New Indenylidene‐Schiff Base‐Ruthenium Complexes for Cross‐Metathesis and Ring‐Closing Metathesis

We here report on the stability and catalytic activity of new indenylidene‐Schiff base‐ruthenium complexes 3a – f through representative cross‐metathesis (CM) and ring‐closing metathesis (RCM) reactions. Excellent activity of the new complexes was found for the two selected RCM reactions; prominent conversion was obtained compared to the commercial Hoveyda–Grubbs catalyst 2 . Moreover, excellent results were obtained for a standard CM reaction. Higher conversions were achieved with one of the indenylidene catalysts compared with Hoveyda–Grubbs catalyst. Unexpectedly, an isomerization reaction was observed during the CM reaction of allylbenzene. To the best of our knowledge, isomerization reactions in this model CM reaction in closed systems have never been described using first generation catalysts, including the Hoveyda–Grubbs catalyst. The first model CM reactions as well as the RCM reactions have been monitored using ¹H NMR. The course of the CM reaction of 3‐phenylprop‐1‐ene ( 8 ) and cis‐1,4‐diacetoxybut‐2‐ene ( 9 ) was monitored by GC. The isomerization reaction was studied by means of GC‐mass spectrometry and in situ IR spectroscopy. All catalysts were structurally characterized by means of ¹H, ¹³C, and ³¹P NMR spectroscopy.     

Transport of Iron and Cobalt Complex Ions through Liquid Membrane Mediated by Methyltrioctylammonium Ion with the Aid of Redox Reaction

Abstract

A new type of carrier-mediated metal transport through liquid membrane is presented. The system involves redox reactions rather than acid-base reactions which have often been utilized in metal transport systems. Iron ion was selectively transported and concentrated through the membrane via a chloride complex by use of a lipophilic quaternary ammonium ion, methyltrioctylammonium (MTOA, Q⁺), as a carrier. The two aqueous solutions of different redox potentials were separated by a polymer-supported liquid membrane in which MTOA · chloride (Q⁺·CI^?) was dissolved as the carrier. Iron(III) ion in hydrochloric acid media formed a FeCl₄ ^? type complex which was readily extracted to the organic membrane phase as an ion-pair complex Q⁺·FeCl₄ ^?. On contact with a reducing agent on the other side of the membrane, iron(III) was reduced to iron(II) and liberated into aqueous solution; the chloride complexes of iron(II) are too hydrophilic to stay in the membrane phase. On the other hand, cobalt ion was transported via nitrilotriacetic acid (NTA) complex by MTOA carrier in a similar manner to the iron transport. The nature of the transport reactions was studied under various operational conditions (redox agents, carrier and ligand concentration, pH, coexisting metals, etc.). The extension of these transport reactions to a water-in-oil-in-water type emulsion system as well as to a photoassisted transport system was studied.     

Kinetics of the thermo-oxidative and thermal cracking reactions of Athabasca bitumen

The thermo-oxidative and thermal cracking reactions of Athabasca bitumen were examined qualitatively and quantitatively using differential thermal analysis (DTA). Reaction kinetics of low temperature oxidation (LTO) and high temperature cracking (HTC) were determined. The rate of the LTO reaction was found to be first order with respect to oxygen concentration. The activation energy and the Arrhenius pre-exponential factor were 64 MJ kg^?1 mol^?1 and 10^5.4 s^?1, respectively. The effects of atmosphere, pressure, heating rate and support material on the thermal reactions of bitumen were studied. In general, it was found that partial pressures of oxygen > 10% O₂ favoured exothermic oxidation reactions. High pressure increased the rates of LTO and HTC as well as the exothermicity of these reactions. A major contribution of this study to thermal in-situ processes is that heating rate can be used effectively to control the extent of low temperature oxidation and hence fuel availability during in-situ combustion. Low linear heating rates (2.8 °C min^?1) favoured low temperature oxidative addition and fission reactions. The reaction products readily formed coke and combusted upon heating. High linear heating rates (24.5 °C min ^?1) led to rapid oxidation reactions in the high temperature zone; the high temperature and the energy released during oxidation appeared to promote combustion. Finally, when sand was used as the support material there appeared to be a catalytic effect in both LTO and HTC reactions.     

Polymerization of Triazolinediones with trans-3,3-Dichloro-1-phenyl-1-propene

The reaction of 4-phenyl-1,2,4-triazoline-3,5-dione (PhTD) ( 2 ) with trans-3,3-dichloro-1-phenyl-1-propene ( 4 ) was investigated at room and reflux temperatures in methylene chloride solution. Although the reaction is slow, it gives quantitative yield. This reaction leads to the formation of two 2:1 adducts via double Diels–Alder and Diels–Alder-Ene reactions in a ratio of about 1: 7. The major product was isolated by means of fractional crystallization as a pure compound and was characterized by infra-red (IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR, mass spectra and elemental analysis. The structure of the minor product was determined by IR and ¹H NMR. These compounds were used as models for the polymerization reactions. The reaction of bistriazolinediones (1,6-bis-(3,5-dioxo-1,2,4-triazoline-4-yl)hexane and bis-(p-3,5-dioxo-1,2,4-triazoline-4-ylphenyl)methane) with ( 4 ) was carried out in dimethylformamide (DMF). The reactions gave novel polymers via repetitive double Diels–Alder and Diels–Alder-Ene polyaddition reactions, with the major component being a Diels–Alder-Ene structure. These polymers have intrinsic viscosities in a range from 0·08 to 0·18dlg^-1 in DMF. The physical properties and structural characterization of these polymers have been studied and are reported. © of SCI.     

Influence of preflame reactions on combustion of hydrocarbons in shock-heated air

The reactions leading to the propagation of a flame have been studied in shock-heated air containing small amounts of either (normal) octane or 1,1-dimethyl hexane (isooctane). Preflame reactions, associated with the production of excited hydroxyl radicals, have been shown to occur with both octanes. Such reactions would account for the observed acceleration of the flame with octane and its retardation with isooctane, provided that the products from octane were more reactive (as found here) and the products from isooctane less reactive (as found by Cullis⁹ for heptane) than the parent hydrocarbons. Isooctane, as expected, was more resistant to preflame reactions; nevertheless they were observed at temperatures as low as 1050 K. The temperature coefficients of the reactions governing the growth of chemiluminescent radiation are similar for the two octanes: 330 and 350 kJ mol^?1 for octane and isooctane respectively. The temperature coefficients for the reactions controlling the overall burning are lower, falling to about 190 kJ mol^?1. The marked differences between the growth of pressure in what is essentially a premixed flame, and the growth of pressure in the combustion of droplets of (normal) hexadecane, are noted.     

Formation and growth mechanism of porous,amorphous, and fine particles prepared by chemical vapor deposition. Titania from titanium tetraisopropoxide

The formation and growth mechanism of porous, amorphous, and fine particles were investigated. TiO₂ particles were produced in a tubular flow reactor by a chemical vapor deposition technique using titanium tetraisopropoxide as a starting material at low temperatures (573-973 K) and atmospheric pressure. Prepared particles were of submicron size and had large surface area (as large as 270 × 10³ m²/kg). According to the proposed mechanism, reactions begin on the reactor wall and then the primary particles form in the gas phase by chemical reactions. The primary particles collide, coalesce with each other and grow. However, significant experimental deviations from the Brownian collision and coalescence theory imply that other processes, such as the surface reactions on the particle, play an important role in the growth, in addition to coalescence. Intraparticle reactions decreased the surface area by filling the pores.     

Study of the reaction between resorcinol and formaldehyde

The reactions between resorcinol and formaldehyde were led in aluminium pans of a d.s.c. Perkin Elmer calorimeter. The products were separated by means of high performance liquid chromatography and identified by ¹H and ¹³C n.m.r. Depending on the catalyst concentration and molar ratio the mixtures reacted at two different temperature ranges, 317–332K and 332–366K. The heat of the reaction in the first temperature range was between 16.8 and 45.0 kJ mol^?1 for molar ratios 1:1 and 1:3 respectively. By ¹H and ¹³C n.m.r. spectroscopy five addition products were determined. The reaction heat in the second temperature range was 73.5 kJ mol^?1 and was attributed to condensation reactions. The activation energies were 95.0 and 120.0 kJ mol^?1 for addition and condensation reactions respectively. For addition, order two and for condensation, order one of reaction was established. On the basis of these foundings tentative reaction schemes were prepared.     

Kinetics of methyl ester production from mixed crude palm oil by using acid-alkali catalyst

The production of biodiesel from high free fatty acid mixed crude palm oil using a two-stage process was investigated. The kinetics of the reactions was determined in a batch reactor at various reaction temperatures. It was found that the optimum conditions for reducing high free fatty acid (FFA) in MCPO (8-12 wt.%/wt oil) using esterification was a 10:1 molar ratio of methanol to FFA and using 10 wt.%/wt of sulfuric acid (based on FFA) as catalyst. The subsequent transesterification reaction to convert triglycerides to the methyl ester was found to be optimal using 6:1 molar ratio of methanol to the triglyceride (TG) in MCPO and using 0.6 wt.%/vol_TG sodium hydroxide as catalyst. Both reactions were carried out in a stirred batch reactor over a period of 20 min at 55, 60 and 65 °C. The concentration of compounds in each sample was analyzed by Thin Layer Chromatography/Flame Ionization Detector (TLC/FID), Karl Fischer, and titration techniques. The results were used for calculating the rate coefficients by using the curve-fitting tool of MATLAB. Optimal reaction rate coefficients for the forward and reverse esterification reactions of FFA were 1.340 and 0.682 l mol⁻¹ min⁻¹, respectively. The corresponding optimal transesterification, rate coefficients for the forward reactions of TG, diglyceride (DG), and monoglyceride (MG) of transesterification were 2.600, 1.186, and 2.303 l mol⁻¹ min⁻¹, and for the reverse reactions were 0.248, 0.227, and 0.022 l mol⁻¹ min⁻¹, respectively.     

Determination of transition state theory rate constants to describe mercury oxidation in combustion systems mediated by Cl, Cl2, HCl and HOCl

Transition state theory rate constants for the 8-step homogeneous Hg-Cl reaction mechanism were computed based on high level quantum chemistry calculations for the temperature range of 298-2000 K. ECP basis sets were used for Hg and accurate all-electron basis sets with polarization and diffuse functions were used for Cl/O/H species. The quantum computational method for each reaction was chosen by validating the calculated values of properties such as molecular structure, vibration frequency and reaction enthalpy. Activation energies for the Hg + Cl + M reaction calculated using the QCISD and QCISD(T) methods were inconsistent with those expected for radical recombination reactions. The three-body Hg/HgCl recombination reactions with Cl were observed to be the fastest mercury-chlorine reactions. The rate constants of Hg/HgCl reactions with HOCl were faster or comparable to that with Cl₂ whereas the reactions involving Hg/HgCl and HCl were the slowest. The conversion of Hg⁺ to Hg²⁺ is faster than the conversion of Hg⁰ to Hg⁺ suggesting that HgCl is a reactive intermediate under these conditions.     

From catalysis by metals to bifunctional photocatalysis

“Catalysis by metals”, was transposed to “Bifunctional Photocatalysis”, based on noble metals deposited on titania. Both, participation (i) of the photo-active oxidic support and (ii) of the deposited metal have been successfully analyzed, delimited and associated. For both reactions involving hydrogen (Cyclopentane-Deuterium Isotope Exchange (CDIE) and alcohol dehydrogenation), the respective roles of electrons and holes were clearly put in evidence. The photogenerated electrons were found to be spontaneously transferred to the metal nano-particles because of the alignment of the Fermi levels of both solid phases. They neutralize protons H⁺ (or deuterons D⁺) into atoms before their recombination and evolution of dihydrogen (or HD). Simultaneously, photogenerated holes h⁺ neutralize anionic species in oxidation reactions responsible for the activation of organic molecules. These two anionic species were OD⁻ deuteroxyl surface groups in CDIE and alcoholate anions RO⁻ in alcohol dehydrogenation, respectively. Both reactions exhibited a stoichiometric threshold which was exceeded several hundreds of times, clearly defining the real catalytic character of both reactions. The titania-deposited noble metals appeared as auxiliaries or co-catalysts working independently of UV-irradiation for making the reaction run catalytically. Eventually, the concepts of bifunctional photocatalysis were applied to account for interphasic photocatalytic processes such as hydrogen transfer, electron transfer, photosensitization in the visible via CdS addition.     

Chemoenzymatic synthesis: a strategy to obtain xylitol monoesters

BACKGROUND: Fatty acid sugar esters are used as non‐ionic surfactants in cosmetics, foodstuffs and pharmaceuticals. In particular, monoesters of xylitol have attracted industrial interest due to their outstanding biological activities. In this work, xylitol monoesters were obtained by chemoenzymatic synthesis, in which, first, xylitol was made soluble in organic solvent by chemo‐protecting reaction, followed by enzymatic esterification reaction using different acyl donors. A commercial immobilized Candida antartica lipase was used as catalyst, and reactions with pure xylitol were carried out to generate data for comparison. RESULTS: t‐BuOH was found to be the most suitable solvent to carry out esterification reactions with both pure and protected xylitol. The highest yields were obtained for reactions carried out with pure xylitol, but in this case by‐products, such as di‐ and tri‐esters isomers were formed, which required a multi‐step purification process. For the systems with protected xylitol, conversions of 86%, 58% and 24% were achieved using oleic, lauric and butyric acids, respectively. The structures of the monoesters were confirmed by ¹³C‐ and ¹H‐NMR and microanalysis. CONCLUSION: The chemoenzymatic synthesis of xylitol monoesters avoided laborious downstream processing when compared with reactions performed with pure xylitol. Monoesters production from protected xylitol was shown to be a practical, economical, and clean route for this process, allowing a simple separation, because there are no other products formed besides xylitol monoesters and residual xylitol. Copyright © 2009 Society of Chemical Industry     

The cationic oligomerization of p-aminostyrene 2. Dimerization in the intial stage

Summary It was found that p-aminostyrene (PAS) could be oligomerized by using several aminium perchlorates as catalysts in acetonitrile to give a dimer D in the initial stage of the reaction and finally the isomerization oligomer 1 at the end, in quite similar manner to the preceding paper (1), where dimerization (hydroamination) is the main reaction in the initial stage. The pK_a values for the amines were evaluated by the indicator method, and the [H⁺]₀ and [MH⁺]₀ values were calculated from equilibrium equations. As a result, the rate increased with decreasing pK_a of the catalytic amine used and reached an overall constant value. From the relationships between the rate of the reaction and the [H⁺]₀ or [MH⁺]₀ values calculated numerically, however, it was determined that the rate was more affected by the [H⁺]₀ or [M⁺]₀ values rather than the pK_a of the catalyst. It was assumed that the reaction would be initiated by the electrophilic attack of MH⁺ on the double bond of the monomer. Three successive reactions were proposed for the dimerization step: slow protonation followed by subsequent fast reactions; amine addition to the resultant styryl cation and proton elimination. It was assumed that oligomerization might proceed via the same three successive reactions as proposed for the dimerization step. Received: 24 July 2000/Revised version: 8 September 2000/Accepted: 18 September 2000     

Spectral Probe for Electron Transfer and Addition Reactions of Azide Radicals with Substituted Quinoxalin-2-Ones in Aqueous Solutions

The azide radical (N₃^●) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N₃^● reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N₃^● addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO₄^●−, CO₃^●−) and Tl²⁺ ions with the reduction potentials higher, and one radical (SCN)₂^●− with the reduction potential slightly lower than the reduction potential of N₃^● were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N₃^● with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N₃^● differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N₃^● is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N₃^● with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ)^●+, radicals (7-R-3-MeQ)^● and N₃^● adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning’s aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions.     

Controlling Product Composition of Metathesized Triolein by Reaction Concentrations

Triolein was used as a model material to investigate the effect of concentration on self metathesis of vegetable oils. The metathesis reaction using Grubbs' second generation catalyst (used at a level of 2.5?mol?% of triolein) was carried out at 38?°C using dichloromethane as the solvent. The products from three reaction concentrations were investigated: neat, 10 and 20?mmol/L. The products from the reactions were separated by column chromatography and the fractions were characterized by ¹H-NMR, ¹³C-NMR, MS and FTIR. Mono-cyclic and multi-cyclic triacylglycerol-based compounds and different level aliphatic triacylglycerol-like oligomers were produced, but the compositions of the products were found to be significantly controlled by the reaction concentrations. Cyclic compounds were favorably produced at lower reaction concentrations, whereas, linear oligomers were favorably produced at higher reaction concentrations. Cyclic compounds were formed mainly from adjacent fatty acid chains on the glycerol backbone. In the neat reactions, only linear oligomers were produced. The trans/cis ratios increased as concentration was increased.     

Chemical processes initiated by a nonequilibrium plasma in solutions

Oxidation of I^-, Br∼, S²∼, Cr²⁺, and Mn²⁺ ions, as well as monochlorotriazine blue, in aqueous solutions was studied. The process was initiated by a steady-state discharge between a metal anode and an electrolyte solution. These reactions were found to be associated with active particles generated in both the gas-discharge plasma zone and the surface layer of the solution.     

A Synthetic Approach to Oligomeric Phenylethynylsilylenes

Oligomers consisting of alternating phenylethynyl and monosilyl or disilanyl moieties were synthesized in 15–64% precipitated yields by the reactions of dilithiated ethynylbenzene with dichlorodimethylsilane, dichlorodiphenylsilane, and 1,2-dichloro-1,1,2,2-tetramethyldisilane. Degrees of polymerization were fairly low due to chain termination reactions involving the deprotonation of ethynyl groups by aryllithium species. The presence of butyl chain ends was confirmed by ¹H and ²⁹Si NMR spectroscopy. ²⁹Si NMR spectroscopy was utilized to illustrate the random pattern of connectivity along the oligomer backbones. The oligomers exhibit fluorescent behavior in solution.     

Chemical modification of crosslinked phenyl acrylate copolymers with monoethanolamine

Copolymerisation of phenyl methacrylate, 4-chlorophenyl acrylate, 4-nitrophenyl acrylate and 2,4,6-tribromophenyl acrylate with divinyl benzene was carried out in aqueous suspension medium at 80°C using benzoyl peroxide as radical initiator. The resulting beaded copolymers were characterised by FTIR. optical and scanning electron microscopy. Polymer analogue reactions of these particulate copolymers with monoethanolamine were carried out at 60.80 and 100°C in dimethyl sulphoxide as solvent. The progress of the reactions was followed by observing the disappearance of phenyl ester carbonyl absorption at 1750 cm⁻¹ and the appearance of 1650cm⁻¹ vibration corresponding to the characteristic amide carbonyl. The percentage conversions were calculated, and the effect of polar substituents in the phenyl acrylates as well as temperature on the reaction are discussed.     

Bulk polymerization of hydroxyl terminated polybutadiene (HTPB) with tolylene diisocyanate (TDI): A kinetics study using 13C-NMR spectroscopy

The bulk polymerization of hydroxyl-terminated polybutadene with tolylene diisocyanate has been studied in uncatalyzed isothermal reactions. The conversion in urethane was monitored by ¹³C-NMR spectroscopy of the C?O function at level up to 70%. Effects of reagents ratio and temperature were investigated. The experimental data were modeled by a set of two competitive second-order reactions to account for the difference in reactivity of o-NCO and p-NCO groups of tolylene 2,4 diisocyanate. The apparent kinetic constants calculated appeared to be statistically higher than previous results found in literature from work in aromatic solvents. Deviations from second-order law were observed during the last stage of polymerization. Activation energies were estimated at 12.3 kJ. mol^?1 and 42.8 kJ. mol^?1 for the p-NCO and o-NCO groups, respectively. The difference in their reactivity tended to decrease as temperature of reaction was increased. © 1995 John Wiley & Sons, Inc.     

Modification of maleic anhydride–styrene copolymer with noradrenaline by chemical and enzymatic methods

Maleic anhydride copolymer was modified with another biologically active agent, noradrenaline (NA), using both chemical and enzymatic methods. The modification and synthesized products were named as follows: chemical modification, MASTNAc; enzymatic modification, MASTNAe; enzymatically synthesized MASTNA from individual monomers, MASTNAem. Chemical and enzymatic reactions were performed at 70°C and 38°C, respectively. In the chemical reactions azobisisobutyronitrile was used as the initiator. In the enzymatic reactions, an extracellular extract, including an enzyme with peroxidase‐like activity, was used. All the reactions were performed in an organic medium, methyl ethyl ketone. Structural characterization of the copolymer and modified copolymer were carried out by Fourier transform infrared (FTIR) and nuclear magnetic resonance (¹H NMR). FTIR and ¹H NMR spectra confirmed that NA was successfully covalently bound onto the MAST copolymer backbone by both chemical and enzymatic methods. Surface morphology of the samples was studied by scanning electron microscopy. Results obtained indicated that chemical and enzymatic addition of NA to MAST backbone yielded products having quite similar physical and chemical properties. On the other hand, MASTNA‐modified copolymer synthesized by individual monomers appeared to be different in its chemical structure. Furthermore, enzymatic modification and synthesis appeared to provide a good alternative method because it required much milder conditions such as low temperature, and better product qualities: higher solubility in water, higher yield and purity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Desulfurization of gasoline by a new method of electrochemical catalytic oxidation

A new deep desulfurization process for gasoline was obtained by means of electrochemical catalytic oxidation with an electrochemical fluidized-bed reactor on particle group anode. The particle group anode was activated carbon-supported cerium dioxide (CeO₂/C), and the electrolyte was aqueous cerium nitrate solution, and copper pillar was cathode in the electrochemical reactions. The CeO₂/C particle group anode could remarkably accelerate the electrochemical reaction rate and promote the electrochemical catalysis performance for the electrochemical desulfurization reaction. Thermodynamics feasibility analysis clarified that the theoretical decomposition voltage ranged from 0.1–0.5 V in pure acid electrolyte system and desulfurization reactions could not spontaneously carry out, but the reactions were spontaneous when aqueous cerium nitrate solution serves as electrolyte. And the rule of the gasoline desulfurization by the means of electrochemical catalytic oxidation was investigated. The experimental results indicated that the optimal desulfurization conditions were as follows: the cell voltage, concentration of the Ce³⁺ ions, feed volume flow rate and the CeO₂ percentage by weight were 3.2 V, 0.08 mol l⁻¹, 300 ml min⁻¹ and 5.0 wt%, respectively. Under these conditions the concentration of sulfur in gasoline was reduced from 310 to 50 parts per million by weight (ppmw). Based on these experimental results, a mechanism of indirect electrochemical oxidation was also proposed.