Micellar effects upon the reactions of complex ions in solution. Part 4. Kinetics of aquation and base hydrolysis of some cis-(chloro)(amine)bis(ethylenediamine)cobalt(III) complexes in the presence of neutral and anionic surfactants in an aqueous medium

The binding of the substrates cis-[Co(en)2BCl]2+(en = 1,2-diaminoethane, B = alkylamines, imidazole, N-methylimidazole) to the micellar surface of sodium dodecyl sulphate resulted in the retardation of their dissociative aquation rates, the effect being sensitive to the hydrophobicity of the nonlabile amine ligand B. A contrastingly small rate acceleration for the corresponding ethanolamine and propan-2-ol amine complexes was observed under similar conditions. Triton X-100 (0.02 ≤ [Triton X]T/mol dm-3 ≤ 0.1) had virtually no effect on the aquation rates of such complexes except for cis-[Co(en)2(C6H11NH2)Cl]2+, in which case a small rate retardation was also observed. The rates of base hydrolysis of the cobalt(III) substrates were strongly retarded by the anionic micelles of SDS; the neutral micelles of Triton X-100 were effective in decelerating the rate of base hydrolysis of the cyclohexylamine complex cis-[Co(en)2(C6H11NH2)Cl]2+ only. The pseudo-phase ion-exchange equilibrium model satisfactorily explained the binding of the cationic substrates to the anionic micellar pseudo-phase of SDS. The values of the ion-exchange equilibrium constant and the relative base hydrolysis rates (kW/kM) indicated that both micellar binding and retardation of hydrolysis are governed by hydrophobic and electrostatic interactions

Reactions in micellar solutions: Part 9†-Kinetics of base hydrolysis of cis-(imidazole)(salicylato)bis(ethylenediamine)cobalt(III) and (ɑβS)-(sulphito)(tetraethylenepentamine)cobalt(III) in the presence of neutral, anionic and cationic surfactants in aqueous medium

670-675The base hydrolysis of cis-(imidazolato)(salicylato)bis(ethylene-diamine)cobalt(III) is moderately catalysed by CTAB (cationic), retarded by SDS (anionic) and influenced only a little by Triton X-100 (neural). The rate retardation by SDS is due to the less reactive phenol species, cis- in which form the complex exists exclusively in the micellar pseudo-phase of S S. The rate of base hydrolysis of (a ~S)-(tetraethylenepentamine Xsulphito )cobalt(III)(stable S- onded isomer) is retarded by Triton X 100, SOS and CTAB, the effect increasing with increase in surfactant] in the order SOS > > Tliton-X-IOO> CTAB. The rate data for this substrate at varying [SOS] and [Triton X 100] are interpreted in terms of pseudo-phase equilibrium model taking into account ion-exchange in the case of SDS. The rate retardation by CTAB is due to the formation of less reactive premicellar aggregate (1:1 ion pair) of this substrate with the CTA+ cation. The roles of electrostatic and hydrophobic effects of the micelles on the hydrolysis reactions of the micelle-bound Co (III) substrates under consideration are discussed