transition of tetragonal phase into trigonal phase was also explored for different co‐units and incorporations. It was found that both of the cyclohexene co‐units and vinylcyclohexane co‐units effectively slow down the kinetics of phase transition. However, the vinylcyclohexane co‐units have a much higher efficiency in suppressing phase transition than the cyclohexene co‐units, where 0.53 mol% vinylcyclohexane can completely stop phase transition within 1320 h. Considering the fact that copolymers with vinylcyclohexane co‐units actually have lower glass transition temperatures, it was indicated that the suppression of phase transition is also largely influenced by the steric co‐units in the side chain for the helical and positional adjustments, not only by the segmental mobility.

Application of silver ionic liquid in the separation of olefin and alkane

AbstractBACKGROUNDThe separation of olefins and alkanes remains one of the most challenging industrial processes due to their similar structure and boiling points. Traditional industrial methods are limited as a consequence of high equipment cost and energy consumption. Ionic liquids (ILs) for olefin separation systems have been developed in recent years. This study aimed to synthesize silver (Ag+) IL and apply it in both extraction and membrane processes to enhance the separation performance.RESULTSQuantum chemical calculation results show that the interaction energy between the IL and cyclohexene is much larger than the values for interactions between the IL and alkanes. The highest selectivities for cyclohexene in the extraction process were 33.4 and 51.9 in the presence of cyclohexane and hexane, respectively. The gel membrane was prepared by casting a mixture of 12HSA and Ag+ IL solution onto the PVDF membrane. In vapor permeation, high separation performance was obtained together with a stable membrane phase when the 12HSA content was 1.50% and the operating temperature was 45 °C. With the increase of the mole fraction of cyclohexene, the permeation flux gradually increased and the separation factor was maintained at >9.CONCLUSIONReversible π‐complex formation between Ag+ ions and cyclohexene can effectively enhance the separation performance in both extraction and membrane process. This study presents a promising alternative to conventional technology for olefin and alkane separations. © 2021 Society of Chemical Industry (SCI).

Influence of Naphthenic Hydrocarbons and Polar Solvents on the Composition and Structure of Heavy-Oil Aquathermolysis Products

Estimates of the conventional proven hydrocarbon reserves show a tendency toward depletion, and in the near future they will be insufficient to meet the ever-growing global energy demand. The problem of crude oil deficiency can be solved by involving unconventional hydrocarbon resources in both recovery and refinery. However, the hydrogen deficiency of heavy oil and natural bitumen requires technical and technological solutions. Therefore, the hydrogen-donating capacity of water and solvents, particularly in reservoir conditions, is very attractive. In this paper, we study the hydrogen-donating capacity of naphthenic and polar solvents during hydrothermal treatment of heavy oil from Ashal’cha reservoir (Republic of Tatarstan, Russia). It was established that naphthenic solvents significantly influence the viscosity reduction due to the destructive hydrogenation of resins and asphaltenes. Among naphthenic solvents, decalin significantly increases the amount of evolved gases, particularly C4–C10 isomers and aromatics. However, the maximum evolved gases among all of the used solvents correspond to formic acid. The results of elemental analysis revealed that the H/C ratio rises in crude oil samples after hydrothermal treatment in the presence of cyclohexane and decalin. FT-IR spectral indices revealed an increase in crude oil aliphaticity in case of using solvents from the cyclohexane–tetralin–decalin series due to the cleavage of carbon–heteroatom bonds in aliphatic substitutes of resins and asphaltenes. Significant changes in the FT-IR spectra of crude oil are observed in the presence of tetralin.

Ethyl esters production catalyzed by immobilized lipases is influenced by n-hexane and ter-amyl alcohol as organic solvents.

Lipase stability in organic solvent is crucial for its application in many biotechnological processes as biocatalyst. One way to improve lipase's activity and stability in unusual reaction medium is its immobilization on inert supports. Here, lipases from different sources and immobilized through weak chemical interactions on hydrophobic and ionic supports had their transesterification ability dramatically dependent on the support and also on the solvent that had been used. The ethanolysis of sardine oil was carried out at the presence of cyclohexane and tert-amyl alcohol, in which Duolite A568-Thermomyces lanuginosa lipase derivative achieved 49% of ethyl esters production after 24h in cyclohexane. The selectivity of immobilized lipases was also studied and, after 3h of synthesis, the reaction with Duolite A568-Thermomyces lanuginosa derivative in cyclohexane produced 24% ethyl ester of eicosapentaenoic acid and 1.2% ethyl ester of docosahexaenoic acid, displaying a selectivity index of 20 times the ethyl ester of eicosapentaenoic acid. Different derivatives of Candida antarctica lipases fraction B (CALB) and phospholipase Lecitase® Ultra (Lecitase) were also investigated. Along these lines, a combination between these factors may be applied to improve the activity and selectivity of immobilized lipases, decreasing the total cost of the process.

Thermodynamic modeling and experimental measurement of semi-clathrate hydrate phase equilibria for CH4 in the presence of cyclohexane (CH) and tetra-n-butyl ammonium bromide (TBAB) mixture

In the current study, the effect of tetra-n-butyl ammonium bromide (TBAB) and cyclohexane mixture on CH4 semi-clathrate hydrate formation was studied. Semi-clathrate dissociation conditions for CH4 + TBAB + cyclohexane + water were investigated at different concentrations of TBAB (0.05, 0.10, and 0.15) mass fraction in the presence of cyclohexane at the pressure and temperature ranges of 1–8 MPa and 275.1–295 K, respectively. In addition, a thermodynamic model was suggested to predict the phase equilibria of our system, which is divided into four phases, where the van der Waals–Platteeuw Solid Solution Theory has been used to predict the hydrate phase. For gas phase, The SRK equation of state was applied. For oil phase, the cyclohexane activity coefficient in the organic phase was calculated by the non-random two-liquid model (NRTL). Finally, to determine the activity coefficient of the electrolyte species in the aqueous phase, the semi-empirical electrolyte NRTL (eNRTL) activity model was used. The results showed that the proposed model has an acceptable agreement with the experimental semi-clathrate hydrate dissociation data with an approximately average absolute relative deviation of 5.4%.

Understanding the influence of alumina supported ruthenium catalysts synthesis and reaction parameters on the hydrodeoxygenation of lignin derived monomers

Up-gradation of lignin derived monomers to value-added and fuel grade products is important to make overall bio-refinery process economical. Although, few studies are devoted on this work yet, systematic study on commercially viable (low loading of metal, recyclable catalyst, mild conditions, high selectivities etc.) is scarce and typically done under harsh conditions. Herein, we report, the methodical effect of support (SiO2, Al2O3 (acidic, basic and neutral), SiO2-Al2O3) on the hydrodeoxygenation (HDO) of lignin derived various monomers, guaiacol, veretrol, eugenol, phenol using very low loading (0.5 wt%) Ru catalyst. Very high yield (82%) of cyclohexanol from guaiacol could be achieved in presence of cyclohexane as a solvent and Ru/Al2O3-Acidic catalyst at 225 °C and under 1 MPa H2 pressure. The detailed study on the effect of solvent, stability and adsorption of reactant & products etc. is done and it was observed that products are more prone to adsorb and undergo further reactions. The complete characterization of fresh and spent catalysts revealed that lower catalyst reduction temperature and presence of Ru in partially higher oxidation state proved by XPS, helps in enhancing the cyclohexanol formation. Subsequently, role of Ru particle size and support on the activity was also investigated.

Study the effect of organic promoters on thermodynamics behaviour for refrigerant gas clathrate hydrate

The present work consists of an experimental and theoretical investigation dealing with hydrate formation for the binary system (water+ refrigerant gas) and ternary systems (water+ refrigerant gas+ promoter) at constant initial conditions (pressure and temperature). Isochoric method (constant volume) search was used in current study to measure the formation data (pressure, temperature) for hydrate. Refrigerant R134a gas and different organic promoters such as benzene and cyclohexane were used in this study. For ternary systems at the different concentrations of promoters shifted hydrate formation data when benzene and cyclohexane decree pressure and increasing temperature. Many objective functions were obtained from kinetic models such as the amount of gas consumed (Δn), the growth rate (r (t)), and conversion of the water to hydrate. The gas consumed (Δn) of the binary system increased lead to increase in hydrate formation, also the hydrate growth rate (r(t)) and increase water conversion to hydrate. The gas consumed in the presence of cyclohexane was higher than at using benzene as a promoter. The experimental results show that the presence of different promoters in the ternary systems have an effect on thermodynamic promotion of refrigerant hydrates formation. The promotion effect increased with increasing the concentration of promoter in the select range. Also, the results manifested that benzene and cyclohexane had a clear effect in reducing the pressure and raising the temperature of the hydrate formation. The storage capacity was investigated. It has been noticed that the existence of the promoters in the hydrate formation system led to a slight increase in the storage capacity with maximum value about (78.66) V/V.

Cyclohexane, naphthalene, and diesel fuel increase oxidative stress, CYP153, sodA, and recA gene expression in Rhodococcus erythropolis.

In this study, we compared the expression of CYP153, sodA, sodC, and recA genes and ROS generation in hydrocarbon‐degrading Rhodococcus erythropolis in the presence of cyclohexane, naphthalene, and diesel fuel. The expression of cytochrome P450, sodA (encoding Fe/Mn superoxide dismutase), recA, and superoxide anion radical generation rate increased after the addition of all studied hydrocarbons. The peak of CYP153, sodA, and recA gene expression was registered in the presence of naphthalene. The same substrate upregulated the Cu/Zn superoxide dismutase gene, sodC. Cyclohexane generated the highest level of superoxide anion radical production. Hydrogen peroxide accumulated in the medium enriched with diesel fuel. Taken together, hydrocarbon biotransformation leads to oxidative stress and upregulation of antioxidant enzymes and CYP153 genes, and increases DNA reparation levels in R. erythropolis cells.

Cotransformations of n-Hexadecane, Hexene-1, and Cyclohexane over Dual-Zeolite Cracking Catalysts

Characteristic features of the conversion of n-hexadecane, hexene-1, cyclohexane, and their mixtures over dual-zeolite catalysts for co-cracking of light and heavy fractions are considered. The maximum yield of olefins (the yield of C2–C4 olefins reaches 66.8 wt %) is achieved in the case of the use of hexene-1 possessing maximum reactivity under cracking conditions as a feedstock. Cotransformation of n-hexadecane and hexene-1 do not indicate the presence of any significant interaction between the components. The presence of cyclohexane in the feedstock has substantial influence on the transformation of n-hexadecane, which is due to the high hydrogen donor ability of naphthenes. It is found that the ratio of HREEY and P/HZSM-5 zeolites in the composition of the catalyst has substantial influence on the value of the interaction between the components of the feedstock. The use of hydrocarbons containing “labeled” hydrogen atoms (deuterium) makes it possible to estimate the distribution of the naphthene hydrogen between the main gaseous products.

Optimization of process parameters using response surface methodology for Pd(II) extraction with quaternary ammonium salt from chloride medium: kinetic and thermodynamics study

In this study, liquid–liquid extraction with Aliquat 336 in the presence of cyclohexane as a mobile carrier was investigated to purify Pd(II) from industrial wastewater. Kinetic and thermodynamics analysis showed that Pd(II) extraction was of first-order reaction: the reaction was endothermic reaction which was governed by the diffusion region. The influence of temperature on isotherm model was also investigated. With an increase in reaction temperature, all three isotherms Langmuir, Freundlich and Temkin isotherm become inaccurate. Results show that the Langmuir isotherm model was preferred for the study of the Pd(II) ion experimental isotherm. Response surface methodology was employed to study the five independent variables which have an effect on the percentage of extraction of palladium(II) ions as a dependent variable. Optimum extraction conditions for the five independent variables were as follows: Aliquat 336 concentration (0.6 M), pH of feed solution (2.0), stirring speed (600 rpm), reaction time (10 min.) and reaction temperature (318 K).

Mechanistic Understanding towards the Role of Cyclohexene in Enhancing the Efficiency of Manganese Porphyrin‐Catalyzed Aerobic Oxidation of Diphenylmethane

The selective aerobic oxidation of nonactivated C–H bonds is a key challenge in both industrial and academic research. The catalytic activity of manganese porphyrins (MnTPPCl) towards the aerobic oxidation of diphenylmethane (DPM) is investigated. Compared with the oxidation‐catalyzed MnTPPCl alone, the conversion of DPM is enhanced ca. 6 times (from 7.0 % to 42.5 %) in the presence of cyclohexene. Some in situ characterizations, such as in situ EPR (electron paramagnetic resonance) spectroscopy and in situ UV/Vis spectroscopy are used to investigate the role of cyclohexene in catalytic oxidation. Mechanistic studies suggest that both high‐valent manganese species and cyclohexenyl alkoxyl radicals are favorable for the formation of the carbon radicals. The enhanced activity is related to the easier generation of secondary carbon radicals, triggered by high‐valent manganese species and cyclohexenyl alkoxyl radicals.

Zeolite encapsulated host-guest Cu(II) Schiff base complexes: Superior activity towards oxidation reactions over homogenous catalytic systems

Crystalline copper Schiff base complexes of general formula [CuL1NO3]n(1) and [CuL2Cl] (2) (where HL1 = 1-[(3-dimethylaminopropylimino)-methyl]-naphthalen-2-ol and HL2 = 3-[(3-dimethylamino-2,2-dimethyl-propylimino)-methyl]-naphthalen-2-ol) were prepared and well characterized. The guest, metal complexes were entrapped in the supercages of NaY zeolite (host) in the solvent phase through two stage process (i) ion exchange of the selected transition metal (Cu(II)-salt) in the porous structure and (ii) encapsulation of Schiff-base ligands (HL1/HL2) in Cu(II) exchanged zeolite. The novel Cu(II) complexes as well as host-guest catalysts were characterized using various physicochemical [Single crystal XRD, elemental analysis, EDX, scanning electron microscopy (FE-SEM), the Brunauer-Emmet-Teller (BET) adsorption technique (N2 gas), Inductively coupled plasma (ICP-MS), powder X-ray diffraction (PXRD), thermal analysis (TGA), cyclic voltametry] and spectroscopic techniques [1H and 13C NMR, FT-IR, ESI-MS, electro spin resonance (ESR), diffuse reflectance spectroscopy (DRS), FT-Raman and GC-MS]. Herein, this study reveals the advantage of heterogeneous catalytic methods for the stability of metal complexes into the supercages of zeolite-Y and the selective oxidation of phenol, styrene and cyclohexene in presence of H2O2 at mild reaction conditions. The catalytic activities of the zeolite entrapped Cu(II) complexes were tested with their homogeneous analogous as well. The heterogeneous catalyst can be re-used after recovering for several cycles without decay of activity which was confirmed by PXRD, cyclic voltammetry, SEM and FTIR studies.

Poly(amino acid)-based nanogel by horseradish peroxidase catalyzed crosslinking in an inverse miniemulsion

We present an investigation of horseradish peroxidase (HRP)/H2O2-mediated crosslinking in an inverse miniemulsion for the successful preparation of a stable colloidal nanogel from a poly(amino acid)-based polymer precursor. The precursor was obtained by the aminolysis of polysuccinimide with aminoethan-2-ol and tyramine, resulting in a poly(α,β-N-(2-hydroxyethyl)-D,L-aspartamide-co-N-(2-(4-hydroxyphenyl)ethyl)-D,L-aspartamide) polymer (PHEA-Tyr). Various concentrations of the PHEA-Tyr in aqueous solution with HRP were emulsified in the presence of cyclohexane and SPAN 80. The addition of a hydrogen peroxide solution induced crosslinking between the polymer chains via the phenol groups (Tyr) and targeted nanogel formation. The hydrodynamic radii (R h 0), mean size documented by hydrodynamic radius (R h ), and morphology of the nanoparticles were investigated by dynamic light scattering (DLS) measurements, nanoparticle tracking analysis (NTA), and cryogenic transmission electron microscopy (cryo-TEM). It was found out that nanoparticle radius, morphology, and architecture of the nanogel could be regulated by the initial concentration of the precursor.

Isomerization of n-Heptane on Platinum-Zeolite Catalysts in the Presence of Cyclohexane and Benzene

Effect of cyclohexane and benzene on the isomerization of n-heptane on Pt/BEA-Al2O3 and Pt/MORAl2O3 catalysts was studied. In the presence of catalysts with platinum deposited from a [Pt(NH3)4]Cl2 solution, cyclohexane and benzene inhibit the conversion of n-heptane. At the same time, the presence of cycloalkanes and aromatic hydrocarbons leads to an increase in the isomerization selectivity due to the suppression of side reactions of hydrocracking. Samples based on the BEA zeolite were found to be more active as compared with similar samples based on mordenite.

Different Covalent Immobilizations Modulate Lipase Activities of Hypocrea pseudokoningii.

Enzyme immobilization can promote several advantages for their industrial application. In this work, a lipase from Hypocrea pseudokoningii was efficiently linked to four chemical supports: agarose activated with cyanogen bromide (CNBr), glyoxyl-agarose (GX), MANAE-agarose activated with glutaraldehyde (GA) and GA-crosslinked with glutaraldehyde. Results showed a more stable lipase with both the GA-crosslinked and GA derivatives, compared to the control (CNBr), at 50 °C, 60 °C and 70 °C. Moreover, all derivatives were stabilized when incubated with organic solvents at 50%, such as ethanol, methanol, n-propanol and cyclohexane. Furthermore, lipase was highly activated (4-fold) in the presence of cyclohexane. GA-crosslinked and GA derivatives were more stable than the CNBr one in the presence of organic solvents. All derivatives were able to hydrolyze sardine, açaí (Euterpe oleracea), cotton seed and grape seed oils. However, during the hydrolysis of sardine oil, GX derivative showed to be 2.3-fold more selectivity (eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA) ratio) than the control. Additionally, the types of immobilization interfered with the lipase enantiomeric preference. Unlike the control, the other three derivatives preferably hydrolyzed the R-isomer of 2-hydroxy-4-phenylbutanoic acid ethyl ester and the S-isomer of 1-phenylethanol acetate racemic mixtures. On the other hand, GX and CNBr derivatives preferably hydrolyzed the S-isomer of butyryl-2-phenylacetic acid racemic mixture while the GA and GA-crosslink derivatives preferably hydrolyzed the R-isomer. However, all derivatives, including the control, preferably hydrolyzed the methyl mandelate S-isomer. Moreover, the derivatives could be used for eight consecutive cycles retaining more than 50% of their residual activity. This work shows the importance of immobilization as a tool to increase the lipase stability to temperature and organic solvents, thus enabling the possibility of their application at large scale processes.

Selective Oxygenation of Cyclohexene by Dioxygen via an Iron(V)-Oxo Complex-Autocatalyzed Reaction

An iron complex with a tetraamido macrocyclic ligand, [(TAML)FeIII]-, was found to be an efficient and selective catalyst for allylic oxidation of cyclohexene by dioxygen (O2); cyclohex-2-enone was obtained as the major product along with cyclohexene oxide as the minor product. An iron(V)-oxo complex, [(TAML)FeV(O)]-, which was formed by activating O2 in the presence of cyclohexene, initiated the autoxidation of cyclohexene with O2 to produce cyclohexenyl hydroperoxide, which reacted with [(TAML)FeIII]- to produce [(TAML)FeV(O)]- by autocatalysis. Then, [(TAML)FeV(O)]- reacted rapidly with [(TAML)FeIII]- to produce a μ-oxo dimer, [(TAML)FeIV(O)FeIV(TAML)]2-, which was ultimately converted to [(TAML)FeV(O)]- when [(TAML)FeIII]- was not present in the reaction solution. An induction period was observed in the autocatalytic production of [(TAML)FeV(O)]-. The induction period was shortened with increasing catalytic amounts of [(TAML)FeV(O)]- and cyclohexenyl hydroperoxide, whereas the induction period was prolonged by adding catalytic amounts of a spin trapping reagent such as 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The allylic oxidation of cycloalkenes was also found to depend on the allylic C-H bond dissociation energies, suggesting that the hydrogen atom abstraction from the allylic C-H bonds of cycloalkenes is the rate-determining radical chain initiation step. In this study, we have shown that an iron(III) complex with a tetraamido macrocyclic ligand is an efficient catalyst for the allylic oxidation of cyclohexene via an autocatalytic radical chain mechanism and that [(TAML)FeV(O)]- acts as a reactive intermediate for the selective oxygenation of cyclohexene with O2 to produce cyclohex-2-enone predominantly.