Mass transfer characteristics for VOC permeation through flat sheet porous and composite membranes: The impact of the different membrane layers on the overall membrane resistance

In this paper, the mass transfer coefficients for trichloroethylene (TCE), toluene (TOL) and dimethyl sulfide (DMS) are experimentally determined for different porous and composite membranes. For polypropylene/polyvinylidenedifluoride porous layer/thin film polydimethylsiloxane dense layer composite membranes, membrane mass transfer coefficients are 2.55E−03, 2.82E−03 and 2.90E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. For polyester/polyacrylonitrile porous layer/thin film polydimethylsiloxane dense layer composite membranes, they are higher, namely 4.28E−03, 4.55E−03 and 4.81E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. Analysis of the contribution of the dense layer of both composite membranes to the total membrane resistance for mass transfer, showed that this contribution was small for both composite membranes. The higher mass transfer coefficients of the thin film polydimethylsiloxane composite membranes from this study in comparison to others from the literature are primarily due to improvement of the mass transfer characteristics of the porous layer. Analysis of the mass transfer characteristics of the different porous layers of which the total porous layer is composed, showed that the contribution of the porous “backing” layer for mechanical support can be substantial in comparison to the porous layer in contact with the dense layer.     

Kinetics,catalysis, and mechanism of isomerization of N-[(benzotriazol-1-yl)methyl]anilines into the benzotriazol-2-yl derivatives

The ¹H NMR technique was applied for the measurement of the isomerization rates of N-ethyl-N-[(benzotriazol-1-yl)methyl]aniline ( 4 ) and 4-butyl-N-[(benzotriazol-1-yl)methyl]aniline ( 7 ) to the corresponding benzotriazol-2-yl isomers in dioxane-d₈ at 35°C. The rate constants obtained for pure dioxane-d₈ were 1.62 and 0.28 h^?1 for 4 and 7 , respectively. For both compounds, addition to acetic acid to the dioxane solutions accelerated the isomerizations whereas addition of triethylamine retarded it strongly. Addition of water slowed the isomerization of 4 but accelerated that of 7 : the different effects operating in the two cases are discussed and rationalized. © 1995 John Wiley & Sons, Inc.     

Kinetics of CO2 absorption by aqueous mixtures of N,N′-diethylethanolamine and polyamines

Aqueous solutions of N,Nʹ-diethylethanolamine (DEEA) are prospective high-capacity CO₂-capturing solvents. Their reactivity can be enhanced by promotion with absorption activators. Two polyamines were chosen as activators in this work, viz. (methylamino)propylamine (MAPA) and diethylene triamine (DETA). In a stirred cell reactor, kinetics of CO₂ absorption into aqueous DEEA/MAPA and DEEA/DETA mixtures was studied at 303 K. The molarity of DEEA was varied in the 2–2.5 M range, whereas the polyamine concentration was changed between 0.1 and 0.5 M. Pseudo–first-order rate constants were reported. Second-order rate constants for the CO₂ reactions with MAPA and DETA were determined too. DETA reacts faster than MAPA.     

Kinetics of heat release during the reaction ofn-decane with nitrogen dioxide in the liquid phase

The rates of heat release in the nitrogen dioxide—n-decane system at a molar ratio of nitrogen oxides ton-decane (β) from 2.4·10⁻³ to 3.1 and gaseous volumes per mole ofn-decane (V(g)) equal to 0.05–4.5 were studied in the 55.2–92.8 °C temperature range. The initial rate of the process is determined by the interaction of NO₂ withn-decane. The equilibrium constants of dissociation of N₂O₄ inn-decane and Henry's constants of NO₂ and N₂O₄ in ann-decane solution were determined by complex analysis of the thermodynamic equilibrium in the NO₂—n-decane system and dependences of the initial rates onV(g) and β. The experimentally observed self-acceleration of the process in the region of high β and lowT values was suggested to be due to the reaction of N₂O₄ with intermediate oxidation products. The rate constants of the reaction of NO₂ withn-decane were compared with analogous values determined in its mixtures with HNO₃ solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1789–1794, October, 1997.     

The standard partial molar entropy of the aqueous tetra-n-butylammonium cation

The standard partial molar entropy of the aqueous tetrabutylammonium cation, not known previously, has now been obtained, based on the molar entropy of two of its crystalline salts, the iodide and the tetraphenylborate, recently determined experimentally for this purpose. The calculation required also published molar enthalpies of solution and solubilities of these two salts as well as of the perchlorate. The choice of the anions depended mainly on the limited solubilities of the examined salts in water, facilitating the estimation of the relevant activity coefficients. The result is S^∞(Bu₄N⁺, aq) = (380 ± 20) J · K⁻¹ · mol⁻¹ at T = 298.15 K, on the mol · dm⁻³ scale and based on S^∞(H⁺, aq) = (−22.2 ± 1.2) J · K⁻¹ · mol⁻¹ (yielding the ‘absolute’ value). The molar entropy of this cation in the ideal gas standard state, S(Bu₄N⁺, g) = (798 ± 8) J · K⁻¹ · mol⁻¹ then yielded the molar entropy of hydration Δ_hydS^∞ (Bu₄N⁺) = (−418 ± 23) J · K⁻¹ · mol⁻¹.     

Researches on the reactivity of mannich bases part VIII synthesis of N-methyl(vinylaryl)quinolinium salts and their photosensitivity

Described in this communication is a new synthesis of N-methyl-4-(vinylaryl)quinolinium salts by cyclization of the aminoketones, Ar-CH=CH-CO-CH₂-CH₂-N(CH₃)-C₆H₄-X. The aminoketones were obtained by replacement of the alkyiamino group of the ketoarylidene Mannich bases with various N-methylarylamines. The U.V. spectra of the compounds were obtained. The photosensitivity characteristics in solution are reported. These data show the possibility of dimerization and probable trans → cis isomerization on exposure to visible and ultraviolet light.     

Schwingungsspektren und normalkoordinatenanalyse von CF3,-verbindungen : XXVI. Molekülstrukturen und schwingungsspektren von α-CF3HgN3 und CF3HgNCO

The crystal structures of the isostructural compounds α-CF₃HgN₃ (I) and CF₃HgNCO (II) were determined by X-ray methods. Centrosymmetric dimers are formed with weak Hg---n′ bonds of 2.74(2) Å in I and 2.88(2) Å in II. The Hg---N distance and Hg---N---N angle are 2.02(2) Å and 127(2)° in the monomeric fragment of I, the corresponding values in II are 2.03(2) Å and 137(2)°. Raman and, in part, IR spectra of both compounds in the solid state were recorded and assigned for Cs and C_2h symmetry of the monomers and dimers, respectively. A normal coordinate analysis proved that the stretching vibrations of the (HgN)₂ four-membered ring appeared at ≈400 and ≈75 cm^-1; the force constants amounted to ≈2.0 for the short and to ≈0.25 X 10² N/m for the long HgN bonds.     

Voltammetric studies on the α-tocopherol anion and α-tocopheroxyl (Vitamin E) radical in acetonitrile

The α-tocopheroxyl radical was generated voltammetrically by one-electron oxidation of the α-tocopherol anion (E ^r_1/2=−0.73 V versus Ag|Ag⁺) that was prepared by reacting α-tocopherol with Et₄NOH in acetonitrile (with Bu₄NPF₆ as the supporting electrolyte). Cyclic voltammograms recorded at variable scan rates (0.05–10 V s⁻¹), temperatures (−20 to 20°C) and concentrations (0.5–10 mM) were modelled using digital simulation techniques to determine the rate of bimolecular self-reaction of α-tocopheroxyl radicals. The k values were calculated to be 3×10³ l mol⁻¹ s⁻¹ at 20°C, 2×10³ l mol⁻¹ s⁻¹ at 0°C and 1.2×10³ l mol⁻¹ s⁻¹ at −20°C. In situ electrochemical-EPR experiments performed at a channel electrode confirmed the existence of the α-tocopheroxyl radical.     

Study of the degradation of polyurethane—Part 5: Photo-decomposition of ethyl N-phenylcarbamate, methylene bis (ethyl N-phenylcarbamate) and polyurethane in solution

In order to elucidate the photo-decomposition mechanism of polyurethane based on polyester diol-diphenylmethane-p,p′-diisocyanate, the effects of triplet quenchers, piperylene and oxygen on the photo-decomposition of the polymer, methylene bis (ethyl N-phenylcarbamate) (MEPC) and ethyl N-phenylcarbamate (EPC) were examined in solution. Energy levels and lifetimes of the excited states of these compounds were also determined.Piperylene and oxygen did not affect the photo-decomposition of the samples examined. The results imply that the photo-decomposition of the polymer starts from the excited singlet state. The energy levels and lifetimes for the photo-decomposition of the polymer were as follows: the excited singlet state (S₁): 98·6 kcal/mol (3·2 nsec): the excited triplet state (T₁): 76·7 kcal/mole (2·9 sec).     

Quantification of the Electrophilicities of Diazoalkanes: Kinetics and Mechanism of Azo Couplings with Enamines and Sulfonium Ylides

Kinetics and mechanism of the reactions of methyl diazoacetate, dimethyl diazomalonate, 4-nitrophenyldiazomethane, and diphenyldiazomethane with sulfonium ylides and enamines were investigated by UV-Vis and NMR spectroscopy. Ordinary alkenes undergo 1,3-dipolar cycloadditions with these diazo compounds. In contrast, sulfonium ylides and enamines attack at the terminal nitrogen of the diazo alkanes to give zwitterions, which undergo various subsequent reactions. As only one new bond is formed in the rate-determining step of these reactions, the correlation lg k₂(20 °C)=s_N(N+E) could be used to determine the one-bond electrophilicities E of the diazo compounds from the measured second-order rate constants and the known reactivity indices N and s_N of the sulfonium ylides and enamines. The resulting electrophilicity parameters (−21<E<−18), which are 11–14 orders of magnitude smaller than that of the benzenediazonium ion, are used to define the scope of one-bond nucleophiles which may react with these diazoalkanes.     

Linkage isomerism and redox properties of ruthenium–polypyridine benzotriazole complexes

A new series of mono- and di-substituted ruthenium–polypyridine complexes of the type cis-[Ru^III,II (bpy)₂(L1)(L2)] ^{n +} (L1 = Cl^–, bta or py; L2 = bta; bpy = 2,2-bipyridine; bta = benzotriazole; py = pyridine) has been prepared, isolated as hexafluorophosphate salts, and investigated in organic solutions by means of cyclic voltammetry and spectroelectrochemistry. The chemical oxidation of all the benzotriazole derivatives, starting from cis-[Ru^II(bpy)₂(L1)(bta)] ^x (x = +1 or +2), leads essentially to N(3)-bound products, i.e., cis-[Ru^III(bpy)₂ (L1)(N(3){bta})] ^x+1 isomers. Nevertheless, while the benzotriazole-monosubstituted species undergoes an intramolecular isomerization, N(3) N(2), accompanying the electrochemical reduction centered on the metal ion, Ru^III Ru^II, the disubstituted derivatives do not display any spectral or electrochemical evidence of linkage isomerism. The equilibrium and kinetic constants for the isomerization were determined from the cyclic voltammograms at several scan rates, according to an electrochemical–chemical (EC) coupling scheme. The data were compared with a set of constants and parameters obtained previously for a series of ruthenium and iron complexes. The experimental results were found to be quite consistent with theoretical calculations, and reflect the importance of -backbonding interactions in the stabilization of the metal-centered reduced state (M^II) on such species with low-spin d⁶ configuration.     

Kinetics and mechanism of the oxidation of a heterocyclic thioamide by silver(II)-cyclam

The kinetics of the oxidation of 4,6-dimethyl-2-mercaptopyrimidine (DMP) by Ag(cyclam)²⁺ were studied in buffer solutions from pH 5.8 to 7.2 at constant ionic strength of 0.10?M?(NaClO₄). The reaction is observed to be first-order with respect to [Ag(cyclam)²⁺] and to [DMP]. However, the reaction rate is affected by the pH of the solution owing to the acid–base equilibrium of the thiol. The mechanism postulated to account for the kinetics includes an acid–base equilibrium and oxidation of thiol (RSH) and thiolate ion (RS^?) by Ag(cyclam)²⁺ to RS^· radicals which undergo rapid dimerization to form disulfide (RSSR). From the postulated mechanism and the observed kinetics a rate expression was derived, and second-order rate constants and activation parameters were calculated. The pK _a values of the acid dissociation reaction of DMP were also determined at four temperatures using spectrophotometric methods, and thermodynamic parameters calculated from the K _a values.     

Photometrisch-potentiometrische Bestimmung der Hydrolysenkonstanten vonN-Bromverbindungen

The equilibrium concentrations of all reaction products emerging from the hydrolysis ofN-bromo compounds in the presence of bromide and thereby also the hydrolysis constants (K ₁) have been calculated from the absorbance at 392.8 nm, thepH-value and the initial concentrations of theN-bromo compound and the bromide. The following compounds have been investigated:N-bromo-succinimide:K ₁=2.2·10^–6, 1,3-dibromo-5,5-dimethylhydantoin:K ₁=1.7·10^–5,N-bromoacetamide:K ₁=1.8·10^–6,N-bromo-monochloroacetamide: 5.2·10^–6,N-bromo-dichloroacetamide:K ₁=8.9·10^–6 andN-bromo-trichloroacetamide:K ₁=1.8·10^–5. The precision of the method, which is mainly suited for weak hydrolizingN-bromocompounds (K ₁<10^–4) are discussed and the overall error of the calculated values was found to be in the range of ±5–12%. The reactivities in aqueous solution of the most frequently usedN-bromo compounds are compared by means of the calculated HOBr equilibrium concentrations. The differences to be expected on the basis of the latters are at concentrations >10^–5 mol/l rather great, while they can be neglected in very dilute solutions (-10^–6 mol/l).

     

Determination of the Dimerization Equilibrium Constants of Omeprazole and Pirkle's Alcohol through Optical‐Rotation Measurements

A new procedure to measure the equilibrium constants for the dimerization (homochiral and heterochiral) reactions of enantiomers in solution was applied to two different compounds, namely omeprazole and Pirkle's alcohol, both in CHCl₃. This procedure is based on the measurement of the optical rotation of the solution as a function of its composition, which exhibits a nonlinear dependence on the enantiomer enrichment. Such nonlinearity depends on the extent of dimerization, and it is a strong effect in the case of omeprazole, whose equilibrium constants are 14.0±3.5 l/mol and 25.2±4.0 l/mol for the formation of homochiral and of heterochiral dimers, respectively. Pirkle's alcohol exhibits a weaker effect that allows only to estimate the order of magnitude of these constants, i.e., ca. 0.10 and 0.34 l/mol, respectively.     

SN2’ versus SN2 Reactivity: Control of Regioselectivity in Conversions of Baylis–Hillman Adducts

TiCl₄‐induced Baylis–Hillman reactions of α,β‐unsaturated carbonyl compounds with aldehydes yield the (Z)‐2‐(chloromethyl)vinyl carbonyl compounds 5 , which react with 1,4‐diazabicyclo[2.2.2]octane (DABCO), quinuclidine, and pyridines to give the allylammonium ions 6 . Their combination with less than one equivalent of the potassium salts of stabilized carbanions (e.g. malonate) yields methylene derivatives 8 under kinetically controlled conditions (S_N2’ reactions). When more than one equivalent of the carbanions is used, a second S_N2’ reaction converts 8 into their thermodynamically more stable allyl isomers 9 . The second‐order rate constants for the reactions of 6 with carbanions have been determined photometrically in DMSO. With these rate constants and the previously reported nucleophile‐specific parameters N and s for the stabilized carbanions, the correlation log k (20 °C)=s(N + E) allowed us to calculate the electrophilicity parameters E for the allylammonium ions 6 (?19<E <?18). The kinetic data indicate the S_N2’ reactions to proceed via an addition–elimination mechanism with a rate‐determining addition step.     

The Phase Relations in the System In2O3–TiO2–MgO at 1100 and 1350°C

The phase relations in the system In₂O₃–TiO₂–MgO at 1100 and 1350°C are determined by a classical quenching method. In this system, there are four pseudobinary compounds, In₂TiO₅, MgTi₂O₅ (pseudobrookite type), MgTiO₃ (ilmenite type), and Mg₂TiO₄ (spinel type) at 1100°C. At 1350°C, in addition to these compounds there exist a spinel-type solid solution Mg_2−xIn_2xTi_1−xO₄ (0≤x≤1) and a compound In₆Ti₆MgO₂₂ with lattice constants a=5.9236(7) Å, b=3.3862(4) Å, c=6.3609(7) Å, β=108.15(1)°, and q=0.369, which is isostructural with the monoclinic In₃Ti₂FeO₁₀ in the system In₂O₃–TiO₂–MgO. The relation between the lattice constants of the spinel phase and the composition nearly satisfies Vegard's law. In₆Ti₆MgO₂₂ extends a solid solution range to In₂₀Ti₁₇Mg₃O₆₇ with lattice constants of a=5.9230(5) Å, b=3.3823(3) Å, c=6.3698(6) Å, β=108.10(5)°, and q=0.360. The distributions of constituent cations in the solid solutions are discussed in terms of their ionic radius and site preference effect.     

Structure and spectral characterisation of copper(II) meclofenamate complexes

The synthesis and characterisation of Cu(meclof)₂H₂O and Cu(meclof)₂L₂ (meclof = meclofenamate; L = 2-pyridylcarbinol (2-pyca), 3-pyridylcarbinol (3-pyca), nicotinamide (na), N,N-diethylnicotinamide (dena) are reported. The characterisation of the compounds were based on elemental analyses, electronic, IR and EPR spectra. The carboxyl group of the meclofenamate anions coordinates to the Cu(II) atom as an unidentate or as a chelating ligand. The crystal and molecular structures of one of the products, namely Cu(meclof)₂(2-pyca)₂ were measured. The EPR spectra of the studied complexes show they are monomeric, except for Cu(meclof)₂ · H₂O which shows triplet state feature. On the basis of the spectroscopic parameters observed, a monomeric structure with a tetragonally Jahn–Teller distorted octahedron around the Cu(II) atom is deduced for Cu(meclof)₂L₂ and for Cu(meclof)₂ · H₂O a dimeric structure is proposed. The degree of distortion in the series of the Cu(meclof)₂L₂ complexes increases in the order of L: na < 2-pyca < 3-pyca < dena.     

Effect of annealing temperature on the structural and optical properties of Zn1−xMgxO particles prepared by oxalate precursor

Zn_1−xMg_xO particles were prepared using zinc and magnesium oxalate precursor by co-precipitated method. The lattice constants of Zn_1−xMg_xO proved that the interstitial Mg formed at 500 °C and Mg replaced Zn in ZnO tetrahedral coordination at 800 °C. Compared with the ZnO, the absorbing band edge of the Zn_1−xMg_xO displayed blue shifts. The room temperature photoluminescence was similar to ZnO and variation of Mg content did not change the shape or peak position of the emission spectra markedly when it was annealed at 500 °C. However, its blue emission band disappeared, and a relatively strong green light emission at 498 nm appeared after annealed at 800 °C. The photoluminescence intensity ratios I_(green)/I_(UV) of Zn_1−xMg_xO varied with Mg content and the green light emission peak shifted from 498 nm to 472 nm when Mg content increased from 0 to 2.0 at.%.     

Dinitrogen and carbon monoxide hydrogen bonding in protonic zeolites: Studies from variable-temperature infrared spectroscopy

Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-Y results in hydrogen bonding of the adsorbed N₂ molecules with the zeolite Si(OH)Al Brønsted-acid groups. This hydrogen-bonding interaction leads to activation, in the infrared, of the fundamental N–N stretching mode, which appears at 2334 cm⁻¹. From infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH···N₂ complex was found to be ΔH⁰ = −15.7(±1) kJ mol⁻¹. Similarly, variable-temperature infrared spectroscopy was used to determine the standard enthalpy change involved in formation of H-bonded CO complexes for CO adsorbed on the zeolites H-ZSM-5 and H-FER; the corresponding values of ΔH⁰ were found to be −29.4(±1) and −28.4(±1) kJ mol⁻¹, respectively. The whole set of results was analysed in the context of other relevant data available in the literature.     

Rate constants of the thermal cis‐trans isomerization of azobenzene dyes in solvents,acetone/water mixtures,and in microheterogeneous surfactant solutions

Rate constants k_iso of the thermal cis‐trans isomerization of four 4,4’‐nitro‐aminoazobenzenes with different amino groups have been determined in homogeneous aprotic solvents and polyglykol oligomers, primarily by means of conventional flash photolysis. The rate constants have been correlated with polarity (according to λ_max from UV/Vis absorption spectra of the trans isomers) and bulk viscosity of the solvents. Qualitative conclusions about the influence of varying concentrations of water with respect to polarity and hydrogen bonding on k_iso‐ and λ_max‐values in acetone/water mixtures were derived. Based on these results the data from microheterogeneous solutions have been interpreted. In microheterogeneous water/surfactant solutions k_iso‐values of selected azo dyes were strongly dependent on the concentrations of SDS, Triton^®X‐100, C₁₂EO₈ in water, and varied with the composition of bicontinuous microemulsions of Igepal^® CA‐520/ heptane/water. The large spread of isomerization rate constants is in part due to varying microviscosity. Replacement of H₂O by D₂O in aqueous surfactant solutions produced surprisingly large kinetic solvent isotope effects. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 337–350, 1999