Anionic polymerization of ethylene oxide with cryptates as counterions: 1

A kinetic study of the anionic polymerization of ethylene oxide has been made in tetrahydrofuran at 20°C, with the cryptate K⁺ + [222] as counterion. The ion pair dissociation constant K_D has been deduced from conductivity measurements made on seeds solutions. Some ionic associations higher than cryptated ion pairs could be detected but they are negligible for living end concentrations lower than 6 × 10^?4 mol/l. k_± and k_? were determined from both sets of kinetic data obtained with and without added salt. Free alkoxide ions are one hundred times more reactive than cryptated 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.     

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.     

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.     

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.     

Ion—solvent interaction: viscosity of ternary electrolytes in dioxane-water mixtures at 35°

The viscosities of the chlorides, bromides and nitrates and perchlorates of Mg²⁺ and Ba²⁺, of the chlorides and nitrates of Ca²⁺ and Sr²⁺, and of the sulphates of Na⁺ and K⁺ at mass fraction of dioxane, 10, 20 and 30% have been measured at 35°. The values of the constant A and B of the viscosity equation indicate ion—ion and ion—solvent interaction respectively. The ion-solvent interaction is found to be of the order NO^?₃ > ClO^?₄ > Br^? > Cl^? and K⁺ > Na⁺.     

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.     

Acceleration of the redox kinetics of VO2+/VO2 + and V3+/V2+ couples on carbon paper

The redox kinetics of VO²⁺/VO₂ ⁺ and V³⁺/V²⁺ couples on a carbon paper (CP, HCP030 N, Shanghai Hesen, Ltd., China) electrode were investigated in terms of their standard rate constant (k ₀) and reaction mechanism. The values determined for k ₀ for VO²⁺ ?? VO₂ ⁺ and V³⁺ ?? V²⁺ using the CP electrode are 1.0 × 10^?3 and 1.1 × 10^?3 cm s^?1, respectively. The value of k ₀ increases by one or two order(s) of magnitude compared with values obtained using electrodes composed of pyrolytic graphite and glassy carbon. The acceleration of the redox kinetics of vanadium ions is a result of the large surface area of the CP electrode. An inner-sphere mechanism for the reaction on the surface of the electrode is proposed. The kinetic features of vanadium redox reactions on the CP electrode reveal that CP is suitable for use as the electrodes in vanadium redox-flow batteries.     

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.     

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.     

Counterion‐Switched Reversibly Hydrophilic and Hydrophobic TiO2‐Incorporated Layer‐By‐Layer Self‐Assembled Membrane for Nanofiltration

The manipulation of surface wettability has been regarded as an efficient strategy to improve the membrane performances. Herein, the counterion‐switched reversibly hydrophilic and hydrophobic surface of TiO₂‐loaded polyelectrolyte membrane are prepared by layer‐by‐layer assembly of poly(sodium 4‐styrene sulfonate) (PSS) and poly(diallydimethyl‐ammoniumchloride (PDDA) containing TiO₂@PDDA nanoparticles (NPs) on the hydrolyzed polyacrylonitrile (PAN) substrate membrane. The obtained polyelectrolyte multilayer (PEM) membranes [PEM‐TiO₂]_4.5⁺X^? (X^? = Cl^?, PFO^? [perfluorooctanoate] etc.) show different hydrophilicity and hydrophobicity with various counterions. The integration of TiO₂ NPs obviously improves the wettability and nanofiltration (NF) performance of PEM membrane for (non)aqueous system of dyes (crystal violet, eriochrome black T) with a high recyclability. The highly hydrophilic [PEM‐TiO₂]_4.5⁺Cl^? (water contact angle [WCA]: 13.2 ± 1.8°) and hydrophobic [PEM‐TiO₂]_4.5⁺PFO^? (WCA: 115.4 ± 2.3°) can be reversibly switched via counterion exchange between Cl^? and PFO^?, verifying the surface with a reversible hydrophilic–hydrophobic transformation. For such membranes, the morphology, wettability, and NF performance rely on the loading of TiO₂@PDDA NPs and surface counterion. Meanwhile, the motion and interaction of water or ethanol in the hydrophilic or hydrophobic membrane are revealed by low‐field nuclear magnetic resonance. This work provides a facile and rapid approach to fabricate smart and tunable wetting surface for potential utilization in (non)aqueous NF separation.     

Optimisation of the biological treatment of hypersaline wastewater from Dunaliella salina carotenogenesis

The reutilisation of Dunaliella salina carotenogenesis medium, after microalgal biomass separation by centrifugation, was assessed. The wastewater had an NaCl concentration between 174 g dm^?3 and 254 g dm^?3 and an average total organic matter concentration of 1540 mg dm^?3 ash‐free dry weight, of which 41% (w/v) was glycerol. The biological treatment was established at laboratory scale and batch operations used halophilic bacteria from the wastewater itself. The wastewater was supplemented with NH₄⁺,PO₄^3?, K⁺ and Mg²⁺ ions to enhance growth. The effect of each ion added per se was initially investigated and a response surface methodology (RSM) used to identify the optimal conditions for maximisation of glycerol removal from the wastewater, which was considered to be the main objective. Addition of NH₄⁺ ions alone achieved 79% glycerol removal compared with only 59% in the absence of supplement, after 8 days incubation. The combined addition of ions ([NaCl] = 214 g dm^?3, [Mg²⁺] = 114 mg dm^?3, [K⁺] = 131 mg dm^?3, [NH₄⁺] = 113 mg dm^?3, [PO₄^3?] = 40 mg dm^?3) increased glycerol removal from the wastewater such that, after 2 days incubation, no residual glycerol was apparent in cultures. These ion combinations enabled the halophilic bacteria to efficiently remove glycerol from the wastewater and consequently reduce organic matter. This treated wastewater should be appropriate for reutilisation as a carotenogenesis medium for β‐carotene production from D salina. © 2001 Society of Chemical Industry     

The influence of chloride ions on the kinetics of iron dissolution

The anodic dissolution of pure iron was studied in oxygen-free solutions at high concentrations of chloride and hydrogen ions at 25°C under potentiostatic steady-state conditions. In the range c_H⁺ ? 1 M the following kinetic data were obtained: Tafel slope b₊ ? +100 mV, electrochemical reaction order related to C_H⁺, n_+.H⁺ = +1·1, and electrochemical reaction order related to the chloride ion concentration, n_+,Cl^? = +0·6. These values cannot be correlated to the currently proposed mechanisms of iron dissolution, another mechanism is suggested for the described conditions. The correlations to known mechanisms are discussed.     

Experimental Foam Fractionation Selectivity Coefficients for the Alkali (Group IA) Metals

Abstract

An experimental investigation is presented of the continuous-flow foam fractionation of each of the colligends Li⁺, K⁺, Rb⁺, and Cs⁺ versus Na⁺, the counterion of the dodecylsulfate anion over the aqueous solution concentration range of 1.0 × 10^?4 to 6.0 × 10^?4 M. Initial experiments with K⁺ confirm the achievement of a single-equilibrium-stage separation. Surfactant selectivity coefficients, defined in terms of a colligend-surfactant counterion exchange model at the interfaces of the rising gas bubbles, are established. They represent the ratio of colligend to sodium in the interfacial “stream” to that in the residual steam and are Li⁺, 0.92; K⁺, 1.10; Rb⁺, 1.51; Cs⁺, 1.65. The selectivity sequence is compared to the sequence of absolute partial molal entropies of the cations in aqueous solution.     

Kinetics of ylide-initiated radical copolymerization of 4-vinylpyridine and methyl methacrylate

The ylide-initiated radical copolymerization of 4-vinylpyridine (4-VP) with methyl methacrylate (MMA) at 60°C using carbon tetrachloride as inert solvent yields non-alternating copolymers. The kinetic parameters, average rate of polymerization (R_p) and orders of reaction with respect to monomers and initiator, have been evaluated and the kinetic equation is found to be R_pα[ylide]^0.94 [MMA]^1.0 [4-VP]^1.5. The values of the energy of activation and k_p²/k_t are 48 kJ mol^?1 and 6.6 × 10^?5 litre mol^?1s^?1, respectively. The copolymers have been characterized by IR and NMR spectroscopy.     

The synthesis and complexation study of some novel 3-methoxyphenyl chromenone crown ethers using conductometry

7,8-Dihydroxy-3-(3,4-dimethoxyphenyl)-2H-chromenones, 7,8-dihydroxy-3-(3,5-dimethoxyphenyl)-2H-chromenones and 7,8-dihydroxy-3-(3,4,5-trimethoxyphenyl)-2H-chromenones, o-dihydroxy-3-methoxyphenylcoumarins, were prepared from 2,3,4-trihydroxybenzaldehyde and corresponding methoxyphenylacetic acid in NaOAc/Ac₂O, respectively. 3-Methoxyphenyl-7,8-dihydroxy-2H-chromenone reacted with the polyethylene glycol ditosylate or dichloride in CH₃CN/alkali carbonate to afford [12]crown-4, [15]crown-5 and [18]crown-6-chromonones.The chromatographically purified novel chromenone crown ethers were identified with IR, ¹H NMR, ¹³C NMR and low and high resolution mass spectroscopy and elemental analysis.Stability constants for the 1:1 complexes of Na⁺ and K⁺ with different substituted methoxyphenyl derivatives of coumarino[12]crown-4, coumarino[15]crown-5 and coumarino[18]crown-6 (5a–5i) have been determined by conductometry at 25 °C in a binary solvent, dioxane/water. For all the coumarino crown ether derivatives, the stability constant decreases for K⁺ ion compared to Na⁺ ion.The selectivity sequence of these crown ethers in dioxane/water has showed an irregular order with respect to their cavity size.     

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.