Stability of the first-generation Grubbs metathesis catalyst in a continuous flow reactor

Ethylene pretreatment of the (PCy₃)₂Cl₂RuCHPh catalyst (1) prior to cross-metathesis of ethylene and cis-2-butene to form propylene in the continuous flow reactor produced a direct effect on catalyst deactivation. Similar cis-2-butene pretreatment of the same catalyst exhibited far less change in the catalyst activity. These results support the assumption that the ruthenium methylidene intermediate generated from ethylene and 1 is unstable and promotes catalyst loss while ruthenium alkylidenes, e.g. derived from 2-butene, exhibit significantly enhanced stability and sustained catalyst integrity. Continuous removal of products in the continuous flow reactor was important for separating the catalyst decay and the catalyst deactivation caused by a terminal olefin, in this case propylene.The amount of produced propylene during the 1 lifespan was determined in a series of tests using identical catalyst concentrations ([Ru] = 60 ppm) in pentadecane while varying the olefin pretreatment times from 0 to 420 min. The catalyst turnover numbers in the cross-metathesis experiments proved inversely proportional to the duration of ethylene treatment prior to the reaction. The activity of 1 pre-exposed to ethylene closely matched with the activity of the catalyst that decayed in the reaction mixture containing ethylene and cis-2-butene for the same period of time. A significant contribution of the Ru-methylidene decay to the activity losses in metathesis reactions was demonstrated directly in the cross-metathesis reaction environment. The catalyst proved to be less sensitive to cis-2-butene pretreatment and showed turnover numbers for subsequent cross-metathesis essentially similar to the reference cross-metathesis test.     

(Vapour + liquid) equilibria for the binary mixtures (cis-pinane + α-pinene) and (cis-pinane + 1-butanol)

The isothermal and isobaric (vapour + liquid) equilibria for (cis-pinane + α-pinene) and (cis-pinane + 1-butanol) measured with an inclined ebulliometer are presented. The experimental results are analysed using the UNIQUAC equation with the temperature-dependence binary parameters with satisfactory results. Experimental vapour pressures of cis-pinane are also included.     

Reactivity of chlorodeoxypseudoephedrines with oxo-, thio-, and selenocyanates

Herein, the reactivity of chlorodeoxypseudoephedrine hydrochlorides with oxo-, thio-, and selenocyanate nucleophiles is reported. 1,3-Heterazolidine-2-iminium or ammonium salts were obtained stereoselectively in most cases. The hard–soft nature of the calcogen atom determines the mechanistic pathway via an S_N2 (X = O), aziridine intermediate (X = Se), or both (X = S). A simple method to synthesize stereoselectively the trans-isomer of 3,4-dimethyl-5-phenyl-oxazolidine-2-iminium chloride and the cis-isomer of 4-methyl-5-phenyl-oxazoline-2-ammonium chloride, was also found. In addition, heterazolidine-2-imines or amines were liberated from the corresponding salts [Cl⁻ or XCN⁻ (X = O, S, Se)] with aqueous NaOH. Finally, cis-3,4-dimethyl-5-phenyl-oxazolidine-2-iminium chloride, cis-4-methyl-5-phenyl-oxazoline-2-amine, and trans-4-methyl-5-phenyl-selenazoline-2-amine compounds were studied by X-ray diffraction.     

Spin-crossover in dimeric hydrogen-bonded iron(II) 2-(pyrazolyl)-pyridine and 2-(imidazolyl)-pyridine complexes

Five new hydrogen-bonded solvated iron(II) complexes of pyrazolyl- and imidazolyl-based N,N-chelating ligands have been synthesised. Water to ligand-NH hydrogen-bonded bridges occur in the pseudo-dimeric complexes {cis-[Fe(pypzH)₂(NCX)₂]₂(μ-OH₂)(H₂O)₂} · H₂O · MeOH (where X = S or Se), and in the chain complex {cis-[Fe(pypzH)₂(NCS)₂](μ-OH₂)}_n. A “half” spin-crossover (T_c = 125 K) was observed in the dimeric X = Se complex by means of magnetic measurements and no thermal hysteresis occurred between 4 and 300 K. The crystal structure at 123 K showed Fe–N distances consistent with the magnetism. Each Fe in the dimeric unit was structurally equivalent in the HS–LS state. Removal of the solvate molecules led to HS–HS behaviour over the temperature range 4–300 K. The pseudo-dimer with X = S also showed HS–HS behaviour as did the monomeric analogue cis-[Fe(pypzH)₂(NCS)₂]H₂O and a structurally different methanol-bridged dimer {cis-[Fe(pyimH)₂(NCS)₂]₂(μ-MeOH)₂} · 2MeOH (pypzH = 2-(1H-pyrazol-3-yl)-pyridine; pyimH = 2-(1H-imidazol-2-yl)-pyridine).     

Lewis acid-assisted olefin cross-metathesis reaction: an efficient approach for the synthesis of glycosidic-pyrroloquinolinone based novel building blocks of camptothecin and evaluation of their antitumor activity

A series of glycosidic-pyrroloquinolinone based novel building blocks of camptothecin (2a–g) were synthesized via Lewis acid-assisted olefin cross-metathesis reaction using Ti(OⁱPr)₄ 30 mol % and 10 mol % of Grubb’s second generation catalyst with good to excellent yields. Most of these compounds exhibited significant growth inhibitory effects on all the tested cancer cell lines and three compounds (2c, 2d and 2e) showed potent cytotoxic activity.     

Enantioselective synthesis of chiral 1,2-diamines by the catalytic ring opening of azabenzonorbornadienes: application in the preparation of new chiral ligands

In the presence of a rhodium catalyst (5 mol %) generated in situ from [Rh(cod)Cl]₂ and (S,S′)-(R,R′)-C₂-ferriphos-tolyl, the asymmetric ring-opening reaction of N-Boc-azabenzonorbornadienes with dibenzylamine proceeded with excellent enantioselectivity (up to >99% ee) to give the corresponding 1,2-diamine scaffolds in high yields. The sequential deprotection of the ring-opened products and treatment with tartaric acid gave the enantiomerically pure 1,2-diamine tartrate salts. These salts were used for the preparation of new chiral ligands such as the salen-type ligands and Trost-type ligands.     

Catalytic cyclopropanation of olefins using copper(I) diphosphinoamines

Catalytic cyclopropanation reactions of olefins with ethyl diazoacetate were carried out using copper(I) diphosphinoamine (PPh₂)₂N(R) (R = ⁱPr, H, Ph and –CH₂–C₆H₄–CHCH₂) complexes at 40 °C in chloroform. High yields of the cyclopropanes were obtained in all cases. The rate of the reaction was influenced by the nuclearity of the complex and the binding mode of the ligand which was either bridging or chelating. Comparison of isostructural complexes shows that the rate follows the order R = ⁱPr > H > Ph, where R is the substituent on the N. However, cyclopropane formation versus dimerization of the carbene, and trans to cis ratios of cyclopropane was similar in all cases. The nearly identical selectivity for different products formed was indicative of a common catalytic intermediate. A labile “copper–olefin” complex which does not involve the phosphine or the counterion is the most likely candidate. The differences in the reaction rates for different complexes are attributed to differences in the concentration of the catalytically active species which are in equilibrium with the catalytically inactive copper–phosphinoamine complex. To test the hypothesis a diphosphinoamine polymer complexed to copper(I) was used as a heterogeneous catalyst. Leaching of copper(I) and deactivation of the catalyst confirmed the proposed mechanism.     

Isothermal phase (vapour + liquid) equilibrium data for binary mixtures of propene (R1270) with either 1,1,2,3,3,3-hexafluoro-1-propene (R1216) or 2,2,3-trifluoro-3-(trifluoromethyl)oxirane in the temperature range of (279 to 318) K

Isothermal (vapour + liquid) equilibrium data (P–x–y) are presented for the 1-propene 1,1,2,3,3,3-hexafluoro-1-propene and the 1-propene + 2,2,3-trifluoro-3-(trifluoromethyl)oxirane binary systems. Both binary systems were studied at five temperatures, ranging from (279.36 to 318.09) K, at pressures up to 2 MPa. The experimental (vapour + liquid) equilibrium data were measured using an apparatus based on the “(static + analytic)” method incorporating a single movable Rapid On-Line Sampler-Injector to sample the liquid and vapour phases at equilibrium. The expanded uncertainties are approximated on average as T = 0.07 K, 0.008 MPa, and 0.007 and 0.009 for the temperature, pressure, and the liquid and vapour mole fractions, respectively. A homogenous maximum-pressure azeotrope was observed for both binary systems at all temperatures studied. The experimental data were correlated with the Peng–Robinson equation of state using the Mathias–Copeman alpha function, paired with the Wong–Sandler mixing rule and the Non-Random Two Liquid activity coefficient model. The model provided satisfactory representation of the phase equilibrium data measured.     

The infrared spectrum of bis(fluorosulfonyl)imide revisited: Attractive performances of the PBE0/6-31G** model

We report a systematic investigation of the far- and mid-infrared spectra of ionic liquids (ILs) containing the bis(fluorosulfonyl)imide (FSI) anion, both in the liquid state at room temperature and in solid phases at low temperatures. We extended to lower frequencies a previous study, and we observed four additional vibration bands below 500 cm⁻¹, attributable to FSI. Moreover, DFT calculations of vibration frequencies were performed using three combinations of theory and basis set: (1) B3LYP/6-31G**, (2) B3LYP/6-311 + G(3df) and (3) PBE0/6-31G**. Model 1, largely used in the previous literature concerning ILs, shows the poorest performances; model 2, which generally gives a good agreement with the experiments, misses the vibration frequencies by ∼40 cm⁻¹ in the range 650–900 cm⁻¹ where one finds the largest spectral differences between cis- and trans-FSI; model 3 gives the best agreement with the experiments and, moreover, is much less time consuming than model 2. The comparison with calculations suggests that the band centered around 1217 cm⁻¹ is a good marker of the occurrence of the cis-FSI conformer. Finally, the bands located around 730 and 750 cm⁻¹ are attributable to cis- and trans- conformer of FSI, respectively.     

Experimental and theoretical study of quaternary (liquid + liquid) equilibria for mixtures of (methanol or water + ethanol + toluene + n-decane)

Experimental (liquid + liquid) equilibrium data were obtained for the extraction of toluene from n-decane by mixed-solvents (ethanol + water) and (ethanol + methanol) at three temperatures (298.15, 303.15, and 313.15) K and ambient pressure.The measured tie-line data for two quaternary mixtures of {(ethanol +  water) + toluene + n-decane} and {(ethanol + methanol) + toluene + n-decane} are presented. The experimental quaternary (liquid + liquid) equilibrium data have been correlated using the NRTL activity coefficient model to obtain the binary interaction parameters of these components. The NRTL models predict the equilibrium compositions of the quaternary mixtures with small deviations. The partition coefficients and the selectivity factor of the mixed-solvents used were calculated and presented. From our experimental and calculated results, we conclude that for the extraction of toluene from n-decane mixtures the mixed-solvent (ethanol + methanol) has a higher selectivity factor than the other mixed-solvent at the three temperatures studied.     

A thermodynamic study of the (difluoromethane + water) system

A study of the (difluoromethane + water) system was conducted at temperatures between (255 and 298) K, and pressures from (0.06 to 1.30) MPa. The solubility of difluoromethane in liquid water was measured from (280 to 298) K, at pressures up to the hydrate formation pressure. The (p, T) behavior of the (liquid + hydrate + vapor) three-phase equilibrium was measured from (274 to 292) K. The (p, T) behavior of the (ice + hydrate + vapor) three-phase equilibrium was measured from (257 to 273) K. Solubility-corrected enthalpies of dissociation were determined at the lower quadruple point (Q1) using the Clapeyron equation. The de Forcrand method was used to determine the hydration number of the hydrate at Q1. The results show that not all of the cages in the SI hydrate structure are filled.     

High-pressure phase equilibria of {carbon dioxide (CO2) + n-alkyl-imidazolium bis(trifluoromethylsulfonyl)amide} ionic liquids

Ionic liquids (ILs) and carbon dioxide (CO₂) systems have unique phase behavior that has been applied to applications in reactions, extractions, materials, etc. Detailed phase equilibria and modeling are highly desired for their further development. In this work, the (vapor + liquid) equilibrium, (vapor + liquid + liquid) equilibrium, and (liquid + liquid) equilibrium of n-alkyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ionic liquids with CO₂ were measured at temperatures of (298.15, 323.15, 343.15) K and pressure up to 25 MPa. With a constant anion of bis(trifluoromethylsulfonyl)amide, the n-alkyl chain length on the cation was varied from 1-ethyl-3-methyl-imidazolium ([EMIm][Tf₂N]), 1-hexyl-3-methyl-imidazolium ([HMIm][Tf₂N]), to 1-decyl-3-methyl-imidazolium ([DMIm][Tf₂N]). The effects of the cation on the phase behavior and CO₂ solubility were investigated. The longer alkyl chain lengths increase the CO₂ solubility. The Peng–Robinson equation of state with van der Waals 2-parameter mixing rule with estimated IL critical properties were used to model and correlate the experimental data. The models correlate the (vapor + liquid) equilibrium and (liquid + liquid) equilibrium very well. However, extrapolation of the model to much higher pressures (>30 MPa) can results in the prediction of a mixture critical point which, as of yet, has not been found in the literature.     

(Liquid + liquid) equilibrium for the system {ethyl stearate(1) + ethanol(2) + glycerol(3)}

This paper reports the results of a new experimental study on the (liquid + liquid) equilibrium of the system {ethyl stearate(1) + ethanol(2) + glycerol(3)} at atmospheric pressure and at T = (313.15 and 323.15) K. The equilibrium compositions were measured by gas chromatography. Ternary diagrams were obtained for each temperature and the equilibrium data were compared to the system in the presence of salt (NaCl) at T = 323.15 K. The experimentally determined (liquid + liquid) equilibrium data were satisfactorily correlated with NRTL and UNIQUAC equations. A comparative analysis was performed using the UNIFAC-LLE group contribution method. From the results presented herein good predictions were obtained for this ternary system.     

Ternary (liquid + liquid) equilibria for mixtures of (methanol + aniline + n-octane or n-dodecane) at T = 298.15 K

(Liquid + liquid) equilibrium (LLE) data for the ternary mixtures of (methanol + aniline + n-octane) and (methanol + aniline + n-dodecane) at T = 298.15 K and ambient pressure are reported. The compositions of liquid phases at equilibrium were determined and the results were correlated with the UNIQUAC and NRTL activity coefficient models. The partition coefficients and the selectivity factor of methanol for the extraction of aniline from the (aniline + n-octane or n-dodecane) mixtures are calculated and compared. Based on these comparisons, the efficiency of methanol for the extraction of aniline from (aniline + n-dodecane) mixtures is higher than that for the extraction of aniline from (aniline + n-octane) mixtures. The phase diagrams for the ternary mixtures including both the experimental and correlated tie lines are presented. From the phase diagrams and the selectivity factors, it is concluded that methanol may be used as a suitable solvent in extraction of aniline from (aniline + n-octane or n-dodecane) mixtures.     

Vapour pressures,densities, and viscosities of the (water + lithium bromide + potassium acetate) system and (water + lithium bromide + sodium lactate) system

Measurements of thermophysical properties (vapour pressure, density, and viscosity) of the (water + lithium bromide + potassium acetate) system LiBr:CH₃COOK = 2:1 by mass ratio and the (water + lithium bromide + sodium lactate) system LiBr:CH₃CH(OH)COONa = 2:1 by mass ratio were measured. The system, a possible new working fluid for absorption heat pump, consists of absorbent (LiBr + CH₃COOK) or (LiBr + CH₃CH(OH)COONa) and refrigerant H₂O. The vapour pressures were measured in the ranges of temperature and absorbent concentration from T = (293.15 to 333.15) K and from mass fraction 0.20 to 0.50, densities and viscosities were measured from T = (293.15 to 323.15) K and from mass fraction 0.20 to 0.40. The experimental data were correlated with an Antoine-type equation. Densities and viscosities were measured in the same range of temperature and absorbent concentration as that of the vapour pressure. Regression equations for densities and viscosities were obtained with a minimum mean square error criterion.     

(Liquid + liquid) equilibrium of systems involved in the stepwise ethanolysis of vegetable oils

Current concerns about adverse impacts to the environment and human health have encouraged the research and development of renewable fuels, such as biodiesel. The transesterification reaction is a three-stage reaction, which produces two intermediate products (diacylglycerols and monoacylglycerols). Accurate and proper knowledge of the phase equilibrium behaviour during the transesterification process is crucial for a better understanding of the reaction pathway, for the optimisation of reactors and the separation of the products. Thus, in order to thoroughly understand the entire transesterification system for biodiesel production, which consists of six different kinds of components, this study reports experimental results and the thermodynamic modelling of the (liquid + liquid) equilibrium (LLE) of two systems composed by {vegetable oils (sunflower or high oleic sunflower oils) + monoacylglycerols + diacylglycerols (+ethyl esters + fatty acids) + ethanol} at T = (303.15 and 318.15) K, at atmospheric pressure. The LLE experimental values were used to estimate NRTL parameters and to evaluate the UNIFAC model, using its original version with two different set of parameters. Results showed that, due to differences in the number of polar groups, mono- and diacylglycerols behave in opposite ways regarding phase distribution. Experimental data were well correlated using NRTL, in which the maximum deviation value was 0.434%. As for UNIFAC, the model predicted the experimental data with deviations varying within the range of (1.80 to 9.24)%.     

High-pressure phase equilibrium data for systems with carbon dioxide, α-humulene and trans-caryophyllene

The aim of this work is to report phase equilibrium data for the binary systems (CO₂ + α-humulene) and (CO₂ + trans-caryophyllene), and for the ternary system (CO₂ + α-humulene + trans-caryophyllene). Results from literature show that α-humulene and trans-caryophyllene are the main compounds responsible for the anti-inflammatory and anti-allergic characteristics attributed to the medicinal plant Cordia verbenacea D.C., hence giving importance to the phase behaviour investigation performed in this work. Phase equilibrium experiments were performed in a high-pressure, variable-volume view cell over the temperature range of T = (303 to 343) K and pressures up to 20 MPa. (Liquid + liquid) and (vapour + liquid + liquid) equilibrium were observed at T = 303 K, while (vapour + liquid) phase transitions were verified to occur from T = (313 to 343) K, for all systems studied. Thermodynamic modelling was performed using the Peng–Robinson equation of state and the classical quadratic mixing rules, with a satisfactory agreement between experimental and calculated values.     

Thermodynamic study of (anthracene + benzo[a]pyrene) solid mixtures

To characterize better the thermodynamic behavior of a binary polycyclic aromatic hydrocarbon mixture, thermochemical and vapor pressure experiments were used to examine the phase behavior of the {anthracene (1) + benzo[a]pyrene (2)} system. A solid–liquid phase diagram was mapped for the mixture. A eutectic point occurs at x₁ = 0.26. The eutectic mixture is an amorphous solid that lacks organized crystal structure and melts between T = (414 and 420) K. For mixtures that contain 0.10 < x₁ < 0.90, the enthalpy of fusion is dominated by that of the eutectic. (Solid + vapor) equilibrium studies show that mixtures of anthracene and benzo[a]pyrene at x₁ < 0.10 sublime at the vapor pressure of pure benzo[a]pyrene. These results suggest that the (solid + vapor) equilibrium of benzo[a]pyrene is not significantly influenced by moderate levels of anthracene in the crystal structure.     

Evaluation of (vapor + liquid) equilibria for the binary systems (1-octanol + cyclohexane) and (1-octanol + n-hexane), at low alcohol compositions

Isobaric (vapor + liquid) equilibrium at p = 101.32 kPa of pressure has been determined for the systems (1-octanol + cyclohexane) and (1-octanol + n-hexane), at low alcohol mole fractions. These data were satisfactorily correlated, using ASPEN PLUS^® commercial software, with Wilson, NRTL, and UNIQUAC activity coefficient models to obtain the binary interaction parameters of both mixtures. Also, UNIFAC group contribution method was employed to predict the equilibrium of both mixtures. With regression values an accurate knowledge of (vapor + liquid) equilibrium for both mixtures can be reached in a range of 1-octanol mole fractions less than 0.1. UNIFAC method provides acceptable results for (1-octanol + n-hexane) system but not for (1-octanol + cyclohexane) system.     

Do lipases also catalyse the ring cleavage of inactivated cyclic trans-β-lactams?

Twelve-membered cyclic cis- and trans-β-lactams 1b and 2b and the corresponding cyclic cis- and trans-β-amino acid enantiomers, 1a, 1c and 2a, 2c were prepared through the CAL-B-catalysed enantioselective ring cleavage of racemic cis-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-1, and trans-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-2. High enantioselectivities (E >200) were observed for the ring opening of both the cis- and trans-β-lactams when the Lipolase-catalysed reactions were performed with 0.5 equiv of H₂O in i-Pr₂O at 70 °C. The resolved β-lactams 1b and 2b (yield ⩾47%) and β-amino acids 1a and 2a (yield ⩾32%) could be easily separated.