Preparation of high energy fuel JP-10 by acidity-adjustable chloroaluminate ionic liquid catalyst

The isomerization of endo-tetrahydrodicyclopentadiene (endo-THDCPD) to its exo-isomer (JP-10) has been investigated by using chloroaluminate ionic liquids (ILs) as catalysts. The catalyst activity and selectivity could be optimized by varying the mole fraction of AlCl₃ in the IL. Undesirable by-products derived from side-reactions such as skeletal rearrangement, alkylation, cracking, and dimerization could be minimized by appropriate catalyst design and adjustment of the reaction conditions. The catalyst system was further optimized by selecting 1-butyl-3-methylimidazolium chloride as the basic IL and adding 0.60-0.65 mole fraction of AlCl₃ as the promoter. Using the optimized catalyst system, the isomerization of endo-THDCPD to exo-THDCPD proceeded at a fast rate at 50 °C with 98.9% conversion and 100% selectivity. The catalyst longevity has been demonstrated by recycling the IL several times without a noticeable reduction in catalytic activity.     

Diels–Alder Reaction of Cyclopentadiene and Alkyl Acrylates in the Presence of Pyrrolidinium Ionic Liquids with Various Anions

Abstract  

The conversion and stereoselectivity of transformation to endo and exo norbornene derivatives was determined in the Diels–Alder reaction of cyclopentadiene with alkyl acrylates. The reactions were carried out in the pyrrolidinium ionic liquids in the presence of metal chlorides and trifluoromethanesulfonates as the catalysts. Shorter reaction times and higher conversions of dienophile were observed in a comparison with analogous cycloadditions carried out in the presence of conventional organic solvents. A higher stereoselectivity to the endo isomer was found in the majority of cases. The ionic liquids composed of 1-butyl-1-methylpyrrolidinium cation (Pyrr_1.4) and various anions were used. The influence of ionic liquid anion and several metal chlorides and metal triflates used as the catalysts on the conversion was determined.     

Synthesis and characterization of hydrogenated poly(norbornene endo-dicarboximide)s prepared by ring opening metathesis polymerization

Poly(norbornene imide)s prepared by ring opening metathesis polymerization (ROMP) have been generally synthesized from 5-norbornene-exo,exo-2,3-dicarboximides (exo-NDIs), since 5-norbornene-endo,endo-2,3-dicarboximides (endo-NDIs) exhibit considerably lower reactivity toward conventional ROMP catalysts as compared with exo-NDIs. Therefore, there has been limited information on poly(endo-NDI)s, although the endo-stereoisomer monomers are the principal products in Diels–Alder reaction between cyclopentadiene and maleimides. Here we synthesized various poly(endo-NDI)s using available Grubbs catalysts, and subsequently hydrogenated their backbone double bonds to obtain high molecular weight samples with M_n > 150,000. The thermal, thermo-mechanical, mechanical, and optical properties of poly(endo-NDI)s before and after hydrogenation were then investigated, together with the structural properties by wide-angle X-ray scattering and refractive index, in comparison with those of the corresponding poly(exo-NDI)s. Surprisingly, poly(endo-NDI)s exhibit significantly higher glass transition temperatures (by ca. 34 °C) and refractive index values than the exo-counterparts, probably due to increased intermolecular packing. Other properties such as thermal stability, tensile modulus, coefficient of thermal expansion, optical transparency, water absorption, and water transmission rate are quite comparable. Overall, convenient monomer preparation coupled with attractive physical properties makes poly(endo-NDI)s very interesting for practical applications such as optical films and flexible substrates for optoelectronics.     

Study on Selective Dimerization of α-Methylstyrenes Promoted by Ionic Liquids

The catalytic systems composed of ionic liquids containing BF₄⁻ anion and HBF₄ showed high catalytic activity to produce 4-methyl-2,4-diphenyl-1-pentene (MDP-1) or 1,1,3-trimethyl-3-phenylindan (TPI) under different temperature conditions. Up to 90.8% selectivity to MDP-1 with a 98.7% conversion of α-methylstyrene was obtained at 60 °C in the presence of [HexMIm]BF₄–HBF₄, while exclusive TPI was yielded when the reaction temperature increased to 120 °C. Further studies showed that another ionic liquid, [BMIm]Cl · 2AlCl₃, could act as an excellent catalyst and solvent for the dimerization of α-methylstyrene to produce TPI. The dimerization of α-methylstyrene catalyzed by [HexMIm]BF₄–HBF₄ and [BMIm]Cl · 2AlCl₃ performed the same reaction mechanism and the proton was the active species.     

Molecular dimensions of tetrahydrodicyclopentadiene isomers and shape selectivity of zeolitic catalysts

Acid-catalyzed isomerization of tetrahydrodicyclopentadiene upon zeolitic catalysts with different pore channels was studied. With the aid of ACD/ChemSketch 5.0, the dimensions of three tetrahydrodicyclopentadiene isomers are estimated to compare with the channels sizes of zeolitic catalysts. The experimental data, comparisons between molecules dimensions and channel sizes show that reactant selectivity is the reason why HZSM-5 and H-β show no activities at lower temperature. Because of large pore channels (0.74 nm), HY zeolites have sufficient activities for isomerization of tetrahydrodicyclopentadiene to form both exo-tetrahydrodicyclopentadiene and adamantane.     

Ring-opening metathesis polymerization of amino acid-functionalized norbornene diester monomers

Amino acid-derived novel norbornene diester derivatives, 5-norbornene-endo,endo-2,3-dicarboxylic acid bis((S)-2-N-(tert-butoxycarbonyl)aminopropyl) ester (1a), 5-norbornene-exo,exo-2,3-dicarboxylic acid bis((S)-2-N-(tert-butoxycarbonyl)aminopropyl) ester (1b), bis(N-α-(tert-butoxycarbonyl)-l-alanine) 5-norbornene-2,3-endo,endo-dimethyl ester (2a), bis(N-α-(tert-butoxycarbonyl)-l-alanine) 5-norbornene-2,3-exo,exo-dimethyl ester (2b) were synthesized and polymerized by the Grubbs catalyst, 2nd generation. Ring-opening metathesis polymerization of the monomers satisfactorily proceeded to give the polymers with fairly high molecular weights in good yields. The polymerization rate was not affected by the stereostructure of the monomers, endo,endo- and exo,exo-, while largely affected by solvents. The order of polymerization rate was as follows: acetone-d₆ > benzene-d₆ > DMF-d₇ ≈ CD₂Cl₂ > CDCl₃.     

Unusual CC Bond Isomerization of an α,β‐Unsaturated γ‐Butyrolactone Catalysed by Flavoproteins from the Old Yellow Enzyme Family

An unexpected, redox‐neutral C?C bond isomerization of a γ‐butyrolactone bearing an exo‐methylene unit to the thermodynamically more favoured endo isomer (k_cat=0.076 s^?1) catalysed by flavoproteins from the Old Yellow Enzyme family was discovered. Theoretical calculations and kinetic data support a mechanism through which the isomerization proceeds through FMN‐mediated hydride addition onto exo‐Cβ, followed by hydride abstraction from endo‐Cβ′, which is in line with the well‐established C?C bond bioreduction of OYEs. This new isomerase activity enriches the catalytic versatility of ene‐reductases.     

pTSA/[bmim][BF4] Ionic Liquid: A Powerful Recyclable Catalytic System for the Synthesis of α-2-Deoxyglycosides

??-2-Deoxyglycosides were synthesized in ionic liquid ([bmim]BF₄)by stereoselective glycosylation of endo-glycals with various o-nucleophiles in the presence of catalytic amount of pTSAin 71?C95?% yield. High yields, easy recovery of the products, and reusable reaction medium (pTSA/IL couple) with consistent activity makes this protocol efficient and environmentally benign.     

Effect of immobilization of titanocene catalyst in aralkyl imidazolium chloroaluminate media on performance of biphasic ethylene polymerization and polyethylene properties

1-(2-Phenylethyl)-3-methylimidazolium and 1-benzyl-3-methylimidazolium chloroaluminates, [Ph-C₂mim][AlCl₄] and [Bzlmim][AlCl₄], were applied as media of the Cp₂TiCl₂ catalyst for biphasic ethylene polymerization. The studied aralkyl ionic liquids ensure greater stability of the catalyst at higher temperatures and more regular morphology of the produced polyethylene than analogous 1-n-alkyl-3-methylimidazolium chloroaluminates. The alkylaluminium compound participates in the termination reaction of the polymer chain. The catalyst is stable and enables recycling of the ionic liquid phase in the consecutive polymerization reactions. The [Ph-C₂mim][AlCl₄] ionic liquid and AlEt₂Cl alkylaluminium compound turned out to be the most suitable for the biphasic process. The influence of the kind of ionic liquid, alkylaluminium compound (AlEt₂Cl and AlEtCl₂), activator/catalyst molar ratio, reaction temperature, reaction time and catalyst recycling on the polymerization performance as well as polyethylene properties such as molecular weight (M _w ), polydispersity, melting temperature, crystallinity degree, bulk density and particle size is presented.     

Addition polymerization of norbornene, 5-vinyl-2-norbornene and 2-methoxycarbonyl-5-norbornene with a catalyst based on a palladium(0) precursor complex

Pd(dibenzylideneacetone)₂, when activated in situ with 1 equiv of [CPh₃][B(C₆F₅)₄] in the presence of 1 equiv of P(C₆H₁₁)₃, efficiently catalyzed the addition polymerization and copolymerization of norbornene and its derivatives. Homopolymerization of 5-vinyl-2-norbornene took place regio-selectively with the endo-cyclic double bond to give high-molecular weight polymers, while the exocyclic double bond remained intact so that the resulting polymer had pendent vinyl groups along the polymer chain. In the polymerization of a mixture of the endo-/exo- isomers of 2-methoxycarbonyl-5-norbornene, the endo-isomer was consumed prior to consumption of the exo-isomer, contrary to the well-known tendency in Pd(II)-based catalyst systems. Another notable feature of the present catalytic system was the strong dependency of the molecular weight on the reaction temperature, which was studied in detail for the copolymerization of 2-methoxycarbonyl-5-norbornene with norbornene: we could control the molecular weight without the use of a chain transfer agent. The extracted oligomeric fraction of poly(norbornene) showed the presence of a terminal CC double bond as well as a C₆F₅ unit that was bound to the first norbornane unit in the polymer chain.     

Synthesis and Evaluation of Nifurtimox–Adamantane Adducts with Trypanocidal Activity

The synthesis and pharmacological evaluation of C1-substituted adamantane hydrazones, their C2-substituted isomers, and C1-substituted adamantane furanoic carboxamides is described. These new adamantane derivatives exhibited an interesting pharmacological profile in terms of trypanocidal activity and selectivity. The most active adduct with the best selectivity in this study was found to be the phenylacetoxy hydrazone 1 b (2-[4-(tricyclo[3.3.1.1^3,7]dec-1-yl)phenyl]-N′-[(5-nitrofuran-2-yl)methylene]acetohydrazide; EC₅₀=11±0.9 nm , SI_Tb=770).     

Acylation of salicylamide to 5-acetylsalicylamide using ionic liquids as dual catalyst and solvent

The Lewis acidic ionic liquids, 1-butyl-3-methylimidazolium chloroaluminate ([BMIM]Cl-nAlCl₃) and N-butylpyridinium chloroaluminate ([BPy]Cl-nAlCl₃), were used as both catalyst and solvent in Friedel–Crafts acylation of salicylamide with acetyl chloride to 5-acetylsalicylamide. The Lewis acidic ionic liquids, substituting for the conventional carcinogenic nitrobenzene solvent and anhydrous AlCl₃ catalyst, showed excellent catalytic activity in the acylation of salicylamide to 5-acetylsalicylamide. When [BMIM]Cl-2AlCl₃ was used as the catalyst, the yield of 5-acetylsalicylamide reached 81.3%. When [BPy]-2AlCl₃ was used as the catalyst, the maximum yield of 5-acetylsalicylamide was 89.2%. The content of AlCl₃ and the structure of the cations in the ionic liquids had synergistic effect on the acylation reaction.     

Oligomerization of n‐Butenes in a Two‐Phase Reaction System with Homogeneous Ni/Al‐Catalysts

The oligomerization of n‐butenes in a two‐phase catalyst system consisting of a Lewis acidic ionic liquid (IL) and a nonpolar phase is described. A highly active catalyst system with NiCl₂(PMe₃)₂ was investigated, resulting in 91 % dimers with N‐methylpyrrole as a buffer. The reaction was found to be dependent on the molar ratio of the IL to the catalyst. Additionally, the influence of the Lewis acid was investigated and AlCl₃ was determined as the most suitable for activating the nickel complex. The concentration of AlCl₃ played an important role in achieving high catalyst activity and dimer selectivity. Several reactions with different pyrrole derivatives demonstrated that the use of a buffer with low steric hindrance was also important with regard to increased dimer selectivity.     

The synthesis and characterisation of poly( 14-cyclopentenylene-5,6-ethylidene-2,3-disodium dicarboxy1ate)s and Pendant functional group isomerisation

Summary Poly(l,4-cyclopentenylene-5,6-ethylidene-2,3-disodium dicarboxy1ate)s have been synthesised from the exo,exo-, endo,endo- and exo, endo- isomers of dimethyl bicyclo[2.2.l]hept-5-ene-2,3-dicarboxylates in a three step process involving ring opening metathesis polymerisation, hydrogenation and hydrolysis. Exo,exo- and endo,exo- pendant functional group stereochemistries were unchanged throughout these processes, whereas, the Polymers derived from the endo,endo-monomer underwent fragmentation during hydrogenation and isomerisation during hydrolysi s to give to the more stable endo,exo- form of the polymer. Received: 25 July 2002/ Accepted: 7 October 2002 Correspondence to W. J. Feast     

An unusual epimerization of a thioether

Reaction of 6-exo-methylthio-2-exo-phenylbicyclo[2.2.1]heptan-2-endo-ol with sodium azide and acid afforded the corresponding 2-exo-azide. This azide was reduced and acetylated to give a crystalline derivative whose structure was unequivocally established by X-ray crystallographic analysis. Surprisingly, the isomeric 6-endo-methylthio-2-exo-phenylbicyclo[2.2.1]heptan-2-endo-ol on reaction with sodium azide and acid yielded the same azide as the 6-exo-methylthio analogue. Evidence for the mechanism of thioisomerization is presented.     

An Economical,Green Pathway to Biaryls: Palladium Nanoparticles Catalyzed Ullmann Reaction in Ionic Liquid/ Supercritical Carbon Dioxide System

In this paper, an economical, green pathway involving the palladium nanoparticles (Pd NPs) catalyzed reductive Ullmann reaction of an aryl chloride to afford a biaryl with high conversion and selectivity in an ionic liquid (IL)/supercritical carbon dioxide (ScCO₂) system was developed. The combination of IL and ScCO₂ provides superior advantages in product separation, catalyst recycling and reuse of reaction media over traditional organic solvents. Further investigations showed that the Brønsted‐acidic imidazolium IL {e.g., (1‐butyl‐3‐(sulfobutyl)‐imidazolium) hydrogen sulfate, [bmim(HSO₃C₄)][HSO₄]}, can replace the traditional active hydrogen donor readily with much enhanced product separation efficiency, the use of IL also led to an obvious improved stability of the Pd NPs, which was very helpful for catalyst recycling. Carbon dioxide, a naturally abundant, non‐flammable, relatively non‐toxic, economical and recyclable “greenhouse” gas, was found to significantly promote the selectivity of the Pd NPs‐catalyzed aluminium‐induced reductive Ullmann reaction of aryl chlorides. Investigations showed that the Pd NPs catalyst and IL can be recycled for at least five runs, indicating the economic viability of this process.     

A Highly Efficient Hβ Zeolite Supported Pt Catalyst Promoted by Chromium for the Hydroisomerization of n-Heptane

Hβ zeolite supported Pt catalysts promoted by Cr, La, Ce, Al or Zn were prepared by the co-impregnation method, and characterized by XRD, BET, NH₃-TPD and H₂-TPR. Their catalytic activities were evaluated in the hydroisomerization of n-heptane with an atmospheric fixed-bed reactor. The Pt-bearing catalyst doped with Cr, La or Ce, especially Cr, is found to exhibit a much higher catalytic activity and isomerization selectivity than the catalyst without the dopant. At the low reaction temperature of 230 °C, the catalyst with a Pt loading of 0.4% and a molar ratio of Cr to Pt of 5:1 shows a high conversion of n-heptane of 77.1% coupled with a high selectivity to isomerization products of 94.4%. In contrast, over the counterpart catalyst without Cr, the conversion of n-heptane is 50.6% with a low selectivity to isomerization products of 82.4%. The substantial promotion effect of Cr is suggested to associate with the improved Pt dispersion, as well as the increased strong acid amount, due to the introducing of Cr into the catalyst.     

Synthesis of novel block copolymers containing polyhedral oligomeric silsesquioxane (POSS) pendent groups via ring-opening metathesis polymerization (ROMP)

Ring-opening metathesis copolymerization of norbornene ethyl polyhedral oligomeric silsesquioxane monomer (NBEPOSS) and 2-endo-3-exo-5-norbornene-2,3-dicaboxylic acid trimethyl ester (NBETMS) was performed using a Ru-based catalyst, RuCl₂(CHPh)(PCy₃)₂. The block copolymers poly(NBETMS-b-NBEPOSS) were then converted to poly(NBECOOH-b-NBEPOSS) by hydrolysis and precipitation. The polymers were characterized by NMR and GPC and the actual NBEPOSS contents were found in good correspondence with the theoretical values. A linear dependence of M_n on conversion and a linear dependence of ln([M₀]/[M]) on reaction time observed in the polymerization of NBETMS suggest that chain breaking reactions such as termination and chain transfer are minimal. Low PDI values and smooth GPC peak shifts during polymerization after addition of a second batch of the same monomer or a NBEPOSS monomer also reflect a living process.     

Triethylsulfonium Bistriflimide as the Reaction Medium in Catalyzed and Uncatalyzed Cycloaddition [4 + 2]

Triethylsulfonium bistriflimide, [S_2.2.2][NTf₂], has been tested and compared with other ionic liquids and molecular solvents as a medium in Diels–Alder reaction between cyclopentadiene and dimethyl maleate. Triflates and chlorides of different metals have been combined with [S_2.2.2][NTf₂] and the catalytic activity of the systems formed have been determined. The effect of concentration of the catalysts in sulfonium ionic liquid and reactants on the yield and endo:exo ratio has been established. The representative catalyst—Yb(OTf)₃·xH₂O in [S_2.2.2][NTf₂] has been examined in the reaction of cyclopentadiene with various dienophiles. The use of sulfonium ionic liquids permitted recycling the catalysts. For the best four catalytic systems, the products have been isolated.     

Benzylation of benzene to diphenylmethane using zeolite catalysts

The catalytic liquid phase benzylation of benzene to diphenylmethane (DPM) with benzyl chloride (BC) is investigated over a number of zeolite catalysts at 358 K and under atmospheric pressure. Conventional homogeneous Lewis acid catalyst, AlCl₃, is also included for comparison. Zeolite H-β is found to be more selective but less active compared to HY and H-ZSM-5 zeolites in the benzylation of benzene. The conversion of BC, rate of BC conversion and selectivity to DPM over H-β after 6 h of reaction time are 33.3 wt%, 4.7 × 10⁻³ mmol g⁻¹ h⁻¹ and 89.1 wt%, respectively. For comparison, the conversion of BC, rate of BC conversion and selectivity to DPM over AlCl₃, under identical reaction condition, are found to be 100 wt%, 170 × 10⁻³ mmol g⁻¹ h⁻¹ and 58 wt%, respectively. Higher amounts of consecutive products are obtained over AlCl₃ due to its non shape selectivity. The acidity of the zeolite catalysts is measured by temperature programmed desorption method. The effect of the duration of the run, SiO₂/Al₂O₃ ratio of H-β, catalyst concentration, reaction temperature and benzene to BC molar ratio on the catalyst performance is also investigated in order to optimize the conversion of BC and selectivity for DPM. The conversion of BC using H-β is increased with the increase in the reaction time, catalyst concentration, reaction temperature and molar ratios whereas it decreases with the increase in SiO₂/Al₂O₃ molar ratio of H-β. H-β is recycled two times and a slight decrease in BC conversion is observed after each cycle, which is related to the minor dealumination of the zeolite catalyst by HCl, which is produced during the reaction as by product. The formation of DPM is explained by an electrophilic attack of the benzyl cation (C₆H₅CH₂⁺) on the benzene ring, which is produced by the polarization of BC over acidic sites of the zeolite catalysts.