Aquation

About: Aquation is a research topic. Over the lifetime, 1443 publications have been published within this topic receiving 17507 citations.

Kinetics and mechanism of chromium(III)-picolinato and chromium(III)-dipicolinato complexes aquation in HNO3 solutions

Abstract: The acid-catalyzed aquation of [Cr(pic)(H2O)4]22+ and [Cr(dpic)(H2O)3]+(pic = picolinic acid anion, dpic = dipicolinic acid dianion) in nitrate(V) media was studied. The reaction is reversible in the case of the pic-complex and practically irreversible in the case of the dpic-complex. It is assumed that the reactive form of the substrate undergoes fast chelate ring-opening followed by protolytic equilibria, followed by the rate of the Cr—O bond breaking of the monodentate bonded ligand which is the rate-determining step. The kinetics of pic/dpic ligand liberation were followed spectrophotometrically in the 0.4–2.0 M HNO3 range at I= 2.0 M. The following dependences of the pseudo-first order rate constants on [H+] have been established:kobs=a+b[H+](where b and a are apparent rate constants for the forward and the reverse reaction of the pic-complex) and kobs=b[H+]+c[H+]2(where b and c are apparent rate constants for the dpic liberation). Fast protolytic pre-equilibria, leading to protonation of the carboxylic oxygen atom on the monodentate bonded ligand, preceeds ligand liberation.

Micellar Effects on the Kinetics of the Aquation and the Base Hydrolysis of Tris(1,10-phenanthroline)iron(II) and Chloropentaamminecobalt(III) Ions.

Abstract: Les constantes de vitesse ne presentent pas de variations remarquables au-dessus de c.m.c. Pour Fe(phen) 3 2+ , au-dessous de c.m.c., les variations des constantes de vitesse sont liees a la formation d'agregats premicellaires. Effet de l'addition de NaCl

Base hydrolysis and mercury(ii)-catalysed aquation of bis(ethylenediamine-nn′)(ethylenediamine-n)halogenocobalt(iii) complexes

Abstract: The kinetics of base hydrolysis of the complexes cis-[CoX(en)2(en-N)]2+(X = Cl or Br) have been studied at 25 °C and I= 0.1M(Na[ClO4]) and kOHCl=(6.3 ± 0.3) and kOHBr=(4.1 ± 0.2)× 101 l mol–1s–1. The main product is [Co(en)2(en-N)OH]2+(ca, 97%) rather than [Co(en)3]3+. The ionization constants for the equilibria (i) and (ii) are pKlm 5.05 and pK2m 7.23. The mercury(II)-catalysed aquations have also been studied at 25 °C [Co(en)2(Hen-N)OH2]4+[graphic omitted][Co(en)2(Hen-N)OH]3++ H+(i), [Co(en)2(Hen-N)OH]3+[graphic omitted][Co(en)2(en-N)OH]2++ H+(ii)(I= 3.94M and [H+]= 0.94M) and kHgCl=(5.6 ± 0.3)× 10–3 and kHgBr=(5.0 ± 0.15)× 10–3 l mol–1 s–1. The major product (ca, 95%) is the complex [Co(en)2(Hen-N)OH2]4+. In dimethyl sulphoxide solution the complex [CoCl(en)2(en-N)]2+, in the presence of n-butylamine, undergoes cyclisation to [Co(en)3]3+. The reaction is first order in the complex and n-butylamine concentrations with k= 1.19 × 10–3 l mol–1 s–1 at 25 °C.

Chemical and Electrochemical Equilibria and Kinetics in Aqueous Cr(III)/Cr(II) Chloride Solutions.

Abstract: The effects of Cr(III) speciation and electrolyte composition on the voltammetric behaviour of the Cr(III)/Cr(II) couple, were studied by voltammetry at a hanging mercury drop electrode in chloride and sulphate electrolytes, which were analysed by spectrophotometry. Previous authors on Cr(III)-Cl − electrochemistry appear not to have characterised their electrolytes adequately, ignoring the well known slow chemical kinetics of the system. The thermodynamics of the Cr/H 2 O-Cl system were summarised in the form of potential ( E h )-pH and spedation diagrams calculated from published Gibbs energy of formation data. These were used to provide predictions of equilibrium compositions in kinetic experiments, and, together with spectrophotometric measurements, for characterising electrolytes immediately prior to electrochemical experiments. The aquation and chloride complexation kinetics of Cr(III) species, studied by visible spectrophotometry, were found to be dependent on the H + and Cl − ion concentrations and occurred slowly even at 333 K. In strongly addic chloride solutions at 293 K, equilibrium solution compositions were not achieved even after several months. From results of cyclic voltammetry at a hanging mercury drop electrode, the heterogeneous rate constants were calculated for the CrCl + 2 /Cr 2+ CrCl 2+ /Cr 2+ and Cr 3+ /Cr 2+ couples, the kinetics of which were found to be irreversible or quasi-reversible, dependent on the initial Cr(III) species and the electrolyte composition. The reduction of CrCl + 2 ions occurred via a CrCl 2+ intermediate and successive elimination of Cl − ligands, the presence of which greatly enhanced the electrode kinetics.

Aquation of penta-ammine(dimethyl sulphoxide)cobalt(iii) perchlorate in water-non-aqueous solvent mixtures

Abstract: The aquation rate constant of penta-ammine(dimethyl sulphoxide) cobalt(III) ion in various aqueous and aqueous–non-aqueous solvent mixtures has been determined. The rate constant does not correlate well with water activity, the Grunwald–Winstein solvating-power Y parameter, or the heat of mixing of dimethyl sulphoxide with the solvent components. The data support an Id mechanism more readily than a D mechanism. The activation enthalpy and entropy are 23·9 ± 0·7 kcal mol–1 and 0·36 ± 2·29 cal K–1 mol–1, respectively.