Epoxidation Of 1-octene Research Articles

Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

The effect of calixarene ligand symmetry, as dictated by lower-rim substitution pattern, on the coordination to a Ti(IV) cation is assessed in solution and when grafted on SiO2, and its effect on epoxidation catalysis by Ti(IV)-calixarene grafted on SiO2 is investigated. C2v symmetric Ti-tert-butylcalix[4]arene complexes that are 1,3-alkyl disubstituted at the lower rim (di-R-Ti) are compared to previously reported grafted Cs symmetric complexes, which are singly substituted at the lower rim (mono-R-Ti). 13C MAS NMR spectra of complexes isotopically enriched at the lower-rim alkyl position indicate that di-R-Ti predominantly grafts onto silica as the conformation found in solution, exhibiting a deshielded alkyl resonance compared to the grafted mono-R-Ti complexes, which is consistent with stronger alkyl ether→Ti dative interactions that are hypothesized to result in higher electron density at the Ti center. Moreover, 13C MAS NMR spectroscopy detects an additional contribution from an “endo” conformer for grafted di-R-Ti sites, which is not observed in solution. Based on prior molecular modeling studies and on 13C MAS NMR spectroscopy chemical shifts, this “endo” conformer is proposed to have similar Ti–(alkyl ether) distances at the lower-rim and electron density at the Ti center relative to grafted mono-R-Ti complexes. Differences between grafted mono-R-Ti and di-R-Ti sites can be observed by ligand-to-metal charge transfer edge-energies, calculated from diffuse-reflectance UV–visible spectroscopy at 2.24 ± 0.02 and 2.16 ± 0.02 eV, respectively. However, rates of tert-butyl hydroperoxide consumption in the epoxidation of 1-octene are found to be largely unchanged when compared to those of the grafted mono-R-Ti complexes, with average rate constants of ~1.5 M−2 s−1 and initial TOF of ~4 ks−1 at 323 K. This suggests that an “endo” conformation of grafted di-R-Ti may prevail during catalysis. Despite this, grafted di-C1-Ti complexes can be more selective than mono-C1-Ti complexes (45 vs. 34 % at a 50 % conversion at 338 and 353 K), illustrating the importance of the Ti coordination environment on epoxidation catalysis.

The effect of reaction conditions on MoB activation in 1-octene epoxidation with tert-butyl hydroperoxide

The change in the surface composition of a MoB catalyst in the epoxidation of 1-octene with tert-butyl hydroperoxide and the effects of the reactant concentrations and reaction products (tert-butanol and 1,2-epoxyoctane) on this process have been studied.

An efficient epoxidation of terminal aliphatic alkenes over heterogeneous catalysts: when solvent matters

With a peculiar combination of catalyst/oxidant/solvent, it is possible to obtain good yields and excellent selectivities in the epoxidation of 1-octene.

Properties and catalytic performance of sulphate-vanadia impregnated fumed silica as oxidative catalyst

A series of sulphate-vanadia impregnated fumed silica oxidative catalysts were synthesized via impregnation method. The samples were prepared by impregnation of 1 wt% of vanadium and 0.2 M of sulphuric acid onto fumed silica as support. Surface area of the silica supported samples were similar of 118 m2/g. UV-Vis DRS results showed existence of o supported V species and the charge transfer bands associated with O2- to V5+ in tetrahedral environments. Catalytic performance were evaluated via epoxidation of 1-octene to 1,2-epoxyoctane using hydrogen peroxide as an oxidant. It had been demonstrated that sulphate-vanadia impregnated fumed silica had high catalytic activity of 626 ± 0.2 mmol epoxide was produced after 24 h reaction. This may indicate that more oxidative sites were generated after the impregnation of V and sulphate onto the SiO2 matrixes.

Synthesis and Catalytic Applications of Chemically Grafted SiH-Functionalized Tripodal Ti-POSS Complexes in Crosslinked Hyperbranched Poly(siloxysilane)

This study investigated the synthesis, activity, epoxide selectivity, H2O2 efficiency, and recyclability of new heterogeneous alkene epoxidation catalysts prepared by chemical grafting of new SiH-functionalized tripodal Ti–polyhedral oligomeric silsesquioxane (Ti-POSS) complexes in hyperbranched poly(siloxysilane) via hydrosilation. Crosslinked hyperbranched poly(siloxysilane)-grafted [{(p-HSiMe2(CH2)2C6H4)(c-C6H11)6Si7O12}Ti(NMe2)] (11) and crosslinked hyperbranched poly(siloxysilane)-grafted [{(HSiMe2(CH2)3)(i-C4H9)6Si7O12}- Ti(NMe2)] (12) displayed high activity, epoxide selectivity (≥98 %), and H2O2 efficiency (≥97 %) in cyclohexene and 1-octene epoxidation with aqueous H2O2. Moreover, these catalysts were highly recyclable with retained activity and durability and proved to be truly heterogeneous. Using chemical grafting for the synthesis of 11 and 12 enhanced their recyclability and durability with retained activity. The high H2O2 efficiency can be attributed to the uniformly non-polar environment provided about Ti in 11 and 12 by the polymer; this results in low water concentrations and higher [alkene] : [H2O2] ratios at the Ti active site than in the rest of the solution. These effects enhance the epoxide selectivity and minimize leaching of titanium.

Catalytic activity of hexagonal MoO3 modified with silver, palladium and copper

Abstract Catalytic activity of solvothermally-synthesized hexagonal molybdenum trioxide (h-MoO3) in epoxidation of 1-octene by tert-butyl hydroperoxide and the effect of deposition of metal (Ag, Pd, Cu) nanoparticles on the properties of catalyst have been investigated. It has been shown that silver-modified MoO3 demonstrates the highest catalytic activity and selectivity in the reaction of 1,2-epoxyoctane formation, whereas MoO3 modified with Pd nanoparticles exhibits worse catalytic performance than bare MoO3; by contrast, copper-modified MoO3 does not catalyze the epoxidation reaction. The Ag/MoO3 catalyst was also found to be active in the reaction of 1-octene oxidation by molecular oxygen at the initial stage of the oxidation process.

Design, Synthesis and Characterization of Bimetallic Palladium Complexes for Terminal Olefin Epoxidation

A series of aromatic ring spaced binuclear Pd(II) complexes were synthesized from sterically tuned Schiff base ligands derived from 4,6-diacetylresorcinol and 2,6-dialkyl substituted anilines to provide a general and flexible set of complexes for terminal olefin epoxidation studies using “green” oxidant 30 % hydrogen peroxide as a terminal oxidant. All the compounds were fully characterized by analytical and spectrometric methods. Additionally, the ligands L1 and L2 were characterized by single crystal X-ray diffraction technique. The complexes C1 and C2 displayed high activity and substrate selectivity in the oxidation of 1-octene, whereas mixed products were observed in case of styrene with reasonable yields, arguably assignable to stringent steric and electronic factors of the complexes employed. Up to 98.5 % conversion is observed for epoxidation of 1-octene with high substrate selectivity, whereas up to 95 % conversion is observed for styrene with poor selectivity. A series of Pd(II) complexes were synthesized from sterically tuned Schiff base ligands derived from 4,6-diacetylresorcinol and 2,6-dialkyl substituted anilines to provide a flexible set of complexes for olefin epoxidation studies using hydrogen peroxide as a terminal oxidant. The complexes C1–C3 showed substrate selectivity in the oxidation of 1-octene, where as mixed products were observed in case of styrene with reasonable yields.

Sterically modulated palladium(II)−N-heterocyclic carbene complexes for the catalytic oxidation of olefins: Synthesis, crystal structure, characterization and DFT studies

The synthesis of a series of sterically modulated palladium(II)–NHC complexes (9–11) of the general formula [Pd(NHC)2Cl2] (NHC=1-benzyl-3(2′-methyl)-propylbenzimidazol-2-ylidine, 1-benzyl-3(2′-methyl)-butylbenzimidazol-2-ylidine and 1-benzyl-3-hexylbenzimidazol-2-ylidine) from their respective silver(I) counterparts (6–8) is presented. Two novel triazine-tethered Zwitterionic (benz)imidazolium salts, 4 and 5, were prepared and tested as NHC precursors for the preparation of silver(I) complexes. However, all our attempts to prepare silver(I) derivatives from salts 4 and 5 ended with negative results due to the low acidity of the C2 protons. The Zwitterionic derivative 4 was additionally characterized by the single crystal X-ray diffraction technique. The molecular structure of 4 evidenced π–π stacking interactions between the triazine rings of two crystallographically independent units. The palladium complexes 9–11 showed good catalytic activities in the epoxidation of 1-octene and styrene under homogeneous conditions with aqueous hydrogen peroxide as an oxidant. The effect of temperature and solvent on the epoxidation of the aforementioned olefins using complexes 9–11 was also explored. Density functional theory (DFT) was used to model the structures of the isomers of the palladium complexes. Geometry parameters, electronic energy, molecular orbital energies, band gap, vibrational frequencies and the cis–trans energy barrier were calculated.

Synthesis and catalytic properties of titanium containing extra-large pore zeolite CIT-5

Titanium containing extra-large pore zeolite CIT-5 (IZA code: CFI) was successfully prepared by direct synthesis using Cab-O-Sil M5 and titanium(IV) butoxide in the presence of LiOH. N-Methylsparteinium hydroxide was used as a structure directing agent. The product crystallized into thin plate crystals with an approximate size of 20×5×0.2μm. The lowest achieved Si/Ti ratio was 23. The necessary duration of hydrothermal synthesis increased with increasing concentration of Ti in the reaction mixture from 11 days (Si/Ti=63 in product) to 17 days (Si/Ti=36) at 155°C. Prepared Ti-CFI samples exhibit BET surface areas in the range of 308–346m2/g and micropore volumes of 0.094–0.097cm3/g. CFI possesses extra-large pores (14-ring, 7.2×7.5Å) accessible for bulky molecules, therefore, Ti-CFI is a useful catalyst for epoxidation of double bonds in bulky molecules used in perfumery and pharmacy. The Ti-CFI samples proved to be catalytically active in epoxidation of 1-octene, cyclooctene, α-pinene, and norbornene with hydrogen peroxide as oxidation agent.

Synthesis and characterization of homoleptic titanium bulky alkoxo complexes and their application in 1-octene epoxidation

A new series of titanium alkoxo complexes [Ti(OR)4] (1–8) have been synthesized by the alcoholysis reaction of Ti(OiPr)4 with the corresponding alcohol (ROH = Adamantanol, (1R,2S,5R)-(−)-menthol, 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose, 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose, (1R)-(−)-myrtenol, 1,2:5,6-Di-O-cyclohexylidene-α-D-glucofuranose, (1S-endo)-(−)-borneol and (−)-sclareol). These homoleptic alkoxo titanium (IV) complexes have been characterized by spectroscopic and electrochemical techniques. In addition, they have been tested in the epoxidation reaction of 1-octene with ethylbenzene hydroperoxide as oxidant; obtaining yields of up to 90% and selectivity values of 50%. The conversion profile of EBHP was found to depend on the amount of titanium and on the chemical environment of titanium sites.

Improvement of the hierarchical TS-1 properties by silanization of protozeolitic units in presence of alcohols

The synthesis of hierarchical TS-1 zeolites has been accomplished following a strategy based on the silanization of protozeolitic units. This kind of zeolites is characterized by having a secondary porosity in the supermicro/mesopore range and, therefore, enhanced textural properties. The generation of this secondary porosity is caused by the presence of the silanization agent, which acts as crystal growth inhibitor. However, when a high proportion of organosilane is introduced into the synthesis medium, a highly viscous gel is formed, which reduces the anchoring of the organosilane molecules onto the protozeolitic units. In order to improve the silanization process in these conditions, a variety of alcohols (methanol, ethanol and 2-propanol) has been tested as solvents during the silanization step. The alcohol addition increases the incorporation of the silanization agent onto the zeolite, which is attributed to a reduction in the synthesis media viscosity. Likewise, the alcohols may also undergo grafting onto the external surface of the protozeolitic units through alkoxylation reactions, improving the crystal growth inhibitor effect of the silanization agent. As a consequence, these materials exhibit enhanced textural properties, with a higher secondary porosity contribution, especially when ethanol is used as solvent. Hierarchical TS-1 zeolites prepared adding alcohols in the silanization step show improved catalytic activity in 1-octene epoxidation using tert-butylhydroperoxide as oxidant, due to a higher proportion of more accessible titanium sites. Moreover, it is noteworthy that a reasonable correlation exists between the catalytic activity and the surface attributed to the secondary porosity.

Physical–chemical and catalytic properties of deposited MoO3 and V2O5

Abstract The deposition of molybdenum and vanadium oxides onto fumed silica, titania, and alumina as supports through dry milling has been carried out. The structure of prepared compositions has been investigated by means of XRD, DTA–TG, FTIR, and UV–Vis spectroscopy, nitrogen adsorption. The deposited crystal phases are sufficiently uniformly distributed on support surface. The supported oxides are subjected to dispersion in process of milling to the state of oligomeric or isolated species. Milled bulk and deposited MoO3 (first of all, on alumina) possesses improved catalytic performance in process of epoxidation of 1-octene. Vanadium pentoxide also has higher activity in this process.

Performance evaluation of mesoporous host materials in olefin epoxidation using Mo(II) and Mo(VI) active species—Inorganic vs. hybrid matrix

The [Mo VIO 2Cl 2(thf) 2] and [Mo III 2(CO) 3(MeCN) 2] precursor complexes, were immobilized in a hybrid periodic mesoporous organosilicas (PMO)-type material. These new hybrid matrix materials were prepared in one pot synthesis, containing the bidentate N, N′-ligand ( glypy) in the material. In a second approach, the ordered mesoporous silica MCM- glypy was prepared using a tethered approach by a stepwise procedure. The metal complexes were grafted in both types of materials to obtain heterogeneous pre-catalysts. The modified materials have been characterized by powder X-ray diffraction, N 2 adsorption, and solid-state CP MAS NMR ( 13C, 29Si). All metal containing materials were tested as catalysts in epoxidation of 1-octene, cyclooctene and styrene with tert-butylhydroperoxide (TBHP) at 328 K. Selectivity to octene and cyclooctene epoxides was complete. The new PMO materials described in this work are outstanding catalysts for any of the transformations described. In fact, cyclooctene selectivity based on TBHP consumption is found to be almost independent of the mol ratio attesting the efficiency of the catalysts. They are also effective under stoichiometric olefin/oxidant ratio. In addition, a mechanism for acid catalyzed benzaldehyde formation is proposed as well as the conversion of Mo(II) to Mo(VI) under catalysis.

Synthesis and characterisation of (hydroxypropyl)-2-aminomethyl pyridine containing hybrid polymer–silica SBA-15 materials supporting Mo(vi) centres and their use as heterogeneous catalysts for oct-1-ene epoxidation

Hybrid organic–inorganic amino alcohol containing PGMA–SBA-15 materials have been prepared by first tethering poly(glycidyl methacrylate) (PGMA) chains onto the surface of SBA-15 materials using the atom transfer radical polymerization (ATRP) technique. The procedure involves the functionalization of silica-based SBA-15 materials with aminopropyl groups and 2-bromo-2 methylpropionyl bromide to form ATRP initiator species. Subsequent graft ATRP of glycidyl methacrylate leads to a large decrease of the textural properties in the final material, but nevertheless, the use of the ultra large pore SBA-15 support is beneficial for the achievement of porous hybrid organic–inorganic materials. Reaction of the glycidyl pendant groups in the tethered PGMA chains with 2-aminomethyl pyridine allows the formation of the (hydroxypropyl)-2-aminomethyl pyridine ligands to which molybdenum(VI) species catalytically active for epoxidation of terminal alkenes are bound. The materials thus prepared display high catalytic activity and excellent stability and reusability in the epoxidation of 1-octene with TBHP as oxidant. The presence of mesoporosity in the final Mo(VI)-containing hybrid materials boosts the catalytic activity of supported metal centres.

Tripodal titanium silsesquioxane complexes immobilized in polydimethylsiloxane (PDMS) membrane: Selective catalysts for epoxidation of cyclohexene and 1-octene with aqueous hydrogen peroxide

We investigated the activity, epoxide selectivity, H 2O 2 efficiency, and recyclability of heterogeneous alkene epoxidation catalysts prepared by encapsulation of tripodal Ti silsesquioxane complexes in polydimethylsiloxane (PDMS) membrane. We found that [Ti(NMe 2){( c-C 6H 11) 7Si 7O 12}]/PDMS ( 3) and [Ti(NMe 2){( i-C 4H 9) 7Si 7O 12}]/PDMS ( 4) displayed high activity, epoxide selectivity (⩾97%), and H 2O 2 efficiency (⩾97%) in cyclohexene- and 1-octene epoxidation with aqueous H 2O 2. Moreover, these catalysts were highly recyclable. The high H 2O 2 efficiency can be attributed to the uniformly non-polar environment provided about the Ti silsesquioxane complex in 3 and 4 by the PDMS membrane, which presumably results in low local water concentrations and higher [alkene]:[H 2O 2] ratios at the Ti center than in the bulk reaction medium; both of these effects favor the epoxide selectivity and minimal leaching of titanium. Our study of the effect of solvent on catalyst activity revealed that acetonitrile is to be preferred as solvent, since methanol inhibits the epoxidation at long reaction times.

Catalytic epoxidation of alkenes with 30% H2O2 over Mn2+-exchanged zeolites

The Mn2+-exchanged zeolites Mn-Y, Mn-beta, Mn-A and Mn-ZSM-5 were prepared and used as heterogeneous catalysts for the liquid phase epoxidation of alkenes with aqueous hydrogen peroxide (30% H2O2) at 273–298 K in the NaHCO3 buffer system. The structures of catalysts were characterized by powder X-ray diffraction (XRD), UV–vis, ICP, BET and IR techniques. Mn-beta and Mn-Y exhibited the best recyclable activity for the epoxidation of styrene to achieve styrene conversions higher than 96.0 and 98.5 mol%, respectively. Mn-beta showed higher activity for cyclohexene and norbornene but lower activity for α-methylstyrene, cinnamyl chloride, indene, cyclooctene and α-pinene than Mn-Y, which could be correlated with the difference of their pore sizes. However, these catalysts did not show any activity for the epoxidation of 1-octene with H2O2, possibly due to low electron density of double bonds of linear terminal alkenes.

Highly Ti-loaded MCM-41: Effect of the metal precursor and loading on the titanium distribution and on the catalytic activity in different oxidation processes

Ti-MCM-41 materials have been prepared by co-condensation of tetraethylorthosilicate with two different titanium sources: titanocene dichloride and titanium isopropoxide. The hydrophobic nature of cyclopentadienyl rings has been used to enhance the interaction between the titanocene dichloride starting compound and the surfactant micelles leading to, after calcination, titanium centres finally located in the surface of the mesopores. In this way, increasing the content of titanocene dichloride in the synthesis gel causes the formation of titanium dioxide nanofibers inside the mesoporous system – clearly visible by TEM analysis – for high metal loadings. Such Ti distribution, which has not been observed when using titanium isopropoxide, confers to these Ti-MCM-41 materials a different catalytic behaviour to that of conventional Ti-MCM-41 materials for a given Ti content. Thus, samples prepared with titanocene dichloride display higher catalytic activity in the epoxidation of 1-octene and in the oxidative bromination of phenol red than samples prepared with titanium isopropoxide. Besides, in both reactions, the maximum of catalytic activity is reached for lower titanium loading when titanocene dichloride is the starting Ti source as a consequence of a better accessibility of reactants to the final Ti centres.

Kinetic study of hydroperoxide epoxidation of 1-octene in the presence of molybdenum disilicide as a catalyst in a low concentration range of olefin

The kinetic regularities of the influence of low 1-octene concentrations on its epoxidation by tert-butyl hydroperoxide in the presence of molybdenum disilicide (MoSi2) as a catalyst were investigated. The minimum in the dependence of the initial rate of hydroperoxide consumption on 1-octene concentration was observed. The kinetic scheme of epoxidation, which includes the competition between hydroperoxide and olefin for the catalytic active centers, was proposed. The equation for the reaction rate was derived according to the kinetic scheme. The kinetic parameters of epoxidation were calculated. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 623–628, 2009

Investigation of Batch Alkene Epoxidations Catalyzed by Polymer-Supported Mo(VI) Complexes

Polymer-supported Mo(VI) catalysts (PBI.Mo and Ps.AMP.Mo) have been prepared and characterized. The activities of both of these catalysts in epoxidation of alkenes (e.g., cyclohexene; 1-octene; limonene; α-pinene) with dry tert-butyl hydroperoxide (TBHP) as oxidant have been studied under different reaction conditions in a batch reactor. The long-term stability and Mo leaching of each polymer catalyst was also assessed by recycling a sample in batch reaction using conditions that will form the basis of a continuous process. Both catalysts have been shown to be sufficiently stable to be considered as real candidates for use in such a process. In the case of the PBI.Mo catalyst, the order of reactivity of the alkenes was found to be the following: cyclohexene > limonene > α-pinene > 1-octene. “Wet” TBHP can also be used for cyclohexene epoxidation catalyzed by PBI.Mo without any significant decrease in the final TBHP conversion. In the case of limonene epoxidation, however, the presence of water reduced the TBHP conversion and also affected the cis−trans ratio of the main product 1,2-limonene epoxide. The reusability studies with PBI.Mo revealed that the largest fall in the final TBHP conversion was observed for α-pinene epoxidation among the alkenes studied. For 1-octene epoxidation, the loss of Mo from each support has been investigated by isolating any residue from the reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions.

Turning TS-1 zeolite into a highly active catalyst for olefin epoxidation with organic hydroperoxides

A new synthesis route, based on the silanization of zeolitic seeds, has been applied to prepare nanocrystalline TS-1 zeolite with hierarchical porosity, leading to materials exhibiting high catalytic activity in 1-octene epoxidation with organic hydroperoxides as oxidizing agents.