NOPR Collection:

A polymeric membrane ion selective electrode based on organic-inorganic composite ion exchanger for the determination of thorium(IV)

Sat, 01 Oct 2005 00:00:00 GMT

Title: A polymeric membrane ion selective electrode based on organic-inorganic composite ion exchanger for the determination of thorium(IV) Authors: Chandra, Sulekh; Agarwal, Himanshu; Singh, Chandan Kumar; Sindhu, Susheel Kumar; Kumar, Pankaj Abstract: A poly(vinyl chloride) membrane electrode based on organic-inorganic composite ion exchanger, tin(IV) tungstoselenatepyridine, has been prepared and tested for the selective determination of thorium(IV) ions. The PVC membrane electrode comprising 16% composite ion exchanger as the electroactive phase, 50% o-dioctyl phthalate as plasticizer, 4% tetraphenyl borate as anionic excluder and 30% poly(vinyl chloride) displays a linear response to thorium(IV) ions over a wide concentration range of 1.0×10^-1-8.0×10^-6 M with a Nernstain slope of 14.2 mV/ decade. The electrode shows a very short response time (~15 s) and may be used in the pH range 2.5-9.0. The selectivity coefficient for alkali, alkaline earth and transition is smaller than 4.0×10^-4. The sensor has been successfully used as an indicator electrode in the potentiometric titration of Th⁴⁺ with EDTA as well as also for the determination of Th⁴⁺ in the binary mixtures. Page(s): 2060-2063

Solvent effects on alkaline hydrolysis of N-benzylphthalimide in mixed water-acetonitrile and mixed water-N,N-dimethylformamide

Sat, 01 Oct 2005 00:00:00 GMT

Title: Solvent effects on alkaline hydrolysis of N-benzylphthalimide in mixed water-acetonitrile and mixed water-N,N-dimethylformamide Authors: Ye, Cheong May; Ariffin, Azhar; Khan, Mohammad Niyaz Abstract: The nucleophilic second-order rate constant (kOH) for the reaction of OHˉ with Nˉ benzylphthalimide appears to follow a reaction mechanism similar to that for reactions of OHˉ with phthalimide and its N-alkylphthalimides. The rate of hydrolysis reveals an insignificant contribution of water-catalysed cleavage of NBPT compared with its hydroxide ion catalysed reaction. The observed pseudo first-order rate constant, k_obs for alkaline hydrolysis of NBPT decreases with increase in the content of organic cosolvents (up to 70%, v/v) in mixed water-CH₃CN and water-DMF solvents. Page(s): 2055-2059

Adsorption kinetics of Brij 35 at air/solution interface

Sat, 01 Oct 2005 00:00:00 GMT

Title: Adsorption kinetics of Brij 35 at air/solution interface Authors: Wang, Zhongni; Liu, Feng; Zhang, Quanxuan; Wei, Xilian; Sun, Dezhi; Li, Ganzuo; Zhang, Gaoyong Abstract: Dynamic surface tension and surface adsorption kinetics at the air/aqueous solution interface of dodecyl polyoxyethylene(23) ether (Brij®35, C₁₂H₂₅O(CH₂CH₂O)₂₃H) have been investigated at different bulk surfactant concentrations and temperatures. Apparent diffusion coefficients, D_a, activation barrier, ε_a, and the adsorption kinetic parameters, n and t*, are obtained from the extended Ward and Tordai approach, and Rosen's empirical model, respectively. It is shown that Brij 35 solutions follow a mixed diffusion-activation adsorption mechanism. Results evaluated by the extended Ward and Tordai approach are consistent with those obtained from Rosen's empirical model With increase in bulk concentration from 0.1 CMC to 10 CMC (mol/dm³) ε_a increases from 2.40 to 6.96 kJ/mol, and n decreases from 0.620 to 0.393, while with increase in temperature from 25 to 45°C, ε_a decreases from 4.59 to 3.54 kJ/mol, and n decreases from 0.534 to 0.456. This indicates that the diffusion tendency decreases with increase in the interaction between surfactant molecules while the thermo-motion of the molecules favours surface adsorption. Page(s): 2051-2054

Oxidation of tellurium(IV) by tetrabutylammonium tribromide

Sat, 01 Oct 2005 00:00:00 GMT

Title: Oxidation of tellurium(IV) by tetrabutylammonium tribromide Authors: Kalantre, VA; Gokavi, G S Abstract: The reaction between tetra butylammonium tribromide and tellurium(IV) has been studied in 50% (vlv) acetic acid under second order conditions. The overall order of reaction is found to be two, unity each in both the reactants. The reaction involves a direct two-electron transfer step since the test for the formation of free radicals due to single electron step was negative. The reaction is retarded by hydrogen ions due to protonation prior equilibria of the reductant, tellurium(IV). The active species of the reactants is found to be tribromide ion of the oxidant and HTeO₃ˉ of the reductant. Considerable decrease in the entropy of activation of the reaction indicates formation of an ordered transition state between the two reactants analogous to that in alcohol oxidation by tetrabutylammonium tribromide ion. Page(s): 2048-2050