No abstract

The temperature-jump method has been used to investigate the kinetics of formation and dissociation of monocomplexes of iron(iii) with some substituted phenols (HA) in aqueous solution at 25" and ionic strength 0.10M over the acidity range 0.01 0-0.090~. The only reaction observed is FeOH*+ + HA FeA2+ + H20. All the estimated rate constants for the forward reaction are of the same order of magnitude as those found for other analogous reactions previously studied. This result is consistent with a mechanism in which release of a coordinated water molecule from the inner sphere of the cation is rate-determining. The rates for the reverse process decrease with decreasing base strength of the ligands and follow the Hammett relationship with a reaction constant p = -0.33.'

The stopped-flow technique has been used to study the effect of cationic (CTAN), nonionic (Triton X-loo), and anionic (SDS) micelles on the rate of the reaction between nickel(I1) ion and the ligand pyridine-2-azo-p-dimethylaniline (PADA) at 20.0"C and ionic strength 0.03 mol dm-3. The complex formation reaction is markedly inhibited by both CTAN and Triton X-100 micelles. The kinetic data are found to conform to a reaction mechanism which implies only partitioning of the ligand between water and the micellar phase, the estimated binding constant of PADA being significantly larger in the presence of CTAN aggregates. Anionic micelles strongly speed the complexation reaction, which occurs in the micellar phase with the same rate and the same mechanism as in water. The extent of binding of PADA to anionic micelles is similar to that found for the cationic micellar aggregates.

Kinetic studies on the hydrolysis of some benzoic anhydrides in the presence of 0.1 00M-hydrochloric acid have been performed in various dioxan-water mixtures over the temperature range 50-70 "C. The kinetic data indicate that the hydrolysis of p-methoxybenzoic anhydride proceeds by an A1 mechanism, whereas benzoic anhydride and its p-t-butyl and p-chloro-derivatives hydrolyse by an A2 mechanism in the water-rich mixtures, but a shift of the reaction mechanism towards the A1 type occurs when the water content in the solvent mixture decreases.IN extension of previous studies 1-4 on the factors affecting the mixed mechanism (A1 and A 2 ) involved in the acid-catalysed hydrolysis of some $ara-substituted benzoic anhydrides, the present paper deals with results

The observed first-order rate constant hoba for the hydrolyses in acid solution is given l y 3 bywhere k , is the first-order rate constant for the catalysecl