Browsing by Author "Robinson, Brian H."

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Application of the pressure-jump technique to the measurement of rates of fast reactions in non-aqueous solvents
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (04), 1977) Buschmann, Hans-J.; Knoche, Wilhelm; Day, Robert A.; Robinson, Brian H.
Modifications to a pressure-jump autoclave are described which permit the measurement of rapid rates of reaction in aprotic solvents. In such solvents, a chemical system at equilibrium will generally be perturbed primarily by the temprature decrease which accompanies the adiabatic expansion process. The factors which determine the amplitude of the resulting relaxation transient are discussed, and kinetic data are reported for the fast proton-transfer reaction between the phenolic indicator acid bromophenol blue and the weak base pyridine in chlorobenzene and 1,2-dichlorobenzene. Results obtained by means of the pressure-jump method are in excellent agreement with those obtained using other fast reaction techniques.
Kinetics and Mechanism of Fast Metal-Ligand Substitution Processes in Aqueous and Micellar Solutions Studied by means of a Dye Laser Photochemical Relaxation Technique
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Robinson, Brian H.; White, Neal C.
Rapid metal–ligand substitution reactions have been studied in aqueous and sodium lauryl sulphate (SLS) micellar solutions by means of a dye-laser induced photochemical relaxation method. Perturbation of the system involving Ni2+(aq) and the bidentate nitrogen ligand PADA produces two relaxation effects in both aqueous and micellar solutions. The faster relaxation process is concentration independent and is identified with a ring-closure reaction to reform the initial Ni(PADA)2+ complex. Rate constants and activation energies for this process are found to be similar in both media. The slower relaxation time is associated with the recombination reaction between Ni2+(aq) and PADA, for which k298.2f in water is found to be 1.4 × 103 dm3 mol–1 s–1, which is in good agreement with previous measurements. In the surfactant solutions, the rate of complexation is greatly enhanced close to the c.m.c. followed by a decrease as the concentration of SLS is further increased. This is due to the increased local concentration of Ni2+ at the micelle surface as the c.m.c. is approached. It is shown that it may not be valid to make the assumption kRC[double greater-than, compressed]k–2 in the kinetic scheme of the reaction. However, the effect on kf is small, such that kf is still dominated by the rate of loss of water from the metal ion. The faster reaction between Zn2+(aq) and PADA was also studied, but only one concentration dependent relaxation time was observed. This was consistent with the complex re-formation reaction and k298.2 was found to be 6.4 × 106 dm3 mol–1 s–1.
Micellar Catalysis of Metal-Complex Formation: Kinetics of the Reaction between Ni11 and Pyridine-2-azo-p-dimethylaniline (PADA) in the Presence of Sodium Dodecylsulphate Micelles; a Model System for the Study of Metal Ion Reactivity at Charged Interfaces.
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (01), 1978) James, Alan D.; Robinson, Brian H.
The kinetics of the reaction between Ni2+(aq) and the bidentate ligand pyridine-2-azo-p-dimethyl- aniline have been investigated in sodium dodecylsulphate micellar solutions. Considerable catalysis effects (up to 103) are observed on the rate of complexation. The rate dependence on pH and micelle concentration can be quantitatively explained, the former in terms of the surface potential of the micelle. The reaction occurs in the region of the micelle surface, over the detergent concentration range studied, and rate constants appropriate to a surface reaction are derived. The catalysis effect resides in the concentrative effect of the micelle surface on the reagents, since the rate of water loss from Ni2+ at the surface of the micelle is little changed from that in bulk water. The effect of added electrolyte on the micelle-catalysed rate has also been investigated.