Anionic polymerization of ethylene oxide with cryptates as counterions: 2

A kinetic study of the anionic polymerization of ethylene oxide has been made in tetrahydrofuran at 20°C, with the cryptate Cs⁺ + [TC] as counterion, [TC] being a spheroidal macrotricyclic ligand. Conductance measurements have been made on THF solutions of ?₄BCs + [TC]. Ionic associations higher than cryptated ion pairs are negligible for living end concentrations lower than 3 × 10^?4 moll^?1. k_± and the alkoxide ion pair dissociation constant K_D were determined from both sets of kinetic data obtained with and without added salt knowing the value of k_? from kinetic data performed with K⁺ + [222] as counterion. Free alkoxide ions are about twenty times more reactive than cryptated caesium ion pairs.     

Anionic polymerization of α,α-disubstituted β-propiolactones with cryptates as counterions

A kinetic study of the anionic polymerization of α-methyl-α-propyl-β-propiolactone has been made in tetrahydrofuran at ?20°C, with the cryptate K⁺+[222] as counter-ion. Conductance measurements have been made on THF solutions of potassium β-naphthoate complexed by [222] as a model of cryptated carboxylates. Propagation reaction proceeds through cryptated ion pairs and free ions. Cryptated carboxylate ion pairs are more reactive than free ions.     

Reactivity and mechanism in the cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate

The cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate in dichloromethane solution has been studied in some detail. Reactions proved to be highly exothermic, and rates of monomer consumption were measured using an adiabatic calorimetric technique. Termination was deduced to be insignificant during kinetic lifetimes, and $\text{M}\text{?}{}_{\mathrm{n}}$ values in the range 10000–50000 showed chain breaking to occur by transfer mechanisms. Appropriate analysis of conversion/time curves allowed computation of enthalpies of polymerization and rate coefficients for propagation, k_p (obs), under various conditions. Data for k_p (obs) were found to vary with the initial concentrations of initiator and monomer employed, and these dependences are discussed in terms of current theories regarding ion pair/free ion equilibria in nonaqueous solvents. In particular values of 3.6 × 10³ M^?1s^?1 and 4.8 × 10³ M^?1s^?1 at 0° and +10°C respectively for the rate constant for propagation by free poly (p-methoxystyryl) cation have been deduced, and a tentative value of 450 M^?1s^?1 at 0°C has been estimated for the rate constant for propagation by the corresponding hexachloroantimonate ion pairs. These data and the related activation parameters are compared with independent results in the literature. Polymerizations carried out in the presence of excess common ion salt, dimethyl benzyl phenyl ammonium hexachloroantimonate, showed rate depressions far in excess of those predicted by a simple mass law effect, arising possibly as a result of a more dramatic ionic association than simple ion pairing.     

Anionic polymerization of styrene in triglyme-benzene mixtures

Living anionic polymerization of styrene was kinetically investigated in triglyme-benzene mixtures. At low concentrations of triglyme the overall propagation rate constant, k_p, was much larger than at the same concentration of monoglyme (DME) in DME-benzene mixtures. The Szwarc-Schulz plot did not have negative slopes for lithium and sodium salts at triglyme contents of 5～20vol%, and no contribution of free anions to the propagation was observed for the sodium salt. The sodium ion pair was more highly reactive than the lithium ion pair; thus at 25°C, the ion pair rate constant, k′_p, for the lithium salt was 43, 102, 135 and 165 M^?1sec^?1 at triglyme concentrations of 5, 10, 15, and 20%, respectively, while that for the sodium salt was 410, 920, and 1460 M^?1sec^?1 in 5, 10, and 15% triglyme, respectively. The dissociation constant, K, for the lithium salt was 2·4×10^?11, 1·9×10^?10 and 1·3×10^?9 M in 10, 15, and 20% triglyme, respectively and the free ion rate constant, k″_p, was 2～2·5×10⁴ M^?1sec^?1 for the lithium salt.     

Kinetics of the metal exchange reaction of a Cu(II)-poly(vinyl alcohol) complex with Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between Cu(II)-poly(vinyl alcohol) [Cu(II)-PVA] and Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid [Zn(II)-EDTA] has been studied by mixing both solutions in a spectrophotometer at pH 10.0 to 11.0, ionic strength μ=0.10(KNO₃), and 15 to 35°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA through attack of H⁺ ion on the Cu(II)-PVA complex, and both reactions, ligand exchange and metal exchange, proceed simultaneously. The metal exchange step may be rate determining. The rate equation and rate constants of this reaction were determined as follows: ?d[Cu(II)-PVA]/dt=k _0(H)[PVA^?][Cu(II)-PVA] [Zn(II)-EDTA], wherek _0(H)=k ₁+(k′₂+k′₃)[H⁺],k ₁=5.98±1.64M ^?1 s^?1, andk ₂+k ₃=k′₂ K _Cu(II)-H-PVA ^?H +k′₃ K _Zn(II)-EDTA ^H =(5.91±0.89)×10⁷ M ^?2 s^?1.     

Absolute reactivity in the cationic polymerization of methyl and other alkyl vinyl ethers

The cationic polymerizations of methyl-, 2-chloroethyl-, ethyl-, cyclohexyl- and t-butyl- vinyl ethers initiated by cycloheptatrienyl hexachloroantimonate in methylene chloride solutions have been studied in detail. Reaction rates were measured by an adiabatic calorimetric technique and rate constants for propagation of each of the monomers, k_p (obs), were determined by appropriate kinetic analysis of the experimental curves. The results obtained are discussed in terms of current theories regarding ion pair/free ion equilibria in non-aqueous solvents. Although ethyl-, cyclohexyl- and t-butyl- vinyl ethers behave very similarly to isobutyl vinyl ether, and their reactivities are comparable [k_p (obs) ～ 3 × 10³M^?1sec^?1 at 0°C] both methyl- and 2-chloroethyl- vinyl ethers show markedly different characteristics to the others, and in particular exhibit a reactivity approximately one order of magnitude less [k_p (obs) ～ 2 × 10²M^?1sec^?1 at 0°C]. These variations in reactivity are discussed in terms of preferred monomer conformations, and the resulting differences in activation energy which are likely to arise when such conformers are approached by an electrophile.     

Potentiometric and polarographic studies of cadmium(II) complexes with tetraethylenepentamineheptaacetic acid

Stability constants for cadmium(II) complexes with tetraethylenepentamineheptaacetic acid (TPHA, H₇L) were determined by the pH titration method. In an aqueous solution (μ = 0.1), three complex species, CdH₂L, CdHL and CdL are confirmed. The structure of uninuclear complexes are discussed. The formation constants of the complexes stated above have been calculated as follows (at 25 ± 0.1°C): log K_CdL = 15.35, log K_CdHL = 13.33 and log K_CdH2L = 7.89. The polarographic behaviour of the cadmium(II) in the presence of TPHA was studied over the pH range 3–5. Mechanisms of the electrode processes were elucidated and electrochemical kinetic parameters were evaluated from dependence of the half-wave potentials on the hydrogen ion and TPHA concentration. In the presence of an excess of TPHA, the wave B is assigned to the irreversible reductions of the complex, CdH₂L^3? (pH range 3–4) or CdHL^4? (pH range 4–5). The electrode reaction can be written:

and

Where k_e (the rate constant) = 2.3 × 10^?2 cm s^?1 and k′_e = 1.59 × 10^?4 cm s^?1. The other polarographic methods were also used in the elucidation of the electrode process.     

Kinetics of ring opening of propylene sulphide: 1. Alkali metal and cryptated alkali metal carbazyl salts

The reactivities of free ions and ion pairs have been determined for the ring opening of propylene sulphide with carbazyl salts, in THF at ?30°C. A large increase of the ion pair reactivity is observed on increasing the size of the counterion (Na⁺ < Cs⁺ < Na⁺ + |222|). Moreover, cryptated carbazyl ion pairs are three times more reactive than free ions in the same manner as thiolate species for the propagation of propylene sulphide in similar conditions.     

Candida rugosa Lipase Supported on High Crystallinity Chitosan as Biocatalyst for the Synthesis of 1-Butyl Oleate

Lipase from Candida rugosa was immobilized onto chitosan using four different protocols. The variation of crystallinity (5.57–92.86%), which was a result of thermal treatments and crosslinking of the chitosan, influenced the protein load (7.46–25.15 mg g^?1 chitosan) and protein load efficiency (21.67–41.68%) for immobilization assays made with identical lipase solution concentration (1.3 mg of protein/mL). The effects of protein load (10, 30, 50 and 70 mg of lipase), reaction temperature (30, 40, 50, 60, 70 °C) and substrates molar ratio (0.05–0.30 M) have been studied in the butyl oleate synthesis in iso-octane when water activity of the free and immobilized enzymes were fixed around 0.53 ± 0.04. The catalytic activity of the immobilized lipase has also been tested. The Ping–Pong bi–bi mechanism with dead end complex of n-butanol was found to fit the initial rate data. The values of the apparent kinetic parameters were determined by graphic and parametric method as: V _max = 18.2–19.0 mmol min^?1 g^?1; K _{M; Acid} = 0.599–0.640 mol L^?1; K _{M; Alcohol} = 0.128–0.149 mol L^?1; and K _{i; Alcohol} = 1.933 mol L^?1.     

Solvent effect on the dissociation of o-nitroanilinium ion in methanol-propylene glycol media at 25°C

The dissociation constants (K_s) of o-nitroanilinium ion have been determined at 25° in methanol, propylene glycol and mixtures of the two components containing 10, 30, 50, 70 and 90 wt. % propylene glycol by spectrophotometric measurements. Standard free energies of transfer, ΔG°_t(B) of o-nitroaniline from methanol to the other solvents have been evaluated from the measurement of solubilities at 25°C. The solvent effect on the proton transfer process of this acid: ΔG°_t[BH⁺?B]_sys = 2.303RT[p(K_s?p(K_m)] has been discussed in terms of the free energies of transfer ΔG°_t from methanol to other solvents, of the uncharged based B, of the hydrochloride of the base (BHCl) computed from the corresponding values for HCl and also of the individual ions assessed from the previous knowledge of ΔG°_t(Cl^?). The corresponding data for the protonated tris(hydroxymethyl)methyl amine [TrisH⁺] and p-nitroanilinium ion in the same solvent system obtained from the literature are also compared. ΔG°_t[BH⁺?B]_sys values for the dissociation of o-nitroanilinium ion have been found to increase less readily with wt.% propylene glycol compared to p-nitroanilinium ion and are in contrast with the decreasing nature of the corresponding values for the TrisH⁺ ion of different chemical nature. Electrostatic effect being negligible in this solvent system, the overall behaviour of these acids is found to be dictated by specific chemical nature of solute-solvent interactions besides the effect of relative solvent basicities.     

A comprehensive study on the kinetics of aqueous free-radical homo- and copolymerization of acrylamide and diallyldimethylammonium chloride by online 1H-NMR spectroscopy

Free-radical homo- and copolymerization of acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC) initiated with potassium persulfate (KPS) were performed in the presence of 0.1 M NaCl solution in D₂O at 50 °C. Online ¹H-NMR kinetic experiments were used to study polymerization kinetics via determination of the individual and overall conversion of the comonomers and compositions of the comonomer mixture and produced copolymer as a function of the reaction time. Reactivity ratios of the AAm and DADMAC were calculated by Mao-Huglin (MH) and extended Kelen-Tudos (KT) methods to be 7.0855?±?1.3963, 0.1216?±?0.0301 and 6.9458?±?2.0113, 0.1201?±?0.0437 respectively. “Lumped” kinetic parameter (k _p k _t ^??0.5 ) was estimated from experimental data. Results showed that k _p k _t ^??0.5 value increases by increasing mole fraction of the AAm in the initial reaction mixture. Drift in the comonomer mixture and copolymer compositions with reaction progress was evaluated experimentally and theoretically. Theoretical values were calculated from Meyer-Lowry equation by using reactivity ratios obtained from MH method. A good fitting between the experimental and theoretical values was observed, indicating accuracy of the reactivity ratios estimated in the present work. It was found from following changes in the copolymer composition with the comonomer conversion that produced copolymer has a statistical structure.     

Counterion Effect on Krafft Temperature and Related Properties of Octadecyltrimethylammonium Bromide

In the present work, we have investigated the effect of some counterions on the Krafft temperature (T _K) and the micelle formation of octadecyltrimethylammonium bromide (OTAB) in aqueous solution. The results showed that the ions with more chaotropic nature increase the T _K while those with a kosmotropic, hydrotropic and less chaotropic nature lower the T _K of the surfactant. More chaotropic SCN^? and I^?, being weakly hydrated, form contact ion pairs with the octadecyltrimethylammonium ion and reduce the electrostatic repulsion between the surfactant molecules. As a result, these ions exhibit salting out behavior and raise the T _K of the surfactant. On the other hand, less chaotropic Cl^? and NO₃ ^?, kosmotropic SO₄ ^2? and F^? and hydrotropic benzoate and salicylate ions increase the solubility of the surfactant, with a consequent decrease in the T _K. SO₄ ^2?, F^?, benzoate and salicylate cannot form contact ion pairs with the weakly hydrated cationic part of OTAB. Rather, being extensively hydrated and kosmotropic in nature, these ions do not show any tendency to shed their hydrated water molecules to form contact ion pairs with the weakly hydrated octadecyltrimethylammonium ion and therefore, stay apart. As a result, the T _K of the surfactant decreases significantly in the presence of these ions. The critical micelle concentration (CMC) of the surfactant decreases significantly in the presence of these ions due to screening of the micelle surface charge by the added counterions. Consequently, the surfactant molecules attain better packing because of substantial reduction in the electrostatic repulsion between the charged head-groups, showing a significant decrease in the CMC.     

Conductivities and ion association of 1:1 electrolytes in mixed aprotic solvents

Molar conductivities of the 1:1 electrolytes LiClO₄, LiAsF₆, n-Bu₄NClO₄ and n-Bu₄NBPh₄ were measured in mixtures of propylene carbonate and dimethoxymethane over the concentration range 0.01?1 × 10^?4 mol dm^?3. In all cases a maximum in molar conductivity (and hence in electrolytic conductivity) is observed in a solvent mixture having a composition of around 40 mass % propylene carbonate. Molar conductivities at infinite dilution (Λ^∞) and thermodynamic ion association constants (K^∞_a) were evaluated from these data. Single ion molar conductivities (λ^∞_i) were evaluated using the assumption that λ^∞(n-BuN⁺₄) = λ^∞(BPh^?₄). In order to account for the observed conductivity behavior it is necessary to assume that lithium salts from solvent separated ion pairs in ethereal solvents. All other salts from contact ion pairs.     

Equilibria,Kinetics, and Modeling of Extraction of Citric Acid from Aqueous Solutions with Alamine 336 in 1-Octanol

Experimental equilibrium and kinetic data on the extraction of citric acid from aqueous solutions using Alamine 336 in 1-octanol have been determined. The distribution coefficient has increased from 0.029 to 71.727 with increase of Alamine 336 concentration from 0 to 30% (v/v). The chemical equilibria was interpreted as a result of consecutive formation of acid-amine species with 1:1 stoichiometry and the equilibrium complexation constant, K _E1 , has been estimated as 20.186 m³ kmol^?1. The mass-transfer coefficients of citric acid, Alamine 336, and 1:1 acid-alamine complex in 1-octanol were calculated from acetic acid mass-transfer coefficient, which was determined by measuring its fluxes of simple diffusion from kerosene to water. Based on the Hatta number and the criterion given by Doraiswamy and Sharma, the reaction regime has been found to be instantaneous reaction regime occurring at the interface on the organic phase side. An extraction model comprising 1:1 equilibrium complextion constant, K _E1 , and complex mass-transfer coefficient, k _BA (3.79 × 10^?6 m s^?1), has been developed, and it explained the present system satisfactorily.     

The oxidation of aqueous sodium sulphite solutions

In this paper new experimental work on the kinetics of the absorption of oxygen in an aqueous solution of sodium sulphite with cobaltous sulphate as a catalyst, has been presented and compared with already published data. It is shown that the reaction of oxygen with sodium sulphite is zero order in sulphite, first order in cobalt and second order in oxygen for 2 × 10⁴ N/m² <p_O2 < 10⁵ N/m², 150°C <T < 60°C, 3 × 10^?6 kmol/m³ <c_Co⁺⁺ < 3 × 10^?3 kmol/m 7.50 < pH < 8.50 and 0.4 kmol/m² <c_SO2-- < 0.8 kmol/m³. The reaction rate constant can be varied by more than two decades by changing the cobalt concentration, pH and temperature.The specific interfacial areas, a, and mass transfer coefficients, k_L, measured by DeWaal and Beek [14, 15] using an incorrect kinetic model of this reaction, are reinterpreted with the results of the present kinetic investigation. It is shown that their values of a and k_L are a factor 2.2 too low and too high, respectively, but that their values of k_La are correct.     

Reactions of hydrogen peroxide on a silver electrode in alkaline solution

Reactions with hydrogen peroxide on silver in alkaline solutions with H₂O₂ concentration 5 × 10^?7 mol/ml have been studied with the ring-disk electrode. The amount of oxygen formed on the disk as the result of catalytic decomposition of hydrogen peroxide and its oxidation was established on the ring-electrode made from pyrographite. The rate constants of H₂O₂ electrochemical reduction (k₃), its oxidation (k′₂) and catalytic decomposition (k₄) and their dependence on potential have been evaluated. The constant k₄ scarcely depends on potential; it is ca 10^?2 cm/s.     

A reversible oxygen electrode in an equimolar KNO3-NaNO3 melt saturated with sodium peroxide—I. An equilibrium study

A reversible graphite oxygen electrode has been found in molten (K-Na)NO₃ eutectic, saturated with sodium peroxide. The measured emf of ?1150 ± 5 mV at 503 K vs Ag|Ag⁺ (0.1 m) and its temperature dependence ?0.44 mV K^?1 are compared with theoretical values, obtained with thermodynamic data.An independent value of the superoxide disproportionation constant K_p = (5.3 ± 0.3) × 10^?2 kg atm mol^?1 at 503 K has been obtained. Our equilibrium experiments confirm the results of Zambonin et al.     

Kinetics of ligand exchange reaction of Cu(II)-ammine complex with poly(vinyl alcohol) in aqueous solution

The kinetics of the ligand exchange reaction of the Cu(II)-ammine complex with poly(vinyl alcohol) (PVA) has been studied by a stopped-flow method at pH 9–10, at μ=0.1 (NH₄Cl) and at 25°C. The reaction is initiated by the formation of unstable [Cu(NH₃)₃]²⁺ by the attack of H⁺ on Cu(II)-ammine complex, and proceeds through the mixed complex {[Cu(NH₃)₃(O?PVA)]²⁺}. This step may be rate-determining, followed by a rapid reaction. Finally, the Cu(II) ion is taken up by PVA. The rate is given by d[Cu(II)?PVA]/dt=k[H⁺]{[Cu(NH₃)₄]²⁺}[PVA]/[NH₄Cl], where k=k₁ + k′₂[H⁺], k₁=4.25× 10s^?1 and k′₂=5.20× 10¹¹l mol^?1s^?1.     

Synthesis and Characterization of Pyridine Compounds for Amperometric Measurements of Leukocyte Esterase

We introduce a new class of substrates (compounds I – III ) for leukocyte esterase (LE) that react with LE yielding anodic current in direct proportion to LE activity. The kinetic constants K_m and k_cat for the enzymatic reactions were determined by amperometry at a glassy carbon electrode. The binding affinity of I – III for LE was two orders of magnitude better than that of existing optical LE substrates. The specificity constant k_cat/K_m was equal to 2.7, 3.8, and 5.8×10⁵ m ^?1 s^?1 for compounds containing the pyridine ( I ), methoxypyridine ( II ), and (methoxycarbonyl)pyridine ( III ), respectively, thus showing an increase in catalytic efficiency in this order. Compound III had the lowest octanol/water partition coefficient (log p=0.33) along with the highest topological surface area (tPSA=222 Ų) and the best aqueous solubility (4.0 mg mL^?1). The average enzymatic activity of LE released from a single leukocyte was equal to 4.5 nU when measured with compound III .     

REACTIVE EXTRACTION OF LEVULINIC ACID FROM AQUEOUS SOLUTIONS WITH TRI-n-OCTYLAMINE (TOA) IN 1-OCTANOL: EQUILIBRIA,KINETICS, AND MODEL DEVELOPMENT

Levulinic acid, a carboxylic acid containing a ketone structure, can be used as an acidulant in foods and beverages. Reactive extraction is a promising alternative for the recovery of carboxylic acids from aqueous streams. The design of an amine extraction process requires kinetic data for the acid-amine + solvent system used. In this study, equilibrium and kinetic data on the extraction of levulinic acid from aqueous solutions using tri-n-octylamine (TOA) in 1-octanol have been determined. The mass transfer coefficients of levulinic acid, TOA, and 2:1 levulinic acid-amine complex in 1-octanol were calculated from the acetic acid mass transfer coefficient, which was determined by measuring its fluxes of simple diffusion from kerosene to water. Based on the Hatta number and the criterion given by Doraiswamy and Sharma, the reaction regime has been found to be instantaneous reaction regime occurring at the interface on the organic phase side. An extraction model comprising equilibrium complexation constant w.r.t 2:1 levulinic acid-TOA complex formation, K_E2i (14.794 (m³ kmol^?1)²), and complex mass transfer coefficient, k_B2A (2.193 × 10^?6 m s^?1), has been developed.